Tomoaki Takebe

Structure and properties of low-isotacticity polypropylene elastomeric fibers prepared by sheath-core bicomponent spinning: effect of localization of high-isotacticity component near the fiber surface

Abstract Sheath-core type bicomponent melt-spun fibers were produced by extruding the melts of low-isotacticity polypropylene (LPP) as the core component and the blend of LPP and high-isotacticity PP (IPP) as the sheath component. IPP content in the sheath was changed from 8 wt% to 40 wt% while sheath/core composition was varied from 50/50 to 10/90. Accordingly overall IPP content was kept constant at 4 wt%. Even though the overall IPP content was intact, bicomponent fibers with lower contraction ratio after spinning, higher elastic recovery and slightly higher modulus and strength were obtained by increasing the IPP content in the sheath and decreasing the sheath layer composition, i.e., localizing the IPP to the region near the surface in the fiber cross-section. Structure analysis of the as-spun fibers suggested the suppression of crystallization of LPP in the sheath by blending IPP. By contrast, enhancement of molecular orientation and crystallization of the sheath component were found to occur by localizing the IPP to the region near the fiber surface. It was speculated that this behavior was caused by the kinematic mutual interaction of the sheath and core components in the melt spinning process.

INFLUENCE OF COOLING WATER TEMPERATURE ON FILM STRETCHABILITY, SUPERSTRUCTURE AND FILM PHYSICAL PROPERTIES OF RANDOM COPOLYPROPYLENE IN DOUBLE BUBBLE TUBULAR PROCESS

It is commonly said that the molten resin of polyolefin extruded from die in the double bubble tubular process should be cooled by low temperature cooling water. This is because restraining the crystallization progress by low temperature cooling water makes it possible to obtain good stretchability and good physical properties of the stretched film. Therefore the cooling water temperature is customarily set low. However, the correlations among the cooling water temperature, the stretchability and the physical properties of stretched film have not been reported thoroughly. This report discusses the influence of the cooling water temperature in the double bubble tubular process on the stretchability, the physical properties of the stretched film and the film superstructure of random copolypropylene (r-PP) which is commonly used for this process. It was found that the stretchability was not influenced by the cooling water temperature in the double bubble tubular process, also the physical properties of the stretched film and the film superstructure of r-PP was slightly changed by the cooling water temperature. However such changes could be compensated by adjusting the preheating process temperature so that the stretching stress could be of the same value.

Influence of Cooling Water Temperature on Properties of LLDPE Film in Double Bubble Tubular Film Process

The polymer melt of polyolefin is commonly extruded from a circular die in a double bubble tubular film (DBTF) process while cooled by chilled water. It is generally thought that restraining the crystallization progress by low temperature cooling water may make it possible to obtain good stretchability and good physical properties of film. Therefore the cooling water temperature is customarily set low in the manufacturing process of DBTF. This report deals with linear low density polyethylene (LLDPE) film widely used as well as random copolypropylene (r-PP) film reported in the previous work /1/. From this study, the following results were obtained. Generally, the higher cooling water temperature leads to the higher film temperature in the stretching zone of DBTF process so that the stretching stress and shrinkage of film become lower. Therefore the cooling water temperature influences the quality of stretched film (SF). Those properties can be compensated by adjusting the preheating temperature, even if the cooling water temperature is high.