Comparison of Two End-of-Life Options for Post-Consumer Polylactic Acid Waste

Abstract

Municipal solid waste (MSW) management is a costly necessity. Petroleum-based plastics are commonplace in MSW of modern, throw-away societies. Petroleum-based plastics do not breakdown from natural processes in landfills and take up large amounts of valuable space. Compostable plastics offer a sustainable solution to petroleum-based plastics. Polylactic acid (PLA) is a plastic made from 100% renewable resources, is compostable at industrial composting conditions (high heat, high moisture) and is also recyclable. Published research describing responsible waste management of PLA is scarce. The University of Wisconsin-Stevens Point (UWSP) currently implements PLA plastic ware at dining facilities on campus. This research compared two end-of-life options of post-consumer PLA waste. First, efficiency of industrial compostability of PLA waste was investigated. The composting experiments were performed using controlled conditions at 55°C comparing the degradation effects on 5, 10, 20 and 30 % (by weight) additions of PLA cups vs. paper cups to equal amounts of compost feedstock. PLA treatments degraded significantly more than paper treatments at all treatment levels. A subsequent plant germination trial evaluated the effects of this compost on plant growth. No significant difference was found among treatments, suggesting that degraded PLA is not toxic to plant growth. As an alternative to composting, chemical recycling of PLA was investigated. Chemical recycling of PLA has potential to be a closed-loop process, increasing the sustainability of PLA product use. Collection for chemical recycling has been implemented at UWSP, titled the FRESH project, and is being managed by the WI Institute for Sustainable Technology. No standards currently exist for the cleaning/processing of PLA waste in preparation for chemical recycling. Chemical recycling of post-consumer PLA waste was performed via hydrolysis with a focus on two industrial rinse-processing methods (high- and low-level) and compared to pre-consumer PLA. Results indicated no significant differences between the high- and low-level treatments on the quality of the lactic acid/oligomer product.