The microbial degradation of cellulose acetate
thesisposted on 13.12.2012 by Eleftherios Samios
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Cellulose acetate is a chemical of great industrial importance. Its uses range from the manufacture of textiles to cigarette filters. Cellulose acetate is not biodegraded easily. The aim of this project was to identify, micro-organisms that would attack cellulose acetate and to propose a possible mechanism for the biodegradation process. Discarded cigarette filters were taken from the street and they were plated onto Sabouraud medium, a selective medium for fungi. The growth observed was on the outside of the filters. The middle portion of discarded cigarette filters was opened asceptically, and added in flasks containing nutrient broth. Eighty percent of the flasks showed no signs of bacteriological growth after 24 hours, showing that the inside of the filters was sterile. It would appear, that cigarette filters are a very effective barrier towards microbial penetration. Cigarette filters were laid on potting compost, sand and tile surfaces, in order to monitor their progress over a period of 12 months. These experiments took place under moist and warm conditions, in order to enhance biological growth. The sand and tile experiments were abandoned after a relatively short period as no obvious changes could be seen. The experiments on compost did not show any visible signs of biodegradation for 7 months. After that period, algal growth developed on the filters exposed to light, and a slight decrease in the degree of substitution (the average number of acetyl groups per anhydroglucose unit) was observed. Cellulose acetates with varying degrees of substitution were synthesised and used as carbon source for the growth of the fungus Aspergillus jilmigatus, a common soil species. Previous experiments had shown that this species was the predominant one growing on the filters. It was found that biodegradability varied with the degree of substitution. The higher the degree of substitution, the slower the biodegradation. Biodegradation could not be shown in cellulose acetate with a degree of substitution of 2.5, the material from which cigarette filters are made. The degradation products were analysed by means of FTIR spectroscopy, IH and \3C NMR, solution viscosity and GPC. From the results obtained, it could be deduced that the biodegradation proceeded by a mild de-acetylation (esterase) prior to de-polymerisation (cellulase).