Abstract
ABSTRACTl‐Isoleucine (l‐Ile) was identified as an efficient anti‐nucleating agent for isotactic polypropylene (iPP). At 0.08 wt %, l‐Ile could significantly decrease the peak crystallization temperature (Tcp) of iPP by up to 8 °C at a cooling rate of 20 °C/min. Furthermore, l‐Ile exhibited both anti‐nucleation and pro‐nucleation abilities; i.e., a low content of l‐Ile inhibited iPP crystallization, whereas a high content promoted iPP crystallization. The unique crystallization behavior of iPP in the presence of l‐Ile was investigated by differential scanning calorimetry, polarized optical microscopy (POM), and rheological measurement. According to POM, a low content of l‐Ile completely dissolved in the iPP melt, whereas a high content of l‐Ile did not. Therefore, a mechanism by which l‐Ile inhibits and promotes the nucleation of iPP was proposed. Dissolving l‐Ile molecules in the iPP melt hindered the homogeneous nucleation of iPP as a “dilution effect”; however, as the content increases, l‐Ile could not be completely dissolved in molten iPP, and the residual crystals of l‐Ile thus provided heterogeneous nucleation sites for iPP and further promoted its crystallization. Experimental evidence from rheology and POM supported this mechanism. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45956.
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