Making Silicone Parts: The Chemistry That Makes LSR Such an Outstanding Material

Making Silicone Parts

The Chemistry That Makes LSR Such an Outstanding Material

Liquid Silicone Rubber (LSR) is part of the family of thermoset elastomers that have a backbone of alternating silicone and oxygen atoms with methyl (-CH3) or vinyl side groups (-CH=CH2). They offer outstanding properties for making silicone parts, not obtainable with today’s TPEs. The solidification process of all heat-activated thermosets, including silicone rubber, is dominated by an exothermic and irreversible chemical reaction called cure, vulcanization or network polymerization. The curing process when making silicone parts, forms a three dimensional network in which each chain is connected to all others by a sequence of junction points. The curing process of making silicone parts improves the general properties of the final product when making silicone parts and provides resistance to heat and hot air (180˚C, stabilized up to 250˚C, short-term up to 300˚C), due to the fact that these network polymers do not melt upon heating. The curing of Liquid Silicone Rubber (LSR) is almost exclusively carried out with a platinum-catalyzed hydrosilylation reaction, which does not generate by-products.

Silicone rubbers are incomparable when making silicone parts, because they maintain their mechanical properties over a wide range of temperatures (-100˚C for special grades, -60˚C for standard grades up to 300˚C short term) and the presence of the methyl-groups in silicone rubbers makes these materials extremely hydrophobic. In addition, Liquid Silicone Rubber (LSR) has high aging and chemical resistance, biological inertness, inherent lubricity, purity, transparency, and physiological compatibility. The addition of chemical bonding agents during crosslinking results in good adhesion on substrates such as thermoplastics, steel, or aluminum. Coupled with their ability to withstand sterilization processes. This makes LSR’s ideal when making silicone parts for many medical uses, as well as for baby care applications and appliances.

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LSR is also commonly used for the production of seals in the automotive and aerospace industry, connectors and cables for appliances and telecommunications, implants and devices for medical purposes, and packaging and baking pans for the food industry. Injection molding of LSR products, as well as the revolution in technology enabling the application of two shot injection molding technology with LSR, is creating additional opportunities for component designers, parts and component integrators and OEM as it enables an ideal combination of a rigid material (thermoplastic) with a soft material (LSR) for consistent high-volume production, fast cycle times, automated processing and manufacturing of intricate shapes and geometries.

LSR Chemical Structure

[1] Dull, G.: Getting Started in LSR: Understanding the Materials, Part I; Plastics Technology, 6/2010

[2] Kudchadkar, V.: Liquid Silicone Rubber Molding Simulation; MoldMaking Technology, 1/2011

[3] Lopez, L.: Modeling the Vulcanization of Liquid Silicone Rubbers, M.Sc. Thesis, Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, 2004.

[4] Osswald, T. A.; Baur, E.; Brinkmann, S.; Oberbach, K.; Schmachtenberg, E.: International Plastics Handbook; 4th edition, Hanser Gardner Pubilcations, Cincinatti, 2006

[5] Odian, G.: Principles of Polymerization, 3rd Edition, John Wiley & Sons, New York, 1991

At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and components, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.

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