Disintegration of commercial biodegradable plastic products under simulated industrial composting conditions

Biodegradable plastics are often promoted as sustainable alternatives to conventional plastics. Nevertheless, significant knowledge gaps exist regarding their degradation under relevant conditions, particularly when compounded into commercial products. To this end, the present research investigates the disintegration of ten commercially available biodegradable plastic products under simulated industrial composting conditions. The tested products included polymer compositions of either polylactic acid (PLA), polybutylene adipate terephthalate (PBAT)/starch, or polyhydroxyalkanoate (PHA), covering both flexible and rigid plastics. These products comprised three waste bags, one waste bag drawstring, one food bag (flexible plastics), two flower pots, one food container, one plate, and one lid (rigid plastics). Among the tested products, nine were marketed as compostable. Of these, six were certified under the European standard EN 13432 for compostable packaging, two held TÜV Austria's "OK compost home" certification, and one was labeled as compostable but lacked certification. Additionally, one product was labeled as 100% biodegradable but lacked certification, and the environment in which the product could biodegrade was not specified. Disintegration was determined according to ISO 20200 in laboratory scale tests conducted at 58 °C with 55% moisture content over 90 days. Results showed disintegration degrees ranging from 75 to 100%, with five products achieving complete disintegration. Two products, however, reached only 75% disintegration. Following the disintegration test, compost particles smaller than 2 mm were examined for microplastics (MPs) via light microscopy. MPs were detected in compost undersieves for two of the ten biodegradable plastic products, while no MPs were detected for the conventional plastics. Notably, the visual inspection was performed without pretreating the compost matrix due to the observed degradation of biodegradable plastics when using chemicals for oxidative digestion. Considering the limitations of visual MP observation without pretreatment, future research should prioritize the development of methods for extracting biodegradable MPs from complex matrices like compost. Enhanced extraction methods are essential for understanding compost's potential role as a source of MPs in the environment.