Hydrolysis of polydimethylsiloxane fluids in controlled aqueous solutions
Résumé
Accelerated degradation tests were performed on polydimethylsiloxane (PDMS) fluids in aqueous
solutions and in extreme chemical conditions (pH 2–4 and 9–12). Results confirmed that silicones can
be degraded by hydrolysis. Higher degradation levels were achieved in very acidic and alkaline conditions. Degradation products are probably polar siloxanols. In alkaline conditions, the counterion was found to have a strong influence on degradation level. Degradation kinetic studies (46 days) were also performed at different pH values. Supposing zeroth-order kinetics, degradation rate constants at 24 WC were estimated to 0.28 mgSi L-1 day-1 in NaOH solution (pH 12), 0.07 mgSi L-1 day-1 in HCl solution (pH 2) and 0.002 mgSi L-1 day-1 in demineralised water (pH 6). From these
results, the following hypothesis was drawn: PDMS hydrolysis could occur in wastewater treatment plants and in landfill cells. It may be a first step in the formation of volatile organic silicon compounds (VOSiCs, including siloxanes) in biogas: coupled to biodegradation and (self-) condensation of degradation products, it could finally lead to VOSiCs.