Yuhei Watanabe

Radiation effect on polyesters

Abstract Poly(3-hydroxybutyrate)(PHB) and its copolymer poly(3-hydroxybutyrate-3-hydroxyvalerate) [P(HB-HV)] were irradiated with γ-rays in air or vacuum. Polymer chain scission occurred and resulted in depression of melting points (Tm), glass-transition temperatures (Tg) and number-average molecular weight ( M n ). Decrease in M n of the sample irradiated in vacuum was smaller than that irradiated in air, implying introduction of crosslinking. The Tm and Tg of samples irradiated in air were inversely proportional to M n . Their biodegradability was clearly promoted with decreasing M n . Radiation grafting of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) was carried out by in-source polymerization. Degree of grafting (Xg) increased as irradiation dose increased and leveled off around 5 kGy. The Xg of PHB grafted was lower than that of P(HB-HV) because of higher crystallinity of the former. Crosslinking between the grafted PMMA chains was easily formed. Biodegradability of both polymers steeply decreased by introduction of MMA grafting, while that of polymers grafted with HEMA increased at first because of improvement of wettability then steeply decreased with increasing Xg of HEMA.

Radiation-Induced Graft Polymerization of Poly(3-Hydroxybutyrate) and Its Copolymer

Abstract Graft copolymerization of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) onto poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) {P(HBHV)} was carried out by using simultaneous radiation and preirradiation techniques from a 60Co γ-rays source. Degree of grafting (X g) of MMA onto both polymers increased as the irradiation dose increased. The X g for PHB graft-polymerized by simultaneous radiation was lower than that for the copolymer of 24 mol% HV content (24 M sample). On the contrary, X g of PHB graft-polymerized after preirradiation was higher than that of the 24 M sample. The X g depended on differences in regularity in the crystalline regions or crystallinity and rate of radical decay. Crystalline regions of PHB remained almost unchanged after grafting, while crystalline regions of the 24 M sample were partially destroyed by the introduction of grafting. Glass transition temperatures of both grafted polymers increased up to 8°C. The ...

Radiation-induced degradation of poly(3-hydroxybutyrate) and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Poly(3-hydroxybutyrate) {P(3HB)} and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) {P(3HB-co-3HV)} were irradiated with γ-rays at 25°C in air and in vacuum. Melting points (Tm) and glass-transition temperatures (Tg) were measured by differential scanning calorimetry. Number-average molecular weights (Mn) were analyzed by gel permeation chromatography. No significant differences were observed between Tm values of P(3HB) and P(3HB-co-3HV) irradiated in air and in vacuum, which decreased almost linearly with increasing irradiation dose. The Mn values of both samples decreased sharply with increasing dose, reflecting typical random chain scission. The decrease in Mn of the sample irradiated in vacuum was smaller than that irradiated in air with the same dose, implying the occurrence of crosslinking. The Tg values for both polymers irradiated in vacuum remained almost unchanged over a wide dose range, while those irradiated in air decreased as the irradiation dose increased. Both the Tm and Tg of samples irradiated in air were inversely proportional to Mn. Biodegradability was clearly promoted with decreasing molecular weight.

Radiation induced oxidative degradation of polymers—II: Effects of radiation on swelling and gel fraction of polymers

Abstract The degradation of polyethylene (PE) and ethylene-propylene copolymer (EPR) by γ-ray irradiation in oxygen under pressure was studied by gel fraction and swelling measurements. Irradiation in oxygen produced mainly chain scission, therefore the molecular weight decreased with dose. The G values of chain scission are 4±0.5 for PE, and 1 ≈2 for EPR. When the crosslinked PE and EPR are irradiated in oxygen, gel fraction decreases and swelling ratio increases with dose. A linear relation between the swelling ratio (Q) and the dose (R) is observed for EPR, that is, log[Q/Q 0 ] = K·Q 3 2 ·R . With the addition of antioxidants, the relation still holds but the factor K is changed, so the efficiency of antioxidants can be determined from the value of K.

Sterilization of Bacillus spores by converted X rays

Abstract Relative sensitivities of endospores of Bacillus pumilus E601, B. subtilis IAM1069, B. megaterium S31 and B. brevis S5 to gamma rays, converted X rays (bremsstrahlung) and electron beams were examined in order to estimate the conditions in which converted X rays kill Bacillus spores. The radiation sensitivities to gamma rays and electron beams of each strain dried on glass fiber filter without additives were found to be almost equivalent, and D values were obtained as follows: 1.5–1.6 kGy for B. pumilus, 1.4–1.5 kGy for B. subtilis, 1.9–2.0 kGy for B. megaterium and 1.6–2.0 kGy for B. brevis. The radiation sensitivities of endospores of each strain to electron beams were slightly lower than those to gamma rays in the dry condition with additives of 2% peptone + 1 % glycerin on glass fiber filters. The increase of radiation resistance in the presence of additives was also observed with X rays, and it was on an intermediate level between those with gamma rays and electron beams. In the dry condition using cellulose filter paper, only the radiation resistances of B. megaterium and B. brevis in the presence of additives B. megaterium and B. brevis in the presence of additives were increased.

Radiation-Induced Copolymerization of Thiophene with Maleic Anhydride

Abstract Radiation-induced copolymerization of thiophene with maleic anhydride has been studied. On the copolymerization in chloroform solution, the effects of dose rate, polymerization temperature, and, monomer composition and concentration on the yield and molecular weight of the copolymer were determined. The copolymerization proceeds via a radical mechanism with bimolecular termination of propagating polymer radicals, and the apparent activation energy is 5.3 kcal/mole. By NMR spectroscopy of copolymer, it was also found that these monomers copolymerize alternately to give a copolymer having structure I. In this copolymerization, the higher initial rates were obtained at an equimolar composition of monomers and by using solvents containing chlorine, such as CC14, CHC13, and C6H5C1.

Study on the long life radicals of hexanediol diacrylate in irradiated urea canal complexes in relation to post-polymerization by irradiation

Abstract The properties of radicals formed on irradiating long chain monomers in urea canal complexes were studied by ESR and related to the results of post-polymerzation. The initiating radicals (CH 3 -ĊHCOOR) were trapped in canal complexes as a result of γ-irradiation at relatively high temperature such as 25° and the radicals converted to propagating radicals (∼CH 2 -ĊHOOR0 on heating to 70°. The temperature dependence of radical concentration was followed and the decay curves corresponded well with the results of post-polymerization.

Radiation-Induced, Solid-State Copolymerization of Tetraoxane with 1,3-Dioxolane

Abstract The radiation-induced, solid-state copolymerization of tetraoxane with 1,3-dioxolane has been investigated. The results were discussed in comparison with those of trioxane-1, 3-dioxolane copolymerization reported previously. In the copolymerization in vacuo, it was found that the thermal stability of the copolymer increases with increasing polymerization temperature, time, and the pre irradiation dose, although that of trioxane-1,3-dioxolane copolymer decreases with increasing preirradiation dose and is nearly constant irrespective of polymerization temperature and time. The yield and intrinsic viscosity behavior of the copolymer are similar to those found in trioxane-1,3-dioxolane copolymerization. The copolymerization in air, however, was found to be very complicated. Trioxane formation in this system was also investigated in detail.