REVIEW OF EVALUATION METHODS FOR BIODEGRADABILITY OF POLYMERIC MATERIALS

Abstract

Development and further use of biodegradable polymeric materials requires prior assessment the degree of their biodegradation. There are a large number of methods developed taking into account the specifics of the destruction of polymeric materials. The purpose of this review is to systematize scientific and technical information regarding methods for assessing the biodegradation of polymeric materials. Laboratory methods of researches, including the following: influence of abiotic factors (temperature, moisture, UV irradiation), impact of microorganisms (fungi, bacteria, yeast), respiratory methods (Sturm, Zahn-Wellness, etc.), conditions of composting, enzyme analysis methods, ecotoxicity tests are given. Test methods in both aqueous and solid media are also presented. The parameters of biodegradability, which determine the degree of destruction (mass, strain strength, molecular weight distribution, temperature characteristics, macro-and microstructure of samples, etc.) or the composition and properties of the biological system in which biodegradation takes place (acidity, respiratory activity, chemical and microbiological composition of soil or other biological environment, etc.) are considered as well. Advantages of laboratory methods for studying the biodegradation of polymeric materials could be realized in the given directions: varying of the experimental conditions (temperature, humidity, UV and IR radiation, the presence of aggressive media, etc.), biochemical compositions of the environment; study of the ability of individual strains of microorganisms to dispose of polymer composites and targeted selection of the most active microbial associations (in particular, for the manufacture of special biocomposts); utilize of simple and fast methodical approaches and modern devices for evaluation experiments. However, laboratory methods do not always allow modeling a set of endogenous and exogenous factors that define the process of biodegradation in the natural environment. Therefore, this review also considers methods for assessing biodegradation in the environment. So, the essence of the test regarding the samples’ burial in the ground is given. International standards governing methods for assessing the biodegradability of organic substances and polymeric materials are summarized. Applying different test methods, one can evaluate the whole process of biodegradation of polymeric materials, consisting of several stages, which occur regardless the type of microorganisms and accompanying abiotic factors, and can be represented as follows: adhesion → colonization → biodeterioration → biofragmentation → assimilation → mineralization. Thus, the adhesion and colonization of microorganisms can be estimated by visual, bioindicator and spectral methods. Abiotic degradation and biodeterioration are associated with physical tests (e.g., thermal and physico-mechanical). Biofragmentation is detected by identifying fragments of lower molecular weight (i.e. by chromatographic methods). In turn, assimilation is assessed by the amount of metabolites produced using, for example, respirometric methods or involving analysis of microbial biomass (e.g., macroscopic and microscopic observations). The most productive should be considered a comprehensive approach to the study of biodegradation of polymers. To determine the reliable kinetic parameters and link the mechanism of this process, it is necessary to carry out a comparative analysis of the results of physical, chemical, microbiological experiments, which are carried out in both laboratory and natural conditions.