Effects of torrefaction on hemicellulose chemical structure in cell walls of Japanese cedar

Torrefaction is a promising technique for improving the thermochemical characteristics, including calorific value and hydrophobicity, of wood pellets. These properties of torrefied pellets are attributed to the degradation of the cell wall polymers, such as the hemicellulose structure, during the torrefaction process. This study investigated the effects of torrefaction on the chemical components of the cell wall polymers and hemicellulose structure in Japanese cedar. Wood chips were subjected to torrefaction at different temperatures (230 to 500 ºC) and characterized using various techniques, such as thermogravimetric analysis, Fourier transform infrared spectroscopy, and liquid chromatography. The torrefied samples exhibited lower hemicellulose content (glucomannan/galacto-glucomannan (GM/GGM) and arabinoglucuronoxylan (AGX)) than the control sample. In addition, the hemicellulose content of the cell wall decreased with increasing torrefaction temperature. The GM/GGM-to-AGX ratio remarkably changed after torrefaction. As the torrefaction temperature increased, high-molecular-weight assemblies of GM/GGM and AGX shifted toward low-molecular-weight assemblies. Furthermore, the side-chain structure and molecular-weight distribution of AGX decomposed at a lower torrefaction temperature (230 °C), indicating that the AGX polymeric structure had lower thermal stability than GM/GGM. These results provide information concerning the thermal degradation of the behavior of each hemicellulose polymeric structure during the torrefaction.