The effects of various absorbed dose amounts, especially during gamma ray radiation in the presence and absence of oxygen, on the mechanical properties and the dissolution performance of medical rubber products made of chlorobutyl rubber were investigated. From the results of physical property measurements, it was found that the reaction type of chlorobutyl rubber was not a “degradation-type”reaction, but a “crosslinking-type”reaction. Regarding the dissolution performance, the effect of oxygen was the main factor, and when gamma ray was irradiated in the absence of oxygen, it was found that the dissolution performance was almost at the same level as that of original sample. Furthermore, a compound thought to be an oxidant of the triazine vulcanizing agent, which was confirmed by LC-TofMS analysis, was detected only in the case of radiation in the presence of oxygen. This is thought to be due to the decomposition of the cross-linked bonds by the polymer radical reaction accompanying the gamma ray radiation. However, such a phenomenon was not confirmed in the absence of oxygen. These results suggest that the gamma ray sterilization of chlorobutyl rubber in the absence of oxygen enables both sterilization assurance and material degradation prevention. This method can be expected to expand its practical application to medical rubber products in the future.

Prediction of tensile properties by pulsed NMR measurements is improved by swelling the sample with a deuterated solvent. However, in recent years, the use of organic solvents has been avoided from the viewpoint of safety and health risks and the environmental impact of volatile organic compounds. In this study, we investigated a method for predicting the tensile properties of rubber by pulsed NMR measurements without using a swelling solvent. Spin-spin relaxation measurements in dry state and tensile tests were performed on sliced sheets sampled from the surface and interior of thermally oxidized thick-walled rubber. As a result of multivariate analysis using NMR parameters obtained from spin-spin relaxation, it was found that the spin-spin relaxation time of network component (T_2HS) and its Weibull coefficient (W_HS) are effective as explanatory variables for tensile properties. Regression equations using T_2HS and W_HS could predict the extension ratio at break (λ_B) and the stress at 100% strain (S₁₀₀) of surface and inner layers of thermally oxidized products with high accuracy.

Due to its unique elastic deformation characteristics, rubber is used in all kinds of industrial products. However, the huge amount of energy consumed during the vulcanization and molding processes and the recyclability of rubber, which has been used industrially in the past, have become problems. Thermoplastic elastomers (TPEs) are attracting attention as a material to solve this problem. TPEs are microphase-separated into the hard segment (HS) phase and the soft segment (SS) phase. The SS phase serves as the rubber component that provides softness, while the HS phase is fluid at high temperatures but serves as a physical cross-linking point that prevents deformation at room temperature. As a result, it is attracting attention as an alternative material to rubber because it is easy to mold and process and can be recycled. In this study, Styrene-ethylene-butylene-styrene triblock copolymers (SEBS) , which is a styrenic-based thermoplastic elastomer, and α-methylstyrene-ethylene-butylene-α-methylstyrene triblock copolymers, in which the PS blocks are replaced by α-methylstyrene is prepared and differences in structure and physical properties at the nanoscale were discussed using a nano-palpation atomic force microscopy (AFM) .