The Preparation Of Acetylated Straw And Study On The Mechanical Properties

Composites with biological fiber as filling materials have unexampled advantages over the composites filled with other fibers. As a type of plant fiber, rice straw has special significance of utilization.In this dissertation, acetylation reaction was applied to modify rice straw into a thermoplastic material. Under microwave radiation, acetylation of rice straw pretreated over aqueous NaOH was carried out with acetic anhydride as esterifying agent and concentrated sulfuric acid as catalyst. Herein, several factors on weight percent gained were investigated, such as solvent dose, reaction time and so on. Weight percent gained (WPG), infrared spectrum (IR spectrum), elemental analysis, X-ray diffraction (XRD) and thermal analysis (TA) were used to study the differences on structure between rice straw and acetylated rice straw.Reaction time had great effect on WPG of rice straw in acetylation. Prolonging reaction time, WPG increased, which was up to the maximum (25.07%) when time was60min. WPGs were close when ratios of the solid (rice straw mass) to liquid (acetic anhydride volume)(g/mL) were1:15and1:20, but the WPG with ratio of1:10was lower. Three characteristic absorption peaks of ester group in IR spectrums indicated that rice straw was acetylated. The thermal stability of acetylated rice straw was better than rice straw. The temperatures of50%weight loss were316.2℃and343.0℃, respectively for rice straw and acetylated rice straw.This dissertation dealt with the acetylated rice straw fiber reinforced low-density polyethylene (LDPE) resin composites. The mechanical properties and fracture morphology of composites under different blending conditions were studied.The orthogonal design was utilized to determine the optimum blending conditions. Polyethylene was blended with both rice straw and acetylated rice straw under different content, temperature and rotating speed. The rheological curves of blending were gained. Tensile properties of the dumbbell samples were tested according to the State Standard GB/T1040-92. For both rice straw and acetylated rice straw composites, the tensile strength and elongation at break of composites decreased as the content of the rice straw increased. The torque rheometer was used to test the rheology of the composites. The relationship between shear stress and shear rate was studied, and the effects of the content of rice straw in the composites and shear rate on rheological behavior were discussed. Composite of polyethylene and the acetylated rice straw was a non-Newtonian fluid. The viscosity of composites increased as the content of rice straw increased.