Aging mechanisms in RTV polysiloxane foams

Abstract The long-term use of polysiloxane foams requires a good understanding of the diverse factors that may influence their performance. The aim of the present work was to understand the interplay between in-service environments and reactive species that reside in the foams. Two foams (SX358 and S5370) were thermally aged under compressive strain to gauge the onset of compression set, an indicator of degradation. Experiments were performed by either aging the foams in open air containers or in high humidity environments. Our results indicated that foams aged in open air environments exhibited less compression set than when aged in presence of moisture. These results were analyzed in terms of post-curing reactions, hydrolysis and rearrangement of the network, which are promoted by active residues that are left in the foam from the curing process. In particular, the residues from tin octoate, the catalyst used in the cure of the foams, were identified and their role in promoting aging was determined. Reactions were either catalyzed by tin(II) species or by a combination of trace amounts of water and octanoic acid, a product of the hydrolysis of tin octoate. More precisely, this work demonstrated that reactive residues promote chemical changes in the polymer, which resulted in compression set. On the other hand, the oxidized residues of the tin octoate show no catalytic activity towards promoting condensation reactions between silanol groups. Our work established that, depending on service conditions, certain residues are more harmful to the foam's lifetime than others.