Chemical degradation of fluoroelastomer in an alkaline environment

• Published in: Polymer degradation and stability Vol. 83; no. 2; pp. 195 - 206
• Main Authors: Mitra, Susanta, Ghanbari-Siahkali, Afshin, Kingshott, Peter, Almdal, Kristoffer, Kem Rehmeier, Helle, Christensen, Anders G
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-02-2004; Elsevier Science
• Subjects: Ageing; Applied sciences; Chemical degradation; Exact sciences and technology; FKM (Viton A); Fluoroelastomer; Mechanical properties; Physical properties; Polymer industry, paints, wood; Properties and testing; Technology of polymers; XPS and ATR-FTIR; Mechanical properties; XPS and ATR-FTIR; Chemical degradation; FKM (Viton A); Fluoroelastomer; Experimental study; Quantitative surface analysis; Hexafluoropropylene copolymer; Vinylidene fluoride copolymer; Reaction mechanism; Artificial ageing; Basic medium; Kinetics
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/S0141-3910(03)00235-0

We have investigated the time-dependent chemical degradation of a fluoroelastomer, FKM (Viton® A), in an alkaline environment (10% NaOH, 80 °C). Optical microscopy and SEM analysis reveal that degradation starts with surface roughness right from the earliest stage of exposure (e.g., 1 week) and finally results in cracks on the surface after prolonged exposure. Initially the extent of degradation is mainly confined to the surface regions (a few nanometers) but with longer exposure (e.g., 12 weeks) it extends to below the subsurface region of the fluoroelastomer. The extent of this surface degradation is found to be strong enough to affect the bulk mechanical properties. The molecular mechanisms of the surface chemical degradation were determined using surface analysis (XPS and ATR-FTIR) where the initial degradation was found to proceed via dehydrofluorination. This leads to double bond formation on the rubber backbone which accelerates the degradation even further with longer exposure. Furthermore, the cross-link sites of the exposed rubber samples are also found to be vulnerable to hydrolytic attack under the studied chemical environment as evidenced by the decrease in cross-link density and gel fraction (%).