Silicone rubber is an elastomer (rubber-like material) composed of silicone resin (itself a polymer), which contains silicon as well as carbon, hydrogen and oxygen. Silicone rubber is widely used in industry and comes in a variety of formulations. Silicone rubber is usually one or two polymers and may contain fillers to improve properties or reduce cost. Silicone rubber is generally non-reactive, stable, and can withstand extreme environments and temperatures from -55 to 300 °C (-70 to 570 °F) while still maintaining its useful properties. Because of these properties and its ease of manufacture and molding, silicone rubber is used in a wide variety of products, including voltage line insulators; automotive applications; cooking, baking and food storage products; apparel, such as undergarments, athletic apparel and footwear; electronics; medical devices and implants; and products such as silicone sealants in home repair and hardware.

Curing

In its uncured state, silicone rubber is a highly adhesive gel or liquid. To convert it to a solid, it must be cured, vulcanized or catalyzed. This is usually done in a two-stage process when fabricated into the desired shape, followed by a long post-curing process. It can also be injection molded or 3D printed.

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 heat or pressure.

Platinum-based curing systems

In platinum-based silicone curing systems, also known as addition systems (because the key reaction building the polymer is an addition reaction), hydrides and vinyl-functional siloxane polymers react in the presence of a platinum complex catalyst to produce There is an ethyl bridge between the two. [1] The reaction has no by-products. This silicone rubber cures quickly, but in the presence of elemental tin, sulfur, and many amine compounds, the rate and even the ability to cure is easily inhibited. [2]

Condensation curing systems

Condensation curing systems can be either one-piece or two-piece systems. [3] In one-piece or RTV (Room Temperature Vulcanization) systems, the crosslinker exposed to ambient humidity (i.e., water) undergoes a hydrolysis step and leaves behind hydroxyl or silanol groups. The silanol is further condensed with another hydrolyzable group on the polymer or crosslinker and continues to condense until the system is fully cured. Such systems will self-cure at room temperature and (unlike platinum-based addition-curing systems) are less likely to be inhibited by contact with other chemicals, although the process may be affected by contact with some plastics or metals and may not occur at all if contact is made with the cured silicone compound. Crosslinking agents used in condensation curing systems are typically alkoxy, acetoxy, ester, allyloxy or oxime silanes, such as methyltrimethoxysilane for alkoxy curing systems and methyltriacetoxysilane for acetoxy curing systems. In many cases, additional condensation catalysts are added to fully cure the RTV system and obtain a non-stick surface. Organotitanate catalysts such as tetraalkoxytitanate or chelated titanate are used in alkoxy cured systems. Tin catalysts such as dibutyltin dilaurate (DBTDL) are used in oxime and acetoxy cured systems. Acetoxy tin condensates are one of the oldest curing chemicals used to cure silicone rubber and are used in home bathroom caulking. Depending on the type of molecule isolated, silicone systems can be categorized as acidic, neutral or alkaline.