Effects of self-assembled sorbitol-derived compounds on the structures and properties of biodegradable poly(L-lactic acid) prepared by melt blending

The microstructures and characteristics of biodegradable poly(L-lactic acid) (PLLA) with 1,3: 2,4-dibenzylidene-D-sorbitol (DBS) prepared by melt blending were investigated in this study. DBS was added as a diluent to PLLA in the melted state, leading to the disentanglement of PLLA chains and the enhancement of PLLA mobility. Upon cooling from the melt, the formation of self-assembled DBS nanofibrils enhanced the hardness and stiffness of PLLA. DBS nanofibrils were measured with diameters of 40-50 nm, as observed using scanning electron microscopy (SEM). In addition, the thermal and crystallization behaviors of PLLA were significantly influenced by the addition of DBS. The ordered and regular alpha-crystals of PLLA were favored when DBS was added. The crystallization rates of PLLA are tunable by varying the isothermal crystallization temperatures of PLLA and the amounts of DBS. The presence of DBS interfered with the crystallization rates of PLLA. However, at higher crystallization temperatures of PLLA, DBS facilitated the formation of nuclei, leading to an increase in the crystallization rates of PLLA. Furthermore, the hydrophilicity of PLLA was significantly improved by a further increase in DBS concentration.