Higher-Order Structure and Crystallization Behavior of a Crystalline/Crystalline Polymer Blend Composed of Components with Significantly Different Crystallization Rates

Effects of the preexisting crystal lamellar structure on the crystallization behavior of the other component were investigated for the blend of poly(oxymethylene)/poly(L-lactide) (POM/PLLA), using DSC, polarizing optical microscopy, SAXS, and dielectric relaxation measurements. In this system, even at a low POM fraction of 10 wt%, POM crystallized first and formed the crystal lamellar structure due to its significantly faster crystallization rate. PLLA, which crystallizes later, was found to crystallize from the unique confined space between the POM crystal lamellae. Despite the restricted space between the POM crystal lamellae, the crystallization rate of PLLA was improved compared to that of bulk PLLA. Analysis of the nucleation rate and spherulite growth rate showed that while the spherulite growth rate was slightly reduced by the presence of the POM crystal lamellae, the nucleation rate was significantly improved, which resulted in the increase of the overall crystallization rate. Furthermore, the dielectric relaxation measurements suggested that the formation of the POM crystal lamellae suppressed the mobility of the amorphous PLLA molecular chains, which is thought to contribute to the increase in the nucleation rate.