PLA Depolymerization: MyLastTrash
Sustainable Food Systems
This project is a sister project to PLA Reclamation
Despite efforts to reduce plastic waste, PLA and other bioplastics have proven to be quite problematic for recycling facilities ill-equipped to handle PLA effectively. The already unmanageable problem of the PLA wastestream from dining halls contaminating recycling bins, has only served to exacerbate this problem, which is responsible for UCSC's plastics being diverted to landfills.
These bioplastics, most commonly polylactic acid (PLA) is derived from biomass (often sugarcane or corn starch) and is biodegradable. However, special conditions are necessary to biodegrade this material effectively; industrial composting can decompose PLA within 3 months. Compare this with 100 - 1000 years it would take in a landfill. Although these facilities exist in California, waste from 3D printing often does not end up in one, due to the lack of education and logistical impediments.
1. Biodegredation of PLA
This team is investigating methods of degradation and recycling of bioplastic polymers with a focus on poly-lactic acid (PLA). Many bioplastics are not degrading in either aerobic or anaerobic environments as quickly as anticipated and so alternative solutions are needed. Studies of the degradation rates of bioplastics in soil have analyzed different bioplastics showing that while some degraded 1-24% after 28 days there was no evidence of PLA degradation over the same time period. Efforts to degrade PLA more quickly typically require high energy inputs and/or toxic chemicals and can result in a loss of structural integrity in attempts to upcycle the material which reduce its value as a market commodity. The team is experimenting with microbial alternatives to catalyst-based methods which require technology and controlled conditions often not present at waste management facilities. Specifically the team is looking at how certain enzymes, such as bromelain or combinations of enzymes replicated and released by microbial agents can decrease the time required for degradation while bypassing the need for caustic chemicals or high energy inputs.
2. Depolymerization into monomers
An overarching aim of this project is to develop methods for processing PLA waste into its monomeric products as a step towards creating a cradle to cradle approach for chemically recycling PLA. Experimentation will compare kinetics for the depolymerization of PLA into LA of multiple solvents and catalysts. According to the literature, sonification of PLA samples shows promise as a means of increasing the conversion rate of PLA into it’s monomeric substituents. The success of depolymerization techniques applied to PLA is measured from the overall mass loss of the PLA in solution. Several performance criteria can be used to assess whether the successful reactions should also be considered sustainable such as required energy inputs and release of toxic byproducts . Variables that can impact depolymerization/transesterification of PLA to LA include: heat of reaction, pH, and the concentration of catalysts. Initial experimentation will apply knowledge of ionic liquids and metallic catalysts to the methanolysis or hydrolysis of PLA. The objective of this experiment is to measure the rate of mass loss and overall % conversion with respect to different catalysts and conditions. After determining the actual yield of initial experiments we will alter methods to optimize our requirements (low time, high yield).
The PLA characterization teams would like to thank CITRIS and the Banatao Institute for their support.