Use this URL to cite or link to this record in EThOS:
Title: Environmental degradation of the compostable plastic packaging material poly(lactic) acid and its impact on fungal communities in compost
Author: Karamanlioglu, Mehlika
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
Availability of Full Text:
Access from EThOS:
Access from Institution:
Conventional plastics have been used for decades in a diverse range of applications, however, many are resistant to degradation, leading to environmental pollution and their manufacture is dependent on non-renewable fossil fuels. Therefore, there has been an increasing need for eco-friendly biodegradable materials from renewable resources. Poly(lactic acid) (PLA) is a compostable polyester with a hydrolysable backbone that is susceptible to biodegradation and produced from renewable feedstocks. PLA has mechanical qualities comparable to non-biodegradable plastics, and currently is commercialized as food-packaging polymer for short shelf-life products. However, while PLA hydrolysis at elevated temperatures proceeds abiotically, ultimately releasing lactic acid and short chain oligomers, the role of microorganisms is unclear. Since PLA short-shelf life products are disposed after use, understanding the role of microorganisms and the effect of degradation on microbial populations in the environment is important. Therefore, the aims of this research was to (a) determine the relative importance of biotic and abiotic factors on PLA degradation; (b) to isolate putative fungal PLA degraders from the surface of PLA when buried in compost or soil and to test their ability to degrade PLA; (c) to assess the impact of PLA degradation on fungal communities when entering compost systems. The roles of abiotic and biotic factors in the degradation of high molecular weight PLA were investigated by comparing degradation rates in compost, soil and sterile water at temperatures of 25°, 37°, 45°, 50° and 55°C. Tensile strength loss and molecular weight decline of PLA in microorganism-rich compost and soil were greater than chemical hydrolysis in sterile water at elevated temperatures (above 45°C) indicating microorganisms can directly enhance PLA degradation. Since extensive fungal growth was observed on the surface of PLA when buried in compost and soil, putative fungal PLA degraders were isolated from PLA surface and their community profile on PLA surface was compared with the compost and soil community with a molecular method, terminal restriction fragment polymorphism (TRFLP). Among the identified fungi, Thermomyces lanuginosus was the dominant isolate recovered and shown to enhance PLA degradation in compost at 50°C. The fungal community profile on PLA surface was different than the fungal profile in compost and soil suggesting enrichment for PLA degraders on the surface of PLA. In order to determine the impact of PLA degradation on the fungal compost community, two different high molecular weight PLA sources, films and granules were buried in compost at 10%, 25% and 50% (w/w) concentration for 4 months at 25°C and 50°C and the community profile analysed by TRFLP and pyrosequencing. TRFLP revealed that when PLA did not degrade, the fungal community shifted back toward the initial compost community profile, however, when PLA degraded to its monomers releasing lactic acid at 50°C at a concentration of 50% (w/w) it changed the fungal community profile and decreased the fungal diversity. Pyrosequencing revealed that the presence of PLA enriched for Thermomyces in the compost population over time.
Supervisor: Robson, Geoffrey Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Plastics, polylactic acid, PLA, biodegradation, TRFLP, pyrosequencing