Effects of Microwave Treatment on the Chemical Structure of Lignocarbohydrate Matrix of Softwood and Hardwood

Abstract

A comparative study of the modification of chemical composition of softwood and hardwood by torrefaction at different temperatures (150–300 °C) was carried out using microwave treatment and convective heating. The nonthermal effect was established for softwood, revealing increased aromaticity of the samples obtained under microwave treatment. A difference of the effects of microwave treatment on softwood and hardwood was revealed. In the case of softwood, both carbonization processes and unsaturation development of the matrix structure were promoted, whereas for hardwood only promotion of the carbonization processes was observed. Formation of extractable compounds as the result of wood microwave treatment was monitored, and the significant increase in formation of hydrophilic extractable compounds in the range of 210–280 °C (hardwood) and 250–300 °C (softwood) was found. The destructive changes of lignin macromolecules at relatively low temperatures (beginning with 150 °C) were confirmed by decreasing Kla...