Avaliação das propriedades físico-mecânicas da madeira de árvores de Hevea brasiliensis em três condições de sanidade no estado de São Paulo

Abstract

Latex is the main product extracted from rubber tree (Hevea brasiliensis). In Brazil, at the end of the production cycle of latex, rubber wood is traditionally used for energy purposes but international studies have reported consolidated practice that result in added-value products. Several researchers have observed raised and worsening of tapping panel dryness, a disease that impairs the production of latex. The main objective of this study was to evaluate the quality of rubber wood of commercial clones GT 1 and RRIM 600 in three distinct health conditions: trees producing latex (healthy), trees with tapping panel dryness of abiotic/physiological origin and trees with tapping panel dryness of biotic/pathological origin. Six trees of each health condition of the two clones from plantations in the São José do Rio Preto region – Sao Paulo State, Brazil - aged 20 years or more were sampled. Anatomical and physical-mechanical parameters evaluated were fibers length (occurrence and delimitation juvenile–mature wood), specific gravity and apparent density, shrinkage and anisotropy index, compression parallel to grain strength, bending strength and rigidity and Janka hardness. Results showed that juvenile wood occurs from pith up to 40% and 32% of ray for GT 1 and RRIM 600 clones respectively, allowing the association of the age of 6 to 8 years of plantation as transition between juvenile and mature wood. The mean specific gravity of rubber wood from both clones varied from 580 kg/m3 to 595 kg/m3 and there wasn’t statistical difference of this parameter among health conditions and between clones. Rubber wood apparent density from both clones presented four preferential patterns of radial variation. The most common pattern (occurrence of 60.5%) revealed initial decrease from pith to bark, with posterior increase and eventual variations in the outer trunk. Wood from both clones was classified as low shrinkage wood and juvenility affect shrinkage properties. GT 1 clone presented compression parallel to grain strength ranging from 41.55 MPa to 48.22 MPa and for RRIM 600 clone this variation was from 34.96 MPa to 47.89 MPa. In bending test, GT 1 clone presented strength and rigidity from 79.67 MPa to 90.98 MPa and from 9,353 MPa to 10,863 MPa, respectively. For RRIM 600 clone these properties ranged from 61.05 MPa to 94.11 MPa and from 7,138 MPa to 11,579 MPa. Janka hardness ranged from 57.27 MPa to 73.71 MPa for GT 1 clone and from 50.03 MPa to 84.92 MPa for RRIM 600 clone. The effect of juvenility in mechanical properties was very discreet, been observed only in Janka hardness. Overall there wasn’t statistical difference of mechanical properties in relation to three trees health conditions. Considering these results for this study conditions rubber wood had constant quality in the radial direction, revealing equivalent technological potential in three tree health conditions studied.