Changes in chemical properties and microstructure of Pinus taeda and Eucalyptus bosistoana woods modified by contact charring

Abstract

This study evaluated the effect of contact charring plus linseed oil submersion on wood chemistry and microstructure in Pinus taeda and Eucalyptus bosistoana wood specimens. Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and Raman spectroscopy analyses were performed to characterize charred wood in comparison to uncharred controls. Total lignin content increased to nearly 53% and 55% in the outer surfaces of the charred P. taeda and E. bosistoana specimens, respectively. The inner parts of the charred specimens also demonstrated increases higher than 50% in total lignin content. Total carbohydrate content of charred wood specimens decreased after the carbonization process. In the charred P. taeda specimens, the highest reductions in carbohydrate units observed were arabinan, xylan, and mannan. In the charred E. bosistoana specimens, arabinan, galactan and xylan showed the highest reductions in carbohydrate units. After charring, all wood specimens exhibited elevated contact angles when compared to control specimens due to increased hydrophobicity. The FTIR spectra analyses also indicated polysaccharide depolymerization and the formation of furans and alkylated aromatic compounds in charred specimens. Oil submersion led to saturation of cell lumens in both wood species used in this study. Charring led to sensitivity and homogeneity in cell walls although cells and pits retained their structural integrity and shape. Additionally, crack formation and separation occurred along the cell wall in some tracheid and fiber cells.