Biodegradability assessment of aliphatic polyesters using standard methods

Abstract

Important information concerning polymer’s final fate in the environment can be achieved in biodegradation studies performed in the aquatic environment. In this context, the focus of the present work was to evaluate the biodegradability level of blends containing aliphatic polyesters using standard methods. Blends of high density polyethylene (HDPE) and five biodegradable polymers (poly(lactic acid) (PLA), poly(ε-caprolactone) (PCL) and Mater-Bi (thermoplastic starch with PLA or PCL)) were prepared in a co-rotating twin-screw extruder, together with polyethylene modified with maleic anhydride used as compatibiliser. Biodegradation tests were carried out using the standard ISO 14851 (1999) which specifies a method for determining the biochemical oxygen demand in a closed respirometer, the standard ASTM D 5209 (1992) which specifies a method for determining the carbon dioxide evolution and the standard ASTM G 22-76 which specifies a method for determining the microbial growth of a test microorganism. The results show that the blend containing PCL is more biodegradable than the blend containing PLA based on both microbial growth (ASTM G 22-76) and biochemical oxygen demand (ISO 14851:1999) biodegradability tests. The biodegradability of the blend containing PLA was increased by the addition of starch, in turn the same was not observed for the case of PLC. The biodegradability tests suggest that starch is more biodegradable than PLA but less than PCL. The biodegradability of the blends evaluated in the presented study by the biochemical oxygen demand method ranged from 22 % to 48 %. Therefore the blends may not be considered “readily biodegradable” according to the OECD standard.