# Durability, mechanical recycling and environmental impacts of poly-lactic acid (PLA) based natural fiber reinforced composites: Effect of reactive agents and fiber surface treatment

Herve Nlandu Mayamba, Aurélie Taguet, Didier Perrin, J. Beigbeder, Sébastien Joannès, Florence Delor-Jestin, Haroutioun Askanian, J. Lopez-Cuesta

► To cite this version:

Herve Nlandu Mayamba, Aurélie Taguet, Didier Perrin, J. Beigbeder, Sébastien Joannès, et al., Durability, mechanical recycling and environmental impacts of poly-lactic acid (PLA) based natural fiber reinforced composites: Effect of reactive agents and fiber surface treatment. Industrial Crops and Products, 2025, 237, pp.122296. 10.1016/j.indcrop.2025.122296. hal-05373355

HAL Id: hal-05373355

https://imt-mines-ales.hal.science/hal-05373355v1

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# Durability, mechanical recycling and environmental impacts of poly-lactic acid (PLA) based natural fiber reinforced composites: Effect of reactive agents and fiber surface treatment

Hervé Nlandu<sup>a</sup>, Aurélie Taguet<sup>a, *, b</sup>, Didier Perrin<sup>a</sup>, Joana Beigbeder<sup>b, ID</sup>, Sébastien Joannes<sup>c</sup>, Florence Delor-Jestin<sup>d</sup>, Haroutioun Askanian<sup>d</sup>, Jose-Marie Lopez-Cuesta<sup>a</sup>

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

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## ARTICLE INFO

### Keywords:

- Biopolymers

- Flax fibers

- Bamboo fibers

- Silane treatment

- Coupling agent

- Ageing

- Recycling

- Life cycle assessment

- Environmental impacts

## ABSTRACT

This study presents the recyclability analysis of PLA/flax and PLA/bamboo biocomposites comprising silane treated fibers with and without the addition of a chain extender agent. To assess their mechanical recyclability, PLA biocomposites were reprocessed using multiple cycles of hygrothermal ageing, grinding process, followed by injection molding. The environmental impact of producing the biocomposites on a laboratory scale was evaluated by a life cycle assessment (LCA). An ecodesign approach was adopted to identify hotspots in the production process. The influence of fiber treatment with and without the addition of Joncryl™ as a reactive chain extender agent, on the properties of the biocomposites after reprocessing cycles was evaluated by examining changes in the molecular structure and physico-mechanical properties of the samples. In general, the study showed that all biocomposites exposed to hygrothermal ageing, grinding and the re-injection process underwent a chain scission mechanism which was responsible for the decrease in average molecular weight, thermal stability and tensile properties. However, fiber treatment with silane and the addition of Joncryl™ helped to limit these effects. LCA results showed that fiber treatment was the most impactful stage, followed by PLA production. Despite the fact that it exhibits poorer mechanical properties after recycling cycles, the PLA/bamboo biocomposite has a smaller environmental footprint than the PLA/Flax biocomposite. This discrepancy arises from variations in both the biomass cultivation conditions and the subsequent processing steps, including fiber treatment and compounding in an internal mixer. Recycling PLA/Flax or Bamboo biocomposites beyond the third and second recycling stages, respectively, is not recommended.

## 1. Introduction

Most polymers used to produce composites are derived from fossil resources. With an exponential growth rate and an annual production reaching around 400 million tons, plastic materials are estimated to be responsible for 4.5 % of global greenhouse gas emissions (Nayanathara Thathsarani Pilapitiya and Ratnayake, 2024; Stegmann et al., 2022; Nayanathara Thathsarani Pilapitiya and Ratnayake, 2024; Stegmann et al., 2022). Moreover, their use leads to the dissemination of micro-/nanoplastics, caused by the degradation of the polymer matrices. These substances accumulate in all environmental compartments of the planet,

including in human beings (Allen et al., 2022; Jambeck et al., 2015). This has prompted researchers to develop composites based on biobased and biodegradable polymers reinforced with natural fibers (Ghalme et al., 2025; Gonçalves et al., 2025; Gurunathan et al., 2015; Mohanty et al., 2000). Compared with conventional fossil-based synthetic composites, bio-composites offer significant benefits such as being renewable and biodegradable and having a lower density than mineral reinforcements (Gholampour and Ozbakkaloglu, 2020). These features are essential for various commercial applications. Moreover, in some industrial sectors, such as the automotive industry, end-of-life materials must be recyclable (ELV directive) (Liu et al., 2025). In the European strategy for plastics in

<footnote><sup>a</sup> Polymers Composites and Hybrids (PCH), IMT Mines Ales, Ales 30319, France</footnote>

<footnote><sup>b</sup> IPREM, IMT Mines Ales, Université de Pau et des Pays de L'Adour, E2S UPPA, CNRS, Pau, France</footnote>

<footnote><sup>c</sup> MINES Paris, Université PSI, Centre des Matériaux (CMAT), UMR7633 CNRS, Evry 91003, France</footnote>

<footnote><sup>d</sup> Clermont Université, CA INP, ICCF, Institut de Chimie de Clermont-Ferrand, UMR CNRS 6296, Aubière Cedex 63177, France</footnote>

<footnote>* Corresponding author.
E-mail address: aurelie.taguet@mines-ales.fr (A. Taguet).</footnote>
a circular economy, recycling is one of the key challenges in reducing the consumption of raw materials, as well as limiting pollution that can occur at the end of a product's life (landfill, incineration). Since a significant part of the composite is wasted during the production stage (around 25 wt%) (Bourmaud et al., 2011), recycling appears to be a promising alternative to incineration or landfilling, because it allows material to be reused during production. Injection molding can be viewed as a viable way to re-process and re-use these wastes. Ensuring that materials maintain their performance throughout successive recycling cycles remains one of the major challenges in the context of material reuse. The interest of the re-use of biocomposite waste after a lifecycle has also to be discussed. The feasibility of recycling will depend on the ageing of the polymer, particularly for biobased polymers as well as on the quality of adhesion between natural fibers and the polymer matrix (Zhou et al., 2016) after several reprocessing cycles. The relevance of this reprocessing approach after grinding end-of-life biocomposite parts will be assessed by standardized procedures. Life cycle assessment (LCA) is a standardized method used to evaluate the environmental impacts of products or processes. It is one of the essential tools for transitioning to a circular economy (Peña et al., 2021). It helps to identify hotspots, i.e. subprocesses or materials responsible for significant environmental impact, and to compare several scenarios. In recent years, LCA has been widely applied to natural fiber-reinforced composites using fibers such as kenaf, pine, starch, and modified cellulose (e.g., Baniasadi et al., 2024; Mai et al., 2024; Operato et al., 2023). However, few papers address the compatibilization of natural fibers and its effect on the recyclability of biocomposites. Regarding recycling LCA, although there is no consensus yet on the ideal allocation method (Schrijvers et al., 2016), reducing the consumption of raw materials production generally makes it possible to reduce environmental impacts (Schwarz et al., 2021). Bourmaud et al. have demonstrated the environmental benefits of recycling PP/hemp fiber through several injection cycles using a simplified environmental assessment (Bourmaud et al., 2011). As reported in a previous article (Nlandu-Mayamba et al., 2024), the use of Joncryl™, a grafted chain-extending polymer, and aminosilane surface treatment, whether applied separately or synergistically, resulted in a marked improvement in the interfacial adhesion between fibers and the PLA matrix in flax- (PLA/flax) and bamboo-reinforced biocomposites (PLA/bamboo). Furthermore, the tensile modulus and strength of aminosilane-treated fiber-based composites were enhanced by the addition of Joncryl™. Rheological and molecular weight measurements concluded that Joncryl™ could act as both a PLA chain extender and a coupling agent. The present study investigated the recycling of PLA/flax and PLA/bamboo composites through reprocessing stages combined with hygrothermal ageing, simulating the lifecycle of composites. To maintain mechanical performance by limiting polymer ageing and fiber/matrix degradation, the use of a coupling agent and a polymer chain extender was employed. Previous studies have highlighted the beneficial effects of these additives on the mechanical properties of PLA-based biocomposites, particularly by promoting improved fiber-matrix interactions and enhancing the overall structural performance of the material. The present study aims to demonstrate the potential of PLA-based biocomposites, not only for high-performance applications but also for effective mechanical recycling at their end-of-life, thereby contributing to a circular economy for materials. To complete this assessment, the environmental impacts associated with the production of these biocomposites - considering both raw material sourcing and processing steps - were quantified using a life cycle assessment (LCA) approach in accordance with ISO 14040/44 standards.

## 2. Materials and methods

### 2.1. Materials

The PLA used in this study was a 4043D from NatureWorks LLC

(Minnetonka, MN, USA), available in pellets, with a density of 1.24 g/cm³ containing 4.8 % D-lactide. The glass transition temperature (Tg) of this biopolymer is about 55 – 60 °C and the melting point (Tm) is 145–165 °C. The melt flow index (MFI) of this PLA is 6 g/10 min at 190°C under the load of 2.16 kg (according to the D1238 ASTM standard).

The lignocellulosic biomasses used in this study are flax tows and bamboo shavings. Flax tow is a non-woven fiber by-product resulting from the scutching of flax. It is supplied as cut part of a length of 6 mm by Terre de lin's firm (St Pierre le Viger, France). While bamboo shavings are of around 300 µm in length and are wastes from the manufacture of continuous ribbons of single unidirectional bamboo fiber obtained by a high-tech process developed and patented by Cobratex's enterprise (Carbonne, France).

Joncryl™ ADR 4468 from BASF's company, a copolymer consisting of a styrene unit, an acrylic acid unit and a glycidyl methacrylate unit, was used as a reactive compatibilizer. Its epoxy functionality allows it to react with polycondensates (polyesters, polycarbonates, polyamides), enabling it to act as a chain extender and potential interfacial coupling agent.

### 2.2. Fibers surface treatment

Fibers were first pretreated by mercerization. They were soaked in a 5 wt% solution of sodium hydroxide (NaOH) at room temperature for 3 h, after which they were washed several times with water until neutral pH was reached, to remove any residual alkali. Finally, they were oven-dried at 60 °C for 24 h.

Secondly, the NaOH pretreated fibers were treated by silanization. The pretreated fibers were immersed for 1 h in a 1 wt% solution of (3-aminopropyl) triethoxysilane (APS) prepared in acetone, adjusted to pH 3.5 with acetic acid. Then, fibers were filtered, oven-dried at 65 °C for 12 h, then carefully washed with water and oven-dried again at 80 °C, overnight.

As described in our previous article (Nlandu-Mayamba et al., 2024), the experimental conditions allow the hydrolysis of ethoxysilane groups of APS:

$$ (EtO)_3Si-(CH_2)_3-NH_2 + 3H_2O \rightarrow (HO)_3Si-(CH_2)_3-NH_2 + 3EtOH $$

The silanol groups (–Si(OH)3) formed then react with the hydroxyl groups (–OH) present on the surface of the fibers (resulting from the mercerization pretreatment) to form covalent bonds (–Si–O–fiber). This is a condensation reaction:

$$ Fibre-OH + HO-Si-(CH_2)_3-NH_2 \rightarrow Fibre-O-Si-(CH_2)_3-NH_2 + H_2O $$

### 2.3. Compounding

The extrusion step was carried out using a BC21 Cletral (Firminy, France) co-rotating twin-screw extruder (21 mm screw diameter and a 900 mm screw length) with two feeders (one for pellets and one for fibers). The heating barrel system was composed of 12 zones with independently controlled temperature. The first zone, located at the material feed inlet, was maintained at 60 °C to prevent premature melting, while the remaining zones along the barrel were set to a uniform temperature of 185 °C to ensure consistent melting and homogenization of the material during processing. The screw speed was set at 250 rpm, with a total feed rate of 5 kg/h. Prior to extrusion, the polymer granules and fibers (bamboo fibers) were dried under vacuum overnight at 65°C.

For the bamboo-based composites, PLA pellets were introduced through the first feeding hopper located at the entrance to zone 1 of the barrel and the 10 wt% bamboo fiber was incorporated through the second feeder at zone 5. Joncryl™ was gradually introduced in a quantity corresponding to a final amount of 0.8 wt%, via the second
hopper located in zone 5.

Due to the morphology of flax tows, it was impossible to incorporate them directly into the PLA via the twin-screw extruder. A masterbatch of PLA/flax (70/30 wt%) was then produced in a rotating internal laboratory mixer (Haake Rheomix 3000, with a 300cc mold from Thermo Fisher Scientific, USA) equipped with roller rotors. The obtained precompound, which was saturated with flax fibers (30 wt%), was cut into small particles and ground in an Alpine cutting mill using a sieve of 8 mm in diameter, in order to recover the ground pre-compound. These shredded materials were then extruded with Joncryl™ and fresh PLA pellets to produce a final composite containing 10 wt% flax fibers and 0.8 % of Joncryl™ after extrusion. The shredded and diluted precompound and the virgin PLA pellets were all introduced through the first feeding hopper, with the Joncryl™ being introduced gradually through the second hopper in zone 5 as described above.

To the output of the extruder, filament-shaped compounds were cooled in a water bath and quickly dried by air pulses and finally granulated.

## 2.4. Injection molding

A Krauss-Maffei KM50-T180CX press (Germany) was used to manufacture dogbone samples ISO 1 A according to ISO 527–2. The temperature profile was 195°C-195°C-195°C-195°C and 210°C for the nozzle. The injection pressure was 600 bars during 15 s for first stage, then 500 bars during 15 s for the second one, and the mold temperature was fixed at 30°C. The plasticization and injection speeds were set at 100 rpm and 20 cm³.s⁻¹, respectively, and the cooling time was 15 s. Prior to injection, the pellets were dried under vacuum overnight at 65°C, in order to remove residual moisture.

## 2.5. Hygrothermal ageing process and mechanical recycling

The ageing process under hygrothermal conditions was adapted from Standard NF T51–181. This standard recommends a 24 h cycle consisting of an initial phase of 8 h at 40°C and 90 % RH, followed by a second phase of 16 h at 90°C and 45 % RH. In our case, the second phase was modified to include 16 h of moderate ageing at 60°C and 45 % RH. This 24h-cycle was repeated three times using a WEISS Technik WKL34 weathering chamber (France).

The mechanical recycling process was conducted on an experimental basis over three successive cycles, each comprising hygrothermal ageing, mechanical grinding, and reprocessing by injection molding, under conditions identical to those described above. The resulting samples were designated according to the following coding convention: “samples-Ri” or “samples-Ai”, where A and R stand for ageing and reprocessing, respectively and i denotes the number of reprocessing or ageing cycles.

Table 1 presents the complete set of formulations investigated. All biocomposites were prepared with a fixed fiber content of 10 wt%. The sequence of hygrothermal ageing and reprocessing steps for each cycle is detailed as follows:

$$A_1 \rightarrow R_1 \rightarrow A_2 \rightarrow R_2 \rightarrow A_3 \rightarrow R_3$$

## 2.6. Characterizations

### 2.6.1. Microstructural analysis

Composite fracture surface morphology was studied using a Sigma 300 Scanning Electron Microscope, SEM (Carl Zeiss Microscopy, Oberkochen, Germany). Images were performed on tensile fracture surface. Prior to examination, all specimens were sputter-coated with gold to enhance electrical conductivity.

<caption>**Table 1**</caption>

Formulations obtained after extrusion and after each ageing step (Hygrothermal ageing and reprocessing). Grey cells point out the fact that it was not possible to perform the ageing treatment three times.

<table><thead><tr><th rowspan="2">Materials</th><th rowspan="2">Name</th><th rowspan="2">Additives (S: silane, J: Joncryl)</th><th colspan="2">Ageing treatment</th></tr><tr><th>Hygrothermal ageing (A<sub>1,2,3</sub>)</th><th>Reprocessing (R<sub>1,2,3</sub>)</th></tr></thead><tbody><tr><td rowspan="5">Pure PLA<br>PLA-Flax<br>biocomposites</td><td>PLA</td><td>-</td><td>PLA-A<sub>1,2,3</sub></td><td>PLA-R<sub>1,2,3</sub></td></tr><tr><td>PLA-FF</td><td>-</td><td>PLA-FF-A<sub>1,2,3</sub></td><td>PLA-FF-R<sub>1,2</sub></td></tr><tr><td>PLA-SFF</td><td>Silane treated fibers</td><td>PLA-SFF-A<sub>1,2,3</sub></td><td>PLA-SFF-R<sub>1,2,3</sub></td></tr><tr><td>PLAJ-FF</td><td>Joncryl</td><td>PLAJ-FF-A<sub>1,2,3</sub></td><td>PLAJ-FF-R<sub>1,2,3</sub></td></tr><tr><td>PLAJ-SFF</td><td>Silane treated fibers and Joncryl</td><td>PLAJ-SFF-A<sub>1,2,3</sub></td><td>PLAJ-SFF-R<sub>1,2,3</sub></td></tr><tr><td rowspan="5">PLA-bamboo<br>biocomposites</td><td>PLA-BF</td><td>-</td><td>PLA-BF-A<sub>1,2</sub></td><td>PLA-BF-R<sub>1,2</sub></td></tr><tr><td>PLA-SBF</td><td>Silane treated fibers</td><td>PLA-SBF-A<sub>1,2</sub></td><td>PLA-SBF-R<sub>1,2</sub></td></tr><tr><td>PLAJ-BF</td><td>Joncryl</td><td>PLAJ-BF-A<sub>1,2</sub></td><td>PLAJ-BF-R<sub>1,2</sub></td></tr><tr><td>PLAJ-SBF</td><td>Silane treated fibers and Joncryl</td><td>PLAJ-SBF-A<sub>1,2,3</sub></td><td>PLAJ-SBF-R<sub>1,2,3</sub></td></tr></tbody></table>

### 2.6.2. Thermogravimetric analysis (TGA)

The thermal stability of the materials was conducted on a TGA 4000 thermogravimetric instrument (Perkin Elmer, Waltham (MA), USA) in an inert gas (nitrogen) atmosphere from 25 to 700 °C at a heating rate of 10 °C.min⁻¹.

### 2.6.3. Thermal characterization with differential scanning calorimetry (DSC)

DSC thermograms of the biocomposites were obtained using a DSC 3 (Mettler Toledo, Greifensee, Switzerland). A sample weighing approximately 10 mg was sealed in an aluminum pan, held for 2 min at 0°C, submitted to a first heating to 200 °C, then held at 200 °C for 1 min, followed by a cooling cycle to 0 °C and maintained for 1 min at 0 °C. Finally, a second heating to 200°C was conducted. All the cycles were conducted under a nitrogen atmosphere with a flow of 20 ml/min using a heating rate of 10 °C/min.

Glass transition temperature (T<sub>g</sub>), cold crystallization temperature and corresponding enthalpy (T<sub>cc</sub> and ΔH<sub>cc</sub>) as well as melting temperature and corresponding enthalpy (T<sub>m</sub> and ΔH<sub>m</sub>) were determined from the second heating cycle using the STARe system software. The crystalline index (X<sub>C</sub>) was calculated according to Eq. 1:

$$X_c = 100 * \frac{\Delta H_m - \Delta H_{cc}}{w * \Delta H_0} \quad (1)$$

Where, ΔH<sub>0</sub> is the melting enthalpy of 100 % crystalline PLA, taken as 93 J/g (Fortunati et al., 2012), and w is the weight fraction of PLA in the biocomposite.

### 2.6.4. Gel permeation chromatography (GPC)

To obtain information about molecular weight changes during manufacturing, the number average molecular weights (M<sub>n</sub>) and the weight average molecular weights (M<sub>w</sub>) were determined using an OmniSec GPC (Malvern Panalytical, Malvern U.K.) equipped with two columns branded PLGel mixed-B, as well as a refractive index detector. Fragments were cut from the injected samples and solubilized into THF at a concentration of 1 mg.ml⁻¹. Solutions were stirred for 15 min at 40 °C and filtered through a 0.02 µm PTFE membrane filter before test. The temperature was set at 30 °C, the flow rate was 1 ml.min⁻¹ and the injection volume was 20 µl. A calibration curve was established using four Polystyrene Shodex® narrow standards of respective molecular
weights of 1864000, 194500, 30300, 7350 and 945 g mol⁻¹. Data acquisition and processing were performed using the OmniSEC software.

### 2.6.5. Tensile mechanical tests

Quasi-static tensile tests were conducted using an Instron 5900 universal testing machine (Instron, Norwood (MA), USA), with a maximum load capacity of 100 kN. The tensile strength, failure strain and modulus of the fabricated composites were measured in accordance with the ISO 527-4 standard. The composites' strain was measured using an Advanced Video Extensometer (AVE) non-contact setup attached to the Instron UTM. The deformation rate was 1 mm/min. Tensile strength was determined using the stress-strain curve, while the tensile modulus was calculated from the slope of the initial linear portion of the obtained curve.

## 2.7. Life cycle assessment

### 2.7.1. Goal and scope

The aim of this LCA is to identify the hotspots in the production, at the lab-scale, of the two studied biocomposites, including fiber treatment. The functional unit was defined as: "producing 1 kg of bio-composites granules with a Young's modulus higher than 3200 MPa and a tensile stress greater than 52 MPa while retaining mechanical integrity through two reprocessing cycles after hygrothermal ageing". This definition reflects the mechanical performance and recyclability requirements expected during the material's intended service life. The perimeter is from cradle to gate, the pellets are supposed to be produced in Alès, France (Fig. 1). The LCA modeling was performed using Sphera's Gabi software (Sphera 2015) and the ecoinvent database (ecoinvent Life Cycle Impact Assessment Database, version 3.6, 2006). The environmental impacts were assessed using the hybrid Recipe method, adapted to European territory (Goedkoop et al., 2008; Huijbregts et al., 2017).

### 2.7.2. Life cycle inventory and hypothesis

Most of the production processes for raw materials have been taken from the ecoinvent database (polylactic acid, sodium hydroxide, deionized water, acetone). Due to a lack of data, Joncryl™ and silane have been assimilated to a generic chemical organic compound from ecoinvent. Bamboo cultivation and bamboo fiber production in China were modelled using bibliographic data. For bamboo cultivation, supposed to have taken place in Tangsan (China), a yield of 20 tons/hectare every 5 years was assumed, with no chemical inputs to the cultivated surface and manual cutting. The cultivation of bamboo for industrial purposes is supposed to be done without deforestation, as bamboo grows

very quickly. A 50 km transport stage was added to the fiber production plant. Data from the article by Riofrio et al. (Riofrio et al., 2022) were selected for bamboo shredding. For one ton of bamboo fibers, an electricity consumption of 20.8 kWh was used, resulting in a mass loss of 11 %. The flax fiber production process, based on an Indian retting scenario from the ecoinvent database, was adjusted for application in France through the adaptation of the electrical energy mix to align with local grid characteristics. Data on the scutching of flax fibers were taken from the publication of Gomez Campos et al. (Gomez-Campos et al., 2021). A mass allocation was carried out to inventory the inputs for producing short flax fibers. This led us to only consider the production of retted flax and to neglect the electricity needed for sputting. The distance for transporting PLA granulates and natural fibers, were evaluated from the production sites and modeled using the different transport options available in the ecoinvent database (lorries and boats). For the other raw materials, an average distance of 500 km was chosen and modeled using a truck.

The surface treatment of the natural fibers was modelled according to the processes described in §2.2. For the oven-drying step, a power of 3660 W was used. It was assumed that the oven was only used to dry 100 g of material at a time. The waste solutions produced were treated as either wastewater (in the case of mercerization) or as spent solvents (in the case of syllication). Spent solvents were modelled as being incinerated using an ecoinvent process. It was assumed that 35 % of the used incinerators can produce electricity in France (Anon, 2018). The impacts avoided by the production of electricity were considered using the avoided burdens approach. A 100 km lorry journey has been added to transport the used solvents to the incineration site.

The preparation of biocomposites required sequential processing, starting with internal mixing for PLA-flax fiber (PLA-FF) composites, requiring 4.23 kWh/kg of electrical energy, followed by extrusion, modeled according to the corresponding entry in the ecoinvent database.

# 3. Results and discussion

## 3.1. Thermogravimetric analyses (TGA)

Firstly, the influence of ageing (hygrothermal and reprocessing steps) on the thermal properties of biocomposites was studied by thermogravimetric analysis (TGA), to investigate the thermal stability of the PLA and the biocomposites after recycling. Fig. 2 shows the TG curves and derivative curves (DTG) of the PLA and the biocomposites after the 3 cycles of reprocessing. Table 2 summarizes the maximum degradation temperatures of all specimens at each stage of the recycling process. The

<figure><img src="image_4.png" /><figcaption>Fig. 1. Boundaries of the studied system.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Effect of hygrothermal ageing and reprocessing on thermal stability of (A) flax fiber and (B) bamboo fiber PLA biocomposites. Graphs on the right are the derivative curves of TGA.</figcaption></figure>

<table><caption>**Table 2**
The main degradation temperatures in TGA for PLA and PLA biocomposites.</caption><thead><tr><th>Samples</th><th>Reference</th><th>A<sub>1</sub></th><th>R<sub>1</sub></th><th>A<sub>2</sub></th><th>R<sub>2</sub></th><th>A<sub>3</sub></th><th>R<sub>3</sub></th></tr></thead><tbody><tr><td>PLA</td><td>359</td><td>364</td><td>358</td><td>357</td><td>358</td><td>354</td><td>352</td></tr><tr><td>PLA-FF</td><td>348</td><td>346</td><td>346</td><td>345</td><td>344</td><td>344</td><td>*</td></tr><tr><td>PLA-SFF</td><td>350</td><td>350</td><td>346</td><td>349</td><td>326</td><td>347</td><td>313</td></tr><tr><td>PLAJ-FF</td><td>336</td><td>349</td><td>342</td><td>344</td><td>343</td><td>346</td><td>344</td></tr><tr><td>PLAJ-SFF</td><td>349</td><td>328</td><td>348</td><td>349</td><td>338</td><td>346</td><td>345</td></tr><tr><td>PLA-BF</td><td>332</td><td>343</td><td>321</td><td>344</td><td>341</td><td>*</td><td>*</td></tr><tr><td>PLA-SBF</td><td>345</td><td>306</td><td>328</td><td>332</td><td>350</td><td>*</td><td>*</td></tr><tr><td>PLAJ-BF</td><td>331</td><td>350</td><td>340</td><td>343</td><td>340</td><td>*</td><td>*</td></tr><tr><td>PLAJ-SBF</td><td>349</td><td>330</td><td>327</td><td>329</td><td>331</td><td>333</td><td>314</td></tr></tbody></table>

PLA-FF biocomposite was not reprocessable after the third ageing stage (A3), whereas the modified biocomposites with flax fibers (either by adding Joncryl™ PLA-FF or with silane treated fibers PLA-SFF or both PLA-SFF) were reprocessable up to Reprocessing 3 (R3). Regarding the bamboo fiber biocomposites, the PLA-BF, PLA-SBF and PLA-BF specimens could not be reprocessed after the second reprocessing step (R2), because of a very low viscosity, due to a high thermal degradation.

PLAJ-SBF, however, was reprocessed up to R3. Therefore, the unmodified biocomposites (PLA-FF and PLA-BF) could not undergo 3 cycles of reprocessing, and their TGA analysis are shown in *Supporting Information* (SI-1 Thermo Gravimetric analysis of PLA-FF and PLA-BF biocomposites after several recycling steps).

The TG curves in Fig. 2 reveal the 3 stages of the thermal degradation of biopolymers. In particular, the first stage (50–250 °C) is attributed to the moisture loss and the pyrolysis of hemicellulose present in the natural fibers. The second stage (260–365 °C) is the most important, mainly due to the pyrolysis of PLA, but also of cellulose and some lignin. The final stage (above 365 °C) is ascribed to the pyrolysis of residual lignin. Regarding the main degradation step between 260 and 365 °C, it is evident that the thermal stability of the recycled PLA diminishes after 3 cycles of reprocessing (from R₁ to R₃), irrespective of the biocomposite (FF or BF, with or without Joncryl™, with or without silane-modified fibers). This decrease in thermal stability can be attributed to the degradation of both fibers and the PLA matrix during reprocessing (Srebrenkoska et al., 2014), bearing in mind that incorporating unmodified fibers into the PLA matrix contributes to the degradation of the biocomposites. As shown in a previous study (Nlandu-Mayamba et al., 2024), the incorporation of 10 wt% flax or bamboo fibers into PLA

<footnote>*Non reprocessable at that stage because the biocomposite was highly degraded.</footnote>
resulted in a reduction of the polymer's thermal stability, with the onset
degradation temperature decreasing from 360 °C for neat PLA to 348 °C
and 332 °C for PLA/flax and PLA/bamboo composites, respectively. It
was also shown that silane treatment of flax and bamboo increased the
thermal stability of the corresponding biocomposites (PLA-SFF and
PLA-SBF) compared to non-treated fiber composites. This has an impact
on the recycling of composites. Although silane treatment limits the
thermal degradation of the biocomposites, only the silane-treated
flax-based composites (PLA-SFF, PLAJ-SFF) could undergo 3 cycles of
reprocessing; bamboo-based composites could not exceed two cycles
(R2). The previous work also demonstrated that the addition of
Joncryl™, a polymeric chain-extending agent, substantially lowers the
thermal stability of PLA composites, reducing the onset degradation
temperature (from 360°C to 349°C). However, and in accordance with
the rheological measurements described in our previous article,
Joncryl™ appears to continue reacting during multiple reprocessing
cycles, thereby improving the thermal stability of the composites,
especially those containing flax fibers. PLAJ-FF could therefore undergo
3 cycles of reprocessing, whereas PLAJ-BF was limited to 2. One of the
most significant results regarding thermal degradation is that, the
addition of Joncryl™, combined with the silane coupling agent enables
both PLAJ-SFF and PLAJ-SBF to undergo 3 cycles of reprocessing (R3).
The main thermal degradation temperatures shifted from 349 °C
(PLAJ-SFF non recycled) to 345 °C (PLAJ-SFF-R3) and from 349 °C
(PLAJ-SBF non recycled) to 314 °C (PLAJ-SBF-R3).

## 3.2. Differential scanning calorimetry (DSC)

The influence of reprocessing on the thermal properties and crys-
tallinity of PLA and its biocomposites was investigated using DSC. Fig. 3
Fig. 3. Effect of hygrothermal ageing and reprocessing on DSC thermal
properties of (A) PLA-FF composites and (B) PLA-BF composites, during
second heating step. shows the DSC second heating curves of pure,
hygrothermally aged and reprocessed PLA and the corresponding bio-
composites. In the Supporting Information (SI-2- DSC results of flax and
bamboo- PLA biocomposites after several recycling steps), DSC results are
presented for the second heating step, of Flax/PLA and bamboo/PLA
biocomposites, respectively.

Regarding the glass transition temperature, there is no clear ten-
dency for the influence of reprocessing steps on T<sub>g</sub> (Le Duigou et al.,
2008). Hence, the mobility of the amorphous phase is not influenced by
recycling. Regarding cold crystallization, although T<sub>cc</sub> seams to keep
constant or increase all along the thermal ageing, ΔH<sub>cc</sub> mainly decreases
for ageing A<sub>1</sub>, and then increases through the subsequent reprocessing
steps (R<sub>1</sub>, A<sub>2</sub>, R<sub>2</sub>, A<sub>3</sub>, R<sub>3</sub>) for both flax and bamboo composites. This
tendency on ΔH<sub>cc</sub> value is dictated by that of the PLA.

Hygrothermal ageing tends to increase the crystalline rate of PLA.
Indeed, when PLA is aged at a temperature higher than its glass transi-
tion temperature, the polymer chains are hydrolyzed in their amorphous
zone, resulting in lower molecular weight, higher chain mobility and
rearrangement. This subsequently increases crystallization (Aouat et al.,
2019). After ageing and reprocessing, the literature reports the
appearance of a secondary melting peak at a temperature lower than the
main α-crystal melting peak. This reflects the transformation of the
original well-ordered crystalline structures into secondary β-crystal
structures (Yoo et al., 2021). This phenomenon, observed for pure PLA,
is also seen in some flax and bamboo fiber biocomposites and can also
explain that T<sub>cc</sub> has been maintained or slightly increased during ageing.
The incorporation of Joncryl™, either alone (PLAJ-FF, PLAJ-BF) or in
combination with silane-treated fibers (PLAJ-SFF, PLAJ-SBF), appears to
reduce the enthalpy of cold crystallization of PLA in biocomposites. This
effect is attributed to the chain-extending and branching action of
Joncryl™, which restricts polymer chain mobility and alters nucleation
kinetics, while the overall melting enthalpy remains largely unchanged,
indicating that the total crystalline content is preserved despite modi-
fications in crystal growth behavior. Therefore, the higher X<sub>c</sub> for these

biocomposites, is probably due to a lower hydrolysis phenomenon (the
Joncryl™ and fiber modifications protect the polymer chains from
degradation by hydrolysis) and the fibers' nucleating effect, which can
also increase the crystallinity of the PLA during recycling (Jiang et al.,
2020).

3.3. *Gel permeation chromatography*

Fig. 4 illustrates the changes in the average molecular weight (M̄n and M̄w) for all the biocomposites that were subjected to hydrothermal ageing and reprocessing. The values of the bars are reported in the Supporting Information (SI-3 GPC results of flax and bamboo- PLA bio-composites after several recycling steps). As discussed in our previous article, it is important to note that the molecular weight of the bio-composite was significantly lower than that of pure PLA specimens (Le Duigou et al., 2009) (Le Duigou et al., 2009). This molecular weight drop is due to a hydrolytic degradation of PLA, greatly amplified by the presence of hydrophilic fibers. Moreover, the effect of the silane treatment of the fibers limited the reduction in the molecular weight of the matrix, whereas the addition of a coupling agent, either alone or in combination with the silane, increased the molecular weight. Following successive ageing and reprocessing, both M̄n and M̄w show a dramatic decrease. This could be attributed to the chain scissions (hydrolysis) caused by ageing and continuous thermomechanical stress that has occurred during reprocessing (Foulc et al., 2005; Grigore, 2017).

Reprocessing of raw fiber biocomposites (PLA-FF and PLA-BF) could
only be performed up to 2 cycles, whereas PLA-SFF, PLAJ-FF, PLAJ-SFF
and PLAJ-SBF were reprocessed up to 3 cycles (R3). Even neat PLA loses
around 42 % and 52 % of its M̄n molecular weight after 2 and 3 cycles of
reprocessing, respectively. With silane-treated fibers, PLA-SFF bio-
composite has lost around 50 % and 66 % of its molecular weight after 2
and 3 cycles of reprocessing, respectively. For bamboo fiber composites,
only the biocomposite based on bamboo treated with silane in combi-
nation with the coupling agent (PLAJ-SBF) could be reprocessed 3 times,
with a loss of 53 and 69 % of M̄n molecular weight after R2 and R3,
respectively. Finally, the addition of Joncryl alone (PLAJ-FF) or in
combination with silane treatment (PLAJ-SFF) resulted in a loss of
around 42 % and 75 % of M̄n after R2 and R3, respectively.

Successive reprocessing cycles result in a progressive decrease of the
PLA matrix molecular weight, likely due to chain scission induced by
thermal and mechanical stresses during recycling. The silane treatment
of the fibers and the addition alone or in combination of Joncryl™ limits
this reduction. The formulations containing Joncryl™ has the highest
M̄n molecular weights after 3 cycles of reprocessing for both bio-
composites. This coupling agent delays chain scission slightly due to a
chain extension reaction occurring during the reprocessing steps via
thermomechanical mechanisms.

3.4. *Mechanical tensile properties*

### 3.4.1. Effect of ageing and reprocessing cycles on elastic modulus

The native curves of tensile properties are reported in the *supporting information* only for flax fiber based biocomposites before any recycling step. (SI –4 Example of the Load-strain curve for flax - PLA biocomposites before recycling steps). Fig. 5 shows the tensile modulus properties of all materials at each stage of ageing or reprocessing. The values of the bars are reported in the *Supporting Information* (SI-5 Mechanical properties results of flax and bamboo- PLA biocomposites after several recycling steps). Previous works (Nlandu-Mayamba et al., 2024), demonstrated that the elastic modulus of PLA biocomposites is enhanced compared to neat PLA, due to fiber reinforcement. Silane-mediated surface treatment, and, most significantly, the inclusion of Joncryl™, either individually or synergistically with modified fibers, likely results in improved fiber-matrix interfacial adhesion and polymer chain extension effects. For each material, as expected, the main tendency for the Young's modulus
<figure><img src="image_6.png" /><figcaption>Fig. 3. Effect of hygrothermal ageing and reprocessing on DSC thermal properties of (A) PLA-FF composites and (B) PLA-BF composites, during second heating step.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 4. Effect of ageing and reprocessing on average molecular weight (A)PLA-FF composites and (B) PLA-BF composites.</figcaption></figure>

is a slight decrease with successive ageing or reprocessing steps. By the end of the second reprocessing process R₂, the tensile modulus of the initial samples has decreased by 7 % for PLA-FF, 18.5 % for PLA-BF; 12.2 % for PLA-SFF and 16.1 % for PLA-SBF; 10.4 % for PLAJ-FF and 17.9 % for PLAJ-BF; and finally, 12.7 % for PLAJ-SFF and 17.1 % for PLAJ-SBF. In the third reprocessing cycle, the tensile modulus of PLAJ-SBF is 3217 MPa, which is a 24 % loss compared to the initial sample. PLA-SFF, PLAJ-FF and PLAJ-SFF show tensile moduli of 3137 MPa, 3458 MPa and 3410 MPa, respectively. Compared to their initial samples, they have lost 19 %, 12 % and 19 % of their tensile modulus respectively. The explanation of this slight decrease of tensile Young's modulus is multiple. Firstly, all along the reprocessing steps, the size and aspect ratio of the fibers are decreased. Secondly, in the case of fiber treated and Joncryl™ added biocomposites (PLA-SFF, PLAJ-FF, PLAJ-SFF, PLA-SBF, PLAJ-BF and PLAJ-SBF), the stress transfer at the interface is becoming weak due to a less efficient interfacial adhesion between fibers and matrix with the ageing steps.

### 3.4.2. Effect of ageing and reprocessing cycles on maximum tensile strength
Fig. 6 shows the tensile strength properties of all materials at each ageing or reprocessing step. The values of the bars are reported in the Supporting Information (SI-5 Mechanical properties results of flax and bamboo- PLA biocomposites after several recycling steps). Previous works (Nlandu-Mayamba et al., 2024), demonstrated that the addition of 10 wt

% flax or bamboo fibers to PLA results in a reduction of tensile strength ($\sigma_{max}$) from 57 MPa, for neat PLA to approximately 50 MPa for the composites, likely due to insufficient fiber–matrix interfacial bonding, which limits effective stress transfer under load. Surface modification of fibers with silane leads to a slight increase in tensile strength ($\sigma_{max}$ = 54 MPa for PLA-SFF and 51 MPa for PLA-SBF), which can be attributed to enhanced fiber–matrix adhesion. The addition of Joncryl™, either alone or in combination with silane treatment further increases the tensile strength. This improvement is likely due to the combined effects of chain extension, restricted polymer chain mobility, and improved interfacial bonding, which promote more effective stress transfer. DSC analyses indicate that these modifications also influence crystallization behavior, suggesting that the observed mechanical improvements are associated with changes in crystalline morphology and thermal stability of the composites.

In essence, the tensile strength of all recycled materials decreases with each subsequent recycling step. Neat PLA maintains its tensile strength of 57 MPa after the first reprocessing cycle (R₁), whereas the tensile strength of the PLA-FF and PLA-BF biocomposites declined from 50 MPa to 48 MPa and 36 MPa, respectively, i.e a loss of 4 % and 18 %. For the silane-treated fiber-based biocomposites, the tensile strength of PLA-SFF (54 MPa) and PLA-SBF (51 MPa) has declined to 50 MPa and 42 MPa, respectively. Compared to the initial samples, they lose 7.4 % and 17.6 % of their tensile strength. Adding Joncryl™ to the PLA-FF and
<figure><img src="image_8.png" /><figcaption>Fig. 5. Effect of ageing and reprocessing on tensile modulus: (A) PLA-FF composite and (B) PLA-BF composites.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 6. Effect of ageing and reprocessing on tensile strength: (A) PLA-FF composite and (B) PLA-BF composites.</figcaption></figure>

PLA-BF biocomposites lead to a decline in tensile strength, from 58 MPa for both, to 57 MPa and 46 MPa, respectively. However, the addition of Joncryl™ to PLA-FF and PLA-BF composites significantly increases tensile strength after the first reprocessing cycle ($R_1$), by 15.8% and 21.7%, respectively, reflecting enhanced chain connectivity and

interfacial stress transfer. When combined with silane-treated fibers (PLAJ-SFF and PLAJ-SBF), tensile strength is maintained at 56 MPa after $R_1$, suggesting that the synergistic effects of polymer chain extension and improved fiber-matrix bonding effectively mitigate the mechanical degradation typically induced by reprocessing.
The second and third reprocessing cycles result in a gradual reduc-
tion of tensile strength for neat PLA, from 53 MPa (–7 %) after the
second cycle to 45 MPa (–21 %) after the third cycle, indicative of
progressive polymer chain scission and the associated deterioration of
load-bearing capacity. For biocomposites, incorporating Joncryl™ alone
is more effective for PLA/flax composites than for the PLA/bamboo
ones. Only the silane + Joncryl™ combination maintains the tensile
stress level for both types of composites beyond 2 cycles of reprocessing
and ageing.

Thus, Joncryl™ demonstrates greater efficiency in maintaining ten-
sile strength during multiple recycling cycles in PLA/flax composites
relative to PLA/bamboo. This difference is likely due to the combined
effects of fiber morphology (size and surface area), the extent of fiber-
-matrix interfacial contact. It is also possible that Joncryl™ exhibits a
preferential reactivity with cellulose rather than lignin, resulting in
improved chain extension and interfacial adhesion (Basri et al., 2019;
Sánchez-Safont et al., 2018). Combining Joncryl™ with fiber treatment
enables a high tensile strength to be maintained for both biocomposites,
even after R₂ step. Some biocomposites that have not undergone silane
treatment and/or had Joncryl™ added do survive the R₂ reprocessing
step.

**3.4.3. Effect of ageing and reprocessing cycles on elongation at break**

Neat PLA, being intrinsically brittle, shows very low elongation at
break (< 3 %). The introduction of flax or bamboo fibers further de-
creases ductility due to the rigid reinforcement effect (Fig. 7). The values
of the bars are reported in the Supporting Information (SI-5 Mechanical
properties results of flax and bamboo- PLA biocomposites after several
recycling steps). However, either the incorporation of Joncryl™ or fiber
surface functionalization effectively maintains elongation at break,
suggesting that enhanced polymer chain extension and improved
fiber-matrix bonding reduce strain localization and allow for better
deformation of the composite. Combining Joncryl™ and fiber func-
tionalization is the most efficient way to maintain elongation at break,
especially for flax fibers, as PLAJ-SFF exhibits an elongation at break of
1.5 %, even after R₃.

3.5. Influence of fiber functionalization and reactive agent on the surface morphology

SEM analyzes were performed on fractured surfaces of failed tensile
specimens. The main effects of hygrothermal ageing on the polymer
characteristics are associated with water absorption, resulting in phys-
ical modifications, such as plasticization, and/or in chemical reactions,
such as hydrolysis. The fractured surface of the failed tensile specimens

of neat PLA showed a stretched, smooth, polished edge surface before
ageing and reprocessing. Loss of initial surface smoothness was observed
with multiple ageing and reprocessing, with holes and micro cracks
appearing on the edge after 3 cycles (blue arrows in Fig. 8). When fibers
are incorporated into PLA, PLA biocomposites (PLA-FF and PLA-BF)
exhibit cracks and holes in the matrix. This is due to the fibers being
pulled-out (green arrows in Fig. 8), reflecting poor interfacial adhesion
between the PLA matrix and the fibers. This decohesion phenomenon
between flax or bamboo fibers and the PLA matrix observed becomes
more pronounced with multiple ageing and reprocessing cycles. Bio-
composites containing silane-functionalized fibers and Joncryl™ display
a rougher surface with well-preserved fiber–matrix adhesion relative to
raw composites, even after several reprocessing cycles (yellow arrows in
Fig. 8). The increase in surface roughness is associated with the cumu-
lative thermal and mechanical degradation of the PLA matrix, high-
lighting the interplay between matrix integrity and interfacial
morphology. Repeated recycling of PLA results in its hydrolytic degra-
dation, lowering its molecular weight and increasing its melt flow rate
(Åkesson et al., 2016).

**3.6. Environmental impacts assessment via LCA**

**3.6.1. PLAJ-SBF composite production**

Fig. 9 illustrates the contribution of each of the six sub-stages
involved in producing PLAJ-SBF biocomposites, on each environ-
mental impact. This representation is used in an ecodesign process to
identify the most impacting stages of the life cycle studied, from cradle
to gate here. The production of the PLA matrix accounts for the majority
of 4 of the studied impacts (freshwater consumption, land use, marine
eutrophication, stratospheric ozone depletion), contributing between
60 % and 90 %. These high impacts are linked to the corn cultivation
stage, as corn is the raw material used to produce PLA (Vink et al.,
2003). Bamboo fiber surface treatment accounts for the majority of 8 of
the studied impacts (climate change, fossil depletion, freshwater eco-
toxicity, freshwater eutrophication, human toxicity cancer and
non-cancer, ionizing radiation and marine ecotoxicity). For the impacts
of fine particulate matter formation, metal depletion, photochemical
ozone formation (ecosystems and human health) and terrestrial acidi-
fication, the PLA production stage and fiber treatment stage have similar
contributions, ranging from around 36–50 %. The transport stages have
a negligible share, except for the impacts of metal depletion, photo-
chemical ozone formation (ecosystems, and human health) and terres-
trial ecotoxicity, for which they have a significant contribution of
around 30 %. Production of bamboo fibers has a negligible impact,
except on land use (13 %). Natural fibers generally have a lower

<figure><img src="image_10.png" /><figcaption>Fig. 7. Effect of ageing and reprocessing on elongation at break: (A) PLA-FF composite and (B) PLA-BF composites.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Fig. 8. Effect of ageing and reprocessing on tensile fracture surface of flax-biocomposite specimens.</figcaption></figure>

environmental impact than polymer matrices. Hence, their production has little impact on the environmental assessment of composite production (Haylock and Rosentrater, 2018; Mansor et al., 2015). Finally, the extrusion stage contributes very little (less than 4 %).

When focusing only on the share of impacts related to fiber surface

treatment, which was identified as the most impactful step for a majority of impacts (Figs. 9 and 11), the fiber drying and waste solvent incineration steps make a significant contribution (see Fig. 10). Incinerating used solvents requires a very high temperature increase, resulting in notable contributions to two of the studied impacts (climate change and
<figure><img src="image_12.png" /><figcaption>Fig. 9. Share of the environmental impacts for the PLAJ-SBF production.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>Fig. 10. Share of the environmental impacts for the bamboo fibers treatment.</figcaption></figure>
freshwater eutrophication). However, the production of electricity during incineration enables negative contributions to some impacts (fossil depletion, freshwater consumption, freshwater ecotoxicity, ionizing radiation, land use, marine ecotoxicity). The oven drying stage is not optimized on a laboratory scale, resulting in high electrical consumption for the three long drying steps. The acetone production stage also contributes significantly to certain impacts (fine particulate matter formation, photochemical ozone formation, terrestrial acidification). These impacts are mainly linked to the cumene process, which involves the transformation of benzene and propylene into acetone and phenol (raw materials production, energy consumption).

### 3.6.2. PLAJ-SFF composites production

As with PLAJ-SBF composites, the fiber treatment stage has the greatest impact on many environmental impacts (11 out of 18) for the PLAJ-SFF biocomposite (Fig. 11). Since the surface treatment of flax requires greater quantities of chemical inputs (sodium hydroxide, acetone), the contribution of this stage is even greater than for PLAJ-SBF composites. Flax cultivation significantly contributes to marine eutrophication and water consumption. The emission of nitrates into the water and the use of water to produce the chemicals used in cultivation are at the root causes of these two impacts. Regarding compounding, the additional step of using an internal mixer has a visible impact on most of the impacts, contributing between 2 % and 27 %, due to the energy consumption of the equipment.

Fig. 12 presents the details of the sub-stages for the flax fiber treatment. The same trends can be observed as for the bamboo treatment, with a higher proportion of impacts linked to the production of acetone, due to the greater quantity required for this treatment.

### 3.6.3. Comparison of biocomposites and sensitivity analysis

When the environmental impact of producing 1 kg of each bio-composite is compared, it is found that PLAJ-SFF has a higher impact than PLAJ-SBF (between 13 % and 44 % increase), except in terms of land use (see Fig. 13). The same trend was observed by Gu et al. when

comparing the environmental impacts of polypropylene reinforced with bamboo or flax fibers (Gu et al., 2018). This can be explained mainly by the differences in the cultivation of the two types of fibers, but also by the processing of biocomposites. While the production stage of bamboo fibers has a negligible impact on the distribution of impacts (excluding land use) (Fig. 9), the production stage of flax fiber production made a small but significant contribution (Fig. 11). Bamboo cultivation uses no chemical inputs or agricultural machinery; the plants grow naturally and rapidly without outside intervention, making it a very frugal process. In contrast, the production of flax fiber is a more mechanized process, requiring the soil to be prepared (fall tillage) before sowing. Fertilizers are then used, and the flax plants are harvested. In terms of biocomposite production, the surface modification of flax fibers requires greater quantities of sodium hydroxide and acetone, resulting in more solvent waste that needs to be processed. Moreover, an additional step of internal mixer is needed for PLAJ-SFF, resulting in increased power consumption. Bianchi et al. have compared the environmental impacts of three different surface treatments for flax fibers used in composites: alkali, silane and plasma treatments (Bianchi et al., 2025). They found that the silane treatment had the greatest impact which is mainly due to the use of ethanol, the use of (3-aminopropyl)triethoxysilane and energy consumption for the climate change impact.

As certain stages of fiber processing were not optimized, a sensitivity analysis was performed on two parameters for PLAJ-SFF composites: 1) the quantity of fibers dried during the drying stages (a scenario called Optimized Drying (OD), noted as PLAJ-SFF-OD) and 2) the percentage of the incinerators used to recover electricity during the processing of the used solvents (a scenario called Optimized Incineration (OI)). Optimized incineration combined with optimized drying was also studied and noted as OD+OI. In the PLAJ-SFF-OD scenario, it was assumed that the drying oven was used at 100 % of its total drying capacity (compared to 2.5 % of its total capacity in the initial scenario). To optimize incineration, it was assumed that all incinerators could produce electricity (compared to 35 % in the initial scenario). The impact scores for these two new scenarios are shown in Fig. 13. Significant reduction in all

<figure><img src="image_14.png" /><figcaption>Fig. 11. Share of the environmental impacts for the PLAJ-SFF production.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>Fig. 12. Share of the environmental impacts for the flax fiber's treatment.</figcaption></figure>

impacts is observed when the use of the drying oven is optimized, due to the major reduction in electricity consumption at these stages. When incineration is optimized, the reduction in impacts compared with the PLAJ-SFF scenario is even greater. The most notable reductions (> 50 %) are observed for fossil depletion, freshwater ecotoxicity, human toxicity (non-cancer), ionizing radiation, marine ecotoxicity, for the PLAJ-SFF-OD scenario. In addition, reductions are seen for human toxicity (cancer), metal depletion and terrestrial ecotoxicity for the PLAJ-SFF-OD+OI scenario. The greater recovery of electricity during solvent incineration and the reduction in electricity consumption during drying lead to a significant reduction in PLAJ-SFF composite production. For most of the studied impacts, the PLAJ-SFF-OD+OI scenario scores the same as or lower than the PLAJ-SBF scenario. When the surface treatment of flax fibers is optimized, this step has a less impact with a share of about 7 % on the environmental impact scores of the production of the composite (Bianchi et al., 2025).

## 4. Conclusion

The present work has assessed how fiber functionalization and the use of a chain extender affect both the mechanical recycling potential and the environmental performance of PLA biocomposites containing 10 wt% flax or bamboo fibers, providing insights into strategies for improving circularity and sustainability of natural fiber-reinforced polymers. The main conclusion is that incorporating Joncryl™ and silane-treated fibers dramatically improves the biocomposite's ability to withstand successive ageing and reprocessing steps, especially for flax

fiber-based PLA biocomposites which can undergo 3 cycles of ageing and reprocessing while maintaining their Young's modulus. Generally speaking, flax fiber-based PLA biocomposites have better performances all along the ageing cycles than bamboo fiber-based PLA biocomposites. This can be explained by several factors such as the biochemical composition of each fiber, and the size and shape of each fiber. Moreover, Bamboo fiber-based biocomposites are more susceptible to thermal degradation than flax fiber biocomposites, even when fibers are treated and Joncryl™ is used. Only 2 steps of recycling are possible for bamboo based biocomposites, whereas 3 steps are possible for flax-biocomposites. PLAJ-SFF and PLAJ-SBF biocomposites show great promise in terms of their Young's modulus and tensile strength, which are maintained even after 2 complete steps of mechanical recycling (hygrothermal ageing and reprocessing).

LCA results show that the surface treatment of fibers on a laboratory scale, significantly increases environmental impacts. A sensitivity analysis of the fiber drying and solvent incineration stages shows that optimizing those stages significantly reduces environmental impacts. Therefore, it is conceivable that transitioning to an industrial scale in the processing of fiber treatment would greatly reduce the environmental impacts of producing recyclable biocomposites. Altogether, this work offers valuable insights for the development of high-performance, recyclable natural fiber-reinforced polymers, paving the way toward more circular and environmentally responsible biocomposite materials.
<figure><img src="image_16.png" /><figcaption>Fig. 13. Comparison of environmental impacts of biocomposites and sensitivity analysis on PLAJ-SFF.</figcaption></figure>

CRediT authorship contribution statement

**Florence Delor-Jestin:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Haroutioun Askanian:** Writing – review & editing, Visualization, Validation, Supervision, Formal analysis. **Lopez-Cuesta José-Marie:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. **Hervé Nlandu:** Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Didier Perrin:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Joana Beigbeder:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation. **joannes Sébastien:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Aurélie Taguet:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Jose Marie Lopez Cuesta reports financial support was provided by Carnot M.I.N.E.S. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

Acknowledgement

This study is part of the RecComBioS project entitled "Recyclability of Biosourced Composites", supported and funded by the Carnot M.I.N. E.S Institute.

Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.indcrop.2025.122296.

Data Availability

Data will be made available on request.

References

Åkesson, D., Fazelinejad, S., Skrifvars, V.-V., Skrifvars, M., 2016. Mechanical recycling of polylactic acid composites reinforced with wood fibres by multiple extrusion and hydrothermal ageing. J. Reinf. Plast. Compos. 35 (16), 1248–1259. https://doi.org/10.1177/0731684416647507.

Allen, S., Allen, D., Karbalaei, S., Maselli, V., Walker, T.R., 2022. Micro(nano)plastics sources, fate, and effects: What we know after ten years of research. J. Hazard. Mater. Adv. 6, 100057. https://doi.org/10.1016/j.hazadv.2022.100057.

Anon, 2018. Electricity production in France. https://www.notre-environnement.gouv.fr/themes/economie/les-dechets-ressources/article/le-traitement-des-dechets#Le-traitement-des-dechets-par-categorie.

Aouat, T., Kaci, M., Lopez-Cuesta, J.-M., Devaux, E., 2019. Investigation on the durability of PLA bionanocomposite fibers under hygrothermal conditions. Front. Mater. 6. https://doi.org/10.3389/fmats.2019.00323.

Baniasadi, H., Åkräs, L., Madani, Z., Silvenius, F., Fazeli, M., Lipponen, S., Vapaavuori, J., Seppälä, J., 2024. Development and characterization of polylactic acid/starch biocomposites – From melt blending to preliminary life cycle assessment. Int. J. Biol. Macromol. 279, 135173. https://doi.org/10.1016/j.ijbiomac.2024.135173.
Basri, M.H., Mohamad, Z., Hassan, A., Kumar, A., 2019. Properties enhancement of biocomposite based on poly (lactic acid) and banana fiber. Chem. Eng. Trans. 72, 439-444. https://doi.org/10.3303/CET1972074.

Bianchi, I., Forcellese, A., Taha, I., 2025. Comparative LCA of fully biobased and synthetic polymer composites accounting for fiber treatment. J. Clean. Prod. 530, 146846. https://doi.org/10.1016/j.jclepro.2025.146846.

Bourmaud, A., Le Duigou, A., Bailey, C., 2011. What is the technical and environmental interest in reusing a recycled polypropylene-hemp fibre composite? Polym. Degrad. Stab. 96 (10), 1732-1739. https://doi.org/10.1016/j.polymdegradstab.2011.08.003.

Fortunati, E., Armentano, I., Zhou, Q., Puglia, D., Terenzi, A., Berglund, L.A., Kenny, J. M., 2012. Microstructure and nonisothermal cold crystallization of PLA composites based on silver nanoparticles and nanocrystalline cellulose. Polym. Degrad. Stab. 97 (10), 2027-2036. https://doi.org/10.1016/j.polymdegradstab.2012.03.027.

Foulc, M.P., Bergeret, A., Ferry, L., Ienny, P., Crespy, A., 2005. Study of hygrothermal ageing of glass fibre reinforced PET composites. Polym. Degrad. Stab. 89 (3), 461-470. https://doi.org/10.1016/j.polymdegradstab.2005.01.025.

Ghalme, S., Hayat, M., Harne, M., 2025. A comprehensive review of natural fibers: bio-based constituents for advancing sustainable materials technology. J. Renew. Mater. 13 (2), 273-295. https://doi.org/10.32604/jrm.2024.056275.

Gholampour, A., Ozbakkaloglu, T., 2020. A review of natural fiber composites: properties, modification and processing techniques, characterization, applications. J. Mater. Sci. 55 (3), 829-892. https://doi.org/10.1007/s10853-019-03990-y.

Goedkoop, M.J., Huijbregts, M.A., Heijungs, R., De Schryver, A., Struijs, J., van Zelm, R., 2008. ReCiPe 2008: A life cycle impact assessment method which comprises harmonised category indicators at the midpoint and the endpoint level.

Gomez-Campos, A., Vialle, C., Rouilly, A., Sablayrolles, C., Hamelin, L., 2021. Flax fiber for technical textile: a life cycle inventory. J. Clean. Prod. 281, 125177. https://doi.org/10.1016/j.jclepro.2020.125177.

Gonçalves, R., Serra, J., Reizabal, A., Correia, D.M., Fernandes, L.C., Brito-Pereira, R., Lizundia, E., Costa, C.M., Lanceros-Méndez, S., 2025. Biobased polymers for advanced applications: towards a sustainable future. Prog. Polym. Sci. 162, 101934. https://doi.org/10.1016/j.progpolymsci.2025.101934.

Grigore, M., 2017. Methods of recycling, properties and applications of recycled thermoplastic polymers. Recycling 2 (4), 24. https://doi.org/10.3390/recycling2040024.

Gu, F., Zheng, Y., Zhang, W., Yao, X., Pan, D., Wong, A.S.M., Guo, J., Hall, P., Sharmin, N., 2018. Can bamboo fibres be an alternative to flax fibres as materials for plastic reinforcement? A comparative life cycle study on polypropylene/flax/bamboo laminates. Ind. Crops Prod. 121, 372-387. https://doi.org/10.1016/j.indcrop.2018.05.025.

Gurunathan, T., Mohanty, S., Nayak, S.K., 2015. A review of the recent developments in biocomposites based on natural fibres and their application perspectives. Compos. Part A Appl. Sci. Manuf. 77, 1-25. https://doi.org/10.1016/j.compositesa.2015.06.007.

Haylock, R., Rosentrater, K.A., 2018. Cradle-to-grave life cycle assessment and techno-economic analysis of polylactic acid composites with traditional and bio-based fillers. J. Polym. Environ. 26 (4), 1484-1503. https://doi.org/10.1007/s10924-017-1041-2.

Huijbregts, M.A.J., Steinmann, Z.J.N., Elshout, P.M.F., Stam, G., Verones, F., Vieira, M., Zijp, M., Hollander, A., van Zelm, R., 2017. ReCiPe2016: a harmonised life cycle impact assessment method at midpoint and endpoint level. Int. J. Life Cycle Assess. 22 (2), 138-147. https://doi.org/10.1007/s11367-016-1246-y.

Jambeck, J.R., Geyer, R., Wilcox, C., Siegler, T.R., Perryman, M., Andrady, A., Narayan, R., Law, K.L., 2015. Plastic waste inputs from land into the ocean. Science 347 (6223), 768-771. https://doi.org/10.1126/science.1260352.

Jiang, N., Li, Y., Li, Y., Yu, T., Li, Y., Li, D., Xu, J., Wang, C., Shi, Y., 2020. Effect of short jute fibers on the hydrolytic degradation behavior of poly(lactic acid). Polym. Degrad. Stab. 178, 109214. https://doi.org/10.1016/j.polymdegradstab.2020.109214.

Le Duigou, A., Davies, P., Bailey, C., 2009. Seawater ageing of flax/poly(lactic acid) biocomposites. Polym. Degrad. Stab. 94 (7), 1151-1162. https://doi.org/10.1016/j.polymdegradstab.2009.03.025.

Le Duigou, A., Pillin, I., Bourmaud, A., Davies, P., Bailey, C., 2008. Effect of recycling on mechanical behaviour of biocompostable flax/poly(l-lactide) composites. Compos. Part A Appl. Sci. Manuf. 39 (9), 1471-1478. https://doi.org/10.1016/j.compositesa.2008.05.008.

Liu, X., Park, H., Ackermann, Y.S., Avérous, L., Ballerstedt, H., Besenmatter, W., Blázquez, B., Bornscheuer, U.T., Branson, Y., Casey, W., de Lorenzo, V., Dong, W., Floehr, T., Godoy, M.S., Ji, Y., Jupke, A., Klankermayer, J., León, D.S., Liu, L., Chen, G.-Q., 2025. Exploring biotechnology for plastic recycling, degradation and upcycling for a sustainable future. Biotechnol. Adv. 81, 108544. https://doi.org/10.1016/j.biotechadv.2025.108544.

Mai, V.-D., Kang, D., Kim, Y., Jang, Y., Min, J., Han, J., Kim, S.-K., 2024. Preparation and environmental analysis of biodegradable polylactic acid and modified cellulose nanofiber composites. J. Ind. Eng. Chem. 130, 401-411. https://doi.org/10.1016/j.jiec.2023.09.046.

Mansor, M.R., Salit, M.S., Zainudin, E.S., Aziz, N.A., Ariff, H., 2015. Life Cycle Assessment of Natural Fiber Polymer Composites. Agricultural Biomass Based Potential Materials. Springer International Publishing, pp. 121-141. https://doi.org/10.1007/978-3-319-13847-3-6.

Mohanty, A.K., Misra, M., Hinrichsen, G., 2000. Biofibres, biodegradable polymers and biocomposites: an overview. Macromol. Mater. Eng. 276-277 (1), 1-24. https://doi.org/10.1002/(SICI)1439-2054(20000301)276:1<1::AID-MAME1>3.0.CO;2-W.

Nayanathara Thathsarani Pilapitiya, P.G.C., Ratnayake, A.S., 2024. The world of plastic waste: a review. Clean. Mater. 11, 100220. https://doi.org/10.1016/j.clema.2024.100220.

Nlandu-Mayamba, H., Taguet, A., Perrin, D., Joannès, S., Delor-Jestin, F., Askanian, H., Lopez-Cuesta, J.-M., 2024. Influence of surface treatments and addition of a reactive agent on the properties of PLA/flax and PLA/bamboo composites. J. Thermoplast. Compos. Mater. 37 (11), 3436-3459. https://doi.org/10.1177/08927057241231733.

Operato, L., Vitiello, L., Aprea, P., Ambrogi, V., Salzano de Luna, M., Filippone, G., 2023. Life cycle assessment of poly(lactic acid)-based green composites filled with pine needles or kenaf fibers. J. Clean. Prod. 387, 135901. https://doi.org/10.1016/j.jclepro.2023.135901.

Peña, C., Civit, B., Gallego-Schmid, A., Druckman, A., Caldeira-Pires, A., Weidema, B., Mieras, E., Wang, F., Fava, J., Canals, L.M. i, Cordella, M., Arbuckle, P., Valdivia, S., Fallaha, S., Motta, W., 2021. Using life cycle assessment to achieve a circular economy. Int. J. Life Cycle Assess. 26 (2), 215-220. https://doi.org/10.1007/s11367-020-01856-z.

Riofrio, A., Cornejo, M., Baykara, H., 2022. Environmental performance of bamboo fibers and sugarcane bagasse reinforced metakaolin-based geopolymers. Case Stud. Constr. Mater. 17, e01150. https://doi.org/10.1016/j.csmc.2022.e01150.

Sánchez-Safont, E.L., Arrillaga, A., Anakabe, J., Cabedo, L., Gamez-Perez, J., 2018. Toughness enhancement of PHBV/TPU/cellulose compounds with reactive additives for compostable injected parts in industrial applications. Int. J. Mol. Sci. 19 (7), 2102. https://doi.org/10.3390/ijms19072102.

Schrijvers, D.L., Loubet, P., Sonnemann, G., 2016. Critical review of guidelines against a systematic framework with regard to consistency on allocation procedures for recycling in LCA. Int. J. Life Cycle Assess. 21 (7), 994-1008. https://doi.org/10.1007/s11367-016-1069-x.

Schwarz, A.E., Ligthart, T.N., Godoi Bizarro, D., De Wild, P., Vreugdenhil, B., van Harmelen, T., 2021. Plastic recycling in a circular economy; determining environmental performance through an LCA matrix model approach. Waste Manag. 121, 331-342. https://doi.org/10.1016/j.wasman.2020.12.020.

Srebrenkoska, V., Bogoeva-Gaceva, G., Dimeski, D., 2014. Biocomposites based on polylactic acid and their thermal behavior after recycling. Maced. J. Chem. Chem. Eng. 33 (2), 277-285. https://doi.org/10.20450/mjccce.2014.479.

Stegmann, P., Daioglou, V., Londo, M., van Vuuren, D.P., Junginger, M., 2022. Plastic futures and their CO2 emissions. Nature 612 (7939), 272-276. https://doi.org/10.1038/s41586-022-05422-5.

Vink, E.T.H., Rábago, K.R., Glassner, D.A., Gruber, P.R., 2003. Applications of life cycle assessment to NatureWorks™ polylactide (PLA) production. Polym. Degrad. Stab. 80 (3), 403-419. https://doi.org/10.1016/S0141-3910(02)00372-5.

Yoo, H.M., Jeong, S.-Y., Choi, S.-W., 2021. Analysis of the rheological property and crystallization behavior of polylactic acid (Ingeo™ Biopolymer 4032D) at different process temperatures. E-Polymers 21 (1), 702-709. https://doi.org/10.1515/epoly-2021-0071.

Zhou, Y., Fan, M., Chen, L., 2016. Interface and bonding mechanisms of plant fibre composites: an overview. Compos. Part B Eng. 101, 31-45. https://doi.org/10.1016/j.compositesb.2016.06.055.