Crystallization morphologies and non-isothermal crystallization kinetics of isotactic polypropylene modified by α/β compounded nucleating agents

Crystallization morphologies and non-isothermal crystallization kinetics of isotactic polypropylene（iPP)modified by three α/β compounded nucleating agents（NAs)were studied by means of polarized optical microscope（POM)and differential scanning calorimeter（DSC).The size of spherulites in nucleated iPP appeared much smaller than that in pure iPP.However, iPP nucleated by different ratios of α/β compounded NAs showed different crystallization morphologies.Crystallization morphologies of nucleated iPP depended on ΔT_Cp(ΔT_Cp refers to the difference in crystallization peak temperature between nucleated iPP and pure iPP)of α and β NAs.The one with the higherΔT_Cp played a leading role in the crystallization process, resulting in that the crystallization morphology of nucleated iPP appeared close to that with the NA alone.Competitive nucleation would occur when the difference ofΔT_Cp between two NAs was not pronounced. ΔT_Cp was related to the concentration of NA.Thus crystallization morphologies could be adjusted by changing the ratio of α/β compounded NA.The Caze method was used to deal with non-isothermal crystallization kinetics obtained by DSC.The obtained parameters showed addition of α/β compounded nucleating agents could greatly raise crystallization peak temperature of iPP and shorten the crystallization half-time.Avrami exponent of α/β compounded nucleated iPP was close to that of iPP nucleated by the NA with the higherΔT_C pindividually, which demonstrated that the crystallization process of iPP nucleated with α/β compounded NAs also depended onΔT_Cp of α and β NAs within the compounded system.