Preparation and Properties of Wheat Straw Fiber-polypropylene Composites. Part II. Investigation of Surface Treatments on the Thermo-mechanical and Rheological Properties of the Composites

Composites made of polypropylene (PP) and wheat straw fiber treated by alkalization, acetylation, and maleic anhydride polypropylene (MAPP) were prepared, and the dynamic mechanical, thermal, and rheological properties of the treated composites have been investigated. The PP composites reinforced with the treated wheat straw fiber exhibited higher brittleness. The melt flow studies were carried out at the temperature of 170, 180, and 190°C and shear rate of 0.01—0.1 s—1. The PP composites reinforced with the alkalized wheat straw fiber showed the high melt viscosity due to the strong chemical interaction among polymer and wheat straw fiber. The introduction of MAPP to the system increased the flow behavior of the polymer dispersed the wheat straw fiber uniformly, and decreased the melt viscosity. The PP composites introduced by 2 wt% MAPP showed the lowest storage flexural modulus (E′) over the entire temperature range from 25—150°C, due to better compatibility between the wheat straw fiber and matrix. The PP composites made of with 20 wt% alkalized and MAPP treated wheat straw fiber showed the highest E′. The differential scanning calorimeter (DSC) study revealed that introducing the wheat straw fiber to PP matrix increased the melting temperature and crystallization temperature. The PP composites reinforced with the alkalized and MAPP treated fiber had the highest rate of crystallization as a consequent of the co-effect of alkalization and esterfication.