Toughening of polylactide by tailoring phase-morphology with P[CL-co-LA] random copolyesters as biodegradable impact modifiers

The utilization of partially miscible impact modifiers was investigated in the design of impact polylactide (PLA)-based materials. Rubbery random aliphatic copolyesters namely poly(ε-caprolactone-co-d,l-lactide) (P[CL-co-LA]) containing different compositions in LA comonomers were employed as impact modifiers. The relative content in LA comonomer spread along the copolymer chain was varied and its effect on the toughness of the resulting PLA-based materials was investigated. Dependence between toughness improvement and morphology of the resulting blends was established in terms of domain shape, average size and related size-distribution of the dispersed rubbery microdomains within the PLA matrix as shown by SEM, TEM and AFM. However, using Peak Force Tapping techniques (PFT-AFM) revealed peculiar morphologies upon the affinity and the interfacial compatibilization between the blend components. The overall results indicated that the dispersion of a P[CL-co-LA] copolymer containing 28 mol% LA comonomer provided a fourfold increase in impact strength for the resulting PLA blend, which could be correlated to the presence of ribbon-like rubbery microdomains.