Segmental Mobility in Polyethylene Near-Surface Layers

Abstract

The comparison study of segmental mobility in the near-surface layers and in the bulk of polyethylene of various , crystallized under different conditions, was carried out with the help of plasma-induced thermoluminescent and radiothermoluminescent methods, differential scanning calorimetry, dynamic mechanical analysis, and wide angles X-ray scattering. The morphology was investigated by scanning and transmission electron microscopy. The samples were quenched from the melt or isothermally crystallized during 6 h at 125°C. It was found that the defreezing temperature of segmental mobility in the near-surface layers of high density polyethylene crystallized from quiescent melts was less than in the bulk by 60 K. Quite to the contrary, the segmental mobility in the near-surface layers of ultrahigh molecular weight polyethylene nascent particles that crystallize during synthesis in confinement conditions is hindered as compared with that in the bulk. The reason for the observed difference is discussed.

Keywords:

• near-surface layers
• polyethylene
• relaxation
• segmental mobility
• thermoluminescence
• ultrahigh molecular weight polyethylene

Acknowledgment

The authors would like to thank the support of a research grant from the Russian Foundation of Basic Research (project No. 13-03-00634).

Dedicated to Prof. B. M. Ginzburg on his 75th anniversary

Notes

It is noted that there is still disagreement over the use of the terms relaxation and transitions. Although first- and second-order transitions are well defined in terms of the Ehrenfest criteria, neither term, by itself, as applied to the results of such techniques as dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), RTL, etc., is defined by the latest IUPAC Polymer Terminology report (Glossary of Terms Relating to Thermal and Thermo-mechanical Properties of Polymers, Project 2006-041-1-400). The term “relaxation-transition” is used here to describe both types of changes in properties (Myasnikova, L. P. Transitions and Relaxations. Encyclopedia of Polymer Science and Technology. Wiley & Sons, published online 11/15/10 DOI: 10.1002?0471440264.pst375)