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The Use of Expanding Monomers in Embedding and Related Processes
Published in Rajender K. Sadhir, Russell M. Luck, Expanding Monomers, 2020
Silicone resins are not generally classified as organic resins, although they do have carbon-based side chains. Silicones are resistant to oxidation, have excellent electrical resistance and retain their mechanical properties over a wide temperature range. Also of importance is the fact that they exhibit fairly low shrinkage (∼2%) upon curing. The disadvantages encountered with silicone resins are their poor adhesion and their high cost. Room temperature vulcanizing (curing), RTV silicones, and flexible silicones are the most widely used types. They are usually cured by free radicals (generated by peroxides). Silicone resins are used primarily for the construction of flexible molds and for the embedment of electronics components and assemblies. The shrinkage of silicone resins could be reduced by the addition of expanding monomers that are amenable to free radical cure. The problem is that all known expanding monomers have significantly worse thermal properties than the silicones, and so their use would cause a degradation of the mixed resin’s thermal properties.
Thermoset Polymer Matrix–Based Natural Fiber Composites
Published in Shishir Sinha, G. L. Devnani, Natural Fiber Composites, 2022
Silicone resins are silicon material that has good thermal resistance up to 350°C. Silicones are prepared by the Muller-Rochow method using methyl chlorosilanes at a temperature range of 250°C–300°C and 2 to 5 bar of pressure. To improve the activity, the copper catalyst can be used along with metals such as zinc, cadmium, antimony, tin, and aluminium. The homogeneous mixture of copper and silicon is entered into a fluidized bed reactor, which is fluidized using gaseous methyl chloride. In the separation unit, reactants are set apart from solid, and primitive liquid silane is formed on cooling. The heat is released during the reaction; thus, it is an exothermic reaction that needs accurate control. The main product formed is dimethyl dichlorosilane, along with some more products at different yields are methyl dichlorosilane, methyl trichlorosilane, and trimethylchlorosilane (Fink, 2013). They contain oxygen, silicon, and organic groups. They possess a branch of alternating silicon and oxygen atoms in a three-dimensional network that can be dissolved in an organic solvent. Silicone resins are characterized by the properties like great resistance to tearing, hydrophobicity, and hardness (Z. Liu et al., 2020). They are used in pressure-sensitive adhesives and as water repellent due to their hydrophobicity nature. Silicones are non-toxic in nature; hence, they are used in the medical sector and pharmaceutical industry. They have good resistance to corrosion and heat resistance and thus are used for surface coatings. They can also be used as adhesives due to their excellent flip and high thermal resistance. They exhibit low surface tension, which makes them anti-foaming agents and also an essential constituent in the polymerization of PVC.
Industrial Polymers
Published in Manas Chanda, Plastics Technology Handbook, 2017
Silicone resins are manufactured batchwise by hydrolysis of a blend of chlorosilanes. For the final product to be cross-linked, a certain amount of trichlorosilane must be incorporated into the blend. (In commercial practice, R/Si ratios are typically in the range of 1.2:1–1.6:1) The cross-linking of the resin is, of course, not carried out until it is in situ in the finished product. The cross-linking takes place by heating the resin at elevated temperatures with a catalyst, several of which are described in the literature (e.g., triethanolamine and metal octoates).
Expansion inhibition of steel slag in asphalt mixture by a surface water isolation structure
Published in Road Materials and Pavement Design, 2020
Lili Ma, Dingbin Xu, Shengyue Wang, Xingyu Gu
Technical indicators of the silicone waterproof agent were displayed as follows: solid content ≥50%, drying time ≤1 h/25°C, setting time: 1.5 h/200°C. The original agent had great consistency and had difficulty in dispersing on steel slag surface. Methylbenzene (original agent: methylbenzene = 1:1) was used to dilute silicon acrylate resin. Then 4% additives composing of penetrant and defoaming agents were added to finally get the silicone waterproof agent. The silicone acrylate resin, the main ingredient in the agent, was silicone resin modified by acrylate. It combined the toughness, cohesiveness and strength of acrylate polymer and the heat resistance, hydrophobicity and sealing of silicone resin. After cured at high temperature, the resin developed highly cross-linked structure to form a dense coating.
Latest trends for structural steel protection by using intumescent fire protective coatings: a review
Published in Surface Engineering, 2020
Muhammad Yasir, Faiz Ahmad, Puteri Sri Melor Megat Yusoff, Sami Ullah, Maude Jimenez
Silicone resins (silica, silicone, silicalite) are used in ICs because of their high thermal stability, weathering resistance, hydrophobicity, low surface tension and high oxidation resistance. The credit of thermal stability goes to the Si-O-Si bond in the structure [97–99]. Moreover, the soluble alkali silicates are also famous for their fire retardancy [100]. Ying et al. [101] studied the self-cross linking of polyacrylate emulsion and silicone emulsion in waterborne ICs. The effects of silicone emulsion on the thermal properties and char formation were analysed by TGA and SEM with energy-dispersive X-ray (SEM-EDX), and through fire tests. The results showed a high fire resistance of the coating, with residual mass percentage of the char increased at elevated temperatures [102,103]. Moreover, an appropriate amount of silicone emulsion improved the rheological property of the combined self-cross linking polyacrylate emulsion (SCPA) and silicone, leading to the improved thermal performance of the coatings as shown in Figure 7. The ratio of the loss modulus to the storage modulus was tan δ, which represented the materials deformation capacity. When the silicone emulsion content increased, the oxygen content in the char decreased, enhancing the oxidative stability of the coating.