Thermal reactivity of hemicellulose and cellulose in cedar and beech wood cell walls

Wood cell walls have complex ultra-structures, in which cellulose microfibrils are surrounded by a hemicellulose-lignin matrix. This is the first paper to discuss the effect of cell wall on the pyrolytic reactivity of hemicellulose and cellulose in wood by using Japanese cedar (Cryptomeria japonica, a softwood) and Japanese beech (Fagus crenata, a hardwood), along with isolated xylan and glucomannan. Pyrolysis was conducted by subjecting the samples to temperatures in the range of 220-380 degrees C, at a heating rate of 10 degrees C/min, under a N-2 flow with the reactor quenched as soon as the temperature reached the set value. The remaining hemicellulose and cellulose in the heat-treated wood were evaluated by determining the yields of hydrolysable sugar. Isolated xylan containing the uronic acid group, probably acting as a catalyst, was more reactive than isolated glucomannan, whereas the xylan in both woods was remarkably stable and degraded across a similar temperature range to the glucomannan degradation. Thus, the majority of the hemicellulose fractions in cedar and beech unexpectedly exhibited similar reactivity, except for glucomannan in beech that degraded at lower temperatures. Differing thermogravimetric (TG) and derivative TG (DTG) profiles, measured for cedar and beech under similar heating conditions, were explained by the different cellulose reactivity, rather than the hemicellulose reactivity; cellulose decomposed with hemicellulose in cedar, while such decomposition was independent in beech. The observed reactivity is a new finding that is different from the currently understood ideas and may originate from the effects of the cell walls. The research herein provides important information on the kinetics and thermochemical conversion of lignocellulosic biomass.