Mechanical properties and water absorption behavior of injection-molded wood fiber/carbon fiber high-density polyethylene hybrid composites

High-density polyethylene (HDPE) has been widely used to make wood–plastic composites (WPC) in the past decades for building materials, automotive, packaging, and furniture industry. However, the relatively poor mechanical properties have limited the applications of WPC. To address this issue, this study introduced a small of amount of lightweight and high-strength carbon fiber (CF) into the WPC matrix, to make hybrid composites through a cost-effective direct injection molding process. This paper investigated the mechanical properties and water absorption behaviors of hybrid HDPE composites with wood fiber (WF) and CF. Compared with WPC with the same fiber loading, the hybrid composites had 40% increase in tensile strength and 253% increase in tensile modulus. The effects of water absorption on the mechanical properties of hybrid composites were interpreted with two competing mechanisms (i.e., interfacial bond weakening and fiber swelling). This study implies that adding a small amount of CF to WPC in direct injection molding would be another approach for enhancing the mechanical properties without additional operating cost.