Accelerated biodegradation testing of slowly degradable polyesters in soil

Abstract

According to the impending EU regulations, all polymer products used in agriculture and applied into soil must be biodegradable to prevent their accumulation in the environment. However, some of these products must serve their purpose for months up to years before their degradation and mineralization is desirable. Current international standards describing the biodegradability in soil are more directed towards materials that undergo relatively fast biodegradation, which hampers the development and certification of slowly biodegrading polymeric materials. Here, an accelerated soil biodegradation test is proposed, where by increasing the incubation temperature from 25 °C to 37 °C, up to about 4-fold increase in the biodegradation rate is achieved. The polymers tested include TÜV AUSTRIA Belgium certified polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), polybutylene adipate-terephthalate and polylactic acid blend (PBAT/PLA) and an experimental polyester network (ICL-PN). The biodegradation rates of the given polymers at the two temperatures was examined by carbon dioxide evolution. Independent testing was done in two independent laboratories and the results were compared. The biodegradation of the materials was further assessed by electron microscopy and the microbial community present was analyzed by next-generation sequencing. Criteria were proposed for the accelerated test method, which include that the polymers eligible for the accelerated test should not manifest any phase transition, like e.g. a glass transition, in the interval from 25 °C to 37 °C. The proposed accelerated test can be helpful in the development of polymeric materials with a functional life of several years and with ultimately quantitative biodegradability. © 2019 Elsevier Ltd