Enhancing the Fractionation Efficiency of Hemicellulose from Agricultural Waste using Expansion Pretreatment

Abstract

Hemicellulosic fractions isolated from agricultural wastes (rice straw and rice husk) were investigated using expansion pretreatment and subsequent alkali extraction, which is a method that combines the advantages of extrusion and milder steam explosion. The structure of the obtained hemicellulosic samples was determined by high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared spectroscopy (FT-IR), 2D heteronuclear single quantum coherence nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA). The expansion pretreatment resulted in a remarkable increase in the hemicellulose extraction efficiency from the rice straw compared with that of the controlled sample, while that from the rice husk was relatively unnoticeable. It was concluded from the FT-IR, molecular weight, sugar analysis, and NMR spectra results that the molecular weights of the hemicellulosic fractions extracted with this process significantly decreased and then rose, which was probably due to the prominent degradation and then generation of condensation substances. Moreover, the obtained hemicelluloses of the rice husk had a relatively more linear polymer structure than the rice straw. Considering the extraction efficiency and composition of each component, the expansion pretreatment was confirmed to be a promising method for the comprehensive separation and utilization of agricultural wastes.