Calorific Value and Chemical Properties in Juvenile and Mature Wood of Thermally-Modified Eucalyptus Grandis

During thermal modifi cation, timber is exposed to temperatures approaching 200 oC for several hours and wood properties change. This study was aimed at evaluating the calorifi c value and chemical properties of juvenile and mature wood of thermally modifi ed Eucalyptus grandis. Boards were taken from 30-year-old E. grandis trees and thermally modifi ed at 180oC. Samples of the untreated and thermally modifi ed wood were transformed into chips and then processed into sawdust for the energy and chemical characterization of juvenile and mature wood. The results show that the thermal modifi cation causes: (1) signifi cant increases of 3.7 % and 6.8 %, respectively, in the net calorifi c value of juvenile and mature wood; (2) signifi cant increases of 24.8 % and 47.6 %, respectively, in the extractive content of juvenile and mature wood; (3) signifi cant decreases of 4.2 % and 8.3 % in the respective holocellulose content; and (4) signifi cant decreases in the galactose, xylose and glucose contents. It was demonstrated that the infl uence of thermal treatment was lower in juvenile wood than in mature wood.


INTRODUCTION 1. UVOD
During thermal modifi cation, timber is exposed to temperatures approaching 200 ºC for several hours.Several heat treatments are used commercially in Europe.They differ in the temperature applied, the use of nitrogen or steam or oils as an inert fl uid, and their application to wet or dry wood (Brito et al., 2008;Calonego et al., 2010Calonego et al., , 2012;;Esteves et al., 2007;Wikberg and Maunu, 2004).
Studies showed an improvement of equilibrium moisture content and dimensional stability of 61.0 % and 90.0 % in Eucalyptus globulus wood after thermal modifi cation at 190-210 ºC (Esteves et al., 2007), and reductions of 21.5 % and 23.2 % in equilibrium moisture content and volumetric swelling in E. grandis wood when thermally-modifi ed at 180 ºC (Calonego et al., 2012).The same wood showed signifi cant reductions of 15.7 % in the weight loss after exposure to Pycnoporus sanguineus fungi when thermally-modifi ed at 180 ºC (Calonego et al., 2010).
When the thermal treatment temperature is increased from 180 ºC to 220 ºC, an increase occurs in the number of specimens of E. grandis with fragile failures of 10.5 % to 100.0 % in compression to parallel to grain, and of 15.8 % to 100.0 % in static bending (Calonego et al., 2012).Temperatures greater than 180 °C caused internal cracks in wood of thermally-modifi ed E. grandis (Calonego and Severo, 2010).The thermal treatment of Eucalyptus saligna at 180 °C caused a decrease of up to 53.2 %, 62.8 %, 33.8 %, and 35.1 % in the arabinose, galactose, mannose, and xylose contents, respectively, whereas there was a proportional increase of up to 32.5 % in the lignin content of wood (Brito et al., 2008).
Untreated Pinus pinaster wood and thermally modifi ed wood at 260 ºC for 0.5 h, 1.0 h, 2.0 h and 4.0 h showed lignin contents of 28 %, 41 %, 51 %, 54 % and 84 %, respectively.The respective gross calorifi c values were 17932.1,21076.4,22164.9,22181.7 and 25845.1 kJ/kg (Bourgois and Guyonnet, 1988).Felfti et al. (2005) studied briquette of thermally modifi ed wood between 220 ºC and 270 ºC during 0.5 to 1.5 h and concluded that the increase in the temperature and time of the thermal treatment caused degradation of hemicelluloses and improved the calorifi c value.The gross calorifi c value was 20020.0kJ/kg for untreated wood and 21065.1 kJ/kg and 21209.1 kJ/kg, respectively, for thermally modifi ed wood at 220 ºC for 1.5 h and 250 ºC for 0.5 h.
Ključne riječi: biomasa, energija, kemijska svojstva, eukaliptus, toplinski modifi cirano drvo cially the wood anatomy.Juvenile wood can be defi ned as being close to the pith and technologically, it differs from mature wood on account of several properties such as: fi ber length, density, stability of wood and chemical properties (Bao et al., 2001 Since there is no information about the effects of thermal treatment on calorifi c value of E. grandis wood, the aim of this study was to evaluate the calorifi c value and chemical properties of juvenile and mature wood of this species after thermal modifi cation.

MATERIJAL I METODE
This study utilized wood from 30-year-old E. grandis trees from the Forestry Institute of São Paulo located in Manduri, São Paulo, Brazil.Four trees were felled and sectioned into 2.9 m logs.The fi rst log from each tree with diameters between 30 cm and 35 cm (measured at half height) were cut into fl at saw boards.The boards that contained the pith were cut into 28-mm thick pieces.Subsequently, all the boards were dried up to 10.0 % moisture content in a dry kiln.

Thermal treatments of boards 2.1. Toplinska obrada piljenica
Four dried boards were planed to 24-mm thickness and cut into smaller pieces measuring 0.60 m in length.Regions with cracks and knots were discarded.One of these smaller pieces was kept in its original condition (untreated wood), and the other pieces were reserved for the thermal treatment (thermally modifi ed wood).
The material was placed in an electric oven with a programmable controller and thermally modifi ed in the Laboratory of Wood Drying and Preservation of UNESP, Botucatu, SP, in Brazil.The treatment started at an initial temperature of 100 over a period of 14 h and then was increased (1.34 ºC/minutes) up to 180 ºC and maintained over a period of 2.5 h according to the application of the patent developed by Severo and .......Calonego, Durgante Sever, Sansígolo, Rezende, Bruder, Costa: Calorifi c Value and... Calonego (2011).After the end of the thermal treatment, wood pieces were allowed to cool naturally until they reached 30 ºC.
Subsequently, samples of the untreated and thermally modifi ed woods were transformed into chips and then processed into sawdust in a slicer type Willey with 20 mesh sieve size (0.85mm) for the energy and chemical characterization of juvenile and mature wood.The juvenile and mature wood regions were defi ned according to Oliveira et al. (1997).The anatomical characterization of the wood used in this study showed that the juvenile wood is confi ned up to 80 mm from the pith.

Calorifi c value of wood 2.2. Kalorijska vrijednost drva
The untreated and thermally modifi ed wood sawdust were transformed into pellets and placed in an oven at 103±2 ºC, and maintained in this condition until they reached 0 % moisture content.
The pellet was placed in a calorimeter PARR 1201 in the Laboratory of Applied Physics in the Department of Physics and Biophysics, IB -UNESP, Botucatu, SP, in Brazil.The gross calorifi c value was determined by bomb calorimeter method according to the standards presented in ABNT NBR-8633 (1984).After the combustion, the Equation 1 was used for determining the gross calorifi c value of the pellets. ( Where: GCV -gross calorifi c value, kcal/kg; W W -weight of water used in the calorimeter, 2.5 kg; W P -oven-dry weight of pellet, kg; t -temperature gradient before and after combustion, ºC; K -calorimeter constant, 489. The net calorifi c value was determined by gross calorifi c value and equilibrium moisture content of the wood according to the Equation 2 presented in Zanuncio et al. (2013).
The arabinose, galactose, xylose, mannose and glucose were analysed by High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAE -PAD) in the fi ltrate obtained of the acid-insoluble Klason lignin.The analysis was carried out by using a chromatograph Thermo-Dionex, ICS-5000 with Pulsed Amperometric Detection, CarboPac PA 1 column and NaOH 0,5M as eluent at a fl ow rate of 1 mL/min (Sullivan, 1994).
For the evaluation of calorifi c value and chemical properties, a Kolmogorov-Smirnov's normality test was performed at 5 % signifi cance.All variables had normal distribution.Subsequently, a parametric test (two-way ANOVA) was performed at 5 % signifi cance taking into account the type of wood and the thermal treatment for the comparison of means of calorifi c value, extractive, lignin, holocellulose and sugar contents of wood.The Jandel SigmaStat version 2.0 was used for statistical analysis.

Kalorijska vrijednost toplinski modifi ciranog drva
The gross calorifi c values of juvenile and mature wood from untreated E. grandis were 19998.3 and 19355.6 kJ/kg (Table 1).These results are similar to those cited by Calonego et  Table 1 shows that the gross calorifi c value of E. grandis wood has not been signifi cantly changed by thermal modifi cation at 180 ºC, although the respective treatment promoted a decrease of up to 3.2 % in terms of physical property studied.Similar results were showed by Felfti et al. (2005), who concluded that the minimum condition that promotes signifi cant improvements in a wood calorifi c value was 250 ºC.
Juvenile wood of untreated and thermally modifi ed E. grandis wood, at air conditions (20 ºC and 74 % RH), presents equilibrium moisture content of 10.9 % and 9.1%, respectively.In mature wood, the respective moisture contents were 11.1 % and 8.4 %.
Table 1 shows that the thermal treatment at 180 ºC promoted signifi cant reductions of 16.5 % and 24.3 % in the equilibrium moisture content of juvenile and mature woods.The infl uence of thermal treatment was lower on juvenile wood than on mature wood both in terms of calorifi c value and moisture content.Similar behavior was reported by Severo et al. (2012) and Calonego et al. (2014), who studied the changes of some properties of E. grandis and P. elliotti var.elliottii woods during thermal modifi cation.According to the authors, the juvenile wood has an adverse effect on modifi cation.
Due to smaller equilibrium moisture content in the thermally-modifi ed wood of E. Grandis, more useful energy is generated through combustion, since the moisture present in certain materials uses part of the gross energy released.Thus the net calorifi c value is the better way to quantify the energy potential of wood.shows that the thermal treatment at 180 ºC promoted signifi cant increase of 3.7 % and 6.8 %, respectively, in the net calorifi c value of juvenile and mature woods.
The results of qualitative determination of sugars are also presented in Figure 1 and 2. The peak of    The effect of thermal treatment on the chemical properties of E. grandis wood is shown in detail in Table 2 and 3.
The current study demonstrates that the juvenile and mature wood from thermally modifi ed E. grandis presented 2.57 % and 3.63 % in the respective extractive contents when compared with the values found for untreated wood, which were 2.06 % and 2.46 %.Mature wood, when thermally modifi ed, showed a proportional increase of 7.6 % in the insoluble lignin content, whereas juvenile wood showed no change by thermal treatment.The mature wood, when thermally modifi ed, showed greater signifi cant reduction (8.3 %) in holocellulose content than juvenile wood (4.2 %).
The thermal treatment of mature wood of E. grandis at 180 °C caused a decrease of 38.2 %, 13.9 %, and 6.7 % in the galactose, xylose, and glucose contents.The infl uence of thermal treatment in juvenile wood was lower than in mature wood.Similar changes were reported by Bourgois and Guyonnet (1988) The changes in chemical properties of thermally modifi ed E. grandis wood can explain the increase in the calorifi c value.Similar behavior was reported by Bourgois and Guyonnet (1988), who concluded that the thermal treatment in Pinus pinaster wood at 260 ºC during 0.5 to 4 h caused an increase between 46.4 % and 200 % in the lignin contents, and between 17.5 % and 44.1 % in the gross calorifi c value.These results are similar to those reported by Felfti et al. (2005) who concluded that the increase in the temperature and the time of the thermal treatment causes degradation of hemicelluloses and increase the calorifi c value of wood.

ZAKLJUČAK
This study shows that thermal modifi cation of Eucalyptus grandis wood increases its net calorifi c value up to 6.8 %.Regarding chemical properties, signifi cant increase was detected in the extractive content of juvenile and mature wood and reduction in the holoceluloses and sugar contents, when it was submitted to the thermal modifi cation at 180 ºC.Finally, the infl uence of thermal treatment in juvenile wood was lower than in mature wood.