The effects on the internal defects of the rice straw (RS)/high-density polyethylene (HDPE) composites are investigated by removing the extractives with cold water (CW), hot water (HW), and 1% alkaline (AL) solution. The characteristics of the RSs are measured by chemical composition, Fourier transform infrared, X-ray diffractometry, scanning electron microscopy, thermogravimetric analysis, and bulk density testing. The three extractive removal methods change the surface features of the RS and increase the interphase adhesion between the RS and the HDPE matrix. As a result, the inner defects of the RS/HDPE composites are eradicated and the die swell phenomenon disappear. The flexural modulus, flexural strength, and impact strength of the final composites increase by 95.59, 83.29, and 154.79% in the HW extraction method. The CW and the AL extraction also significantly improve the static mechanical properties of the obtained RS/HDPE composites.

In this work, titanium dioxide (TiO2)-incorporated rice straw fiber (RS)/poly(butylene succinate) (PBS) biocomposites were prepared by injection molding with different TiO2 powder loadings. The RS/PBS with 1 wt% TiO2 demonstrated the best mechanical properties, where the flexural strength and modulus increased by 30.34% and 28.39%, respectively, compared with RS/PBS. The non-isothermal crystallization of neat PBS, RS/PBS composites, and titanium-dioxide-incorporated RS/PBS composites was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The non-isothermal crystallization data were analyzed using several theoretical models. The Avrami and Mo kinetic models described the non-isothermal crystallization behavior of neat PBS and the composites; however, the Ozawa model was inapplicable. The crystallization temperature (Tc), half-time of crystallization (t1/2), and kinetic parameters (FT) showed that the crystallizability followed the order: TiO2-incorporated RS/PBS composites > RS/PBS > PBS. The RS/PBS with 1 wt% TiO2 showed the best crystallization properties. The Friedman model was used to evaluate the effective activation energy of the non-isothermal crystallization of PBS and its composites. Rice straw fiber and TiO2 acted as nucleating agents for PBS. The XRD results showed that the addition of rice straw fiber and TiO2 did not substantially affect the crystal parameters of the PBS matrix. Overall, this study shows that RS and TiO2 can significantly improve the crystallization and mechanical properties of PBS composites.