EFFECT OF HEAT TREATMENT ON MECHANICAL PROPERTIES OF Pinus taeda AND Eucalyptus grandis WOODS

Abstract

A presente pesquisa objetivou investigar o efeito da t\ue9cnica de retifica\ue7\ue3o t\ue9rmica, empregada sob duas condi\ue7\uf5es de tratamento, nas propriedades mec\ue2nicas das madeiras de Pinus taed L. e Eucalyptus grandis W. Hill ex Maiden. De cada esp\ue9cie foram amostradas tr\ueas \ue1rvores com 25 anos e, de cada uma, retirada a primeira tora com 2 m de comprimento da qual foi obtida duas pranchas de dimens\ue3o 7,0 x 20,0 cm (espessura x largura, respectivamente) diametralmente opostas e destas confeccionados 30 corpos de prova para cada tratamento. No primeiro deles, denominado combinado, as madeiras foram submetidas \ue0 termorretifica\ue7\ue3o em autoclave a 130/\ub13\ub0C e press\ue3o de 2 kgf/cm\ub2, por 3 horas e, ap\uf3s um per\uedodo de condicionamento, submetidas ao calor em estufa el\ue9trica a 160/\ub11\ub0C, pelo mesmo per\uedodo. O segundo tratamento consistiu apenas na termorretifica\ue7\ue3o em estufa. Avaliaram-se ainda pe\ue7as de madeira sem tratamento (testemunha). As propriedades mec\ue2nicas foram avaliadas por meio dos ensaios para determina\ue7\ue3o dos m\uf3dulos de elasticidade e ruptura em flex\ue3o est\ue1tica, resist\ueancia m\ue1xima \ue0 compress\ue3o paralela \ue0 gr\ue3 e dureza Janka, conforme norma ASTM D 143 (1995), e resist\ueancia ao impacto, conforme norma ABNT NBR 7190 (1997). Para a madeira de Pinus taeda, observou-se que o tratamento em estufa forneceu os piores resultados, tanto em fun\ue7\ue3o da redu\ue7\ue3o nos valores de carga suportada de um maior n\ufamero de propriedades mec\ue2nicas avaliadas, como em rela\ue7\ue3o aos menores incrementos na resist\ueancia quando observado um aumento das mesmas atribu\ueddas ao tratamento t\ue9rmico. Na madeira de Eucalyptus grandis, o tratamento combinado reduziu um maior n\ufamero de propriedades mec\ue2nicas da madeira.This study investigated the effect of thermal treatment, employed under two treatment conditions on mechanical properties of wood of Pinus taeda L. and Eucalyptus grandis W. Hill ex Maiden. From each species, three 25-year tress were sampled, and from each one, it was taken the first 2-meter long log, which was obtained from two boards of size 7,0 x 20,0 cm (thickness x width respectively) diametrically opposite from where 30 specimens were saw for each treatment. At the first one, called the combined one, the woods were subjected to heat treatment by autoclaving at 130 / \ub1 3\ub0C and pressure of 2 kgf / cm \ub2 for 3 hours and, after a conditioning period, subjected to heat in an electric oven at 160 / \ub1 1\ub0C for the same period. The second treatment consisted only of heat treatment in oven. It was also evaluated the pieces of wood without treatment (control). The mechanical properties were evaluated by means of tests for determining the modulus of elasticity and rupture in bending, maximum resistance to compression parallel to the grain and Janka hardness according to ASTM D 143 (1995), and the impact resistance according to ABNT NBR 7190 (1997). For Pinus taeda wood, it was observed that treatment in an oven gave the worst outcomes, both due to the reduction in the values of supported load of a greater number of mechanical properties evaluated, but also as compared to the lowest increments in resistance when it was observed an increase to the same ones with heat treatment. In Eucalyptus grandis, the combined treatment decreased the greatest number of mechanical properties of wood