Enhanced crystallization rate of poly(L-lactic acid) (PLLA) by polyoxymethylene (POM) fragment crystals in the PLLA/POM blends with a small amount of POM.

Phase diagrams and glass transition behaviors of poly(L-lactic acid)/polyoxymethylene (PLLA/POM) blends have been investigated in our previous work (Macromolecules 2013, 46, 5806-5814). In this work, the crystallization behaviors and physical properties of the PLLA/POM blends with the PLLA as the major component have been systematically studied. POM was crystallized into the fragment crystals that were finely dispersed in the PLLA matrix when cooling down from the melt of the blends. It was found that the POM fragment crystals accelerated the crystallization process of PLLA matrix and increased the final crystallinity of PLLA significantly in the blends. At the same time, the PLLA spherulites nucleated by POM fragment crystals were much smaller than those obtained from neat PLLA. It was further found that the crystallization rate of PLLA was quite dependent upon the POM loadings and the highest crystallization rate was observed at POM loadings of 7 wt %. It is considered that the POM fragment crystals take the nuclei role to initiate the crystallization of PLLA at low POM loadings, while a high content of POM in the blends leads to the large POM spherulites that cannot nucleate PLLA crystallization effectively. The obtained PLLA/POM blends at low POM loadings with small PLLA spherulites exhibited excellent optical transmittance and good mechanical performance.