Thesis-1990-Blacker.pdf (23.54 MB)
Electrostatic phenomena in polyethylene
thesis
posted on 2012-09-13, 11:39 authored by Richard BlackerMeasurement of the electrostatic nature of materials is an essential step towards
understanding the underlying processes and to the eventual modification of charge
behaviour. Indirect monitoring was achieved by resistivity measurements, however, this
approach is limited to studying the material and not the electrostatic charge and is, in general,
not a satisfactory method. Electrostatic field meters allowed the electrical behaviour of
polyethylene to be monitored; its charge accumulation and decay processes were accurately
monitored, thus giving a good information base for material modification later in the
programme. The use of a data-logging system (based on the Apple//e computer) allowed the
manipulation and long term storage of information, whilst giving improved presentation of
results.
High Density Polyethylene is an intrinsically insulating polymer whose electrostatic properties
can be greatly modified by the use of internal antistats. Such additives migrate to a surtace
and become effective [at reducing surtace resistivity] over a period of time depending on the
diffusivity of the antistat species, and on the external atmospheric conditions, particularly
humidity. The effusion of antistat onto a surface was monitored by surtace analysis
techniques including X-ray photoelectron scattering, goniometry and infra-red spectroscopy,
however, whilst such techniques offered a direct indication of the surtace state and the effect
of any surtace modification, electrostatic testing was found to be the most sensitive technique
for following antistat action.
It is possible to tailor individual antistats to specific applications, however such usage provides
only specific protection (fast acting but short lived, or slow acting but long lived). Two single
antistat species were combined, and a synergistic effect was obtained for fast acting and long
lived systems.
It was found that antistats operate by welting (coating) an insulating surtace, and then
absorbing atmospheric water vapour, thus lowering the surtace resistivity. Complete surtace
coverage is not possible over an HDPE surtace due to its low surtace energy (28mNm'1),
however, more complete surtace coverage was achieved by surtace oxidation [raising the
polar surlace energy). Natural HDPE is not readily susceptible to surface oxidation; therefore
oxidation treatment had only a limited effect. An addition of the fully compatible polymer
LLDPE raised the oxidation level and allowed more complete antistat coverage, thereby
improving antistatic activity and raising the level of protection gained by using a standard level
of antistat. A patent is being taken out covering the use of LLDPE in conjunction with mixed
antistat systems.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Publisher
© Richard BlackerPublication date
1990Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.240780Language
- en