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# Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards

Elise Bertheau, Valérie Simon, Christine Delgado Raynaud

► To cite this version:

Elise Bertheau, Valérie Simon, Christine Delgado Raynaud. Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards. Applied Sciences, 2024, 14 (3), pp.1266. 10.3390/app14031266. hal-04571314

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# Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards

Elise Bertheau, Valérie Simon, Christine Delgado Raynaud

► To cite this version:

Elise Bertheau, Valérie Simon, Christine Delgado Raynaud. Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards. Applied Sciences, 2024, 14 (3), pp.1266. 10.3390/app14031266. hal-04571314

HAL Id: hal-04571314

https://hal.inrae.fr/hal-04571314v1

Submitted on 7 May 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

Review

# Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards

Elise Bertheau<fnref n="1" /> ID, Valérie Simon <fnref n="1" />,*, ID and Christine Delgado Raynaud <fnref n="1" />,<fnref n="2" /> ID

**Abstract:** Wood-based panels are ubiquitous in our daily lives, both as building materials and as furnishing materials. Numerous studies have revealed that these materials emit volatile organic compounds, such as formaldehyde, into indoor air, which can be harmful to human health. These volatile organic compounds come both from the wood itself, more specifically cellulose, hemicellulose, and lignin, and from the resins used to bind the wood fibers or particles together. Today, new panels bonded with bio-based adhesives and binderless panels are emerging. The aim of this article is to highlight the importance of measuring VOC emissions from binderless wood-based panels, and more specifically, to identify the VOCs, originating from the wood and thermal transformation processes, likely to be emitted during the production of such panels, as well as how to sample them and measure their emissions. This work provides a useful approach to identifying and quantifying VOC emissions from these new materials. These methodologies should be applied more widely to gain knowledge about VOCs, which are relevant indicators for the development of environmentally friendly materials.

**Keywords:** lignocellulosic material; pollutants; volatile organic compounds; wood-based composites; sustainable materials; free formaldehyde

<figure><img src="image_4.png" /></figure>

check for
updates

**Citation:** Bertheau, E.; Simon, V.; Delgado Raynaud, C. Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards. *Appl. Sci.* **2024**, *14*, 1266. https://doi.org/10.3390/app14031266

Academic Editors: Vardan Galstyan, Ziwei Chen, Ru Ji and Hao Wang

Received: 30 November 2023

Revised: 22 January 2024

Accepted: 30 January 2024

Published: 3 February 2024

<figure><img src="image_5.png" /></figure>

**Copyright:** © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

## 1. Introduction

The wood industry is a major worldwide industry. The global forest products trade was estimated in 2020 by the Food and Agriculture Organization of the United Nations [1] and represented over USD 234 billion in imports and over USD 226 billion in exports. Forest products englobes roundwood; wood charcoal, chips and particles, residues, pellets, and other agglomerates; sawnwood and veneer sheets; wood-based panels; pulp and recovered paper; and paper and paperboard. In 20 years, wood-based board global production increased from 178 million of m³ in 2001 to 396 million of m³ in 2021 [2], for use in various sectors such as construction and furniture, depending on the board characteristics. As the panels are manufactured from different wood species, in various sizes and shapes, bonded with different petrochemical binders and using diverse manufacturing processes, they have different specificities, particularly in terms of mechanical strength and hydrophobicity [3–5].

These wood-based panels are more than ever present in our homes, workplaces, or schools, yet building and furnishing materials including wood-based panels have been found to emit volatile organic compounds (VOCs) [6]. Emissions of these VOCs depend on environmental factors, such as temperature or humidity [7–10], but also on factors intrinsic to the boards themselves [11–13]. Some VOCs have been classified as carcinogenic, genotoxic, and reprotoxic molecules, in particular formaldehyde [14]. The nature and quantity of VOCs emitted from wood-based boards can originate, among other things, from the petrochemical binders used in the process of production to bond particles or fibers together.

Over the last decades, numerous studies have been carried out to replace these petroleum-based binders with biobased binders [15–17] or even to produce binderless

<footnote n="1">¹ Laboratoire de Chimie Agro-Industrielle (LCA), Université de Toulouse, INRAE, Toulouse INP, 31030 Toulouse, France; elise.bertheau@toulouse-inp.fr (E.B.); christine.raynaud@toulouse-inp.fr (C.D.R.)</footnote>

<footnote n="2">² Centre d'Application et de Traitement des Agro-Ressources (CATAR), Toulouse INP, 31030 Toulouse, France</footnote>

<footnote>* Correspondence: valerie.simon@toulouse-inp.fr</footnote>
Review

# Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards

Elise Bertheau¹ ID, Valérie Simon ¹,*, ID and Christine Delgado Raynaud ¹,² ID

¹ Laboratoire de Chimie Agro-Industrielle (LCA), Université de Toulouse, INRAE, Toulouse INP, 31030 Toulouse, France; elise.bertheau@toulouse-inp.fr (E.B.); christine.raynaud@toulouse-inp.fr (C.D.R.)

² Centre d'Application et de Traitement des Agro-Ressources (CATAR), Toulouse INP, 31030 Toulouse, France

* Correspondence: valerie.simon@toulouse-inp.fr

**Abstract:** Wood-based panels are ubiquitous in our daily lives, both as building materials and as furnishing materials. Numerous studies have revealed that these materials emit volatile organic compounds, such as formaldehyde, into indoor air, which can be harmful to human health. These volatile organic compounds come both from the wood itself, more specifically cellulose, hemicellulose, and lignin, and from the resins used to bind the wood fibers or particles together. Today, new panels bonded with bio-based adhesives and binderless panels are emerging. The aim of this article is to highlight the importance of measuring VOC emissions from binderless wood-based panels, and more specifically, to identify the VOCs, originating from the wood and thermal transformation processes, likely to be emitted during the production of such panels, as well as how to sample them and measure their emissions. This work provides a useful approach to identifying and quantifying VOC emissions from these new materials. These methodologies should be applied more widely to gain knowledge about VOCs, which are relevant indicators for the development of environmentally friendly materials.

**Keywords:** lignocellulosic material; pollutants; volatile organic compounds; wood-based composites; sustainable materials; free formaldehyde

<figure><img src="image_2.png" /></figure>

check for
updates

**Citation:** Bertheau, E.; Simon, V.; Delgado Raynaud, C. Emissions of Volatile Organic Compounds (VOCs) as Safety Indicators in the Development of Wood-Based Binderless Boards. *Appl. Sci.* **2024**, *14*, 1266. https://doi.org/10.3390/app14031266

Academic Editors: Vardan Galstyan, Ziwei Chen, Ru Ji and Hao Wang

Received: 30 November 2023

Revised: 22 January 2024

Accepted: 30 January 2024

Published: 3 February 2024

<figure><img src="image_3.png" /></figure>

**Copyright:** © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

## 1. Introduction

The wood industry is a major worldwide industry. The global forest products trade was estimated in 2020 by the Food and Agriculture Organization of the United Nations [1] and represented over USD 234 billion in imports and over USD 226 billion in exports. Forest products englobes roundwood; wood charcoal, chips and particles, residues, pellets, and other agglomerates; sawnwood and veneer sheets; wood-based panels; pulp and recovered paper; and paper and paperboard. In 20 years, wood-based board global production increased from 178 million of m³ in 2001 to 396 million of m³ in 2021 [2], for use in various sectors such as construction and furniture, depending on the board characteristics. As the panels are manufactured from different wood species, in various sizes and shapes, bonded with different petrochemical binders and using diverse manufacturing processes, they have different specificities, particularly in terms of mechanical strength and hydrophobicity [3–5].

These wood-based panels are more than ever present in our homes, workplaces, or schools, yet building and furnishing materials including wood-based panels have been found to emit volatile organic compounds (VOCs) [6]. Emissions of these VOCs depend on environmental factors, such as temperature or humidity [7–10], but also on factors intrinsic to the boards themselves [11–13]. Some VOCs have been classified as carcinogenic, genotoxic, and reprotoxic molecules, in particular formaldehyde [14]. The nature and quantity of VOCs emitted from wood-based boards can originate, among other things, from the petrochemical binders used in the process of production to bond particles or fibers together.

Over the last decades, numerous studies have been carried out to replace these petroleum-based binders with biobased binders [15–17] or even to produce binderless
boards, based on the self-adhesive properties of the various raw materials used, due to their chemical composition [18–21]. These boards show great promise, particularly in terms of mechanical properties. To be able to replace existing industrial boards, biobased and binderless boards need to offer similar or even higher mechanical resistance, as well as complying with VOC emission standards.

This paper aims to highlight the importance to measure the VOC emissions of wood-
based binderless boards and specifically to identify the VOC from wood and thermal
transformation processes that are likely to be emitted during the production of such wood
panels, as well as how to sample them and measure their emissions.

2. Wood and Its Pectocellulosic Cell Wall Organization

Lignocellulosic materials such as wood are complex materials, composed of a variety
of cells with very different functions. All these cells have in common a pectocellulosic wall,
composed mainly of cellulose, hemicelluloses, lignin, and pectins, organized to protect
the cell [22].

*Cellulose* is a homopolymer of β-D-glucopyranose units, linked by β-(1-4) glycosidic bonds [23–27]. It is thus formed by long linear chains that can reach a degree of polymerization of 15,000 [24,28]. As each unit has alcohol functions, the linear chains come together through hydrogen bonds and Van der Waals forces to form cellulose microfibrils [25,29–31]. When the microfibrils are perfectly ordered, they are referred to as crystalline cellulose or non-accessible cellulose [23–25,29]. The cellulose microfibrils can then combine to form a cellulose fiber or macrofibril. The cellulose, arranged in microfibrils and macrofibrils, thus provides mechanical strength to the cell wall, enabling the plant to expand in height [28,29].

*Hemicelluloses* are heteropolymers of pentoses (xylose and arabinose), hexoses (mannose, glucose, and galactose) and acidoses (uronic acids), linked by β-(1-4) osidic bonds, with degrees of polymerization ranging from 100 to 300 [23,24,32]. There are four types of hemicelluloses [33]:

* Xyloglucans: backbone of β-(1-4)-linked glucoses, with branches of xylose, galactose, and fucose;

* Glucuronoxylans and glucuronoarabinoxylans: skeleton of xyloses linked by β-(1-4) bonds, with glucuronic acid and arabinose branches;

* Mannans and glucomannans: skeleton made up entirely of mannose (for mannans and galactomannans) or glucose and mannose (for mannans and galactoglummannans), linked by β-(1-4) bonds;

* β-(1-3,1-4)-glucans: backbone of glucoses linked by β-(1-3) or β-(1-4).

The type of hemicelluloses and their quantities depend on the organism studied. In fact, xyloglucans are found in greater quantities in the primary cell walls of plants, particularly hardwoods. Glucuronoxylans are mainly found in the secondary cell walls of hardwoods. As for galactoglummannans, they are mostly found in the secondary walls of softwood [33]. Hemicelluloses bind to cellulose microfibrils via hydrogen bonds. They thus play a bridging role between cellulose microfibrils, but also with other wall components. Hemicelluloses also bind to lignin via covalent bonds. In this way, hemicelluloses reinforce the cell wall [23,24,28,33].

*Lignin* is an amorphous, three-dimensional heteropolymer made up of three monomers called monolignols (phenylpropanoids): *p*-coumaryl alcohol (H unit), coniferyl alcohol (G unit), and sinapyl alcohol (S unit) [24,25,34,35]. Each unit is found in different quantities depending on the plant type: hardwood lignin is predominantly composed of S and G units, while softwood lignin is predominantly constituted of G units. All these monolignols are linked together by various ether bonds of different strengths [35]. Lignin therefore has a highly complex structure. Lignin gives cells rigidity, enabling woody plants to grow vertically. Lignin also helps protect cells from microbial and fungal attack by rendering wall polysaccharides inaccessible [36,37].

*Pectins* are polysaccharides found mainly in the middle lamella and primary wall.
There are different types of pectin [38,39]:
boards, based on the self-adhesive properties of the various raw materials used, due to their chemical composition [18–21]. These boards show great promise, particularly in terms of mechanical properties. To be able to replace existing industrial boards, biobased and binderless boards need to offer similar or even higher mechanical resistance, as well as complying with VOC emission standards.

This paper aims to highlight the importance to measure the VOC emissions of wood-
based binderless boards and specifically to identify the VOC from wood and thermal
transformation processes that are likely to be emitted during the production of such wood
panels, as well as how to sample them and measure their emissions.

2. Wood and Its Pectocellulosic Cell Wall Organization

Lignocellulosic materials such as wood are complex materials, composed of a variety of cells with very different functions. All these cells have in common a pectocellulosic wall, composed mainly of cellulose, hemicelluloses, lignin, and pectins, organized to protect the cell [22].

*Cellulose* is a homopolymer of β-D-glucopyranose units, linked by β-(1-4) glycosidic bonds [23–27]. It is thus formed by long linear chains that can reach a degree of polymerization of 15,000 [24,28]. As each unit has alcohol functions, the linear chains come together through hydrogen bonds and Van der Waals forces to form cellulose microfibrils [25,29–31]. When the microfibrils are perfectly ordered, they are referred to as crystalline cellulose or non-accessible cellulose [23–25,29]. The cellulose microfibrils can then combine to form a cellulose fiber or macrofibril. The cellulose, arranged in microfibrils and macrofibrils, thus provides mechanical strength to the cell wall, enabling the plant to expand in height [28,29].

*Hemicelluloses* are heteropolymers of pentoses (xylose and arabinose), hexoses (mannose, glucose, and galactose) and acidoses (uronic acids), linked by β-(1-4) osidic bonds, with degrees of polymerization ranging from 100 to 300 [23,24,32]. There are four types of hemicelluloses [33]:

* Xyloglucans: backbone of β-(1-4)-linked glucoses, with branches of xylose, galactose, and fucose;

* Glucuronoxylans and glucuronoarabinoxylans: skeleton of xyloses linked by β-(1-4) bonds, with glucuronic acid and arabinose branches;

* Mannans and glucomannans: skeleton made up entirely of mannose (for mannans and galactomannans) or glucose and mannose (for mannans and galactoglummannans), linked by β-(1-4) bonds;

* β-(1-3,1-4)-glucans: backbone of glucoses linked by β-(1-3) or β-(1-4).

The type of hemicelluloses and their quantities depend on the organism studied. In fact, xyloglucans are found in greater quantities in the primary cell walls of plants, particularly hardwoods. Glucuronoxylans are mainly found in the secondary cell walls of hardwoods. As for galactoglummannans, they are mostly found in the secondary walls of softwood [33]. Hemicelluloses bind to cellulose microfibrils via hydrogen bonds. They thus play a bridging role between cellulose microfibrils, but also with other wall components. Hemicelluloses also bind to lignin via covalent bonds. In this way, hemicelluloses reinforce the cell wall [23,24,28,33].

*Lignin* is an amorphous, three-dimensional heteropolymer made up of three monomers called monolignols (phenylpropanoids): *p*-coumaryl alcohol (H unit), coniferyl alcohol (G unit), and sinapyl alcohol (S unit) [24,25,34,35]. Each unit is found in different quantities depending on the plant type: hardwood lignin is predominantly composed of S and G units, while softwood lignin is predominantly constituted of G units. All these monolignols are linked together by various ether bonds of different strengths [35]. Lignin therefore has a highly complex structure. Lignin gives cells rigidity, enabling woody plants to grow vertically. Lignin also helps protect cells from microbial and fungal attack by rendering wall polysaccharides inaccessible [36,37].

*Pectins* are polysaccharides found mainly in the middle lamella and primary wall.
There are different types of pectin [38,39]:
* Homogalacturonans: linear chains of uronic acids linked by α-(1-4) bonds, which account for around 65% of pectin. The homogalacturonans are often methylated and sometimes acetylated.

* Rhamnogalacturonans I: homogalacturonan and rhamnose skeletons, with arabinose and galactose branches on the rhamnose units. The uronic acid units of the backbone can be methylated and sometimes acetylated. Rhamnogalacturonanes I account for between 20 and 35% of pectin.

* Rhamnogalacturonans II: branched homogalacturonan skeletons with more than 12 types of sugar and 20 different types of bonds. The rhamnogalacturonans II account for around 10% of pectin.

* Xylogalacturonans: homogalacturonan skeletons with some branches of β-(O-3)-xylose.

The non-methylated units of homogalacturonans are negatively charged and can interact with calcium $Ca^{2+}$ to form a gel. A hypothetical structure called the "egg box" represents the compaction of homogalacturonans that occurs during $Ca^{2+}$-induced gelation. This phenomenon accounts for 70% of the pectic gel in pectocellulosic walls [29,38]. The different types of pectin are thought to be linked by covalent bonds between their skeletons. Pectins are also linked to other wall polysaccharides, such as xyloglucans or xylans, by covalent bonds [38,39]. Thanks to these interactions, pectins contribute to the mechanical strength (non-methylated homogalacturonan blocks linked by ionic bonds with calcium), adhesion, and rigidity of the pectocellulose wall [38].

Cellulose, hemicelluloses, lignin, and pectins thus form a complex network of molecules protecting the plant cell and providing the rigidity and flexibility required for the development of lignocellulosic material.

### 3. Wood-Based Composite Boards

Numerous wood-based boards exist. They are characterized by their manufacturing process; the nature, size, and geometry of the raw material; and the presence or not of a binder, and if so, the nature of the binder.

#### 3.1. Wood-Based Boards Containing a Binder

The rising price of wood during the 20th century led manufacturers to develop new materials, less expensive but with the same or even better characteristics of solid wood. This is how wood-based panels emerged.

Different varieties of wood-based panels were then developed with different properties depending on their composition. Figure 1 shows the variety of wood-based industrial composite panels that exist, as well as their manufacturing processes. Wood can be simply ground to produce boards from particles, or it can undergo a thermomechanical process to preserve longer fibers. Wood-based boards that are currently on the market can be divided into three groups: fiberboard, particleboard, and veneer panels.

##### 3.1.1. Different Types of Industrial Wood-Based Boards

Fiberboards are made from wood fibers using a thermomechanical process. Fiberboards are produced by adding a synthetic binder to fibers, followed by a thermocompression process involving heat and pressure. There are different types of fiberboards, depending not only on the process used but also on the final density of the board, ranging from a few hundred $kg m^{-3}$ to over 800 $kg m^{-3}$ [40]. Among fiberboards, the following are particularly worthy of mention medium density fiberboard (MDF), hard density fiberboard (HDF), or hardboard (HB), most of which are used in furniture.

The particleboard group includes panels made from wood ground into a variety of grain sizes and geometries. Particles can range from a few millimeters (particleboard in particular) to tens of centimeters (for the oriented strand board or OSB) [40]. Like fiberboards, particleboards are manufactured by thermocompression, with the addition of a petrochemical binder. These panels are used in furniture and construction.
* Homogalacturonans: linear chains of uronic acids linked by α-(1-4) bonds, which account for around 65% of pectin. The homogalacturonans are often methylated and sometimes acetylated.

* Rhamnogalacturonans I: homogalacturonan and rhamnose skeletons, with arabinose and galactose branches on the rhamnose units. The uronic acid units of the backbone can be methylated and sometimes acetylated. Rhamnogalacturonanes I account for between 20 and 35% of pectin.

* Rhamnogalacturonans II: branched homogalacturonan skeletons with more than 12 types of sugar and 20 different types of bonds. The rhamnogalacturonans II account for around 10% of pectin.

* Xylogalacturonans: homogalacturonan skeletons with some branches of β-(O-3)-xylose.

The non-methylated units of homogalacturonans are negatively charged and can interact with calcium $Ca^{2+}$ to form a gel. A hypothetical structure called the "egg box" represents the compaction of homogalacturonans that occurs during $Ca^{2+}$-induced gelation. This phenomenon accounts for 70% of the pectic gel in pectocellulosic walls [29,38]. The different types of pectin are thought to be linked by covalent bonds between their skeletons. Pectins are also linked to other wall polysaccharides, such as xyloglucans or xylans, by covalent bonds [38,39]. Thanks to these interactions, pectins contribute to the mechanical strength (non-methylated homogalacturonan blocks linked by ionic bonds with calcium), adhesion, and rigidity of the pectocellulose wall [38].

Cellulose, hemicelluloses, lignin, and pectins thus form a complex network of molecules protecting the plant cell and providing the rigidity and flexibility required for the development of lignocellulosic material.

### 3. Wood-Based Composite Boards

Numerous wood-based boards exist. They are characterized by their manufacturing process; the nature, size, and geometry of the raw material; and the presence or not of a binder, and if so, the nature of the binder.

#### 3.1. Wood-Based Boards Containing a Binder

The rising price of wood during the 20th century led manufacturers to develop new materials, less expensive but with the same or even better characteristics of solid wood. This is how wood-based panels emerged.

Different varieties of wood-based panels were then developed with different properties depending on their composition. Figure 1 shows the variety of wood-based industrial composite panels that exist, as well as their manufacturing processes. Wood can be simply ground to produce boards from particles, or it can undergo a thermomechanical process to preserve longer fibers. Wood-based boards that are currently on the market can be divided into three groups: fiberboard, particleboard, and veneer panels.

##### 3.1.1. Different Types of Industrial Wood-Based Boards

Fiberboards are made from wood fibers using a thermomechanical process. Fiberboards are produced by adding a synthetic binder to fibers, followed by a thermocompression process involving heat and pressure. There are different types of fiberboards, depending not only on the process used but also on the final density of the board, ranging from a few hundred $kg m^{-3}$ to over 800 $kg m^{-3}$ [40]. Among fiberboards, the following are particularly worthy of mention medium density fiberboard (MDF), hard density fiberboard (HDF), or hardboard (HB), most of which are used in furniture.

The particleboard group includes panels made from wood ground into a variety of grain sizes and geometries. Particles can range from a few millimeters (particleboard in particular) to tens of centimeters (for the oriented strand board or OSB) [40]. Like fiberboards, particleboards are manufactured by thermocompression, with the addition of a petrochemical binder. These panels are used in furniture and construction.
<figure><img src="image_6.png" /><figcaption>**Figure 1.** Variety of wood-based boards (adapted from [40]).</figcaption></figure>

Finally, the last group of wood-based panels is called veneer panels. These boards have the distinctive feature of being manufactured from solid wood, which can be either thin layers of wood or planks. Wood can be glued in a variety of ways, depending on the intended application and therefore on mechanical requirements (in case of a use in construction) or aesthetics (for furnishings). Plywood panels, glued laminated panels, or laminated veneer lumber boards (LVL) are used in construction, as their particular structure (gluing sheets together) gives them high mechanical strength at lower cost than solid wood. Finger-jointed panels, on the other hand, as their name implies, are glued at the edge of the panel. The aesthetics of solid wood are conserved, and these boards are used for furnishings.

Panels made from reconstituted wood (MDF or particleboard) and intended for furniture use can then be laminated (i.e., covered with a wood veneer to give them the appearance of solid wood) or laminated (covered with a layer of plastic of a certain color) for aesthetic purposes. These boards account for the majority of wooden furniture on the market today.

All these boards are bonded with an adhesive system. Numerous binders have been developed to respond to the diverse characteristics expected of the panels, but also for economic reasons. Numerous synthetic petrochemical binders are used in panel manufacturing today, classified into two categories: thermosetting binders and thermoplastic binders (Table 1).

<table><caption>**Table 1.** Wood-based panel adhesives.</caption><thead><tr><th>Categories</th><th>Resin Type</th><th>Typical Adhesive System</th></tr></thead><tbody><tr><td rowspan="6">Thermosetting</td><td rowspan="3">Amino</td><td>Urea-formaldehyde (UF)</td></tr><tr><td>Melamine-formaldehyde (MF)</td></tr><tr><td>Melamine-urea-formaldehyde (MUF)</td></tr><tr><td rowspan="3">Phenolic</td><td>Phenol-formaldehyde (PF)</td></tr><tr><td>Resorcinol-formaldehyde (RF)</td></tr><tr><td>Phenol-resorcinol-formaldehyde (PRF)</td></tr><tr><td>Isocyanate</td><td>Diphenylmethane-4,4'-diisocyanate (pMDI)</td></tr><tr><td rowspan="2">Thermoplastic</td><td rowspan="2">Vinyl</td><td>Polyvinyl acetate (PVAC)</td></tr><tr><td>Polyvinyl alcohol (PVA)</td></tr></tbody></table>

### 3.1.2. Development of New Panels with Biobased Binders

A considerable amount of research has been carried out to develop boards with non-petrochemical binders. New bio-based binders have emerged from tannins [41], lignin [18,19,42], proteins [43–46], carbohydrates [47], or unsaturated oils [48].
<figure><img src="image_4.png" /><figcaption>**Figure 1.** Variety of wood-based boards (adapted from [40]).</figcaption></figure>

Finally, the last group of wood-based panels is called veneer panels. These boards have the distinctive feature of being manufactured from solid wood, which can be either thin layers of wood or planks. Wood can be glued in a variety of ways, depending on the intended application and therefore on mechanical requirements (in case of a use in construction) or aesthetics (for furnishings). Plywood panels, glued laminated panels, or laminated veneer lumber boards (LVL) are used in construction, as their particular structure (gluing sheets together) gives them high mechanical strength at lower cost than solid wood. Finger-jointed panels, on the other hand, as their name implies, are glued at the edge of the panel. The aesthetics of solid wood are conserved, and these boards are used for furnishings.

Panels made from reconstituted wood (MDF or particleboard) and intended for furniture use can then be laminated (i.e., covered with a wood veneer to give them the appearance of solid wood) or laminated (covered with a layer of plastic of a certain color) for aesthetic purposes. These boards account for the majority of wooden furniture on the market today.

All these boards are bonded with an adhesive system. Numerous binders have been developed to respond to the diverse characteristics expected of the panels, but also for economic reasons. Numerous synthetic petrochemical binders are used in panel manufacturing today, classified into two categories: thermosetting binders and thermoplastic binders (Table 1).

<table><caption>**Table 1.** Wood-based panel adhesives.</caption><thead><tr><th>Categories</th><th>Resin Type</th><th>Typical Adhesive System</th></tr></thead><tbody><tr><td rowspan="6">Thermosetting</td><td rowspan="3">Amino</td><td>Urea-formaldehyde (UF)</td></tr><tr><td>Melamine-formaldehyde (MF)</td></tr><tr><td>Melamine-urea-formaldehyde (MUF)</td></tr><tr><td rowspan="3">Phenolic</td><td>Phenol-formaldehyde (PF)</td></tr><tr><td>Resorcinol-formaldehyde (RF)</td></tr><tr><td>Phenol-resorcinol-formaldehyde (PRF)</td></tr><tr><td>Isocyanate</td><td>Diphenylmethane-4,4'-diisocyanate (pMDI)</td></tr><tr><td rowspan="2">Thermoplastic</td><td rowspan="2">Vinyl</td><td>Polyvinyl acetate (PVAC)</td></tr><tr><td>Polyvinyl alcohol (PVA)</td></tr></tbody></table>

### 3.1.2. Development of New Panels with Biobased Binders

A considerable amount of research has been carried out to develop boards with non-petrochemical binders. New bio-based binders have emerged from tannins [41], lignin [18,19,42], proteins [43–46], carbohydrates [47], or unsaturated oils [48].
These new binders will not be developed further in this paper, since numerous reviews have already covered the subject [21,49–54].

## 3.2. Wood-Based Binderless Boards

In order to replace binders derived from the petroleum industry, another solution today is to produce panels without any binder (binderless boards) by activating the intrinsic adhesive properties of the lignocellulosic raw material. By applying heat and/or pressure, the components of the raw material are transformed and create bonds. Various reviews have already reported on the characteristics of binderless panel production, mentioning the various raw materials used, as well as the processing and self-adhesion mechanisms [55–60]

### 3.2.1. Self-Adhesion Mechanisms for Wood-Based Binderless Boards

Binderless panels can be made from lignocellulosic materials, since these have intrinsic adhesive properties that can be activated when certain components are subjected to elevated temperature or pressure. Several reactions such as hydrolysis, dehydration and thermal oxidation have been observed [55,58]. Hemicelluloses have lower temperature stability unlike cellulose and lignin, so hemicelluloses are the first components of the lignocellulosic material modified during the panel-forming process, releasing compounds such as organic acids and acetone [61]. These organic acids, such as acetic acid, will then catalyze degradation reactions of cellulose and hemicelluloses [62], releasing furan compounds from pentoses or hexoses in the hemicellulose. These furan compounds include furfural or hydroxymethylfurfural, which can later recondense or establish new bonds with other compounds during cooling [63].

The compounds released by cellulose and hemicelluloses will then take part in other reactions, notably with lignin. Lignin undergoes plasticization under the effect of heat; its glass transition temperature is exceeded, and it begins to soften [64–66]. The inter-monomer bonds will thus break, making the lignin more condensed on the one hand and, on the other hand, allowing for the creation of bonds with other compounds, such as cellulose and hemicelluloses [63,67,68]. An increase in the number of β-O-4 bonds in lignin was observed by Sun et al. [69].

Thus, as a result of the reactions undergone by the components of lignocellulosic material with an increase in temperature, acidic compounds are released from hemicelluloses, catalyzing the degradation of cellulose and hemicelluloses. The compounds then recondense with each other, forming a natural resin, or form bonds with lignin. Lignin, having undergone plasticization, surrounds the cellulose and hemicelluloses before hardening when the temperature is lowered at the end of the process. This plays an important role in the mechanical properties of the final material. Lignocellulosic materials, thanks to their various components and properties, are therefore perfectly suited to the production of binderless panels.

The parameters of the production process of these binderless boards have an impact on panel properties. It has been demonstrated that increasing the temperature and/or the pressure applied during the process can lead to binderless boards with better mechanical characteristics and water resistance [70,71]. The time of process, the size, shape, quantity, and moisture content of the raw material also influence the properties of the binderless boards produced depending on the raw material [72–75].

### 3.2.2. Some Examples of Wood-Based Binderless Boards

A wide range of lignocellulosic raw materials have been used to produce binderless panels. These raw materials can be divided into two groups: woody raw materials, i.e., wood, and non-woody raw materials. Many non-woody raw materials have been used to manufacture binderless boards, from bagasse [76,77] to kenaf [67,78] or even coconut husk [66,79].

Concerning the wood-based binderless boards, various wood species have been studied, as mentioned in Table 2 for the production of wood-based binderless boards by the compression-cooking process.
These new binders will not be developed further in this paper, since numerous reviews have already covered the subject [21,49–54].

## 3.2. Wood-Based Binderless Boards

In order to replace binders derived from the petroleum industry, another solution today is to produce panels without any binder (binderless boards) by activating the intrinsic adhesive properties of the lignocellulosic raw material. By applying heat and/or pressure, the components of the raw material are transformed and create bonds. Various reviews have already reported on the characteristics of binderless panel production, mentioning the various raw materials used, as well as the processing and self-adhesion mechanisms [55–60]

### 3.2.1. Self-Adhesion Mechanisms for Wood-Based Binderless Boards

Binderless panels can be made from lignocellulosic materials, since these have intrinsic adhesive properties that can be activated when certain components are subjected to elevated temperature or pressure. Several reactions such as hydrolysis, dehydration and thermal oxidation have been observed [55,58]. Hemicelluloses have lower temperature stability unlike cellulose and lignin, so hemicelluloses are the first components of the lignocellulosic material modified during the panel-forming process, releasing compounds such as organic acids and acetone [61]. These organic acids, such as acetic acid, will then catalyze degradation reactions of cellulose and hemicelluloses [62], releasing furan compounds from pentoses or hexoses in the hemicellulose. These furan compounds include furfural or hydroxymethylfurfural, which can later recondense or establish new bonds with other compounds during cooling [63].

The compounds released by cellulose and hemicelluloses will then take part in other reactions, notably with lignin. Lignin undergoes plasticization under the effect of heat; its glass transition temperature is exceeded, and it begins to soften [64–66]. The inter-monomer bonds will thus break, making the lignin more condensed on the one hand and, on the other hand, allowing for the creation of bonds with other compounds, such as cellulose and hemicelluloses [63,67,68]. An increase in the number of β-O-4 bonds in lignin was observed by Sun et al. [69].

Thus, as a result of the reactions undergone by the components of lignocellulosic material with an increase in temperature, acidic compounds are released from hemicelluloses, catalyzing the degradation of cellulose and hemicelluloses. The compounds then recondense with each other, forming a natural resin, or form bonds with lignin. Lignin, having undergone plasticization, surrounds the cellulose and hemicelluloses before hardening when the temperature is lowered at the end of the process. This plays an important role in the mechanical properties of the final material. Lignocellulosic materials, thanks to their various components and properties, are therefore perfectly suited to the production of binderless panels.

The parameters of the production process of these binderless boards have an impact on panel properties. It has been demonstrated that increasing the temperature and/or the pressure applied during the process can lead to binderless boards with better mechanical characteristics and water resistance [70,71]. The time of process, the size, shape, quantity, and moisture content of the raw material also influence the properties of the binderless boards produced depending on the raw material [72–75].

### 3.2.2. Some Examples of Wood-Based Binderless Boards

A wide range of lignocellulosic raw materials have been used to produce binderless panels. These raw materials can be divided into two groups: woody raw materials, i.e., wood, and non-woody raw materials. Many non-woody raw materials have been used to manufacture binderless boards, from bagasse [76,77] to kenaf [67,78] or even coconut husk [66,79].

Concerning the wood-based binderless boards, various wood species have been studied, as mentioned in Table 2 for the production of wood-based binderless boards by the compression-cooking process.
<table><caption>**Table 2.** Wood-based binderless boards.</caption><thead><tr><th>Wood Species</th><th>Pretreatment</th><th>References</th></tr></thead><tbody><tr><td><em>Abies alba</em> and <em>Pinus insignis</em></td><td>Steam explosion</td><td>[80]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[70]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[72]</td></tr><tr><td><em>Picea mariana</em> bark</td><td>Refining</td><td>[81]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[82]</td></tr><tr><td><em>Pinus radiata</em></td><td>Fenton reaction</td><td>[83]</td></tr><tr><td>Aspen</td><td>Steam stabilization</td><td>[84]</td></tr><tr><td><em>Picea abies</em> and <em>Fagus sylvatica</em></td><td>Fenton reaction</td><td>[85]</td></tr><tr><td><em>Populus euramevicana</em></td><td>/</td><td>[86]</td></tr></tbody></table>

/: no pretreatment.

## 4. Why and How to Measure Volatile Organic Compound Emissions from a Material?

Volatile organic compounds (VOCs) have many definitions, depending on the organizations that publish them and the regulations to which they apply. The World Health Organization (WHO) [87] characterizes VOCs as compounds with boiling points between 50–100 °C and 240–260 °C. Based on this definition, many compounds are included in VOCs, with diverse compositions and structures: aliphatic hydrocarbons (alkanes, alkenes and alkynes), alicyclic hydrocarbons (cyclic hydrocarbons derived from the aliphatic series), aromatic hydrocarbons (including some polycyclic aromatic hydrocarbons), and substituted hydrocarbons (halogens, alcohols, aldehydes, ketones, ethers and esters, acids, amines, amides, and nitriles).

Although there is no universal definition of VOCs, their impacts on human health and on the environment are acknowledged worldwide [88,89]. First, VOCs affect human health with direct and indirect effects. VOCs can be toxic substances at various levels, with some VOCs even classified as carcinogenic, mutagenic, and reprotoxic (CMR), such as formaldehyde or benzene. Furthermore, since VOCs are precursors of ozone in the air, they can lead to an overproduction of ozone, a gas that is itself toxic, causing various symptoms in humans depending on the level of exposure: coughing, shortness of breath, nasal, eye and throat irritation, among others. Ozone can also have harmful effects on vegetation, altering plant resistance to pathogens and accelerating the degradation of certain materials. Moreover, the overproduction of ozone generates an additional greenhouse effect. It should be noted that VOCs can generally be of biogenic or anthropogenic origin. Table 3 presents some VOCs commonly studied.

<table><caption>**Table 3.** Some VOCs and some of their characteristics.</caption><thead><tr><th></th><th>Compound</th><th>CAS</th><th>MW (g mol<sup>-1</sup>)</th><th>Bp (°C) [90,91]</th><th>CMR Classification [14]</th></tr></thead><tbody><tr><td>C<sub>1</sub></td><td>Formaldehyde</td><td>50-00-0</td><td>30</td><td>-19</td><td>Carc. 2</td></tr><tr><td rowspan="2">C<sub>2</sub></td><td>Acetaldehyde</td><td>75-07-0</td><td>44</td><td>21</td><td>Carc. 2</td></tr><tr><td>Acetic acid</td><td>64-19-7</td><td>60</td><td>118</td><td>Carc. 3</td></tr><tr><td rowspan="4">C<sub>3</sub></td><td>Acetone</td><td>67-64-1</td><td>58</td><td>56</td><td>Carc. 3</td></tr><tr><td>Acrolein</td><td>107-02-8</td><td>56</td><td>52</td><td>Carc. 3</td></tr><tr><td>Propanal</td><td>123-38-6</td><td>58</td><td>48</td><td>Carc. 3</td></tr><tr><td>Tetrachloroethylene</td><td>127-18-4</td><td>166</td><td>121</td><td>Carc. 2</td></tr><tr><td rowspan="2">C<sub>4</sub></td><td>Butanal</td><td>204-646-6</td><td>72</td><td>75</td><td>Carc. 3</td></tr><tr><td>2-Butenal</td><td>4170-30-3</td><td>70</td><td>102</td><td>Muta. 2</td></tr><tr><td>C<sub>5</sub></td><td>Furfural</td><td>98-01-1</td><td>96</td><td>162</td><td>Carc. 2</td></tr><tr><td rowspan="4">C<sub>6</sub></td><td>Benzene</td><td>71-43-2</td><td>78</td><td>80</td><td>Carc.1, Muta. 2</td></tr><tr><td>2-Butoxyethanol</td><td>111-76-2</td><td>118</td><td>170</td><td>Carc. 3</td></tr><tr><td>1,4-Dichlorobenzene</td><td>106-46-7</td><td>147</td><td>173</td><td>Carc. 2</td></tr><tr><td>n-Hexane</td><td>110-54-3</td><td>86</td><td>69</td><td>Repr. 2</td></tr><tr><td rowspan="2">C<sub>7</sub></td><td>Benzaldehyde</td><td>100-52-7</td><td>106</td><td>179</td><td>Carc. 3</td></tr><tr><td>Toluene</td><td>108-88-3</td><td>92</td><td>111</td><td>Repr. 2</td></tr></tbody></table>
<table><caption>**Table 2.** Wood-based binderless boards.</caption><thead><tr><th>Wood Species</th><th>Pretreatment</th><th>References</th></tr></thead><tbody><tr><td><i>Abies alba</i> and <i>Pinus insignis</i></td><td>Steam explosion</td><td>[80]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[70]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[72]</td></tr><tr><td><i>Picea mariana</i> bark</td><td>Refining</td><td>[81]</td></tr><tr><td>Oil palm trunk</td><td>/</td><td>[82]</td></tr><tr><td><i>Pinus radiata</i></td><td>Fenton reaction</td><td>[83]</td></tr><tr><td>Aspen</td><td>Steam stabilization</td><td>[84]</td></tr><tr><td><i>Picea abies</i> and <i>Fagus sylvatica</i></td><td>Fenton reaction</td><td>[85]</td></tr><tr><td><i>Populus euramevicana</i></td><td>/</td><td>[86]</td></tr></tbody></table>

/: no pretreatment.

**4. Why and How to Measure Volatile Organic Compound Emissions from a Material?**

Volatile organic compounds (VOCs) have many definitions, depending on the organizations that publish them and the regulations to which they apply. The World Health Organization (WHO) [87] characterizes VOCs as compounds with boiling points between 50–100 °C and 240–260 °C. Based on this definition, many compounds are included in VOCs, with diverse compositions and structures: aliphatic hydrocarbons (alkanes, alkenes and alkynes), alicyclic hydrocarbons (cyclic hydrocarbons derived from the aliphatic series), aromatic hydrocarbons (including some polycyclic aromatic hydrocarbons), and substituted hydrocarbons (halogens, alcohols, aldehydes, ketones, ethers and esters, acids, amines, amides, and nitriles).

Although there is no universal definition of VOCs, their impacts on human health and on the environment are acknowledged worldwide [88,89]. First, VOCs affect human health with direct and indirect effects. VOCs can be toxic substances at various levels, with some VOCs even classified as carcinogenic, mutagenic, and reprotoxic (CMR), such as formaldehyde or benzene. Furthermore, since VOCs are precursors of ozone in the air, they can lead to an overproduction of ozone, a gas that is itself toxic, causing various symptoms in humans depending on the level of exposure: coughing, shortness of breath, nasal, eye and throat irritation, among others. Ozone can also have harmful effects on vegetation, altering plant resistance to pathogens and accelerating the degradation of certain materials. Moreover, the overproduction of ozone generates an additional greenhouse effect. It should be noted that VOCs can generally be of biogenic or anthropogenic origin. Table 3 presents some VOCs commonly studied.

<table><caption>**Table 3.** Some VOCs and some of their characteristics.</caption><thead><tr><th></th><th>Compound</th><th>CAS</th><th>MW (g mol<sup>-1</sup>)</th><th>Bp (°C) [90,91]</th><th>CMR Classification [14]</th></tr></thead><tbody><tr><td>C<sub>1</sub></td><td>Formaldehyde</td><td>50-00-0</td><td>30</td><td>-19</td><td>Carc. 2</td></tr><tr><td rowspan="2">C<sub>2</sub></td><td>Acetaldehyde</td><td>75-07-0</td><td>44</td><td>21</td><td>Carc. 2</td></tr><tr><td>Acetic acid</td><td>64-19-7</td><td>60</td><td>118</td><td>Carc. 3</td></tr><tr><td rowspan="4">C<sub>3</sub></td><td>Acetone</td><td>67-64-1</td><td>58</td><td>56</td><td>Carc. 3</td></tr><tr><td>Acrolein</td><td>107-02-8</td><td>56</td><td>52</td><td>Carc. 3</td></tr><tr><td>Propanal</td><td>123-38-6</td><td>58</td><td>48</td><td>Carc. 3</td></tr><tr><td>Tetrachloroethylene</td><td>127-18-4</td><td>166</td><td>121</td><td>Carc. 2</td></tr><tr><td rowspan="2">C<sub>4</sub></td><td>Butanal</td><td>204-646-6</td><td>72</td><td>75</td><td>Carc. 3</td></tr><tr><td>2-Butenal</td><td>4170-30-3</td><td>70</td><td>102</td><td>Muta. 2</td></tr><tr><td>C<sub>5</sub></td><td>Furfural</td><td>98-01-1</td><td>96</td><td>162</td><td>Carc. 2</td></tr><tr><td rowspan="4">C<sub>6</sub></td><td>Benzene</td><td>71-43-2</td><td>78</td><td>80</td><td>Carc.1, Muta. 2</td></tr><tr><td>2-Butoxyethanol</td><td>111-76-2</td><td>118</td><td>170</td><td>Carc. 3</td></tr><tr><td>1,4-Dichlorobenzene</td><td>106-46-7</td><td>147</td><td>173</td><td>Carc. 2</td></tr><tr><td>n-Hexane</td><td>110-54-3</td><td>86</td><td>69</td><td>Repr. 2</td></tr><tr><td rowspan="2">C<sub>7</sub></td><td>Benzaldehyde</td><td>100-52-7</td><td>106</td><td>179</td><td>Carc. 3</td></tr><tr><td>Toluene</td><td>108-88-3</td><td>92</td><td>111</td><td>Repr. 2</td></tr></tbody></table>
<table><caption>**Table 3. Cont.**</caption><thead><tr><th></th><th>Compound</th><th>CAS</th><th>MW (g mol<sup>-1</sup>)</th><th>Bp (°C) [90,91]</th><th>CMR Classification [14]</th></tr></thead><tbody><tr><td rowspan="6">C<sub>8</sub></td><td>Ethylbenzene</td><td>100-41-4</td><td>106</td><td>136</td><td>Carc. 3</td></tr><tr><td>Styrene</td><td>100-42-5</td><td>104</td><td>145</td><td>Carc. 3</td></tr><tr><td>Vanillin</td><td>121-33-5</td><td>152</td><td>285</td><td>Carc. 3</td></tr><tr><td>m-Xylene</td><td>108-38-3</td><td>106</td><td>139</td><td>Carc. 3</td></tr><tr><td>o-Xylene</td><td>95-47-6</td><td>106</td><td>144</td><td>Carc. 3</td></tr><tr><td>p-Xylene</td><td>106-42-3</td><td>106</td><td>138</td><td>Carc. 3</td></tr><tr><td rowspan="2">C<sub>9</sub></td><td>Syringaldehyde</td><td>134-96-3</td><td>182</td><td>192</td><td>Carc. 3</td></tr><tr><td>1,2,4-Trimethylbenzene</td><td>95-63-6</td><td>120</td><td>169</td><td>Carc. 3</td></tr><tr><td rowspan="2">C<sub>10</sub></td><td>Naphtalene</td><td>91-20-3</td><td>128</td><td>218</td><td>Carc. 2</td></tr><tr><td>Sabinene</td><td>3387-41-5</td><td>136</td><td>163</td><td>Carc. 3</td></tr><tr><td>C<sub>11</sub></td><td>Undecane</td><td>1120-21-4</td><td>156</td><td>196</td><td>Carc. 3</td></tr></tbody></table>

Bp: boiling point; CMR: carcinogenic, mutagenic, reprotoxic.

## 4.1. How to Sample and Analyse VOCs

### 4.1.1. VOC Sampling

VOC sampling techniques are diverse. They depend in particular on the matrix being studied, the compounds being sampled, the equipment available, and the cost of the various devices. A distinction is generally made between sampling without preconcentration and sampling with preconcentration [92,93].

Sampling without preconcentration involves isolating a portion of the air in which the compounds to be studied are present, with no selection of compounds. In this way, all the compounds in the matrix are considered in the analysis. This sampling method is known as “whole-air sampling”. It can be carried out using

- a bag (made from the following materials: polyvinyl fluoride (tradename: Tedlar), polytetrafluoroethylene and fluorinated ethylene propylene copolymer (tradename: Teflon), polyethyleneterephtalate (tradename: Nalofan), polyvinylidene difluoride (tradename: Altef).) offering a wide range of volumes (from a few mL to several dozen liters) and being low-cost but fragile;

- a polished stainless-steel canister, reusable, with a range of volumes from a few mL to several dozen liters, but are expensive;

- a glass vial or ampoule, infinitely reusable after cleaning.

The advantage of these collection devices is that several analyses can be carried out on the same sample. However, when sampling “whole air”, the humidity of the sample is the same as that of the air and can therefore be high. This can lead to artefacts during analysis. It is therefore important to dehumidify the sample when this type of sampling is carried out. Even et al. [94] highlighted the points that still need to be explored towards the standardization of a suitable procedure, in particular investigations on sorbent combinations and the suitability of chromatography columns. The major challenge is that strong sorbents adsorb water together with very VOCs.

Pre-concentration sampling involves the absorption or adsorption of compounds on a substrate in order to extract them from the air. The choice of sorbent depends on the type of compounds to be studied and the sampling method chosen: passive or dynamic. Sampling is considered to be dynamic if the air is pumped through the collection medium to fix the compounds. Dynamic sampling can be carried out using sorbent(s) contained in a cartridge. A multitude of adsorbents are available: graphitized carbons (Carbograph, Carbotrap, Carbopack) for carbon number C3 to C30, carbon molecular sieves (Carbosieves, Anasorb, Carboxen) for carbon number C1 to C9, and porous organic polymers (Tenax, Porapak, Chromosorb) for carbon number C6 to C26 [94]. As each adsorbent has specific properties, it is essential to study them carefully to select the most appropriate one [94,95]. Adsorbent beds can be built up to extend the range of compounds studied.

In contrast, with passive sampling, there is no movement of the matrix, only the diffusion of analytes comes into play. Passive sampling of analytes can be performed with
<table><caption>**Table 3. Cont.**</caption><thead><tr><th></th><th>Compound</th><th>CAS</th><th>MW (g mol<sup>-1</sup>)</th><th>Bp (°C) [90,91]</th><th>CMR Classification [14]</th></tr></thead><tbody><tr><td rowspan="6">C<sub>8</sub></td><td>Ethylbenzene</td><td>100-41-4</td><td>106</td><td>136</td><td>Carc. 3</td></tr><tr><td>Styrene</td><td>100-42-5</td><td>104</td><td>145</td><td>Carc. 3</td></tr><tr><td>Vanillin</td><td>121-33-5</td><td>152</td><td>285</td><td>Carc. 3</td></tr><tr><td>m-Xylene</td><td>108-38-3</td><td>106</td><td>139</td><td>Carc. 3</td></tr><tr><td>o-Xylene</td><td>95-47-6</td><td>106</td><td>144</td><td>Carc. 3</td></tr><tr><td>p-Xylene</td><td>106-42-3</td><td>106</td><td>138</td><td>Carc. 3</td></tr><tr><td rowspan="2">C<sub>9</sub></td><td>Syringaldehyde</td><td>134-96-3</td><td>182</td><td>192</td><td>Carc. 3</td></tr><tr><td>1,2,4-Trimethylbenzene</td><td>95-63-6</td><td>120</td><td>169</td><td>Carc. 3</td></tr><tr><td rowspan="2">C<sub>10</sub></td><td>Naphtalene</td><td>91-20-3</td><td>128</td><td>218</td><td>Carc. 2</td></tr><tr><td>Sabinene</td><td>3387-41-5</td><td>136</td><td>163</td><td>Carc. 3</td></tr><tr><td>C<sub>11</sub></td><td>Undecane</td><td>1120-21-4</td><td>156</td><td>196</td><td>Carc. 3</td></tr></tbody></table>

Bp: boiling point; CMR: carcinogenic, mutagenic, reprotoxic.

## 4.1. How to Sample and Analyse VOCs

### 4.1.1. VOC Sampling

VOC sampling techniques are diverse. They depend in particular on the matrix being studied, the compounds being sampled, the equipment available, and the cost of the various devices. A distinction is generally made between sampling without preconcentration and sampling with preconcentration [92,93].

Sampling without preconcentration involves isolating a portion of the air in which the compounds to be studied are present, with no selection of compounds. In this way, all the compounds in the matrix are considered in the analysis. This sampling method is known as “whole-air sampling”. It can be carried out using

- a bag (made from the following materials: polyvinyl fluoride (tradename: Tedlar), polytetrafluoroethylene and fluorinated ethylene propylene copolymer (tradename: Teflon), polyethyleneterephtalate (tradename: Nalofan), polyvinylidene difluoride (tradename: Altef).) offering a wide range of volumes (from a few mL to several dozen liters) and being low-cost but fragile;

- a polished stainless-steel canister, reusable, with a range of volumes from a few mL to several dozen liters, but are expensive;

- a glass vial or ampoule, infinitely reusable after cleaning.

The advantage of these collection devices is that several analyses can be carried out on the same sample. However, when sampling “whole air”, the humidity of the sample is the same as that of the air and can therefore be high. This can lead to artefacts during analysis. It is therefore important to dehumidify the sample when this type of sampling is carried out. Even et al. [94] highlighted the points that still need to be explored towards the standardization of a suitable procedure, in particular investigations on sorbent combinations and the suitability of chromatography columns. The major challenge is that strong sorbents adsorb water together with very VOCs.

Pre-concentration sampling involves the absorption or adsorption of compounds on a substrate in order to extract them from the air. The choice of sorbent depends on the type of compounds to be studied and the sampling method chosen: passive or dynamic. Sampling is considered to be dynamic if the air is pumped through the collection medium to fix the compounds. Dynamic sampling can be carried out using sorbent(s) contained in a cartridge. A multitude of adsorbents are available: graphitized carbons (Carbograph, Carbotrap, Carbopack) for carbon number C3 to C30, carbon molecular sieves (Carbosieves, Anasorb, Carboxen) for carbon number C1 to C9, and porous organic polymers (Tenax, Porapak, Chromosorb) for carbon number C6 to C26 [94]. As each adsorbent has specific properties, it is essential to study them carefully to select the most appropriate one [94,95]. Adsorbent beds can be built up to extend the range of compounds studied.

In contrast, with passive sampling, there is no movement of the matrix, only the diffusion of analytes comes into play. Passive sampling of analytes can be performed with
* a solid-phase microextraction (SPME) fiber;

* a stir bar sorption extraction system (SBSE);

* a passive dosimeter containing a sorbent, as previously mentioned, with various ge-ometries (Radiello tube, badge G.A.B.I.E, 3M type 3500, PerkinElmer tube).

The choice of sampling method depends on the matrix under study and the sensitivity of the detection equipment. If the detection equipment is sufficiently sensitive, sampling without preconcentration may be sufficient for the sample to be directly analyzed. On the other hand, if matrix is very low concentrated in VOCs, it is preferable to consider a preconcentration step. It may also be possible to sample compounds without preconcentration, then concentrate them a posteriori by sorption (e.g., sampling in a bag and adsorption on SPME fiber).

For some VOCs, it is necessary to go through a derivatization stage before analysis, during sampling. This is particularly the case for certain carbonyl compounds [96]. Derivation consists in grafting a group visible with conventional detection methods onto non-detectable compounds. There are a number of different derivatization methods, as well as various derivatization agents. For carbonyl compounds, 2,4-dinitrophenylhydrazine (DNPH) and O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) are frequently used. If analytes are sampled using a SPME fiber, the derivation can be carried out either in the sampling matrix or directly on the SPME fiber. If the analytes are sampled on an adsorbent cartridge, the derivatization agent is located directly on the cartridge (DNPH-impregnated silica gel cartridges).

There may be artefacts linked to the presence of water or ozone in the sampled atmosphere. Palluau et al. [97] demonstrated that the presence of ozone in samples taken from canisters led to a decrease in the concentration of certain unsaturated reactive compounds such as ethylene and propylene. This can also be observed in the study of terpene compounds collected on Tenax TA® cartridges [98]. Palluau et al. [99] also demonstrated that there is a loss of compounds on Carbotrap/Carbosieve adsorbent cartridges when these are exposed to humidity (90% relative humidity).

It should be noted that emissions from a material can also be studied by thermodesorption and pyrolysis analysis [100,101].

### 4.1.2. VOC Analysis

There are two families of VOC analysis techniques: off-line and on-line. For off-line techniques, a sample is taken from the matrix, the compounds are stored in/on their collection media, and then they are usually analyzed by gas or liquid chromatography techniques coupled with mass spectrometry or flame ionisation and UV detection, respectively. On-line analysis techniques can also be used, in particular PTR-MS and SIFT-MS [102–104].

When analyzing VOCs by gas chromatography, the notion of total VOCs (TVOCs) is often introduced, being defined in the European standard ISO is ISO 16000-6 [105] as "the sum of volatile organic compounds, sampled on a Tenax TA® cartridge which elutes between *n*-hexane and *n*-hexadecane included on a non-polar capillary column, detected by flame ionization or mass spectrometry and quantified by converting the total surface area of the chromatogram in this range into toluene equivalent". Consequently, the TVOC parameter differs from the sum of all the VOCs detected.

### 4.2. *How to Measure VOC Emission Rates from Wood-Based Materials?*

There are a variety of emission chambers, depending on their size (from a few cm³ to several hundred liters), material (glass, stainless steel), operating temperature, etc. Thanks to their flexibility, emission cells have become the benchmark for VOC analysis and are frequently used for standardized analyses. Table 4 lists the various emission chambers found in the literature, together with the associated method and emission parameters. Finally, Table 5 presents the characteristics of some commercially available chambers and cells.
* a solid-phase microextraction (SPME) fiber;

* a stir bar sorption extraction system (SBSE);

* a passive dosimeter containing a sorbent, as previously mentioned, with various ge-ometries (Radiello tube, badge G.A.B.I.E, 3M type 3500, PerkinElmer tube).

The choice of sampling method depends on the matrix under study and the sensitivity of the detection equipment. If the detection equipment is sufficiently sensitive, sampling without preconcentration may be sufficient for the sample to be directly analyzed. On the other hand, if matrix is very low concentrated in VOCs, it is preferable to consider a preconcentration step. It may also be possible to sample compounds without preconcentration, then concentrate them a posteriori by sorption (e.g., sampling in a bag and adsorption on SPME fiber).

For some VOCs, it is necessary to go through a derivatization stage before analysis, during sampling. This is particularly the case for certain carbonyl compounds [96]. Derivation consists in grafting a group visible with conventional detection methods onto non-detectable compounds. There are a number of different derivatization methods, as well as various derivatization agents. For carbonyl compounds, 2,4-dinitrophenylhydrazine (DNPH) and O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) are frequently used. If analytes are sampled using a SPME fiber, the derivation can be carried out either in the sampling matrix or directly on the SPME fiber. If the analytes are sampled on an adsorbent cartridge, the derivatization agent is located directly on the cartridge (DNPH-impregnated silica gel cartridges).

There may be artefacts linked to the presence of water or ozone in the sampled atmosphere. Palluau et al. [97] demonstrated that the presence of ozone in samples taken from canisters led to a decrease in the concentration of certain unsaturated reactive compounds such as ethylene and propylene. This can also be observed in the study of terpene compounds collected on Tenax TA® cartridges [98]. Palluau et al. [99] also demonstrated that there is a loss of compounds on Carbotrap/Carbosieve adsorbent cartridges when these are exposed to humidity (90% relative humidity).

It should be noted that emissions from a material can also be studied by thermodesorption and pyrolysis analysis [100,101].

### 4.1.2. VOC Analysis

There are two families of VOC analysis techniques: off-line and on-line. For off-line techniques, a sample is taken from the matrix, the compounds are stored in/on their collection media, and then they are usually analyzed by gas or liquid chromatography techniques coupled with mass spectrometry or flame ionisation and UV detection, respectively. On-line analysis techniques can also be used, in particular PTR-MS and SIFT-MS [102–104].

When analyzing VOCs by gas chromatography, the notion of total VOCs (TVOCs) is often introduced, being defined in the European standard ISO is ISO 16000-6 [105] as "the sum of volatile organic compounds, sampled on a Tenax TA® cartridge which elutes between *n*-hexane and *n*-hexadecane included on a non-polar capillary column, detected by flame ionization or mass spectrometry and quantified by converting the total surface area of the chromatogram in this range into toluene equivalent". Consequently, the TVOC parameter differs from the sum of all the VOCs detected.

### 4.2. *How to Measure VOC Emission Rates from Wood-Based Materials?*

There are a variety of emission chambers, depending on their size (from a few cm³ to several hundred liters), material (glass, stainless steel), operating temperature, etc. Thanks to their flexibility, emission cells have become the benchmark for VOC analysis and are frequently used for standardized analyses. Table 4 lists the various emission chambers found in the literature, together with the associated method and emission parameters. Finally, Table 5 presents the characteristics of some commercially available chambers and cells.
<table><caption>**Table 4.** Examples of emission cells used in studies and associated parameters.</caption><thead><tr><th>Reference</th><th>Associated Standard</th><th>Volume of the Chamber (L)</th><th>Chamber Model (Material)</th><th>Emission Surface (m²)</th><th>Air Flow (L min<sup>-1</sup>)</th><th>Specific Air Flow Rate (m³ m<sup>-2</sup> h<sup>-1</sup>)</th><th>Air Velocity (m s<sup>-1</sup>)</th><th>Loading Rate (m<sup>2</sup> m<sup>-3</sup>)</th><th>Air Change Rate (h<sup>-1</sup>)</th><th>Temperature, Relative Humidity (°C, %)</th></tr></thead><tbody><tr><td>[108]</td><td>ASTM D5116-06 [109]</td><td>216</td><td>(Polished stainless steel)</td><td>/</td><td>1.8</td><td>/</td><td>/</td><td>/</td><td>0.5</td><td>25 °C, 50%</td></tr><tr><td>[110]</td><td>QB 1952.2-2011 [111]</td><td>1000</td><td>/</td><td>0.4</td><td>/</td><td>/</td><td>0.2</td><td>0.4</td><td>1</td><td></td></tr><tr><td>[112]</td><td>/</td><td>1000</td><td>(Stainless steel)</td><td>0.9</td><td>/</td><td>/</td><td>0.1-0.3</td><td>0.9; 1.8 and 3.6</td><td>1</td><td>23 °C, 45%</td></tr><tr><td rowspan="3">[113]</td><td rowspan="3">/</td><td>203</td><td>Model VCE 200, Vötsch Industrietechnik (polished stainless steel)</td><td>26.6 × 10<sup>3</sup></td><td>/</td><td>3.83</td><td>/</td><td>0.131</td><td>0.502</td><td rowspan="3">25 °C, 50%</td></tr><tr><td>24</td><td>Designed for the study using a desiccator (glass)</td><td>60 × 10<sup>3</sup></td><td>/</td><td>4.04</td><td>/</td><td>0.250</td><td>1.01</td></tr><tr><td>0.044</td><td>μ-CTE, Markes (stainless steel)</td><td>0.267 × 10<sup>3</sup></td><td>/</td><td>4.28-5.06</td><td>/</td><td>6.07</td><td>26.1-30.7</td></tr><tr><td rowspan="3">[114]</td><td>EN 717-1 [115]</td><td>225</td><td>(Stainless steel)</td><td>0.225</td><td>/</td><td>/</td><td>0.1-0.3</td><td>1</td><td>1</td><td>23 °C, 45%</td></tr><tr><td>ASTM D 6007-02 [116]</td><td>1000</td><td>(Aluminum)</td><td>4.84</td><td>/</td><td>/</td><td>2-5</td><td>0.43</td><td>2</td><td>24 °C, 50%</td></tr><tr><td>EN 717-2 [117]</td><td>4</td><td>(Glass)</td><td>0.02</td><td>1</td><td>/</td><td>/</td><td>/</td><td>60</td><td>60 °C, ≤3%</td></tr><tr><td>[118]</td><td>/</td><td>30</td><td>/</td><td>0.588</td><td>15 × 10<sup>3</sup> or 30 × 10<sup>3</sup></td><td>/</td><td>/</td><td>19.6</td><td>0.5 or 1</td><td>23, 35, 50, or 60 °C, 50%</td></tr><tr><td>[119]</td><td>/</td><td>60 × 10<sup>-3</sup></td><td>MOSEC (Glass)</td><td>0.0017</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>23 °C</td></tr><tr><td>[120]</td><td>/</td><td>8000</td><td>(stainless steel)</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td></td></tr><tr><td>[121]</td><td>/</td><td>0.044</td><td>μ-CTE, Markes (stainless steel)</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>40, 60, or 80 °C</td></tr><tr><td>[122]</td><td>ENV 13419-1 [123]</td><td>1000</td><td>Glass</td><td>/</td><td>/</td><td>1</td><td>0.1-0.3</td><td>1.5; 1 and 1.35</td><td>/</td><td></td></tr><tr><td>[124]</td><td>ISO 16000-9 [125]</td><td>50.9</td><td>CLIMPAQ, Climtech (glass, stainless steel, and aluminum)</td><td>0.099</td><td>/</td><td>0.16</td><td>/</td><td>1.96</td><td>0.3</td><td>23 °C, 50%</td></tr><tr><td>[126]</td><td>ISO 16000-10 [127]</td><td>0.035</td><td>FLEC, Chematech (stainless steel)</td><td>0.0177</td><td>/</td><td>0.0106</td><td>/</td><td>506</td><td>514</td><td></td></tr></tbody></table>

/: unspecified information.
<table><caption>**Table 4.** Examples of emission cells used in studies and associated parameters.</caption><thead><tr><th>Reference</th><th>Associated Standard</th><th>Volume of the Chamber (L)</th><th>Chamber Model (Material)</th><th>Emission Surface (m²)</th><th>Air Flow (L min<sup>-1</sup>)</th><th>Specific Air Flow Rate (m³ m<sup>-2</sup> h<sup>-1</sup>)</th><th>Air Velocity (m s<sup>-1</sup>)</th><th>Loading Rate (m<sup>2</sup> m<sup>-3</sup>)</th><th>Air Change Rate (h<sup>-1</sup>)</th><th>Temperature, Relative Humidity (°C, %)</th></tr></thead><tbody><tr><td>[108]</td><td>ASTM D5116-06 [109]</td><td>216</td><td>(Polished stainless steel)</td><td>/</td><td>1.8</td><td>/</td><td>/</td><td>/</td><td>0.5</td><td>25 °C, 50%</td></tr><tr><td>[110]</td><td>QB 1952.2-2011 [111]</td><td>1000</td><td>/</td><td>0.4</td><td>/</td><td>/</td><td>0.2</td><td>0.4</td><td>1</td><td></td></tr><tr><td>[112]</td><td>/</td><td>1000</td><td>(Stainless steel)</td><td>0.9</td><td>/</td><td>/</td><td>0.1-0.3</td><td>0.9; 1.8 and 3.6</td><td>1</td><td>23 °C, 45%</td></tr><tr><td rowspan="3">[113]</td><td rowspan="3">/</td><td>203</td><td>Model VCE 200, Vötsch Industrietechnik (polished stainless steel)</td><td>26.6 × 10<sup>3</sup></td><td>/</td><td>3.83</td><td>/</td><td>0.131</td><td>0.502</td><td rowspan="3">25 °C, 50%</td></tr><tr><td>24</td><td>Designed for the study using a desiccator (glass)</td><td>60 × 10<sup>3</sup></td><td>/</td><td>4.04</td><td>/</td><td>0.250</td><td>1.01</td></tr><tr><td>0.044</td><td>μ-CTE, Markes (stainless steel)</td><td>0.267 × 10<sup>3</sup></td><td>/</td><td>4.28-5.06</td><td>/</td><td>6.07</td><td>26.1-30.7</td></tr><tr><td rowspan="3">[114]</td><td>EN 717-1 [115]</td><td>225</td><td>(Stainless steel)</td><td>0.225</td><td>/</td><td>/</td><td>0.1-0.3</td><td>1</td><td>1</td><td>23 °C, 45%</td></tr><tr><td>ASTM D 6007-02 [116]</td><td>1000</td><td>(Aluminum)</td><td>4.84</td><td>/</td><td>/</td><td>2-5</td><td>0.43</td><td>2</td><td>24 °C, 50%</td></tr><tr><td>EN 717-2 [117]</td><td>4</td><td>(Glass)</td><td>0.02</td><td>1</td><td>/</td><td>/</td><td>/</td><td>60</td><td>60 °C, ≤3%</td></tr><tr><td>[118]</td><td>/</td><td>30</td><td>/</td><td>0.588</td><td>15 × 10<sup>3</sup> or 30 × 10<sup>3</sup></td><td>/</td><td>/</td><td>19.6</td><td>0.5 or 1</td><td>23, 35, 50, or 60 °C, 50%</td></tr><tr><td>[119]</td><td>/</td><td>60 × 10<sup>-3</sup></td><td>MOSEC (Glass)</td><td>0.0017</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>23 °C</td></tr><tr><td>[120]</td><td>/</td><td>8000</td><td>(stainless steel)</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td></td></tr><tr><td>[121]</td><td>/</td><td>0.044</td><td>μ-CTE, Markes (stainless steel)</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>40, 60, or 80 °C</td></tr><tr><td>[122]</td><td>ENV 13419-1 [123]</td><td>1000</td><td>Glass</td><td>/</td><td>/</td><td>1</td><td>0.1-0.3</td><td>1.5; 1 and 1.35</td><td>/</td><td></td></tr><tr><td>[124]</td><td>ISO 16000-9 [125]</td><td>50.9</td><td>CLIMPAQ, Climtech (glass, stainless steel, and aluminum)</td><td>0.099</td><td>/</td><td>0.16</td><td>/</td><td>1.96</td><td>0.3</td><td>23 °C, 50%</td></tr><tr><td>[126]</td><td>ISO 16000-10 [127]</td><td>0.035</td><td>FLEC, Chematech (stainless steel)</td><td>0.0177</td><td>/</td><td>0.0106</td><td>/</td><td>506</td><td>514</td><td></td></tr></tbody></table>

<footnote>/: unspecified information.</footnote>
<table><caption>**Table 5.** Characteristics of some emission cells mentioned previously.</caption><thead><tr><th>Emission Chamber</th><th>Chamber Volume(s)<br>(Internal Dimensions)</th><th>T<br>(°C)</th><th>RH<br>(%)</th><th>d<br>(L min<sup>-1</sup>)</th><th>ACR<br>(h<sup>-1</sup>)</th><th>Examples of<br>Standards</th></tr></thead><tbody><tr><td>Model VCE 200 or 1000,<br>Vötsch Industrietechnik</td><td>200 L (61 cm × 61 cm × 56 cm)<br>1000 L (75 cm × 163 cm × 75 cm)</td><td>20–130</td><td>5–95</td><td>/</td><td>0.1–1.8</td><td>ISO 16000-1 [128]<br>ENV 13419-1 [123]</td></tr><tr><td>μ-CTE, Markes</td><td>44 mL<br>114 mL</td><td>20–120<br>20–250</td><td>/</td><td>10–70<br>50–500</td><td>/</td><td>ISO 16000-25 [129]<br>ISO 12219-3 [130]<br>ASTM D7706-17 [131]</td></tr><tr><td>CLIMPAQ, Climtech</td><td>50 L (21 cm × 81 cm × 22 cm)</td><td>ambient</td><td>/</td><td>/</td><td>0.02–140</td><td>EN 717-1 [115]<br>ISO 16000 [132]</td></tr><tr><td>FLEC, Chematech</td><td>35 mL<br>(Φ = 150 mm; h<sub>max</sub> = 18 mm)</td><td>ambient</td><td>/</td><td>/</td><td>/</td><td>ISO 16000-10:2006<br>[127]</td></tr></tbody></table>

RH: relative humidity; T: temperature; d: air flow; ACR: air change rate, /: unspecified information.

The surface emission rates (SER) in µg m⁻² h⁻¹ can be calculated for every compound or for the TVOCs using the following equation:

$$ SER = \frac{m - m_0}{V} \times \frac{q}{S} \qquad (1) $$

where m is the mass of the compound(s) studied (µg), m₀ is the mass of compound(s) already present in the environment (µg), V is the the sampled volume (m³), q is the the sampling rate (m³ h⁻¹), and S is the sample surface area (m²).

VOC emissions from materials depend on three parameters: the initial emittable concentration (C₀), the diffusion coefficient (Dₘ), and the partition coefficient (K) [106,107]. Emissions from materials have been modeled and shown to be influenced by factors such as temperature, humidity, and air flow, through the three parameters mentioned above.

## 5. Wood-Based Panel Emissions

### 5.1. Wood Panels Bonded with an Adhesive

#### 5.1.1. VOC Emissions from Wood-Based Panels with a Petrochemical Binder

Formaldehyde is the most widely researched compound. It has been found in the emissions of various wood-based boards such as MDF [133,134], particleboards [118,134], OSB [133–135], or plywood [114,134,136,137]. Formaldehyde was found to originate in a larger amount from the formaldehyde-based binders used, but also from the wood species, in smaller quantities. Other VOCs have been identified in the emissions of wood panels bonded with petrochemical resins (Table 6).

<table><caption>**Table 6.** Type of wood boards and their emissions.</caption><thead><tr><th>Type of Wood Panel</th><th>VOCs Identified in Emissions</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">MDF</td><td>Formaldehyde *</td><td>[133]</td></tr><tr><td>Formaldehyde, acetaldehyde, hexanal</td><td>[134]</td></tr><tr><td>Acetic acid, tetrahydrofuran, α-pinene, styrene, hexane, camphene, p-xylene, dichloromethane, naphthalene</td><td>[138]</td></tr><tr><td rowspan="2">Particleboards</td><td>Formaldehyde, acetaldehyde, propanal, hexanal, pentanal, benzaldehyde, acrolein, acetone</td><td>[134]</td></tr><tr><td>Formaldehyde, n-hexane, 3-methylheptane, 2,2-dimethylhexane, undecane, dodecane, toluene, benzene, xylenes, 1,4-dichlorobenzene, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, 2-methylfuran, 2,3-dimethylnaphthalene, 1,7-dimethylnaphthalene, pentanal, hexanal, nonanal, decanal, 2-pentanone, 4-methyl-2-pentanone, 2-ethylhexanol, isobutanol, n-butanol, ethyl acetate, n-butyl acetate, isoocyl acetate, dibutyl phthalate, dimethyl carbonate, trichloromethane, phthalic anhydride, TVOCs</td><td>[118]</td></tr></tbody></table>
<table><caption>**Table 5.** Characteristics of some emission cells mentioned previously.</caption><thead><tr><th>Emission Chamber</th><th>Chamber Volume(s)<br>(Internal Dimensions)</th><th>T<br>(°C)</th><th>RH<br>(%)</th><th>d<br>(L min<sup>-1</sup>)</th><th>ACR<br>(h<sup>-1</sup>)</th><th>Examples of<br>Standards</th></tr></thead><tbody><tr><td>Model VCE 200 or 1000,<br>Vötsch Industrietechnik</td><td>200 L (61 cm × 61 cm × 56 cm)<br>1000 L (75 cm × 163 cm × 75 cm)</td><td>20–130</td><td>5–95</td><td>/</td><td>0.1–1.8</td><td>ISO 16000-1 [128]<br>ENV 13419-1 [123]</td></tr><tr><td>μ-CTE, Markes</td><td>44 mL<br>114 mL</td><td>20–120<br>20–250</td><td>/</td><td>10–70<br>50–500</td><td>/</td><td>ISO 16000-25 [129]<br>ISO 12219-3 [130]<br>ASTM D7706-17 [131]</td></tr><tr><td>CLIMPAQ, Climtech</td><td>50 L (21 cm × 81 cm × 22 cm)</td><td>ambient</td><td>/</td><td>/</td><td>0.02–140</td><td>EN 717-1 [115]<br>ISO 16000 [132]</td></tr><tr><td>FLEC, Chematech</td><td>35 mL<br>(Φ = 150 mm; h<sub>max</sub> = 18 mm)</td><td>ambient</td><td>/</td><td>/</td><td>/</td><td>ISO 16000-10:2006<br>[127]</td></tr></tbody></table>

RH: relative humidity; T: temperature; d: air flow; ACR: air change rate, /: unspecified information.

The surface emission rates (SER) in µg m⁻² h⁻¹ can be calculated for every compound or for the TVOCs using the following equation:

$$ SER = \frac{m - m_0}{V} \times \frac{q}{S} \qquad (1) $$

where m is the mass of the compound(s) studied (µg), m₀ is the mass of compound(s) already present in the environment (µg), V is the the sampled volume (m³), q is the the sampling rate (m³ h⁻¹), and S is the sample surface area (m²).

VOC emissions from materials depend on three parameters: the initial emittable concentration (C₀), the diffusion coefficient (Dₘ), and the partition coefficient (K) [106,107]. Emissions from materials have been modeled and shown to be influenced by factors such as temperature, humidity, and air flow, through the three parameters mentioned above.

## 5. Wood-Based Panel Emissions

### 5.1. Wood Panels Bonded with an Adhesive

#### 5.1.1. VOC Emissions from Wood-Based Panels with a Petrochemical Binder

Formaldehyde is the most widely researched compound. It has been found in the emissions of various wood-based boards such as MDF [133,134], particleboards [118,134], OSB [133–135], or plywood [114,134,136,137]. Formaldehyde was found to originate in a larger amount from the formaldehyde-based binders used, but also from the wood species, in smaller quantities. Other VOCs have been identified in the emissions of wood panels bonded with petrochemical resins (Table 6).

<table><caption>**Table 6.** Type of wood boards and their emissions.</caption><thead><tr><th>Type of Wood Panel</th><th>VOCs Identified in Emissions</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">MDF</td><td>Formaldehyde *</td><td>[133]</td></tr><tr><td>Formaldehyde, acetaldehyde, hexanal</td><td>[134]</td></tr><tr><td>Acetic acid, tetrahydrofuran, α-pinene, styrene, hexane, camphene, p-xylene, dichloromethane, naphthalene</td><td>[138]</td></tr><tr><td rowspan="2">Particleboards</td><td>Formaldehyde, acetaldehyde, propanal, hexanal, pentanal, benzaldehyde, acrolein, acetone</td><td>[134]</td></tr><tr><td>Formaldehyde, n-hexane, 3-methylheptane, 2,2-dimethylhexane, undecane, dodecane, toluene, benzene, xylenes, 1,4-dichlorobenzene, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, 2-methylfuran, 2,3-dimethylnaphthalene, 1,7-dimethylnaphthalene, pentanal, hexanal, nonanal, decanal, 2-pentanone, 4-methyl-2-pentanone, 2-ethylhexanol, isobutanol, n-butanol, ethyl acetate, n-butyl acetate, isoocyl acetate, dibutyl phthalate, dimethyl carbonate, trichloromethane, phthalic anhydride, TVOCs</td><td>[118]</td></tr></tbody></table>
<table><caption>**Table 6. Cont.**</caption><thead><tr><th>Type of Wood Panel</th><th>VOCs Identified in Emissions</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">OSB</td><td>Formaldehyde, hexanal, and α-pinene, among others</td><td>[135]</td></tr><tr><td>Formaldehyde, acetaldehyde, propanal, pentanal, hexanal, benzaldehyde, furfural, acrolein</td><td>[134]</td></tr><tr><td>Formaldehyde *</td><td>[133]</td></tr><tr><td rowspan="2">Plywood</td><td>Formaldehyde *</td><td>[114,134,136,137]</td></tr><tr><td>Formaldehyde acetaldehyde, propanal, hexanal, pentanal</td><td>[134]</td></tr></tbody></table>

These VOCs can be emitted for months or even years after panel production [139,140]. The nature of these VOCs emitted is linked to a wide range of factors, such as wood species, binder rate, or binder type [141], including carbonyl compounds (formaldehyde, benzaldehyde, hexanal) and terpene compounds (α- and β-pinene, camphene, limonene) [139,140,142].

### 5.1.2. VOC Emissions from Wood-Based Panels with Bio-Based Adhesive

Tupciauskas et al. [143] produced biobased panels from birch. They extracted suberinic acid from the wood, mixed it with birch particles, and thermocompressed it at 226 °C for 9.5 min. They then studied the molecules emitted by these panels by SPME-GC-ToF-MS and detected 49 compounds, including furfural, acetic acid, and 5-methylfurfural as the majority compounds with relative peak areas of 21, 14, and 13%, respectively.

Jia et al. [48] elaborated plywood panels bonded with phenolic resins (PF) based on bio-oil, obtained by the pyrolysis of birch co-products. Emissions of formaldehyde and other VOCs by these panels were then measured according to the percentage replacement of phenol by bio-oil. We observed an increase in formaldehyde emissions with the percentage of bio-oil. The panels also emitted various compounds such as furfural, acetic acid, and hexanal. In addition, some toxic VOCs were detected, such as N,N-dimethylformamide, furfural, and phenol, which are carcinogenic mutagenic reprotoxic (CMR) compounds, or benzofuran, suspected of being carcinogenic.

Panels made with biobased binders therefore emit compounds linked to the thermal degradation of raw material components, such as furfural or acetic acid. In the case of panels bonded with bio-based resins with the phenol-formaldehyde adhesive system, compounds typical of these resins have been identified, notably formaldehyde.

Bio-based panels therefore offer an alternative to petrochemical resins, but the result does not seem entirely satisfactory, since they may emit higher levels of compounds such as formaldehyde [48] than industrial panels marketed today.

### 5.2. Wood Panels Bonded without Adhesive

Since few studies have tracked VOC emissions from unbonded panels and since the thermocompression process can be likened to heat treatment of the raw material, a state of the art on the impact of heat treatment on the VOCs emitted by wood is presented.

#### 5.2.1. VOC Emissions from Heat-Treated Softwoods

Scots pine has been extensively studied. In particular, Manninen et al. [11] compared emissions from simply dried pine with those from pine heat-treated (at 230 °C with steam for 24 h). They identified 41 volatile organic compounds, but only 14 were common to both untreated and treated pine. They showed that the main VOCs in untreated pine are terpenes (notably α-pinene and α-terpinene) and aldehydes (mainly hexanal), accounting for 71% and 25% of total emissions, respectively. Alcohols, ketones, and aromatic hydrocarbons were also detected in small quantities. In the case of treated pine, the main compounds emitted were aldehydes, accounting for 35% of emissions (notably furfural), and carboxylic

<footnote>*: Compound specifically researched.</footnote>
<table><caption>**Table 6. Cont.**</caption><thead><tr><th>Type of Wood Panel</th><th>VOCs Identified in Emissions</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">OSB</td><td>Formaldehyde, hexanal, and α-pinene, among others</td><td>[135]</td></tr><tr><td>Formaldehyde, acetaldehyde, propanal, pentanal, hexanal, benzaldehyde, furfural, acrolein</td><td>[134]</td></tr><tr><td>Formaldehyde *</td><td>[133]</td></tr><tr><td rowspan="2">Plywood</td><td>Formaldehyde *</td><td>[114,134,136,137]</td></tr><tr><td>Formaldehyde acetaldehyde, propanal, hexanal, pentanal</td><td>[134]</td></tr></tbody></table>

These VOCs can be emitted for months or even years after panel production [139,140]. The nature of these VOCs emitted is linked to a wide range of factors, such as wood species, binder rate, or binder type [141], including carbonyl compounds (formaldehyde, benzaldehyde, hexanal) and terpene compounds (α- and β-pinene, camphene, limonene) [139,140,142].

### 5.1.2. VOC Emissions from Wood-Based Panels with Bio-Based Adhesive

Tupciauskas et al. [143] produced biobased panels from birch. They extracted suberinic acid from the wood, mixed it with birch particles, and thermocompressed it at 226 °C for 9.5 min. They then studied the molecules emitted by these panels by SPME-GC-ToF-MS and detected 49 compounds, including furfural, acetic acid, and 5-methylfurfural as the majority compounds with relative peak areas of 21, 14, and 13%, respectively.

Jia et al. [48] elaborated plywood panels bonded with phenolic resins (PF) based on bio-oil, obtained by the pyrolysis of birch co-products. Emissions of formaldehyde and other VOCs by these panels were then measured according to the percentage replacement of phenol by bio-oil. We observed an increase in formaldehyde emissions with the percentage of bio-oil. The panels also emitted various compounds such as furfural, acetic acid, and hexanal. In addition, some toxic VOCs were detected, such as N,N-dimethylformamide, furfural, and phenol, which are carcinogenic mutagenic reprotoxic (CMR) compounds, or benzofuran, suspected of being carcinogenic.

Panels made with biobased binders therefore emit compounds linked to the thermal degradation of raw material components, such as furfural or acetic acid. In the case of panels bonded with bio-based resins with the phenol-formaldehyde adhesive system, compounds typical of these resins have been identified, notably formaldehyde.

Bio-based panels therefore offer an alternative to petrochemical resins, but the result does not seem entirely satisfactory, since they may emit higher levels of compounds such as formaldehyde [48] than industrial panels marketed today.

### 5.2. Wood Panels Bonded without Adhesive

Since few studies have tracked VOC emissions from unbonded panels and since the thermocompression process can be likened to heat treatment of the raw material, a state of the art on the impact of heat treatment on the VOCs emitted by wood is presented.

#### 5.2.1. VOC Emissions from Heat-Treated Softwoods

Scots pine has been extensively studied. In particular, Manninen et al. [11] compared emissions from simply dried pine with those from pine heat-treated (at 230 °C with steam for 24 h). They identified 41 volatile organic compounds, but only 14 were common to both untreated and treated pine. They showed that the main VOCs in untreated pine are terpenes (notably α-pinene and α-terpinene) and aldehydes (mainly hexanal), accounting for 71% and 25% of total emissions, respectively. Alcohols, ketones, and aromatic hydrocarbons were also detected in small quantities. In the case of treated pine, the main compounds emitted were aldehydes, accounting for 35% of emissions (notably furfural), and carboxylic

<footnote>*: Compound specifically researched.</footnote>
acids and their esters, accounting for 30% (mainly acetic acid). Ketone emissions also increased compared to untreated pine (from 1% before treatment to 16% following heat treatment). On the other hand, terpene emissions dropped sharply with heat treatment, accounting for just 10% of total emissions. It is important to note that terpene composition changed with heat treatment, as the authors identified 13 terpenes in emissions from untreated pine, compared with 5 in emissions from treated pine.

Mayes and Oksanen [144] also studied VOC emissions from pine (*Pinus sylvestris*) in connection with Thermowood heat treatment at 180 °C or 230 °C. TVOC emissions decreased after heat treatment (1486 µg m⁻² h⁻¹ for untreated wood versus 828 µg m⁻² h⁻¹ and 235 µg m⁻² h⁻¹ for pine treated at 180 °C and 230 °C, respectively). Emissions from untreated pine were mainly terpenes: α-pinene (174 µg m⁻² h⁻¹), camphene (232 µg m⁻² h⁻¹), and limonene (191 µg m⁻² h⁻¹). Hexanal was also emitted by untreated pine (43 µg m⁻² h⁻¹). Terpene and hexanal emissions decreased with heat treatment temperature (between 180 °C and 230 °C): from 312 to 24 µg m⁻² h⁻¹ for α-pinene, from 32 µg m⁻² h⁻¹ to below the detection limit for camphene, from 153 to 1 µg m⁻² h⁻¹ for limonene, and from 8 µg m⁻² h⁻¹ to below the detection limit for hexanal. Conversely, acetic acid emissions increased with heat treatment temperature: 5 µg m⁻² h⁻¹ for untreated pine, 78 µg m⁻² h⁻¹ for pine treated at 180 °C, and 110 µg m⁻² h⁻¹ for pine treated at 230 °C. Furfural was emitted in greater quantities at 180 °C (29 µg m⁻² h⁻¹) than at 230 °C (10 µg m⁻² h⁻¹).

Sivrikaya et al. [145] also studied VOC emissions from Scots pine (sapwood or heart-wood) but subjected to two types of treatment: heat treatment and vacuum heat treatment, at temperatures of 180 °C or 200 °C. VOC emissions from untreated pine were measured for comparison with those from heat treatment. VOC emissions from untreated heart-wood were found to be more than 10 times higher than those from untreated sapwood (413 mg m⁻² h⁻¹ and 33 mg m⁻² h⁻¹ respectively). The main compound emitted by untreated heartwood and sapwood was α-pinene, with 714 mg m⁻² h⁻¹ for heartwood and 77 mg m⁻² h⁻¹ for sapwood. Camphene, β-pinene, hexanal, and limonene were also identified as the main compounds in heartwood emissions, with 9 mg m⁻² h⁻¹, 8 mg m⁻² h⁻¹, 6 mg m⁻² h⁻¹, and 5 mg m⁻² h⁻¹, respectively. For sapwood emissions, hexanal and pentanal represent 51 mg m⁻² h⁻¹ and 17 mg m⁻² h⁻¹, respectively. TVOC emissions increased for both heat treatments between 180 °C and 200 °C for heartwood and sap-wood. Terpene emissions (α-pinene, β-pinene, camphene, limonene) from heartwood decreased after both types of heat treatment and were lower at 180 °C than at 200 °C, except for pinenes, which were higher at 200 °C for vacuum heat treatment. Sapwood terpene emissions were lower after heat treatment at 180 °C, but higher after heat treatment at 200 °C, except for β-pinene, whose emissions after heat treatment were all higher. Aldehyde emissions varied from compound to compound. The aldehydes initially emitted (pentanal and hexanal) were emitted in very low quantities, or were no longer emitted (pentanal) after heat treatment. Other aldehydes, such as furfural, crotonaldehyde, and benzaldehyde, appeared after treatment or were emitted in larger quantities, although these remained low (<1 mg m⁻² h⁻¹). Other compounds were also released after heat treatment, including alcohols (1-methoxy-2-propanol), ketones (cyclohexanone), and aromatic hydrocarbons (benzene, toluene, and their derivatives), but the quantities emitted were low (<1 mg m⁻² h⁻¹).

Three Tunisian pine species (*Radiata pine*, *Pinus pinaster*, and *Pinus halepensis*) were subjected to different heat treatment severities by Elaieb et al. [146]. Heat treatments were evaluated in terms of sample mass loss: 0% (untreated), 8%, 10%, or 12% mass loss. The three pine species showed similar behavior with regard to VOC emissions. Firstly, the untreated sample emitted significantly more VOCs than the treated samples. The main compounds emitted were hexanal, β-pinene, camphene, nonanal, isobornyl acetate, caryophyllene, humulene, and caryophyllene oxide. Most of these VOCs are no longer emitted after heat treatment. However, at heat treatment corresponding to 8% mass loss, some monoterpenes such as pinene and terpenyl acetate were still detected, and furfural appeared in the emissions. After the most severe heat treatment (12% mass loss), only
acids and their esters, accounting for 30% (mainly acetic acid). Ketone emissions also increased compared to untreated pine (from 1% before treatment to 16% following heat treatment). On the other hand, terpene emissions dropped sharply with heat treatment, accounting for just 10% of total emissions. It is important to note that terpene composition changed with heat treatment, as the authors identified 13 terpenes in emissions from untreated pine, compared with 5 in emissions from treated pine.

Mayes and Oksanen [144] also studied VOC emissions from pine (*Pinus sylvestris*) in connection with Thermowood heat treatment at 180 °C or 230 °C. TVOC emissions decreased after heat treatment (1486 µg m⁻² h⁻¹ for untreated wood versus 828 µg m⁻² h⁻¹ and 235 µg m⁻² h⁻¹ for pine treated at 180 °C and 230 °C, respectively). Emissions from untreated pine were mainly terpenes: α-pinene (174 µg m⁻² h⁻¹), camphene (232 µg m⁻² h⁻¹), and limonene (191 µg m⁻² h⁻¹). Hexanal was also emitted by untreated pine (43 µg m⁻² h⁻¹). Terpene and hexanal emissions decreased with heat treatment temperature (between 180 °C and 230 °C): from 312 to 24 µg m⁻² h⁻¹ for α-pinene, from 32 µg m⁻² h⁻¹ to below the detection limit for camphene, from 153 to 1 µg m⁻² h⁻¹ for limonene, and from 8 µg m⁻² h⁻¹ to below the detection limit for hexanal. Conversely, acetic acid emissions increased with heat treatment temperature: 5 µg m⁻² h⁻¹ for untreated pine, 78 µg m⁻² h⁻¹ for pine treated at 180 °C, and 110 µg m⁻² h⁻¹ for pine treated at 230 °C. Furfural was emitted in greater quantities at 180 °C (29 µg m⁻² h⁻¹) than at 230 °C (10 µg m⁻² h⁻¹).

Sivrikaya et al. [145] also studied VOC emissions from Scots pine (sapwood or heart-wood) but subjected to two types of treatment: heat treatment and vacuum heat treatment, at temperatures of 180 °C or 200 °C. VOC emissions from untreated pine were measured for comparison with those from heat treatment. VOC emissions from untreated heart-wood were found to be more than 10 times higher than those from untreated sapwood (413 mg m⁻² h⁻¹ and 33 mg m⁻² h⁻¹ respectively). The main compound emitted by untreated heartwood and sapwood was α-pinene, with 714 mg m⁻² h⁻¹ for heartwood and 77 mg m⁻² h⁻¹ for sapwood. Camphene, β-pinene, hexanal, and limonene were also identified as the main compounds in heartwood emissions, with 9 mg m⁻² h⁻¹, 8 mg m⁻² h⁻¹, 6 mg m⁻² h⁻¹, and 5 mg m⁻² h⁻¹, respectively. For sapwood emissions, hexanal and pentanal represent 51 mg m⁻² h⁻¹ and 17 mg m⁻² h⁻¹, respectively. TVOC emissions increased for both heat treatments between 180 °C and 200 °C for heartwood and sap-wood. Terpene emissions (α-pinene, β-pinene, camphene, limonene) from heartwood decreased after both types of heat treatment and were lower at 180 °C than at 200 °C, except for pinenes, which were higher at 200 °C for vacuum heat treatment. Sapwood terpene emissions were lower after heat treatment at 180 °C, but higher after heat treatment at 200 °C, except for β-pinene, whose emissions after heat treatment were all higher. Aldehyde emissions varied from compound to compound. The aldehydes initially emitted (pentanal and hexanal) were emitted in very low quantities, or were no longer emitted (pentanal) after heat treatment. Other aldehydes, such as furfural, crotonaldehyde, and benzaldehyde, appeared after treatment or were emitted in larger quantities, although these remained low (<1 mg m⁻² h⁻¹). Other compounds were also released after heat treatment, including alcohols (1-methoxy-2-propanol), ketones (cyclohexanone), and aromatic hydrocarbons (benzene, toluene, and their derivatives), but the quantities emitted were low (<1 mg m⁻² h⁻¹).

Three Tunisian pine species (*Radiata pine*, *Pinus pinaster*, and *Pinus halepensis*) were subjected to different heat treatment severities by Elaieb et al. [146]. Heat treatments were evaluated in terms of sample mass loss: 0% (untreated), 8%, 10%, or 12% mass loss. The three pine species showed similar behavior with regard to VOC emissions. Firstly, the untreated sample emitted significantly more VOCs than the treated samples. The main compounds emitted were hexanal, β-pinene, camphene, nonanal, isobornyl acetate, caryophyllene, humulene, and caryophyllene oxide. Most of these VOCs are no longer emitted after heat treatment. However, at heat treatment corresponding to 8% mass loss, some monoterpenes such as pinene and terpenyl acetate were still detected, and furfural appeared in the emissions. After the most severe heat treatment (12% mass loss), only
acetic acid, due to the thermal degradation of hemicelluloses, vanillin, and guaiacylacetone, the first lignin degradation products, were detected.

Hyttinen et al. [147] studied emissions from untreated and treated wood (spruce, Scots pine, and aspen) for 28 days. They showed that TVOC emissions from spruce and Scots pine decreased with heat treatment (from 550 µg m⁻² h⁻¹ to 220 µg m⁻² h⁻¹ and from 2000 µg m⁻² h⁻¹ to 240 µg m⁻² h⁻¹, respectively). The main emissions from untreated spruce were α-pinene (40–120 µg m⁻² h⁻¹), limonene (40–140 µg m⁻² h⁻¹), and β-pinene (20–66 µg m⁻² h⁻¹). In treated spruce, acetic acid (17–53 µg m⁻² h⁻¹), furfural (14–23 µg m⁻² h⁻¹), and α-pinene (3–18 µg m⁻² h⁻¹) were detected in the majority of cases. For untreated Scots pine, the compounds emitted in the greatest quantities were α-pinene (410–890 µg m⁻² h⁻¹), Δ-3-carene (340–680 µg m⁻² h⁻¹), and hexanal (22–70 µg m⁻² h⁻¹), while for treated Scots pine were acetic acid (4–86 µg m⁻² h⁻¹), furfural (11–26 µg m⁻² h⁻¹), and hexanal (10–17 µg m⁻² h⁻¹).

Peters et al. [148] studied Thermoholz-treated wood (spruce, maple, beech, and ash) at 180 and 200 °C and compared it with its untreated peers. Emissions from untreated spruce were mainly terpenes (mono-, sesqui-, and diterpenes), accounting for around 95% of total VOC emissions. After heat treatment, carboxylic acid and aldehyde emissions increased (representing 25% and 10% of total emissions, respectively), while terpene emissions decreased. However, terpene emissions remained in the majority after treatment, accounting for around 65% of total emissions. Peters et al. [148] identified over 50 terpenes emitted by untreated spruce: α- and β-pinene, sylvestrene, caryophyllene, and γ- and δ-cadinene were the main compounds. As for aldehydes, hexanal accounted for 70% of aldehydes emitted by untreated spruce. After treatment, hexanal accounted for only 1.4% of aldehyde emissions, while furfural and 5-methylfurfural accounted for a very high 96% of the aldehyde fraction.

All these studies concluded that the compounds emitted by untreated softwood were mainly terpene compounds, in particular pinenes, limonene, or camphene, as well as a few aldehydes in smaller quantities (hexanal). On the other hand, after heat treatment, the total quantity of VOCs emitted was lower than before heat treatment, with aldehyde compounds predominating, notably acetic acid and furfural.

### 5.2.2. VOC Emissions from Heat-Treated Hardwoods

Hyttinen et al. [147] compared emissions from poplar (*Populus tremula*) before and after heat treatment at 190 °C and found that poplar before heat treatment emitted more VOCs than after (513 µg m⁻² h⁻¹ vs. 109 µg m⁻² h⁻¹). In addition, they observed that the VOCs most emitted before and after treatment were carbonyl compounds. Before treatment, emissions were mainly represented by hexanal, acetic acid, and pentanal, with respective emission rates of 330 µg m⁻² h⁻¹, 54 µg m⁻² h⁻¹, and 46 µg m⁻² h⁻¹. In contrast, after heat treatment, acetic acid and furfural were the major compounds, with emission rates of 88 µg m⁻² h⁻¹ and 77 µg m⁻² h⁻¹, respectively.

Čech and Tesařová [149] studied VOC emissions from untreated poplar and poplar heat treated at 180 °C or 200 °C, demonstrating in particular that VOC emissions from poplar increased with heat treatment and with treatment temperature. Indeed, 3 h after heat treatment, poplar emissions were linked to 31 µg m⁻³, 73 µg m⁻³, and 178 µg m⁻³ concentration in the emission chamber for untreated wood, wood treated at 180 °C, and wood treated at 200 °C, respectively. They observed a strong influence of treatment temperature on furfural and phenol emissions in particular, which are typical compounds of hemicellulose and lignin degradation.

VOC emissions from heat-treated poplar were analyzed by Xue et al. [145]. For this, the authors compared untreated poplar with poplar treated at 160 °C, 180 °C, 200 °C, or 220 °C. Like Čech and Tesařová [149], they found that VOC emissions were higher after wood treatment. Xue et al. [150] classified VOC emissions by compound type (alcohols, aldehydes, furans, aromatic compounds, esters, and alkanes). Aldehydes were the compounds emitted most at all treatment temperatures (except 220 °C), with a maximum contribution of 83% at 180 °C. For untreated poplar, aldehyde emissions accounted for 30% of total emissions,
acetic acid, due to the thermal degradation of hemicelluloses, vanillin, and guaiacylacetone, the first lignin degradation products, were detected.

Hyttinen et al. [147] studied emissions from untreated and treated wood (spruce, Scots pine, and aspen) for 28 days. They showed that TVOC emissions from spruce and Scots pine decreased with heat treatment (from 550 µg m⁻² h⁻¹ to 220 µg m⁻² h⁻¹ and from 2000 µg m⁻² h⁻¹ to 240 µg m⁻² h⁻¹, respectively). The main emissions from untreated spruce were α-pinene (40–120 µg m⁻² h⁻¹), limonene (40–140 µg m⁻² h⁻¹), and β-pinene (20–66 µg m⁻² h⁻¹). In treated spruce, acetic acid (17–53 µg m⁻² h⁻¹), furfural (14–23 µg m⁻² h⁻¹), and α-pinene (3–18 µg m⁻² h⁻¹) were detected in the majority of cases. For untreated Scots pine, the compounds emitted in the greatest quantities were α-pinene (410–890 µg m⁻² h⁻¹), Δ-3-carene (340–680 µg m⁻² h⁻¹), and hexanal (22–70 µg m⁻² h⁻¹), while for treated Scots pine were acetic acid (4–86 µg m⁻² h⁻¹), furfural (11–26 µg m⁻² h⁻¹), and hexanal (10–17 µg m⁻² h⁻¹).

Peters et al. [148] studied Thermoholz-treated wood (spruce, maple, beech, and ash) at 180 and 200 °C and compared it with its untreated peers. Emissions from untreated spruce were mainly terpenes (mono-, sesqui-, and diterpenes), accounting for around 95% of total VOC emissions. After heat treatment, carboxylic acid and aldehyde emissions increased (representing 25% and 10% of total emissions, respectively), while terpene emissions decreased. However, terpene emissions remained in the majority after treatment, accounting for around 65% of total emissions. Peters et al. [148] identified over 50 terpenes emitted by untreated spruce: α- and β-pinene, sylvestrene, caryophyllene, and γ- and δ-cadinene were the main compounds. As for aldehydes, hexanal accounted for 70% of aldehydes emitted by untreated spruce. After treatment, hexanal accounted for only 1.4% of aldehyde emissions, while furfural and 5-methylfurfural accounted for a very high 96% of the aldehyde fraction.

All these studies concluded that the compounds emitted by untreated softwood were mainly terpene compounds, in particular pinenes, limonene, or camphene, as well as a few aldehydes in smaller quantities (hexanal). On the other hand, after heat treatment, the total quantity of VOCs emitted was lower than before heat treatment, with aldehyde compounds predominating, notably acetic acid and furfural.

### 5.2.2. VOC Emissions from Heat-Treated Hardwoods

Hyttinen et al. [147] compared emissions from poplar (*Populus tremula*) before and after heat treatment at 190 °C and found that poplar before heat treatment emitted more VOCs than after (513 µg m⁻² h⁻¹ vs. 109 µg m⁻² h⁻¹). In addition, they observed that the VOCs most emitted before and after treatment were carbonyl compounds. Before treatment, emissions were mainly represented by hexanal, acetic acid, and pentanal, with respective emission rates of 330 µg m⁻² h⁻¹, 54 µg m⁻² h⁻¹, and 46 µg m⁻² h⁻¹. In contrast, after heat treatment, acetic acid and furfural were the major compounds, with emission rates of 88 µg m⁻² h⁻¹ and 77 µg m⁻² h⁻¹, respectively.

Čech and Tesařová [149] studied VOC emissions from untreated poplar and poplar heat treated at 180 °C or 200 °C, demonstrating in particular that VOC emissions from poplar increased with heat treatment and with treatment temperature. Indeed, 3 h after heat treatment, poplar emissions were linked to 31 µg m⁻³, 73 µg m⁻³, and 178 µg m⁻³ concentration in the emission chamber for untreated wood, wood treated at 180 °C, and wood treated at 200 °C, respectively. They observed a strong influence of treatment temperature on furfural and phenol emissions in particular, which are typical compounds of hemicellulose and lignin degradation.

VOC emissions from heat-treated poplar were analyzed by Xue et al. [145]. For this, the authors compared untreated poplar with poplar treated at 160 °C, 180 °C, 200 °C, or 220 °C. Like Čech and Tesařová [149], they found that VOC emissions were higher after wood treatment. Xue et al. [150] classified VOC emissions by compound type (alcohols, aldehydes, furans, aromatic compounds, esters, and alkanes). Aldehydes were the compounds emitted most at all treatment temperatures (except 220 °C), with a maximum contribution of 83% at 180 °C. For untreated poplar, aldehyde emissions accounted for 30% of total emissions,
with decanal (10% of total VOC emissions), 2-nonenal (10% of total VOC emissions), and nonanal (5% of total VOC emissions) as the main compounds. However, the main compound emitted by untreated poplar was a carboxylic acid: oxalic acid (32% of total VOC emissions). Aromatic compounds were the second most emitted by untreated poplar, along with naphthalene (6% of total VOC emissions) and methylnaphthalene (12% of total VOC emissions). At 160 °C and 180 °C, aldehydes remained the dominant compounds, accounting for over 70% of emissions at 160 °C and over 80% at 180 °C. Indeed, 2-nonenal, furfural, and decanal represented, respectively, 40%, 4%, and 11% of total VOC emissions at 160 °C and 43%, 17%, and 5% of total VOC emissions at 180 °C. At 200 °C, furfural became the majority aldehyde, accounting for 27% of total VOC emissions. However, at 200 °C, phenol appeared and was emitted in greater quantities than furfural, accounting for 29% of total VOC emissions. Emissions of aromatic compounds generally increased with temperature, reaching 30% of total VOC emissions at 220 °C, with phenol (16% of total VOC emissions), methylnaphthalene (10% of total VOC emissions), and naphthalene (4% of total VOC emissions). Esters appeared at 180 °C and increased with temperature, accounting for 13% of total emissions at 220 °C, with methyl benzoate (9% of total VOC emissions) the main compound at 220 °C.

Peters et al. [148] studied emissions from maple (*Acer pseudoplatanus*), beech (*Fagus sylvatica*), and ash (*Fraxinus excelsior*) before and after heat treatment at three temperatures: 60 °C, 180 °C, and 200 °C. The main compounds emitted by the three species before treatment were aldehydes and carboxylic acids. In the case of ash, aldehydes accounted for almost 90% of pre-treatment VOC emissions, while carboxylic acids accounted for around 55% of emissions from maple and poplar. For all three species, hexanal was the aldehyde most emitted by untreated wood. Following heat treatment at 180 °C, aldehyde emissions from all three species decreased, while carboxylic acid emissions increased (particularly acetic acid). On the other hand, when comparing treatment at 180 °C with treatment at 200 °C, carboxylic acid emissions decreased and aldehyde emissions increased (largely dominated by furfural) for all three species studied.

The VOCs emitted by native hardwoods therefore appeared to be very diverse. On the other hand, when subjected to heat treatment, an increase in carbonyl compounds (carboxylic acids and aldehydes) was observed, reflecting the degradation of the various wood components (hemicelluloses and cellulose), as seen above.

### 5.2.3. VOC Emissions from Binderless Boards

To our knowledge, only two studies published results concerning VOC emissions from binderless panels obtained by cooking-compression. The first one concerns binderless panels made from an extrusion-refined coriander straw and a deoiled coriander press cake [151,152]. These cakes were obtained by extrusion and were then thermopressed at 205 °C for 5 min under 21.6 MPa pressure. Acetaldehyde, linalool, camphor, and *p*-cymene were identified as the majority emitted compounds, with emission rates of around 31 µg m⁻² h⁻¹, 23 µg m⁻² h⁻¹, 9 µg m⁻² h⁻¹, and 4.4 µg m⁻² h⁻¹, respectively. Linalool and camphor emissions were attributed in particular to the residual presence of essential oil in the materials. Formaldehyde emissions were below the detection limit estimated at 0.2 µg m⁻² h⁻¹, while those of MDF and chipboard determined under the same conditions were, respectively, 42 and 84 µg m⁻² h⁻¹. For these two materials, formaldehyde was the main compound emitted.

The second study concerns binderless boards produced from *Quercus robur* under various processing parameters (time, pressure, temperature) to observe their impact on the board VOC emissions [101,153]. VOC from these panels were studied in two ways. Firstly, emissions were measured in emission chambers. Secondly, the panels were pyrolyzed. Twenty-eight VOCs were identified by the pyrolysis of the binderless boards such as acetic acid, furfural, oak lactone, isoeugenol, vanillin, coniferaldehyde, and sinapaldehyde. Quantification of the VOC emissions led to the identification of acetaldehyde, formaldehyde,
with decanal (10% of total VOC emissions), 2-nonenal (10% of total VOC emissions), and nonanal (5% of total VOC emissions) as the main compounds. However, the main compound emitted by untreated poplar was a carboxylic acid: oxalic acid (32% of total VOC emissions). Aromatic compounds were the second most emitted by untreated poplar, along with naphthalene (6% of total VOC emissions) and methylnaphthalene (12% of total VOC emissions). At 160 °C and 180 °C, aldehydes remained the dominant compounds, accounting for over 70% of emissions at 160 °C and over 80% at 180 °C. Indeed, 2-nonenal, furfural, and decanal represented, respectively, 40%, 4%, and 11% of total VOC emissions at 160 °C and 43%, 17%, and 5% of total VOC emissions at 180 °C. At 200 °C, furfural became the majority aldehyde, accounting for 27% of total VOC emissions. However, at 200 °C, phenol appeared and was emitted in greater quantities than furfural, accounting for 29% of total VOC emissions. Emissions of aromatic compounds generally increased with temperature, reaching 30% of total VOC emissions at 220 °C, with phenol (16% of total VOC emissions), methylnaphthalene (10% of total VOC emissions), and naphthalene (4% of total VOC emissions). Esters appeared at 180 °C and increased with temperature, accounting for 13% of total emissions at 220 °C, with methyl benzoate (9% of total VOC emissions) the main compound at 220 °C.

Peters et al. [148] studied emissions from maple (*Acer pseudoplatanus*), beech (*Fagus sylvatica*), and ash (*Fraxinus excelsior*) before and after heat treatment at three temperatures: 60 °C, 180 °C, and 200 °C. The main compounds emitted by the three species before treatment were aldehydes and carboxylic acids. In the case of ash, aldehydes accounted for almost 90% of pre-treatment VOC emissions, while carboxylic acids accounted for around 55% of emissions from maple and poplar. For all three species, hexanal was the aldehyde most emitted by untreated wood. Following heat treatment at 180 °C, aldehyde emissions from all three species decreased, while carboxylic acid emissions increased (particularly acetic acid). On the other hand, when comparing treatment at 180 °C with treatment at 200 °C, carboxylic acid emissions decreased and aldehyde emissions increased (largely dominated by furfural) for all three species studied.

The VOCs emitted by native hardwoods therefore appeared to be very diverse. On the other hand, when subjected to heat treatment, an increase in carbonyl compounds (carboxylic acids and aldehydes) was observed, reflecting the degradation of the various wood components (hemicelluloses and cellulose), as seen above.

### 5.2.3. VOC Emissions from Binderless Boards

To our knowledge, only two studies published results concerning VOC emissions from binderless panels obtained by cooking-compression. The first one concerns binderless panels made from an extrusion-refined coriander straw and a deoiled coriander press cake [151,152]. These cakes were obtained by extrusion and were then thermopressed at 205 °C for 5 min under 21.6 MPa pressure. Acetaldehyde, linalool, camphor, and *p*-cymene were identified as the majority emitted compounds, with emission rates of around 31 µg m⁻² h⁻¹, 23 µg m⁻² h⁻¹, 9 µg m⁻² h⁻¹, and 4.4 µg m⁻² h⁻¹, respectively. Linalool and camphor emissions were attributed in particular to the residual presence of essential oil in the materials. Formaldehyde emissions were below the detection limit estimated at 0.2 µg m⁻² h⁻¹, while those of MDF and chipboard determined under the same conditions were, respectively, 42 and 84 µg m⁻² h⁻¹. For these two materials, formaldehyde was the main compound emitted.

The second study concerns binderless boards produced from *Quercus robur* under various processing parameters (time, pressure, temperature) to observe their impact on the board VOC emissions [101,153]. VOC from these panels were studied in two ways. Firstly, emissions were measured in emission chambers. Secondly, the panels were pyrolyzed. Twenty-eight VOCs were identified by the pyrolysis of the binderless boards such as acetic acid, furfural, oak lactone, isoeugenol, vanillin, coniferaldehyde, and sinapaldehyde. Quantification of the VOC emissions led to the identification of acetaldehyde, formaldehyde,
acetic acid, and furfural as the major emitted compounds at, respectively, 109 µg m⁻² h⁻¹, 44 µg m⁻² h⁻¹, 180 µgₐeq toluene m⁻² h⁻¹, and 126 µgₐeq toluene m⁻² h⁻¹.

It clearly appears that binderless boards, although free of petrochemical or bio-based binders, can lead to emission of compounds known for their toxicity (formaldehyde, furfural, etc.) in significant quantities. It is therefore essential to take them into account as part of any strategy to develop such materials.

**6. Conclusions**

Wood is a natural heteropolymer made up of a number of polymers: cellulose, hemi-celluloses, and lignin. These three components vary in quantity, composition, and size, depending on the nature of the wood. They provide both rigidity and flexibility to plant cells, enabling lignocellulosic organisms to grow both in width and height. Cellulose, hemicelluloses, and lignin also confer certain properties to the material. When subjected to heat, hemicelluloses and lignin undergo chemical changes. Hemicelluloses release acetic acid, which catalyzes future depolymerization reactions, releasing furan compounds such as furfural or 5-methylfurfural. At the same time, lignin plasticizes, enabling it to encapsulate cellulose fibers and hemicelluloses. On cooling, the lignin congeals, while the furan compounds released earlier resinify. Thanks to these self-adhesive properties, many lignocellulosic materials have been used to develop binderless panels.

Moreover, indoor air quality, and in particular the presence of VOCs in indoor air, has become a major concern for health authorities. Techniques for sampling and analyzing VOCs have developed to enable the analysis of numerous compounds with ever-lower detection limits, facilitating, among other things, the identification of sources emitting VOCs into indoor air. Numerous laws and decrees have been published over the past two decades to reduce emissions from building materials in particular. While existing materials are subject to studies aimed at reducing their VOC emissions, new materials are in the development phase.

Therefore, binderless panels are now showing their potential as bio-based materials that can be produced from co-products, and as an alternative to the industrialized wood-based panels using petrochemical resins. Numerous studies have been carried out to determine the optimum processing conditions for a given material, in order to obtain panels with satisfactory mechanical strength, dimensional stability, and water resistance. However, very few studies have focused on VOC emissions from these panels. It is nevertheless necessary to identify and quantify the compounds emitted, in order to judge the suitability of binderless panels for use today in sectors such as construction or furnishings, or even to replace existing panels.

This review provides an overview of the main methodologies used to analyze volatile substances in materials, together with examples of standards. It may offer a useful approach to identify and quantify VOC emissions of materials. Such data could be used in life cycle assessment evaluation of bio-based materials in order to reinforce wood binderless boards market attractiveness as regards sustainability representing an alternative to the current wood market. Only a few applications are available, and these methodologies should be more widely applied to gain knowledge on VOCs, which are relevant indicators for the development of environmentally friendly materials.

**Author Contributions:** Conceptualization, E.B., V.S. and C.D.R.; writing—original draft preparation, E.B.; writing—review and editing, E.B., V.S. and C.D.R.; supervision, V.S. and C.D.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the French Ministère de l'Enseignement Supérieur et de la Recherche as part of a Ph.D. grant.

**Conflicts of Interest:** The authors declare no conflicts of interest.
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2. FAOSTAT. Food and Agriculture Data. Available online: https://www.fao.org/faostat/en/#compare (accessed on 26 June 2023).

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109. ASTM D5116-06; Standard Guide for Small Scale Environmental Chamber Determinations of Organic Emissions from Indoor Materials/Products. ASTM International: West Conshohocken, PA, USA, 2006.

110. Cao, S.; Wen, Y.; Xi, C.; Li, X.; Zhang, L.; Wang, G.; Shang, J. Development of a method based on thermal desorption-gas chromatography/mass spectrometry for the determination of 103 volatile organic compounds in mattresses. *Int. J. Environ. Anal. Chem.* **2019**, *100*, 1044–1065. [CrossRef]

111. QB/T 1952.2-2011; Upholstered Furniture-Spring Mattress. Standardization Administration of China: Beijing, China, 2011.

112. Yan, M.; Zhai, Y.; Shi, P.; Hu, Y.; Yang, H.; Zhao, H. Emission of volatile organic compounds from new furniture products and its impact on human health. *Hum. Ecol. Risk Assess.* **2019**, *25*, 1886–1906. [CrossRef]

113. Even, M.; Hutzler, C.; Wilke, O.; Luch, A. Emissions of volatile organic compounds from polymer-based consumer products: Comparison of three emission chamber sizes. *Indoor Air* **2020**, *30*, 40–48. [CrossRef] [PubMed]

114. Salem, M.Z.M.; Böhm, M.; Srba, J.; Beránková, J. Evaluation of formaldehyde emission from different types of wood-based panels and flooring materials using different standard test methods. *Build. Environ.* **2012**, *49*, 86–96. [CrossRef]

115. EN 717-1; Wood-Based Panels—Determination of Formaldehyde Release—Part 1: Formaldehyde Emission by the Chamber Method. European Standard Norm: Geneva, Switzerland, 2004.

116. ASTM D 6007-02; Standard Test Method for Determining Formaldehyde Concentration in Air from Wood Products Using a Small Scale Chamber. ASTM International: West Conshohocken, PA, USA, 2008.

117. EN 717-2; Wood-Based Panels Determination of Formaldehyde Release. Part 2: Formaldehyde Release by the Gas Analysis Method. European Standard Norm: Geneva, Switzerland, 1994.

118. Jiang, C.; Li, D.; Zhang, P.; Li, J.; Wang, J.; Yu, J. Formaldehyde and volatile organic compound (VOC) emissions from particleboard: Identification of odorous compounds and effects of heat treatment. *Build. Environ.* **2017**, *117*, 118–126. [CrossRef]
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93. Król, S.; Zabiegała, B.; Namieśnik, J. Monitoring VOCs in atmospheric air II. Sample collection and preparation. *Trends Anal. Chem.* **2010**, *29*, 1101–1112. [CrossRef]

94. Even, M.; Juritsch, E.; Richter, M. Measurement of very volatile organic compounds (VVOCs) in indoor air by sorbent-based active sampling: Identifying the gaps towards standardisation. *Trends Anal. Chem.* **2021**, *140*, 116265. [CrossRef]

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96. Szulejko, J.E.; Kim, K.-H. Derivatization techniques for determination of carbonyls in air. *Trends Anal. Chem.* **2015**, *64*, 29–41. [CrossRef]

97. Palluau, F.; Mirabel, P.; Millet, M. Influence of Relative Humidity and Ozone on the Sampling of Volatile Organic Compounds on Carbotrap/Carbosieve Adsorbents. *Environ. Monit. Assess.* **2007**, *127*, 177–187. [CrossRef] [PubMed]

98. Dettmer, K.; Engewald, W. Ambient air analysis of volatile organic compounds using adsorptive enrichment. *Chromatographia* **2003**, *57* (Suppl. S1), S339–S347. [CrossRef]

99. Palluau, F.; Mirabel, P.; Millet, M. Influence of ozone on the sampling and storage of volatile organic compounds in canisters. *Environ. Chem. Lett.* **2007**, *5*, 51–55. [CrossRef]

100. Murat, P.; Harohalli Puttaswamy, S.; Ferret, P.-J.; Coslédan, S.; Simon, V. Identification of Potential Extractables and Leachables in Cosmetic Plastic Packaging by Microchambers-Thermal Extraction and Pyrolysis- Gas Chromatography-Mass Spectrometry. *Molecules* **2020**, *25*, 2115. [CrossRef] [PubMed]

101. Bertheau, E.; Simon, V.; Delgado Raynaud, C. Microchamber Extraction and Analytical Pyrolysis to Explore Volatile Organic Compounds from Compression-Cooking Wood Materials Obtained under Different Conditions. *Molecules* **2022**, *27*, 8260. [CrossRef] [PubMed]

102. Baerenzung dit Baron, T.; Yobrégat, O.; Jacques, A.; Simon, V.; Geffroy, O. A novel approach to discriminate the volatilome of *Vitis vinifera* berries by selected ion flow tube mass Spectrometry analysis and chemometrics. *Food Res. Int.* **2022**, *157*, 111434. [CrossRef] [PubMed]

103. Majchrzak, T.; Wojnowski, W.; Lubinska-Szczygeł, M.; Różańska, A.; Namieśnik, J.; Dymerski, T. PTR-MS and GC-MS as complementary techniques for analysis of volatiles: A tutorial review. *Anal. Chim. Acta* **2018**, *1035*, 1–13. [CrossRef]

104. Vitola Pasetto, L.; Simon, V.; Richard, R.; Pic, J.-S.; Violleau, F.; Manero, M.-H. Aldehydes gas ozonation monitoring: Interest of SIFT/MS versus GC/FID. *Chemosphere* **2019**, *235*, 1107–1115. [CrossRef]

105. ISO 16000-6; Indoor Air—Part 6: Determination of Volatile Organic Compounds in Indoor and Test Chamber Air by Active Sampling on Tenax TA Sorbent, Thermal Desorption and Gas Chromatography Using MS or MS-FID. International Organization for Standardization: Geneva, Switzerland, 2011.

106. Zhang, L.Z.; Niu, J.L. Modeling VOCs emissions in a room with a single-zone multi-component multi-layer technique. *Build. Environ.* **2004**, *39*, 523–531. [CrossRef]

107. Deng, B.; Kim, C.N. An analytical model for VOCs emission from dry building materials. *Atmos. Environ.* **2004**, *38*, 1173–1180. [CrossRef]

108. Cheng, Y.-H.; Lin, C.-C.; Hsu, S.-C. Comparison of conventional and green building materials in respect of VOC emissions and ozone impact on secondary carbonyl emissions. *Build. Environ.* **2015**, *87*, 274–282. [CrossRef]

109. ASTM D5116-06; Standard Guide for Small Scale Environmental Chamber Determinations of Organic Emissions from Indoor Materials/Products. ASTM International: West Conshohocken, PA, USA, 2006.

110. Cao, S.; Wen, Y.; Xi, C.; Li, X.; Zhang, L.; Wang, G.; Shang, J. Development of a method based on thermal desorption-gas chromatography/mass spectrometry for the determination of 103 volatile organic compounds in mattresses. *Int. J. Environ. Anal. Chem.* **2019**, *100*, 1044–1065. [CrossRef]

111. QB/T 1952.2-2011; Upholstered Furniture-Spring Mattress. Standardization Administration of China: Beijing, China, 2011.

112. Yan, M.; Zhai, Y.; Shi, P.; Hu, Y.; Yang, H.; Zhao, H. Emission of volatile organic compounds from new furniture products and its impact on human health. *Hum. Ecol. Risk Assess.* **2019**, *25*, 1886–1906. [CrossRef]

113. Even, M.; Hutzler, C.; Wilke, O.; Luch, A. Emissions of volatile organic compounds from polymer-based consumer products: Comparison of three emission chamber sizes. *Indoor Air* **2020**, *30*, 40–48. [CrossRef] [PubMed]

114. Salem, M.Z.M.; Böhm, M.; Srba, J.; Beránková, J. Evaluation of formaldehyde emission from different types of wood-based panels and flooring materials using different standard test methods. *Build. Environ.* **2012**, *49*, 86–96. [CrossRef]

115. EN 717-1; Wood-Based Panels—Determination of Formaldehyde Release—Part 1: Formaldehyde Emission by the Chamber Method. European Standard Norm: Geneva, Switzerland, 2004.

116. ASTM D 6007-02; Standard Test Method for Determining Formaldehyde Concentration in Air from Wood Products Using a Small Scale Chamber. ASTM International: West Conshohocken, PA, USA, 2008.

117. EN 717-2; Wood-Based Panels Determination of Formaldehyde Release. Part 2: Formaldehyde Release by the Gas Analysis Method. European Standard Norm: Geneva, Switzerland, 1994.

118. Jiang, C.; Li, D.; Zhang, P.; Li, J.; Wang, J.; Yu, J. Formaldehyde and volatile organic compound (VOC) emissions from particleboard: Identification of odorous compounds and effects of heat treatment. *Build. Environ.* **2017**, *117*, 118–126. [CrossRef]
119. Souillier, A.; Plaisance, H.; Desauziers, V. New SPME-based method for on-site measurement of gas-phase concentration of phthalates and alternatives at the surface of PVC floorings. *Green Anal. Chem.* **2022**, *1*, 100012. [CrossRef]

120. He, J.; Zou, Z.; Yang, X. Measuring whole-body volatile organic compound emission by humans: A pilot study using an air-tight environmental chamber. *Build. Environ.* **2019**, *153*, 101–109. [CrossRef]

121. Yang, Y.; Zhang, M.; Yin, H.; Deng, Y.; Jiang, Y.; Yuan, H.; Dong, C.; Li, J.; Hua, J.; Wang, J. Rapid profiling of volatile compounds in green teas using Micro-Chamber/Thermal Extractor combined with thermal desorption coupled to gas chromatography-mass spectrometry followed by multivariate statistical analysis. *LWT* **2018**, *96*, 42–50. [CrossRef]

122. Massold, E.; Bähr, C.; Salthammer, T.; Brown, S.K. Determination of VOC and TVOC in Air Using Thermal Desorption GC-MS-Practical Implications for Test Chamber Experiments. *Chromatographia* **2005**, *62*, 75–85. [CrossRef]

123. ENV 13419-1; Produits de Construction—Détermination des Emissions de Composés Organiques Volatils—Partie 1: Méthode de la Chambre D'essai D'émission (Norme X 43-520-1). AFNOR: Paris, France, 2000.

124. Rizk, M.; Verriele, M.; Mendez, M.; Blond, N.; Dusanter, S.; Schoemaecker, C.; Blondeau, P.; Le Calvé, S.; Locoge, N. Fast sorption measurements of VOCs on building materials: Part 2—Comparison between FLEC and CLIMPAQ methods. *Build. Environ.* **2016**, *99*, 239–251. [CrossRef]

125. ISO 16000-9; Indoor Air-Part 9: Determination of the Emission of Volatile Organic Compounds from Building Products and Furnishing. Emission Test Chamber Method. International Organization for Standardization: Geneva, Switzerland, 2006.

126. Rizk, M.; Verriele, M.; Dusanter, S.; Schoemaecker, C.; Le Calve, S.; Locoge, N. Fast sorption measurements of volatile organic compounds on building materials: Part 1—Methodology developed for field applications. *Build. Environ.* **2016**, *99*, 200–209. [CrossRef]

127. ISO 16000-10; Indoor Air. Part 10: Determination of the Emission of Volatile Organic Compounds from Building Products and Furnishing. International Organization for Standardization: Geneva, Switzerland, 2006.

128. ISO 16000-1; Indoor Air. Part 1: General Aspects of Sampling Strategy. International Organization for Standardization: Geneva, Switzerland, 2004.

129. ISO 16000-25; Determination of the Emission of Semi-Volatile Organic Compounds by Building Products—Microchamber Method. International Organization for Standardization: Geneva, Switzerland, 2011.

130. ISO 12219-3; Interior Air of Road Vehicles—Part 3: Screening Method for the Determination of the Emissions of Volatile Organic Compounds from Vehicle Interior Parts and Materials—Micro-Scale Chamber Method. International Organization for Standardization: Geneva, Switzerland, 2012.

131. ASTM D7706-17; Standard Practice for Rapid Screening of VOC Emissions from Products Using Micro-Scale Chambers. ASTM International: West Conshohocken, PA, USA, 2023.

132. ISO 16000; Indoor Air. International Organization for Standardization: Geneva, Switzerland, 2023.

133. Bourdin, D.; Mocho, P.; Desauziers, V.; Plaisance, H. Formaldehyde emission behavior of building materials: On-site measurements and modeling approach to predict indoor air pollution. *J. Hazard. Mater.* **2014**, *280*, 164–173. [CrossRef]

134. Jensen, L.K.; Larsen, A.; Mølhave, L.; Hansen, M.K.; Knudsen, B. Health Evaluation of Volatile Organic Compound (VOC) Emissions from Wood and Wood-Based Materials. *Arch. Environ. Health* **2001**, *56*, 419–432. [CrossRef] [PubMed]

135. Gross, A.; Mocho, P.; Plaisance, H.; Cantau, C.; Kinadjian, N.; Yrieix, C.; Desauziers, V. Assessment of VOCs material/air exchanges of building products using the DOSEC®-SPME method. *Energy Procedia* **2017**, *122*, 367–372. [CrossRef]

136. Böhm, M.; Salem, M.Z.M.; Srba, J. Formaldehyde emission monitoring from a variety of solid wood, plywood, block-board and flooring products manufactured for building and furnishing materials. *J. Hazard. Mater.* **2012**, *221–222*, 68–79. [CrossRef] [PubMed]

137. Risholm-Sundman, M.; Larsen, A.; Vestin, E.; Weibull, A. Formaldehyde emission—Comparison of different standard methods. *Atmos. Environ.* **2007**, *41*, 3193–3202. [CrossRef]

138. He, Z.; Zhang, Y.; Wei, W. Formaldehyde and VOC emissions at different manufacturing stages of wood-based panels. *Build. Environ.* **2012**, *47*, 197–204. [CrossRef]

139. Liang, W.; Yang, S.; Yang, X. Long-Term Formaldehyde Emissions from Medium-Density Fiberboard in a Full-Scale Experimental Room: Emission Characteristics and the Effects of Temperature and Humidity. *Environ. Sci. Technol.* **2015**, *49*, 10349–10356. [CrossRef] [PubMed]

140. Makowski, M.; Ohlmeyer, M.; Meier, D. Long-term development of VOC emissions from OSB after hot-pressing. *Holzforschung* **2005**, *59*, 519–523. [CrossRef]

141. Roffael, E. Volatile organic compounds and formaldehyde in nature, wood and wood based panels. *Holz Roh Werkst.* **2006**, *64*, 144–149. [CrossRef]

142. Peng, Y.; Shi, S.Q.; Ingram, L. Chemical emissions from adhesive-bonded wood products at elevated temperatures. *Wood Sci. Technol.* **2011**, *45*, 627–644. [CrossRef]

143. Tupciauskas, R.; Meile, K.; Godina, D.; Rizhikovs, J.; Syrpas, M.; Venskutonis, P.R. Qualitative Differences and Emission Persistence of Volatile Organic Compounds from Bio-Based Particleboards. *Materials* **2022**, *15*, 5278. [CrossRef] [PubMed]

144. Mayes, D.; Oksanen, O. *ThermoWood Handbook*; Finnish Thermowood Association: Kolho, Finland, 2003.

145. Sivrikaya, H.; Tesařová, D.; Jeřábková, E.; Can, A. Color change and emission of volatile organic compounds from Scots pine exposed to heat and vacuum-heat treatment. *J. Build. Eng.* **2019**, *26*, 100918. [CrossRef]
119. Souillier, A.; Plaisance, H.; Desauziers, V. New SPME-based method for on-site measurement of gas-phase concentration of phthalates and alternatives at the surface of PVC floorings. *Green Anal. Chem.* **2022**, *1*, 100012. [CrossRef]

120. He, J.; Zou, Z.; Yang, X. Measuring whole-body volatile organic compound emission by humans: A pilot study using an air-tight environmental chamber. *Build. Environ.* **2019**, *153*, 101–109. [CrossRef]

121. Yang, Y.; Zhang, M.; Yin, H.; Deng, Y.; Jiang, Y.; Yuan, H.; Dong, C.; Li, J.; Hua, J.; Wang, J. Rapid profiling of volatile compounds in green teas using Micro-Chamber/Thermal Extractor combined with thermal desorption coupled to gas chromatography-mass spectrometry followed by multivariate statistical analysis. *LWT* **2018**, *96*, 42–50. [CrossRef]

122. Massold, E.; Bähr, C.; Salthammer, T.; Brown, S.K. Determination of VOC and TVOC in Air Using Thermal Desorption GC-MS-Practical Implications for Test Chamber Experiments. *Chromatographia* **2005**, *62*, 75–85. [CrossRef]

123. ENV 13419-1; Produits de Construction—Détermination des Emissions de Composés Organiques Volatils—Partie 1: Méthode de la Chambre D'essai D'émission (Norme X 43-520-1). AFNOR: Paris, France, 2000.

124. Rizk, M.; Verriele, M.; Mendez, M.; Blond, N.; Dusanter, S.; Schoemaecker, C.; Blondeau, P.; Le Calvé, S.; Locoge, N. Fast sorption measurements of VOCs on building materials: Part 2—Comparison between FLEC and CLIMPAQ methods. *Build. Environ.* **2016**, *99*, 239–251. [CrossRef]

125. ISO 16000-9; Indoor Air-Part 9: Determination of the Emission of Volatile Organic Compounds from Building Products and Furnishing. Emission Test Chamber Method. International Organization for Standardization: Geneva, Switzerland, 2006.

126. Rizk, M.; Verriele, M.; Dusanter, S.; Schoemaecker, C.; Le Calve, S.; Locoge, N. Fast sorption measurements of volatile organic compounds on building materials: Part 1—Methodology developed for field applications. *Build. Environ.* **2016**, *99*, 200–209. [CrossRef]

127. ISO 16000-10; Indoor Air. Part 10: Determination of the Emission of Volatile Organic Compounds from Building Products and Furnishing. International Organization for Standardization: Geneva, Switzerland, 2006.

128. ISO 16000-1; Indoor Air. Part 1: General Aspects of Sampling Strategy. International Organization for Standardization: Geneva, Switzerland, 2004.

129. ISO 16000-25; Determination of the Emission of Semi-Volatile Organic Compounds by Building Products—Microchamber Method. International Organization for Standardization: Geneva, Switzerland, 2011.

130. ISO 12219-3; Interior Air of Road Vehicles—Part 3: Screening Method for the Determination of the Emissions of Volatile Organic Compounds from Vehicle Interior Parts and Materials—Micro-Scale Chamber Method. International Organization for Standardization: Geneva, Switzerland, 2012.

131. ASTM D7706-17; Standard Practice for Rapid Screening of VOC Emissions from Products Using Micro-Scale Chambers. ASTM International: West Conshohocken, PA, USA, 2023.

132. ISO 16000; Indoor Air. International Organization for Standardization: Geneva, Switzerland, 2023.

133. Bourdin, D.; Mocho, P.; Desauziers, V.; Plaisance, H. Formaldehyde emission behavior of building materials: On-site measurements and modeling approach to predict indoor air pollution. *J. Hazard. Mater.* **2014**, *280*, 164–173. [CrossRef]

134. Jensen, L.K.; Larsen, A.; Mølhave, L.; Hansen, M.K.; Knudsen, B. Health Evaluation of Volatile Organic Compound (VOC) Emissions from Wood and Wood-Based Materials. *Arch. Environ. Health* **2001**, *56*, 419–432. [CrossRef] [PubMed]

135. Gross, A.; Mocho, P.; Plaisance, H.; Cantau, C.; Kinadjian, N.; Yrieix, C.; Desauziers, V. Assessment of VOCs material/air exchanges of building products using the DOSEC®-SPME method. *Energy Procedia* **2017**, *122*, 367–372. [CrossRef]

136. Böhm, M.; Salem, M.Z.M.; Srba, J. Formaldehyde emission monitoring from a variety of solid wood, plywood, block-board and flooring products manufactured for building and furnishing materials. *J. Hazard. Mater.* **2012**, *221–222*, 68–79. [CrossRef] [PubMed]

137. Risholm-Sundman, M.; Larsen, A.; Vestin, E.; Weibull, A. Formaldehyde emission—Comparison of different standard methods. *Atmos. Environ.* **2007**, *41*, 3193–3202. [CrossRef]

138. He, Z.; Zhang, Y.; Wei, W. Formaldehyde and VOC emissions at different manufacturing stages of wood-based panels. *Build. Environ.* **2012**, *47*, 197–204. [CrossRef]

139. Liang, W.; Yang, S.; Yang, X. Long-Term Formaldehyde Emissions from Medium-Density Fiberboard in a Full-Scale Experimental Room: Emission Characteristics and the Effects of Temperature and Humidity. *Environ. Sci. Technol.* **2015**, *49*, 10349–10356. [CrossRef] [PubMed]

140. Makowski, M.; Ohlmeyer, M.; Meier, D. Long-term development of VOC emissions from OSB after hot-pressing. *Holzforschung* **2005**, *59*, 519–523. [CrossRef]

141. Roffael, E. Volatile organic compounds and formaldehyde in nature, wood and wood based panels. *Holz Roh Werkst.* **2006**, *64*, 144–149. [CrossRef]

142. Peng, Y.; Shi, S.Q.; Ingram, L. Chemical emissions from adhesive-bonded wood products at elevated temperatures. *Wood Sci. Technol.* **2011**, *45*, 627–644. [CrossRef]

143. Tupciauskas, R.; Meile, K.; Godina, D.; Rizhikovs, J.; Syrpas, M.; Venskutonis, P.R. Qualitative Differences and Emission Persistence of Volatile Organic Compounds from Bio-Based Particleboards. *Materials* **2022**, *15*, 5278. [CrossRef] [PubMed]

144. Mayes, D.; Oksanen, O. *ThermoWood Handbook*; Finnish Thermowood Association: Kolho, Finland, 2003.

145. Sivrikaya, H.; Tesařová, D.; Jeřábková, E.; Can, A. Color change and emission of volatile organic compounds from Scots pine exposed to heat and vacuum-heat treatment. *J. Build. Eng.* **2019**, *26*, 100918. [CrossRef]
146. Elaieb, M.; Candelier, K.; Pétrissans, A.; Dumarçay, S.; Gérardin, P.; Pétrissans, M. Heat treatment of Tunisian soft wood species: Effect on the durability, chemical modifications and mechanical properties. *Maderas Cienc. Tecnol.* **2015**, *7*, 699-710. [CrossRef]

147. Hyttinen, M.; Masalin-Weijo, M.; Kalliokoski, P.; Pasanen, P. Comparison of VOC emissions between air-dried and heat-treated Norway spruce (*Picea abies*), Scots pine (*Pinus sylvesteris*) and European aspen (*Populus tremula*) wood. *Atmos. Environ.* **2010**, *44*, 5028-5033. [CrossRef]

148. Peters, J.; Fischer, K.; Fischer, S. Characterization of emissions from thermally modified wood and their reduction by chemical treatment. *Bioresources* **2008**, *3*, 491-502. [CrossRef]

149. Čech, P.; Tesařová, D. Comparison of VOC emissions from natural (untreated) Poplar wood and heat treated wood. *Wood Sci. Technol.* **2015**, *90*, 23-28.

150. Xue, L.; Zhao, Z.; Zhang, Y.; Chu, D.; Mu, J. Analysis of Gas Chromatography-Mass Spectrometry Coupled with Dynamic Headspace Sampling on Volatile Organic Compounds of Heat-Treated Poplar at High Temperatures. *BioResources* **2016**, *11*, 3550-3560. [CrossRef]

151. Simon, V.; Uitterhaegen, E.; Robillard, A.; Ballas, S.; Véronèse, T.; Vilarem, G.; Merah, O.; Talou, T.; Evon, P. VOC and carbonyl compound emissions of a fiberboard resulting from a coriander biorefinery: Comparison with two commercial wood-based building materials. *Environ. Sci. Pollut. Res.* **2020**, *27*, 16121-16133. [CrossRef]

152. Uitterhaegen, E.; Burianová, K.; Ballas, S.; Véronèse, T.; Merah, O.; Talou, T.; Stevens, C.V.; Evon, P.; Simon, V. Characterization of volatile organic compound emissions from self-bonded boards resulting from a coriander biorefinery. *Ind. Crop. Prod.* **2018**, *122*, 57-65. [CrossRef]

153. Bertheau, E. Etude des Émissions de Composés Organiques Volatils de Panneaux de Bois de Chêne (*Quercus robur* L.) Sans Liant Issus de Procédés de Cuisson-Compression: Impact de L'eau. Ph.D. Thesis, University of Toulouse, Toulouse, France, 2023.

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
146. Elaieb, M.; Candelier, K.; Pétrissans, A.; Dumarçay, S.; Gérardin, P.; Pétrissans, M. Heat treatment of Tunisian soft wood species: Effect on the durability, chemical modifications and mechanical properties. *Maderas Cienc. Tecnol.* **2015**, *7*, 699-710. [CrossRef]

147. Hyttinen, M.; Masalin-Weijo, M.; Kalliokoski, P.; Pasanen, P. Comparison of VOC emissions between air-dried and heat-treated Norway spruce (*Picea abies*), Scots pine (*Pinus sylvesteris*) and European aspen (*Populus tremula*) wood. *Atmos. Environ.* **2010**, *44*, 5028-5033. [CrossRef]

148. Peters, J.; Fischer, K.; Fischer, S. Characterization of emissions from thermally modified wood and their reduction by chemical treatment. *Bioresources* **2008**, *3*, 491-502. [CrossRef]

149. Čech, P.; Tesařová, D. Comparison of VOC emissions from natural (untreated) Poplar wood and heat treated wood. *Wood Sci. Technol.* **2015**, *90*, 23-28.

150. Xue, L.; Zhao, Z.; Zhang, Y.; Chu, D.; Mu, J. Analysis of Gas Chromatography-Mass Spectrometry Coupled with Dynamic Headspace Sampling on Volatile Organic Compounds of Heat-Treated Poplar at High Temperatures. *BioResources* **2016**, *11*, 3550-3560. [CrossRef]

151. Simon, V.; Uitterhaegen, E.; Robillard, A.; Ballas, S.; Véronèse, T.; Vilarem, G.; Merah, O.; Talou, T.; Evon, P. VOC and carbonyl compound emissions of a fiberboard resulting from a coriander biorefinery: Comparison with two commercial wood-based building materials. *Environ. Sci. Pollut. Res.* **2020**, *27*, 16121-16133. [CrossRef]

152. Uitterhaegen, E.; Burianová, K.; Ballas, S.; Véronèse, T.; Merah, O.; Talou, T.; Stevens, C.V.; Evon, P.; Simon, V. Characterization of volatile organic compound emissions from self-bonded boards resulting from a coriander biorefinery. *Ind. Crop. Prod.* **2018**, *122*, 57-65. [CrossRef]

153. Bertheau, E. Etude des Émissions de Composés Organiques Volatils de Panneaux de Bois de Chêne (*Quercus robur* L.) Sans Liant Issus de Procédés de Cuisson-Compression: Impact de L'eau. Ph.D. Thesis, University of Toulouse, Toulouse, France, 2023.

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.