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Effects of alkalization, acetylation, and maleic anhydride grafted polypropylene (MAPP) treatments on the thermal and chemical properties of the wheat straw fiber were investigated using thermogravimetric analysis, infrared spectrophotometer, X-ray diffraction, and scanning electric microscopy techniques. It was found that the wheat straw fiber was not prone to weight loss at 170 C and the treated wheat straw fiber exhibited more thermal stability than the untreated wheat straw fiber. Alkalization increased relative cellulose content and exhibited more crystalline due to a rearrangement of the crystalline regions. It also prolonged the degradation of the wheat straw fiber at higher temperatures due to the increased crystallinity of cellulose. Compared with alkalization, acetylation had more effect on the thermal and chemical stability in the wheat straw fiber contributing to a formation of ester bonding. MAPP improved the thermal stability partly because of a lower grafted ratio of maleic anhydride. Acetylation and MAPP treatment both decreased the crystallinity of the wheat straw fiber.

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Wheat straw fiber-polypropylene (PP) composites were prepared to investigate the effects of wheat straw fiber content (10,20, 30, 40, and 50 wt %), fiber size (9, 28, and 35 mesh), and maleic anhydride grafted polypropylene (MAPP) concentration (1, 2, 5, and 10 wt %) on the static and dynamic mechanical properties of the wheat straw fiber-PP composites in this study. The tensile modulus and strength of the composites increased linearly with increasing wheat straw fiber content up to 40%, whereas the elongation at break decreased dramatically to 3.78%. Compared with the composites made of the longer wheat straw fiber, the composites made of the fines (>35 mesh) had a slightly higher tensile strength of 31.2 MPa and tensile elongation of 5.39% at break. With increasing MAPP concentration, the composites showed an increase in tensile strength, and the highest tensile strength of 34.0 MPa occurred when the MAPP concentration reached 10 wt %. As wheat straw fiber content increased from 0 to 40%, the flexural modulus of the composites increased gradually from 1335 to 3437 MPa. The MAPP concentration and wheat straw fiber size distribution had no appreciable effect on the static flexural modulus of the composites. The storage flexural modulus of the composites increased with increasing wheat straw fiber content. The scanning electron microscopy (SEM) observation on the fracture surface of the composites indicated that a high wheat straw fiber content (>30 wt %) resulted in fiber agglomeration and a reduction in interfacial bonding strength.