Maderas-Cienc Tecnol 18(2):2016 Ahead of Print: Accepted Authors Version   1 

DOI:10.4067/S0718-221X2016005000025



EFFECT OF THE BRAZILIAN THERMAL MODIFICATION PROCESS ON



THE CHEMICAL COMPOSITION OF Eucalyptus grandis JUVENILE WOOD –



PART 1: CELL WALL POLYMERS AND EXTRACTIVES CONTENTS

5  6  7  8  9  10  11  12  13  14  15  16  17  18 

Djeison Cesar Batista1, Graciela Ines Bolzón de Muñiz2, José Tarcísio da Silva Oliveira1, Juarez Benigno Paes1, Silvana Nisgoski2 1

Department of Forest and Wood Sciences, Federal University of Espírito Santo. Av. Governador Carlos Lindenberg, 316, Centro, Jerônimo Monteiro, Espírito Santo, Brazil. Postal Code 29550-000. 2 Department of Forest Engineering and Technology, Federal University of Paraná, Av. Prefeito Lothario Meissner, 900, Jardim Botânico, Curitiba, Paraná, Brazil. Postal Code: 80210-170.

Corresponding author: [email protected] Received: May 15, 2015 Accepted: January 19, 2016 Posted online: January 20, 2016 ABSTRACT

19 

This article reports the first study of the influence of the Brazilian process of

20 

thermal modification called VAP HolzSysteme® on the chemical composition of

21 

eucalyptus wood. Flatsawn boards of Eucalyptus grandis juvenile wood were tested for

22 

four treatment levels: untreated and thermally modified at final cycle temperatures of

23 

140, 160 and 180 °C. Chemical analyses were carried out according to the standards of

24 

the Technical Association of the Pulp and Paper Industry and encompassed total

25 

extractives, insoluble lignin, holocellulose (cellulose + hemicelluloses) and solvent

26 

soluble extractives in water (cold and hot) and ethanol:toluene (1:2 v.v.) mixture. The

27 

chemical composition of thermally modified Eucalyptus grandis juvenile wood was

28 

significantly changed by the VAP HolzSysteme® process compared to untreated wood.

29 

Only the wood thermally modified at final cycle temperature of 180 °C was

30 

significantly different for all the chemical analyses performed compared to untreated

31 

wood.

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Keywords: Extractives content, holocellulose, insoluble lignin, VAP HolzSysteme®.

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INTRODUCTION

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material for the pulp and paper and charcoal industries in Brazil. On the other hand, its

37 

use as lumber for most added value products is insignificant, because fast growing

38 

eucalyptus juvenile wood’s properties (high dimensional instability, high growing

39 

tensions, low durability and difficult of preservation) make it a difficult material for

40 

processing.

Eucalyptus wood from planted forests plays a very important role as raw

41 

The great majority of studies about thermal modification have been carried out

42 

with softwoods, such as Picea abies and some species of Pinus spp. because of their

43 

economic importance for European countries, where the main industries of thermal

44 

modification are located. Of course, some important hardwoods are also processed in

45 

Europe, such as Populus spp., Fagus spp. and Fraxinus spp.

46 

Some laboratorial scale studies have been performed about thermal modification

47 

of eucalyptus wood, mostly Eucalyptus globulus (Esteves et al. 2007a, Esteves et al.

48 

2007b, Esteves et al. 2008) from Portugal, Eucalyptus grandis (Batista and Klitzke

49 

2010, Batista et al. 2011, Calonego et al. 2010, Moura et al. 2012, Pessoa et al. 2006,

50 

Pincelli et al. 2002) and Eucalyptus saligna (Brito et al. 2008) from Brazil.

51 

These studies have shown that eucalyptus wood has a great potential for thermal

52 

modification, improving mainly its properties of dimensional stability and decay

53 

resistance, what are key points for juvenile wood. Eucalyptus grandis (and its hybrids)

54 

is the most planted species in Brazil and we see a great potential for the

55 

commercialization of its thermally modified wood. That is why it has been the most

56 

studied species regarding the process of thermal modification.

57 

In 2006 a Brazilian company started investigating thermal modification of wood,

58 

using Pinus sp., Eucalyptus sp. and Tectona grandis in its experiments. This research

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led to the development of an industrial process named VAP HolzSysteme® and the

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company is currently producing thermally modified Tectona grandis wood in industrial

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scale for indoor use.

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Nevertheless, its research with other species is continuing and the first paper

63 

published about this Brazilian process of thermal modification studied Eucalyptus

64 

grandis juvenile wood anatomy (Batista et al. 2015).

65 

This study is a continuing of Batista et al. (2015) and its aim was to evaluate the

66 

effect of the VAP HolzSysteme® process on the chemical composition of Eucalyptus

67 

grandis juvenile wood.

68  69 

MATERIAL AND METHODS

70  71 

Wood material and thermal modification

72 

The Eucalyptus grandis W. Hill wood used in this study was from an 18-year-

73 

old stand (from seeds) planted in the municipality of Telêmaco Borba, Paraná state,

74 

southern Brazil. Five trees were felled; but for the study, we sampled only one juvenile

75 

corewood flatsawn board (30 x 200 x 3,000 mm), without pith, cut from the first log of

76 

each tree. The rest of the wood was also brokendown and used to compose the batches.

77 

We sampled only five boards for this study, which were trimmed into four equal

78 

parts in length, and equally distributed among the four treatment levels investigated:

79 

untreated wood (as control) and thermally modified wood at final cycle temperatures of

80 

140, 160 and 180°C. These temperatures are the ones commonly used by the company

81 

where the research was carried out, and the thermally modified wood produced by the

82 

company is intended for indoor use.

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Prior to thermal modification, the wood was seasoned until 15% of final

84 

moisture content, thereafter thermally modified according to the VAP HolzSysteme®

85 

process, in industrial scale equipment (steel cylinder 6m³ of capacity), where one batch

86 

was processed separately for each final cycle temperature. Steam generated in a boiler

87 

was injected in the cylinder and worked as heat-transfer medium, what also limits

88 

oxidative processes, classifying the process as hygrothermal (Hill 2006). VAP

89 

HolzSysteme® is typically divided in five phases, which lengths approximately eight

90 

hours, with some more eight hours of cooling. The exact schedule is proprietary

91 

information, but a more detailed description of the process can be found in Batista et al.

92 

(2015).

93  94 

Chemical analyses

95 

The chemical analyses were performed in the Wood Chemistry Laboratory of

96 

Federal University of Paraná, Brazil. First, the trimmed boards were milled in a Wiley

97 

mill and sieved to obtain a 40 – 60 mesh fraction, which was used for chemical analyses

98 

according to the Tappi T264 cm-97 standard (Tappi 1997b). The sieved fractions were

99 

separated by board (five) and treatment level (four), resulting in five sampling unities by

100 

treatment level.

101 

The sawdust used for the chemical analyses was taken from the sampling unities,

102 

resulting in five repetitions by treatment for the different analyses, which encompassed

103 

the determination of the content of total extractives, insoluble lignin, holocellulose

104 

(cellulose + hemicelluloses) and solvent-soluble extractives (cold water, hot water and

105 

ethanol:toluene).

106 

The total extractives content was determined by successive Soxhlet extraction

107 

from approximately 2 g of each sample with different solvents in sequence: 200 ml of

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the mixture ethanol:toluene (1:2 v.v.) for eight hours; 200 ml of ethanol for six hours

109 

and 500 ml of hot water for one hour.

110 

Insoluble lignin was determined by the Klason method, according to Tappi T222

111 

om-02 (Tappi 2002). The holocellulose content (cellulose + hemicelluloses) was

112 

measured by difference: holocellulose= 100% - (total extractives content + insoluble

113 

lignin content).

114 

The soluble extractives content was determined using three solvents: the mixture

115 

of ethanol:toluene (1:2 v.v.), and water (hot and cold), according to Tappi T204 cm-97

116 

and Tappi T207 cm-99 standards, respectively (Tappi 1997a, 1999).

117  118 

Statistical analysis

119 

Statistical analysis was performed according to a completely randomized design,

120 

with 95% confidence level. The effect of the treatments was checked by applying

121 

analysis of variance (ANOVA), with Bartlett’s test used for its validation, which

122 

verifies a basic premise for the realization of ANOVA, the homogeneity of variances

123 

among treatments (Ribeiro-Júnior 2001). In cases of homogeneous variances, ANOVA

124 

was applied, while in cases of statistically significant difference between means,

125 

Tukey’s multiple range test was used to determine which means were different.

126 

If at least one of the variances was not statistically equal, the Kruskal-Wallis H-

127 

test was applied, which is a non-parametric method for ANOVA, for classification of a

128 

criterion or experiments with one factor, where generalizations can be made (Spiegel

129 

1994). In this test, the original data of all treatments are increasingly ordered and

130 

receive scores, giving a mean score per treatment instead of an overall mean. Where at

131 

least one mean was not statistically equal (p-value<0.05), a box-and-whisker plot was

132 

used to identify which were different.

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RESULTS AND DISCUSSION

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The results of the chemical analyses can be seen in Table 1.

135 

Holocellulose content

136 

The thermal modification temperatures used in this work (140, 160 and 180 °C)

137 

were not high enough to cause mass loss of cellulose, according to previous information

138 

in the literature (Esteves, Graça and Pereira 2008; Esteves, Videira and Pereira 2011;

139 

Fengel and Wegener 1989; Sundqvist 2004).

140  141  142 

Table 1. Chemical composition of untreated and thermally modified Eucalyptus grandis wood. Treatment Holocellulose (%) Insoluble lignin (%) Total extractives content (%) Untreated wood 69.38 a 28.31 b 2.22 b (2%) (3%) (26%) 140 °C 67.51 b 28.71 b 3.60 b (3%) (4%) (28%) 160 °C 53.41 c 27.61 b 19.04 a (2%) (6%) (8%) 180 °C 52.80 c 31.21 a 15.85 a (2%) (6%) (9%) Bartlett’s test 1.16ns 1.21ns 1.24ns ANOVA – F test 415.79** 10.90** 494.30**

143  144  145  146 

Averages followed by the same letter in a column do not differ significantly according to the Tukey test (95% confidence level). Numbers in parentheses correspond to the coefficient of variation. ns: not statistically significant (95% confidence level). **: statistically significant (99% confidence level).

147 

Therefore, it is assumed that the process did not cause cellulose degradation, so

148 

the difference of holocellulose content among the treatments is believed to be attributed

149 

basically to the mass loss of hemicelluloses, which are the most thermally labile

150 

compounds of the cell wall structure (Fengel and Wegener 1989; Hill 2006; Stamm

151 

1964; Sundqvist 2004).

152 

As expected, untreated wood presented higher average holocellulose content

153 

than thermally modified wood, and the absolute averages had a constant pattern of

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reduction as the thermal modification temperature increased. However, the averages of

155 

the treatments at 160 and 180 °C were not significantly different.

156 

The difference of holocellulose content between untreated wood and thermally

157 

modified wood at 140 °C was slight, just 2.7% (or 1.87 p.p.), but statistically

158 

significant, showing that even the lowest processing temperature used can cause

159 

significant mass loss of hemicelluloses. This result is in accordance to that reported by

160 

Sundqvist (2004), who explained that at 140 °C significant degradation of

161 

hemicelluloses already happens. It is known that the mass loss of hemicelluloses causes

162 

some desirable changes in the properties of thermally modified wood, such as improved

163 

dimensional stability and resistance to biodeterioration. According to the Finnish

164 

Thermowood Association (2003), even at 140 °C these desirable changings are noted in

165 

wood thermally modified by the ThermoWood® process.

166 

On the other hand, the processing at 160 and 180 °C caused severe mass loss in

167 

Eucalyptus grandis wood. The holocellulose content declined 23.0% (15.97 p.p.) and

168 

23.9% (16.58 p.p.), respectively, in the wood treated at 160 and 180 °C. It is known that

169 

such severe mass loss of hemicelluloses causes thermally modified wood to

170 

significantly lose its mechanical strength (Hill 2006).

171 

More research about the effect of the VAP HolzSysteme® thermal modification

172 

process on Eucalyptus grandis wood will soon carried out, encompassing physical and

173 

mechanical properties.

174 

There are few published studies about the chemistry of thermally modified

175 

Eucalyptus grandis wood, but we found a very similar Brazilian study where the

176 

process was carried out in laboratory scale with a nitrogen (N2) atmosphere (Moura,

177 

Brito and Silva Júnior 2012). The authors reported higher averages of holocellulose

178 

content for thermally modified 18-year-old (the same age as in this research) Eucalyptus

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grandis wood than we found, with 58.95 and 54.84% respectively for treatments at 160

180 

and 180 °C. However the pattern of marked holocellulose content decrease with

181 

increasing temperature was the same in both studies.

182  183 

Insoluble lignin content

184 

The averages of insoluble lignin content of untreated and thermally modified

185 

wood at 140 and 160 °C did not differ significantly. But the average of the treatment at

186 

180 °C was the highest and significantly different (31.21%). According to Fengel and

187 

Wegener (1989), the lignin content of thermally modified wood starts to present an

188 

apparent (not real) increase from 140 – 150 °C, but we only observed this phenomena

189 

starting at 180 °C. This result is in accordance with Sundqvist (2004), who reported that

190 

the processing temperature of 180 °C is exactly the one where the degradation of

191 

hemicelluloses changes from “small” to “strong”.

192 

We can deduce that at 180 °C, the hemicelluloses degradation is in an advanced

193 

stage when compared to lignin degradation, resulting in a higher proportion of the latter

194 

in the cell wall, so its content apparently increased in the treatment at 180 °C. This

195 

result is in accordance with those of other studies of eucalyptus species (Brito et al.

196 

2008; Esteves, Graça and Pereira 2008) and other species (Esteves et al. 2011, Hill

197 

2006, Kamdem et al. 2002, Mohareb et al. 2012).

198 

Although the averages of insoluble lignin content did not differ between

199 

untreated wood and the treatments at 140 and 160 °C, it is reported in the literature that

200 

lignin degradation also occurs at these temperatures (Esteves et al. 2008, Esteves et al.

201 

2011, Fengel and Wegener 1989, Hill 2006, Sundqvist 2004). So, it is possible that

202 

some degradation of lignin occurred in the present study, but at a small level when

203 

compared to the degradation of hemicelluloses and the increase in extractives content.

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This can explain the non-significant differences of the averages of these three

205 

treatments. The same statistical behavior was reported by Moura et al. (2012), for the

206 

same treatments and species as in this study. The difference was that they thermally

207 

modified wood in laboratory scale, with an oxygen (O2) atmosphere. But the same

208 

pattern of increasing lignin content was reported when they used a nitrogen atmosphere,

209 

when comparing untreated wood to thermally modified wood at 160 and 180 °C.

210  211 

Total extractives content

212 

Untreated wood presented the smallest absolute average of total extractives

213 

content (2.22%), as expected, but it did not differ significantly from the average of the

214 

treatment at 140 °C (3.60%). Treatment at 160 °C presented the highest absolute

215 

average (19.04%) but did not differ from the average of the treatment at 180 °C. Thus,

216 

the averages of total extractives content were statistically divided into two groups

217 

among the treatments.

218 

It is extensively reported in the literature that the extractives content of thermally

219 

modified wood increases compared to untreated wood due to degradation of

220 

hemicelluloses and lignin (Esteves et al. 2008, Esteves et al. 2011, Fengel and Wegener

221 

1989, Hill 2006, Mohareb et al. 2012, Stamm 1964, Sundqvist 2004). In this particular

222 

situation, as can be seen in Table 1, the increase in the total extractives content of

223 

thermally modified wood occurred more by hemicelluloses degradation than by lignin

224 

degradation.

225 

Figure 1 depicts the behavior of the average concentrations of holocellulose,

226 

insoluble lignin and total extractives for each treatment. The letters in the graph

227 

correspond to the statistical decision according to the Tukey test.

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Figure 1 shows that the contents of holocellulose and total extractives are

229 

perfectly antagonistic in the samples in the untreated, 140 and 160 °C groups, meaning,

230 

where the holocellulose content is higher (untreated wood), the total extractives content

231 

is smaller and vice versa. Since the lignin content was not statistically different among

232 

these three treatments, we deduced that the increase in extractives content was mostly

233 

due to degradation of hemicelluloses, which turned into other substances, based on

234 

findings reported for Eucalyptus globulus wood (Esteves et al. 2008). a

b c

b

b

b

b

b

a

c

a

a

235  236  237  238 

Figure 1. Behavior of the chemical composition of untreated and thermally modified Eucalyptus grandis wood.

239 

We expected the holocellulose content of the wood treated at 180 °C to be

240 

significantly lower than that at 160 °C, which did not happen. However, the lignin

241 

content of treatment at 180 °C was higher than that at 160 °C and the behavior of the

242 

absolute average of total extractives content was the contrary. Accordingly, it is possible

243 

to suppose that the apparent increase in lignin content of the treatment at 180 °C was

244 

due to the decrease in the content of total extractives, which at this temperature might

245 

have been volatilized from the wood.

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Soluble extractives content

248 

Table 2 reports the results of soluble extractives content according to the

249 

different solvents used.

250 

According to Bartlett’s test, the variances of the treatments were statistically

251 

different for the ethanol:toluene and cold water treatments. However, the H-test showed

252 

there was a significant difference among the medians of the treatments for both

253 

solvents, so we used the box-and-whisker plots for median comparison, which are

254 

shown in Figure 2.

255  256 

Table 2. Averages of solubility in water (cold and hot) and ethanol:toluene by treatment. Treatment Untreated 140 °C 160 °C 180 °C Bartlett’s test ANOVA – F test H test

257  258  259  260  261 

Cold water (%)

Hot water (%)

Ethanol:toluene (%)

1.35 C (13%) 2.54 C (3%) 10.02 C (12%) 3.88 C (7%) 5.59** 21.6**

1.49 dB (12%) 3.02 cB (5%) 12.53 aB (3%) 6.02 bB (4%) 1.31ns 2,349.92** -

1.94 A (20%) 3.16 A (26%) 16.69 A (12%) 15.64 A (14%) 2.01** 19.41**

Averages followed by the same small letter in a column or the same capital letter in a row do not differ significantly according to the Tukey test (95% confidence level). Numbers in parentheses correspond to the coefficient of variation. ns: not statistically significant (95% confidence level). **: statistically significant (99% confidence level).

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Figure 2. Comparison of medians: ethanol:toluene (a) and cold water (b) soluble extractives.

266 

According to Figure 2b, there was no overlap of the areas of the notches of any

267 

box for the solvent cold water, which means that all the medians of the treatments were

268 

statistically different (95% confidence level). The same cannot be said for solubility in

269 

ethanol:toluene, where the areas of the notches of the boxes of the treatments at 160 °C

270 

and 180 °C are superposed, indicating that their medians were not statistically different.

271 

For the hot water soluble extractives it was possible to perform the Tukey test,

272 

which revealed that the averages of all treatments were statistically different. All the

273 

solvents had the same behavior, where extractives content increased steadily from

274 

untreated wood until thermally modified wood at 160 °C, and decreased from the

275 

treatment at 160 °C to 180 °C. This decrease was more pronounced in the extractions

276 

with water and less so in the extraction with ethanol:toluene, as can be seen in Figure 3.

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Figure 3. Variation in the extractives content according to different solvents. We also performed the F-test to compare the strength of extraction among the

281 

solvents. It revealed there was a statistically significant difference of the averages (F =

282 

162.89**) in a same treatment for the different solvents (Table 2, capital letters in the

283 

same row). This analysis showed that for all treatments the solvent ethanol:toluene had

284 

higher strength of extraction, followed by hot water and cold water.

285 

We expected this result because etanol:toluene has greater strength of extraction

286 

than water, because organic solvents naturally dissolve some substances that are

287 

insoluble in water (fats, fatty acids, sterols, steroids and long-chain alcohols), besides

288 

dissolving substances that are water soluble (phenolic compounds, glycosides, sugars,

289 

starch, proteins and inorganic salts) (Cruz et al. 2006, Esteves et al. 2008, Holmbom

290 

1999, Silvério 2008, Sjöström 1993).

291 

According to Kimo (1986), hot water as solvent in tests of Eucalyptus grandis

292 

wood samples dissolves the same substances as cold water, but dissolves extra fractions

293 

of polysaccharides through hydrolysis, mostly hemicelluloses. According to our results,

294 

this extra fraction was statistically significant.

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Eucalyptus grandis wood has small amounts of water-soluble compounds (Kimo

296 

1986). Other authors have reported that Eucalyptus grandis wood naturally has more

297 

compounds which are soluble in organic solvents, such as steroids, fatty acids, esters

298 

and long-chain alcohols (Barbosa et al. 2005, Cruz et al. 2006, Silvério 2008).

299 

According to data presented in Table 2 and the graph shown in Figure 3, the

300 

increase in the extracted fraction between the treatments at 140 °C and 160 °C was

301 

higher for ethanol:toluene (13.53 p.p.) than for cold and hot water (7.48 and 9.51 p.p.

302 

respectively). These results indicate that from 160 °C compounds were produced

303 

derived from lignin and hemicelluloses that are soluble in ethanol:toluene but not (or

304 

less) soluble in water.

305 

A similar comparison can be made for the decrease in the extracted fraction

306 

between the treatments at 160 °C and 180 °C. For ethanol:toluene, this decrease was

307 

1.05 p.p. and for cold and hot water it was higher: respectively 6.14 and 6.02 p.p. We

308 

deduce that at 180 °C an imbalance occurs between the volatilization and the production

309 

of compounds in the thermally modified wood, where water-soluble extracts are more

310 

volatile.

311 

The analysis of the soluble extractives of thermally modified eucalyptus wood is

312 

complex at the temperatures used in this study. According to some authors who have

313 

studied Eucalyptus spp. (Brito et al. 2008, Esteves et al. 2008, Moura et al. 2012), when

314 

some extractives are volatilized, new substances are produced from degradation of

315 

hemicelluloses (mainly) and lignin, and part of these new substances are also

316 

volatilized. Further research will be carried out about the qualitative nature of the

317 

extractives of thermally modified Eucalyptus grandis wood.

318 

Every forest species has its own particular characteristics regarding chemical

319 

composition of wood. The average contents of holocellulose, insoluble lignin and

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extractives for the thermally modified wood at 180 °C were all statistically different

321 

from those of untreated (or natural) Eucalyptus grandis wood. This result reinforces the

322 

idea that the thermal modification process turns the wood into a really modified

323 

product, different from the original raw material.

324 

Following the same line, thermally modified wood at 140 and 160 °C also

325 

produced samples with different characteristics, but less chemically modified than that

326 

treated at 180 °C. It can be noted from changes in color and smell that thermally

327 

modified wood is a different product, but we would like to highlight that such physical

328 

changes are the result of the chemical modification imparted by the process.

329  330 

CONCLUSIONS

331 

The chemical composition of thermally modified Eucalyptus grandis juvenile

332 

wood was significantly changed by the Brazilian process of thermal modification VAP

333 

HolzSysteme®.

334  335  336  337 

The holocellulose content decreased significantly with increasing temperature until the treatment at 160 °C and remained stable at 180 °C. The content of insoluble lignin remained constant in treatments at 140 and 160 °C and increased (apparently) only at the 180 °C treatment.

338 

The content of total extractives remained constant at 140 °C and increased in the

339 

treatments at 160 and 180 °C. The absolute content of extractives decreased at 180 °C in

340 

relation to 160 °C, caused by volatilization.

341 

Thermal degradation of hemicelluloses from the cell wall (which turned into

342 

other compounds or chains with smaller molecular mass) was the main factor

343 

responsible for the increase in the total extractives content in the treatments at 160 and

344 

180 °C.

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Water-soluble extractives increased significantly with increasing temperature

346 

until 160 °C and decreased significantly from 160 to 180 °C. Hot water dissolved more

347 

substances than cold water.

348 

Ethanol:toluene-soluble extractives increased significantly with increasing

349 

temperature until 160 °C and remained constant at 180 °C. The ethanol:toluene mixture

350 

dissolved more substances than hot water, and water-soluble substances were more

351 

volatile at 180 °C than those soluble in ethanol:toluene.

352  353 

The same behavior was observed for the different solvents: cold and hot water and the ethanol:toluene mixture (1:2 v.v.).

354 

Only the wood thermally modified at 180 °C was significantly different for all

355 

the chemical analyses performed when compared to untreated Eucalyptus grandis

356 

wood.

357  358 

ACKNOWLEDGEMENTS

359 

The first author would like to thank CAPES – Coordenação de Aperfeiçoamento

360 

de Pessoal de Nível Superior (Office to Coordinate Improvement of University

361 

Personnel) for the research grant.

362  363 

REFERENCES

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BATISTA, D.C.; TOMASELLI, I.; KLITZKE, R.J. 2011. Efeito do tempo e temperatura de modificação térmica na redução do inchamento máximo da madeira de Eucalyptus grandis Hill ex Maiden. Ciência Florestal 21(3):533-540. BRITO, J.O.; SILVA, F.G.; LEÃO, M.M.; ALMEIDA, G. 2008. Chemical composition changes in eucalyptus and pinus wood submitted to heat treatment. Bioresource Technology 99 (18):8545-8548. CALONEGO, F.W.; SEVERO, E.T.D.; FURTADO, E.L. 2010. Decay resistance of thermally-modified Eucalyptus grandis wood at 140 °C, 160 °C, 180 °C, 200 °C and 220 °C. Bioresource Technology 101 (23):9391-9394. CRUZ, M.P.; BARBOSA, L.C.A.; MALTHA, C.R.A.; GOMIDE, J.L.; MILANEZ, A.F. 2006. Caracterização química do “pitch” em indústria de celulose e papel de Eucalyptus. Química Nova 29 (3): 459-466. ESTEVES, B.M.; MARQUES, A.V.; DOMINGOS, I.; PEREIRA, H. 2007a. Influence of steam heating on the properties of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood. Wood Science and Technology 41 (3): 193-207. ESTEVES, B.M.; DOMINGOS, I.; PEREIRA, H. 2007b. Improvement of technological quality of eucalypt wood by heat treatment in air at 170-200°C. Forest Products Journal 57 (1/2): 47-52. ESTEVES, B.M.; GRAÇA, J.; PEREIRA, H. 2008. Extractive composition and summative analysis of thermally treated eucalypt wood. Holzforschung 62 (3): 344-351. ESTEVES, B.M.; VIDEIRA, R.; PEREIRA, H. 2011. Chemistry and ecotoxicity of heat-treated pine wood extractives. Wood Science and Technology 45 (4): 661-676. FENGEL, D.; WEGENER, G. 1989. Wood: chemistry, ultrastructure, reactions. Walter De Gruyter, New York. FINNISH THERMOWOOD ASSOCIATION. 2003. ThermoWood® handbook. Finnish Thermowood Association, Helsink. HILL, C. 2006. Wood modification: chemical, thermal and other processes. John Wiley & Sons, West Sussex. HOLMBOM, B. 1999. Extractives. In: SJÖSTRÖM, E.; ALÉN, R. (ed.) Analytical methods in wood chemistry, pulping and papermaking. Springer, Heidelberg, pp. 25148. KAMDEM, D.P.; PIZZI, A.; JERMANNAUD, A. 2002. Durability of heat-treated wood. Holz als Roh- und Werkstoff 60 (1): 1-6. KIMO, J.W. 1986. Aspectos químicos da madeira de Eucalyptus grandis W.Hill ex Maiden, visando à produção de polpa celulósica. MSc. Dissertation, Universidade

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