Abstract
Plastics discarded as litter are both a nuisance to man and a danger to wildlife. Low density polyethylene (LDPE) is one of the most widely used plastics but its environmental degradation is very slow. This may be in part due to its hydrophobicity making microbial colonisation difficult. Treatments were carried out to modify the surface of LDPE film in order to reduce its hydrophobicity with the aim of increasing microbial attachment, colonisation and subsequent microbial degradation. Surfactant and vegetable oils were applied, chemical oxidation, ultra-violet light exposure and corona discharge pre-treatments were used to enhance microbial colonisation. Changes to tensile strength, extension, free surface energy and surface chemistry (by FTIR) were measured in addition to studies on microbial colonisation and degradation. Corona discharge treatment (CDT) was found to be the most successful treatment. It reduced hydrophobicity and enhanced colonisation and degradation. Results indicated that modification by CDT was only to the very surface of the LDPE film leaving its usage unaffected. Practical problems associated with most of the other treatments meant CDT was the treatment with the most potential for commercial exploitation. After CDT there was visible biodegradation when LDPE film was exposed to aerobic compost for 100 days, but only when backing paper was attached to the film. Untreated film and film without backing paper were not visibly affected. LDPE-degrading microorganisms were isolated from the degraded LDPE film by repeated incubation in media with LDPE as the sole carbon source. Two fungi (tentatively identified as Aspergillus fumigatus and Acremonium charticola) and a Gram negative coccus were isolated. Significant biodegradation was not observed when each isolate was separately re-inoculated on to fresh CDT polyethylene film. However CDT and untreated LDPE film were degraded by the consortium of organisms in the culture using LDPE as a carbon source. The CDT-treated film showed significantly greater degradation. It was concluded that it is possible to make LDPE film more suitable for microbial attachment and colonisation by surface modification and to thus enhance the rate of biodegradation of the film.