Effect of fusion conditions ofβ-polypropylene on the new crystallization

Abstract

The new crystallization of β-modification of polypropylene (β-PP) was studied after melring as a function of the final temperature of fusion (T _F ). The new crystallization, thermal characteristics, polymorphic composition, and structure of recrystallized samples were highly influenced by theT _F level. As a function ofT _F , three characteristic regions were outlined: Region I below the melting point of β-modification, region II between the melting points of β- and α-modifications, and region III above the melting point of α-modification. In the vicinity of the melting points of both modifications, two narrow transition regions are observed where the crystallization and structural characteristics changed abruptly withT _F . AtT _F values in region I, recrystallization of β-modification proceeded without any change in the modification. IfT _F fell in region II, the sample crystallized newly into α-modification. The optically negative β-ring-spherulites were replaced by positive microclusters of α-modification and a marked structural memory effect was observed. In region III, the above characteristic became invariant withT _F (region of blank melt). These observations may be interpreted by the role of self nuclei.