Effects of melt structure on non-isothermal crystallization behavior of isotactic polypropylene nucleated with α/β compounded nucleating agents

Abstract

In this study, the effects of melt structure (tuned by controlling the fusion temperature Tf) on non-isothermal crystallization and subsequent melting behaviors of isotactic polypropylene (iPP) nucleated with α/β compounded nucleating agents (α/β-CNAs) have been further investigated. The results show that under all cooling rates studied (2–40°C/min), the crystallization temperature on cooling curves increased gradually with decrease of Tf, meanwhile, when Tf was in temperature range of 166–179°C where ordered structures survived in the melt (defined as Region II), crystallization activation energy ΔE was found to be evidently lower compared with that when Tf>179°C or Tf < 166°C. The results of subsequent heating showed that occurrence of Ordered Structure Effect can be observed at all the cooling rates studied; the location of the Region II was constant when cooling rate varied; Low cooling rate encouraged formation of more β-phase triggered by ordered structure. Moreover, the role of ordered structure on β-α recrystallization was comparatively studied by tuning the end temperature of recooling (Tend) after held at Tf, and it was found that ordered structure encouraged the formation of β-phase with high thermal stability at low temperature part of Region II, while enhanced the β-crystal with relatively low thermal stability at high temperature part of Region II. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers