STRUCTURE DEVELOPMENT IN POLYOLEFIN PROCESSING
Prof. James L. White
Institute of Polymer Engineering, University of Akron
U. K.

Keywords: -

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Polyolefins, including polyethylene and polypropylene, comprise the largest volume of commercial thermoplastics. To these must be added isotactic polybutene-1, isotactic poly(4methyl pentene-1) and cyclopolyolefins.

While cyclopolyolefins vitrify into glasses the other commercial polyolefin thermoplastics crystallize. While polyethylene invariably crystallizes into an orthorhombic unit cell, the other crystallizing polyolefins are polymorphic. Depending upon their temperature, and deformation history (or if handled in solution), they will crystallize into different polymorphs. This is the case with isotactic polypropylene, syndiotactic polypropylene, isotactic polybutene-1 and isotactic poly(4-methyl pentene-1).

The variations in deformation history also affect the nature and levels of polymer chain orientation introduced. Uniaxially stretched filaments and melt-spun fibers have uniaxial orientation. Film and blow molded bottles have biaxial orientation. Usually injection molded parts have complex orientation distributions which vary with position throughout the part cross-section.

In this lecture we summarize studies on the variation of crystalline form, morphology and orientation in fabricated polyolefin parts as a function of processing conditions.