Year

1997

Degree Name

Master of Engineering

Department

Department of Materials Engineering

Abstract

Macroscopic and microscopic adhesion tests were performed in an attempt to make quantitative adhesion measurements. The microscopic adhesion measurements using the AFM provided an opportunity to juxtapose these results with values predicted by wellestablished thermodynamic theory. Good correlation was found when probing lowenergy interactions. Interactions measured on high-energy surfaces were lower than theory predicts, however, these results are consistent with other AFM results.

Several limitations of the AFM as a microscopic adhesion tester were elucidated - in particular the necessity for the accurate evaluation of the tip radius and cantilever spring constant. Scan rate an applied load also appeared to play a minor role in the measured adhesion -low loads and low scan rates appearing to produce more accurate data.

Macroscopic adhesion tests performed on polyester and fluorocarbon paint coated sheet steel, found the white polyester in question to be significantly poorer than all other paint combinations evaluated in terms of pull-off strength, and environmental durability, irrespective of ageing environment. This appears to be a result of the poor adhesion of the pigment to the binder. Primer "B" (standard duty) primer appeared to provide superior pull-off strength to Primer "A" (severe environment) primer, and it was noted that a thinner layer of primer vastly increased the measured pull-off strength of the paint coating to the substrate.

The results of the macroscopic tests indicate that the adhesive properties of the paint coatings are much superior to their cohesive strength, and that attempts to improve the performance of these coatings should concentrate on their mechanical properties rather than their adhesion.

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