Thermal, Mechanical and Morphological Properties of Binary and Ternary PLA Blends Containing a Poly(ether ester) Elastomer

In a first step, binary poly(lactic acid)-poly(ether ester) elastomer (PLA-PEEs) blends were prepared on a twin screw extruder with a PEEs content varying between 0 and 24 wt%. The effect of PEEs on the thermal, mechanical and toughening properties were investigated. Differential scanning calorimetry and dynamical thermal analysis investigations confirmed that binary blends were immiscible and formed a phase separated system characterized by a pure soft and rigid phases containing PEEs and PLA, respectively. PEEs affected the crystallization rate of PLA as well as its thermal stability. The tensile strength and elastic modulus of blends decreased steadily with increasing PEEs content and fragile-ductile transition was observed in the 12-20 wt% PEEs range depending on the tests method used. In a second step, reactive copolymers, namely poly(maleic anhydride-alt-octadecene) (PMAOD) and poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) (PEAGM) were incorporated in various proportions (0-12 wt%) in the PLA-PEEs blends. These blends were compared to their analogues containing polyethylene glycol (PEG). PEG was completely incorporated in the PLA rigid phase and the typical effects of the plasticization of the PLA rigid phase were observed. In contrast, PMAOD was mixed to the PEEs soft phase while PEAGM was mainly involved in the occurrence of a new phase whose rigidity is between the soft and the rigid phases. MEB observations also revealed the interfacial effect of the incorporation of the reactive copolymers between the soft and rigid phases. Superimposing onto the PEEs effect, PMAOD and PEAGM decreased the crystallization rate of PLA and interfered with the development of the PLA crystalline phase. Combining PEEs with equivalent amounts of PEAGM (12 wt%) led to super-toughened PLA blends.