Synthetic organofluoromica/poly(lactic acid) nanocomposites: Structure, rheological and thermal properties

Organically modified fluoromica/poly(lactic acid) (PLA) nanocomposites were prepared by melt processing at different compositions in an internal mixer at the same conditions. Gel permeation chromatography (GPC) was used to measure the molar masses of PLA alone, before and after processing. The results indicated that PLA presented some degradation during melt mixing. With the addition of the organically-modified fluoromica, higher reduction in the polymer molar masses was found. The structure of the synthetic mica and of the clay polymer nanocomposites (CPN) was studied by small-angle X-ray scattering (SAXS), which revealed the presence of nanometer-sized clay mineral aggregates. Dynamical rheological measurements were carried out in the linear viscoelastic region for both PLA and CPN molten samples. A predominantly viscous behavior was obtained for the polymer samples, whereas the CPN presented a pronounced elastic behavior. Addition of mica to PLA also had a significant effect on the complex viscosity of PLA, imparting an increasing shear thinning behavior with increasing mica composition. Below Tg, dynamical mechanical analysis results showed a substantial decrease of rigidity of the CPN in relation to PLA alone, attributed to the presence of high content of organic intercalant in the synthetic fluoromica. Lower cold crystallization rate was detected for the CPN in comparison with processed PLA alone.