Thesis-1995-Shingleton.pdf (3.58 MB)
Characterisation of peroxide crosslinked polyethylene
thesis
posted on 2017-05-18, 15:54 authored by Jason A. ShingletonBritish Gas have been using polyethylene pipe and fittings for gas
distribution since 1969. The medium density, and more recently high density
polyethylene pipes are produced by a simple and well established extrusion
process. Unfortunately the production of fittings, especially large diameter
fittings is not so simple. Traditionally pipe fittings are made from either
injection moulding or by other fabrication techniques which require
subsequent cutting and welding of different parts to produce the finished
article. Recently however the methodology has been developed to facilitate
the production of fittings by rotational moulding. Incorporated into the new
methodology is the ability to produce crosslinked fittings by peroxide
inclusion. Crosslinking of the pipe fittings has a major advantage in that it
produces a substantial improvement in the mechanical properties of the
polymer. Of particular importance is the improvement in stress crack
resistance. Stress cracking is presently the primary mode of failure in
polyethylene pipelines. Cross linking should help to reduce the susceptibility
of the pipeline to failure by this method.
The purpose of this project has been to investigate the crosslinking
process in two rotational moulding grades of polyethylene. In particular a
study has been made of the relationships between various chemical and
physical properties, and of how these change upon material modification.
A series of compression moulded samples containing increasing levels
of peroxide have been produced for both polymers. Characterisation of these
samples was undertaken using such techniques as Differential Thermal
Analysis, Fourier Transform Infrared Spectroscopy, Gel Permeation
Chromatography, Gel Content and Microscopy. The results have shown that
as peroxide concentration is increased gel content rises sharply before
reaching a maximum value. In contrast to the gel content, the crystallinity of
the samples was shown to decrease. Infrared analysis provided the facility to
monitor the variation in molecule end group concentration with changing
peroxide levels. It was found that increasing the level of peroxide resulted in
a decrease in the concentration of terminal vinyl unsaturation in an inverse
relationship to gel content results. Subsequent gel permeation
chromatography analysis demonstrated that the terminal vinyl groups were
being lost in a chain extension mechanism which resulted in an increase in
the molecular weight of the samples.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Publisher
© J.A.ShingletonPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
1995Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en