Elimination of stress whitening in high‐molecular‐weight polyethylene

Abstract

AbstractHigh‐molecular‐weight polyethylene (HMWPE) sheets have been cold rolled biaxially to different reductions in thickness. After 40% or more reduction in thickness by cold rolling, the stress‐whitening phenomenon in HMWPE was eliminated. To find out the reason of elimination of stress whitening by cold rolling, different techniques were employed. The measurement of hardness, density, and strain distribution of the specimens were carried out for the study of the differences in mechanical and physical properties of the stress whitened and nonwhitened specimens. Recovery of density, hardness, and dimensions of the specimens due to heating were also studied. Differential scanning calorimetry (DSC) and polarized‐light microscopy were used to study the melting, and recrystallization behavior and scanning electron microscopy (SEM) were used to study the surface texture of the specimens. Based on the results of the different techniques employed, it is concluded that after cold rolling, especially biaxially rolled, due to the combined forces of compression and shear acting on the specimens from different directions, the macro‐and micro‐imperfections of the material may be eliminated to some extent. At 40% or more rolling reduction, the imperfections were largely eliminated; hence stress whitening did not occur.