Studies on the Biodeterioration of Polyurethanes by Fungi

Abstract

The work reported in this thesis was carried out to increase knowledge of the mechanisms by which fungi deteriorate polyurethanes and the conditions which encourage this to take place. Five fungi, Gliocladium roseum, Chaetomium globosum, Penicillium citrinum, Aspergillus fumigatus and Nigrospora spherica, were selected as potential biodeteriogens of polyurethanes from initial screening experiments. This list included three species which had not been previously reported as polyurethane deteriogens. Their response to temperature, pH and their modes of attack on polyurethanes were studied. The results indicated that exoenzymes were the major cause of the biodeterioration which took place, and therefore, protease, esterase and urease activities of the fungi were studied using modifications of Rautela and Cowling's test tube method. A comparison of enzyme activities, among the test fungi and their respective degradation rates was made in order to study the relationship between enzymes and biodeterioration. For this purpose, percent weight losses, changes in tensile strengths and percent ultimate elongations of four polyester polyurethane and one polyether polyurethane elastomers were used. The results indicated that 'polyurethane degrading' enzymes are inducible and very closely resemble esterases. The susceptibility of polyester types and the resistance of polyether types, in conjunction with the results from chemical and spectral analysis of degraded products supported these findings. The investigation suggested that the splitting of the molecular chains by the 'polyurethane degrading' enzyme systems took place probably via two paths, i.e. random splitting and regular splitting. This study has increased knowledge of the fungal deterioration of polyurethanes by establishing the contribution of esterases in the breakdown process and the physical and mechanical changes which accompany this.