Methyl Vinyl Silicone Rubber
One of the main areas of application of silane coupling agents is the treatment of inorganic fillers used in organic polymers. The latter can be treated with silane coupling agent to transform its hydrophilic surface into a pro-organic surface, which can avoid particle agglomeration and rapid thickening of the polymer in the system, and also improve the wettability of the organic polymer to the reinforcing filler, which can be firmly bonded to the polymer by carbon functional silane. However, the effect of silane coupling agent is also related to the type and amount of silane coupling agent, the characteristics of the substrate, the nature of the resin or polymer, and the occasion, method and conditions of application. There are two methods of using silane coupling agents: surface treatment method and integral blending method.
This method is through the silane coupling agent will be inorganic and polymer two interfaces linked together, in order to obtain the best wetting value and dispersion. Surface treatment method needs to acid silane coupling agent into dilute solution, in order to facilitate full contact with the treated surface. The solvent used is mostly water, alcohol or water-alcohol mixture, and water without fluorine ions and cheap non-toxic ethanol, isopropanol is preferred. Except for ammoniacal silane, the solutions prepared by other silanes need to add acetic acid as hydrolysis catalyst and adjust the pH to 3.5-5.5. Long-chain alkyl and phenylsilane are not suitable for aqueous solutions because of their poor stability. Chlorosilane and acetoxysilane will be accompanied by serious condensation reaction during hydrolysis, so they are not suitable for aqueous solution or hydroalcoholic solution. For silane coupling agent with poor water solubility, 0.1%-0.2% (mass fraction) of non-ionic surfactant can be added first, and then water can be added to make water emulsion. In order to improve the economic efficiency of the hydrolytic stability of the product, the silane coupling agent can be mixed with a certain proportion of non-carbon functional silane. When dealing with difficult-to-adhere materials, mixed silane coupling agent or with the use of carbon-functional siloxane can be used. After preparing the treatment solution, it can be treated by dipping, spraying or brushing. Generally speaking, block materials, granular materials and glass fibers are treated by impregnation method; powder materials are treated by spray method; and the substrate surface needs to be coated as a whole, it is treated by brush coating method.
The overall blending method is to mix the silane coupling agent liquid into the resin or polymer before the filler is added. Therefore, the resin or polymer is required not to react with the silane coupling agent prematurely, so as not to reduce its viscosity-enhancing effect. In addition, before the material is cured, the silane coupling agent must migrate from the polymer to the filler surface and subsequently complete the hydrolytic condensation reaction. For this reason, metal carboxylate can be added as a catalyst to accelerate the hydrolytic condensation reaction. This method is particularly convenient and effective for fillers that are suitable for surface treatment with silane coupling agents, or for systems where the resin and filler need to be mixed and stirred prior to molding, and can overcome some of the disadvantages of the filler surface treatment method. Some people have used various resins to compare the advantages and disadvantages of blending and surface treatment methods. It is believed that: in most cases, the blending method is less effective than the surface treatment method. The process of blending is that the silane coupling agent migrates from the resin to the fiber or filler surface and acts on the filler surface. Therefore, the silane coupling into the resin, must be left for a period of time to complete the migration process, and then curing, in order to obtain better results. It is also theoretically speculated that the migration of silane coupling agent molecules to the filler surface is only equivalent to the amount of the filler surface to generate a single molecular layer, so the amount of silane coupling agent is only 0.5%-1.0% of the resin mass. It should also be noted that in the composite formulation, when using additives with good compatibility with the filler surface and low molar mass, special attention should be paid to the feeding sequence, i.e., adding the silane coupling agent first, and then adding the additives to obtain better results.
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