Plasticization of Biodegradable Poly(Lactic Acid) by Different Triglyceride Molecular Sizes: A Comparative Study with Glycerol

In this paper, poly(lactic acid) (PLA) was toughened and softened by four different molecular size plasticizers namely; glycerol, tributyrin, trilaurin and tristearin. Among four plasticizers studied, tributyrin seems the most appropriate plasticizer for PLA due to its proper molecular size. It increased the tensile elongation at break and impact strength by around ten and three times respectively, with only 10 wt% addition. For PLA with trilaurin and tristearin, they did not show the remarkable toughness improvement. Scanning electron microscope (SEM) observation indicated some phase separations of PLA plasticized with glycerol, trilaurin and tristearin, while tributyrin showed its homogeneity to PLA matrix with higher plastic deformations. Under dynamic load, some shifts of the E' drop and tan delta peak around 10-40 A degrees C were observed, when glycerol and tributyrin was added. Differential scanning calorimeter (DSC) measurements showed some significant shifts of the transition temperatures, while the degree of crystallinity increased slightly. Heat distortion temperature of the blends fluctuated in a small range of 2-3 A degrees C, which still restricted the use of PLA products above 60 A degrees C.