What are the vulcanization systems of silicone rubber

The easiest way to vulcanize silicone rubber at low temperature is to use silica with OH group on the surface. Such fillers are treated with chloro-containing heptamethylcyclotetrasiloxane in the presence of protophobic solvents. Polydimethylsiloxane-α filled with fumed silica in the presence of dibutyltin laurate and ω-diol can also be vulcanized at room temperature. Some kinds of polysiloxanes can be vulcanized in the presence of silica treated with silicon-terminated hydroxyl oligomers.
Silicon-oxygen bond can be formed by self-vulcanization of silicon-terminated alkoxy saturated elastomers when sulfur-containing antioxidants are used. Vulcanized rubber has good heat resistance.
The general principles of cold vulcanization of silicone rubber unrelated to filler modification are described in the research paper:
The conjugations are generated in a "one component" system consisting of raw rubber with OH end group and RSiX3 type crosslinker. (Where X is a hydroxyl group, imine group, silazyl group, or oxamide group). These groups are hydrolyzed under the action of water in the air to form OH groups, and then Si-O-Si bonds are formed by polycondensation without a catalyst.
In the presence of catalysts (derivatives of Pt, Sn, Ti), a "two-component" system consisting of two types of silicone rubber containing active groups that can interact is formed.
In the presence of fillers and in the absence of catalysts, the end groups of two or more silicone rubbers may interact.
In fact, the second and third cases are self-vulcanizing rubber materials with the same properties, but containing different active groups.
Currently, a large number of patents describe different aspects of these processes. But most of them differ only in detail. For example, a rubber that can be printed 12×104 times and used for laser printers (strength of 5MPa) is methyl-silicone rubber or diphenyl silicone rubber without catalyst, and even other silicone rubber. The system composed of two kinds of dimethylsilicone rubber containing hydroxyl and trimethylsilicon, heptamethylvinyl silicone rubber and carbon black can also be vulcanized. In addition, the vulcanization reaction can also be carried out in the mixed compound of silicone rubber containing hydroxy-terminated and polysiloxane with ON=CR2 crosslinking agent. Hydroxy-terminated dimethylsilicone rubber can be vulcanized by the second, third and fourth functional derivatives of silane when anhydrous.
Silicone rubber containing silanol end groups can be vulcanized with vinyl (trihydroxyl) silane in the presence of inorganic fillers. Silicone rubber containing trimethylsilanol end groups can be vulcanized with vinyl trimethoxysiloxane in the presence of a catalyst. The vulcanization condition was 20℃×7d. The obtained vulcanized adhesive strength was 5.6MPa. It is used in the production of coatings and adhesives, as well as in the electronics, medical and food industries.
The compound consisting of polysiloxanes containing olefin end groups, polysiloxanes containing SiH group, catalysts and siloxane adhesives can also be vulcanized. Its vulcanizates have excellent adhesion to thermoplastics and resins. In the presence of Pt catalyst and NH3, a mixture of polysiloxane containing olefin can also be vulcanized. Vulcanizates have very low compressive permanent deformation.
Heterocyclic silanes, such as bis (trialkyl-hydroxy-silalkyl-alenyl oxidation) pyridine, are viscosifiers for metal and plastic bonding. In the presence of Pt catalyst and filler, they can be used in the mixture of vulcanized vinylsiloxane and polyhydroxysiloxane. The duration of the vulcanization reaction was 7 days. The shear strength of bonding with aluminum is 3.8MPa.
Rubber co-vulcanization containing a variety of reactive functional groups of rubber (different properties) in the harmless special vulcanization agent can be co-vulcanized, which is not only feasible for low temperature vulcanization of silicone rubber, but also suitable for high temperature vulcanization of other rubber. For example, chlorinated natural rubber and hydroxyl nitrile butadiene rubber can be co-vulcanized to produce oil-resistant and wear-resistant rubber. Chlorinated butyl rubber and hydroxy-nitrile butadiene rubber can be co-vulcanized at 180℃ without vulcanizing agent. Hydroxy-nitrile butadiene rubber and chlorosulfonated polyethylene rubber, including carbon black-filled rubber compound can also be co-vulcanized. The combination of polyvinyl chloride and hydrogenated nitrile rubber can be co-vulcanized at 180-200℃ to generate amine and ether cross-linking bonds. The epoxy natural rubber and chlorosulfonated polyethylene filled with carbon black can be co-vulcanized when there is no vulcanizing agent. Vulcanized rubber has very high strength and tear strength, and good wear resistance. In the absence of crosslinking agents, epoxy natural rubber can be co-vulcanized with neoprene rubber and carboxyl nitrile butadiene rubber. Polyvinyl chloride and carboxyl nitrile butadiene rubber are co-vulcanized at 180℃, and the vulcanized rubber has high oil resistance and wear resistance.
Therefore, the selection of paired rubber with active functional groups for co-vulcanization without special crosslinking agents is one of the main directions to solve the ecological problems caused by vulcanization and improve the properties of vulcanized rubber in the past ten years.