Caracterização química, física e mecânica da madeira de cinco espécies do Sahel Africano

Abstract

The principal objective of this study was the chemical, physical and mechanical characterization of the five wood species from African Sahel: Combretum glutinosum, Combretum micranthum, Combretum nigricans, Guiera senegalensis and Piliostigma reticulatum from four regions of the Niger Republic. The specific objectives were to evaluate the effect of the growing site on specific gravity, color, extractive content and stiffness of the wood, and determine the relationship between wood color and extractive content in order to verify the potential of the colorimetry to select species rich in tannins. Wood discs and increment core from trees of natural plantations were used, which were collected in four regions: 1-La Tapoa-Ouallam, 2-Gaya-Dogondoutchi, 3-Tafouka-Bouza and 4-Aguie-Kornaka. The discs were used for color and extractives analysis while increment core were used to determine the dynamic modulus of elasticity in parallel and perpendicular to the grain. Color measurements were taken by the portable spectrophotometer in the CIE L*a*b* space. Dynamic modulus of elasticity was determined by the ultrasonic nondestructive method. The growing site affected only the Guiera senegalensis wood specific gravity and the region 3 had the denser woods. Higher densities were observed to Combretum micranthum and Combretum nigricans woods while the lower density was obtained to Piliostigma reticulatum wood. Guiera senegalensis species presented the darker wood while Combretum glutinosum and Combretum nigricans species presented the ligher woods. Combretum micranthum wood had more red hue (a*) and more tannin while Combretum woods presented the highest b* values (yellow). Growing site affected the color of the all wood species. The highest tannin content were found Combretum micranthum, Combretum glutinosum and Guiera senegalensis woods while Piliostigma reticulatum and Combretum nigricans had the lowest contents. Combretum glutinosum, Combretum nigricans and Guiera senegalensis wood from region 1 presented a significant correlation between tannin and b* and L* coodinates. Piliostigma reticulatum wood from regions 3 and 4 with high extractive content are redder than other regions. Combretum nigricans woods presented the highest while Piliostigma reticulatum had the lowest modulus of elasticity. Growing site affected the dynamic modulus of elasticity in perpendicular to the grain to all wood species, except to Combretum nigricans. For dynamic modulus of elasticity in parallel to the grain, the growing site affected only the Combretum micranthum wood.