Complexities associated with moisture in foamed polysiloxane composites

Patel, Mogon; Morrell, Paul; Cunningham, Jenny L.; Khan, Niaz Ali; Maxwell, Robert S.; Chinn, Sarah C.

doi:10.1016/j.polymdegradstab.2007.10.026

Cited by 37 publications

(38 citation statements)

References 13 publications

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“…The large peak at 0.0 ppm is associated with 17 O signal from free water, whereas the peak at 71.2 ppm is due to eSie 17 OeSie groups, confirming the proposed chemical reaction described in Fig. 11 [29,30]. It is interesting to note that the non-post-cured sample also shows a peak at 43.9 ppm, which we assume to be associated with eSie 17 OH groups.…”

Section: Catalytic Activity Of Tin Residuessupporting

confidence: 75%

Aging mechanisms in RTV polysiloxane foams

Labouriau

Robison

Meincke

et al. 2015

Polymer Degradation and Stability

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a b s t r a c tThe 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 inservice 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 postcuring 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.

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Section: Catalytic Activity Of Tin Residuessupporting

confidence: 75%

Aging mechanisms in RTV polysiloxane foams

Labouriau

Robison

Meincke

et al. 2015

Polymer Degradation and Stability

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“…Moisture increased the rates of stress relaxation on condensation-cured S5370 foamed siloxanes, while dry environments generally cause reduced stress relaxation rates. 15 Several studies on polymer diffusion have also shown that the diffusion process in FRP composites changes with the temperatures. It is reported that the rate of moisture diffusion in FRP increased with increasing temperatures.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of water in glass fiber reinforced polymer composites at different temperatures

Fan

Gomez

Ferraro

et al. 2018

Journal of Composite Materials

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This study examines the effects of temperature and fiber and matrix diffusivities on the diffusion of fluid in glass fiberreinforced polymer composites. Glass fiber-reinforced polymer thin plates were immersed in deionized water at two temperatures: room temperature and 50 C. During the diffusion process, the overall mass changes and dimension changes were recorded, which relate to the volumetric change and the through-the-thickness strain. Different constitutive models are considered in order to understand the diffusion of fluid through the glass fiber-reinforced polymer plates. The macroscopic models of this work, Fickian and Gurtin coupled deformation-diffusion, are first considered in order to describe the macroscopic diffusion behaviors. Two microscopic models that include fiber volume contents and diffusivities of the constituents (fiber and matrix) are then considered in order to gain fundamental insight into the effects of microstructural morphologies and constituents' diffusivities on the diffusion process in the glass fiber-reinforced polymer specimens.

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“…36 Condensed phase configurations were generated by isotropically straining the cell to cubic dimensions with side lengths 1.57, 1.42, 1.32, and 1.24 nm, which yield systems with densities 0.6, 0.8, 1.0, and 1.2 g cm −3 . The lowest condensed phase density nominally corresponds to the bulk density of a typical cellular foam 8,11 and the highest density is similar to pure PDPS crystal. 36 ELD configurations correspond to local packing environments of particularly low density, such as near pores in a silicone foam, whereas the condensed phase configurations correspond to local regions of material that are at or near bulk density.…”

Section: Model Pdps:pdms Systemmentioning

confidence: 99%

Chemical Degradation Pathways in Siloxane Polymers Following Phenyl Excitations

Kroonblawd¹,

Goldman²,

Lewicki³

2018

Preprint

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We use ensembles of quantum-based molecular dynamics simulations to predict the chemical reactions that follow radiation-induced excitations of phenyl groups in a model copolymer of polydimethylsiloxane and polydiphenylsiloxane. Our simulations span a wide range of highly porous and condensed phase densities, and include both wet and dry conditions. We observe that in the absence of water, excited phenyl groups tend to abstract hydrogen from other methyl or phenyl side groups to produce benzene, with the under-hydrogenated group initiating subsequent intrachain cyclization reactions.These systems also yield minor products of diphenyl moieties formed by the complete abstraction of both phenyl groups from a single polydiphenylsiloxane subunit. In contrast, we find that the presence of water promotes the formation of free benzene and silanol side groups, reduces the likelyhood for intrachain cyclization reactions, and completely suppresses the formation of diphenyl species. In addition, we predict that water plays a critical role in chain scission reactions, which indicates a possible synergistic effect between environmental moisture and radiation that could promote alterations of a larger polymer network. These results could have impact in interpreting accelerated aging experiments, where polymer decomposition reactions and network rearrangements are thought to have a significant effect on the ensuing mechanical properties. IntroductionPolysiloxane-based materials, or silicones, are widely used in a range of technological applications where favorable long term mechanical response, chemical inertness, and shape filling factor over a broad temperature range are required. Applications include space-filling rubber or foam gaskets and shock absorbers to biomedical implants, lubricants, and adhesives. 1,2Many applications of silicone rubber and foam components have specific requirements for mechanical properties such as elastic moduli (bulk, Young's, and shear), viscoelastic response, and hardness. The mechanical properties of silicones are often tuned by controlling L z = 3.0 nm to avoid complications from steric effects. Scans were performed by displacing the phenyl group along the the Si-C(phenyl) bond separation vector and then optimizing the configuration while holding the Si and C(phenyl) atoms fixed. Two separate scans were per-

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Complexities associated with moisture in foamed polysiloxane composites

Cited by 37 publications

References 13 publications

Aging mechanisms in RTV polysiloxane foams

Aging mechanisms in RTV polysiloxane foams

Diffusion of water in glass fiber reinforced polymer composites at different temperatures

Chemical Degradation Pathways in Siloxane Polymers Following Phenyl Excitations

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