Biodegradable boron-containing poly(lactic acid) for fertilizers with prolonged action

Abstract

A new strategy for obtaining long-acting fertilizers in the process of joint polycondensation of lactic and boric acids is presented. The article shows the effect of boric acid or boric anhydride additives in an amount of 0.1-1%wt. on the synthesis and final properties of poly(lactic acid). With increase in the amount of boric acid or boric anhydride in poly(lactic acid), polymers show higher T g and T m at approximately equal molecular weights compared to poly(lactic acid) without additives. Comprehensive studies of the structure of the obtained compositions were carried out: theoretical calculations using method DFT (Becke-Lee-Yang-Parr) and experimental - proton NMR, IR spectroscopy and melt rheometry. It has been suggested that the addition of boric acid when heated promotes the formation of B-O-C bonds and the branching of lactic acid oligomer chains. The compositions and the dynamic of boric acid release by granules obtained from boron-containing poly(lactic acid) melts were studied using elemental analysis for aqueous systems. During 7 days of testing in aqueous medium, the granules lose from 16 to 72% of boric acid. This study can serve as further development of the use of low-molecular-weight poly(lactic acid) with different molecular weights in the design of long-acting fertilizers. • Boric acid and boric anhydride were added to a lactic acid during synthesis of poly(lactic acid); • The effect of additives on the thermophysical, molecular-mass and rheological properties of poly(lactic acid) is estimated; • B-O-C bonds are not preserved in polycondensation products; • The results of hydrolysis indicate a prospect of using boric acid-containing poly(lactic acid) as a slow-release fertilizer.