Promoting the material properties of xylan-type hemicelluloses from the extraction step

Abstract

Using originally isolated xylan-type hemicelluloses for material application suffers from poor mechanical properties including low tensile strength and brittleness. The subsequent chemical modifications of hemicelluloses are facing the problems of high costs and toxic chemicals. Consequently, this study tried to investigate the factors affecting the film-forming properties of the originally isolated xylan-hemicelluloses and promoting their material properties from the extraction step. Two different extraction methods, a one-step alkali or alkaline peroxide solution method and a two-step alkali extraction-delignification method were used to extract the hemicellulose with different chemical structures from sugarcane bagasse. For the two-step alkali extraction-delignification method, hemicelluloses were first extracted by alkali solution and then delignified by dioxane/water, hydrogen peroxide solution or sodium hypochlorite solution. The lignin contents of all the extracted hemicelluloses ranged from 1.6%-9.5%, of which the lowest value was obtained through delignification by sodium hypochlorite. The number average molecular weight ranged from 8200 to 26800, while the xylan/arabinan ratio ranged from 5.0 to 9.1. The hemicelluloses were characterized and processed into films. Tensile strength of films could be considerably improved up to ˜52% when using sodium hypochlorite solution as the delignification agents and the lignin content was greatly reduced for the hemicellulose fraction. Statistical models were generated between film mechanical properties and hemicellulose structural characteristics. The models predicted that hemicellulose with higher molecular weight, more linear structure and lower lignin content would result in better mechanical properties.

Keywords: Bagasse; Film; Hemicellulose; Material property; Tensile strength; Xylan.