U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5292

Changes in Composition and Porosity Occurring During the 

Thermal Degradation of Wood and Wood Components

Changes in Composition and Porosity 

Occurring During the Thermal Degradation 

of Wood and Wood Components

By David W. Rutherford, Robert L. Wershaw, and Larry G. Cox

Scientific Investigations Report 2004-5292

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

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iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Materials and Methods ............................................................................................................................... 2

Materials ............................................................................................................................................... 2

Char Preparation .................................................................................................................................. 2

Elemental Analysis .............................................................................................................................. 2

Surface Area Measurement .............................................................................................................. 3

Nuclear Magnetic Resonance Spectrometry ................................................................................. 3

Infrared Spectrometry ........................................................................................................................ 3

Reproducibility of the Charring Process .......................................................................................... 3

Compositional and Porosity Changes ........................................................................................................ 3

Percentage Char Remaining .............................................................................................................. 3

Infrared Spectral Evidence of Changes ........................................................................................... 6

Nuclear Magnetic Resonance Spectral Evidence of Changes ................................................... 7

Elemental Composition of Char ....................................................................................................... 11

Hydrogen/Carbon Ratios and Oxygen/Carbon Ratios of Chars .................................................. 16

Aromatic and Aliphatic Carbon Content of Chars ........................................................................ 16

H/C and O/C Atomic Ratios of Material Lost from Char ............................................................... 16

Surface Area and Porosity Changes .............................................................................................. 25

Summary ...................................................................................................................................................... 30

Literature Cited ............................................................................................................................................ 31

Appendix A. Replicate Charring and Analyses ...................................................................................... 33

Appendix B. Fourier Transform Infrared (FTIR) Spectra ....................................................................... 38

Appendix C. 13C Nuclear Magnetic Resonance (NMR) Spectra ......................................................... 59

Figures

1–7. Graphs showing:

1. Percentage mass remaining (yield) for cellulose, lignin, poplar wood, pine wood, 

 and pine bark after charring at A, 250oC, B, 300oC and C, 350oC for various times. ... 5

2. Chemical structures of cellulose and lignin monomeric units. ............................................ 9

3. Calculated aromatic and aliphatic carbon content (Grams Carbon/100 Grams 

Starting Material) in cellulose and cellulose char at various heating times and 

temperatures. ............................................................................................................................. 19

4. Calculated aromatic and aliphatic carbon content (Grams Carbon/100 Grams 

Starting Material) in lignin and lignin char at various heating times and 

temperatures. ............................................................................................................................. 20

5. Calculated aromatic and aliphatic carbon content (Grams Carbon/100 Grams 

Starting Material) in poplar wood and chars at various heating times and 

temperatures. ............................................................................................................................. 21

6. Calculated aromatic and aliphatic carbon content (Grams Carbon/100 Grams 

Starting Material) in pine wood and chars at various heating times and 

temperatures. ............................................................................................................................. 22
iv

Figures—Continued

7. Calculated aromatic and aliphatic carbon content (Grams Carbon/100 Grams 

Starting Material) in pine bark and chars at various heating times and 

temperatures. ............................................................................................................................. 23

Tables

1. Percentage char remaining after heating. .............................................................................. 4

2. 13C NMR chemical shifts of cellulose and of guaiacylpropanoid and syringylpropanoid lignin units where C-4 is linked by an ether linkage to another phenylpropanoid unit (data from Hassi and others, 1987). ............................................................... 8

3. Percentage aromatic carbon in chars after heating. .......................................................... 10

4. Percentage carbon remaining in char after heating, normalized to a dry and 

ash-free basis. ............................................................................................................................ 13

 5. Percentage hydrogen remaining in char after heating, normalized to a dry and 

ash-free basis. ............................................................................................................................ 14

6. Percentage oxygen remaining in char after heating, determined by difference from 

ash, carbon and hydrogen content. ........................................................................................ 15

7. Hydrogen/carbon atomic ratios and oxygen/carbon atomic ratios of chars. ................. 17

8. Grams of aromatic carbon or aliphatic carbon in char per 100 grams of starting 

material. ....................................................................................................................................... 18

9. Hydrogen/carbon atomic ratios and oxygen/carbon atomic ratios of material lost 

from char during heating intervals. ........................................................................................ 24

10. Micropore volume in char after heating. ............................................................................... 27

11. Total pore volume in char after heating. ................................................................................ 28

12. Surface area in char after heating. ....................................................................................... 29

A-1. Replicates for pine wood samples. ........................................................................................ 34

A-2. Replicates for pine bark samples. .......................................................................................... 35

A-3. Replicates for cellulose samples. ........................................................................................... 36

A-4. Replicates for lignin samples. ................................................................................................. 37

Appendix figures

 B-1–C-21. Graphs showing:

 B-1. Fourier Transform Infrared (FTIR) spectra of unheated cellulose, lignin, 

pine wood, poplar wood and pine bark. ................................................................................. 38

 B-2. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 250oC 

for various times. ....................................................................................................................... 39

 B-3. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 300oC 

for various times. ....................................................................................................................... 40

 B-4. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 350oC 

for various times. ....................................................................................................................... 41

 B-5. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 400oC 

for various times. ....................................................................................................................... 42

 B-6. Fourier Transform Infrared (FTIR) spectra of lignin heated at 250oC for 

various times. ............................................................................................................................. 43
v

Appendix figures—Continued

 B-7. Fourier Transform Infrared (FTIR) spectra of lignin heated at 300oC for 

various times. ............................................................................................................................. 44

 B-8. Fourier Transform Infrared (FTIR) spectra of lignin heated at 350oC for 

various times. ............................................................................................................................. 45

 B-9. Fourier Transform Infrared (FTIR) spectra of lignin heated at 400oC for 

various times. ............................................................................................................................. 46

 B-10. Fourier Transform Infrared (FTIR) spectra of lignin heated at 500oC for 

various times. ............................................................................................................................. 47

 B-11. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 250oC 

for various times. ....................................................................................................................... 48

 B-12. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 300oC 

for various times. ....................................................................................................................... 49

 B-13. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 350oC 

for various times. ....................................................................................................................... 50

 B-14. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 400oC 

and 500oC for one hour. ............................................................................................................. 51

 B-15. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 250oC 

for various times. ....................................................................................................................... 52

 B-16. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 300oC 

for various times. ....................................................................................................................... 53

 B-17. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 350oC 

for various times. ....................................................................................................................... 54

 B-18. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 400oC, 

500oC, and 600oC for one hour. ................................................................................................. 55

 B-19. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 250oC 

for various times. ....................................................................................................................... 56

 B-20. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 300oC for 

various times. ............................................................................................................................. 57

 B-21. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 350oC for 

various times. ............................................................................................................................. 58

 C-1. 13C Nuclear Magnetic Resonance (NMR) spectra of unheated cellulose, 

lignin, pine wood, poplar wood and pine bark. ..................................................................... 59

 C-2. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at 

250oC for various times. ............................................................................................................. 60

 C-3. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at

300oC for various times. ............................................................................................................. 61

 C-4. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at

350oC for various times. ............................................................................................................. 62

 C-5. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at

400oC for various times. ............................................................................................................. 63

 C-6. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 250oC 

for various times. ....................................................................................................................... 64

 C-7. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 300oC 

for various times. ....................................................................................................................... 65

 C-8. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 350oC 

for various times. ....................................................................................................................... 66
vi

Appendix figures—Continued

 C-9. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 400oC 

for various times. ....................................................................................................................... 67

 C-10. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 500oC 

for various times. ....................................................................................................................... 68

 C-11. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 

250oC for various times. ............................................................................................................. 69

 C-12. 13C Nuclear Magnetic Resonance (NMR)spectra of poplar wood heated at 

300oC for various times. ............................................................................................................. 70

 C-13. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 

350oC for various times. ............................................................................................................. 71

 C-14. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 

400oC and 500oC for one hour. .................................................................................................. 72

 C-15. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 

250oC for various times. ............................................................................................................. 73

 C-16. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 

300oC for various times. ............................................................................................................. 74

 C-17. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 

350oC for various times. ............................................................................................................. 75

 C-18. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 

400oC, and 500oC for one hour. ................................................................................................. 76

 C-19. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 

250oC for various times. ............................................................................................................. 77

 C-20. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 

300oC for various times. ............................................................................................................. 78

 C-21. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 

350oC for various times. ............................................................................................................. 79
Changes in Composition and Porosity Occurring During 

the Thermal Degradation of Wood and Wood Components

By David W. Rutherford, Robert L. Wershaw, and Larry G. Cox

Abstract

Samples of pine and poplar wood, pine bark, and purified 

cellulose and lignin were charred at temperatures ranging from 

250oC to 500oC for times ranging from 1 hour to 168 hours. 

Changes in composition were examined by Fourier Transform 

Infrared (FTIR) and 13C Nuclear Magnetic Resonance (NMR) 

spectrometry, mass loss, and elemental composition (carbon, 

hydrogen, and oxygen) of the char. Structural changes were 

examined by changes in porosity as measured by nitrogen gas 

adsorption. 13C NMR spectrometry, mass loss, and elemental 

composition were combined to estimate the mass of aromatic 

and aliphatic carbon remaining in the char. Mass loss and elemental composition were combined to estimate the chemical 

composition of material lost for various time intervals of heating. These analyses showed that aliphatic components in the 

test materials were either lost or converted to aromatic carbon 

early in the charring process. Nitrogen adsorption showed that 

no porosity develops for any of the test materials with heating 

at 250oC, even though substantial loss of material and changes 

in composition occurred. Porosity development coincided with 

the loss of aromatic carbon, indicating that micropores were 

developing within a fused-ring matrix.

Introduction

Pyrolytic carbon (the so-called black carbon fraction) 

is the least studied component of soil organic carbon (SOC). 

Black Carbon (BC) has been detected in many soils and sediments (Cambardella and Elliot, 1992; Karapanagiotti and 

others, 2000; Schmidt and others, 1999; Skjemstad and others, 

1996; Skjemstad and others, 2002) and is probably present in 

most soils. Some workers have estimated that BC constitutes 

as much as 55 percent of SOC; however, it now appears that 

many of the estimates of the amount of BC in soils are too 

high (see Gelinas and others, 2001; Simpson and Hatcher, 

2004b). Simpson and Hatcher (2004a,b), using a method that 

is much improved over previous methods, found that BC constituted 22.3 percent of the total organic carbon in a Canadian 

chernozem; they measured much lower values in other soils. 

Gelinas and others (2001) divided BC into two components: 

char/charcoal BC (CBC) and soot/graphitic BC (GBC). 

The CBC fraction is formed by charring biomass of mainly 

plant origin, whereas the GBC fraction is formed by vaporphase reactions. Gelinas and others (2001) pointed out that 

GBC particles are much smaller than CBC particles, and that 

they are “* * * rapidly dispersed through aerosol formation 

and atmospheric transport and deposition.” The CBC particles, 

on the other hand, generally will remain in the soil near where 

they are produced. In this report we shall be concerned only 

with the CBC fraction.

BC can markedly alter the physical chemical properties 

of soils. For example, Glaser and others (2001) demonstrated 

that BC is crucial in maintaining fertility of the so-called 

“terra preta” black soils of the Amazon Basin of Brazil. These 

soils occur in relatively small, isolated sites averaging about 

20 hectares (ha) in area. The sites generally are surrounded 

by highly leached oxisols of low fertility. The presence of 

charcoal (CBC) in the terra preta soils differentiates them from 

the surrounding oxisols. This charcoal possibly was formed by 

campfires and incorporated into the terra preta soils by native 

Indian farmers prior to the arrival of Europeans in the New 

World and has persisted until the present. The presence of the 

CBC greatly increases the capacity of these soils to bind nutrients such as nitrogen, phosphorus, calcium, and potassium; 

pH values and water-holding capacities also are enhanced. In 

addition to the binding of inorganic constituents, BC strongly 

binds hydrophobic organic compounds. BC has a much higher 

sorption capacity for hydrophobic organics than other SOC 

components (Karapanagiotti and others, 2000).

The physical chemical properties of activated carbons 

have been extensively studied; however, it is likely that the 

properties of soil CBC will be substantially different from 

those of activated carbon. Activated carbons are generally prepared at high temperatures in the presence of activating agents 

such as steam (Patrick, 1995). Soil CBC, on the other hand, is 

generally produced at much lower temperatures by forest or 

grass fires or, in the case of the terra preta soils, by campfires. 

No comprehensive studies have been conducted on the properties of charcoals produced at low temperatures from biomass.

The compositional changes occurring during the charring 

of cellulose, lignin, and wood have been studied previously 

(Shafizadeh, 1982; Pastorova and others, 1994; Amen-Chen 

and others, 2001; González-Vila and others; 2001). Williams 

and Besler (1996) found that under slow pyrolysis, hemicellulose and cellulose begin decomposition at 250o Celsius (C) 
with the majority of weight loss by 400oC. Lignin showed 

more gradual weight loss from 200oC to 720oC. Baldock and 

Smernik (2002) used solid-state 13C nuclear magnetic resonance (NMR), diffuse-reflectance infrared (IR), and elemental 

analysis to study the composition changes brought about by 

the charring of red pine wood at different temperatures. In all 

of their experiments, the wood was heated at a given temperature for 24 to 72 hours until a constant mass of residual 

char was obtained. No short-term heating experiments were 

conducted, and they did not measure the surface areas of the 

chars.

Surface area is a particularly important parameter to 

measure because the sorption and ion exchange properties of 

charcoals are directly related to surface area. Surface areas 

of charcoal can vary from 1 square meter (m2)/gram (g) to 

500 m2/g. The creation of high surface area, as measured by 

the nitrogen-sorption Brunauer, Emmett, and Teller (BET) 

method (see Brunauer and others, 1938), is related to the 

creation of micropores; that is, pores with diameters less than 

2 nanometers (nm). Porous carbons have been modeled as 

being composed of aggregates of fused-ring carbon structures 

that form small lamellar crystallites. The structure of the crystallites is similar to that of graphite; however, ordering is of 

much shorter range than in graphite (Byrne and Marsh, 1995; 

Jorge and others, 2002). The creation of pores in charcoal is 

not well understood, but it has been related to heating temperature and duration of heating. Improved understanding of composition and porosity of charcoal has application to studies of 

the environmental effects of black carbon in soils, either from 

natural causes such as forest fires or from the use of charcoal 

as a soil amendment for agricultural purposes.

This report provides the results of changes in composition 

(measured by char yield, elemental composition, NMR, and 

IR) and changes in structure (measured by porosity) made on 

chars produced in the laboratory from cellulose, lignin, pine 

and popular wood, and pine bark under controlled conditions 

of temperature and heating duration. Chars were prepared 

under nitrogen to eliminate combustion so that temperature 

could be controlled and a reproducible char produced. Thus, 

comparisons of the physical and chemical changes brought 

about in different materials due to variations in heating temperature and duration can be made.

Materials and Methods

Materials

Cellulose was obtained commercially as a microcrystalline powder (approximately 20 micrometer (μm) particle 

size) and had been purified from wood pulp. The Organosolv 

lignin was obtained commercially as a powder that had been 

extracted from mixed hardwoods by the Organosolv process 

(Allan, 1971, p. 540-541).

The pine samples were obtained from a cross-section 

of ponderosa pine log (Pinus ponderosa). Pine bark material 

was collected and treated separately. The wood was shredded 

with a hand-held electric plane. The shavings were 1 millimeter (mm) or less in thickness, 2 to 4 mm in width, and 1 centimeter (cm) or less in length. Wood samples were air-dried 

prior to use. The bark was air-dried and ground using a hand 

mill.

The poplar samples were obtained from a hardwood 

board procured at a local lumberyard (exact species unknown). 

The material was shredded on a lathe. The shavings were 

1 mm or less in thickness, 2 to 5 mm in width, and 2 to 5 mm 

in length. Samples were air-dried prior to use.

Char Preparation

Char was prepared by weighing the shredded or powdered sample into 250 milliliter (mL) porcelain crucibles. 

The crucibles were heated without tops with between 10 and 

20 grams (g) of material per crucible. The crucibles were 

placed in a preheated muffle furnace with nitrogen flow sufficient to produce three air changes per minute within the 

furnace. The nitrogen used was ultra high purity (UHP) grade 

with less than 1 parts per million (ppm) oxygen. After heating, 

crucibles were placed in a nitrogen-filled desiccator to cool to 

room temperature. The percentage yield was determined by 

weighing samples before and after heating. The char was then 

pulverized with a mortar and pestle.

Elemental Analysis

Carbon and hydrogen were determined by combustion 

in oxygen at 1000oC; the combustion products were passed 

through catalysts to ensure complete oxidation. Water was 

trapped, and carbon dioxide (CO2) was measured with a 

CO2 coulometer. Water was then released from its trap and 

quantitatively converted to CO2 and measured by a second 

coulometer. Moisture was determined by loss on drying at 

105oC overnight. Ash content was determined by combustion 

in air at 750oC. Carbon, hydrogen, and ash were converted to 

a dry-weight basis. Oxygen was determined by difference. All 

results reported for carbon, hydrogen, and ash have been normalized to an ash-free basis. Where ash was not determined 

directly (21 samples out of 81 samples), an estimate was made 

on the basis of the percentage mass remaining by using a 

power function numerical fit in the form:

percentage ash = A (percentage mass remaining)B.

2 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
The following results from the numerical fit were 

obtained:

A B

Correlation 

coefficient (R2)

Pine wood 24.5 -0.905 0.88

Poplar wood 23.2 -0.887 0.98

Pine bark 235 -0.956 0.98

Surface Area Measurement

The surface area was determined by adsorption of nitrogen (N2

) at liquid nitrogen temperature by using an automated 

surface area analyzer. The samples were out-gassed by heating 

at 110oC under a flow of ultrahigh purity helium at 10 cubic 

centimeters (cm3)/minute (min) for 16 to 24 hours (hr) prior 

to analysis. Isotherm data were recorded at partial pressures 

of nitrogen between 0.05 and 0.95 atmospheres. The apparent surface areas of samples were obtained from the statistical 

monolayer capacities of N2 from the BET plots (Brunauer and 

others, 1938). The micropore volumes were determined by the 

t-method of de Boer and others (1966). 

Nuclear Magnetic Resonance Spectrometry

Solid-state 13C NMR spectra of the charcoals were measured on a Chemagnetics CMX 200-megahertz (MHz) proton 

frequency spectrometer (Wershaw and others, 1998) equipped 

with a 7.5-mm Chemagnetics ceramic probe. The samples 

were packed in zirconia rotors and spun at 5,000 hertz (Hz). 

The acquisition parameters were contact time of l millisecond (ms) or 5 ms, pulse delay of 1 second (s), and 4.5 microsecond (μs) 90o pulse. 

Infrared Spectrometry

Infrared spectra were collected by using 2 to 5 milligrams (mg) of sample in a potassium bromide (KBr) pellet. 

The Perkin Elmer System 2000 Fourier Transform Infrared 

(FTIR) used an infrared source with a pulsed laser carrier and 

a deuterated triglycine sulfate detector. The instrument was 

scanned from 4,000 to 400 reciprocal centimeters (cm-1), 

averaging 10 scans at 1.0 cm-1 intervals with a resolution of 

4.0 cm-1. All spectra were normalized after acquisition to a 

maximum absorbance of 1.0 for comparison purposes.

Reproducibility of the Charring Process

Selected raw materials were charred four or five times at 

the same temperature and time to evaluate the reproducibility 

of the charring process. For each replicate at a given time and 

temperature, the percentage char remaining, surface area, and 

total pore volume were measured. These data are presented in 

appendix A.

The char composition, based on percentage char remaining, was very reproducible. The percentage char remaining 

ranged from 60.2 to 13.9 percent with standard deviations 

ranging from 4.26 to 0.56 percent. The median yield was 

32.9 percent with a median standard deviation of 1.90 percent.

The reproducibility of char structure, based on total pore 

volume, was more variable than compositional changes. The 

total pore volume ranged from 0.240 to 0.001 cm3 with standard deviations ranging from 0.039 to 0.0002 cm3

. The median 

total pore volume was 0.034 cm3 with a median standard 

deviation of 0.0048 cm3. The data show that there are three 

populations of pore volumes. The population with little or no 

pore volumes was near the detection level, and standard deviations ranged from 10 to 100 percent of the average. When pore 

volumes began to increase, standard deviations ranged from 

30 to 70 percent of the average. At higher temperatures and 

longer charring times, which resulted in higher pore volumes, 

standard deviations ranged from 10 to 30 percent of the average.

Compositional and Porosity Changes

Percentage Char Remaining

The percentage char remaining from cellulose, lignin, 

poplar and pine wood, and pine bark for various heating times 

and temperatures are listed in table 1. The yield of char is a 

useful measurement of the total decomposition and volatilization of material from a sample.

When heated to 250oC for 1 hour, cellulose showed 

little weight loss (6.4 percent), but lost about 60 percent of 

its weight when heated for 8 hours. Weight loss continued 

with time, though more gradually, with 68.6 percent lost after 

72 hours heating (fig. 1a). When heated at 300oC, cellulose 

lost 66.7 percent of its weight after 1 hour, 69.1 percent after 

8 hours, and 72.8 percent after 24 hours (fig. 1b). Increased 

temperature caused increased weight loss with most of the 

weight loss occurring in the first hour of heating (fig. 1c).

With heating at 250oC, lignin lost 15.3 percent of its 

weight after 24 hours and 20 percent after 144 hours. When 

heated at 300oC for 24, 48 and 72 hours, the weight losses 

were 32.4 percent, 36.3 percent, and 40.7 percent, respectively. 

Higher temperatures increased the rate of weight loss with 

80 to 85 percent loss after 24 hours at 400oC and 8 hours at 

500oC. For comparable temperatures and times, lignin weight 

loss was consistently less than half that of cellulose.

At 250oC and 300oC, both pine and poplar wood showed 

weight losses nearly identical to cellulose. At 350oC, the 

weight loss from both species of wood exceeded that of cellulose for heating times greater than 8 hours. Pine and poplar 

wood were reduced to ash after 48 hours. For all heating 

conditions, the yield of char for both woods was less than 

what would have been expected on the basis of estimates of 

the char remaining from cellulose and lignin components of 

Compositional and Porosity Changes 3
wood. This could be the result of reaction between degradation 

products in the mixture or could result from a catalytic effect 

of the ash components, which became more concentrated in 

the wood char as weight loss progressed. The inert gas used 

in the oven was nitrogen produced from the boil off of liquid 

nitrogen, with an oxygen content of less than 1 ppm. The 

small amount of oxygen in the nitrogen gas could account for 

some of the continued loss of weight observed for long heating 

times.

Pine bark exhibited a similar exponential decrease in 

mass with heating time as the wood samples but had 5 to 

10 percent higher char yield at all times and temperatures, 

except for heating for one hour at 250oC; the char yield for 

bark was slightly lower than for wood.

Table 1. Percentage char remaining after heating.

[oC, degrees Celsius; --, no data]

Preparation temperatures

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose

1 93.6 33.3 27.8 22.3 --

8 44.1 30.7 23.5 -- --

24 35.5 27.2 18.9 7.8 --

48 34.7 23.9 12.8 -- --

72 31.4 22.2 9.02 -- --

Lignin

1 -- 76.8 64.3 51.8 38.9

8 -- 70.0 55.3 38.2 19.1

24 84.7 67.8 41.2 15.6 --

48 -- 63.7 32.8 -- --

72 80.6 59.3 23.9 -- --

144 80.0 -- -- -- --

Poplar wood

1 75.9 41.6 27.1 22.9 16

8 42.5 27.8 20.4 -- --

24 38.3 21.8 11.3 -- --

48 -- 18.5 3.1 -- --

72 33.0 15.7 0.65 -- --

144 29.7 -- -- -- --

Pine wood

1 79.2 42.4 26.8 22.5 11.2

8 55.8 32.9 21.1 -- --

24 43.3 25.1 5.1 -- --

48 36.2 19.9 0.65 -- --

72 -- 17.2 0.34 -- --

168 30.2 -- -- -- --

Pine bark

1 73.3 53.7 44.5 -- --

8 60.2 47.5 33.3 -- --

24 51.9 35.5 19.5 -- --

48 -- 24.3 9.1 -- --

72 42.7 18.1 -- -- --

168 34.3 -- -- -- --

4 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
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Figure 1 [a-c]. Percentage mass remaining (yield) for cellulose, lignin, poplar wood, pine wood, and pine bark after charring at 

A, 250oC, B, 300oC and C, 350oC for various times.

Compositional and Porosity Changes 5
Infrared Spectral Evidence of Changes

The FTIR spectra of the unheated wood samples consist 

mainly of bands that may be attributed to carbohydrates (cellulose and hemicellulose) and lignin. To follow more easily 

the chemical changes that take place during the pyrolysis of 

wood, the changes that occur when pure cellulose and lignin 

are pyrolyzed will be examined first. The most prominent 

carbohydrate bands in the unheated cellulose were between 

1,000 and 1,200 cm-1 (figure B-1, appendix B). These bands at 

1,035, 1,060, 1,110, and 1,159 cm-1 are essentially in the same 

positions as those observed by Chen and Jakes (2002) in the 

IR spectra of single cotton fibers. The major lignin bands are 

shown in figure B-1, appendix B. Faix (1991) has identified 

diagnostic lignin bands at approximately 1,221, 1,269, 1,326, 

1,367, 1,423, 1,464, 1,510, and 1,596 cm-1. In addition, there 

are lignin bands at 1,035, 1,086, 1,140, and 1,166 cm-1 (Faix, 

1991); however, these bands are obscured in wood by the 

much stronger carbohydrate bands.

The FTIR spectra of cellulose heated to 250oC for different time intervals are given in appendix B, figure B-2. Heating 

to 250oC for 1 hour caused no discernable alteration of the 

cellulose spectrum. However, heating for 8 hours caused all of 

the characteristic cellulose bands to disappear. They have been 

replaced by broad bands centered at about 1,240, 1,435, 1,610, 

and 1,720 cm-1. At higher temperatures, these same bands 

were observed after shorter heating times (see figures B-3 to 

B-5 in Appendix B). In contrast, heating of lignin for different 

time intervals at 250oC only causes some broadening of the IR 

bands and a concomitant loss of resolution (appendix B, 

figure B-6). At higher temperatures the lignin bands coalesce 

into broad bands that were at similar positions to those 

observed in the 8-hour 250oC cellulose spectrum (see figures 

B-7 to B-10 in appendix B).

Four bands at very similar positions to the four major 

bands in the spectrum of cellulose were present in the pine and 

poplar wood spectra. Heating the wood to 250oC for 1 hour 

increases the resolution of these bands (appendix B, figures 

B-11 and B-15). This increased resolution was not observed 

when pure cellulose was heated (appendix B, figure B-2), and 

therefore, it is probably due to drying and partial decomposition of the hemicelluloses that would be expected to have 

bands in slightly different positions than crystalline cellulose. 

Further heating of the wood at 250oC (from 8 to 168 hours) 

causes a continuous reduction in the relative intensities of the 

cellulose bands as the carbohydrate material decomposes.

The diagnostic lignin bands in the region between 

1,200 and 1,600 cm-1 are present in the FTIR spectra of the 

unheated wood and 1-hour 250oC samples. Further heating 

at 250oC causes a slight broadening of the bands. At higher 

temperatures, much more broadening of the bands is observed, 

and many of the bands coalesce. A prominent band at about 

1,600 cm-1 develops at the higher temperatures. This band 

probably represents skeletal vibrations of fused-ring aromatic 

structures (see discussion of NMR data in the next section). In 

as much as the longer heating intervals at 250oC only slightly 

altered the FTIR spectra of the pure lignin, it is likely that the 

broadening observed in the wood spectra at 250oC is due to 

overlap of charred cellulose bands.

The bands in the FTIR spectrum of unheated pine bark 

(appendix B, figure B-1) are in the same positions as those 

of the unheated pine wood; however, the relative intensities 

of the bands are different. The ratio of the intensities of the 

lignin bands to the intensities of carbohydrate bands is larger 

in the bark than in the wood, indicating that the concentration 

of lignin is higher in the bark than in the wood. Heating of the 

bark brought about changes similar to those observed in the 

wood samples.

The heating experiments for different lengths of time at 

250oC show the sequence of decomposition of the carbohydrate and lignin components in wood and bark. The 1-hour 

heating at 250oC has caused a substantial diminution of the 

cellulose bands in the FTIR spectra relative to the lignin 

bands; however, the carbohydrate spectral bands are better 

resolved. These results most likely indicate decomposition of 

the hemicellulose in the wood and bark. Heating at 250oC for 

8 hours caused further diminution of the FTIR carbohydrate 

bands of the wood and bark samples and broadening of the 

bands. The heating for eight hours apparently caused decomposition of cellulose in addition to hemicellulose. Further heating of the wood and bark samples caused the aromatic band 

to grow at the expense of the other bands, and indicates an 

increase in fused-ring aromatic structures. Recognizable lignin 

and cellulose bands were still present in the 8-hour FTIR 

spectra; however, upon further heating FTIR bands coalesce 

into broad peaks. The broad bands centered near 1,600 cm-1, 

1,430 cm-1, and in the region between 1,200 and 1,260 cm-1, 

probably arise from different types of aromatic structures. 

Quinones and quinone methide have strong bands in the 1,600 

cm-1 region, and phenols absorb in the region between 1,200 

and 1,260 cm-1 (Colthup and others, 1990).

Bands between 1,700 and 1,850 cm-1 in the IR spectra 

of the charred cellulose, lignin, wood, and bark probably 

represent different types of carbonyl carbons. The charred 

cellulose has bands at about 1,750, 1,772, and 1,840 cm-1, 

whereas the charred lignin only has a band at about 1,717 cm-1

(appendix A, figure A-6). The strong band at 1,772 cm-1 and 

the weaker band at 1,840 cm-1 in the cellulose spectrum fit 

the pattern observed in five-membered ring cyclic anhydrides 

(Colthup and others, 1990). The band at 1,750 cm-1 probably 

represents five- or six-membered ring lactones. The band at 

1,717 cm-1 in the charred lignin spectrum probably represents 

carboxylic acid groups. Pradhan and Sandle (1999) have 

shown that charcoal oxidized with nitric acid has a IR band at 

1,719 cm-1; a careful examination of the IR spectra of their 

samples before and after oxidation led them to conclude that 

this band represents carboxylic acid groups attached to graphitic carbon atoms.

Spectra for charring at higher temperatures are available 

in appendix B (figs. B-12 to B-21). Except for lignin, which 

does not appear to fully decompose at 250oC, increasing the 

charring temperature above 250oC for the other components 

6 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
only shortened the time required to produce a spectrum of 

completely charred material.

Nuclear Magnetic Resonance Spectral 

Evidence of Changes

The NMR spectra of unheated cellulose and cellulose 

heated to 250oC for different time intervals are shown in 

appendix C, figure C-2. All of the major cellulose bands with 

the exception of the anomeric carbon band (C-1) are well 

separated from the major lignin bands (table 2). The C-4 carbon for cellulose (fig. 2) is actually represented by two bands 

in our spectra, one at about 84 ppm and one at about 88 ppm. 

Larsson and others (1999) have shown that the 88 ppm band 

represents crystalline or paracrystalline cellulose, and the 

84 ppm band, less well-ordered cellulose. The spectrum of 

cellulose heated for 1 hour at 250oC is essentially the same 

as that of the unheated cellulose (appendix C, fig. C-2). After 

8 hours of heating, the major cellulose bands have been 

replaced by a series of broad bands centered at about 25, 

70, 127, and 210 ppm. A shoulder at about 150 ppm also is 

present. The most probable assignments for these bands are: 

25 ppm, aliphatic hydrocarbon groups; 70 ppm, aliphatic alcohols; 127 ppm, fused-ring aromatic structures; and 210 ppm, 

ketones or aldehydes. Pastorova and others (1994) found that 

heating of cellulose to 250oC for 2.5 hours in a stream of nitrogen produced a new polymer that consisted of “* * * furanoid 

skeletons, hydroxyaromatic skeletons, unsaturated hydrocarbon chains, and a high number of carboxyl and carbonyl carbons.” When they heated the cellulose to 310oC for 2.5 hours 

condensed aromatic polymers formed. They also detected 

aliphatic structures and residual carbohydrate polymers.

Heating of cellulose at temperatures higher than 250oC 

caused a very rapid loss of the characteristic cellulose bands 

and the appearance of a broad band at about 127 ppm, 

representing fused-ring aromatic structures (figs. C-3 to C-5 

in appendix C). A shoulder at about 152 ppm in the 1-hour 

and 8-hour 300oC spectra may represent phenolic structures. 

The band at about 158 ppm first seen in the 24-hour 300oC 

spectrum probably represents benzofuranyl structures (see 

Pastorova and others, 1994, for possible examples). This band 

also is observed in the 8-hour and 24-hour 350oC spectra and 

in both the 400oC spectra.

The spectrum of unheated lignin is shown in appendix C, 

figure C-1. A generalized lignin structural diagram is shown in 

figure 2, and the chemical shifts of the different carbon atoms 

in lignin polymers are given in table 2. The spectrum of this 

organosolve lignin has a sharp band at about 148 ppm and a 

much weaker band between 150 and 151 ppm. The constituent units of this lignin, therefore, are mainly guaiacylpropanoid units. Heating of the lignin at 250oC for up to 72 hours 

only causes a broadening of the spectral bands (appendix C, 

figure C-6). Much more alteration of the lignin structure is 

apparent on heating to 300oC for 24 hours. The bands between 

100 and 140 ppm have coalesced into a single band at about 

127 ppm that probably represents fused-ring aromatic structures. The shift of the 148 ppm band to about 145 ppm is 

indicative of cleavage of the ß-O-4 ether linkages. The band 

at about 55 ppm in the spectrum of the heated lignin indicates 

that the methyl-ether linkages have largely survived the heating to 300oC for 24 hours. In addition, there is a very broad 

band centered at about 30 ppm in the heated lignin spectrum; 

this band probably represents a variety of aliphatic structures.

Similar conclusions can be drawn from the changes 

observed in the carbohydrate and lignin bands of the heated 

wood NMR spectra (appendix C, figures C-11 to C-18). The 

positions of the bands observed in the carbohydrate regions of 

the ground woods and the woods heated for 1 hour at 250oC 

match those of cellulose. Lignin is represented by well-defined 

bands at 56, 134, and 148 ppm in the unheated pine spectrum 

and at 56, 137, and 154 ppm in the unheated poplar spectrum. 

The 148 ppm band in the pine spectrum has a shoulder at 

about 154 ppm, and the 154 ppm band in the popular spectrum 

has a shoulder at about 148 ppm. In addition, there is a broad 

band between 110 and 125 ppm in the pine spectrum that is 

probably due to lignin. Assignments for guaiacylpropanoid 

and syringylpropanoid bands are given in table 2. As indicated 

in the table, the 148 ppm band most likely represents guaiacylpropanoid units, and the 154 ppm band, syringylpropanoid 

units.

The bands between 50 and 180 ppm in the NMR spectrum of the unheated pine bark have similar chemical shifts 

to those in the unheated pine wood; however, the lignin bands 

are more intense in the bark than in the wood. The higher 

concentration of lignin in the bark than in the wood evidenced 

by the FTIR and NMR is probably indicative of cell-wall 

thickening in the bark. This secondary cell-wall thickening is 

probably similar to that which takes place in the compression 

wood of conifers (Croteau and others, 2000). When the wood 

is subjected to unusual compressional stress, the cell walls 

are thickened by addition of lignin, which provides additional 

compressional strength. In the case of the bark, the cell-wall 

thickening is necessary to reduce water loss from the vascular 

organs (xylem and phloem) of the living tissue of the tree that 

is located behind the outer bark.

In addition to the lignin and carbohydrates bands, two 

relatively weak bands at about 20 and 30 ppm are present in 

the bark spectrum. The band at 30 ppm is most likely due to 

suberin (Gil and others, 1997). Suberin is a polyester material that is found in the bark and underground parts of higher 

plants. Suberin also is secreted by plants to cover wounds. The 

band at about 20 ppm is mostly due to terminal methyl groups. 

As in the case of the carbohydrate bands in the FTIR 

spectra, heating of the wood and bark samples to 250oC 

causes an increase in resolution of the carbohydrate bands in 

the NMR spectra. A major change is observed in the lignin 

portion of the spectra with the disappearance of the 154 ppm 

band and a concomitant increase in intensity of the 148 ppm 

band. Haw and Schultz (1985) observed a similar behavior 

when they heated lignin to 250oC. They attributed the changes 

to cleavage of ß-O-4 ether linkages of syringylpropanoid units. 

Compositional and Porosity Changes 7
The chemical shifts of the C-3 and C-5 carbon atoms change 

from about 154 ppm to 148 ppm when the ether linkage is 

replaced by an OH group. The corresponding shift for the 

C-3 and C-4 carbons of guaiacylpropanoid units is only about 

2 ppm from about 148 ppm to about 146 ppm. The resolution 

of the spectra in this region is not sufficient to see this shift. 

It is likely that the broad band observed at about 148 ppm in 

the woods heated to 250oC represents both guaiacylpropanoid 

and syringylpropanoid units in which the ß-O-4 ether linkages 

have been cleaved. The ß-O-4 ether bonds account for at least 

50 percent of the polymer linkages in most lignins (ten Have 

and Teunissen, 2001); and therefore, cleavage of these bonds 

results in substantial depolymerization of lignin.

The first step in the formation of the graphite-like crystallites is the development of fused-ring aromatic structures in 

the char. A useful index of the concentration of fused-ring 

aromatic carbon may be obtained by integration of the spectral 

regions of the NMR spectra. The regions integrated were 

chemical shifts from 0 to 110 ppm, 110 to 180 ppm, and 220 

to 260 ppm. The spinning side bands of the aromatic bands 

appear in the region of chemical shifts from 0 to 40 ppm and 

220 to 260 ppm. The spinning side band in the region from 

0 to 40 ppm cannot be distinguished from aliphatic bands in 

the same region. The area indicative of aliphatic components 

has been calculated by subtracting the area of the integration for 220 to 260 ppm from the area of the integration for 

0 to 110 ppm. This assumes that the spinning side bands are 

symmetrical and that the region of chemical shifts from 220 to 

260 ppm is due solely to spinning side band. The area indicative of aromatic components is corrected by adding twice the 

area of the integration for 220 to 260 ppm to the area of the 

integration for 110 to 180 ppm. The percentage aromatic carbon shown in table 3 was computed by dividing the aromatic 

area by the sum of the aliphatic and aromatic area.

Table 2. 13C NMR chemical shifts of cellulose and of guaiacylpropanoid and syringylpropanoid lignin units where C-4 

is linked by an ether linkage to another phenylpropanoid unit (data from Hassi and others, 1987).

[ppm, parts per million]

Lignin

Guaiacylpropanoid

Lignin

Syringylpropanoid Cellulose

Chemical shift 

(ppm) Carbon atom

Chemical shift 

(ppm) Carbon atom

Chemical shift 

(ppm) Carbon atom

111 C-2 104 C-2, C-6 65 C-6

113 C-5 136 C-4 72-74 C-2,C-3,C-5

121 C-6 138 C-1 83-89 C-4

135 C-1 153 C-3, C-5 105 C-1

148 C-4

149 C-3

8 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
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Compositional and Porosity Changes 9
Table 3. Percentage aromatic carbon in chars after heating.

[

0

C, degrees Celsius; --, no data]

Preparation temperatures

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 5.3 percent) 

1 1.1 71.3 78.7 81.7 --

8 61.8 83.3 88.7 -- --

24 77.8 90.1 85.8 87.1 --

48 80.7 92.8 80.4 -- --

72 83.1 82.1 81.2 -- --

Lignin (unheated 49.2 percent)

1 -- 61.7 71.9 80.7 88.4

8 -- 66.4 85.1 91.3 91.6

24 57.3 77.5 87.1 87.2 --

48 -- 81.0 -- -- --

72 63.2 79.8 -- -- --

144 65.8 -- -- -- --

Poplar wood (unheated 16.8 percent)

1 22.1 48.8 80.3 83.6 95.3

8 54.4 80.9 86.4 -- --

24 78.9 86.4 84.5 -- --

48 84.0 88.6 -- -- --

72 -- 84.1 -- -- --

144 86.9 -- -- -- --

Pine wood (unheated 20.6 percent)

1 25.7 56.5 85.2 91.7 100

8 60.1 81.7 91.3 -- --

24 72.0 82.7 76.7 -- --

48 82.3 89.6 -- -- --

72 -- 84.6 -- -- --

168 85.1 -- -- -- --

Pine bark (unheated 35.1 percent)

1 39.8 62.0 79.1 -- --

8 62.0 72.2 85.8 -- --

24 66.8 72.7 80.4 -- --

48 -- 75.6 90.2 -- --

72 81.7 80.9 -- -- --

168 87.4 -- -- -- --

10 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
The data in table 3 show that the percentage of aromatic 

carbon increases for all samples with increasing heating temperature at any fixed heating time. Cellulose, pine and poplar 

woods, and pine bark all show a rapid increase in percentage 

of aromatic carbon in the first 8 hours of heating at 250oC 

and within the first hour of heating at 300oC. Lignin starts at 

a much higher aromatic carbon content in the unaltered state 

and shows more gradual increases with charring at 250oC 

and 300oC. Cellulose and both pine and poplar wood reach 

greater than 80 percent aromatic carbon at 250oC between 24 

and 48 hours. Pine bark reaches 80 percent aromatic carbon 

at 250oC between 24 and 72 hours. Lignin does not reach 

80 percent aromatic carbon at 250oC at any heating time up 

to 144 hours. At 300oC, cellulose and pine and poplar woods 

reach 80 percent aromatic carbon between 1 and 8 hours, and 

lignin reaches 80 percent aromatic carbon between 24 and 

48 hours heating. At 350oC, all samples have reached greater 

than 80 percent aromatic carbon by 8 hours. At temperatures 

above 400oC, all samples tested reached greater than 80 percent aromatic carbon by 1 hour.

Elemental Composition of Char

Cellulose and lignin samples did not contain substantial 

ash at any heating time or temperature. Unheated pine and 

poplar wood contained 0.54 and 0.53 percent ash respectively, 

with the highest ash content of char reaching approximately 

10 percent after heating pine wood for 24 hours at 350oC and 

poplar wood for 48 hours at the same temperature. Unheated 

pine bark contains 3.23 percent ash, which makes up 32 percent of the char when heated at 350oC for 48 hours.

The carbon contents of lignin, cellulose, pine wood, 

poplar wood, and pine bark and the chars produced from them, 

are shown in table 4. The data in table 4 have been normalized to a dry weight and ash-free basis. The percentage carbon 

in unheated cellulose is calculated to be 44.4 percent. With 

heating for 1 hour at 250oC the percentage carbon did not 

change. With heating for 1 hour at 300oC, 350oC, and 400oC, 

the percentage carbon in the char increased to about 73, 75, 

and 79 percent, respectively. With heating at 250oC for times 

greater than 1 hour, the percentage carbon increased to about 

65 percent. Longer heating at 300oC, 350oC, and 400oC did not 

cause any substantial change in percentage carbon.

The percentage carbon in unheated lignin is about 68 percent. With heating for 24 hours at 250oC and 1 hour at 300oC, 

350oC, 400oC, and 500oC, the percentage carbon in the char 

increased to about 72, 71, 74, 77, and 85 percent, respectively. 

Longer heating time did not cause any substantial change in 

percentage carbon in the char at any temperature.

The percentage carbon in unheated pine and poplar wood 

is about 51 and 50 percent, respectively. When pine wood is 

heated for 1 hour at 250oC, 300oC, 350oC, 400oC, and 500oC, 

the percentage carbon in the char increased to about 54, 69, 

76, 77, and 84 percent, respectively. With heating at 250oC for 

times greater than 1 hour, the percentage carbon increased to 

approximately 65 percent. Longer heating at 300oC and 350oC 

did not cause any substantial change in percentage carbon. 

Poplar wood behaves in a similar fashion.

The percentage carbon in unheated pine bark is about 

51 percent. With heating for 1 hour at 250oC, 300oC, and 

350oC, the percentage carbon in the char increased to about 

57, 66, and 68 percent, respectively. Longer heating at 250oC, 

300oC, and 350oC did not cause any substantial change in 

percentage carbon.

Normalized hydrogen percentages for starting materials 

and their chars are given in table 5. The percentage hydrogen 

in unheated cellulose is calculated to be about 6.2 percent. 

With heating for 1 hour at 250oC the percentage hydrogen 

did not change substantially. With heating for 1 hour at 

300oC, 350oC, and 400oC, the percentage hydrogen in the 

char decreased to about 4.0, 3.8, and 3.4 percent, respectively. 

Heating for times greater than 1 hour caused the percentage 

hydrogen to decrease for all temperatures.

The percentage hydrogen in unheated lignin is about 

5.8 percent. With heating for 24 hours at 250oC, and 1 hour at 

300oC, 350oC, 400oC, and 500oC, the percentage hydrogen in 

the char decreased to about 5.2, 5.2, 4.1, 3.5, and 2.9 percent, 

respectively. Longer heating caused further decrease in percentage hydrogen in the char for the temperatures studied.

The percentage hydrogen in unheated pine and poplar 

wood is about 6.3 percent and 6.1 percent, respectively. When 

pine wood is heated for 1 hour at 250oC, 300oC, 350oC, 400oC, 

and 500oC, the percentage hydrogen in the char decreased to 

about 5.9, 4.2, 3.2, 2.6, and 2.7 percent, respectively. With 

heating at 250oC, 300oC, and 350oC for times greater than 

24 hours, the percentage hydrogen decreased to between 1.8 

and 2.5 percent. Poplar wood behaved in a similar fashion.

The percentage hydrogen in unheated pine bark is about 

6.0 percent. With heating for 1 hour at 250oC, 300oC, and 

350oC, the percentage hydrogen in the char decreased to 

about 5.3, 4.3, and 3.7 percent, respectively. Longer heating at 

250oC, 300oC, and 350oC caused further decrease in percentage hydrogen to between 1.9 to 2.5 percent.

The percentage oxygen shown in table 6 has been estimated by difference, assuming that carbon, hydrogen, oxygen, 

and ash make up approximately 100 percent of the dry material. The percentage oxygen in unheated cellulose was calculated to be 49.4 percent. With heating for 1 hour at 250oC the 

percentage oxygen did not change substantially. With heating 

for 1 hour at 300oC, 350oC, and 400oC the percentage oxygen 

in the char decreased to 23.0, 20.9, and 18.1 percent, respectively. Heating for times greater than 1 hour at 250oC did not 

change the percentage oxygen substantially. Heating for longer 

than 1 hour at 300oC, 350oC, and 400oC caused the percentage 

oxygen to increase.

The percentage oxygen in unheated lignin is 26.7 percent. 

With heating for 24 hours at 250oC and 1 hour at 300oC, 

350oC, 400oC and 500oC, the percentage oxygen in the char 

decreased to 23.2, 23.6, 21.6, 19.8 and 12.6 percent, respectively. Longer heating causes a slight increase in percentage 

oxygen in the char for the temperatures studied.

Compositional and Porosity Changes 11
The percentage oxygen in unheated pine and poplar 

wood is 42.5 percent and 44.0 percent, respectively. When 

pine wood is heated for 1 hour at 250oC, 300oC, 350oC, 400oC 

and 500oC, the percentage oxygen in the char decreased to 

40.4, 26.6, 20.5, 20.0, and 13.3 percentage respectively. With 

heating at 250oC for times greater than 1 hour, the percentage 

oxygen decreased slightly. With heating at 300oC and 350oC 

for times greater than 1 hour, the percentage oxygen increased 

slightly. Poplar wood behaves in a similar fashion.

The percentage oxygen in unheated pine bark is 42.7 percent. With heating for 1 hour at 250oC, 300oC, and 350oC, the 

percentage oxygen in the char decreased to 37.3, 30.1, and 

28.0 percent, respectively. Longer heating at 300oC, and 350oC 

caused an increase in percentage oxygen.

12 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Table 4. Percentage carbon remaining in char after heating, normalized to a dry and ash-free basis.

[oC, degrees Celsius; --, no data]

Preparation Temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 44.4 percent)

1 44.1 73.0 75.4 78.5 --

8 65.1 71.0 74.3 -- --

24 63.7 69.3 69.2 72.0 --

48 64.5 65.4 66.2 -- --

72 63.3 64.4 65.3 -- --

Lignin (unheated 67.6 percent)

1 -- 71.2 74.3 76.7 84.6

8 -- 72.2 73.5 73.9 82.2

24 71.6 73.8 69.3 73.2 --

48 -- 71.2 67.6 -- --

72 70.3 69.9 66.3 -- --

144 70.0 -- -- -- --

Poplar wood (unheated 49.9 percent)

1 53.4 67.6 76.2 79.1 86.6

8 61.4 72.7 75.6 -- --

24 65.4 67.1 68.7 -- --

48 -- 65.4 65.3 -- --

72 65.5 66.0 -- -- --

144 64.2 -- -- -- --

Pine wood (unheated 51.2 percent)

1 53.7 69.1 76.2 77.4 84.0

8 63.0 71.2 69.8 -- --

24 65.4 67.1 68.9 -- --

48 65.5 67.3 -- -- --

72 -- 65.9 -- -- --

168 62.8 -- -- -- --

Pine bark (unheated 51.3 percent)

1 57.4 65.6 68.3 -- --

8 62.4 64.6 68.5 -- --

24 62.6 63.0 65.0 -- --

48 -- 60.2 52.0 -- --

72 60.1 57.2 -- -- --

168 59.2 -- -- -- --

Compositional and Porosity Changes 13
Table 5. Percentage hydrogen remaining in char after heating, normalized to a dry and ash-free basis.

[oC, degrees Celsius; --, no data]

Preparation temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 6.17 percent)

1 6.30 3.97 3.75 3.39 --

8 3.66 3.02 2.54 -- --

24 2.39 1.44 1.93 1.58 --

48 2.45 1.87 1.77 -- --

72 2.19 1.90 1.78 -- --

Lignin (unheated 5.78 percent)

1 -- 5.24 4.09 3.46 2.94

8 -- 4.68 2.99 2.32 2.25

24 5.23 3.97 1.77 1.02 --

48 -- 3.67 1.65 -- --

72 4.95 2.68 1.60 -- --

144 4.88 -- -- -- --

Poplar wood (unheated 6.06 percent)

1 5.66 4.65 3.30 2.82 2.62

8 4.11 2.98 2.66 -- --

24 2.60 1.94 2.13 -- --

48 -- 2.15 2.01 -- --

72 1.86 1.79 -- -- --

144 1.81 -- -- -- --

Pine wood (unheated 6.31 percent)

1 5.88 4.25 3.23 2.58 2.72

8 4.49 3.03 2.17 -- --

24 2.92 2.30 2.51 -- --

48 2.43 1.80 -- -- --

72 -- 2.10 -- -- --

168 2.15 -- -- -- --

Pine bark (unheated 5.97 percent)

1 5.28 4.32 3.74 -- --

8 3.92 3.29 3.27 -- --

24 3.18 2.85 2.86 -- --

48 -- 2.38 1.94 -- --

72 2.43 2.51 -- --

168 2.34 -- -- -- --

14 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Table 6. Percentage oxygen remaining in char after heating, determined by difference from ash, carbon and 

hydrogen content.

[oC, degrees Celsius; --, no data]

Preparation temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 49.4 percent)

1 49.6 23.0 20.9 18.1 --

8 31.2 26.0 23.1 -- --

24 33.9 29.3 28.9 26.4 --

48 33.0 32.8 32.0 -- --

72 34.5 33.7 32.9 -- --

Lignin (unheated 26.7 percent)

1 -- 23.6 21.6 19.8 12.5

8 -- 23.1 23.5 23.8 15.6

24 23.2 22.2 28.9 25.8 --

48 -- 25.1 30.8 -- --

72 24.7 27.5 32.1 -- --

144 25.2 -- -- -- --

Poplar wood (unheated 44.0 percent)

1 40.9 27.8 20.5 18.0 10.8

8 34.5 24.3 21.7 -- --

24 32.0 30.9 29.2 -- --

48 -- 32.5 32.6 -- --

72 32.7 32.3 -- -- --

144 34.0 -- -- -- --

Pine wood (unheated 42.5 percent)

1 40.4 26.6 20.5 20.0 13.3

8 32.5 25.7 28.0 -- --

24 31.7 30.6 28.5 -- --

48 32.0 30.9 -- -- --

72 -- 32.0 -- -- --

168 35.0 -- -- -- --

Pine bark (unheated 42.7 percent)

1 37.3 30.1 28.0 -- --

8 33.7 32.1 28.2 -- --

24 34.2 34.1 32.1 -- --

48 -- 37.4 46.0 -- --

72 37.5 40.3 -- -- --

168 38.5 -- -- -- --

Compositional and Porosity Changes 15
Hydrogen/Carbon Ratios and Oxygen/Carbon 

Ratios of Chars

The hydrogen/carbon (H/C) atomic ratios and oxygen/

carbon (O/C) atomic ratios of the chars, listed in table 7, show 

the evolution of the char with time and temperature treatments 

on a molar basis. The increase in concentration of fused-ring 

aromatic structures with heating time and temperature for the 

charcoal samples from cellulose, lignin, and the charred wood 

and bark samples that was demonstrated by the NMR analyses 

also was supported by the elemental composition data. The 

H/C atomic ratios decrease with duration of heating and heating temperature (table 7). Ratios less than one are indicative 

of fused-ring aromatic structures in which only the peripheral 

carbon atoms are protonated (Yang and others, 2002). Song 

and others (2002) isolated BC from soils and sediments from 

suburban Guangzhou City, China, by using a wet chemical 

oxidation procedure. The H/C ratios of their BC samples from 

soils and sediments varied from 0.5 to 0.71. In addition, they 

measured a H/C ratio of 0.37 for char they produced by heating “arbor wood” in a kiln.

The chars produced in this study, regardless of starting 

material, evolved with time into a fairly uniform elemental composition. Cellulose and both pine and poplar woods 

developed H/C ratios of 0.3 to 0.4 and O/C ratios of 0.1 to 0.4 

for temperatures from 250oC to 500oC. Lignin did not substantially alter at 250oC. For temperatures from 300oC to 500oC, 

lignin developed H/C ratios of 0.3 to 0.5 and O/C ratios of 0.1 

to 0.4. For temperatures from 300oC to 350oC, pine bark developed a H/C ratio of 0.5, and O/C ratios of 0.5 to 0.7.

Aromatic and Aliphatic Carbon Content of Chars

The NMR spectra showed an increase in percentage 

aromatic carbon that can be caused either by the formation of 

aromatic carbon in the charring process or by the preferential 

removal of aliphatic components during the charring process. 

Further insight into this process can be gained by transforming the percentage carbon data into grams of aromatic carbon 

or aliphatic carbon per 100 grams of starting material. This 

was done by multiplying the percentage carbon from table 4 

by the fraction of aromatic carbon or aliphatic carbon in the 

char (from table 3) and by the fraction of char remaining (from 

table 1). These data are presented in table 8 and in figures 3-7.

At 250oC, the total mass of aromatic carbon in cellulose 

and both wood samples and the pine bark increased during the 

first 8 to 24 hours of heating and decreased only slightly with 

longer heating durations. Lignin showed a slight increase in 

aromatic carbon throughout the heating periods studied. This 

shows that at this temperature there is formation of aromatic 

carbon from aliphatic carbon and little or no decomposition of 

the aromatic components. At 300oC, the total mass of aromatic carbon in cellulose and both wood samples increased 

with heating for 8 hours and then decreased more rapidly with 

further heating than observed at 250oC. Pine bark increased 

in aromatic carbon only for the first hour and then decreased. 

Aromatic carbon in lignin continued to increase for 24 hours 

and then decreased. At 350oC and above, all samples showed 

a more rapid decrease in aromatic carbon after the first hour of 

heating.

Aliphatic carbon content decreased with increased heating temperature with the rate of loss increasing with increasing 

heating temperature.

H/C and O/C Atomic Ratios of Material Lost from 

Char

The change in the percentage of carbon, hydrogen, and 

oxygen in the char indicated that these elements were leaving 

the char at different rates. When the elemental composition 

in tables 4–6 are multiplied by the fraction of char remaining (table 1), an estimate is made of the elemental composition normalized to 100 g of starting material. From this, an 

estimate of elemental loss can be made for each time interval 

of heating. Table 9 shows the H/C and O/C atomic ratios of 

material lost during heating. Ratios greater than 1 show when 

hydrogen and oxygen are being lost at a greater rate than 

carbon.

For heating of cellulose, wood, and bark at 250oC, the 

loss of hydrogen exceeds carbon loss for the first 24 hours 

by as much as 8 to 1. After 24 hours, the loss of hydrogen 

equals or is less than the loss of carbon. For lignin the loss of 

hydrogen exceeds the loss of carbon for all intervals of heating 

at 250oC. The duration during which hydrogen loss exceeds 

carbon loss becomes shorter at higher temperatures. With 

increased heating time, at any temperature the ratio decreases 

and more closely equals that of the char material.

Oxygen loss for all materials and temperatures, except for 

lignin at 250oC, is at a maximum within the first 8 hours and 

then decreases to a ratio that resembles the ratio in the char.

The H/C and O/C ratios of material lost are consistent 

with the data presented on the composition of the char, which 

indicate that aliphatic matter is lost early in the charring 

process and at increasing rates with increasing temperature, 

and that the aliphatic components are lost before the aromatic 

components start to degrade.

16 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Table 7. Hydrogen/carbon atomic ratios and oxygen/carbon atomic ratios of chars.

[oC, degrees Celsius; --, no data. The oxygen/carbon ratios are in brackets.]

Preparation temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 1.7 [0.8])

1 1.7 [0.8] 0.7 [0.2] 0.6 [0.2] 0.5 [0.2] --

8 0.7 [0.4] 0.5 [0.3] 0.4 [0.2] -- --

24 0.5 [0.4] 0.3 [0.3] 0.3 [0.3] 0.3 [0.3] --

48 0.7 [0.4] 0.3 [0.4] 0.3 [0.4] -- --

72 0.4 [0.4] 0.4 [0.4] 0.3 [0.4] -- --

Lignin (unheated 1.0 [0.3])

1 -- 0.9 [0.3] 0.7 [0.2] 0.5 [0.2] 0.4 [0.1]

8 -- 0.8 [0.2] 0.5 [0.2] 0.4 [0.2] 0.3 [0.1]

24 0.9 [0.2] 0.6 [0.2] 0.3 [0.3] 0.2 [0.3] --

48 -- 0.6 [0.3] 0.3 [0.3] -- --

72 0.9 [0.3] 0.5 [0.3] 0.3 [0.4] -- --

144 0.9 [0.3] -- -- -- --

Poplar wood (unheated 1.5 [0.7])

1 1.2 [0.6] 0.8 [0.3] 0.5 [0.2] 0.4 [0.2] 0.4 [0.1]

8 0.8 [0.4] 0.5 [0.3] 0.4 [0.2] -- --

24 0.5 [0.4] 0.4 [0.4] 0.4 [0.3] -- --

48 -- 0.4 [0.4] 0.4 [0.4] -- --

72 0.3 [0.4] 0.3 [0.7] -- -- --

144 0.3 [0.4] -- -- -- --

Pine wood (unheated 1.5 [0.6])

1 1.3 [0.6] 0.7 [0.3] 0.5 [0.2] 0.4 [0.2] 0.4 [0.1]

8 0.9 [0.4] 0.5 [0.3] 0.4 [0.3] -- --

24 0.5 [0.4] 0.4 [0.3] 0.4 [0.3] -- --

48 0.4 [0.4] 0.3 [0.3] -- -- --

72 -- 0.4 [0.4] -- -- --

168 0.4 [0.4] -- -- -- --

Pine bark (unheated 1.4 [0.6])

1 1.1 [0.5] 0.8 [0.3] 0.7 [0.3] -- --

8 0.8 [0.4] 0.6 [0.4] 0.6 [0.3] -- --

24 0.6 [0.4] 0.5 [0.4] 0.5 [0.4] -- --

48 -- 0.5 [0.5] 0.5 [0.7] -- --

72 0.5 [0.5] 0.5 [0.5] -- -- --

168 0.5 [0.5] -- -- -- --

Compositional and Porosity Changes 17
Table 8. Grams of aromatic carbon or aliphatic carbon in char per 100 grams of starting material.

[oC, degrees Celsius; --, no data. The grams of aliphatic carbon are in brackets.]

Preparation temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 0.0 [44.4])

1 0.45 [40.8] 17.3 [6.98] 16.5 [4.46] 14.3 [3.20] --

8 17.8 [11.0] 18.2 [3.63] 15.5 [1.98] -- --

24 17.5 [5.00] 17.0 [1.86] 11.2 [1.86] 4.89 [1.73] --

48 18.1 [4.33] 14.5 [1.12] 6.82 [1.66] -- --

72 16.5 [3.37] 11.7 [2.56] 4.78 [1.11] -- --

Lignin (unheated 33.3 [34.3])

1 -- 33.7 [20.9] 34.4 [13.4] 32.1 [7.67] 29.1 [3.81]

8 -- 33.6 [17.0] 34.6 [6.06] 25.8 [2.46] 14.4 [1.32]

24 34.7 [25.9] 38.8 [11.2] 24.9 [3.67] 9.95 [1.46] --

48 -- 36.7 [8.61] 18.4 [3.81] -- --

72 35.8 [20.9] 33.0 [8.38] 13.7 [2.12] -- --

144 36.8 [19.2] -- -- -- --

Poplar wood (unheated 8.35 [41.3])

1 8.92 [31.4] 13.6 [14.3] 16.4 [4.02] 14.9 [2.93] 13.0 [0.64]

8 14.1 [11.8] 16.2 [3.81] 13.1 [2.06] -- --

24 19.6 [5.22] 12.5 [1.95] 6.39 [1.17] -- --

48 -- 10.5 [1.35] -- -- --

72 18.0 [3.43] 8.54 [1.61] -- -- --

144 16.4 [2.47] -- -- -- --

Pine wood (unheated 10.5 [40.4])

1 10.9 [31.5] 16.4 [12.7] 17.2 [2.99] 15.8 [1.43] 11.5 [0.0]

8 21.0 [13.9] 19.0 [4.25] 13.2 [1.26] -- --

24 20.2 [7.88] 13.7 [2.88] 2.43 [0.74] -- --

48 19.3 [4.17] 11.8 [1.37] -- -- --

72 -- 9.41 [1.71] -- -- --

168 16.0 [2.8] -- -- -- --

Pine bark (unheated 17.5 [32.2])

1 16.1 [24.3] 20.7 [12.7] 22.5 [5.93] -- --

8 22.1 [13.6] 20.8 [8.01] 17.8 [2.93] -- --

24 20.5 [10.2] 14.2 [5.34] 8.71 [2.13] -- --

48 -- 9.97 [3.23] 2.90 [0.32] -- --

72 19.4 [4.35] 7.05 [1.67] -- -- --

168 16.2 [2.35] -- -- -- --

18 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
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Compositional and Porosity Changes 19
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Figure 4. Calculated aromatic and aliphatic carbon content (grams carbon/100 grams starting material) in lignin and lignin 

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20 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
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Figure 5. Calculated aromatic and aliphatic carbon content (grams carbon/100 grams starting material) in poplar wood and 

chars at various heating times and temperatures.

Compositional and Porosity Changes 21
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Figure 6. Calculated aromatic and aliphatic carbon content (grams carbon/100 grams starting material) in pine wood and 

chars at various heating times and temperatures.

22 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
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Figure 7. Calculated aromatic and aliphatic carbon content (grams carbon/100 grams starting material) in pine bark and chars at 

various heating times and temperatures.

Compositional and Porosity Changes 23
Table 9. Hydrogen/carbon atomic ratios and oxygen/carbon atomic ratios of material lost from char during heating intervals.

[oC, degrees Celsius; --, no data. The oxygen/carbon ratios are in brackets.]

Preparation temperature

Time interval 

(hours) 250oC 300oC 350oC 400oC 500oC

Cellulose

0-1 1.0 [0.7] 2.9 [1.6] 2.6 [1.4] 2.4 [1.27] --

1-8 3.5 [1.7] 2.0 [0.0] 1.4 [0.1] -- --

8-24 1.7 [0.2] 1.4 [0.1] 0.7 [0.0] 0.6 [0.1] --

24-48 0.6 [0.1] 0.0 [0.0] 0.4 [0.2] -- --

48-72 0.8 [0.2] 0.3 [0.2] 0.3 [0.3] -- --

Lignin 

0-1 -- 1.6 [0.5] 1.9 [0.5] 1.7 [0.4] 1.6 [0.5]

1-8 -- 2.2 [0.4] 1.6 [0.1] 0.9 [0.1] 0.5 [0.1]

8-24 2.3 [0.8] [1.5] 0.9 [0.1] 0.5 [0.2] --

48-72 -- 0.8 [0.0] 0.3 [0.2] -- --

0-1 1.3 [0.0] 2.1 [0.0] 0.3 [0.3] -- --

72-144 1.4 [0.0] -- -- -- --

Poplar wood 

0-1 2.3 [1.0] 2.3 [1.1] 2.1 [1.0] 2.0 [0.9] 1.9 [0.9]

1-8 2.1 [0.8] 1.7 [0.5] 0.8 [0.2] -- --

8-24 8.4 [1.7] 0.9 [0.0] 0.5 [0.1] -- --

24-48 -- 0.1 [0.2] 0.4 [0.3] -- --

48-72 1.3 [0.3] 0.8 [0.4] -- -- --

72-144 0.4 [0.2] -- -- -- --

Pine wood 

0-1 2.3 [0.9] 2.7 [1.1] 2.1 [0.9] 2.0 [0.8] 1.8 [0.7]

1-8 3.5 [1.4] 1.6 [0.4] 0.8 [0.0] -- --

8-24 2.2 [0.5] 0.8 [0.1] 0.4 [0.3] -- --

24-48 1.0 [0.4] 0.8 [0.3] -- -- --

48-72 -- 0.0 [0.2] -- -- --

72-168 0.6 [1.6] -- -- -- --

Pine bark 

0-1 2.7 [1.2] 2.5 [1.2] 2.4 [1.1] -- --

1-8 3.1 [1.0] 1.3 [0.3] 0.8 [0.3] -- --

8-24 1.8 [0.4] 0.8 [0.3] 0.6 [0.3] -- --

24-48 -- 0.7 [0.2] 0.6 [0.3] -- --

48-72 0.9 [0.3] 0.4 [0.4] -- -- --

72-168 0.6 [0.4] -- -- -- --

24 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Surface Area and Porosity Changes

The porosity and surface areas measurements for the 

chars examined in this study are given in tables 10–12. The 

surface areas are determined by the N2 BET method, which 

uses the nitrogen uptake in the partial pressure range of 0.05 to 

0.3 in its calculation. If micropores (pores with a diameter less 

than 2 nm) are present, they will fill in this partial pressure 

range, which will add to the nitrogen uptake on surfaces and 

confound the surface area calculation. Therefore, if microporosity is determined to be present by using the t-method, it 

is more accurate to examine the porosity directly than to rely 

on the apparent surface area calculated by the BET method. 

There is a 0.99 correlation between the micropore volume 

and the apparent BET surface area showing that the development of micropores is primarily responsible for the dramatic 

differences in apparent surface areas for these chars. The 

development of porosity can be used as a gage for structural 

changes occurring during the charring process; however, to be 

measured by nitrogen uptake, the pores must be accessible to 

nitrogen.

The cellulose used in this study had a micropore volume 

of less than the detection limit of 0.001 cm3/g. At 250oC, the 

micropore volume remained low, at or near the detection level 

for times up to 144 hours. At 300oC, the micropore volume 

was below the detection level for 1 hour of heating but rose 

to 0.069 cm3/g when heated for 8 hours and to 0.080 cm3/g 

with heating for 24 hours. At 350oC, the micropore volumes 

were 0.026, 0.169, and 0.235 cm3/g when heated for 1, 8, 

and 24 hours, respectively. At 400oC, the micropore volumes 

were 0.070 and 0.308 cm3/g after heating for 1, and 24 hours, 

respectively.

The lignin used in this study had a micropore volume of 

less than the detection limit. At 250oC for heating times up 

to 144 hours, and at 300oC for heating times up to 24 hours, 

the micropore volume remained below the detection level. At 

300oC for heating times of 48 and 72 hours, the micropore 

volumes were 0.043 and 0.072 cm3/g, respectively. At 350oC, 

the micropore volumes were <0.001, 0.070, and 0.222 cm3/g 

when heated for 1, 8, and 24 hours, respectively. At 400oC, 

the micropore volumes were <0.001, 0.201, and 0.306 cm3/g 

when heated for 1, 8, and 24 hours, respectively. At 500oC, the 

micropore volumes were 0.079, and 0.209 cm3/g when heated 

for 1, and 8 hours, respectively.

Both cellulose and lignin show similar trends of increasing micropore volume with increasing heating time at a fixed 

temperature or increasing temperature at a fixed heating time, 

once the micropores start to develop. The point at which the 

microporosity develops is delayed for lignin compared to cellulose, which is consistent with the observation that cellulose 

decomposes at a lower temperature than lignin. The micropore 

volume for cellulose and lignin converge with time and are 

similar after 24 hours heating (0.235 and 0.222 cm3/g, respectively at 350oC, and 0.308 and 0.306 cm3

/g, respectively at 

400oC), indicating that both are developing the same structure 

with charring.

Both charred pine and poplar wood behaved in a similar 

manner to charred cellulose as to the development of microporosity with time and temperature of charring. Both species 

had micropore volumes below or near the detection limit for 

times up to 144 hours at 250oC, and for one hour heating at 

300oC. Both species showed rapid increase in microporosity 

between 1 and 8 hours heating at 300oC. Both pine and poplar 

initially developed greater microporosity than cellulose, but 

both woods decreased in microporosity with prolonged heating (after 24 hours for pine, and 48 hours for poplar). After 

24 hours heating at 350oC, both pine and poplar had micropore 

volumes similar to cellulose and lignin (0.244, 0.257, 0.235, 

and 0.222 cm3/g, respectively).

Pine bark showed similar trends as pine wood, but in all 

cases once microporosity was detected, charred pine bark had 

substantially less porosity than charred pine wood.

Porous carbons have been divided into two different 

categories: graphitizable carbon and nongraphitizable carbon (Byrne and Marsh, 1995). In both categories the carbon 

atoms are arranged in fused hexagonal rings similar to those in 

graphite. In graphite, the fused rings are arranged in continuous sheets that are stacked one on top of another to form a 

three-dimensional crystalline structure. In nongraphitizable 

carbon; however, the fused-ring sheets are stacked in small 

crystallites that are randomly oriented. Graphitizable porous 

carbons, in contrast to nongraphitizable porous carbon, will 

form a graphite-like material when heated to high temperatures. At elevated temperatures, the crystallites in graphitizable 

carbon reorient themselves such that the sheets in all of the 

crystallites are parallel one to another, thereby forming continuous sheets as in graphite. This reorientation destroys the 

porosity of the carbon. In nongraphitizable carbon this reorientation does not take place and porosity is preserved. The chars 

produced from wood and bark are nongraphitizable.

Franklin (1951) has shown that the reorientation of the 

crystallites in nongraphitizable carbons is impeded by “strong 

cross-linking between neighboring crystallites and by their 

random orientation.” Franklin (1951) observed that nongraphitizable carbons form from materials that are high in oxygen. 

She postulated that as the graphite-like crystallites form 

in these high-oxygen materials, strong cross-links develop 

between the crystallites that maintain their random orientation. The random orientation of the crystallites leaves voids 

between the crystallites that constitute the porosity of the char. 

Char from wood is considered to be nongraphitizing carbon. The wood or wood components do not contain measurable porosity but develop this porosity during charring. These 

materials do not develop porosity with charring at 250oC and 

for times less than 1 hour at 300oC. The NMR and the FTIR 

spectra and the yield and elemental data show substantial 

change in the composition of the char occurring at 250oC. 

These results show the formation of aromatic carbon from aliphatic carbon and the loss of mass. This lost mass has a higher 

hydrogen and oxygen content than the char. This is consistent 

with the loss of aliphatic components. It is possible that structural changes may be taking place that produce micropores, 

Compositional and Porosity Changes 25
but these micropores may be filled with condensable degradation products or enclosed by impermeable material, which prevents nitrogen from entering the pore. If this is occurring, long 

charring times do not remove this material. The appearance of 

porosity does coincide with the loss of aromatic carbon, which 

indicates that porosity does not develop until after the conversion of aliphatic to aromatic carbon has ceased and aromatic 

carbon is being removed. This is consistent with the fused-ring 

aromatic carbon providing the rigid structure within which the 

micropores can develop.

26 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Table 10. Micropore volume in char after heating.

[Volume units: cubic centimeter per gram (cm3/g); oC, degrees Celsius; <, less than; --, no data]

Preparation temperature

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated <0.001)

1 <0.001 0.001 0.026 0.070 --

8 <0.001 0.069 0.169 -- --

24 0.001 0.080 0.235 0.308 --

48 0.002 0.048 0.212 -- --

72 0.002 0.012 0.199 -- --

Lignin (unheated <0.001)

1 -- <0.001 <0.001 <0.001 0.079

8 -- <0.001 0.070 0.201 0.209

24 <0.001 <0.001 0.222 0.306 --

48 -- 0.043 0.237 -- --

72 <0.001 0.072 0.225 -- --

144 <0.001 -- -- -- --

Poplar wood (unheated <0.001)

1 <0.001 <0.001 0.060 0.067 0.138

8 0.010 0.123 0.181 -- --

24 <0.001 0.140 0.257 -- --

48 -- 0.143 -- -- --

72 <0.001 0.052 -- -- --

144 <0.001 -- -- -- --

Pine wood (unheated <0.001)

1 <0.001 0.002 0.119 0.143 0.253

8 <0.001 0.123 0.265 -- --

24 0.001 0.205 0.244 -- --

48 0.001 0.121 -- -- --

72 -- 0.084 -- -- --

168 0.001 -- -- -- --

Pine bark (unheated <0.001)

1 <0.001 <0.001 0.012 -- --

8 <0.001 0.069 0.062 -- --

24 0.001 0.093 0.110 -- --

48 -- 0.112 0.098 -- --

72 0.001 0.100 -- -- --

168 0.001 -- -- -- --

Compositional and Porosity Changes 27
Table 11. Total pore volume in char after heating.

[Volume units: cubic centimeter per gram (cm3/g); oC, degrees Celsius; <, less than; --, no data;]

Preparation temperature 

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 0.005)

1 0.005 0.003 0.034 0.087 --

8 0.004 0.089 0.210 -- --

24 0.004 0.122 0.256 0.334 --

48 0.005 0.081 0.239 -- --

72 0.005 0.020 0.225 -- --

Lignin (unheated 0.001)

1 -- <0.001 <0.001 0.002 0.095

8 -- <0.001 0.077 0.216 0.232

24 <0.001 <0.001 0.243 0.341 --

48 -- 0.048 0.260 -- --

72 <0.001 0.085 0.253 -- --

144 <0.001 -- -- -- --

Poplar wood (unheated 0.003)

1 0.002 0.002 0.069 0.077 0.163

8 0.014 0.145 0.204 -- --

24 0.002 0.167 0.291 -- --

48 -- 0.172 -- -- --

72 0.002 0.088 -- -- --

144 0.002 -- -- -- --

Pine wood (unheated 0.004)

1 0.002 0.005 0.133 0.189 0.286

8 0.002 0.140 0.297 -- --

24 0.002 0.227 0.295 -- --

48 0.002 0.149 -- -- --

72 -- 0.106 -- -- --

168 0.002 -- -- -- --

Pine bark (unheated 0.004)

1 0.001 0.002 0.016 -- --

8 0.002 0.081 0.079 -- --

24 0.002 0.112 0.142 -- --

48 -- 0.142 0.158 -- --

72 0.003 0.143 -- -- --

168 0.004 -- -- -- --

28 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Table 12. Surface area in char after heating.

[Area units: square meter per gram (m2/g); oC, degrees Celsius; <, less than; --, no data;]

Preparation temperature 

Time (hours) 250oC 300oC 350oC 400oC 500oC

Cellulose (unheated 2.14)

1 1.55 2.88 54.9 147 --

8 3.06 145 362 -- --

24 3.59 189 461 602 --

48 3.99 122 422 -- --

72 3.73 29.7 397 -- --

Lignin (unheated <1)

1 -- <1 <1 2.03 162

8 -- <1 138 394 418

24 <1 <1 440 614 --

48 -- 84.5 471 -- --

72 <1 146 454 -- --

144 <1 -- -- -- --

Poplar wood (unheated 1.46)

1 <1 1.40 136 172 354

8 21.7 250 359 -- --

24 2.20 288 509 -- --

48 -- 293 -- -- --

72 2.17 133 -- -- --

144 2.10 -- -- -- --

Pine wood (unheated 2.00)

1 <1 4.90 214 301 501

8 1.20 246 517 -- --

24 2.00 401 486 -- --

48 1.00 211 -- -- --

72 -- 176 -- -- --

168 2.11 -- -- -- --

Pine bark (unheated 2.22)

1 <1 1.00 24.2 -- --

8 1.32 140 127 -- --

24 2.68 190 226 -- --

48 -- 234 213 -- --

72 3.40 216 -- -- --

168 3.03 -- -- -- --

Compositional and Porosity Changes 29
Summary

The purpose of the study described in this report was to 

examine the compositional and structural changes occurring 

during the thermal degradation of wood and wood components. Pine and poplar wood, pine bark, and purified cellulose and lignin were studied. Charring temperatures from 

250oC to 500oC were used with charring times from 1 hour to 

168 hours. The two major components in wood are cellulose 

and lignin, with cellulose making up approximately two thirds 

and lignin making up about one third of the mass. The changes 

that each of these two components undergo during heating 

allow us to better understand the changes that take place when 

wood and bark are heated.

Cellulose showed substantial weight loss with charring at 

250oC, with 60 percent loss between 1 and 8 hours of heating. At higher temperatures, most of the weight loss occurred 

within the first hour of heating. Lignin char retained 80 percent of its original mass when heated at 250oC for 144 hours, 

indicating that very little degradation of lignin has occurred. 

The percentage char remaining after heating of lignin for 

72 hours at 300oC was approximately 60 percent. Higher 

temperatures increased the rate of weight loss with 80 to 

85 percent loss after 24 hours at 400oC and 8 hours at 500oC. 

Both pine and poplar wood showed mass loss comparable to 

cellulose with charring at 250oC and 300oC. At 350oC, both 

woods showed greater mass loss than cellulose for heating 

times in excess of 8 hours. Pine bark showed slightly less mass 

loss than pine wood at all charring times and temperatures. 

This difference became more pronounced as the temperature 

increased to 300oC and 350oC.

At 250oC for heating times of 1 hour, neither the 13C 

nuclear magnetic resonance nor Fourier Transform Infrared spectra showed much change in composition for any of 

the materials tested. For longer heating at 250oC, cellulose 

showed substantial decomposition while lignin showed little 

degradation. The changes in cellulose indicate the loss of 

aliphatic components and the formation of aromatic components. For the wood and bark samples, heating for 8 hours at 

250oC showed the aliphatic components reduced, the aromatic 

content increased, and the lignin signature more pronounced. 

After 24 hours of heating at 250oC for the wood and bark 

samples, the lignin signature and the aliphatic components 

were greatly reduced, and aromatic carbon remained as the 

primary residual carbon. At 300oC, degradation of lignin was 

apparent from NMR and IR spectra, with loss of aliphatic 

components progressing for 72 hours. The degradation of cellulose, wood, and bark occurred more rapidly at 300oC than at 

250oC. Temperatures higher than 300oC caused acceleration of 

the degradation of all the test materials.

The elemental analyses for carbon, hydrogen, and oxygen 

of uncharred and charred materials showed an increase in 

percentage carbon, a decrease of percentage hydrogen, and 

a decrease in percentage oxygen, with charring for all tested 

materials. Analysis of the hydrogen/carbon and oxygen/carbon atomic ratios for the residual char and for the material 

lost from the char showed that hydrogen and oxygen were 

lost more rapidly than carbon from the char during the initial 

periods of charring. This is consistent with the initial loss of 

aliphatic carbon, either to volatile degradation products or the 

conversion of aliphatic carbon to fused aromatic rings.

Combining the fraction of initial mass remaining with the 

fraction carbon and percentage aromatic or aliphatic carbon 

was done to calculate the mass of aromatic or aliphatic carbon 

remaining per 100 g of starting material. This analysis showed 

that at 250oC, all materials tested lost aliphatic carbon for all 

time intervals, while aromatic carbon initially increased and 

then remained relatively constant with little loss. At higher 

temperatures, the loss of aliphatic carbon was accelerated for 

all test materials, and after an initial period of aromatic carbon 

increase, there was loss of aromatic carbon.

No porosity developed in any of the tested materials when charred at 250oC. Porosity appeared for cellulose, 

wood, and bark samples when charred at 300oC between 1 and 

8 hours. Porosity appeared in lignin when charred at 300oC 

between 24 and 48 hours. For a fixed charring time, porosity generally increased with charring temperature. For a fixed 

charring temperature, porosity generally increased to a maximum and then decreased.

The relation between structural changes, as measured 

by the development of porosity and the observed compositional changes, was not well defined for any single parameter 

measured. Decomposition, as measured by mass loss and 

decrease in H/C and O/C ratios and changes in IR and NMR 

spectra occurred at temperatures of 250oC and above for cellulose, pine and poplar wood, and pine bark, and at temperatures above 300oC for lignin. These changes in composition 

varied continuously with time, while the increase in porosity appeared suddenly and showed a maximum, after which 

porosity decreased with time. The measure of aromatic carbon 

mass as determined by NMR spectra, elemental composition, 

and mass loss, provided the best predictor of changes in porosity. The charring process appeared to initially create aromatic 

carbon from aliphatic carbon, forming fused ring structures, 

which provide a matrix in which microporosity can develop. 

It was not until the total mass of aromatic carbon started to 

decrease that porosity began to develop. The formation of 

fused-ring structures occurs at 250oC for cellulose, wood, and 

bark, but no porosity develops, even for long heating times 

that would be expected to volatilize degradation products 

that could be filling pores. This indicates that it is the loss of 

aromatic carbon that creates the micropores in the fused-ring 

matrix. There was some indication that prolonged heating may 

cause fused-ring structures to coalesce and reduce porosity.

30 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Literature Cited

Allan, G.G., 1971, Modification reactions, in Sarkanen, K.V., 

and Ludwig, C.H., eds., Lignins—Occurrence, formation, 

structure and reactions: New York, Wiley-Interscience, 

p. 511-573.

Amen-Chen, Carlos, Pakdel, Hooshang, and Roy, Christian, 

2001, Production of monomeric phenols by thermochemical 

conversion of biomass—A review: Bioresource Technology, 

v. 79, p. 277-299.

Baldock, J.A., and Smernik, R.J., 2002, Chemical composition 

and bioavailability of thermally altered Pinus resinosa (Red 

pine) wood: Organic Geochemistry, v. 33, p. 1093–1109.

Brunauer, S., Emmett P.H., and Teller, E., 1938, Adsorption 

of gases in multimolecular layers: Journal of the American 

Chemical Society, v. 60, p. 309–319.

Byrne, J.F., and Marsh, Harry, 1995, Introductory overview, 

in Patrick, J.W., ed., Porosity in carbons—Characterization 

and applications: New York, Halsted Press, p. 2–48.

Cambardella, C.A., and Elliot, E.T., 1992, Particulate soil 

organic-matter changes across a grassland cultivation 

sequence: Soil Science Society of America Journal, v. 56, 

p. 777–783.

Chen, Runying, and Jakes, K.A., 2002, Effects of pressing on 

the infrared spectra of single cotton fibers: Applied Spectroscopy, v. 56, p. 646–650.

Colthup, N.B., Daly, L.H., and Wiberley, S.E., 1990, Introduction to infrared and raman spectroscopy: Boston, Academic 

Press, 547 p.

Croteau, Rodney, Kutchan, T.M., and Lewis, N.G., 2000, 

Natural products (secondary metabolites), in Buchanan, 

B.B., Gruissem, Wilhelm, and Jones, R.L., eds., Biochemistry & molecular biology of plants: Rockville, Maryland, 

American Society of Plant Physiologists (distributed by 

John Wiley & Sons, Inc.), p. 1250–1318.

de Boer, J.H., Lippens, B.C., Linsen, B.G., Broekhoff, J.C.P., 

van den Heuvel, A., and Osinga, T.J., 1966, The t-curve of 

multilayer N2-adsorption: Journal of Colloid and Interface 

Science, v. 21, p. 405–414.

Faix, O., 1991, Classification of lignins from different botanical origins by FTIR spectroscopy: Holzforschung, v. 45, 

Supplement, p. 21–27.

Franklin, R.E., 1951, Crystallite growth in graphitizing and 

non-graphitizing carbons: Proceedings of the Royal Society, 

v. A209, p. 196–218.

Gelinas, Yves, Prentice, K.M., Baldock, J.A., and Hedges, 

J.J., 2001, An improved thermal oxidation method for the 

quantification of soot/graphitic black carbon in sediments 

and soils: Environmental Science and Technology, v. 35, 

p. 3519–3525.

Gil, A.M., Lopes, M., Rocha, J., and Neto, C.P., 1997, A 13C 

solid state nuclear magnetic resonance spectroscopic study 

of cork cell wall structure—The effect of suberin removal: 

International Journal of Biological Macromolecules, v. 20, 

p. 293–305.

Glaser, Bruno, Haumaier, Ludwig, Guggenberger, Georg, and 

Zech, Wolfgang, 2001, The “Terra Preta” phenomenon: 

A model for sustainable agriculture in the humid tropics: 

Naturwissenschaften, v. 88, p. 37–41.

González-Vila, F.J., Tinoco, Pilar, Almendros, Gonzalo, and 

Martin, Francisco, 2001, Pyrolysis-GC-MS analysis of the 

formation and degradation stages of charred residues from 

lignocellulosic biomass: Journal of Agricultural and Food 

Chemistry, v. 49, p. 1128–1131.

Hassi, H.Y., Aoyama, M., Tai, D., Chen, C.-L., and Gratzl, 

J.S., 1987, Substituent effects on 13C chemical shifts of 

aromatic carbons in ß-O-4 and ß-5 type lignin model compounds: Journal of Wood Chemistry and Technology, v. 7, 

555–581.

Haw, J.F., and Schultz, T.P., 1985, Carbon-13 CP/MAS NMR 

and FTIR study of low-temperature lignin pyrolysis: Holtzforschung, v. 39, p. 289–296.

Jorge, Miguel, Schumacher, Christian, and Seaton, N.A., 2002, 

Simulation study of the effect of the chemical heterogeneity 

of activated carbon on water adsorption: Langmuir, v. 18, 

p. 9296–9306.

Karapanagiotti, H.K., Kleineidam, Sybille, Sabatini, D.A., 

Grathwohl, Peter, and Ligouis, Bertrand, 2000, Impacts of 

heterogeneous organic matter on phenanthrene sorption: 

Equilibrium and kinetic studies with aquifer material: Environmental Science and Technology, v. 34, p.406–414

Larsson, P.T., Hult, E.-L., Wickholm, Kristina, Pettersson, 

Erik, and Iversen, Tommy, 1999, CP/MAS 13C-NMR 

spectroscopy applied to structure and interaction studies of 

cellulose I: Solid State Nuclear Magnetic Resonance, v. 15, 

p. 31–40.

Pastorova, Ivana, Botto, R.E., Arisz, P.W., and Boon, J.J., 

1994, Cellulose char structure: A combined analytical PyGC-MS, FTIR, and NMR study: Carbohydrate Research, 

v. 262, p. 27–47.

Patrick, J.W., 1995, Porosity in carbons—Characteristics and 

applications: New York, Halsted Press, 331 p.

Literature Cited 31
Pradhan, B.K., and Sandle, N.K., 1999, Effect of different 

oxidizing agent treatments on the surface properties of activated carbons: Carbon, v. 37, p. 1323–1332.

Schmidt, M.W.J., Skjemstad, J.O., Gehrt, E., and KogelKnabner, I., 1999, Charred organic carbon in German 

chernozemic soils: European Journal of Soil Science, v. 50, 

p. 351–365.

Shafizadeh, Fred, 1982, Chemistry of pyrolysis and combustion of wood, in Sarkanen, K.V., Tillman, D.A., and Jahns, 

E.C., eds., Progress in biomass conversion: London, Academic Press, p. 51–76.

Simpson, M.J., and Hatcher, P.G., 2004a, Determination of 

black carbon in natural organic matter by chemical oxidation and solid-state 13C nuclear magnetic resonance spectroscopy: Organic Geochemistry, v. 35, p. 923–935.

Simpson, M.J., and Hatcher, P.G., 2004b, Overestimates of 

black carbon in soils and sediments: Naturwissenschaften, 

v. 91, p. 436–440.

Skjemstad, J.O., Clarke, P., Taylor, J.A., Oades, J.M., and 

McClure, S.G., 1996, The chemistry and nature of protected 

carbon in soil: Australian Journal of Soil Research, v.32, 

p. 251–276.

Skjemstad, J.O., Reicosky, D.C., Wilts, A.R., and McGowan, 

J.A., 2002, Charcoal carbon in U.S. agricultural soils: Soil 

Science Society of America Journal, v. 66, p. 1249–1255.

Song, Jianzhong, Peng, Piang’an, and Huang, Weilin, 2002, 

Black carbon and kerogen in soils and sediments. 1 Quantification and characterization: Environmental Science and 

Technology, v. 36, p. 3960–3967.

ten Have, Rimko, and Teunissen, P.J.M., 2001, Oxidative 

mechanisms involved in lignin degradation by white-rot 

fungi: Chemical Reviews, v. 101, p. 3397–3413.

Wershaw, R.L., Leenheer, J.A., and Kennedy, K.R., 1998, 

Use of 13C NMR and FTIR for elucidation of degradation 

pathways during natural litter decomposition and composting. III. Characterization of leachated from different 

types of leaves, in Davies, G., and Ghabbour, E.A., Humic 

substances structures, properties, and uses: Cambridge, 

England, Royal Society of Chemistry, p. 47–60.

Williams, P.T., and Besler, Serpil, 1996, The influence of temperature and heating rate on the slow pyrolysis of biomass: 

Renewable Energy, v. 7, p. 233–250.

Yang, Shaobin, Hu, Haoquan, and Chen, Guohua, 2002, 

Preparation of carbon adsorbents with high surface area 

and a model for calculating surface area: Carbon, v. 40, 

p. 277–284.

32 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components
Appendix A 33

Appendix A. Replicate Charring and Analyses

Code for sample identification:

First letter identifies the starting material.

 P = pine wood

 B = pine bark

 C = cellulose

 L = lignin

The next three-digit number identifies charring temperature

Last group of numbers identifies charring time in hours

Parameters measured:

 Yield is the percentage char remaining.

 S.A. is the surface area in square meters per gram (m2/g).

 TPV is the total pore volume in cubic centimeters per gram (cm3/g.

Abbreviations and Symbols:

 Std. Dev. is the standard deviation

 < is less than

 -- is no data
34 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Table A-1. Replicates for pine wood samples.

Sample identification Replicates Average Std. Dev.

P-250-8 Yield 52.7 54.6 61.9 53.5 56.5 55.8 3.68

S.A. 1.20 1.54 0.16 1.90 1.06 1.2 0.65

TPV 0.002 0.003 0.001 0.001 0.003 0.002 0.001

P-250-24 Yield 40.4 39.9 42.3 44.4 49.5 43.3 3.89

S.A. 2 0.55 3.0 1.2 0.0 1.4 1.19

TPV 0.002 0.000 0.003 0.003 0.000 0.002 0.002

P-250-72 Yield 36.6 37.5 35.4 35.1 36.2 1.11

S.A. 2.67 1.6 1.6 2.4 2.1 0.56

TPV 0.003 0.001 0.001 0.002 0.001 0.001

P-250-168 Yield 23.6 29.2 31.3 31.6 35.2 30.2 4.26

S.A. 2.11 0.00 4.5 0.6 2.3 1.9 1.74

TPV 0.002 0.000 0.005 0.002 0.000 0.002 0.002

P-300-1 Yield 40.7 42.1 44.0 41.9 43.1 42.4 1.25

S.A. 4.9 1.13 5.9 -- 1.4 3.3 2.42

TPV 0.005 0.003 0.006 -- 0.002 0.004 0.002

P-300-8 Yield 32.8 32.0 35.0 32.1 32.8 32.9 1.21

S.A. 246 243 89.9 183 206 194 64

TPV 0.140 0.111 0.115 0.139 0.055 0.112 0.035

P-300-24 Yield 23.7 23.9 25.6 26.0 26.1 25.1 1.17

S.A. 401 269 334 288 305 319 51

TPV 0.112 0.172 0.164 0.191 0.148 0.157 0.030

P-300-48 Yield 19.1 19.6 20.1 18.6 22.3 19.9 1.43

S.A. 211 244 288.0 178 186 221 45

TPV 0.149 0.139 0.170 0.104 0.109 0.134 0.028

P-300-72 Yield 18.1 16.3 14.7 16.5 20.2 17.2 2.08

S.A. 176 219 298 292 169 231 62

TPV 0.106 0.140 0.183 0.176 0.098 0.141 0.039

P-350-8 Yield 15.4 21..3 22.9 23.0 22.9 21.1 3.77

S.A. 517 406 372 363 433 418 62

TPV 0.297 0.241 0.211 0.205 0.245 0.240 0.037

P-400-8 Yield -- 13.6 16.0 13.2 12.8 13.9 1.44

S.A. -- 368 339 419 453 395 51

TPV -- 0.275 0.249 0.201 0.212 0.234 0.034
Appendix A 35

Table A-2. Replicates for pine bark samples.

Sample identification Replicates Average Std. Dev.

B-250-8 Yield 58.0 59.7 59.8 61.1 62.3 60.2 1.62

S.A. 1.32 0.99 1.04 0.97 0.93 1.05 0.16

TPV 0.002 0.002 0.002 0.002 0.002 0.002 0.000

B-250-24 Yield 51.2 50.7 50.4 51.9 55.1 51.9 1.90

S.A. 2.68 1.46 2.03 1.55 1.20 1.78 0.58

TPV 0.002 0.001 0.002 0.002 0.001 0.002 0.000

B-250-72 Yield 37.5 42.6 42.6 43.9 46.9 42.7 3.40

S.A. 3.40 1.99 2.17 2.04 2.12 2.34 0.59

TPV 0.003 0.002 0.002 0.002 0.002 0.002 0.000

B-250-168 Yield 33.3 31.0 32.9 36.7 37.4 34.3 2.70

S.A. 3.03 2.31 2.76 1.97 2.11 2.44 0.45

TPV 0.004 0.003 0.003 0.003 0.003 0.003 0.000

B-300-1 Yield 52.3 51.9 54.1 55.6 54.4 53.7 1.54

S.A. 1.00 9.20 1.38 1.22 1.22 2.80 3.58

TPV 0.002 0.007 0.002 0.002 0.002 0.003 0.002

B-300-8 Yield 40.2 49.5 49.9 47.6 50.2 47.5 4.19

S.A. 140 31 33 94 34 66 49

TPV 0.081 0.019 0.020 0.056 0.021 0.039 0.028

B-300-24 Yield 31.8 30.1 34.7 34.4 36.5 33.5 2.53

S.A. 190 234 213 233 200 214 20

TPV 0.112 0.138 0.122 0.137 0.116 0.125 0.012

B-300-48 Yield 25.3 22.6 22.7 23.0 27.7 24.3 2.22

S.A. 234 177 225 193 143 194 37

TPV 0.142 0.111 0.142 0.120 0.090 0.121 0.022

B-300-72 Yield 16.4 16.4 17.1 19.5 21.0 18.1 2.07

S.A. 190 149 213 205 -- 189 28

TPV 0.143 0.099 0.133 0.130 -- 0.126 0.019

B-350-8 Yield 30.5 33.6 34.8 32.4 35.2 33.3 1.91

S.A. 127 99 92 111 98 105 14

TPV 0.081 0.060 0.056 0.067 0.059 0.064 0.010

B-400-8 Yield -- 28.1 29.9 29.0 27.8 28.7 0.95

S.A. -- 72 70 81 88 78 8

TPV -- 0.047 0.045 0.052 0.056 0.050 0.005
36 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Table A-3. Replicates for cellulose samples.

Sample identification Replicates Average Std. Dev.

C-250-8 Yield 40.1 39.6 40.5 46.2 54.2 44.1 6.24

S.A. 3.23 4.15 3.01 1.86 3.06 0.94

TPV 0.005 0.005 0.004 0.004 0.004 0.001

C-250-24 Yield 33.4 34.3 34.7 37.0 38.2 35.5 2.00

S.A. 3.59 3.11 3.87 3.20 3.46 3.45 0.31

TPV 0.004 0.004 0.005 0.005 0.005 0.005 0.000

C-250-72 Yield 31.2 30.7 31.0 31.1 32.8 31.4 0.83

S.A. 3.73 3.13 3.54 3.41 3.21 3.40 0.24

TPV 0.005 0.005 0.005 0.005 0.005 0.005 0.000

C-250-168 Yield -- 28.7 28.6 28.8 29.8 29.0 0.56

S.A. -- 3.10 2.99 2.99 3.24 3.08 0.12

TPV -- 0.005 0.006 0.007 0.007 0.006 0.001

C-300-8 Yield 30.9 31.6 30.9 30.4 29.9 30.7 0.63

S.A. 147 137 153 148 142 145.4 6.11

TPV 0.087 0.081 0.094 0.091 0.090 0.089 0.005

C-300-24 Yield 24.7 27.1 27.1 27.9 29.0 27.2 1.58

S.A. 189 197 270 204 161 204. 40.3

TPV 0.122 0.122 0.165 0.126 0.117 0.130 0.020

C-300-48 Yield 23.0 23.6 24.2 23.5 25.0 23.9 0.77

S.A. 122 18.5 63.8 31.7 48.20 56.8 40.2

TPV 0.081 0.002 0.050 0.023 0.044 0.040 0.030

C-300-72 Yield 20.9 22.4 23.1 22.5 -- 22.2 0.94

S.A. 29.7 17.7 45.5 57.3 25.2 35.1 16.1

TPV 0.020 0.014 0.034 0.084 0.020 0.034 0.028

C-350-8 Yield 22.8 24.5 24.2 22.1 23.7 23.5 1.00

S.A. 338 347 342 401 384 362 28.3

TPV 0.191 0.202 0.200 0.232 0.223 0.210 0.017

C-400-8 Yield -- 19.25 19.7 17.5 19.4 19.0 0.99

S.A. -- 420 414 464 410 427 25.0

TPV -- 0.243 0.240 0.267 0.237 0.247 0.014
Appendix A 37

Table A-4. Replicates for lignin samples.

Sample identification Replicates Average Std. Dev.

L-250-168 Yield --- 76.4 75.9 76.7 77.9 76.7 0.85

S.A. <0.1 <0.1 <0.1 <0.1 --- ---

TPV --- <0.001 <0.001 <0.001 <0.001 --- ---

L-300-24 Yield 67.8 67.4 67.6 67.3 68.1 67.6 0.32

S.A. <0.1 <0.1 <0.1 1.42 <0.1 --- ---

TPV <0.001 <0.001 <0.001 0.0012 <0.001 --- ---

L-300-48 Yield 62.8 63.2 61.0 64.6 66.9 63.7 2.20

S.A. 84.5 126.0 180 96.4 48.7 107.1 49.26

TPV 0.048 0.075 0.1051 0.0553 0.0277 0.06 0.03

L-300-72 Yield 57.9 58.7 55.4 60.3 64.1 59.3 3.22

S.A. 146 136.0 86 128.8 82.5 115.9 29.52

TPV 0.085 0.080 0.0522 0.082 0.0468 0.07 0.02
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38 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Appendix B. Fourier Transform Infrared (FTIR) Spectra

Figure B-1. Fourier Transform Infrared (FTIR) spectra of unheated cellulose, lignin, pine wood, poplar wood and 

pine bark.
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Appendix B 39

Figure B-2. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 250oC for various times.
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40 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-3. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 300oC for various times.
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Appendix B 41

Figure B-4. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 350oC for various times.
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42 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-5. Fourier Transform Infrared (FTIR) spectra of cellulose heated at 400oC for various times.
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Appendix B 43

Figure B-6. Fourier Transform Infrared (FTIR) spectra of lignin heated at 250oC for various times.
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44 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-7. Fourier Transform Infrared (FTIR) spectra of lignin heated at 300oC for various times.
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Appendix B 45

Figure B-8. Fourier Transform Infrared (FTIR) spectra of lignin heated at 350oC for various times.
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46 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-9. Fourier Transform Infrared (FTIR) spectra of lignin heated at 400oC for various times.
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Appendix B 47

Figure B-10. Fourier Transform Infrared (FTIR) spectra of lignin heated at 500oC for various times.
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48 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-11. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 250oC for various times.
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Appendix B 49

Figure B-12. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 300oC for various times.
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50 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-13. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 350oC for various times.
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Appendix B 51

Figure B-14. Fourier Transform Infrared (FTIR) spectra of poplar wood heated at 400oC and 500oC for one hour.
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52 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-15. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 250oC for various times.
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Appendix B 53

Figure B-16. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 300oC for various times.
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54 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-17. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 350oC for various times.
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Appendix B 55

Figure B-18. Fourier Transform Infrared (FTIR) spectra of pine wood heated at 400oC, 500oC, and 600oC for one hour.
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56 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-19. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 250oC for various times.
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Appendix B 57

Figure B-20. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 300oC for various times.
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58 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure B-21. Fourier Transform Infrared (FTIR) spectra of pine bark heated at 350oC for various times.
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Appendix C 59

Appendix C. 13C Nuclear Magnetic Resonance (NMR) Spectra

Figure C-1. 13C Nuclear Magnetic Resonance (NMR) spectra of unheated cellulose, lignin, pine wood, poplar wood and pine bark.
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60 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-2. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at 250oC for various times.
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Appendix C 61

Figure C-3. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at 300oC for various times.
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62 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-4. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at 350oC for various times.
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Appendix C 63

Figure C-5. 13C Nuclear Magnetic Resonance (NMR) spectra of cellulose heated at 400oC for various times.
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64 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-6. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 250oC for various times.
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Appendix C 65

Figure C-7. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 300oC for various times.
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66 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-8. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 350oC for various times.
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Appendix C 67

Figure C-9. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 400oC for various times.
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68 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-10. 13C Nuclear Magnetic Resonance (NMR) spectra of lignin heated at 500oC for various times.
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Appendix C 69

Figure C-11. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 250oC for various times.
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70 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-12. 13C Nuclear Magnetic Resonance (NMR)spectra of poplar wood heated at 300oC for various times.
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Appendix C 71

Figure C-13. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 350oC for various times.
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72 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-14. 13C Nuclear Magnetic Resonance (NMR) spectra of poplar wood heated at 400oC and 500oC for one hour.
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Appendix C 73

Figure C-15. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 250oC for various times.
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74 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-16. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 300oC for various times.
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Appendix C 75

Figure C-17. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 350oC for various times.
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76 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-18. 13C Nuclear Magnetic Resonance (NMR) spectra of pine wood heated at 400oC, and 500oC for one hour.
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Appendix C 77

Figure C-19. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 250oC for various times.
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78 Changes in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components

Figure C-20. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 300oC for various times.
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Appendix C 79

Figure C-21. 13C Nuclear Magnetic Resonance (NMR) spectra of pine bark heated at 350oC for various times.
Rutherford and others—OChanges in Composition and Porosity Occurring During the Thermal Degradation of Wood and Wood Components—SIR 2004-5292

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