Catalytic reactive extrusion of ethylene(vinyl acetate)-g-polylactide bioplastic

Abstract

Graft copolymerization of polylactide (PLA) onto ethylene (Vinyl acetate) (EVA) by catalytic reactive extrusion in an intermeshing co-rotating twin-screw extruder is the preferable route to enhance the processibility of PLA, with catalyst ratios of 0.1, 0.3, and 0.5% wt, the optimum amount of catalyst giving the highest conversion was studied. Transesterification reaction of EVA was done in a twin-screw extruder at various screw speeds (10, 20, 30, and 40 rpm) with the presence of dibutyl tin dilaurate (DBTL) catalyst prior to reaction with PLA. The results from FTIR and DMA suggested that the lower the screw speed the higher the conversion. Therefore, the modified EVA at the screw speed of 10 rpm was selected to react with PLA. Graft copolymerization of PLA onto EVA main chains, the ratio of EVA: PLA was 40: 60, was bone inside the twin-screw extruder with the help of Sn(Oct)2 catalyst at various catalyst contents (0.1, 0.3, and 0.5%wt) and at screw speeds of 30 and 40 rpm. The results from TGA, DSC and tensile testing suggested that the suitable amount of catalyst producing EVA-g-PLA was 0.3%wt. However, phase separation can be seen for any condition except the EVA-g-PLA produced at 30 rpm with 0.3%wt, which showed the finest dispersion. Therefore, lactide monomer was introduced into the system as an initiator for grafting reaction. However, phase separation were highly pronounced when LA was introduced to the system at screw speeds of 30 and 40 rpm. Moreover, the modular twin-screw extruder (SHJ-36, Nanjing Giant Machinery Co., Ltd.) with five mixing zones was used as a reactor at screw speed of 150 rpm, in order to improve melt mixing of those two phases. SEM images than again showed phase separation, where the finest dispersion presented at EVA-g-PLA produced in two-component system (without LA) with 0.3%wt of Sn(Oct)2.