Mechanical reinforcement and creep resistance of coextruded wood flour/polyethylene composites by shell‐layer treatment with nano‐ and micro‐SiO₂ particles

Nano‐ and micro‐SiO₂ particles (termed nSiO₂ and mSiO₂, respectively) were incorporated in the shell layer of a coextruded wood flour/high density polyethylene composite (WF/HDPE) to improve the mechanical properties and inhibit creep behavior. The effects of loading content, particle size, and surface treatment of the silica with vinyl trimethoxy silane (VTS) were investigated on the properties of the resulting coextruded WF/HDPE composites. Scanning electron microscopy revealed proper interfacial adhesion between the core and shell layers. nSiO₂ exhibited higher reinforcement efficacy than that of mSiO₂ for the shell‐layer materials. Incorporation of the VTS‐treated nSiO₂ caused an increase in flexural‐ and impact strength of the coextruded composites by 29% and 57%, compared to the non‐silica filled coextruded WF/HDPE controls, respectively. Incorporation of nSiO₂, either untreated or VTS‐treated, enhanced creep resistance of shell layer materials; however, only VTS‐nSiO₂ worked for the coextruded composites. These findings demonstrate that filling with silica, particularly VTS‐treated nSiO₂, in the shell layer substantially and economically reinforces coextruded shell/core‐structured WF/HDPE composites. POLYM. COMPOS., 40:1576–1584, 2019. © 2018 Society of Plastics Engineers