Effect of thermal treatment on fiber morphology in wood pyrolysis

Pyrolysis temperature can alter wood cell anatomical components. However, temperature effects applied to fibers during the pyrolysis process are not very clear. Thus, the aim of this study was to evaluate the influence of thermal treatment on the quality of fiber walls of wood in the pyrolysis process. For this, ten trees of Eucalyptus urophylla were cut, five of each hybrid's clones, VM4 and MN463, both 6 years old. Specimens of 0.02 x 0.02 x 0.02 m were prepared for treatment performed at four different temperatures: 100, 250, 350 and 450 degrees C. Fiber width (FW) and fiber lumen diameter (LD) were measured by scanning electron microscopy, and fiber wall thickness (WT) was calculated as a function of these dimensions. FW decreased approximately 40% with treatment at 450 degrees C; this trend was verified for both clones analyzed. It was possible to estimate a reduction of 8% in LD every 100 degrees C of temperature increase. LD of wood was larger than charcoal. LD showed no linear tendency for the thermal treatments analyzed. WT of wood was higher for VM4 clone compared to MN463. The temperature of 100 degrees C did not imply a large WT change. However, both genetic materials showed tendency to a decrease in the thickness of fiber walls with increasing temperature. The temperature of 350 degrees C reduced WT by approximately 45% and 64% for VM4 and MN463, respectively. WT of Eucalyptus urophylla of charcoal reduced by approximately 76%, compared to original thickness. Wood fiber wall thickness was four times greater than wall thickness of carbonized material at 450 degrees C.