Effect of steam explosion pretreatment of fast-growing poplar (Populus deltoides x maximowiczii) wood on selected properties of structural substances

Abstract

Abstract The aim of this study was to determine the changes occurring in the wood cellulose of the fast-growing poplar (Populus deltoides x maximowiczii) under the influence of steam explosion (SE) pretreatment. Cellulose from native wood and after pretreatment at 160°C and 205°C was isolated. Cellulose polymerization degree by size exclusion chromatography (SEC) and cellulose crystallinity index by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) were determined. The profiles of sugars in the native wood and in the solid fraction after pretreatment (using the acid hydrolysis method) were also determined. In addition, the profile of monosaccharides in the liquid fraction obtained after steam explosion and in the liquid fraction after acid hydrolysis of the oligosaccharides were investigated using high-performance liquid chromatography (HPLC). This allowed to determine the change in the content of hexoses and pentoses in the studied material. The behavior of cellulose in wood subjected to steam explosion at 160°C and 205°C and isolated by the Kürschner-Hoffer method was studied by determining the absorption bands of FTIR-ATR spectra. The Lateral Order Index (LOI) of cellulose was calculated from the ratio of the intensity of the corresponding absorption bands A1422 cm-1/ A896 cm-1. Total crystallinity index (TCI) of cellulose was calculated from the ratio of the intensity of absorption bands A1372 cm-1/ A2900 cm-1. TCI of Kürschner-Hoffer cellulose isolated from wood subjected to steam explosion at 160°C and 205°C decreased by 5.6% and 5.0% respectively with regard to the applied temperature. LOI increased in cellulose isolated from wood subjected to steam explosion at 160°C (by 0.7%) and at 205°C (by 19.2%) in relation to the index of cellulose isolated from native wood. Kürschner-Hoffer cellulose isolated from wood subjected to steam explosion at 160°C and 205°C exhibited, respectively, a reduced degree of polymerization of about 11% and about 8%. Polydispersity index in Kürschner-Hoffer cellulose was 1% lower after both pretreatments then native sample.