Effect of Nucleating Agent on Strain-induced Crystallization of Films

To make the nucleating agent and the strain-induced crystallization work synergistically, the effect of nucleating agent on the strain-induced crystallization of poly (lactic acid) (PLA) films is investigated. Amorphous film samples of pure PLA (T0) and PLA/TMC328 (specialized nucleating agent) blends with different contents of TMC328 (0.5 wt%,1 wt% denoted as T0. 5,T1) are prepared and characterized by Xray diffraction (XDR) and differential scanning calorimetry (DSC). Then they are drawn at temperatures of 80 and 90 degrees C, about 24 similar to 34 K above T-g. And the crystallinity of drawn samples is measured by DSC and Fourier transform infrared spectroscopy (FTIR). Unexpected, at 80 and 90 degrees C the crystallinity of T0 is much higher than those of T0. 5 and T1, even though the nucleating agent can improve the cold crystallization of PLA significantly at 90 degrees C. Moreover, the strain-induced crystallization works better and more stably at T-d of 80 degrees C than at T-d of 90 degrees C. Then a new crystallization mechanism can be presented,which is independent of nucleation density even nucleation, but dominated by the formation and retention of strain-induced regular conformation. And the strain-induced crystallization works better with lower T-d, at which the intensity of the chain thermal motion is weaker and the formation of regular conformation can be easier. Therefore, during the process of strain-induced crystallization, the nucleating agent diffusing between the PLA chains plays a role of impurity which impedes the formation of regular conformation of PLA chains. So the synergy of improving crystallization cannot be achieved by the addition of nucleating agent.