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.

The removal of rice straw extractives increases the interphase adhesion between rice straw and the high-density polyethylene (HDPE) matrix, while eradicating the inner defects of rice straw/HDPE composites. This study investigated the effect of rice straw extractives removal on the dimensional stability (water uptake and thermal expansion), dynamic mechanical properties, creep, and stress relaxation of rice straw/HDPE composites. Cold water (CW), hot water (HW), and 1% alkaline solution (AL) extraction methods were utilized to remove rice straw extractives. Extracted and unextracted rice straws were mixed with HDPE, maleated polyethylene (MAPE), and Polyethylene wax to prepare composites via extrusion. Removal of rice straw extractives significantly improved the dimensional stability, dynamic mechanical properties, and creep and stress relaxation of rice straw/HDPE composites, with the exception of the thickness swelling of the AL/HDPE and the thermal expansion of the rice straw/HDPE composites. HW/HDPE exhibited the best comprehensive performance.