A dual role of D-Sorbitol in crystallizing and processing poly (lactic acid)

In this work, the effect of D-Sorbitol (DS) on the crystallization and processibility of PLA was systematically explored by means of DSC, FTIR, POM, WAXD, and as well as dynamic rheological analysis. Our results show that, as expected, DS can act as an effective nucleating agent for PLA and thus strikingly improve its crystallization properties. With 0.25-0.75% DS in blends, the cold crystallization of PLA disappears accompanied by a concomitant elevation of crystallization temperature. Based on analyzing isothermal crystallization kinetics, it is clear that the incorporation of DS can significantly enhance the crystallization rate of all PLA samples. For instance, the semi-crystallization time of neat PLA is 14.2 min at 110 degrees C, while PLA/0.75% DS blend takes only 1.5 min. A rheological characterization demonstrated that, besides playing a role as a nucleating agent, DS also serves as a plasticizer which improves the melt processing performance as reducing the modulus and viscosity of PLA matrix. On the basis of FTIR data, we propose that hydrogen bonding interactions between PLA and DS are responsible for hampering a further improvement of both crystallization properties and rheological performance over adding a high content of DS.