The theme of this report is the examination of the interphase. Three different aspects
of the interphase have been examined.
Firstly, the detrimental effects of contamination upon the interphase were examined. Substrates were contaminated with quantified levels of PDMS (polydimethylsiloxane)
in an attempt to create weak boundary layers, and the resulting performance of joints
manufactured from these substrates was evaluated. A notable reduction in bond
strength was observed with specimens prepared from two different toughened
adhesive systems whilst a similar system formulated without any toughener remained
comparatively unaffected, demonstrating the capability of the epoxide adhesive to
accommodate several monolayers of this contaminant.
The second aspect of the interphasial region studied was the chemical heterogeneity
within the bondlines of adhesive joints. An excess of unreacted curing agent as
discovered in the lower interphasial regions of tensile test specimens coupled with a
tendency for near interfacial failure within this region. The curing reagent was found
to be settling out of the adhesive during cure. Significant differences were also
observed in the interphasial polymer compared to the bulk on samples taken from
annular joints that had undergone premature failure.
Thirdly, the effects of the deliberate creation of an interphase for the enhancement of
the bondabiIity on steel substrates was examined. In this aspect of the work, a new
adhesive and novel surface treatments have been identified as providing potential
improvements in performllnce over the current bonding system. Of particular
importance was the performance of a phosphate-based treatment Bonderite
9Ol/Pyrene 8-90, which gave demonstrable improvements over the existing strip
laminate bonding system. The improved performance was attributed to a very stable
phosphate layer deposited on the steel substrate from the chemical treatment,providing a wettable, uniform, micro-rough, corrosion resistant surface ideal for
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.