Miaki Shibaya

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.

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.

Theoretical consideration of air gap effect on fiber formation during water-quenched melt spinning and application of air gap spinning to characterization of fluid relaxation time

Theoretical studies on the dynamics of water-quenched air gap melt spinning for poly(ethylene terephthalate) (PET) were done. Spinning tension in the air region increases rapidly with decreasing air gap length. Especially, in the case of air gap length less than 2 cm, high spinning tension can be obtained. It might be thought that high spinning tension during spinning process leads to high molecular orientation of super fibers such as Aramid fibers. Maximum deformation rate in the spinning process having narrow air gap appears at the interface of air and water, which is also related to high molecular orientation. Using air gap spinning, draw resonance experiments were performed to characterize the relaxation time of PET. Comparing the experimentally obtained draw resonance wave forms with those of computations for Maxwell fluid model, the relaxation time is estimated to be about 0.002 s. This value almost coincides with that obtained by other methods.