Isothermal crystallization behavior and melting characteristics of injection sample of nucleated polypropylene

The isothermal crystallization behavior and melting characteristics of pure polypropylene (PP) and PPs nucleated with a phosphate nucleating agent (A) and a sorbitol derivative (D) have been studied by differential scanning c alorimetry (DSC). Compared with pure PP, nucleated PPs show a shorter half- times of crystallization. Dependence of crystallization rate of nucleated P P on the crystallization temperature is stronger than that of pure PP at th e higher crystallization temperature, whereas the opposite results are obta ined at the lower crystallization temperature. Addition of nucleating agent shifts the temperature at the deviation from the baseline of DSC melting c urve, T-m(o), and the temperature at the completion of melting, T-m(f), to higher temperatures, indicating that nucleated PPs exhibit a higher perfect ion of PP crystals. A shoulder peak in the high temperature range of meltin g peak of nucleated PP and a wider low temperature region in the melting pe ak of pure PP are observed. Obviously, PP and nucleated PPs form different distribution of crystal perfection in the isothermal crystallization proces s. According to the half-time of crystallization, nucleating agent A is mor e effective than D. (C) 2000 John Wiley & Sons, Inc.