Isothermal Crystallization Kinetics of Poly(lactic acid) Stereocomplex/Graphene Nanocomposites

The isothermal crystallization kinetics of PLA stereocomplex (scPLA) and scPLA/graphene oxide nanocomposites was investigated. scPLA was prepared by symmetric blending the two isomers, PLLA and PDLA and the scPLA nanocomposite by polymerization of the respective lactides in presence of commercial graphene oxide nanoplatelets (GNPO+) followed of blending the two composites. The effect of the filler on the crystallization behavior and thermal properties of scPLA was investigated by using differential scanning calorimetry (DSC). Avrami equation was used to describe the isothermal crystallization kinetics and melting behavior. Addition of 0.5 wt% GNPO+ to PLA matrix increases the crystallization rate, lowering the half-time of crystallization t1/2 to around 5.5 min for scPLA nanocomposites, which is about 2.7 min below that found for scPLA when isothermally crystallized at 165ºC. During the isothermal crystallization, homochiral and stereocomplex crystals are formed, depending on the crystallization temperature. As crystallization temperature reaches 160 and 165ºC, the crystallization of homocrystals become prevented and only stereocomplex crystals are formed.