Silicone rubber is an elastomer (rubber-like material) made of silicone – itself a polymer – that contains silicon together with carbon, hydrogen and oxygen. Silicone rubbers are widely used in the industry and there are several formulations. Silicone rubbers are often one- or two-part polymers and can contain fillers to improve properties or reduce costs. It is generally non-reactive, stable, and resistant to extreme environments and temperatures from -55 to 300 ° C (-67 to 572 ° F) while maintaining its useful properties. Because of these properties and its ease of manufacture and shaping, silicone rubber can be found in a variety of products including: power line insulators, automotive applications; Cooking, baking and food storage products; Clothing such as underwear, sportswear and shoes; Electronics; medical devices and implants; and for home repairs and hardware with products such as silicone sealants.
Post curing process. It can also be injection molded.
Silicone rubber can be cured by platinum-catalyzed curing systems, condensation curing systems, peroxide curing systems or oxime curing systems. For platinum-catalyzed curing systems, the curing process can be accelerated by increasing heat or pressure.
Platinum-based curing system
In a platinum-based silicone curing system (also known as an addition system) (because the key reaction-building polymer is an addition reaction), the hydride and vinyl-functionalized siloxane polymer is in the platinum complex catalyst In the presence of the reaction, an ethyl bridge between the two is formed. [1] The reaction has no by-products. Although in the presence of elemental tin, sulfur and many amine compounds, the vulcanization speed or ability of vulcanized silicone rubber is even easily suppressed, but this vulcanized silicone rubber can be vulcanized quickly. [2]
Condensation and solidification system
The condensation solidification system can be one or two systems. [3] In a one-piece or RTV (room temperature vulcanization) system, the cross-linking agent exposed to ambient humidity (ie water) undergoes a hydrolysis step and carries hydroxyl or silanol groups. The silanol is further condensed with another hydrolyzable group on the polymer or crosslinker until the system is fully cured. Such a system will cure itself at room temperature, and (unlike platinum-based addition curing systems) is not easily exposed to other chemicals and is inhibited, although the process may be affected by contact with certain plastics or metals, and may not It may happen that if it comes into contact with the already cured organosilicon compound, nothing happens at all. The crosslinking agents used in condensation curing systems are usually alkoxy, acetoxy, ester, alkenyloxy or oxime silanes, such as methyltrimethoxysilane for alkoxy curing systems and for acetoxy Methyltriacetoxysilane curing system. In many cases, the addition of additional condensation catalysts can completely cure the RTV system and obtain a non-stick surface. Organic titanate catalysts such as tetraalkoxy titanate or chelate titanate are used in alkoxy curing systems. Tin catalysts such as dibutyltin dilaurate (DBTDL) can be used in oxime and acetoxy curing systems. Acetoxytin condensation is one of the oldest curing chemical methods used to cure silicone rubber, and is one of the caulking agents used in home bathrooms. Depending on the type of separated molecule, the silicone system can be classified as acidic, neutral or alkaline. [4]
Overview of the most commonly used silicone systems
The two-part condensation system packs the crosslinker and condensation catalyst together, while the polymer and any fillers or pigments are in the second part. The mixing of the two parts leads to curing.
Once fully cured, the condensation system can be effectively used as a sealant and caulk in pipes and building structures, as well as for casting polyurethane, epoxy and polyester resins, waxes, gypsum and low-melting metals such as lead Mould. They are usually very soft and have high tear strength. They do not require the use of mold release agents because silicones have non-stick properties.
Peroxide curing system
Peroxide vulcanization is widely used to vulcanize silicone rubber. The curing process can leave by-products, which can be a problem in food contact and medical applications. However, these products are usually processed in a post-curing furnace, which greatly reduces the content of peroxide decomposition products. One of the two main organic peroxides used is dicumyl peroxide (compared to cumene hydroperoxide), and its main decomposition products are acetophenone and phenyl-2-propanol. The other is dichlorobenzoyl peroxide, whose main decomposition products are dichlorobenzoic acid and dichlorobenzene. [5]
Crosslinking of organic peroxides
history
In order to find better insulation materials for motors and generators, the first batch of silicone elastomers was developed. Resin impregnated glass fiber was the most advanced material at the time. Glass has high heat resistance, but phenolic resins cannot withstand the higher temperatures encountered by new smaller motors. Chemists at Corning Glass and General Electric are studying heat-resistant materials used as resin binders. They synthesized the first batch of silicone polymers, proved that they worked well, and found a way to commercialize them.
The term “silicone” is actually a misnomer. Chemists use the suffix -1 to indicate substances with double bond oxygen atoms in the main chain. When it was first discovered, it was mistakenly believed that silicones bonded oxygen atoms in this way. The technically correct term for various silicone rubbers is polysiloxane or polydimethylsiloxane. [2]
A joint venture between Corning Glass and Dow Chemical established Dow Corning in 1943 to produce this new material. With more detailed research on the unique properties of new silicone products, people foresee their potential for wide application, GE opened its own factory to