Tannin improves the processability and delays the biodegradability of poly (lactic acid)-starch-based thermoset materials produced by injection molding made with renewable compounds

The incorporation of tannin in bio-composite biodegradable thermoset materials (BTM) based on poly (lactic acid), starch, sugarcane fiber, and nutrient compounds, to achieve an alternative material for conventional plastics processed by injection molding aiming environmental applications was investigated. The biodegradation of injection molded BTM dog-bone shape specimens prepared with and without incorporation of 1% tannin extract was evaluated up to 60 days with overall characterization by scanning electron microscopy, Fourier transform-infrared spectroscopy, thermogravimetric analyzer, and X-ray diffraction. The BTM produced with 1% tannin showed reduced molding defects with an increased productivity of up to 82%, improved mechanical properties and reduced biodegradation of samples buried in an organic substrate. Based on physicochemical characterization, the observed delay in biodegradation of BTM induced by tannin is suggested to result from its tight interaction with the starch and lignocellulosic fibers, acting as antimicrobial agent and reducing the hydrophilicity of blends. Natural polyphenols such as tannins are suitable additives to improve the processability of injection molded bio-composites and to extend the lifetime of biodegradable materials subjected to contact with high microbial load substrates, such as pots and buckets used to grow plants.