Size effects of silica on the viscosity of ultra‐high molecular weight polyethylene and its disentanglement mechanism

Abstract The viscosity of the polymer composites is closely related to the size effect of the filler. In this study, the size effects of silica fillers on the viscosity of ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The addition of 200 nm and 5 μm silica increase the viscosity, but the 7 nm silica can significantly decrease the viscosity. In order to understand the mechanism of this phenomenon, the multilevel factors of the sample in terms of matrix structure (amorphous phase entanglement, mesophase and crystalline region content) and the mobility of chain segments were analyzed. Rheology and DMA tests have shown that silica affects viscosity mainly by influencing the entanglement in the amorphous phase. Raman tests show that 7 nm silica decrease the viscosity mainly by affecting the content of the mesophase and the mobility of the chain segments in the amorphous region. The annealing process was investigated by Flash DSC, and it was found that 7 nm SiO 2 can accelerate the mobility of UHMWPE chains to form a larger recrystallization area, and the addition of 200 nm and 5 μm SiO 2 did not show a similar phenomenon, proving the strong size effect of SiO 2 on the viscosity and disentanglement of UHMWPE.