Influence of inorganic fillers on PLA crystallinity and thermal properties

Polylactide (PLA) composites with three types of fillers, calcium carbonate, barium sulfate, and mica, have been prepared. Methods of preparation were melt mixing in a Brabender plasticorder at 190 A degrees C and solution mixing in chloroform. The concentration of added fillers was: 0.1, 1, and 5 mass% (only by melt mixing). Thermal properties of prepared composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis. The dispersity of filler in matrix was examined by scanning electron microscopy. There was no agglomeration in any composites. Results of DSC analysis reveal the influence of preparation method on thermal transitions. By the melt mixing method, the introduced filler hindered crystallization but caused mostly just a slight increase in T (g) relative to pure PLA (57.4 A degrees C). By solution-mixing method, the absence of crystallization is noticed in all samples. Concurrently composites displayed T (g) higher for ca. 5-6 A degrees C relative to pure PLA (53.3 A degrees C), with the exception of composite with smallest content of calcium carbonate nanofiller. Thermal stability is improved in all composites, regardless of the filler used and preparation method. It is especially pronounced regarding decomposition temperature (5 mass% loss) where the increase ranges from 11 up to 55 A degrees C in case of melt mixing and 17-35 A degrees C for solution mixing.