EFFECT OF FUSION CONDITIONS OF BETA-POLYPROPYLENE ON THE NEW CRYSTALLIZATION

The new crystallization of beta-modification of polypropylene (beta-PP) was studied after melting 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 the T(F) level. As a function of T(F), three characteristic regions were outlined: Region I below the melting point of beta-modification, region II between the melting points of beta- and alpha-modifications, and region III above the melting point of alpha-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 with T(F). At T(F) values in region I, recrystallization of beta-modification proceeded without any change in the modification. If T(F) fell in region II, the sample crystallized newly into alpha-modification. The optically negative beta-ring-spherulites were replaced by positive microclusters of alpha-modification and a marked structural memory effect was observed. In region III, the above characteristic became invariant with T(F) (region of blank melt). These observations may be interpreted by the role of self nuclei.