Ichiro Sakurada

Preparation of hydrogels by radiation technique

Abstract Moderately concentrated, aqueous solutions of poly(vinyl alcohol) (PVA), poly(ethylene oxide), polyacrylamide, polyvinylpyrrolidone, and methyl cellulose were cast on a glass plate and irradiated with electron beams to yield crosslinked hydrogels. Irradiation was carried out also for water-swollen films of PVA. In all cases, no attempt was made to expel air from the polymer-water mixture to be irradiated, since the hydrogels were readily formed by placing a glass plate or a plastics film on the mixture. The measurement of tensile properties of the hydrogels revealed that the hydrogel from PVA, especially prepared by irradiation of water-swollen films, gave the highest tensile strength among the hydrogels. The swelling of once dried PVA hydrogels was recovered almost to the initial swelling state when boiled in water.

Radiation-induced grafting of acrylic acid onto polyethylene filaments

Abstract Radiation-induced grafting of acrylic acid onto high density polyethylene (PE) filaments was carried out in order to raise softening temperature and impart flame retardance and hydrophilic properties. Mutual γ-irradiation method was employed for the grafting in a mixture of acrylic acid (AA), ethylene dichloride and water containing a small amount of ferrous ammonium sulfate. The rate of grafting was very low at room temperature. On the other hand, large percent grafts were obtained when the grafting was performed at an elevated temperature. Activation energy for the initial rate of grafting was found to be 17 kcal mol between 20 and 60°C and 10 kcal mol between 60 and 80°C. Original PE filament begins to shrink at 70°C, show maximum shrinkage of 50% at 130°C and then breaks off at 136°C. When a 34% AA graft is converted to metallic salt such as sodium and calcium, the graft filament retains its filament form even above 300°C and gives maximum shrinkage of 15%. Burning tests by a wire-netting basket method indicate that graft filaments and its metallic salts do not form melting drops upon burning and are self-extinguishing. Original PE filament shows no moisture absorption, however, that of AA-grafted PE increases with increasing graft percent. The sodium salt of 15% graft shows the same level of moisture regain as cotton. The AA-grafted PE filament and its metallic salts can be dyed with cationic dyes even at 1% graft. Tensile properties of PE filament is impaired neither by grafting nor by conversion to metallic salts.

Some remarks on applied radiation chemistry

Abstract Radiation induced polymerization and grafting are two important reactions in the processing. Numerous reports concerning these subjects have appeared in the literature. There are, however, still many problems which have been left unsolved or neglected. Several problems will be taken up in this paper and discussed on our own experiments carried out in Osaka Laboratory for Radiation Chemistry and Department of Polymer Chemistry of Kyoto University.

Radiation-induced polymerization of styrene in amines

Abstract Radiation-induced polymerization of styrene in amines was carried out mainly under employment of n-butylamine in a wide range of dose rate at room temperature. The rate of polymerization was measured and GPC analysis of the products conducted. It was found that the products are consisted essentially of four fractions, i.e., oligomer, radical polymer, cationic polymer and super polymer. Butylamine is a strong inhibitor for cationic polymerization. For example, 3 × 10 −3 mole l butylamine in styrene solution can inhibit the formation of cationic polymer to a greater extent. Radical polymerization is initiated by radicals formed not only from styrene but also from butylamine. The rate constant of initiating radical formation of butylamine was found to be five times greater than that of styrene independent of dose rate. The dependence of the total rate of polymerization of styrene on the styrene content at various dose rates may be explained with the higher rate of initiating radical formation of butylamine. Chain transfer of growing chains to butylamine was also investigated, however, the contribution of transfer was negligible compared to that of mutual termination of growing chains for the stable polymer formation.