The effect of ionizing radiation on the properties of silicone elastomers cured in the presence of different co-agent

The main purpose of this thesis is to investigate the stability of vinyl-methyl-polysiloxane (VMQ) and phenyl-vinyl-methyl-polysiloxane (PVMQ) elastomers against ionizing radiation and to determine how the energy absorption capacity (damping properties) of these elastomers varies with ionizing radiation.For this purpose, PVMQ and VMQ elastomer blends were prepared by using peroxide as curing agent and triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), zinc diacrylate (ZDA) and zinc dimethacrylate (ZDMA) as accelerator co-agent. The curing rate, cure kinetics of silicone blends which containing different types of accelerators were examined with the Moving Die Rheometer (MDR) and the optimum curing conditions and the curing temperature were determined. After curing, silicone elastomers were irradiated with electron beams in different doses. Sol-gel analyzes were performed to determine how ionizing radiation affects the crosslink density of these silicone elastomers. Hardness tests were conducted to observe how the shore A values of the PVMQ and VMQ elastomer changed depending on the co-agent type and irradiation dose. Cross-link densities were determined by using stress-strain curves obtained from universal test device. It has been tried to ultimate the relationship between the crosslink density and the type of accelerator. The mechanical properties of the elastomers irradiated at different doses were first examined with Universal Test Machine in order to clarify how the type of curing coagulants affects radiation stability. Temperature Scanning Stress Relaxation behaviors (TSSR) were also examined to determine how silicone type, co-agent type and radiation affect the long-term permanent mechanical performance of silicone elastomers. The effect of these variables on the energy damping capacities of silicone elastomers was illuminated using hysteresis curves obtained by applying a 50% compression 10-repeat cyclic compression test using a universal test machine. As a result of all these studies mentioned above, the main effect of radiation on thermally peroxide cured PVMQ and VMQ elastomers was found to be crosslinking. The value of crosslink densities (XLD) which calculated using different approach for PVMQ and VMQ elastomer showed that the crosslinking efficiency of radiation is higher in the presence of co-agents. In the mechanical test results, ionizing radiation did not cause a serious change in the tensile strength. Depending on amount of the radiation dose, the values of elongation at break have decreased and the values of elastic modulus have increased for all silicone elastomer blends. Temperature scanning stress relaxation behaviour showed that the radiation is to an important tool for controlling stress relaxation behavior of silicon elastomers at room temperature, high temperatures and isothermal conditions. In addition, anisothermal stress relaxation behaviors of elastomers have been observed that the T50 service temperatures of VMQ silicones containing Type II co-agent did not change much with the increase in irradiation dose. Although the service temperature tends to increase with irradiation in VMQ elastomers, it is generally reduced in PVMQ elastomers. The addition of co-agents did not change this general trend. When the energy damping capacity values were examined, it was found that the energy damping capacities of PVMQ elastomers without co-agent were higher than the co-agent free VMQ elastomers It has been determined that with the use of co-agent, the energy damping value of VMQ elastomers increases. All of these results understandably showed that functional groups in the structure of silicone elastomers or chemical structures formed by irradiation are important parameters to control the relaxation behavior and energy damping capacities of silicone elastomers. Furthermore, it was concluded that the type of silicone elastomer, the type of co-agent used as a crosslinking agent, and the irradiation dose are other parameters which can be used to control the mechanical, relaxation behavior and energy damping capacities of silicone elastomers.