Environmental Degradation of Starch/Poly(Lactic Acid) Composite in Seawater

In order to study the degradation property of starch/polylactic acid (PLA) composites in a briny environment, injection-moulded tensile bars of starch/PLA composites were investigated by immersion in static seawater controlled at 25 °C for 1 year. SEM micrographs showed that starch particles were lost from the bar because of microbial action. GPC results showed the number average molecular weight ( M _n ) of PLA decreased with degradation time. The glass transition temperature (T _g ) and melting temperature (T _m ) measured by DSC decreased slightly with degradation time. An increase of crystallinity calculated from the DSC data was attributed to the decrease of molecular weight. Weight losses were mainly due to loss of starch. The impact strength of the composites decreased monotonically with degradation time; tensile strength and elongation at break of the composites first decreased, then increased and at last decreased again with degradation time, and the water was acting as a plasticizer. The starch/PLA composites in seawater had degradability, but the degradation rate of composite bars studied in this paper was very slow.