Poli (Epiklorohidrin-Ko-Etilen Oksit-Ko-Allil Glisidil Eter) Elastomerlerinin Isıl Yaşlanma Özelliklerine Antioksidanların Etkisi
Özet
Elastomers are quite sensitive to temperature changes, which can lead to degradation in the chemical and physical properties of the material. Due to their saturated molecular structures, epichlorohydrin elastomers exhibit excellent ozone and oxidation resistance. The Poly (epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (P(ECH-co-EO-co-AGE)) terpolymer, abbreviated as GECO, possesses excellent low-temperature and incredibly good fuel, ozone, and weather resistance, along with better resistance to degradation. Thermal aging can lead to various adverse effects on elastomers, such as reduced material flexibility, weakening of mechanical properties, or increased brittleness due to oxidative degradation. Additionally, temperature fluctuations can influence the chemical structure of elastomers, thus reducing their durability and lifespan.
To enhance the temperature resistance or mitigate thermal aging processes in elastomers, antioxidant chemicals, commonly referred to as thermal stabilizers/anti-aging agents, are added to their formulations. Antioxidants are widely used during the production of rubber-based materials to improve performance, delay aging, and extend service life. By preventing or slowing down the oxidative degradation of elastomers, antioxidants delay or prevent thermal aging processes, thereby extending the material's lifespan and maintaining its performance. However, the optimal dosage and type of antioxidants can vary depending on the properties of the elastomer, application requirements, and processing conditions, which is a significant factor determining the thermal stability and performance of elastomers.
This thesis study evaluates the effects of 2,2,4-Trimethyl-1,2-Dihydroquinoline (6PPD) and N-(1,3-Dimethylbutyl)-N'phenyl-P-P-Phenylenediamine (TDQ) antioxidants on the thermal aging characteristics of P(ECH-co-EO-co-AGE) based elastomers in two stages: before and after thermo-oxidative aging. The influence of two different types of antioxidants widely used in the rubber industry on the rheological, physical, and mechanical properties of P(ECH-co-EO-co-AGE) polymer is compared. Changes in the material structure during aging are evaluated using structural analysis techniques, correlated with antioxidant types and ratios, and elucidated aging mechanisms. Tests indicate that the use of 2 phr TDQ may be the most effective option for increasing the mechanical durability of elastomers against thermal aging. Significant increases in tensile strength and elongation at break are observed, particularly with 1 phr antioxidant usage of 6PPD, suggesting it is an effective option for enhancing the long-term thermal aging resistance of elastomers. The use of antioxidants provided clear protection in terms of cross-link density compared to the reference sample. As oxidative degradation occurs during thermal aging, breakdowns in cross-linked chains and polymer backbone occur. Antioxidant addition minimizes oxidative degradation during thermo-oxidative breakdown, thereby enhancing the thermal stability of the elastomers used. The impact of antioxidant type and ratio on the lifetime/service life of P(ECH-co-EO-co-AGE) elastomers is examined by estimating the lifetime based on mechanical test results. For instance, with 1 phr 6PPD usage, the time required for a 20% decrease in mechanical properties at 25°C is calculated to be 25.6 years (compared to 1.9 years for the reference sample). For a 40% decrease, it is calculated to be 18.8 years (compared to 2.6 years for the reference sample). Elastomer samples containing 3 phr TDQ require 182 years for a 20% decrease in properties at 25°C, indicating an improvement in the time required for a 40% decrease in mechanical properties at room temperature in the presence of antioxidants. Both 6PPD and TDQ antioxidants significantly increase the thermal stability and lifetime of P(ECH-co-EO-co-AGE) elastomers, potentially making them suitable for long-term use over 100 years (at room temperature: 25 ℃).
To determine the service lifetimes of elastomers at higher temperatures (e.g., for military applications), lifetime calculations have been made for a temperature of 70 ℃. It has been shown that the lifetimes of P(ECH-co-EO-co-AGE) elastomers, with the addition of 6PPD and TDQ, are significantly lower at 70 ℃ compared to room temperature. However, it has also been demonstrated that the lifetimes can be increased with the addition of antioxidants compared to the reference sample. It has been found that a P(ECH-co-EO-co-AGE) elastomer without antioxidants may lose approximately 20% of its mechanical properties after approximately 22 days at 70 ℃, and approximately 40% after 45 days. On the other hand, the use of TDQ at a ratio of 3 phr extends the time until the elastomer experiences a 40% loss in mechanical properties to 546 days, resulting in a 12-fold increase in lifetime. This study has shown that the addition of thermal stabilizers (antioxidants) to elastomer formulations is inevitable in terms of the service life of the elastomer.
This study demonstrates that the addition of thermal stabilizer (antioxidant) auxiliary chemicals to elastomer formulations is inevitable, considering the elastomer's lifetime.
