Plasticization of PLA with oligomeric esters of lactic acid: effect of physical aging on properties

During last years a wide number of additives ranging from low to high MW molecules have been employed to reduce brittleness and increse deformability of polylactic acid (PLA). In many cases, even if an interesting plasticization effect was achieved, this improvement revealed to be not stable during time due to phase separation and/or physical aging. In the present study, two hydroxyl (A) or carboxyl (B) end-capped oligomeric esters of lactic acid were tested as plasticizers for PLA. Blends containing up to 25% of A or B were prepared in the melt by using a batch mixer. The effects of A and B on chemico-physical as well as mechanical properties of PLA as a function of aging were investigated. In particular the miscibility of blends was studied by SEM, DSC and DMTA analyses. In detail, PLA and oligomers result miscible at all examined compositions and form homogeneous blends. Regarding mechanical properties, a sharp transition from brittle to ductile behavior was observed above 20 wt% of both oligomer content, with maximum elongation above 400%. At the same time, the modulus (E) and tensile strength (?) decreased while the impact toughness remained almost unchanged. Finally, oxygen and water permeability slightly increased with both oligomer content. Table 1 resumes some mechanical and calorimetric results for the most promising composition.