Influence of different clays on the mechanical, thermal, and water absorption properties of recycled high-density polyethylene/wood flour hybrid composites

Wood plastic composites based on recycled high-density polyethylene (r-HDPE)/wood flour with the addition of organically modified clays were prepared by melt mixing and compression molding. The effect of two different types and contents of clays, bentonite and layered double hydroxide - on the mechanical, thermal, and water absorption properties of the wood plastic composites - was examined to identify the most effective clay type for wood plastic composites. It was found that incorporation of 2wt% modified bentonite (mBNT) clay was the most effective in the composite formulation; it has significantly enhanced the properties of the wood plastic composites. The scanning electron micrographs of the fractured surfaces showed improved interfacial adhesion of the composite components. The tensile strength of wood plastic composites was increased by 9.7% when 2wt% mBNT clay was incorporated in the composite formulation; however, the tensile strength slightly decreased as the clay content was further increased. The izod impact strength was lowered about 10.5% by 2wt% mBNT clay. Moreover, the addition of 2wt% mBNT clay enhanced the water resistance of the wood plastic composites by 27.5% after immersion in water for five days. On the other hand, the modified layered double hydroxide (mLDH) clay did not cause any remarkable improvement in the properties of the wood plastic composites. The tensile strength showed a decreasing trend with an increase in mLDH content. However, both clays did not improve the thermal stability of wood plastic composites. In addition, there are no noticeable changes in the values of melting temperature by increasing the content of clays. The experimental results indicated that the properties of the wood plastic composites were significantly improved when combined with the appropriate clay type and content. However, the interaction between wood flour and the intercalated clay particles as well as the processing conditions will need further study.