Dielectric Relaxation in Blends of Amorphous Poly(<scp>dl</scp>-lactic acid) and Semicrystalline Poly(<scp>l</scp>-lactic acid)

We investigated the thermal and dielectric behavior of blends consisting of semicrystalline poly(l-lactic acid) (L-87) and amorphous poly(dl-lactic acid) (DL-74 and DL-7). Two series of blends L-87/DL-74 coded as B1 and L-87/DL-7 coded as B2 were used where the code number indicates molecular weight Mw in kg/mol. The DSC thermograms of quenched blends exhibited a single glass transition at about 326 K followed by the exothermic peak due to crystallization of L-87. The relatively sharp glass transition indicates that both components are miscible in the molten state. The degree of crystallinity χ was determined from the heat of fusion. Three dielectric loss peaks were observed for B2. They are termed αn, αs, and β as reported previously [Macromolecules 2003, 36, 210] and are assigned to the normal mode relaxation of DL-PLA dissolved in the amorphous region, the segmental mode process, and local twisting motions of the main chains, respectively. The dielectric relaxation time for the αn relaxation was almost...