During the past decades, lots of research efforts have been paid to study and improve the capacities of polymer issued from renewable resources. Particularly, in this class of next generation materials, Poly(lactide)s (PLA) have attracted many attention as this polymer is biodegradable, exhibits good thermomechanical properties and is seen as a potential candidate for the replacement of some polyolefins such as Poly(ethylene Terephtalate). Due to the presence of a chiral carbon, both PLLA and PDLA homopolymers can be synthesized. Homopolymers and random copolymers have been widely studied in the past, and actually research efforts move more and more toward the study of blends of PLLA and PDLA. This arises from the fact that when PLLA and PDLA are blended a particular crystalline form, i.e. the stereocomplex form (sc form), can be induced. One of the main features of the sc-form is its melting point which is about 50°C higher than the one observed for the α crystalline phase, encountered in the case of the homopolymers. Although thermal properties, and especially the crystallization behavior, of these blends are well addressed into the literature, there are actually no studies dealing with the mechanical behavior of these blends. Consequently this study will be devoted to the characterization of the mechanical behavior of PLLA-PDLA blends. Particularly a particular attention has been paid to determine the influence of the initial crystalline phase on the mechanical properties.<br/>This work consists in the first study dealing with the mechanical behavior of PLLA-PDLA blends. It shows that, if initally amorphous or under the sc form, the material exhibits a ductile behavior and large plastic deformation ratios are reached. In opposition the initial presence of the a-form into the blends leads in a brittle mechanical behavior. Thanks to morphological analyses and structural characterizations, this behavior has been ascribed to a phase separation between the PLLA crystalline lamellaes and the PDLA crystalline lamellaes during the crystallization process. Regarding the influence of the drawing conditions it was observed that depending on the draw temperature, either a crystalline or a mesomorphic phase can be induced upon stretching. Finally it is also demonstrated that the sc-form can not be induced upon stretching, contrary to the α-form.

Thermomechanical properties of poly(L-lactide)/poly(D-lactide) blends

249th National Meeting (2015)

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