(621i) Uniqure Crystallization Behavior of Isotactic Polypropylene in the Presence of L-Isoleucine and Its Inhibition and Promotion Mechanism of Nucleation

 A novel and efficient anti-nucleating agent L-isoleucine (L-I) was found and 0.08 wt % L-I could significantly decrease the the peak crystallization temperature (T_cp) of isotactic polypropylene (iPP) up to 8 ^oC at the cooling rate of 20 ^oC/min. To our knowledge, so highly efficient anti-nucleating agent of iPP was reported for the first time. Furthermore, L-isoleucine exhibited two opposite nucleating ability, aiti-nucleation and nucleation ability, i.e., hindering the crystallization of iPP at low content and promoting the crystallization of iPP at high content. The unique crystallization behavior of iPP in the presence of L-I were investigated by Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM) and rheological mesurement. It was found that low content of L-I was completely dissolve in iPP melt, while high contnt of L-I did not by the observation of POM. Therefore, a mechanism which L-I inhibits and promotes nucleation of iPP was proposed. L-I moleculars dissoving in the iPP melt hindered the homogeneous nucleation of iPP moleculars for solvent effect, while with increase of L-I content, L-I could not be completely dissolved in molten iPP, the residual crystals of L-isoleucine provided heterogeneous nucleation for iPP and further promoted the crystallization. Experimental evidence from rheology and POM supported the mechanism.