FRACTOEMISSION FROM HIGH-DENSITY POLYETHYLENE - BOND BREAKING VERSUS TRIBOLOGICAL STIMULATION

We reexamine the emission of electrons and positive ions from high density polyethylene (HDPE) during tensile deformation at strain rates on the order of 30% s-1. Earlier reports have suggested that electron emission due to bond scissions accompanying deformation of HDPE have been observed. Here we focus on the role of small frictional effects on the polymer at the edges of the clamps due to slippage during elongation. We show that when slippage is eliminated, the deformation-induced particle emission vanishes. Thus, the prefailure electron and positive ion emission is apparently not due to bond scissions as a result of tensile deformation of the polymer but to slippage of the polymer in the grips. We discuss the processes occurring during tribological loading which produce intense, longer lasting emission during and after stimulation. We present evidence that the emission due to tribological loading involves charge transfer upon contact between metal and polymer, mechanical separation of charge, and subsequent dynamic stimulation of the polymer surface due to energetic charge motion (surface flashover).