Introduction to Components & Designs of Organic Silicone Sealants & Adhesives

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It is in last article, we have introduced the basis of organic silicone sealants and adhesives to allow us to know that they are full of industrial and commercial value and they are widely used in different industries. Today, we are going to discuss more about their inner side- the components and designs of them.

The design of organic silicone sealant and adhesive have similar designs with silicone rubber, they mainly have base materials, fillers, curing agents, takifiers, antioxidants, heat stabilizers and colorants.

Selection of Base Materials

Base material is the main body material of sealant and adhesive- it is the raw silicone rubber, it could provide heat resistance. After its modification, it could have some kind of adhesion. Its types include methyl silicone rubber, methyl vinyl silicone rubber, phenyl silicone rubber, phenylene silicone rubber and some other kinds of silicone rubber.

Silicone rubber sealants and adhesives usually use RTV silicone rubbers as main body materials. It is according to the mechanisms of vulcanization reactions, it could be categorized into condensation and additional type.

For condensation silicone rubber, it is crosslinked via condensation reaction and it will produce low molecular matters during vulcanization reactions, it will also lead to the shrinkage of sealants. The on-sale RTV silicone rubber usually belongs to low molecular polysiloxane that carries hydroxyl on the ends of its molecular chains.

RTV silicone rubber is like other thermal vulcanized silicone rubbers, its big molecular side chain’s methyl could be replaced by other functional groups to make modification, and it is according to the different structures of its main chain and side chain, it could be divided to different silicone rubbers that carry different properties. Generally, different type of thermal silicone rubber, will mostly like to have a corresponding RTV silicone rubber and have similar properties.

To use phenyl partly replace methyl, it could improve its low-temperature property and increase its oxidation resistance.

The RTV nitrile silicone rubber is a kind of polymer that in the form of emulsifier white oily liquid in room temperature. It has the properties of silicone rubbers and has properties of light resistance, odor resistance, humidity resistance, extremely temperature resistance and excellent electrical properties.

As for RTV fluorinated silicone rubber, its outstanding property is having excellent chemical resistance in room temperature and high temperature.

For additional silicone rubber, it is the unsaturated polysiloxane that carries vinyl or some other functional groups on its edges of molecular chains. It is usually methyl vinyl polysiloxnane.

It is in order to get ideal sealant; it is a must to make a selection of rubbers. The molecular quantity of silicone rubber is the main indicator of the selection. The bigger the molecular quantity is, the higher adhesion the rubber is which will lead to the processing and final sealant adjustment to be more difficult but the vulcanized rubber will have a better mechanical property; however, if the molecular number is lower and the adhesion will be worse, collapsibility problems will be occurred as well. Therefore, for general use silicone sealant, the molecular quantity should be between 30 thousand and 60 thousand.

Fillers

Silicone rubber will not be crystalized and it is not non-polar molecules, intermolecular force is small. Non-reinforced silicone rubber has low mechanical properties and has no practical value. To select proper reinforcing agent could largely improve its mechanical property and lower the shrinkage rate of solidification process, or to grant some special properties to adapt to the usage requirement. Also, some filler could reduce the quantity of heats during the solidification process to increase the rubber layer’s anti-shocking toughness, other mechanical strengths, heat resistance and adhesion.

Fillers could have big influence on some other physical and chemical properties, to add some metal powders like aluminum and bronze into adhesive could increase improve its high-temperature properties and stability.

Also, to add some quartz powder, zinc oxide, calcium carbonate and some other chemical powders could reduce cost. Low-density filler like glass fibers, glass or plastic micro ball could be used to produce low-density polymer. What is more, a large quantity of organic or inorganic pigments could be used to provide colors.

Takifiers

During the adhesion process, takifier is usually the important component that could grant adhesion. It is in order to get a tight stick layer between adhesive and the sticked product; the common takiifers are siloxane coupling agent, siloxane and silicone resin. However, these chemicals are usually added to the glue in the form of silica surface treatment agents. Also, some of them are achieved by forming chemical keys between the coupling agents that carry reactive functional groups and the surfaces of the sticked product.

Curing Agents

Curing agent is the main matching material in the adhesive. It reacts with main body polymer directly or via catalyst to make intermolecular distance, forms, thermal stability and chemical stability all change significantly. To make the thermal crosslinked main body polymer to become highly crosslinked body net structure.

Colorants

RTV silicone rubber is clear and transparent; its color could be adjusted by colorant. It could be used to produce half-transparent aluminum gray sealant for construction materials. To consider thermal stability, colorants are usually use non-colorful pigments. There are only very few types of organic pigments.

Other Additives

It is in order to improve one specific property of adhesive, sometimes we will add some specific additives as well. Like to add anti-aging agent to increase air aging resistance; and to add curing agents to increase the storage ability of rubber liquid.

Summary

It is true that each component of the silicone adhesive and sealant plays an utmost important role in making one or more aspects of them to be more and more functional or be granted some kind of unique property to fulfill the requirements from customers and some other specific industries.

Also, these products have been in the market for years and they are proved to be useful and have a bright future both in domestic and international market.