[The effect of chemical extracts on the physical behaviour of "Girassonde" wood (Pterocarpus angolensis, D.C.) [other wood, other forest trees, Angola]]

English. The influence of chemical extractives on the physical characteristics, related to water-vapor sorption, on wood of Pterocarpus angolensis D.C. is analysed. The behaviour of unextracted wood was compared with wood extracted by the following solubility products: water at 20 deg C, water at 100 deg C, caustic soda 1%, ecetone, ether, alcohol benzol and alcohol-benzol+ether. A notable influence of the capacity on sorption of bound water was found, clearly shown through a great increase in the fibre saturation point and in the total shrinkage of wood. The equilibrium moisture content of wood in the air is also clearly changed. This is shown by different isotherm curves of desorption. The shrinkage coefficients (shrinkage gradients) are less influenced, so the stability coefficients (ratios between shrinkage and air moisture) show more clearly the different behaviour of wood according to environmental conditions.

Portuguese. E analisada a influencia dos extractaveis quimicos nas caracteristicas fiscias, relacionadas com os fenomenos sorcao de agua, na madeira de Pterocarpus angolensis D.C. Comparou-se o comportamento da madeira sem extraccao com madeira extraida pelos seguintes solubilizantes: agua a 20 deg C, agua a 100 deg C, soda caustica a 1%, acetona, eter, alcool-benzol e alcool-benzol+eter. Foi detectada uma influencia marcada na capacidade da madeira para a agua de sorcao evidenciada por aumentos substanciais nas humidades de saturacao das fibras e nas retraccoes totais da madeira extraida. A humidade de equilibrio ao ar e tambem evidentemente alterada o que se traduz por varias curvas de dessorcao bem diferenciadas. Os coeficientes de retraccao e, especialmente, o tangencial, sao os factores menos afectados, em face do que os coeficientes de estabilidade (relacao entre a retraccao da madeira e a humidade do ar) se revelam evidentemente mais capazes de diferenciar o comportamento da madeira perante as condicoes ambientais.