Soy protein isolate/poly(lactic acid) injection-molded biodegradable blends for slow release of fertilizers

A slow release fertilizer system consisting of materials derived exclusively from biomass, and suitable for i) production of injection-molded parts such as containers for growing plants, and ii) use as granules, is reported. Soy (Glycine max L. Merr.) protein isolate/poly(lactic acid) blends plasticized with triacetin (SPI/PLA-TA) were used as matrix for NPK fertilizer incorporation. Upon melt processing, this composite material formed a highly ordered porous matrix of SPI in which PLA domains are homogeneously dispersed with NPK salts. Dynamic conductivity measurements indicated good release properties as the cumulative amount increased much slower with time as compared to pure NPK sample. Biodegradation was accessed by examining weight loss and surface morphology as a function of incubation time in soil.