Controlled graft copolymerization of lactic acid onto starch in a supercritical carbon dioxide medium

This study describes the graft copolymerization of l-lactic acid onto a starch backbone in supercritical carbon dioxide. In the context of this study, the copolymerization parameters such as reaction time, monomer feed ratio, scCO2 flow rate, pressure and temperature were investigated, and the resultant copolymer product was characterized via relevant analysis techniques. This work presents a new approach for the synthesis of a starch-g-poly L-lactic acid (St-g-PLA) copolymer via the graft copolymerization of LA onto starch using stannous 2-ethyl hexanoate (Sn(Oct)2) as a catalyst in a supercritical carbon dioxide (scCO2) medium. The effects of several process parameters, including the pressure, temperature, scCO2 flow rate and reaction time, on the polymerization yield and grafting degree were studied. Amorphous graft St-g-PLA copolymers with increased thermal stability and processability were produced with a high efficiency. The maximum grafting degree (i.e., 52% PLA) was achieved with the following reaction conditions: 6h, 100°C, 200bar and a 1:3 (w/w) ratio of St/LA. It was concluded that these low cost biobased graft biopolymers are potential candidates for several environment-friendly applications.