A kinetic-based criterion for polymer biodegradability applicable to both accelerated and standard long-term composting biodegradation tests

Abstract

Biodegradable plastics are an alternative to reduce the problems caused by the great consumption of plastic products, especially in single-use products such as packaging, disposables, and bags. However, the available standard tests for biodegradability of polymers are of extremely long duration (45 to 180 days). Therefore, research on biodegradability testing is as important as the development of new biodegradable plastics to expand their use as replacement materials for conventional polymers. In this work, a kinetic study has been carried out testing different models using data previously presented in the literature, with the aim of establishing a criterion for the classification of polymers as biodegradable or nonbiodegradable based on the kinetic parameters obtained in composting biodegradation tests and to perform a second step of validation of an accelerated method previously presented. The employed literature data included results from standardized tests (ASTM D5338 and ISO 14855) and from the referred accelerated biodegradation test, which uses the same composting medium and temperature (58 °C) as the standardized tests. The study included the following steps: (i) selection and testing of five different mathematical models to describe the kinetics of the biodegradation process; (ii) identification of the most adequate of these models; (iii) analysis of the correlation between the results of the standard and accelerated biodegradation tests based on the parameters selected for the kinetic model obtained for each data set; and (iv) proposal of a biodegradability criterion based on the values of these parameters. The Hill-like model was shown to be the most appropriate among the five models tested. This model performed well for all the tested data sets and allowed the definition of a biodegradation criterion, which was effective in correctly classifying the materials as biodegradable or nonbiodegradable, regardless of whether the available data came from the standard or from the accelerated method. While the results are promising, further validation and use of the accelerated test and proposed criterion will contribute to refining and strengthening its robustness and applicability for screening purposes.