NATURAL DURABILITY AND CHEMICAL COMPOSITION OF Liquidambar sp. WOOD

Wood is a material of biological origin and because of its chemical composition it is subject to attack by various organisms that use it as a food source. Thus, this study aimed to evaluate the natural durability and chemical composition of the Liquidambar sp. wood. Accelerated rot tests were carried out in the laboratory, using pure culture of the fungus Postia placenta, which causes brown rot, and forced termite feeding Nasutitermes corniger. After biological tests, the samples were dried in an oven at 103 ± 2oC, until they reached constant masses and later weighed, to evaluate the percentage of mass loss. The levels of extractives, lignin (soluble, insoluble and total) and holocellulose were also determined. The wood under study had mass losses of 37.79% and 23.37%, when submitted to the action of the fungus and termites, respectively, and an average extract content equal to 4.13%. It is concluded that the Liquidambar sp. wood presented moderate resistance to the attack of the brown rot fungus and was little resistant to the action of the tested termite.


INTRODUCTION
Over the past few years, the main species used in Brazil by the large-scale timber industries come from trees of the genus Eucalyptus and Pinus, which represent 72 and 21%, respectively, of the total area of reforested areas in the country, as data from the Brazilian Tree Industry -IBÁ (2017), with excellent use of its wood. However, species of the genus Liquidambar can be another alternative for use by Brazilian industry, mainly in the southern region of the country, presenting good growth and excellent quality wood for several uses, such as sawn wood, laminates and plywood, cooperage, fuel, cellulose and paper and boxes (Mattos et al., 2001;Lingbeck et al., 2015).
The genus Liquidambar is the best known of the Altingiaceae family, being constituted by four intercontinental species in the temperate zone of the Northern Hemisphere. Two species are found in East Asia (L. formosana and L. acalycina), one in Western Asia (L. orientalis) and the other is found in North America (L. styraciflua) (Ickert -Bond et al., 2005), and have great potential for reforestation due to its straight shaft and the good quality of its wood, which is quite homogeneous, with little variation in its properties along the tree trunk. 1180FLORESTA, Curitiba, PR, v. 50, n. 2, p. 1179-1184 The wood has average values of basic density between 0.48 gm -3 (Freitas et al., 2015) and 0.52 gm -3 (Mattoset al., 2001).
Despite the favorable dendrological and technological characteristics, wood of the genus Liquidambar without treatment can present low natural durability (Clausen, 2010). The heterogeneity of forest species results in variations in their vulnerability to attack by xylophagous organisms, which in this case, is mainly caused by differences in anatomical arrangement and chemical composition, such as the levels of nutritive substances (sugars and starch) in wood and the presence of toxic substances in the extracts present in the heartwood (Melo, 2013;Carvalho et al., 2015).
Wood is subject to the action of biodeteriorating agents, including biological, physical and chemical agents, causing harm and consequently damage (Carvalho et al., 2015), and no species of wood, not even those of recognized durability natural, it is able to resist these agents indefinitely, since wood is a material of an organic nature and subject to the next stage of the natural sequence of any living being; deterioration and decomposition.
In this context, it is verified the importance of knowledge of the natural resistance of wood for the recommendation of its most appropriate use, avoiding expenses with replacement of parts and reducing the impacts on the environment. Thus, this study aimed to evaluate the natural durability and chemical composition of the Liquidambar sp. wood.

Study material and evaluation of the biological resistance of wood
The wood of Liquidambar sp. used in this study came from a plantation with spacing of 3.0 x 3.0 m, aged 8 years, located in the municipality of Guaçuí, Espírito Santo. Three trees were obtained with average values of commercial height and diameter at breast height (DBH), taken 1.30 m from the ground, 15.7 m and 23.3 cm, respectively.
Tests of accelerated rotting in the laboratory and forced termite feeding were carried out. The execution of the accelerated rot test followed the specifications of the American Society for Testing and Materials -ASTM D-2017 (2008). Twenty specimens with dimensions of 2.5 x 2.5 x 0.9 cm were used, and 12 samples of Pinus sp. with the same dimensions as a comparison standard. Pure culture of the fungus Postia placenta (Fr.) M. Larsen et Lombard causing brown rot was used. The test was kept in an air-conditioned room (25 ± 2ºC and 75 ± 5% relative humidity), for 98 days. After such period, the specimens were dried and the loss of mass was evaluated when comparing the values obtained with those mentioned in the standard.
In the termite feed test Nasutitermes corniger Motsch, the specifications of ASTM D-3345 (2008) were followed with some modifications suggested by Paes et al. (2013), regarding the maintenance of the colony, capture of insects and conducting the experiment. According to the recommendations, the termite colony used in the experiment was collected in the municipality of Jerônimo Monteiro -ES.
Twenty defect free specimens with dimensions of 2.54 x 2.54 x 0.64 cm and 20 samples of Pinus sp. were used as the comparison standard. The samples were exposed to the action of termites for 28 days, in an airconditioned room, under the same conditions of the accelerated rot test.
After the test, the samples were dried in an oven at 103 ± 2ºC, until they reached constant mass and then weighed to assess the percentage loss in mass. The biological resistance of Liquidambar sp. depending on the loss of mass, the wear and tear caused by termites (note), the mortality of termites and the number of days for the death of insects in each flask. The mass loss was corrected by means of the operational mass loss samples, as indicated in ASTM D-2017ASTM D- (2008, and the wear score was the average obtained by five evaluators.

Chemical composition of wood
For the chemical characterization of the wood, two opposite wedges of discs were removed at the height of the DBH of each tree, and the analyzes were performed in duplicates. The wedges were reduced in chips. These were homogenized, air dried and transformed into sawdust in a Willey mill, according to Technical Association of the Pulp and Paper Industry (TAPPI -T 257 om -92, 1992). The sawdust was classified in sieves so that the analyzes were carried out only in the fraction of sufficient granulometry to pass through a 40 mesh (0.42mm opening), however, they were retained in a 60 mesh (0, 25mm).
The extractives analysis was performed according to TAPPI 264 om-88 (1992), with an extraction sequence in ethanol: toluene solution (1: 2) for 5 hours, ethanol for 4 hours, both in a "Soxhlet" extractor, and in hot water for 1 hour.
After removing the extractives, 0.3 g of the sample was weighed, which was subjected to hydrolysis with sulfuric acid for 60 minutes (30.0 ± 1.0 ° C), autoclaved for 60 minutes and filtered. When considering the retained solid as insoluble lignin, which was determined by mass difference (Gomide and Demuner, 1986), the remaining liquid from the filtration of insoluble lignin was analyzed in a UV spectrophotometer, to determine soluble lignin FLORESTA, Curitiba, PR, v. 50, n. 2, p. 1179-1184 (Goldshimid, 1971). The total lignin content consisted of the sum of the soluble and insoluble fractions and the holocellulose was determined by the difference between the initial mass and the amount of extractives and total lignin.

RESULTS
The wood of Liquidambar sp., When submitted to the action of the fungus Postia placenta (brown rot) had a mass loss of 37.79% (variation coefficient of 56.25%), being classified as of moderate resistance ( ASTM D-2017( ASTM D- , 2008 and showed better resistance to attack by xylophagous fungi, when compared to that of Pinus sp., Which was non-resistant to attack, having lost 48.93% (coefficient of variation of 13.34% ) of the original mass.
The values of mass loss caused by termites Nasutitermes corniger, mortality and time elapsed for the death of insects in the forced feeding test are shown in Table 1. For the test of forced feeding caused by termites Nasutitermes corniger, it was noticed that the wood of Liquidambar sp. presented much higher values for mass loss, when compared to Pinus sp., which was practically not attacked. The wear (wood consumption) caused by termites in the wood samples of Liquidambar sp. during the forced feeding test can be seen in Figure 1 Figure 1 Samples of the wood from Liquidambar sp. attacked after termite forced feeding test Nasutitermes corniger.
The average values of extractives content, lignin (soluble, insoluble and total) and holocellulose, obtained by chemical analysis are shown in Table 2.

DISCUSSION
Behavior similar to that observed in this study for the resistance of liquidambar wood to attack by xylophagous fungi was found by Terzi et al. (2012) when studying the biological performance of untreated heartwood from Liquidambar orientalis, who found mass loss percentages equal to 50.66; 40.2 and 37.08% for fungi Trametes palustres, Gloeophyllum trabeum and Trametes versicolor, respectively, and classified it as nonresistant (Palustrine) or moderately resistant (Gloeophyllum trabeum Trametes versicolor), although the heartwood has a reddish color, which is generally associated with the presence of extracts and woods with high natural durability.
When grouping some species of wood, native and exotic from North America, due to natural resistance to fungal deterioration, Clausen (2010) also classified liquidambar wood (Liquidambar styraciflua) as little resistant or non-resistant to attack by xylophages' organisms.
The high resistance to biological deterioration of some wood species is generally explained based on the properties of their chemical components, since it is a consensus that there is a close relationship between the extractive content and the natural durability of the wood. However, this relationship is not a rule. Paes et al. (2016) when studying the effect of extractives content on the natural resistance of five woods to attack by xylophagous termites, found that the content of extractives in the wood does not necessarily correspond to its natural durability, and may present a weak correlation between these variables, depending on composition, type of extract and location in the cell.
According to Gonçalves et al. (2013), another factor that can confer natural durability is the presence of inert elements in the wood, such as silica and other mineral incursions (ashes), which can cause damage to the insects' jaws, making it difficult to access the food source, and, therefore, increasing resistance to attack by xylophagous organisms.
For wear, lower grades indicate higher consumption of wood, according to ASTM D-3345 (2008), which is generally consistent with the values of mass loss (Table 1). The wood of Liquidambar sp. obtained an average score of 3.73, intense attack (Figure 1), while the Pinus sp. obtained an average score of 9.19 and superficial attack, according to ASTM D -3345 (2008).
In the wood of Pinus sp., After 17 days, all individuals had already died, that is, total mortality, while in Liquidambar sp., Even after 28 days had passed (deadline for the end of the test according to ASTM D -3345 (2008), only 40% of individuals died, that is, moderate mortality rate). Based on these values, it was found that this species did not show resistance to termite attack Nasutitermes corniger. This being evaluated based on the loss of mass, wear (note), mortality and survival time of insects.
A mass loss of 16.04% for Liquidambar orientalis wood subjected to the termite forced feeding test Reticulitermes flavipes was obtained by Terzi et al. (2012), who found greater loss of mass for the Pinus slyvestris wood (25.87%) used as a control. However, Lepage et al. (2017) cite that termites of the genus Nasutitermes consume little of the wood of Pinus sp. due to terpenes and terpenoids in it. Thus, the difference in the consumption of Pinus sp. by the termite species mentioned and the one used in this research.
The lower natural durability of liquidambar wood may be related to the chemical characteristics of this species. Another factor to be considered is the age of the trees used, containing a good proportion of younger wood and little heartwood. This, in addition to the nature and the concentration of extractives present in the wood, may have been the cause of moderate termite mortality, since the species had an average extract content equal to 4.13%. FLORESTA, Curitiba, PR, v. 50, n. 2, p. 1179-1184 However, the natural durability depends not only on the quantity or class of extracts, as already mentioned, but also on their location in the wood. Thus, extracts in the cell fire contribute less to the biological resistance of the wood than those in the cell wall.
For wood from Liquidambar styraciflua aged 16, Mattos et al. (2001) found percentages equal to 7.4; 21.6 and 71.0% for the levels of extracts, total lignin and holocellulose, respectively, having been similar to those obtained in the present study. Thus, based on the results obtained and those found in the literature, the studied wood should not be used, without treatment (chemical or thermal), in direct contact with the soil or in places with a high incidence of termites of the genus Nasutitermes.

CONCLUSIONS
• The wood of Liquidambar sp. presented moderate resistance to the attack of the fungus Postia placenta (brown rot). • The damage caused by termites Nasutitermes corniger to the wood of Liquidambar sp. it was intense, presenting a moderate mortality rate, and, therefore, this species behaved little resistant to the action of these insects. • The number of extractives obtained in ethanol: toluene proved not to be sufficient to guarantee the wood's resistance to the xylophagous organisms tested.