| Abstract
| - Silicone polymers undergo clay-catalyzed hydrolyticdegradation in soil. This study investigated the effects ofmoisture levels and exchangeable cations on degradationof a poly(dimethylsiloxane) (PDMS) fluid on clay minerals.Kaolinite, talc, and Arizona montmorillonite saturatedwith Na+, Ca2+, or Al3+ were incubated with 14C-labeledPDMS (∼2000 μg g-1) at 32% and 100% RH. The hydrolyticproducts were extracted sequentially and analyzed withHPLC/GPC, GC/MS, and LSC. It was found that PDMShydrolyzed predominantly through random scission of itsSi−O−Si backbone, regardless of clay type, exchangeablecation, or humidity. The hydrolytic degradation had twostages; both were zero-order reactions. The degradationrates in the initial stage rose with an increase in thepolarizing power of the exchangeable cations (i.e., Al3+≫ Ca2+> Na+) and decreased humidity. Although highhumidity may result in the formation of some volatile cyclicmethylsiloxanes on an artificial catalyst, Al-saturatedmontmorillonite, the ultimate degradation product wasotherwise water-soluble dimethylsilanediol. The conclusionwas that exchangeable cation type, moisture level, andclay type can all influence the degradation rates and productsof silicone polymers.
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