Fumihiko Ozaki

Molecular-weight dependence of morphology and mechanical properties of ultrahigh-molecular-weight polyethylene gel films

Abstract Films of three kinds of ultrahigh-molecular-weight polyethylenes (UHMWPE) with molecular weights of 6 × 106, 3 × 106 and 1 × 106 were produced by gelation/crystallization from dilute solutions. The dried gel films were stretched up to their maximum draw ratios. The molecular-weight dependences of morphology and mechanical properties of the drawn films have been examined using wide-angle X-ray diffraction, small-angle X-ray scattering, birefringence, crystallinity and stress relaxation modulus. It turned out that the long period, molecular orientation and crystallinity were hardly affected by molecular weight, while the stress relaxation modulus was strongly affected. The master curves indicated that the decrease in the stress relaxation modulus was more pronounced as the molecular weight of the test specimens decreased. This was thought to be due to a drastic increase of the slippage of molecular chains, leading to the disappearance of tie molecules and/or entanglement meshes under the external applied stress.

A light scattering study of orientation of liquid‐crystalline rodlike textures of poly(γ‐benzyl‐L‐glutamate) in an electric field by saturation electric birefringence method

The orientation behavior of liquid crystalline solutions of poly (‐γ‐benzyl‐L‐glutamate) (PBLG) in chloroform under an electric field was investigated with respect to characteristic electro‐optical properties of macromolecules using small angle light scattering and birefringence techniques. The Hv light scattering pattern showed a circular type in the absence of an applied field. This indicates large orientation disorder of optical axes with respect to the molecular cluster axis. When an electric field was applied, the scattering pattern became X type, characterizing the scattering from rodlike textures being a sort of molecular cluster and the scattering lobes were extended to the horizontal direction. This means the preferential orientation of the molecular cluster in the direction of an electric field. In order to analyze the variation of the scattering pattern with increasing electric field, we have carried out theoretical calculations of the basis of a model. In this model system, the orientation dis...

Crsslinking effect of ultrahigh molecular weight polyethylene-low molecular weight polyethylene blend films produced by gelation/crystallization from solutions

Polyethylene-polyethylene blend films were prepared by gelation/crystallization from semidilute solution by using ultrahigh molecular-weight (mw) polyethylene (UHMWPE) (mw=6×106) and low molecular weight polyethylene (LMWPE) (mw=4×104). The UHMWPE/LMWPE compositions chosen were 50/50, 67/33, and 91/9. Elongation was carried out in a hot oven at 115–130°C. The drawn films were exposed to an electron beam under nitrogen flow. Radiation doses chosen were 10, 20, 40, and 100 Mrad. crosslinking caused a significant effect in improving high temperature resistance for the blend film with draw ratio of 20 in the case of irradiation doses less than 20 Mrad. The elongation beyond 20 times and high doses beyond 20 Mrad hampered the crosslinking effect and the specimens were easily torn manually. This is thought to be due to the fact that the excess irradiation dose causes main chain scission apart from crosslinking.

A light scattering study of orientation of liquid–crystalline rodlike textures of poly(γ‐benzyl‐L‐glutamate) in an electric field perpendicular to the direction of sample cell surface by means of saturation electric birefringence method. III

The orientation behavior of liquid crystalline solutions of poly(γ‐benzyl‐L‐glutamate) (PBLG) in chloroform was investigated with respect to characteristic electro‐optical properties of macromolecules using polarizing microscope and small angle light scattering techniques, when an electric field was applied parallel to an incident beam. The birefringence phase exhibited an irregular patchwork of predominantly blue, yellow, and pink regions under cross polars without applying the electric field and the corresponding Hv light scattering was circular. When the field was applied, the brightness of the phase decreased with increasing voltage and the corresponding Hv patterns became a typical X‐type characterizing the scattering from rodlike textures. The analysis was made for a model system. In this model system, rods orient randomly in the three‐dimensional space in the absence of the electric field, whereas when the electric field is applied, the rods orient predominantly parallel to the electric field. The ...