Nanocelluloses: Potential 

Materials for Advanced 

Forest Products

Proceedings of Nanotechnology 

in Wood Composites Symposium

Zhiyong Cai

Kristina Oksman Niska

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

General 

Technical

Report

FPL–GTR–218
September 2012

Cai, Zhiyong; Oksman Niska, Kristina. 2012. Nanocelluloses: Potential 

materials for advanced forest products—Proceedings of nanotechnology in 

wood composites symposium. General Technical Report FPL-GTR-218. 

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 76 p.

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Abstract 

This report provides a summary of technical papers presented at the Nanotechnology in Wood Composites Symposium 

held at the USDA Forest Products Laboratory in Madison, 

Wisconsin, May 18, 2011. Papers in this report included 

the oral presentations and posters that explore the adaptability and applicability of using nanocellulose as a potential 

resource to create value-added commodities and innovative 

bio-based composites. Presenters from around the world 

reviewed nanotechnology applications in developing and 

improving forest products in the past, present, and future. A 

variety of nanomaterials are obtained from wood, including 

nanofibrils, nanocrystals, lignin particles, and extractives. 

Most research efforts focus on developing continuous, highperformance composite reinforcement from cellulose nanofibrils; improving performance and value-added features of 

existing wood-based composites; developing coatings and 

additives for improved durability of wood composites; and 

developing films and membranes with tailored mechanical 

and barrier properties, sensing capabilities, and 

biodegradability.

Keywords: nanocellulose, nanofibril, nanocrystal, 

biocomposite, wood product

Acknowledgments

We acknowledge the contributions of symposium participants and especially recognize the extraordinary effort of 

the following individuals in organizing the meeting: Craig 

M. Clemons, Research Materials Engineer, USDA Forest 

Products Laboratory; Nicole M. Stark, Research Chemical 

Engineer, USDA Forest Products Laboratory; Julie Lang, 

Conference Coordinator, Forest Products Society; and, 

Stefan Bergmann, Executive Vice President, Forest 

Products Society.

Contents

Executive Summary............................................................1

Presenters............................................................................1

Nanotechnology Applications in 

Forest Products—Past, Present, and Future........................3

Transparent Polymer Composites Reinforced by 

Nanocrystalline Cellulose ...................................................5

Enhancing Durability of Wood-Based Composites 

with Nanotechnology..........................................................8

Artificial Ligaments/Tendons Based on Cellulose 

Nanofibers.........................................................................13

Nanocellulose/Conducting Polymer Nanocomposite 

Films Based on Bacterial Cellulose ..................................18

Eucalyptus Micro and Nanofibres for Reinforcement 

of Polymeric Nanocomposites..........................................22

Impact Properties and Characteristic Impact Resistance 

Model of Cellulose Nanofibril-Filled Polypropylene 

Composites........................................................................25

Synthesis of Hybrid Porous Cellulose/Metal 

Nanocomposites................................................................45

An Investigation into the Mechanical Behaviour of 

Surface-Modified Fibrillated Cellulose Reinforced 

Composites........................................................................50

Production and Characterization of Nano-Structured 

Carbons from Pine Chips..................................................54

An Investigation of Fabrication Thermal Insulation 

Wood-Based Composite Using Nanotechnology..............64

Mechanical and Thermal Properties of Microcrystalline 

Cellulose/Nanoclay/Polypropylene...................................70
Nanocelluloses: Potential Materials 

for Advanced Forest Products 

Proceedings of Nanotechnology in 

Wood Composites Symposium

Zhiyong Cai, Supervisory Research Materials Engineer

Forest Products Laboratory, Madison, Wisconsin

Kristina Oksman Niska, Professor

Lulea University of Technology, Luleå, Sweden

Executive Summary

Nanotechnology has enormous promise to bring about 

fundamental changes and significant benefit to the forest 

products industry. Cellulose is the most abundant and inexhaustible natural polymer, with an annual production in the 

biosphere of about 90 billion tons. Use of nano-dimensional 

cellulose in nanocomposites will allow the production of 

much higher performance materials to replace nonrenewable metal and plastics, with widespread application in the 

forest products and other industries. This report compiles 

technical papers presented at the Nanotechnology in Wood 

Composites Symposium held at the USDA Forest Products 

Laboratory in Madison, Wisconsin, on May 18, 2011. The 

objective of this symposium was to provide information 

recognizing that the values of wood and bio-based materials at the nanoscale are virtually untapped and have huge 

potential for the economy. Wood-derived nanomaterials will 

offer new revenue streams with high-value-added products. 

Presenters from the world reviewed nanotechnology applications in developing and improving forest products in the 

past, present, and future. Future needs and challenges for 

applying nanotechnology in forest products require the ability to develop chemical and mechanical methodologies for 

converting nano-fibrillated cellulose into user-friendly forms 

and pilot-plant scale-up and industrial collaboration to refine 

and demonstrate the technology.

Presenters

1. Keynote Address: Nanotechnology Applications in 

Forest Products—Past, Present, and Future

Douglas J. Gardner, University of Maine

2. Transparent Polymer Composites Reinforced by 

Nanocrystalline Cellulose

James Snyder, U.S. Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, Maryland; Hong Dong, U.S. Army Research 

Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, Maryland; Joshua Steele, 

U.S. Army Research Laboratory, Weapons and Materials 

Research Directorate, Aberdeen Proving Ground, Maryland; Ken Strawhecker, U.S. Army Research Laboratory, 

Weapons and Materials Research Directorate, Aberdeen 

Proving Ground, Maryland; Joshua Orlicki, U.S. Army 

Research Laboratory, Weapons and Materials Research 

Directorate, Aberdeen Proving Ground, Maryland; Richard Reiner, USDA Forest Service, Forest Products 

Laboratory, Madison, Wisconsin; Alan Rudie, USDA 

Forest Service, Forest Products Laboratory, Madison, 

Wisconsin

3. Enhancing Durability of Wood-Based Composites with 

Nanotechnology

Carol A. Clausen, USDA Forest Service, Forest Products 

Laboratory, Madison, Wisconsin

4. Artificial Ligaments/Tendons Based on Cellulose 

Nanofibers

Aji P. Mathew, Department of Engineering Materials and 

Mathematics, Division of Manufacturing and Design of 

Wood and Bionanocomposites, University of Technology, Luleå, Sweden; Kristiina Oksman, Department of 

Engineering Materials and Mathematics, Division of 

Manufacturing and Design of Wood and Bionanocomposites, University of Technology, Luleå, Sweden

5. Nanocellulose/Conducting Polymer Nanocomposite 

Films Based on Bacterial Cellulose

Byoung-Ho Lee, Laboratory of Adhesion & BioComposites, Program in Environmental Materials Science, Seoul National University, Seoul, Republic of 

Korea; Hyun-Ji Lee, Laboratory of Adhesion & BioComposites, Program in Environmental Materials 

Science, Seoul National University, Seoul, Republic 

of Korea; Taekjun Chung, Laboratory of Adhesion & 

Bio-Composites, Program in Environmental Materials 

Science, Seoul National University, Seoul, Republic of 

Korea; Hyun-Joong Kim, Laboratory of Adhesion & 

Bio-Composites, Program in Environmental Materials 
General Technical Report FPL–GTR–218

2

Science, Seoul National University, Seoul, Republic 

of Korea and Research Team for Biomass-based Biomaterials, Research Institute for Agriculture and Life 

Sciences, Seoul, Republic of Korea

6. Eucalyptus Micro and Nanofibres for Reinforcement 

of Polymeric Nanocomposites

G.H.D. Tonoli, Department of Forest Science, Universidade Federal de Lavras, Lavras, Brazil; L.A. 

Caixeta, Laboratório Nacional de Nanotecnologia para 

o Agronegócio (LNNA), Embrapa Instrumentação Agropecuária, São Carlos, Brazil; J.M. Marconcini, Laboratório Nacional de Nanotecnologia para o Agronegócio 

(LNNA), Embrapa Instrumentação Agropecuária, São 

Carlos, Brazil; A.C. Corrêa, Laboratório Nacional de 

Nanotecnologia para o Agronegócio (LNNA), Embrapa 

Instrumentação Agropecuária, São Carlos, Brazil; M.A. 

Pereira-da-Silva, Instituto de Física de São Carlos, 

Universidade de São Paulo, São Carlos, Brazil; L.M. 

Mendes, Department of Forest Science, Universidade 

Federal de Lavras, Lavras, Brazil; Luiz H. Capparelli 

Mattoso, Laboratório Nacional de Nanotecnologia para 

o Agronegócio (LNNA), Embrapa Instrumentação 

Agropecuária, São Carlos, Brazil

7. Impact Properties and Characteristic Impact Resistance 

Model of Cellulose Nanofibril-Filled Polypropylene 

Composites

Han-Seung Yang, AEWC—Advanced Structures and 

Composites Center and Forest Bioproducts Research 

Institute (FBRI), University of Maine, Orono, Maine; 

Douglas J. Gardner, AEWC—Advanced Structures and 

Composites Center, University of Maine, Orono, Maine; 

Jacques W. Nader, AEWC—Advanced Structures and 

Composites Center, University of Maine, Orono, Maine

8. Synthesis of Hybrid Porous Cellulose/Metal 

Nanocomposites

Tao Wang, Center for Nano Science and Technology 

and Department of Electrical Engineering, University of 

Notre Dame, Notre Dame, Indiana; Zhiyong Cai, USDA 

Forest Service, Forest Products Laboratory, Madison, 

Wisconsin; Abhijit Biswas, Center for Nano Science and 

Technology, Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana; Lei Liu, 

Advanced Diagnostics and Therapeutics, Department of 

Electrical Engineering, University of Notre Dame, Notre 

Dame, Indiana

9. An Investigation into the Mechanical Behaviour of 

Surface-Modified Fibrillated Cellulose Reinforced 

Composites

M.Sc. Bulota M., Aalto University, School of Chemical 

Technology, Department of Forest Products Technology, 

Espoo, Finland; M.Sc. Hänninen T., Aalto University, 

School of Chemical Technology, Department of Forest 

Products Technology, Espoo, Finland; Dr. Jääskeläinen 

A.-S., Aalto University, School of Chemical Technology, Department of Forest Products Technology, Espoo, 

Finland; Dr. Kontturi E., Aalto University, School of 

Chemical Technology, Department of Forest Products 

Technology, Espoo, Finland; Professor Hughes M., Aalto 

University, School of Chemical Technology, Department 

of Forest Products Technology, Espoo, Finland

10. Production and Characterization of Nano-Structured 

Carbons from Pine Chips 

Qiangu Yan, Department of Agricultural & Biological 

Engineering, Mississippi State University, Mississippi; 

Hossein Toghiani, Dave C. Swalm School of Chemical 

Engineering, Mississippi State University, Mississippi; 

Zhiyong Cai, USDA Forest Service, Forest Products 

Laboratory, Madison, Wisconsin; Fei Yu, Department of 

Agricultural & Biological Engineering, Mississippi State 

University, Mississippi; Jilei Zhang, Forest Products 

Laboratory, Mississippi State University, Mississippi

11. An Investigation of Fabrication Thermal Insulation 

Wood-Based Composite Using Nanotechnology

Reza Zahedsheijani, Department of Wood and Paper 

Science & Technology, Faculty of Natural Resources, 

University of Tehran, Karaj, Iran; Mohammad Layeghi, 

Department of Wood and Paper Science & Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran; Hosein Yousefi, Department of Wood 

and Paper Science & Technology, Faculty of Natural 

Resources, University of Tehran, Karaj, Iran; Mehdi 

Faezipour, Department of Wood and Paper Science & 

Technology, Faculty of Natural Resources, University 

of Tehran, Karaj, Iran

12. Mechanical and Thermal Properties of Microcrystalline 

Cellulose/Nanoclay/Polypropylene

Amir Nourbakhsh, Department of Wood and Paper 

Science, Research Institute of Forests and Rangelands 

(RIFR), Tehran, Iran; Alireza Ashori, Department of 

Chemical Technologies, Iranian Research Organization 

for Science and Technology (IROST), Tehran, Iran
Nanocelluloses: Potential Materials for Advanced Forest Products Proceedings of Nanotechnology in Wood Composites Symposium

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General Technical Report FPL–GTR–218

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Nanocelluloses: Potential Materials for Advanced Forest Products Proceedings of Nanotechnology in Wood Composites Symposium

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Transparent Polymer Composites 

Reinforced by Nanocrystalline Cellulose

James Snyder, Chemist

Hong Dong, Chemist

Joshua Steele, Chemist

Ken Strawhecker, Chemist

Joshua Orlicki, Chemist

U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland

Richard S. Reiner, Chemical Engineer

Alan W. Rudie, Supervisory Research Chemist

Forest Products Laboratory, Madison, Wisconsin

The demand for lighter and stronger materials across Army 

platforms is promoting the development of lightweight 

composites. Traditional reinforcement materials such as 

polymers, carbon, and ceramics incur penalties with respect 

to processing costs to achieve high specific strength, and 

they typically frustrate transparency. In contrast, cellulose 

fibers provide a renewable, low-cost alternative with favorable properties that include low densities and high specific 

strength and modulus (Samir and others 2005, van den Berg 

and others 2007, Sturcova and others 2005). Recent work 

by Nogi and others (2009) demonstrating transparency of 

bacterial cellulose nanofibers in thin sheets as well as in 

nanocomposites (Nogi and others 2005) indicates potential 

applicability for nanocellulose in transparent composite defense applications.

At the U.S. Army Research Laboratory (ARL), low-cost, 

high-performance cellulosic reinforcement of transparent 

composites is being investigated by means of advanced 

nanostructured architectures, improved cellulose-matrix 

interfaces, and characterization of bulk laminates. This parallel approach enables simultaneous development of several 

critical properties and facilitates more rapid transition of the 

technology into useful components. The U.S. Forest Service 

is providing most of the cellulose nanomaterials and surface 

modifications for the project, including efforts to scale up 

the laboratory procedures for using wood pulp to produce 

cellulose nanocrystals (CNC) using a modification of the 

procedure reported by Gray and others and the larger and 

less crystalline nanofibrillated cellulose (NFC) using the 

TEMPO oxidation technique (Saito and others 2006).

Solvent-dispersed blends of polymer and cellulose nanoparticles were cast into films and thin laminates for initial evaluation of optical and mechanical properties at high loadings. 

Polymethylmethacrylate (PMMA) was used in this study 

as a test matrix. Films suitable for optical testing were cast 

from solution in N,N- dimethylformamide at 60 °C under 

standard atmospheric pressure onto a tempered glass plate. 

The solution casting methods investigated here are not ideal 

for thicker laminates and are presented for baseline testing 

only (Figs. 1 and 2).

Initial optical characterization was performed using a Gardner Haze-Gard Plus analyzer (BYK-Gardner, Columbia, 

Maryland) to investigate the transmittance, haze, and clarity 

of each specimen. The target sample thickness was 0.8 mm. 

The optical properties in our films demonstrated a reduction 

in transmittance and clarity and an increase in haze with 

CNC loading. The decline in optical properties with CNC 

loading may arise from the processing method used here, 

because solvent casting frequently generates voids and variations in thickness. Although the films investigated appeared 

well-formed and smooth, it is unclear whether the trends 

are inherent to the nanoparticle loadings or whether optical properties degrade due to poorly formed particle-matrix 

Figure 1. Solution cast PMMA films with increasing concentrations of CNC modified with Tween-40.
General Technical Report FPL–GTR–218

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interfaces and/or film imperfections. Continuing studies are 

focused on advanced processing procedures to better quantify optical properties in thicker laminates.

To achieve more control over CNC dispersion and interfacing with the matrix, high-performance fibers and porous networks are being developed that remain transparent in laminates. The initial focus has been on production of cellulosepolymer composite nanofibers of various composition using 

electrospinning, which uses an external electrostatic field to 

generate small fibers with diameters on the nanometer scale 

(Huang and others 2003). These CNC-based nanofibers 

are expected to possess enhanced mechanical properties in 

strength, modulus, and resistance to fracture. The highly 

interpenetrated and porous framework of a nanofiber web 

may then be used to reinforce polymer composites. Moreover, controlled orientation of CNCs in the polymer matrix 

is possible using one-dimensional alignment of CNC-based 

polymer nanofibers. The diameter of the fibers is small and 

controllable to be in the nanometer range to promote optical 

transparency.

Electrospun PMMA reinforced with CNCs yielded uniform 

and smooth nanofibers at all concentrations considered in 

this study, up through 40 wt% CNC. The average diameters 

of the fibers ranged from 500 to 200 nm. Fourier transform infrared (FT-IR) spectroscopy was used to confirm 

the incorporation of CNCs in PMMA. The local moduli of 

the nanofibers were studied by nanoindentation of fibers 

electrospun directly onto glass cover slip substrates. Transverse loadings were performed using a TI-950 nanoindenter 

(Hysitron, Inc., Minneapolis, Minnesota) and employing 

a 500-nm-radius cone-shaped diamond probe. Indentation 

depths were typically between 100 and 200 nm. A plot of 

nanoindentation modulus, E, as a function of CNC concentration (Fig. 3) indicates a trend of increasing modulus 

as CNC loading increases. At 33 wt% CNC the modulus is 

about 25% higher than that of the neat PMMA nanofiber. 

A slight dip at higher concentrations may be indicative of 

CNC aggregation.

The fibers were collected on a rapidly rotating mandrel, 

aligning the electrospun fibers. The orientation of CNC in a 

CNC/PMMA fiber was investigated by etching PMMA out 

from fibers with drops of tetrahydrofuran (THF). Homogeneously dispersed and highly aligned CNCs introduced 

into PMMA fibers were observed along the fiber axis, likely 

caused by high shear force in the electrospinning process. 

Several layers of 33 wt% CNC/PMMA nanofibers were 

stacked into a mold with excess PMMA powder and pressed 

at 150 °C to yield CNC-reinforced PMMA composites. In 

these trial laminates, the final CNC concentration was 1 

wt%. The nanofibers were found to integrate seamlessly into 

the pressed matrix to form CNC-reinforced PMMA sheets, 

and noticeable degradation of transmittance was not detected relative to a 100% PMMA laminate. The optical and 

mechanical properties of PMMA with CNC nanocomposite 

fibers are currently being characterized at a greater range of 

formulations.

More refined control over cellulose architecture may be derived from defining the network prior to matrix integration. 

We have therefore used gelled networks of NFC as a starting point for these networks. Removing the solvent yielded 

aerogels that were subsequently backfilled with resin and 

cured to form the composite. In an alternative method, the 

solvent was directly displaced with resin, maintaining a finer 

cellulosic network and better optical properties. Mechanical 

properties, currently under evaluation, are expected to improve not only from the specific property of NFC, but also 

from the hydrogen bonding that constructs the network.

Figure 2. Electrospun PMMA fibers reinforced with 17 wt% 

CNCs.

Figure 3. Nanofiber modulus as a function of fiber diameter and CNC concentration.
Nanocelluloses: Potential Materials for Advanced Forest Products Proceedings of Nanotechnology in Wood Composites Symposium

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In conclusion, we have successfully fabricated nanofibers 

and thin films of cellulose-polymer transparent composites. Controlled integration of nanostructured cellulose in 

polymer matrices is essential to maintain the desired optical 

qualities of the composite while still providing enhanced 

levels of mechanical reinforcement. Our results indicate that 

cellulose reinforcement of transparent materials is feasible, 

which would enable a potential route to low-cost, scalable 

composite structures using these bioderived resources.

References 

Huang, Z.; Zhang, Y.; Kotaki, M.; Ramakrishna, S. 2003. A 

review on polymer nanofibers by electrospinning and their 

applications in nanocomposites. Composites Science and 

Technology. 63: 2223–2253.

Nogi, M.; Handa, K.; Nakagaito, A.; Yano, H. 2005. Optically transparent bionanofiber composites with low sensitivity to refractive index of the polymer matrix. Applied Physics Letters. 87: 243110.

Nogi, M.; Iwamoto, S.; Nakagaito, A.; Yano, H. 2009. 

Optically transparent nanofiber paper. Advanced Materials. 

21: 1595–1598.

Saito, T.; Nishiyama, Y.; Putaux, J.; Vignon, M.; Isogai, A. 

2006. Homogeneous suspensions of individualized microfibrils from TEMPO-catalyzed oxidation of native cellulose. 

Biomacromolecules. 7: 1687–1691.

Samir, A.; Alloin, F.; Dufresne, A. 2005. Review of recent 

research into cellulosic whiskers, their properties and their 

application in nanocomposite field. Biomacromolecules. 

6: 612–626.

Sturcova, A.; Davies, G.; Eichhorn, S. 2005. Elastic modulus and stress-transfer properties of tunicate cellulose whiskers. Biomacromolecules. 6: 1055–1061.

van den Berg, O.; Capadona, J.; Weder, C. 2007. Preparation 

of homogeneous dispersions of tunicate cellulose whiskers 

in organic solvents. Biomacromolecules. 8: 1353–1357.
General Technical Report FPL–GTR–218

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Enhancing Durability of Wood-Based 

Composites with Nanotechnology

Carol A. Clausen, Supervisory Research Microbiologist

Forest Products Laboratory, Madison, Wisconsin

Abstract

Wood protection systems are needed for engineered composite products that are susceptible to moisture and biodeterioration. Protection systems using nano-materials are 

being developed to enhance the durability of wood-based 

composites through improved resistance to biodeterioration, 

reduced environmental impact from chemical leaching, and 

improved resistance to ultraviolet (UV) degradation. Three 

approaches will be presented: (1) direct application of nanometals to wood-based products, (2) slow release of biocides 

embedded in nano-polymer matrices, and (3) controlled delivery of biocides with a nano-carrier. In the first approach, 

wood was vacuum impregnated with nano-sized particles 

of metals commonly used in wood preservative formulations (e.g., zinc and copper). Nano-zinc oxide particles were 

shown to be leach resistant, protected against UV degradation, and acted as a termite toxicant when compared to 

soluble zinc, a key component of the wood preservative ammoniacal copper zinc arsenate and zinc borate. In the second 

approach, self-assembling hyperbranched nano-polymers 

were loaded with an organic biocide. The complex surface 

of the nano-polymer encapsulated the biocide until a change 

in the physical environment (i.e., elevated heat or moisture) 

triggered its release. Nano-polymer encapsulation could 

provide long-term protection of composites as a surface 

treatment. In the third approach, nano-tubules made from an 

inert material served as a carrier for organic biocides. Loaded nano-tubules released the biocide in a slow, controlled 

fashion and provided superior protection of heat-labile organic biocides during the fabrication process compared to 

treatment with the biocide alone. Loaded nano-tubules may 

be used for surface application, pressure impregnation, or as 

an additive to engineered products.

Introduction

Nano-materials often exhibit novel physical and physiochemical properties that differ significantly from larger 

particles of the same material (Clausen 2007, Clausen and 

others 2011). Recent research looks at ways these properties 

can be exploited in the development of new preservative 

systems. Opportunities exist for using advances in nanotechnology to enhance the moisture tolerance of composites 

in traditional markets such as building materials. Embedding 

biocides in nano-polymer matrices or controlling delivery 

of biocides with nano-carriers is being evaluated to improve 

the durability of engineered composite products. The status 

of research on nano-metals, nano-polymer matrices, and 

nano-carriers is presented and discussed.

Results and Discussion

Nano-Metals

Either used alone or in combination with existing biocides, 

nano-metals may play an important role in the next generation of wood protection products. Nano-metals are created 

by altering particulate size either in the liquid phase (e.g., 

metal oxide sols, colloidal metals), gas phase (e.g., flame 

synthesis, plasma-based vapor phase synthesis), or solid 

phase (e.g., high energy ball milling). Nano-metal preparations of silver, zinc, copper, and other metals have high dispersion stability and low viscosity, allowing for more uniform particulate distribution over a surface (Clausen 2010, 

Kartal and others 2009).

Dispersion stability coupled with the controlled uniformity 

of pyrolyzed particles may greatly improve durability of 

solid and composite wood products in a number of applications: (1) preservative penetration in commercial lumber 

species, (2) treatability of refractory wood species that are 

of low commercial value, (3) organic treatments for engineered composites, (4) stability of finishes and coatings for 

aboveground applications, (5) nonleachable or hydrophobic 

treatments for both solid and composite materials, (6) photostability of treated wood, and (7) leach resistance of aqueous 

treatments.

In the presence of moisture, metals oxidize, which results 

in the release of metal ions. The ionic form of the metal is 

often the form that is responsible for microbial inhibition 

(Clausen 2010, Dorau and others 2004). Smaller particles 

having a higher surface area result in a greater area available 

for oxidation. Particles with diameter less than 100 nm are 

required in order to have the necessary surface area to allow 

a continuous release of metal ions. The size of the metal 

particle has also been shown to affect microbial inhibition; 

the smaller the particle, the greater the antimicrobial activity 

(Nair and others 2009, Reddy and others 2007). Properties 

of nano-zinc oxide (nano-ZnO) particles were evaluated for 

their ability to alter physical and biological deterioration of 

southern pine.

When southern pine sapwood was vacuum impregnated 

with 30-nm particles of zinc oxide, virtually no leaching 

occurred in a laboratory leach test, even at the highest retention of 13 kg/m3 (Clausen and others 2010a). Unleached 
Nanocelluloses: Potential Materials for Advanced Forest Products Proceedings of Nanotechnology in Wood Composites Symposium

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samples were protected from UV damage after 12 months 

of outdoor exposure; photostability was visibly obvious on 

both exposed and unexposed surfaces compared with untreated controls (Fig. 1) (Clausen and others 2010b). Graying was markedly diminished, although checking occurred 

in all specimens. Nano-ZnO treatment at a concentration 

of 2.5% or greater also provided substantial resistance to 

water absorption following 12 months of outdoor exposure 

compared with untreated and unweathered southern pine. In 

laboratory tests against termites and decay fungi, zinc oxide 

(30 nm) caused moderate termite mortality in a no-choice 

bioassay but gave mixed results for inhibition of decay fungi 

(Kartal and others 2009, Clausen and others 2010b). A subsequent study on the effect of particle size compared 30-nm 

and 70-nm particles. Specimens were evaluated for leach 

resistance and termite mortality in laboratory tests (Clausen 

and others 2011). Results showed that there was no difference in leach resistance (<4%) or termite mortality 

(Fig. 2). Eastern subterranean termites consumed less 

than 10% of the leached nano-ZnO-treated wood, with 

93% to 100% mortality in southern pine treated with both 

30-nm and 70-nm ZnO particles.

Because engineered composites have a lower moisture tolerance than does solid wood, the unique properties of nanoZnO (i.e., leach resistance, resistance to water absorption, 

photostability, and termite resistance) are characteristics that 

could greatly improve the durability of engineered 

composites.

Nano-Polymer Matrices

Nano-polymer matrices offer a sophisticated method for 

biocide encapsulation and controlled delivery. Self-assembling nano-polymers, called hyperbranched fluoropolymer−

poly(ethylene glycol) (HBFP−PEG) cross-linked networks, 

were first created by melding two normally incompatible 

polymers and crosslinking the mixture (Fig. 3) (Bartels and 

others 2007). The complex subsurface of the resulting hyperbranched nano-polymer has unusual tensile strength and 

provides nanoscale channels for the uptake and release of 

“guest” molecules such as biocides. The size of the channels, which have been likened to the holes in a sponge, 

can be customized to accommodate the guest molecule of 

choice. The nano-polymer is able to encapsulate and hold a 

chemical until a change in the physical environment (e.g., 

humidity, temperature, or pH) triggers its release. This technology has been successfully demonstrated for applications 

ranging from anti-fouling agents (Gudipati and others 2004) 

to fragrances.

The cross-linked HBFP–PEG45 nano-polymer was loaded 

with an experimental multi-component biocide formulation 

containing carvone as an indicator molecule.

Figure 1. Weathering of nano-ZnO treated southern pine after 12 months of outdoor exposure. Unexposed surface (specimens on right) refers to the underside of the individual 

“exposed surface” specimens shown on the left.
General Technical Report FPL–GTR–218

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The loaded polymer matrix was evaluated for controlled 

release of the biocide over a range of temperatures from 

25 to 75 °C. Gravimetric changes in the loaded nanopolymer following an 8-h exposure to 25, 40, or 75 °C are 

shown in Table 1. Following isothermal release, the nanopolymer matrices were extracted in methylene chloride and 

quantitatively analyzed with GC-MS for residual carvone 

(Table 1).

Results showed that as temperature increased, more of the 

volatile indicator molecule was released from the matrix 

with isothermal weight loss reaching 100% after exposure 

to 75 °C. Quantitative results from the GC-MS analysis suggested that isothermal weight loss alone could not reliably 

predict release of the biocide above 25 °C. Biocides 

encapsulated in customized nano-polymer networks could 

provide prolonged protection as surface treatments for engineered composites.

Nano-Carriers

Several nano-carrier systems are recognized that may find 

an application in the field of wood protection, particularly 

for increased durability of engineered composites (e.g., 

oriented strandboard (OSB)). For example, a patented 

nano-carrier system uses 100-nm plastic beads embedded 

with biocide (Laks and Heiden 2004). Based on the type of 

polymer comprising the bead, pore size in the bead, biocide 

viscosity and solubility, biocide-embedded nanoparticles 

can be designed for slow, controlled release of the biocide. 

Other cylindrical, tubule-shaped materials (i.e., nanotubules) made from ceramics, clay, metal, or lipids that have 

been used as carriers in various medical and industrial applications are now being evaluated for use in engineered composites. Some properties of nano-carriers that would benefit 

the field of wood protection include

•	 delivery and placement of biocide,

•	 slow release of a biocide, and

•	 release of the biocide upon exposure to certain environmental conditions, such as high humidity.

Protection of heat-labile organic biocides during panel 

fabrication has greatly limited the applications of newly 

developed biocides and the number of treatment options for 

engineered composites.

When developing controlled-release nano-tubules for 

biocide delivery in composites, a considerable number of 

variables must be optimized prior to proof of concept. How 

to precisely control release of a biocide, whether the nanotubules are compatible with resin used to fabricate the composite, whether the resin itself may be a barrier to release 

of the biocide, and calculating and regulating actual release 

rate were examined in the preliminary stage of this project. 

Methodology was development for analyzing the thermal 

stability of nano-tubules loaded with a commercial biocide 

over a range of temperatures from 170 to 190 °C and time. 

Release rate of the biocide was based on leach resistance, 

and residual efficacy was evaluated following leaching using two microbial assays that measured the zone of fungal 

Figure 2. Eastern subterranean termite resistance to 

southern pine treated with nano-zinc oxide and soluble 

zinc sulphate indicated by mass loss, i.e., wood consumption. The number above each column represents 

the average percent termite mortality for that treatment 

group.

Table 1—Carvone analysis of loaded 

HBFP–PEG45 following isothermal 

release at varying temperatures

Temperature

(°C)

Carvone

loaded

(μg)

Isothermal

weight loss

(%)

Carvone

extracted

(μg)

Control — 0 0 

25 297 35.5 101 

40 348 95.4 48.5 

75 303 100 20.9 

Figure 3. Self-assembling nano-polymer networks act like 

the holes in a sponge to hold biocides (depicted in purple) until changes in the environment trigger their release 

(Brown and others 2005, Bartels and others 2007).
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inhibition in a Petri plate and fungal resistance in a simulated environmental chamber.

Biocide-loaded nano-tubules were incorporated into OSB, 

medium density fiberboard (MDF), and paper. Samples 

of nano-treated OSB were tested for modulus of rupture 

(MOR), modulus of elasticity (MOE), density, moisture 

swelling, and antifungal resistance in laboratory tests. Preliminary studies on engineered composites demonstrated 

thermal protection, slow release, and enhanced mold inhibition for the biocide loaded into nano-tubules compared 

to controls that incorporated either biocide alone or nanotubules alone. Figure 4 shows the results of paper treated 

with biocide-loaded nano-tubules and exposed to three 

mold fungi, Aspergillus niger, Penicillium chrysogenum, 

and Trichoderma viride. Controls are untreated paper and 

paper treated with the biocide. Not only are the mold fungi 

completely inhibited on the surface of samples treated with 

loaded nano-tubules, but the clearing zone surrounding the 

samples demonstrates the release of biocide from the nanotubules. Improved protection of paper treated with biocideloaded nano-tubules is obvious compared to paper treated 

with the biocide alone or to untreated paper controls.

Similar results were seen for OSB and MDF that were 

treated with biocide-loaded nano-tubules compared with 

untreated controls (Fig. 5). Treated and untreated specimens 

were placed on Petri dishes of malt extract agar, sprayed 

with a suspension of Aspergillus niger mold spores, and 

incubated for 4 weeks according to the ASTM D 4445–10 

standard laboratory test for controlling sapstain and mold 

fungi on unseasoned lumber (ASTM 2010). Mold growth 

occurred on the agar surface and on the surface of untreated 

test specimens, but mold growth was completely inhibited 

on specimens treated with biocide-loaded nano-tubules. Release of biocide from the nano-tubules is also evident from 

the clearing zone surrounding test specimens on agar plates.

Conclusions

Advances in the development of nanotechnology for improved durability of engineered composites are in progress. 

Unique properties such as photostability, leach resistance, 

and biocide behavior against biodeteriorating organisms 

have been identified for select nano-metals. Such properties 

are desirable for development of new preservative systems. 

Encapsulating biocides in designer nano-polymer matrices 

Figure 4. Paper samples treated with biocide-loaded nano-tubules, biocide alone, and 

untreated controls challenged with three mold fungi.
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are promising delivery systems that release the biocide 

when triggered by a specific change in the environment. 

Nano-polymer matrices are ideal for surface treatments of 

solid and composite wood products. Nano-carriers, such as 

nano-tubules, can be loaded with organic biocides for targeted delivery that is protected from heat during the fabrication 

process. Loaded nano-tubules undergo controlled release of 

biocide to provide prolonged protection of composites from 

fungal growth.

Literature Cited

ASTM. 2010. Standard test method for fungicides for controlling sapstain and mold on unseasoned lumber (laboratory 

method). ASTM Standard D 4445–10. Volume 11.01. West 

Conshohocken, PA: American Society for Testing and 

Materials: 446–450.

Bartels, J.W.; Cheng, C.; Powell, K.T.; Xu, J.; Wooley, K.L. 

2007. Hyperbranched fluoropolymers and their hybridization into complex amphiphilic crosslinked copolymer networks. Macromolecular Chemistry and Physics. 208(15): 

1676–1687.

Brown, G.O.; Bergquist, C.; Ferm, P.; Wooley, K.L. 2005. 

Unusual, promoted release of guests from amphiphilic 

cross-linked polymer networks. Journal of American Chemical Society. 127(32): 11238–11239.

Clausen, C.A. 2007. Nanotechnology: implications for the 

wood preservation industry. IRG/WP/07-30415. Stockholm, 

Sweden: International Research Group on Wood Protection. 

13 p.

Clausen, C.A. 2010. Characterizing wood protection properties of nano-metals. Research in Progress RIP-4723-014. 

Madison, WI: USDA Forest Service, Forest Products 

Laboratory. 

Clausen, C.A.; Green, F., III; Kartal, S.N. 2010a. Weatherability and leach resistance of wood impregnated with nanozinc oxide. Nanoscale Research Letters. 5: 1464–1467.

Clausen, C.A.; Yang, V.W.; Arango, R.A.; Green, F., III. 

2010b. Feasibility of nanozinc oxide as a wood preservative. 

In: Proceedings of the American Wood Protection Association. Birmingham, AL: American Wood Protection Association. 105: 255–260. 

Clausen, C.A.; Kartal, S.N.; Arango, R.A.; Green, F., III. 

2011 Role that particle size and leach resistance plays in termite mortality on nano-zinc oxide-treated wood. Nanoscale 

Research Letters. 6:465.

Dorau, B.; Arango, R.; Green, F., III. 2004. An investigation into the potential of ionic silver as a wood preservative. 

Proceedings, Woodframe Housing Durability and Disaster 

Issues Conference. Madison, WI: Forest Products Society: 

133–145.

Gudipati, C.S.; Greenlief, C.M.; Johnson, J.A.; Prayongpan, P.; Wooley, K.L. 2004. Hyperbranched fluoropolymer 

(HBFP) and linear poly(ethylene glycol) (PEG) based amphiphilic crosslinked networks as efficient anti-fouling coatings: an insight into the surface compositions, topographies 

and morphologies. Journal of Polymer Science, Part A: 

Polymer Chemistry. 42(24): 6193–6208.

Kartal, S.N.; Green, F., III; Clausen, C.A. 2009. Do the 

unique properties of nano-metals affect leachability or efficacy against fungi and termites? International Biodeterioration & Biodegradation. 63: 490–495.

Laks, P.; Heiden, P.A. 2004 (June 22). Compositions and 

methods for wood preservation. U.S. Patent 6,753,035.

Nair, S.; Sasidharan, A.; Divya Rani, V.V.; Menon, D.; 

Manzoor, K.; Raina, S. 2009. Role and size scale of ZnO 

nanoparticles and microparticles on toxicity toward bacteria 

and osteoblast cancer cells. Journal of Material Science: 

Materials in Medicine. 20 (Suppl. 1): 235–241.

Reddy, K.M.; Feris, K.; Bell, J.; Windgett, D.G.; Hanley, C.; 

Punnoose, A. 2007. Selective toxicity of zinc oxide nanoparticles to prokaryotic and eukaryotic systems. Applied Physics Letters. 9: 2139021–2139023.

(a)

(b)

Figure 5. Oriented strandboard (OSB) (top) and medium 

density fiberboard (MDF) (bottom) either untreated or treated with biocide-loaded nano-tubules were challenged with 

the mold fungus, Aspergillus niger.
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Synthesis of Hybrid Porous 

Cellulose/Metal Nanocomposites

Tao Wang, Research Assistant Professor

Center for Nano Science and Technology and Department of Electrical Engineering

University of Notre Dame, Notre Dame, Indiana

Zhiyong Cai, Supervisory Research Materials Engineer

Forest Products Laboratory, Madison, Wisconsin

Abhijit Biswas, Research Associate Professor

Center for Nano Science and Technology and Department of Electrical Engineering

University of Notre Dame, Notre Dame, Indiana

Lei Liu, Research Assistant Professor

Advanced Diagnostics and Therapeutics and Department of Electrical Engineering

University of Notre Dame, Notre Dame, Indiana

Abstract

Highly porous metals with millimeter-sized cellular structures have found a broad range of applications from energy 

absorption to machine construction due to their interesting 

combinations of physical/mechanical properties, structural 

morphology, and low densities. However, the mechanical 

properties of these metals scale adversely with the relative 

density, and therefore the porous materials retain only a 

fraction of the bulk values. Recent studies on nanoporous 

metallic materials have revealed a dramatic improvement in 

mechanical properties, such as yield strength, as the dimensions of the pores approach submicron to nanometer range. 

These encouraging results point to a promising approach to 

bridge the gap between high strength and high porosity. The 

reason for this enhancement is attributed to the significant 

size effect of the nanoscale ligament in addition to the relative density. Nevertheless, the implementation of such a 

material is severely hampered due to critical challenges in 

search of viable manufacturing routes and materials. By using celluloses nanofibers, we aim to design and synthesize 

hybrid porous cellulose/metal nanocomposite materials with 

proper metallization processes. In this presentation, we will 

report our initial results in the construction of three-dimensional (3D) microfibrillated cellulose nanocomposites and 

their potential applications in terahertz devices. Our future 

work will focus on investigation of conformal synthesis of 

3D porous nanocomposites.

Acknowledgments

The authors thank the Center for Nano Science and Technology at the University of Notre Dame for financial support 

and Dr. Alexandru S. Biris for providing scanning electron 

microscopy (SEM) and atomic force microscopy (AFM) 

characterization.

Introduction

The pursuit for materials that have versatile functionalities 

but are yet strong and lightweight has long been a dream 

of material scientists and engineers. Bulk materials, which 

have been used since the advent of human activities, almost reach their ends in this context unless a dramatically 

transformative category of materials is discovered. Instead, 

a logical alternative is to intelligently engineer porous or 

cellular materials into a new class whose properties can be 

well tailored to meet various high-performance needs at 

very low relative densities. During the past several decades, 

such a class of material has received much attention due to 

the combination of functionalities and mechanical properties that it displays, and it has been used in a variety of applications ranging from structural components to functional 

devices that show interesting combinations of physical/mechanical properties, structural morphology, and lightweightness (Banhart 2001). However, extensive experimental work 

has concluded that the retained mechanical properties scale 

adversely by following Gibson and Ashby’s theory, which 

suggests that mechanical properties (e.g., Young’s modulus 

or tensile strength) of the porous metals retain only a fraction of the bulk values (Gibson and Ashby 1999).

In the past few years, nanostructured three-dimensional 

(3D) metallic foams with much smaller pore dimensions 

have become a hot research topic. Recent developments include materials made of noble metals such as gold (Au), silver (Ag), and platinum (Pt) (Biener and others 2005, Biener 

and others 2006, Hodge and others 2007). Inspired by the 

localized electrochemical corrosion phenomenon occurring 

with an alloy, the controlled process can be favorably exploited to produce nanoporous metals. This process is called 

dealloying, which is adopted, for example, to generate Au 

nanofoams from an initial binary Au–Ag alloy. Surprisingly, 

mechanical property tests reveal values of the yield stresses 
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that are significantly higher than that of bulk Au. Furthermore, as the ligament size becomes smaller (i.e., 10 nm), 

the yield stress approaches the theoretical limit (Biener and 

others 2005, Biener and others 2006). These findings seem 

contradictory to the previously described, widely accepted 

Gibson and Ashby predication, making it necessary to reevaluate the factors (besides relative density) that determine 

the strength value at nanometer length scale (Hodge and 

others 2007). Overall, this research area is in its early infancy. There remain several bottlenecks in understanding such 

a class of material, and the implementation of such a material is also severely hampered due to critical challenges in the 

course of further development. One key challenge lies in the 

synthesis processes, among which dealloying (preferentially 

etching one element from a binary alloy) is dominant. Another challenge is the availability of viable materials, which 

are generally limited to noble metals such as Au, Ag, and Pt. 

None of these is economically preferred for structural applications and other functional situations. Thus, exploration of 

both new materials and effective synthesis routes are critical 

to bringing these materials to real-world applications.

Interest in cellulose-based porous nanomaterials has recently received a great boost, not only because the cellulose 

microfibrils or nanofibers themselves possess excellent tensile properties and modulus, but also because their substantial tunabilities offer enormous potential for creating new 

hybrid functional nanomaterials. For example, nanofiber 

networks were used either as constituents or templates to 

synthesize new functional materials for magnetic aerogels 

and stiff magnetic nanopaper (Olsson and others 2010), cell 

regeneration (Barreiro and others 2010), nanoparticle synthesis (Ifuku and others 2009), electrically conducting flexible aerogels (Paakko and others 2008), gas sensor (Huang 

and others 2005), and catalysis (Shigapov and others 2001). 

We envision that a combination of atomic-level material 

deposition with properly designed 3D cellulose nanofiber 

networks will lead to a new fabrication route toward novel 

nanocomposites at a true nanoscale and will also enhance 

the diversity of component metals and alloys. As an initial 

step, we report our preliminary studies on synthesis of nanocomposites consisting of cellulose nanofibers and magnetic 

nanoparticles as well as their potential applications in terahertz devices. Our future work will focus on investigation of 

conformal synthesis of 3D porous nanocomposites.

Experimental

The cellulosic nanofibers were generated through a microfluidizer processor, which is essentially a specialized homogenizer and forces liquid streams through microchannels 

at extremely high shear rates, resulting in a size reduction 

of particles in the liquid stream. In this study, eucalyptus 

(Eucalyptus grandis, E. amplifolia) fibers were enzymatically treated to convert some cellulose into fermentable 

sugars for ethanol production. The remaining coarse fibers 

were then passed through the microfluidizer until they were 

reduced to primarily nanofibers. The particles used are 

silica-encapsulated magnetic oxide Fe3O4 nanoparticles with 

controlled dimensions, which were synthesized following 

the microemlusion procedure described in Ifuku and others (2009). The nanocomposite samples were prepared by 

a simple drop-cast method by mixing the nanofibers and 

particles and subsequently sonicating and coating to a microscope slide. This is followed by baking at 50 °C on a hot 

plate overnight. As a comparison, the fibers alone were 

also coated the same way in the absence of magnetite 

nanoparticles.

Scanning electron microscopy (SEM) was carried out by 

a JEOL JSM-7000F (JEOL Ltd., Tokyo, Japan) equipped 

with a field emission gun. Prior to SEM observations, the 

specimens were coated with thin layers (less than 1 nm) of 

carbon. Atomic force microscopy (AFM) was performed 

with Digital Instruments (Veeco) Dimension-3100 (Digital Instruments Veeco Metrology Group, Plainview, New 

York) under tapping mode. Both the height images and the 

amplitude images were collected simultaneously. Surface 

morphology studies were performed by using a SPI Dimension 3100 atomic force microscope that uses standard 

and advanced scanning probe microscopy (SPM) imaging 

modes to measure surface characteristics. The terahertz 

transmission spectroscopy of the cellulose and its composite 

films was performed on a system consisting of a frequency 

extension module covering 0.57–0.63 THz and a Schottky 

diode-based THz detector.

Results and Discussions

Figure 1 shows both SEM images of a sample without magnetite nanoparticles and a nanocomposite sample. It can 

be clearly seen that a porous cellulosic nanofiber network 

is present in the nanofiber-alone coating (Fig. 1(a)). When 

magnetite nanoparticles are added, two distinct regions are 

observed: one is an aggregated area of nanoparticles 

(Fig. 1(b)) and another is a networked area of nanofibers 

(inset of Fig. 1(b)) similar to that in Fig. 1(a). This indicates 

a phenomenon commonly encountered in particle nanocomposites. The morphological features of the two samples from 

AFM measurements are shown in Figure 2. It is readily evidenced that the interwoven networks are formed with long 

cellulose fibers with diameters between 16 and 25 nm 

(Fig. 2(a)). The phase separation of the particle-enriched 

region and nanofiber region is also seen in the AFM image 

(Fig. 2(b)) of the nanocomposite. From the amplitude image, the diameter of the core-shell nanoparticle shown by a 

pair of red arrows is determined to be 21 nm, but the actual 

size is slightly smaller due to apex of the AFM tip.

Both the SEM and AFM analyses seem to suggest that the 

simple preparation procedure yielded a nonuniform but less 

porous nanofiber matrix. However, the heterogeneous dispersion of the nanoparticles is detrimental to the integrity of 

the resultant composites and therefore limits the mechanical loading, adhesion, and local magnetic performances. To 

overcome such a problem, several chemical modification 
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mechanisms using coupling agents, such as organosilanes 

(Paakko and others 2008) and aminopropyl-triethoxylsilane 

(APTES) (Huang and others 2005), have been explored to 

modify the interfacial behaviors of the dispersoids and matrices. Because both surfaces of the cellulosic fiber and the 

silica shell present hydroxyl groups in our system, we will 

address this issue by investigating and establishing an optimal silanization protocol to achieve not only strong covalent 

interfacial bonding but also improved particle dispersion.

The THz transmission spectroscopy system (0.57–0.63 

THz) was applied to characterize cellulose samples shown 

in Figure 3. The nanocomposite samples under examination 

are prepared by dropping and drying liquids on 3-mil Mylar 

thin films, and the measured data are normalized to the voltage response of the blank Mylar thin film measured using 

this system for THz transmission. Shown in Figure 3(b) is 

the THz spectrum of one cellulose sample in the frequency 

range of 0.57–0.63 THz. Stronger absorption is observed 

Figure 1. SEM images showing (a) porous cellulosic nanofiber network morphology of the sample without magnetite 

nanoparticles and (b) magnetite nanoparticles in the nanocomposite sample.

Figure 2. AFM images showing morphology of (a) interwoven network of 16–25-nm-diameter cellulosic nanofibers in the 

sample without nanoparticles and (b) magnetite nanoparticles in the nanocomposite sample.
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at 0.62–0.63 THz, 0.57 THz, and 0.58 THz. The absorption 

peaks show narrow frequency bandwidths less than 

0.01 THz. These spectral features are difficult to be discovered using conventional time-domain THz techniques and 

could be used for characterization and identification of cellulose samples. The THz spectrum of cellulose samples with 

nanoparticles was also measured and compared to cellulose 

samples under the same preparation conditions, as shown 

in Figure 3(c). The sample with nanoparticles shows higher 

transmission than the sample without. In addition, the transmission of the magnetic nanoparticles sample is larger than 

the one over the entire frequency range of 0.57–0.63 THz, 

indicating a field enhancement. This property may find applications in THz-based chemical and biological sensing.

Summary

A nanocomposite was prepared by co-deposition of cellulosic nanofibers and core-shell magnetic Fe3O4-silica 

nanoparticles. While a fine interwoven network of the nanofibers is formed, there exist regions where the particles are 

aggregated. Our future work will focus on developing an 

optimized silanization protocol to create covalent interfacial 

bonding and homogenous particle dispersion and evaluating 

the resultant nanocomposites in magnetic, mechanical, and 

thermal performances. The THz transmission spectroscopy 

examination of the nanocomposite films from 0.57 to 

0.63 THz suggests strong absorption peaks and enhancement of intensity due to incorporation of magnetic nanoparticles. This may indicate potential usefulness of this cellulose nanocomposite in chemical and biological sensing. 

Our future work will focus on investigation of conformal 

synthesis of 3D porous nanocomposites.

References 

Banhart, J. 2001. Manufacture, characterisation and application of cellular metals and metal foams. Progress in Materials Science. 46(6): 559–U3.

Barreiro, A.M.; Recouvreux, D.O.S.; Hotza, D.; Porto, 

L.M.; Rambo, C.R. 2010. Sand dollar skeleton as templates 

for bacterial cellulose coating and apatite precipitation. 

Journal of Materials Science. 45(19): 5252–5256.

Biener, J.; Hodge, A.M.; Hamza, A.V.; Hsiung, L.M.; Satcher, J.H. 2005. Nanoporous Au: a high yield strength material. Journal of Applied Physics. 97(2): January 15.

Biener, J.; Hodge, A.M.; Hayes, J.R.; Volkert, C.A.; ZepedaRuiz, L.A.; Hamza, A.V.; Abraham, F.F. 2006. Size effects 

on the mechanical behavior of nanoporous Au. Nano Letters. 6(10): 2379–2382.

Gibson, L.J.; Ashby, M.F. 1999. Cellular solids: structure 

and properties. 2nd ed. Cambridge, UK: Cambridge University Press.

Hodge, A.M.; Biener, J.; Hayes, J.R.; Bythrow, P.M.; Volkert, C.A.; Hamza, A.V. 2007. Scaling equation for yield 

strength of nanoporous open-cell foams. Acta Materialia. 

55(4): 1343–1349.

Huang, J.; Matsunaga, N.; Shimanoe, K.; Yamazoe, N.; 

Kunitake, T. 2005. Nanotubular SnO2 templated by cellulose 

fibers: synthesis and gas sensing. Chemistry of Materials. 

17(13): 3513–3518.

Ifuku, S.; Tsuji, M.; Morimoto, M.; Saimoto, H.; Yano, 

H. 2009. Synthesis of silver nanoparticles templated by 

TEMPO-mediated oxidized bacterial cellulose nanofibers. 

Biomacromolecules. 10(9): 2714–2717.

Olsson, R.T.; Samir, M.A.S.A.; Salazar-Alvarez, G.; Strom, 

V.; Belova, L.; Berglund, L.A.; Ikkala, O.; Nogues, J.; 

Gedde, U.W. 2010. Making flexible magnetic aerogels and 

stiff magnetic nanopaper using cellulose nanofibrils as templates. Nature Nanotechnology. 5(8): 584–588.

Paakko, M.; Vapaavuori, J.; Silvennoinen, R.; Kosonen, H.; 

Ankerfors, M.; Lindstrom, T.; Berglund, L.A.; Ikkala, O. 

2008. Long and entangled native cellulose I nanofibers 

Figure 3. THz transmission spectroscopy of the resultant nanocomposites at 0.57–0.63 THz: (a) configuration of the solid 

state frequency domain THz system based on quasi-optical, ultra-broadband, Schottky diode detector—system diagram; (b) 

THz transmission spectrum of cellulose sample, narrow absorption features have been observed; and, (c) THz transmission 

comparison of cellulose sample and cellulose with magnetic nanoparticles. Enhanced THz transmission is observed for cellulose with nanoparticles sample.

(a) (b) (c)
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allow flexible aerogels and hierarchically porous templates 

for functionalities. Soft Matter. 4(12): 2492–2499.

Shigapov, A.N.; Graham, G.W.; McCabe, R.W.; Plummer, 

H.K. 2001. The preparation of high-surface area, thermallystable, metal-oxide catalysts and supports by a cellulose 

templating approach. Applied Catalysis A: General. 210

(1–2): 287–300.
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Production and Characterization of 

Nano-Structured Carbons from Pine Chips

Qiangu Yan, Postdoctoral Research Associate

Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, Mississippi

Hossein Toghiani, Associate Professor

Dave C. Swalm School of Chemical Engineering, Mississippi State University, Mississippi State, Mississippi

Fei Yu, Assistant Professor

Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, Mississippi

Zhiyong Cai, Supervisory Research Materials Engineer

Forest Products Laboratory, Madison, Wisconsin

Jilei Zhang, Professor

Forest Products Laboratory, Mississippi State University, Mississippi State, Mississippi

Abstract

This study investigated the influences of temperature, 

heating rate, purge gas type, and flow rate on the production 

of nano-structured carbons from southern pine wood chips 

by pyrolysis. Pyrolysis temperatures were between 450 and 

1,000 °C with heating rates of 1.0, 10, and 50 °C/min. The 

purge gases were nitrogen and hydrogen with flow from 

100 to 1,000 mL/min. The surface morphology of pine 

chars was characterized using scanning electron microscopy 

(SEM) and transmission electron microscopy (TEM). SEM 

analyses indicated that the surface of pine chips had already 

started to decompose at 450 °C if nitrogen was used with a 

flow rate of 500 mL/min, but no nanoparticles were formed. 

The formation of sphere nanoparticles with a diameter from 

50 to 100 nm was observed at 650 °C. More nanoparticles 

were produced as pyrolysis temperature increased to 

1,000 °C, and the particle diameter in the surface was 

around 20 nm. Pine chars produced with nitrogen gas 

showed more nanoparticles on the char surface than those 

with hydrogen. The surface of the pine chars had fewer 

particles with increased purge gas flow. The particle quantity 

was increased at higher heating rates. Nano carbon spheres, 

nano carbon chips, carbon nanofibers, carbon nanotubes, 

some porous carbon particles, and micro-pores and channels 

were observed from the chars produced at 1,000 °C.

Introduction

Driven by the shortage of crude oil and environmental 

concern, research efforts have been made to develop new 

processes for converting renewable biomass to energy. 

The biofuels can be achieved from biomass through 

thermal degradation and biological processes (Kumar 

and others 2009). Three phases are produced during the 

thermal transformation of biomass under inert atmosphere: 

gases, liquids (tars, condensable vapors), and solids (char) 

(Wampler 2006). The operating conditions such as pyrolysis 

temperature and heating rate are key factors affecting three 

phase product fractions (Baumlin and others 2006).

Pyrolysis processes may be conventional or fast pyrolysis, 

depending on the operating conditions. Conventional 

slow pyrolysis has been applied for thousands of years, 

such as for charcoal production (Demirbas 2009). In 

slow pyrolysis, biomass is heated to 500 °C with vapor 

residence times ranging from 5 to 30 min. For fast pyrolysis, 

biomass is rapidly heated in the absence of oxygen. 

Biomass decomposes to generate vapors, aerosols, and 

solid char. Fast pyrolysis processes produce 60−75 wt% 

of liquid bio-oil, 15−25 wt% of solid char, and 10−20 

wt% of non-condensable gases (Mohan and others 2006). 

Carbon content of wood varies from about 47% to 53% 

due to varying lignin and extractives content (Ragland and 

Aerts 1991), and 30% to 50% of the carbon in the wood is 

converted to solid char during the pyrolysis process.

In bio-oil research, most attention has been concentrated 

on liquid product upgrading and syngas formation and 

utilization, but the char, an attractive byproduct, has 

received less attention. Thus far, there is no other valueadded use available for this solid residue besides direct 

combustion for heat production. The synthesis of valueadded, carbonaceous nanomaterials from the bio-chars as 

well as carbon rich and renewable biomass such as wood 

or agriculture plants can be an attractive option to use 

carbon resources in a sustainable and “CO2-neutral” way 

compared to using fossil resources (Hu and others 2010). 

Limited studies were found on systematically analyzing the 

effects of thermal treatment conditions such as temperature, 

heating rate, purge gas type, and gas flow rate on the surface 

morphology change of bio-chars produced from biomass 

and the formation of nanomaterials from these bio-chars. 

The objective of this study was to investigate the effects of 

these thermal treatment variables on the formation process 

of nanomaterials and the surface morphology change of biochars pyrolyzed from southern pine clear wood biomass.
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The different morphologies and structures of bio-chars can 

be produced with various operating conditions. Ohata and 

others (www.geocities.jp/yasizato/Yoshizawa17.pdf) heated 

the sapwood of Hinoki from 400 to 900 °C with a heating 

rate of 20 °C/min and held it for 120 min at 900 °C. Three 

nitrogen gas rates of 100, 200, and 1,000 cm3/min, and 

three oxygen concentrations of 0.7, 0.3, and 0.06 vol% were 

investigated. Tube-like carbon fibers were observed on cell 

walls of the charcoals when the sample was heated at 

900 °C in 0.06 vol% of oxygen concentration. It was 

suggested that cobalt serve as the catalyst and carbon 

monoxide as the carbon source. Saito and Arima (2002) 

observed cone-shaped carbon materials inside the cell lumen 

of pre-heat-treated (300–400 °C) sapwood of Japanese cedar 

heat-treated at 2,500 °C with argon gas for 1 h. The heating 

rate, pressure, and cooling rate were 10 °C/min, 10–20 Pa, 

and 30 °C/min, respectively. There were no carbon particles 

observed for samples heated less than 2,500 °C.

Carbonized microfibrils and onion-shaped graphitic 

nanoparticles were observed from 20-year-old Japanese 

cedar carbonized up to 700 °C for 30 min with a heating 

rate of 4 °C/min and in an argon gas atmosphere (Hata and 

others 2000). Onion-like nanoparticles and nano-size pore 

structures were observed on the surface of Japanese 

cedar carbonized at 700 °C for 1 h with a heating rate of 

10 °C/min (Ishimaru and others 2001). Kurosaki and others 

(2003) flash-heated the sapwood of Japanese cedar at 

800 °C for 1 h and produced well-aligned curved, 

fragmented, and not-closed graphitic plane carbon 

structures. But this was not for the slow heating process 

(in a helium atmosphere at 4 °C /min, gas flow rate 

50 mL/min, and pressure 300 kPa) where the cell structure 

was still maintained. Most particles observed were about 

25 nm in diameter, but larger size particles up to 100 nm 

were also observed, which were elliptical rather than 

spherical.

It was found that under a high heating rate the biomass 

char particles underwent plastic deformation (i.e., melted) 

and developed a structure differing from that of the virgin 

biomass (Cetin and others 2004). Pressure was also found 

to influence the physical and chemical structures of char 

particles. Guerrero and others (2005) characterized the 

chars from pyrolysis of eucalyptus at different temperatures 

and heating rates, and the influence of their morphology 

changes on overall reactivity was investigated. Large 

internal cavities and a more open structure were observed 

over the high heating rate char particles. The globular 

particles with the size of approximately 20 nm were 

observed in the cell wall sections of sycamore maple heated 

to 1,100 °C under nitrogen (Herzog and others 2006). After 

subsequent activation by CO2 at 900 °C for a dwell time of 

0 min, molecular-sized pores with diameters ranging from 

3 to 20 nm and particles containing crystallized minerals 

were observed. There was a fundamental difference in the 

nanoforms before and after activation. Stacked carbon 

structures were found in cellulose-rich regions before 

activation. After activation, additional onion-like, multiwalled clusters were observed.

Hu and others (2008) prepared chars from rice husk 

at different pyrolysis conditions. Scanning electron 

microscopy (SEM) images showed that the surface of 

pores in char particles became increasingly rough in the 

middle of pyrolysis. Biagini and others (2009) produced 

the bio-chars from cacao shells and olive cake using a 

high heating rate and characterized the char morphology 

after the first step of devolatilization. Different chars were 

produced in a drop tube reactor by rapid pyrolysis with 

various nominal temperatures and residence times. It was 

found that char particle size enlarged at 500–600 °C due 

to swelling phenomena and bubble formation, and at a 

higher temperature (800 °C) the final size slightly decreased 

with respect to the parent material for crack formation and 

melting of material.

Fu and others (2009) characterized pyrolysis chars from 

maize stalks with the effects of pyrolysis temperature 

and heating rate on the char properties investigated. The 

pyrolysis was performed at atmospheric pressure and 

temperatures from 600 to 1,000 °C under low and high 

heating rates. As the temperature increased, maize stalk 

chars had a slightly less amorphous structure and fewer 

aliphatic side chains and became more aromatic and 

ordered. At a high heating rate, progressive increases in 

porosity development with increasing pyrolysis temperature 

occurred. The surface area of the chars reached a maximum 

of 81.6 m2/g at 900 °C and decreased slightly at a higher 

temperature. Above 900 °C, structural ordering, pore 

widening, and/or the coalescence of neighboring pores 

led to the decrease in the surface area values, resulting 

in thermal deactivation of the chars. The influence of the 

heating rate on the surface area was not significant.

Material and Methods

Materials and Heating Device

The southern pine wood chips (>1 mm in length) were dried 

on an onsite dryer with a maximum moisture content of 

10%. Pyrolysis of the pine chips was carried out in a fixedbed tubular quartz reactor with an outer diameter of 

25.4 mm and a length of 120 cm (Fig. 1). A K-type 

thermocouple was placed inside the tube and embedded in 

the wood chip sample to monitor the temperature. For each 

experimental run, 15 g of pine chips (Fig. 2) were packed in 

the middle of a 25.4-mm O.D. quartz tubular reactor.

Experimental Design

Temperature effect on the morphology of the pine chars 

was studied at five temperatures (450, 500, 550, 650, and 

1,000 °C) with a nitrogen flow under atmosphere pressure. 
General Technical Report FPL–GTR–218

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For each of five temperature runs, the gas flow rate, heating 

rate, and pyrolysis time were 500 mL/min, 10 °C/min, and 

30 min, respectively.

Heating rate effect on the morphology of the pine 

chars was studied using three heating rates (1, 10, and 

50 °C/min) under nitrogen atmosphere. For each of three 

runs, the gas flow rate, final temperature, and pyrolysis 

time were controlled at 500 mL/min, 1,000 °C, and 30 min, 

respectively.

Three nitrogen gas flow rates (100, 500, and 1,000 mL/min) 

were used to investigated the gas flow rate effect on the 

morphology of the pine chars. For each of three flow runs, 

the final temperature, heating rate, and pyrolysis time were 

controlled at 1,000 °C, 30 °C/min, and 30 min, respectively.

Two types of gases (hydrogen and nitrogen) were used 

to study the effect of gas type on the morphology of the 

pine chars. For each of the two types of gas runs, the final 

temperature, heating rate, gas flow rate, and pyrolysis time 

were controlled at 1,000 °C, 50 °C/min, 500 mL/min, and 

30 min, respectively.

Characterization

The morphologies of the raw wood chips and the pine char 

samples were examined by SEM on a JEOL JSM-6500F 

instrument (JEOL Ltd., Tokyo, Japan) operating at 

5.0 kV. The SEM samples were pre-coated with gold before 

being introduced into the vacuum chamber. The resulting 

char samples were soaked in ethanol and sonicated for 

20 min. The carbon particles washed from the char surface 

were collected and examined with a JEOL JEM-100CX 

II transmission electron microscope (TEM) (JEOL Ltd., 

Tokyo, Japan) operating at 80 kV.

Results and Discussion

Temperature Effect

The SEM images of the raw pine wood chips and the chars 

obtained under pyrolysis temperatures of 450, 500, 650, 

and 1,000 °C are shown in Figures 3 to 7, respectively. 

Figure 3 shows that the surface of the chip is smooth and 

clean. There is no dust or devolatilization coking residue 

on the wood surface. Figure 4 shows that the wood had 

already started to decompose at 450 °C. Smooth regions 

on the surface suggested that the wood had begun to 

melt; however, the decomposition was not significant. No 

particles were found on the surfaces of the char sample 

heated up to 450 °C.

The surface of the chars heated up to 500 °C was in the 

form of continuous melt and decomposition (Fig. 5). The 

most obvious feature observed on the char at 650 °C was 

the formation of sphere particles over its surface (Fig. 6) 

with diameters of 50 to 100 nm. The loss of surface material 

and the growth of crystalline structure suggested that the 

Figure 1. Thermal reaction system (a) and 25.4-mm O.D. quartz reactor (b).

Figure 2. Raw southern yellow pine chips (> 1 mm).
Nanocelluloses: Potential Materials for Advanced Forest Products Proceedings of Nanotechnology in Wood Composites Symposium

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part of decomposition products precipitated to form the 

crystalline deposits. When volatile matter is generated, the 

physical structure of a char changes significantly during the 

devolatilization. Pyrolysis temperature had a notable impact 

on the pore structure of biomass char (Hu and others 2008).

As pyrolysis temperature increased to 1,000 °C, the surface 

of pine chars was covered with more nano sphere particles 

(Fig. 7). The diameter of the particles appearing on the top 

of the pine char surface ranged from 50 to 100 nm, whereas 

the particles underneath the surface were around 20 nm in 

diameter. The formation of surface nanoparticles indicated 

that the more volatile products vaporized and redeposited to 

form the crystalline structures. More micro-pores and microchannels were observed on the char surface as the pyrolysis 

temperature increased.

Figure 3. SEM images of surface morphologies of raw pine 

chips at three magnifications of: (a) ×90; (b) ×1,000; and, 

(c) ×100,000.

Figure 4. SEM images of surface morphologies of pine 

chars treated at 450 °C for 30 min, with a nitrogen gas flow 

rate of 500 mL/min and a heating rate of 10 °C/min at two 

magnifications of: (a) ×500 and (b) ×10,000.
General Technical Report FPL–GTR–218

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Heating Rate Effect

SEM images of pine chars from heating rates of 1, 10, and 

50 °C /min are shown in Figure 8. For all char samples, 

sphere-shaped nanoparticles were observed. These particles 

might be due to pyrolytic carbon deposits resulting from 

organic volatiles. During carbonization, hydrocarbons 

release from the samples as volatile matter. Collisions 

of these compounds with pore walls might bring about 

cracking and carbon deposition.

The surface with the heating rate of 1 °C/min was smooth, 

and 50–100 nm particles were distributed over the surface. 

Under the heating rate of 10 °C/min, the pine char surface 

is covered with different sizes of smooth, open pores and 

more particles with 100–200 nm diameters. More and larger 

particles appeared over the surface of the chars with the rate 

of 50 °C/min. These particles obtained under high heating 

rates may be the result of secondary product formation from 

the precipitation of volatile gases. The higher heating rate 

leads to a rapid formation of volatile matter, causing a rapid 

increase of pressure in the wood particle and an explosive 

release of volatiles (Sharma and others 2001, 2004).

Purge Gas Flow Rate Effect

Figure 9 shows SEM images of pine chars produced with 

three nitrogen flow rates. The surface of pine chars under 

100 mL/min flow rate was covered with nanoparticles 

with sizes ranging from 10 to 50 nm in diameter, and 

fewer micro-pores and micro-channels were formed on the 

Figure 5. SEM images of surface morphologies of pine chars treated at 500 °C for 30 min, with a nitrogen gas flow rate of 

500 mL/min and a heating rate of 10 °C/min at two magnifications of: (a) ×750 and (b) ×10,000.

Figure 6. SEM images of surface morphologies of pine chars treated at 650 °C for 30 min, with a nitrogen gas flow rate of 500 

mL/min and a heating rate of 10 °C/min at two magnifications of: (a) ×750 and (b) ×10,000.
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surface. The surface of pine chars had fewer nanoparticles 

and more micro-pores and micro-channels with the increase 

of the purge gas flow rate from 100 to 1,000 mL/min. In this 

case, the fast volatile release during pyrolysis leads to loss 

of porosity of the char, because part of the volatiles would 

decompose and deposit as the secondary reaction char in 

the micro-channels or the surface of the char matrix at a low 

flow rate, whereas the porosity of the char should increase 

when the purge gas flow rate increases. Therefore, more 

micro-pores and micro-channels are observed over pine 

chars produced at the higher purge gas flow rate.

Purge Gas Type Effect

Figure 10 shows SEM images of pine chars purged with 

nitrogen and hydrogen gases. Many nanoparticles were 

observed over the surface of the char purged with nitrogen. 

The char purged with hydrogen had few or no nanoparticles 

over its surface. Many micro-pores and micro-channels were 

evenly distributed over the surfaces of chars purged both by 

nitrogen and hydrogen. The surface of hydrogen-purge chars 

is relatively smoother compared to nitrogen-purge chars.

Particle Characterization

Figures 11 to 14 show TEM images of nanoparticles washed 

off from pine chars produced under different thermal 

treatment conditions. Typically, nano carbon spheres, nano 

carbon chips, and some porous carbon particles (Fig. 11) 

were observed for the pine chars produced at 1,000 °C with 

heating rate of 1 °C/min under a nitrogen flow rate of 

500 mL/min, and these particles had the diameters between 

20 and 100 nm. Large amounts of nano carbon spheres 

mixed with porous carbon particles (Fig. 12) were found 

for the pine chars produced at 1,000 °C, with a 1 °C/min 

heating rate and a hydrogen flow rate of 500 mL/min, 

and these carbon spheres were between 20 and 50 nm in 

diameter.

For the chars produced at 1,000 °C with a 100 °C/min 

heating rate under a nitrogen flow rate of 500 mL/min, 

porous carbon particles and carbon nanofibers (or carbon 

nanotubes (CNTs)) were observed, as shown in Figure 

13. It was interesting to find some CNTs formed in the 

mixture with carbon particles (Fig. 14) when the chars were 

produced under the condition of 1,000 °C, with 100 °C/min 

heating rate under a 500 mL/min hydrogen flow. Although 

no metal catalysts and hydrocarbons or CO were introduced, 

trace levels of metals (southern pine contains very small 

amounts of inorganic elements such as Ca, K, Mg, Na, 

Si, Fe, and Mn) (Koch 1972) in the chars catalytically 

decomposed the volatile products such as methane, organic 

compounds, and CO to form carbon nanotubes during the 

pine pyrolysis process.

Conclusions

The influences of final pyrolysis temperature, heating rate, 

purge gas type, and flow rate on the surface morphology of 

pine chars were investigated using SEM and TEM. SEM 

images of raw pine chips show that the surface is smooth 

and clean, and there is no dust.

The surface morphologies of pine chars were significantly 

affected by pyrolysis temperature for the pine chips heated 

under a nitrogen flow rate of 500 mL/min and a heating rate 

of 10 °C/min for 30 min. SEM analyses indicated that at 

450 °C, pine chips had already started to decompose. The 

pine char obtained at 500 °C was in the form of a continuous 

melt and decomposition. No nanoparticles were observed on 

the char surfaces as temperature increased to 500 °C.

The most obvious feature observed was the formation of 

sphere particles over the surface of the pine chars heated up 

to 650 °C, where particle diameters ranged from 50 to 

100 nm. As temperature increased to 1,000 °C, the char 

Figure 7. SEM images of surface morphologies of pine chars treated at 1,000 °C for 30 min, with a nitrogen gas flow rate of 

500 mL/min and a heating rate of 10 °C/min at two magnifications of: (a) ×5,000 and (b) ×50,000.
General Technical Report FPL–GTR–218

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Figure 8. SEM images of surface morphologies of pine 

chars produced at three heating rates: (a) 1 °C/min; 

(b) 10 °C/min; and, (c) 50 °C/min to the final temperature 

of 1,000 °C for 30 min, with a nitrogen gas flow rate of 

500 mL/min.

Figure 9. SEM images of surface morphologies of pine 

chars heated to a final temperature of 1,000 °C, with a 

heating rate of 30 °C/min for 30 min under three nitrogen 

flow rates: (a) 100 mL/min; (b) 500 mL/min; and, 

(c) 1,000 mL/min.
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surface was covered with more nano sphere particles. The 

particles distributed on top of the char surface range from 

50 to 100 nm in diameter, whereas the particles underneath 

the char surface were about 20 nm in diameter. More 

micro-pores and micro-channels were seen on the pine 

char surfaces as the temperature increased to 1,000 °C.

The heating rate has a significant influence on the surface 

morphology of pine chars pyrolyzed at 1,000 °C for 30 min 

with a nitrogen gas flow rate of 500 mL/min. The size and 

quantity of nanoparticles on the pine char surface increased 

as the heating rate increased from 1 to 50 °C/min. Different 

sizes of smooth, open pores can be produced on the pine 

char surface with a heating rate of 50 °C/min.

The lower the nitrogen gas flow rate, the more nanoparticles 

and fewer micro-pores and micro-channels are formed on 

the pine char surface. Also, the higher the nitrogen gas flow 

rate, the fewer nanoparticles and the more micro-pores and 

micro-channels there were. The surface of pine chars purged 

with nitrogen yielded significantly more nanoparticles 

than those purged with hydrogen. Both chars purged with 

nitrogen and hydrogen had many evenly distributed 

micro-pores and micro-channels, but the surface of 

Figure 10. SEM images of surface morphologies of pine chars heated to a final temperature of 1,000 °C, with a 

heating rate of 50 °C/min for 30 min using purge gases of (a) nitrogen and (b) hydrogen gases of a constant flow rate 

of 500 mL/min.

Figure 11. TEM images of carbon particles (20–100 nm in diameter) washed off from pine chars heated to the final 

temperature of 1,000 °C for 30 min, with a heating rate of 1 °C/min under a nitrogen flow rate of 500 mL/min.
General Technical Report FPL–GTR–218

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hydrogen-purged chars was relatively smooth compared 

with the nitrogen-purged chars.

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