Biodegradation of Films Based on Natural and Synthetic Biopolymers Using an Aquatic System from Active Sludge

The biodegradability of natural gelatin (GEL) and sodium caseinate (SCas) and synthetic poly(vinyl alcohol) (PVA) and poly(lactic acid) (PLA) biopolymers films, were studied in an aquatic system following OECD 301D guidelines. Biodegradation was determined measuring the dissolved oxygen (DO) over 28 days with closed respirometers. Elementary compositions and changes in physicochemical parameters were analyzed. The results demonstrated that carbon (46 to 60%) and oxygen (31 to 44%) were the most important elements in the composition of all films. Moreover, GEL and SCas films were completely biodegraded (100%) on day 1, showing a DO increased (GEL up to 42.5 mg O-2/l and SCas up to 34.6 mg O-2/l) as a consequence of the biodegradation time. This is in stark contrast to PVA and PLA films, who presented an inverse behavior (PLA up to 1.1 mg O-2/l and PVA up to 0.5 mg O-2/l), which in fact cannot be classified as "readily biodegradable" according to the results of in this study because they required more time to biodegrade than the rules defined for this aquatic system. PLA film showed a more opaque and whitish color, a clear increase in EM values (day 7 = 85.7 +/- 2.0 MPa), Tg temperature (day 28 = 56.8 +/- 0.0 degrees C) and crystallinity (Day 28 = 49.3 +/- 0.6%) over the effects of biodegradation times. FTIR analysis showed changes in the intensity of the typical bands of the PLA samples, and the presence of Pseudomonas, was later observed on their surface by SEM studies.