ARS | Publication request: Degradation of Poly(L-Lactic Acid) and Bio-Composites by Alkaline Medium under Various Temperatures

Submitted to: Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2011
Publication Date: September 3, 2011
Citation: Tisserat, B., Finkenstadt, V.L. 2011. Degradation of poly(L-lactic acid) and bio-composites by alkaline medium under various temperatures. Journal of Polymers and the Environment. 19:766-775.

Interpretive Summary: In order to address the trash and environmental problems produced by industrialized societies new generations of biodegradable plastics are being developed. One of the easiest methods to achieve this goal is to design biodegradable plastics incorporating suitable biofillers (e.g., wood and crop byproducts). Biodegradable plastics (such as poly(lactic acid) (PLA)) are those materials that degrade within a limited period of time as defined by international standards. These standards are not necessarily obtainable in nature though and often can only occur within specialized processing facilities (e.g., composting). Simple exposure of plastics to the outdoors doesn’t ensure their degradation. In order to quickly evaluate PLA and PLA-biocomposites degradability an accelerated in vitro alkaline and temperature test system was developed. This system can quickly evaluate the degradative expression of “biodegradable materials” without the necessity of long term testing and provide valuable biogradable information for biopolymers.

Technical Abstract: Ribbons of poly(lactic acid) (PLA) and PLA containing 10 or 25 % Osage orange (OO) biocomposites of various sized heartwood particles were exposed to non-composting soil conditions either outdoors or in a greenhouse. No appreciable degradation was evident even after 208 day treatments. An artificial alkaline degradation test system was developed to reduce the study time required to evaluate PLA compositional properties on degradation. Ribbons of PLA and PLA-OO biocomposites of various sized particles were subjected to hydrolysis in alkaline concentrations (0, 0.05, 0.1, 0.15, and 0.25 M NaOH) under various temperatures (15, 20, 25, 30, 35, 40, and 80oC) up to 56 days. Higher concentrations of NaOH (e.g., 0.25 M) caused more dramatic and rapid deterioration of PLA and PLA-OO composites than lower NaOH concentrations for all temperatures tested. Incubation in either the low temperatures (15 and 20oC) or the highest temperature (80oC) was consistently more effective in PLA-OO degradation than employing 35 or 40oC. Several alkaline and temperature test combinations are offered to study accelerated PLA degradation. Ribbons immersed NaOH were examined via the scanning electron microscope to analyze for morphology alterations.