Influence of density and lignin content on cleavage strength of Eucalyptus grandis wood

The higher the basic density and the lignin content, the higher the cleavage strength tends to be and the less prone to checking the wood tend to be. The checks that often affect Eucalyptus wood, also called cracks or cleavages, depreciate the material and cause considerable loss of yield in higher value-added products for the sawn wood industry. Information about the influence of basic density and lignin content on the propensity of wood to checks, simulated in a cleavage mechanical test, is scarce in the literature. Therefore, the objective of this work was to investigate and clarify the relationships between the cleavage strength and the basic density and lignin content of the wood within the stem. For this, two Eucalyptus grandis trees were felled at 22 years of age and the stems were sectioned to obtain the base logs, three meters long, which were used during the analysis made in the present research. From these logs, specimens for the cleavage test were made. After the cleavage test, the basic density and lignin content were determined for each specimen, aiming at adjusting regression models that explained the variation of the cleavage strength of the wood as a function of the aforementioned properties. The results showed that the higher the basic density and the lignin content, the higher the cleavage strength tends to be and, consequently, the less prone the wood tend to be to the checks.