Structural consequences arising from the application of stress to polyolefines

Lator, Bruno Gratien (1987) Structural consequences arising from the application of stress to polyolefines. University of Southampton, Doctoral Thesis.

Abstract

Structural consequences involved during the application of stress to high density polyethylene have been studied by infra-red spectroscopy. Two cases were considered: the plastic deformation of polyethylene in the solid state and the smearing-extrusion of polyethylene in the molten state along a moving tube. In the first case, the concentration of carbonyl and vinyl group formed has been correlated to the number of bonds broken during the plastic deformation under different conditions. It was concluded that in a sample exposed to various temperatures, elongations, times, and of various thicknesses, the number of bonds which broke was not consistent with the Peterlin theory of plastic deformation, wherein a set of solid state rearrangements are envisaged producing a fibrous material from a spherulitic lamellar precursor. The research described in the thesis leads to the suggestion that the mechanical work must be concentrated into very small volumes in the neck region leading to localised melting and subsequent recrystallization. In the second case, a high degree of orientation of the molecules has been achieved along the flow direction concentrated mainly at the polymer-tube interface (inside surface). The evidence shows that the structure varies between a spherulitic, or row nucleated structure produced by a `low stress' induced crystallnization on the die-polymer interface (outside surface), and a `high stress' nucleated crystalline structure where chain folded crystals grow epitaxially on very small amounts of highly oriented chains on the inside surface and aligned along the flow direction. (D82525)

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