Control of Chain Orientation in Blends of Polypropylene and Polybutene‐1

Abstract

An extruded sheet having unique molecular orientation is developed using a miscible blend of isotactic polypropylene (PP) and isotactic polybutene‐1 (PB). Blends containing a small amount of N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide are extruded from a ribbon‐shaped die onto a chill roll at various temperatures. It is found that form‐I crystals of PB become oriented in the flow direction, whereas β‐form crystals of PP become oriented perpendicular to the flow direction. The molecular orientation is the most obvious for the blend containing 60 wt% of PB extruded at a chill roll temperature of 80 °C. The anisotropy in the tensile modulus of the obtained extruded sheet is reduced by its extraordinary molecular orientation.

Toward a More Comprehensive Understanding on the Structure Evolution and Assembly Formation of a Bisamide Nucleating Agent in Polypropylene Melt

“…The introduction of a nucleating agent (NA) is one of the most important and effective methods to control the crystalline structure of semicrystalline polymers in practical processing. − NA has the ability to provide a large number of nuclei for polymer crystallization during the melt cooling, thereby significantly accelerating the crystallization and regulating the crystalline morphology. − For isotactic polypropylene (iPP), one of the most extensively used semicrystalline thermoplastics, the introduction of NAs is of crucial importance owing to its relatively low crystallization rate. By adding different kinds of NAs, the processing cycle of iPP has been significantly shortened and the distinct improvements in mechanical, optical, and barrier properties have been achieved, thus expanding the application range of iPP. − Among various NAs, β-NA is one of the most important and extensively used NAs for iPP. β-NA has the ability to handily prepare iPP with high purity of thermodynamically metastable β-modification, which exhibits superior toughness compared to iPP samples containing a thermodynamically stable α-form, thereby endowing products with excellent toughness–stiffness balance.…”