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http://dx.doi.org/10.7473/EC.2018.53.4.213

Study on the Thermal Degradation Behavior of FKM O-rings  

Lee, Jin Hyok (Department of Polymer Engineering, Pusan National University)
Bae, Jong Woo (Rubber Research Team, Korea Institute of Footwear & Leather Technology)
Choi, Myoung Chan (Rubber Research Team, Korea Institute of Footwear & Leather Technology)
Yoon, Yoo-Mi (Rubber Research Team, Korea Institute of Footwear & Leather Technology)
Park, Sung Han (Agency for Defense Development)
Jo, Nam-Ju (Department of Polymer Engineering, Pusan National University)
Publication Information
Elastomers and Composites / v.53, no.4, 2018 , pp. 213-219 More about this Journal
Abstract
The degradation mechanism and physical properties of an FKM O-ring were observed with thermal aging in this experiment. From X-ray photoelectron spectroscopy (XPS) analysis, we could observe carbon (285 eV), fluoro (688 eV), and oxygen (531 eV) peaks. Before thermal aging, the concentration of fluoro atoms was 51.23%, which decreased to 8.29% after thermal aging. The concentration of oxygen atoms increased from 3.16% to 20.39%. Under thermal aging, the FKM O-ring exhibited debonding of the fluoro-bond by oxidation. Analysis of the C1s, O1s, and F1s peaks revealed that the degradation reaction usually occurred at the C-F, C-F2, and C-F3 bonds, and generated a carboxyl group (-COOH) by oxidation. Due to the debonding reaction and decreasing mobility, the glass transition temperature of the FKM O-ring increased from $-15.91^{\circ}C$ to $-13.79^{\circ}C$. From the intermittent CSR test, the initial sealing force was 2,149.6 N, which decreased to 1,156.2 N after thermal aging. Thus, under thermal aging, the sealing force decreased to 46.2%, compared with its initial state. This phenomenon was caused by the debonding reaction and decreasing mobility of the FKM O-ring. The S-S curve exhibited a 50% increase in modulus, with break at a low strain and stress state. This was also attributed to the decreasing mobility due to thermal aging degradation.
Keywords
FKM O-ring; X-ray photoelectron spectroscopy; intermittent CSR method; sealing force; S-S curve; degradation;
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