Temperature-Microstructure Mapping of the Initiation of the Plastic Deformation Processes in Polyethylene via In Situ WAXS and SAXS

Abstract

A mapping of the initiation of the three major plastic deformation processes in polyethylene is established as a function of temperature and microstructure. In this aim, a collection of polyethylene samples covering large ranges of crystallinity 0.50 < Xc < 0.80 and crystal thickness, 8 nm < Lc <29 nm was prepared. The strain onsets of crystal shear, cavitation, and martensitic-like transformation were determined from in situ WAXS and SAXS experiments during uniaxial tensile tests. The construction of the map was made via the determination of the critical Lc values at which a competition exists between two processes for various temperatures in the range 25–100 °C. These critical Lc values were reported on a temperature versus crystal thickness diagram where the various regions are assigning the order of occurrence that the three plastic processes should obey during tensile testing. Examples are given for illustrating the use of the map for predicting the order of occurrence of the three processes as a function of temperature for a given microstructure. Extrapolation is proposed for the behavior of materials having a crystal thickness out of the range of the present study.