Nori Yoshihara

Cold Crystallization Behaviors of Poly(Ethylene Terephtahalate)

Cold crystallization behaviors of poly(ethylene terephthalate) (PET) with respect to injection molding were investigated using a differential scanning calorimeter, a haze meter, a polarizing microscope and a small angle light scattering apparatus. Due to slow crystallization rate of PET, the temperature range between the glass transition temperature and the peak temperature (T cl ) of crystallization from glassy state is wider than those of PBT, PA6 and other semicrystalline polymers. The temperature range is one of the important factors governing the moldability of PET. It was found that T cl of PET can be controlled by co-polymerization or alloying with specific miscible polymers. By cold crystallization, the modified PET compositions generate spherulitic microstructures. For reinforced PET, lowering the value of T cl is effective in obtaining high crystallinity in the article molded even at low mold temperatures and then for improving moldability. For transparent applications, raising the value of T cl by either increasing molecular weight or co-polymerization is effective in enlarging the range of molding conditions and then improving moldability.

Adjusting the Lengths of Glass Fibers and the Relationship Between Fiber Length and Mechanical Properties for Reinforced Polyethylene Terephthalate)

The effects of fiber shape and compounding conditions on the distribution of glass fiber length of reinforced poly(ethylene terephthalate) are studied. The relationships between fiber length and mechanical properties are discussed. The length of the fibers pulled out from the rupture cross section and the critical fiber length are reported in different deformation modes. Fibers of finer diameter showed shorter average length and narrower distribution in the compound. Bundle size showed little effect on the fiber length distribution at the identical diameter. The weight average length, L w , prepared by a dry blending method is shorter than that by a melt blending method. A compound with a Dulmage type screw has fewer short fibers than that with a full-flight type screw. Therefore, the fiber length compounded with a mixing type screw, such as Dulmage type, showed the sharp distribution. The flexural strength depends more on the aspect ratio of fiber, L w /D, than on Lw. The Izod impact strength changed depending on L w and on the content of fibers longer than 0.25mm. The L w values of fibers pulled out from the rupture cross section were shorter in descending order for flexural, tensile and notched impact test specimens. The maximum length of fibers, L m , leads to the approximate critical length, L c , of the fiber fracture; 0.32mm for tensile was comparable to the theoretical one. As for flexural fatigue under small strain at 23 °C or lower temperature, most of the glass fibers were not pulled out, but were broken at the rupture cross section.

Effect of soft segment components on mechanical properties at low temperatures for segmented polyurethane elastomers

Dependence of mechanical properties at low temperature on the chemical structure and molecular weight of soft segment was discussed with regard to segmented polyurethane (SPU). Cast films with various molecular weights (Mn) and with various composition ratios of polytetramethylene glycol (PTMG) and polypropylene glycol (PPG) were used. Segmented polyurethanes having copolymerized soft segments consisting of PTMG and PPG had a single glass transition temperature corresponding to Mn and composition ratio. Dependence of low-temperature elastic recovery on recovery time, measurement temperature and Mn and composition ratio of soft segments was clarified. Stress-induced crystallization of soft segment was reduced by copolymerizing, and elastic recovery at low temperature was improved. SPU with a higher Mn of soft segment had a higher retention ratio of strain energy on cyclic deformation. SPU with a higher Mn of soft segment also had a higher retention ratio of stress. The retention ratio of stress for SPU synthesized by copolymerizing PPG (Mn=1000) with PTMG (Mn=2000) decreased with an increase in the copolymerization ratio of PPG. This fact is considered to be due to a rise in the glass transition temperature.

Effect of dry-spinning and post-treatment conditions on structure and properties of segmented poly(urethane-urea) elastic fibers

Mechanical properties of dry-spun fibers depend much on dry-spinning conditions as well as on polymer structure. A comparison of properties between dry-spun fibers and solvent cast films was made in order to examine the effects of dry-spinning and post-treatment conditions on properties for segmented poly(urethane-urea) (SPUU) samples. The stress-strain (S-S) curves of fibers having slight molecular orientation can be predicted by treating the cast film under a given degree of stretch to adjust the birefringence (Δn) of the film. The value of Δn based on orientation of the hard segment is influenced by dry-spinning conditions and is hardly affected by post-treatment under a relaxed state after dry-spinning. The stress of 300% elongation increases proportionally to be an increase of Δn. Also elastic recovery is improved with an increase of An.