Inlfuence of Thermal History on Crystallization and Melting Behaviors of β-PP
The commercialβ–PP materials are obtained by addingβnucleating agents into PP. Theβcrystal content of final products is significantly influenced by heat history during processing procedure. In order to study the factors affect the formation ofβcrystal,the influence of thermal history on crystallization and melting behaviors ofβ–PP was systematically investigated by using a commercially availableβ–PP through differential scanning calorimetric (DSC) method. The study results show that:β–α phase transition inβ–PP matrix can happen during heating process,which results in a decreasedβcrystal relative content and an increasedαcrystal relative content. In addition,the slower heating rate will introduce more obviousβ–αphase transition,while faster heating rate is less inclined to cause this phenomenon. Recrystallization forα crystal which resulted by incompletely meltαcrystal inherently existed in the matrix together with newly formedα crystal due toβ–αphase transition upon heating will happen during cooling process. The eventually-formedα crystals possess more perfect crystalline structures and higher melting points.
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