Effect of nano TiO2 on the cellular structure and mechanical properties of wood flour/polypropylene composite foams via mold-opening foam injection molding

Microcellular foamed wood-plastic composites (WPCs) have shown good development prospects in environmentally-friendly composites. Herein, the foamed wood flour (WF)/polypropylene (PP) composites were fabricated by mold-opening injection molding using supercritical N 2 as a physical foaming agent. The effects of nano TiO 2 on the microcellular structure and mechanical properties of WF/PP composites were investigated, and the results show that nano TiO 2 accelerates the crystallization rate and reduces the crystallinity of PP, which is beneficial to the formation of foamed homogeneous systems and cell growth in the WF/PP composites. This is mainly due to heteronucleation effect of nano TiO 2 , resulting in the refinement of crystal. Molecular chain movement of PP is limited with the introduction of nano TiO 2 , resulting in increased the melt elasticity of WF/PP composites, thereby reducing cell coalescence and collapse. With the addition of 5 wt% nano TiO 2 , the cell density was increased by 393.8%, the cell size was reduced by 54.4%, and the cell size homogeneity was clearly improved. In addition, impact strength increased by 33.3%. The improved foamability of WF/PP composites using nano TiO 2 shows a great promise for the production and application of WPC foams, especially in automotive, packaging and building areas.