(448f) Evaluation of Compostability of Commercially Available Biodegradable Packages in Real Composting Conditions

Authors: 
Gaurav, K., Michigan State University
Auras, R., Michigan State University
Singh, S. P., Michigan State University


The adoption of biodegradable packaging materials is increasing in food and consumer good packaging applications. Currently, poly(lactide) (PLA) polymers are the biggest commercially available bio-based packaging material. Life cycle analyses show that the production of PLA polymers consumes around two times less energy than conventionally petroleum based polymers. Therefore, the first issue that needs to be addressed is its environmental impact. The disposal of such biodegradable polymeric packaging residues in composting facilities can be an important method of reducing the amount of packaging materials that are disposed as municipal solid waste. To the best of our knowledge, there has been no study done evaluating the compostability of a complete biodegradable package in real-time composting conditions. The real composting conditions differ from the simulated ones due to several factors such as weather, microbial growth and pH; and therefore the compostability of biodegradable packages is affected. This study addresses the compostability of two commercially available PLA packages, a bottle and a tray, in real composting conditions. The degradation of a PLA bottle composed of 96% L-lactide and 4% D-lactide with bluetone additive and a tray composed of 94% L-lactide and 6% D-lactide were evaluated in a composting pile having temperatures around 60ºC ± 5.5ºC (140°F ± 10°F), a relative humidity of 60% ± 5% wet weight moisture content and a pH of 8 ± 1. The packages were placed in a compost in duplicate sets and were taken out on 1, 2, 4, 6, 9, 15, and 30 days. The molecular weight (MW) and the glass transition (Tg), melting (Tm) and decomposition (TD) temperatures were monitored to assess the changes in the packages' physical properties. The MW was assessed by gel permeation chromatography (GPC), the Tg and Tm by differential scanning calorimetry (DSC), and the TD by thermogravimetric analysis. In addition, the packages were visually inspected for color, texture, shape and thickness changes and pictures were taken as the package configurations evolved. After 4 days of being in the compost pile, initial fragmentation of the packages were observed. At 15 days, the trays started to become a part of the compost whereas the bottles showed slower degradation and started breaking apart. After 4 days for the trays and at 6 days for the bottles, a molecular weight reduction of 77% and 85% were observed, respectively. The molecular weight of the bottles and the trays were reduced from 209,324 Daltons to 10,686 Daltons and from 176,315 to 4,708 after 15 days of being in the compost pile, respectively. At 30 days, the bottles showed a molecular weight of 4,000 Daltons, and the trays were completely degraded. Similarly the decline in Tg at 15 days for both bottles and trays were 30% and 18%, and the Tm were 2.4% and 3.9%, respectively. The initial degradation temperatures of the bottles and the trays were 396.1°C and 396.8°C, respectively; whereas after 15 days in the compost they were reduced to 358.1°C and 326.2°C. The difference between the degradation time between the PLA bottles and trays can be attributed to their initial difference in crystallinity. PLA bottles and trays degrade under real-time composting conditions much faster than in previous studies reporting simulated composting conditions.

Keywords: PLA; poly(lactide); composting; biodegradation; packaging

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