Preparation of flexible, self‐extinguishing silicone foams

Abstract

Flexible, self-extinguishing silicone foams (SFs) with a relatively low density (0.25-0.45 g/cm 3 ) were obtained from a mixture of a,x-(dihydroxy)polydimethylsiloxanes, water, flame retardants (melamine and/or expanded graphite), and polyisocyanates [poly(diphenylmethane isocyanate)]. These compositions were crosslinked at room temperature with branched polymethylhydrosiloxanes with the structure (MeSiO 1.5 ) 3 (MeHSiO) 102 (Me 3 SiO 0.5 ) 5 in the presence of tin octoate as a catalyst. The SFs were modified by the addition of linear or graft carbofunctional polysiloxanes containing chydroxypropyl groups. Only the SFs prepared by means of a dehydrocondensation reaction had a good homogeneity of pores, whereas the foams formed with two kinds of blowing agents (hydrogen and carbon dioxide, generated in the reaction of water with isocyanate groups) had lower densities but a poor homogeneity of pores. Unmodified SFs showed a tensile strength of 20 kPa or less, whereas the foams formed with the addition of poly(diphenylmethane isocyanate) and water had a tensile strength of 23-25 kPa. The SFs with 15 and 30% contents of melamine or expanded graphite had tensile strengths in the ranges 38-45 and 51-54 kPa, respectively. All of the prepared SFs were combustible materials. The SFs without the addition of flame retardants had a limiting oxygen index of approximately 21%, whereas the SFs with a 30% content of fire retardant had self-extinguishing properties and a limited oxygen index of 41-43%.

Study of the Coalescence Mechanisms During Silicone Foaming

“…Foamed silicone production includes two parallel processes: crosslinking and foaming reactions. To our knowledge, two conventional methods of silicone elastomer and rubber crosslinking are used: high‐temperature vulcanization and room‐temperature vulcanization . The crosslinking of high‐temperature vulcanization silicone rubber systems occurs according to a radical reaction mechanism (temperature >100 °C).…”

“…When catalysts (mainly platinum or tin compounds) are added, polycondensation and polyaddition reactions occur between polydimethylsiloxane (PDMS) and crosslinking agents. Thus, new siloxane or carbosilane linkages form a polymer network in the crosslinking silicone material …”

Silane Coupling Agents

“…The cornerstone of these is the book by Plueddemann (1), which discusses most of the aspects of coupling agent application. A few symposium-based books have also been produced (2), as well as a few reviews (3)(4)(5). As Plueddemann pointed out, in many cases, with the use of the proper coupling agent under the proper conditions, the failure in composite materials no longer takes place at the interfaces between the dissimilar materials.…”

Effects of platinum compounds/superfine aluminum hydroxide/ultrafine calcium carbonate on the flame retardation and smoke suppression of silicone foams

“…2,3 As a high-performance material, SiFs are applied in the aerospace, national defense, medicine, transport, electrical, and construction industries. 7 Deng et al fabricated flame-retardant and smoke-suppressing SiFs with seven bilayers of chitosan/ammonium polyphosphate coatings; the LOI increased from 20.2 to 23.8%, the peak heat release rate (PHRR) decreased by 27.6%, and the total smoke production (TSP) decreased by 42%. In contrast to SR, SiFs exhibit greater airflow and an increased specific surface area, and they are more conducive to combustion, which has limited their potential applications.…”