Properties of Thermally Modified Wheat Straw through Pressurized Steam Treatment

摘要

Introduction In recent years, natural fibers have been emerging as a viable alternative to glass fiber as reinforced materials in polymer composites in various applications. These materials offer some inherent technical advantages over conventional reinforcements like low cost, light weight, competitive specific mechanical properties, and a "green" concept. However, the poor attraction and low interracial bonding between the hydrophilic natural fibers and hydrophobic polyolefin limit the reinforcement imparted to the plastic matrix by the fiber component. High temperature steam treatment has been used to improve dimensional stability of wood products. It was reported that several chemical changes occurred during heat and steam treatments. These include: (1) degradation of the hemicellulose to produce simple sugars which may undergo reversion reactions to form highly branched polysaccharides; (2) thermal softening of the cell wall matrix, mainly lignin; (3) crosslinking between carbohydrate polymers and/or between lignin and carbohydrate polymers; and (4) an increase in cellulose crystallinity. The extend of degradation was dependent on moisture content, temperature and time of the treatment. It was found that the optimum conditions for degrading hemicellilose of straws by steam were significantly different from those used for wood. So far, little work has been done on the steam treatment to modify straw materials to improve the adhesion between straws and hydrophobic thermoplastic polymer. The objective of this work was to evaluate the effects of pressurized Steam treatments on thermal, chemical, and mechanical properties as well as the sorption behavior of wheat straw.