İyonlaştırıcı Radyasyonun Poli (Epiklorohidrin-KO-Etilen Oksit-KO-Allil Glisidil Eter) Polimerleri Üzerindeki Etkisinin İncelenmesi
Özet
In today's world, the diversity of materials used in industrial and commercial applications is steadily increasing. Among these materials, elastomers, especially, play a significant role in many sectors due to their properties such as flexibility, durability, and chemical resistance. Elastomers are widely used in industries such as automotive, construction, medical, and textiles. In this context, epichlorohydrin-based rubbers have found a solid place, particularly in industrial applications.
Epichlorohydrin-based rubbers are synthetic rubber types obtained through the polymerization of epichlorohydrin monomer alone or with other monomers such as ethylene oxide and allyl glycidyl ether. This type of rubber includes advantages such as mechanical strength, heat resistance, and chemical stability. Therefore, epichlorohydrin-based rubbers have become preferred materials, especially in high-performance applications. The polymer with different monomer ratios of poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO) with four different molecular architectures was studied within the scope of this thesis. These terpolymers are commercial polymers produced with the codes T3108, T3102, T3100, and T3000LL. One of the commercial names is Hidrin, which includes epichlorohydrin homo, co, and ter polymers, namely poly(epichlorohydrin) (ECH or CO), poly(epichlorohydrin-co-ethylene oxide) (ECO), and poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO). Due to their physical and chemical properties, such as high oil, ozone, fuel, and chemical resistance, these polymers have a wide range of applications in the industry, especially in automotive applications. Additionally, their high vibration absorption/damping and low-temperature flexibility are also among the specified properties of these polymers. Recently, it has been observed that the response and durability of epichlorohydrin homo, co, and ter polymers to ionizing radiation differ [2]. There is not enough information in the literature about how the terpolymer of epichlorohydrin behaves under ionizing radiation. In this thesis, structural characterization studies of epichlorohydrin were initially conducted. For this purpose, the structural features of epichlorohydrin polymers with different ratios of epichlorohydrin, ethylene oxide, and allyl glycidyl ether were examined using Fourier transform infrared spectroscopy (FTIR) for structural analysis and nuclear magnetic resonance (NMR) technique for molecular structure analysis, which were not interacted with ionizing radiation.
In the obtained FTIR spectra, bands of -CH2-, -C=C-, -C-O-, and C-Cl were clearly observed. The peak areas of the C=C, C-Cl, and C-O bands were calculated, and ultimately, the ratio of monomer/functional groups was determined by normalizing to the peak area of CH2. According to these results, the order of the amount of C=C double bond was found to be T3100>T3108>T3000LL>T3102.
The monomer ratios in the terpolymer were determined by 1H NMR analysis. When the peaks of T3108 and T3102 polymers were compared, it was observed that T3108 was richer in AGE ratio, while T3102 had the lowest. The ECH monomer ratio is present in the polymers in the order of T3102>T3100>T3000LL>T3108.
Although some technical data on the molecular properties of the epichlorohydrin terpolymers used in the thesis have been known, it was found that the Kuhn-Mark-Houwink-Sakurada (KMHS) constant of GECO elastomers is not available in the literature. These values were found as a result of measurements using size exclusion chromatography. Different but close KMHS values were found for the four different Hydrin polymers.
In the second stage of the thesis, epichlorohydrin polymers were irradiated with high-energy electron beams in the dose range of 0 kGy to 100 kGy, and the effect of the absorbed dose on the chemical structure of the Hidrin polymers was investigated again with spectroscopic studies. According to the FTIR analysis results, it was observed that as the irradiation dose increased from 0 to 100 kGy, the amount of double bonds decreased, while the amount of crosslinks increased.
The most important effect of ionizing radiation on polymers is chain scission and crosslinking. One of the main topics of this thesis was which of these reactions is effective in GECO polymers exposed to ionizing radiation. After exposing the four polymer samples with different molecular architectures to radiation, swelling experiments were completed in acetone solvent, and the % gelation rates were calculated from the obtained data. It was observed that the observed order for % gelation, T3100≥T3108>T3000LL>T3102, was related to the AGE ratio of these polymers, in other words, the ratio of vinyl groups, as 11.0T3100>7.2T3108>5.0T3000LL>3.7T3102.
To determine the solubility parameters of GECO polymers, swelling behaviors of irradiated polymers with doses of 40 kGy and 80 kGy were examined in 13 different solvents. Solubility parameters were calculated theoretically using both the group contribution method and experimental data, and the Flory-Rehner solubility parameter was calculated using these solubility parameters. In addition to the % gelation data calculated after swelling experiments in acetone solvent, % swelling values were also determined. Mc average molecular weight between crosslinks and e crosslink densities were found. It was determined that crosslink densities increased with increasing irradiation dose for all GECO polymers.
After all these results and calculations, % chain scission / crosslinking efficiency (p0/q0) and gelation dose (Dg) were calculated using gelation rates and Charlesby-Pinner and Charlesby-Rosiak equations to examine the effect of ionizing radiation on the chain structure of terpolymers. When comparing the po/qo values, it was observed that according to the Charlesby–Pinner equation, the po/qo ratio changed in the order of T3000LL > T3102 > T3100 > T3108. These results indicated that T3000LL polymer had the highest chain scission efficiency, while T3108 polymer had the highest crosslinking efficiency.
At the end of this thesis, detailed characterizations of GECO polymers with different molecular architectures were performed, and it was determined how ionizing radiation reacted depending on the chain structure of GECO polymers. Many scientific results that contribute to explaining the behavior of elastomers prepared using epichlorohydrin-based rubbers such as GECO against ionizing radiation, which are not available in the literature, were obtained.
