Structural evolution of low-entangled UHMWPE gel films with reserved shish crystals and different entanglement degrees during stretching.

Shish-kebab crystal is a crucial crystalline morphology in polymers, and its formation and evolution are paramount for achieving high-performance materials. In this study, using UHMWPE as an example, we employed precise temperature control in the gel molding process to prepare low-entangled UHMWPE gel films containing reserved shish crystals, Distinguished from other molding systems, gel molding, due to the presence of small-molecule solvents, not only reduces the entanglement degree of the system but also provides a favorable environment for molecular chain disentanglement, and thus is considered as a low-entanglement system that is easily disentangled. We investigated the structural evolution of the films at different stretching temperatures by employing in-situ WAXD, SAXS, USAXS, along with ex-situ SEM and DSC methods. Furthermore, the impact of entanglement degree on the evolution of crystal structures was explored through the change of molecular weight. 2D-USAXS results reveal the longer stripe scattering signals than previous studies, indicating a more pronounced ordered arrangement of shish crystals. Simultaneously, we discovered that only when molecular chains with an appropriate degree of entanglement were induced to disentangle by stretching with the presence of small-molecule solvents can the high orientation of crystals be facilitated, thereby promoting the evolution of crystal structure. Reserved shish crystals can induce crystal orientation during stretching and facilitate structural evolution. Building upon earlier investigations, this study innovatively through the dual-factor (the molecular weight and stretching temperature) control of the suitable entanglement degree and disentanglement conditions, allowing for reasonable control of the growth and evolution of shish-kebab crystals in low-entangled systems. During the stretching process of low-entanglement UHMWPE films with solvents, the disentanglement of molecular chains is facilitated. While the reserved shish crystals simultaneously drive the structure evolution of crystals. [Display omitted] • Low-entangled UHMWPE gel films with reserving shish crystals are prepared by precise temperature control. • Reserved shish crystals enhance the shish-kebab structural evolution during the stretching of low-entangled solvent films. • The appropriate degree of chain entanglement can contribute significantly to the evolution of crystal structures. [ABSTRACT FROM AUTHOR]