CHEMICAL AND ENERGETIC CHARACTERIZATION OF Eucalyptus grandis × Eucalyptus urophylla CLONES SUBJECT TO WIND DAMAGE QUÍMICA ENERGÉTICA DE CLONES DE Eucalyptus

– Wind damages are common in forest plantations and the use of this wood can minimize losses. The objective was to evaluate the chemical composition and the energetic potential of wood and charcoal from trees subject to wind damage. Eight (A to H) two-years-old Eucalyptus grandis × Eucalyptus urophylla clones were selected in a region where wind damage is frequent. The basic density, caloriﬁ c value, chemical composition of wood and caloriﬁ c value, immediate chemistry and gravimetric yield of charcoal were determined for all clones. Materials with high lignin content and low S/G ratio had higher gravimetric yield. The energy density of wood and charcoal showed high relationship with the basic and apparent relative density, respectively. All materials showed potential for bioenergy, but the clone E stood out with higher gravimetric yield and energy density.


INTRODUCTION
The winds are characterized by the air movement from areas with high to low pressures (Moore et al., 2013;Kramer et al., 2014;Hale et al., 2015). Wind damage in forests are reported since 1940 (Mitchell et al., 2012) in many regions of the world (Lagergren et al., 2012;Moore et al., 2013;Kramer et al., 2014).
Wind damages occur mainly from 24 to 36 months old in eucalyptus plants and it can bend or break the trees (CENIBRA, 2014). The fi rst causes loss of apical dominance and reduced the productivity. In the second, it is necessary to harvest broken material and plant a new forest. In both cases, losses are considerable and threaten eucalyptus plantations.
Trees broken by winds are mainly young ones with smaller diameter, low density and poor quality fi bers (Veenin et al., 2005;Ramírez et al., 2009), hindering its use in pulp (Severo et al., 2013;Pirralho et al., 2014) and lumber (Luna et al., 2013) production. Therefore, these materials are used mainly for energy purposes (Guerra et al., 2014).
The aim of this study was to characterize the chemical and energetic potential of wood and charcoal from eucalyptus clones subject to wind damage aiming to fi nd a better use for these materials.

Biological Material
Three trees per each of eight (A to H) two-yearsold Eucalyptus grandis × Eucalyptus urophylla diff erent clones were collected in the region of Belo Oriente, Minas Gerais state, Brazil (42º22'30" S and 19º15'00" O). This age and region were chosen because they have high incidence of wind damage.
Disks were withdrawn at 1.3 meters above ground level, from each felled tree, the basic density, chemical and energetic properties of these materials were analyzed.

Wood chemical characterization
One disk from each tree were milled with a Standard Wiley knife mill with a 2 mm screen. This material was sieved with a 40-60 mesh sieve and the retained fraction was used to determine the total extractives according to ASTM D-1105-94 (ASTM, 1994; besides the insoluble lignin (Gomide and Demuner, 1986); soluble lignin (Goldschimid, 1971) and Siringil/Guaiacil (S/G) ratio (Lin and Dence, 1992). The total lignin was obtained with the sum of soluble and insoluble lignin. Finally, the holocellulose content was determined by subtracting these components from 100.
The same sample was used for elemental analysis. The carbon, hydrogen and nitrogen content, based in wood dry mass, were quantifi ed with a universal analyzer Vario Microcube model. The oxygen content was obtained by subtracting the carbon, hydrogen and nitrogen from 100.

Physical and energetic characterization of wood and charcoal
The wood basic density was determined according to NBR 11941 (ABNT, 2003), the gross calorifi c value according to NBR 8633 (ABNT, 1984) and the wood energy density by the product of these two parameters.
The wood was carbonized at 1.67°C/min heating rate, until 450°C and 30 min residence time in electric furnace at atmospheric pressure and controlled presence of oxygen. The ash, volatile matter and fi xed carbon were evaluated according to ABNT NBR 8112 (ABNT, 1983): the gross calorifi c value according to ABNT NBR 8633 (ABNT, 1983) and apparent relative density according to ABNT NBR 9165 (ABNT, 1985). The charcoal energy density was determined by the product of the apparent relative density and gross calorifi c value. The elemental analysis of charcoal was performed similarly to that of the timber.

Statistical analysis
The variance homogeneity (Bartlett's test at 5% signifi cance) and normality test were performed (Shapiro-Wilk test at 5% signifi cance). Means of treatments were compared with the Scott-Knott test at 5% probability.

Wood chemical characterization
The extractives, ash, soluble, insoluble and total lignin, holocellulose and the S/G ratio of the eight diff erent clones evaluated were determined to characterize the wood (Table 1).

Physical and energetic characterization of wood and charcoal
The wood of Eucalyptus grandis × Eucalyptus urophylla clones showed higher basic density, while the charcoal produced presented high calorifi c value and energy density ( Table 2).
The gravimetric yield in charcoal production ranged from 30.60 to 33.84%, the fi xed carbon from 17.99 to 23.28%, volatile matter from 17.99 to 23.28% and ash from 0.600 to 0.685% (Table 3).

Wood chemical characterization
The clone A showed a lower extractive content, while the clones D and F had the highest (Table 1). The extractive content of the eight clones evaluated was lower than those reported for seven-yearsold Eucalyptus grandis × Eucalyptus urophylla, Eucalyptus urophylla and Eucalyptus paniculata, 3.41 and 9.12% (Arantes et al., 2011;Zanuncio et al., 2014). The proportion of extractives in the xylem is higher at the heartwood (Adamapoulos et al., 2005), the process that turns sapwood into heartwood is incipient in twoyears-old trees (Sousa et al., 2013;Gominho et al., 2015), resulting in woods with low extractives content. For energy use, some extractive classes, such as those soluble in dichloromethane have high resistance to thermal degradation (Mészáros et al., 2007), which increases charcoal gravimetric yield, gross calorifi c value and volatile matter (Zanuncio et al., 2014). All materials showed similar ash quantity, which is very resistant, represent impurities and hinder the use of wood for energy (Bustamante-García et al., 2013).
The soluble lignin content of the materials was similar in all the eight clones, therefore, total lignin content followed the trend of insoluble lignin, with higher values for clone H and lower for A and B clones ( Table 1). The lignin is important because of its high carbon content (Fengel and Wegener, 1984) and resistance to high temperatures (Varfolomeev et al., 2015), what makes its presence desirable for energy production. The lignin quality also infl uences the energy use , because wood with high S/G ratio, as that of clone C, have structure with fewer linkages between carbons, and therefore, lower resistance to thermal degradation (Prasad et al., 2015).
The clones with lower lignin content showed higher holocellulose quantity, as reported for the clone B. Holocellulose has high oxygen content (Sjöströn, 1981) and poor resistance in high temperatures (Moreno and Font, 2015), reducing its calorifi c value and gravimetric yield (Liu and Han, 2015) and being unwanted in wood for energy production.
All wood materials showed similar elemental composition (Table 1). Materials with high carbon and low oxygen content are most desirable in the wood for energy production, because they increase wood calorifi c value and the gravimetric yield of carbonization (Soares et al., 2014). High nitrogen content is unwanted due to its pollution potential, Means followed by the same letter does not diff er by the Scott-Knott test at 5%. Values in superscript represent the coeffi cient of variation.

Clone
Grav ( generating toxic oxides during charcoal combustion that can induce acid rain and soil acidifi cation (Demirbas, 2004).

Physical and energetic characterization of wood and charcoal
The charcoal from clones with higher wood basic density had higher apparent relative density with Pearson correlation coeffi cient of 0.891 between these variables (Table 2). This trend was also reported for E. grandis × E. urophylla and E. urophylla with three, four, fi ve and seven years old (Castro et al., 2013). The charcoal with apparent relative density has better mechanical properties and lower fi ne production and therefore desirable for energy production (Antal and Mok, 1990).
The gross calorifi c value showed low variation in the wood and charcoal. This parameter is related with wood chemistry, being directly proportional to the lignin  and extractives content (Zanuncio et al., 2014), and inversely proportional to that of holocellulose (Liu and Han, 2015). The low variation in wood chemistry resulted in low variation of the calorifi c value of wood and charcoal.
Carbonization reduced the basic density and increased the gross calorifi c value of all clones (Table 2), being the second eff ect with highest proportion, and therefore, the charcoal had higher energy density than the wood in most of the clones selected. This trend was observed for Eucalyptus grandis × Eucalyptus urophylla with three, fi ve and seven years old (Soares et al., 2014) and for native wood of Luehea divaricata, Casearia sylvestris, Guazuma ulmifolia and Rapanea ferruginea (Costa et al., 2014). The low variation of the gross calorifi c value of wood and charcoal among clones resulted in high relationship of energy density with wood basic density and charcoal relative apparent density, with Pearson correlation coeffi cient of 0.973 and 0.998, respectively.
The gravimetric yield of the clones E, F and H were higher (Table 3), with Pearson's correlation coeffi cient of 0.6358 and -0.6424 with the total lignin content and S/G ratio. The gravimetric yield is the main quantitative parameter for charcoal production (Rousset et al., 2011) showing how the quantity and quality of lignin in the wood are important for carbonization.
Clones C and G showed higher fi xed carbon and low volatile matter (Table 3). High fi xed carbon contents result in slow burning of the material and better mechanical properties of charcoal, facilitating its use in steelmaking. On the other hand, a high volatile matter content is important to the calorifi c value and charcoal reactivity (Antal and Mok, 1990;Demirbas, 2001;Rousset et al., 2011).
The ash content increases after carbonization in all materials (Table 3). This occurred because the minerals in the wood resist to high temperatures and, therefore, do not degrade during carbonization. Thus, the increase in ash percentage was due to the thermal degradation of other constituents (Moreno and Font, 2015). In the furnace for steel production, minerals present in charcoal may adversely aff ect the mechanical properties of steel, which makes them undesirable in this process (Oliveira et al., 1982).
The charcoal elemental composition varied with the genetic material, unlike the wood elemental composition, showing that the wood behavior at high temperatures can be complex. There was an increase in the carbon content and a decrease in oxygen and hydrogen content in for all materials. Carbon present in greater proportion in wood components with high resistance to thermal degradation, such as lignin, whereas the oxygen and hydrogen are present in in greater proportion in the holocellulose, which has low resistance to high temperatures.

CONCLUSIONS
The clones E, F and H had higher gravimetric yield, while the A, D and E higher energy density in the wood and charcoal. The gravimetric yield was correlated with the lignin content and S/G ratio, while the energy density had a higher relation to density. All clones showed potential for energy generation, especially the clone E, making this an important alternative to use wind broken trees.