Silicone Elastomers

Silicone elastomers are usually composed of several key chemical elements (silicon, oxygen, carbon, hydrogen) and have long-chain polymers that maintain initial resilience over a wide range of operating temperatures. The skeleton raw material it uses is the most common polysiloxane (dimethyl/methyl vinyl), a reinforcing agent, and a curing agent, which are cross-linked into a network structure by mixing. Also known commercially as "silicone rubber," it more clearly and intuitively describes this rubber-like silicone material. To date, the terms silicone elastomers and silicone rubber have been used directly for each other. The elastomer material has versatility and reliability and is preferred by engineers to design key components in medical, civil, and automotive applications.

Components and structures of Silicone Elastomers

Silicone elastomers are usually made by mixing linear polysiloxane, reinforcing fillers, crosslinking agents, and other components. The strength of silicone rubber after the combination is low, so it is necessary to introduce fumed silica with a high specific surface area to increase the strength (strength, hardness) of silicone rubber. This means providing it with more cross-linking bonds and points, making the silicone rubber more resistant to external forces. The overall mechanical properties of silicone rubber are related to the amount of filler and specific surface area. With the increase in the amount of silica, the tensile and tear strengths increase, reach a peak, and then decline. The elongation at the break of silicone rubber also increases with the specific surface area of fumed silica. Add an appropriate amount of fillers to increase the volume of silicone rubber, including inorganic oxides, quartz powder, metal oxide powder, and calcium carbonate, so as to reduce the overall cost of materials and improve its processing performance. Carbon black, titanium dioxide, and pigments (inorganic or organic) can be added to the final mixture of silicone rubber to meet the needs of specific application properties (conductivity, heat resistance, insulation, color).

What are the main forms of Silicone Elastomers?

Processing conditions, molecular weight, and structure determine the type of elastomer:

High Consistency Rubber or High Temperature Vulcanized - HCR

Liquid Silicone Rubbers - LSRs

Room Temperature Vulcanization（RTV-1 and RTV-2） silicone rubber - RTV

Advantages of Silicone Elastomers over other Elastomeric Materials

With so many elastomers to choose from, the benefits of silicone elastomers start with their Si-O bond structure. Its chemical structure and flexibility make it the best choice for the manufacture of seals, flexible molds, and other molding products suitable for industrial and high-cleanliness medical environments. Ordinary rubber bands are brittle in extremely cold temperatures, and the bands that lose their elasticity are easily broken when stretched. Whereas silicone rubber can provide resistance to extreme temperatures (-60°C) without compromising its flexibility. At the same time, this special synthetic elastomer also has the same ozone resistance, high-temperature resistance, and sunlight resistance performance as the main chain structure of quartz, sand, and glass. Unlike polymers containing carbon-carbon double bonds, its silicon-oxygen chains remain highly oxidized at all times, allowing them to easily penetrate ultraviolet rays and protect them from ozone.

The chemical versatility of silicone elastomers also comes from the fact that it is easy to achieve molecular structure modification and changeable formula composition through copolymerization, blending, and other technologies. The side groups of the silicone chain provide cross-linking positions with other chemical groups, and the changes of these substituents endow it with different properties, providing infinite possibilities for customers to develop products with differentiated performance. Using phenyl to replace some methyl groups can improve low-temperature flexibility and radiation performance. The addition of trifluoro propyl groups to the side chain makes the fluoroelastomer have excellent oil resistance. The addition of fewer vinyl groups obtains lower compression set properties.

A key advantage of silicone elastomers is their flame resistance in potentially problematic environments. Its flammable components have an extremely low carbon content, and when exposed to an open flame, its residue is an insulating white silica fume. The material's rapid self-extinguishing properties make silicone rubber especially suitable for building seals, components of kitchen cooking tools, and even automotive parts that are exposed to high temperatures and confined spaces for a long time.

In addition, it has the benefit of meeting applications that other elastomers cannot, such as healthcare. It has strong molecular bond energy and high chemical inertness, so It is suitable for all grades of medical devices, artificial organs, and components. The advantages of this safe, reliable, and high-purity medical-grade elastomer are as follows:

❐ Has excellent bio acceptability and meets USP Class VI biocompatibility standards.
❐ In contrast to other synthetic counterparts, it withstands an ultra-wide temperature range from (-60 °C to 250 °C) and consistently maintains its excellent stress-strain performance.
❐ It is not on the same level as other organic elastomers, and the compression set is better.
❐ With enhanced durability, room-temperature environments can be expected to last for decades.
❐ It has high controllable degradability, and it will not affect the function of tissues or cells even if it comes into contact with blood or tissues of living organisms.
❐ Shows better gas permeability, inhibits bacterial growth, and eliminates skin bacterial allergies.
❐ Resistant to different sterilization methods (irradiation, ethylene oxide).

Inadequacies of Silicone Elastomers

High-performance silicone rubber is the first material in both industrial and medical industries, but it also has some defects as follows:

❐ High overall cost: Silicone rubber is a durable, reliable, high-quality material. But compared with similar products (latex, plastic), its cost is more expensive. Of course, for medical-grade silicone rubber, the production process, quality, and human health may offset the shortage of price to a certain extent. The selection of suitable silicone rubber needs to balance budget and production requirements.

❐ Pollution: Thermoset silicone elastomers generate a lot of waste and environmental problems due to their irreversible cleavage and reorganization of the covalent network. Wearable (disposable medical/electronic) products in particular leave behind a huge amount of waste. Although efficient recycling technology addresses this problem, it cannot eliminate its secondary pollution to the environment.

Based on the above, silicone elastomers with the ability to be used in harsh environments provide designers with more options for processing solutions, thereby producing products that other organic materials cannot do. If you want to know what grade of silicone to choose or if you are not sure which silicone rubber meets your application requirements, please contact Yongrui engineers to solve your doubts one by one.

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