The Influence of Micro-/Nano-CaCO3 on Thermal Stability and Melt Rheology Behavior of Poly(Lactic Acid)

Poly(lactic acid) (PLA) has been an interesting biopolymer that could offer a potential alternative to petrochemical plastics. Modification of PLA by fillers has been widely carried out to obtain desired properties for various applications. This research aims to investigate the effect of micro-/nano-particle size of calcium carbonate (CaCO3) on thermal stability and melt rheology behavior of PLA extrusion sheet. PLA pellets were compounded with CaCO3 particles by a twin-screw extruder, and fabricated by a cast flat sheet process to produce CaCO3-PLA extrusion sheets. Fatty acid treated on CaCO3 surface showed profound impact on thermal stability of CaCO3-PLA extrusion sheets as identified by thermal gravimetric analysis (TGA). The onset temperature of degradation (Tonset) and the peak degradation temperature (Td) of CaCO3-PLA biocomposites were lower than neat PLA. In the rheological study, it was found that addition of fatty acid treated CaCO3 reduced the viscosity of CaCO3-PLA biocomposites due to thermal degradation of PLA. Adding micro-CaCO3 could maintain viscosity of extruded PLA to be close to neat PLA, while adding nano-CaCO3 with the surface treatment, caused easier flow of high loading PLA.