Preparation of waste Camellia oleifera shell and high‐density polyethylene composites: Effect of pretreatment on fiber and materials properties

Abstract The preparation of wood‐plastic composites (WPCs) with high filling fibers and excellent physical properties remained a great challenge. This study used Camellia oleifera shell (COS, agroforestry product waste) as raw material, and prepared 60 wt% COS/high‐density polyethylene (HDPE) WPCs using profile extrusion method through pretreating fibers including hot water, hot steam, alkali, acid, extraction, and fine fiber screening. After pretreatments, the relative contents of cellulose and lignin increased, the relative contents of hemicellulose and extract decreased significantly, and the length‐diameter ratio was improved. The flexural strength, tensile strength and impact strength of hot water and steam heat treated composites reached 31.4, 17.1 MPa and 6.9 kJ/m ² , 31.8, 16.8 MPa and 6.7 kJ/m ² , respectively. Compared with untreated 28.8, 14.7 MPa and 5.5 kJ/m ² , the advantages were more obvious. Alkali treatment and acid treatment improved the thermal stability and residue rate of the material. Extraction treatment and alkali treatment significantly reduced the processing torque force, which was conducive to processing, while acid treatment was the opposite. The highest water absorption and thickness expansion rate were 13.75% and 3.60% respectively at 7 days after alkali treatment, which were considerably higher than 5.60% and 0.78% without treatment, while other pretreatments improved the dimensional stability of the material. Highlights High filling Camellia oleifera shell waste/HDPE composites were prepared. Physical and chemical pretreatments improved interfacial adhesion of the composites. Heat treatments significantly improved mechanical performance of the composites.