Crystallization and melting of polyethylene strongly cross-linked in the molten state

Abstract

We examined the crystallization and melting behavior of highly cross-linked polyethylene (xPE) samples, including structural characterization of the resulting crystalline domains. Using γ-ray irradiation, cross-linking was performed in the molten state and not in the solid state. This approach assured a statistical and homogeneous distribution of the cross-link points. Upon increasing the radiation dose, the molecular weight of the strands connecting the cross-link points reached values even lower than that of the strands between physical entanglements. Results from differential scanning calorimetry as well as small-angle and wide-angle X-ray scattering showed for Mc < ca. 1800 g mol−1 and Mc > ca. 1800 g mol−1, respectively, distinctly different variations of the melting temperature, the crystallization rate, the degree of crystallinity and the fraction of non-crystallizable CH2 units per strand. Both unit cell parameters, a and b, increased with increasing cross-link density, much more than the published changes for corresponding samples cross-linked in the solid state. We conclude that the increase in cross-link density caused the exclusion of a progressively higher number of chemical cross-link points from crystalline domains, which, in turn, generated increasingly higher tensions on all chain segments, thereby reducing their conformational flexibility and chain folding possibility. As a consequence of the respectively induced changes in physical properties especially for our xPE samples with the highest cross-link density, we observed materials with extremely low crystallinity and melting temperatures close to room temperature, transforming polyethylene into a material with rubber-like properties.

Graphical abstract: Crystallization and melting of polyethylene strongly cross-linked in the molten state

Supplementary files

Article information

Article type
Paper
Submitted
15 May 2025
Accepted
23 Jul 2025
First published
24 Jul 2025

Soft Matter, 2025, Advance Article

Crystallization and melting of polyethylene strongly cross-linked in the molten state

J. Li, W. Wang, Y. Shi, B. Heck, C. Luo, J. D. C. Christiansen, D. Yu, G. Reiter and S. Jiang, Soft Matter, 2025, Advance Article , DOI: 10.1039/D5SM00504C

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