Synthesis of Grafted Polylactic Acid and Polyhydroxyalkanoate by a Green Reactive Extrusion Process

Abstract

Grafted polylactic acid (PLA) and polyhydroxyalkanoate (PHA) were synthesized by a reactive extrusion method. The grafted bio-based polymers had either polar functional groups such as hydroxyl (-OH) and polyethylene glycol (PEG) or non-polar functional groups. It was found that grafted biopolymers had significantly reduced melt viscosity, making them more suitable for certain polymer processing such injection molding and fiber spinning. The grafted biopolymers had improved compatibility in blending with other polar polymers such as polyvinyl alcohol and exhibited improved fiber spinning processability in polymer blends. Grafted PHA had a low crystallization rate making continuous reactive extrusion impossible. It was found that a novel co-grafting method, i.e. grafting PHA in the presence of PLA, was effective to overcome the process challenge of PHA. The reactive groups introduced to PLA or PHA can be used for further side chain reactions. The free radical initiated grafting reaction was a green reaction method. It eliminated the use and recovery of organic solvents, the reaction rate was also significantly increased over solution grafting reaction, taking seconds to complete rather than hours.