Automated techniques for surface coating deterioration studies

Abstract

This thesis describes the development of automated techniques for use in accelerated ageing studies involving polymer based surface coatings. These techniques were required in order that the effects of low concentrations of pollutant gases, specifically nitric oxide, on surface coatings could be investigated with a reasonable degree of precision. As part of this programme, an automated accelerated ageing cabinet was constructed, to provide facilities which are capable of simultaneously or independently exposing coatings to various ageing elements under accurately controlled conditions. A second and more widely useful aspect involved the development of an automated goniophotometer interfaced to a micro computer data handling system. The automation and interfacing of the goniophotometer has converted a previously cumbersome and tedious analytical technique into a rapid, highly sensitive, non-destructive method for assessing the reflective characteristics of a surface. The computer programme provides a quick and accurate means of analysing the goniophotometric data, and combines this with rapid storage and retrieval for future analysis and comparison. By recording this data on a disk or cassette, a record is retained which encapsulates the essential reflective properties of a surface which are subjectively considered by an individual in assessing gloss and texture. The automated goniophotometer and the accelerated ageing cabinet have been used, in conjunction with colorimetry and infrared spectroscopy, to investigate the reaction between nitric oxide and various polymer based surface coatings. These were, a series of poly (vinyl chloride) coatings and aselection of commercial powder coatings. The nature and roles of specific chemical intermediates, formed between these coatings and nitric oxide, has been considered. In particular, the results indicated that in weathering environments nitric oxide stabilises degradation caused by ultra-violet light. The computer was used extensively to superimpose goniophotometric curves to isolate individual deteriorative influences on the degradation of the coatings.