Biodegradation Behavior of Poly(lactic acid) (PLA)/Distiller's Dried Grains with Solubles (DDGS) Composites

Poly(lactic acid) (PLA) and distiller's dried grains with solubles (DDGS) are biobased materials with strong potential for industrial applications. This paper reports the biodegradation behavior of PLA/DDGS (80/20 by weight), a composite material developed for use in high-quality, economical, biodegradable, crop containers for the horticulture industry. Biodegradation experiments were performed in soil under landscape conditions. Surface morphology and thermal properties were evaluated by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). We found that adding 20% DDGS to form the PLA/DDGS composite can accelerate the biodegradation rate and enhance the storage modulus compared to pure PLA. The weight loss of the PLA/DDGS composite during 24 weeks of degradation time was 10.5%, while the weight loss of pure PLA was only 0.1% during the same time interval. Cracks and voids caused by erosion and loss of polymer chain length were clearly observed on the surface of the composite material in response to increasing degradation time. The thermal stability of the composite increased with increasing degradation time. The glass transition temperature and melting temperature increased during early stages of biodegradation (up to 16 weeks) and then decreased slightly. We confirm that DDGS can function as a cost-effective biodegradable filler for PLA composites that can provide enhanced mechanical properties with only slight changes in thermal properties when compared to pure PLA.