In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate “smart fertilizers” for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the “bottleneck” for nitrogen–phosphorous–potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers.

This work studies, for the first time, the influence of specific mechanical energy (SME) on the reaction efficiency and blend's performance during reactive extrusion of biopolymer compounds. Poly(lactic acid) (PLA) and poly-(butylene succinate) (PBS) were compounded separately with poly(propylene carbonate) (PPC) and a premade maleic anhydride (MAH) compatibilizer to achieve functionalization. Different screw speeds (reaching 1000 rpm) and flow rates were tested. Results indicated that the grafting efficiency was directly proportional to the SME imparted in the system. The PBS blends compounded at shorter times and faster speeds experienced less degradation and better mechanical properties than blends compounded at longer times. The effect was similar but less pronounced for the PLA formulations. It is possible to optimize the reactive compatibilization of biopolymer blends by means of SME calculations and that better blend performance is achieved when conducting high-speed extrusion at short residence times.

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This work studies two functionalization routes during high-speed reactive extrusion of biobased and biodegradable polymer blends: exchange reactions and free radical grafting with maleic anhydride.