Phase transitions in mixtures based on poly(lactic acid) and two polymeric nucleants processed under a fast or slow cooling from the melt

Mixtures based on two different poly(lactic acid)s (PLA) matrices and two distinct nucleating agents, incorporated at several contents, were prepared by extrusion. Furthermore, two thermal treatments were applied during the processing of films from the melt: a quenching (Q) and a slow (S) cooling. Crystalline characteristics of the resultant polymeric systems were mainly triggered by the PLA matrix used and by the cooling rate applied, turning out less important the nature of the nucleant. Thus, stereocomplex crystals were developed almost exclusively in the Q samples while coexistence of homo and stereocomplex crystallites was noticed when slow cooling was imposed. The type of homocrystallites present in the specimens was also dependent on the cooling rate applied during film processing. In the Q systems, crystals were grown on heating through a cold crystallization, as observed by differential scanning calorimetry; while they were developed along the cooling stage in the S materials. Influence of these structural characteristics on mechanical response was also evaluated by microhardness measurements.