Molecular dynamics simulation of static crystallization and tensile deformation of bimodal HDPE/UHMWPE: Influence of long chain content

Abstract

The effect of long chain content (XL) on the static crystallization and tensile deformation mechanisms of bimodal HDPE/UHMWPE was investigated by molecular dynamics simulations. The crystallization of HDPE/ UHMWPE undergoes three stages: nucleation, rapid growth of lamellar crystals, and stabilization. The increase of XL leads to the formation of more nucleation sites, which promotes nucleation, but at the same time leads to an increase of entanglement sites, which is not conducive to the movement of the long chains to the growth front to fold and form lamellar crystals. Tensile deformation is performed on the crystallized models and the systems exhibit three stages: elastic deformation, plastic deformation and stress hardening. During deformation, the increase of XL improves the orientation nucleation and crystallinity (Xc), but when XL exceeds 4 wt.%, the entanglement effect becomes more pronounced, leading to a decrease in Xc. The effect of temperature is also taken into account: at low temperatures, a suitable range (2-4 wt.%) exists to optimize the mechanical properties of the material. At high temperatures, there is almost no stress-hardening phenomenon, but the addition of long chains has an impeding effect on the melting of the lamellar crystals, and when XL is greater than 8 wt.%, stress-induced melting is more likely to occur, accelerating the melting of the crystals.

Keywords

• molecular dynamics simulation
• static crystallization
• long chain content
• nucleation
• tensile deformation