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Thursday, January 21, 2010

Miscellaneous Thermosetting Adhesives

Thermosetting adhesive are adhesive that can’t be reuse after the limitation condition of these adhesive is over. The limitation of thermosetting adhesive is called as curing, curing condition is affected by chemicals, temperature and time, so even the adhesive is on cold condition below curing temperature but keep too long then adhesive also has cured. If the adhesive has cured then this adhesive can’t use anymore.

Many kind of thermosetting adhesive are describe here:

Silicone Adhesives:
Certain silicone adhesives are thermosetting. They are used mainly for bonding silicone rubber, an application in which crosslinking must be infrequent if the adhesives is to have a rubbery nature after curing.

The silicones is usually dimethyl polysiloxane, which is normally cured by heating with a silicic acid ester and catalyst. Certain form of the adhesive are capable of being cured at room temperature, and of giving good resistance to heat.

Although the bond strength of organo-silicon resins is normally not high, it can be improved by incorporating an epoxide, polyester or phenolic resin, additions which might be expected to reduce hot strength and thermal stability.

Furane Adhesives
These adhesives contain the chemical group known as a furane ring. They include the condensation polymers of furfraldehyde (“furfural”), and furfuryl alcohol. These furane compounds polymerise on addition of an acid, passing through a liquid resinous state, and have adhesive properties. Furfuryl alcohol imparts special properties to urea, phenolic and epoxy resins. Furane resin adhesive are claimed to effectively bond thermoplastic materials and rubbers, also phenolic laminates, with which it is said that adhesion to smooth surface is better than to sanded surfaces.

Thermosetting soluble Nylons
Adhesives utilizing alcohol soluble nylons for example methoxy nylon, can be rendered substantially infusible and insoluble especially by heating in the presence of an acid catalyst, and are claimed to give high adhesion to wood even alter immersion of the joints in boiling water.

Thermosetting Acrylic resins
Considerable interest has been aroused in the various ways of crosslinking acrylic monomers and polymers, e.g. by methylol or epoxide groups. The interest has been largely in coating applications with emphasis on high adhesion but it is felt that interest will develop in the use of these polymers as adhesives.

A number of papers on thermosetting acrylic resins were read at the 138th Meeting of the American Chemical Society, and work on them has also been reported from Japan.

Organic/Inorganic Adhesives
Although the intention is to embrace in this article only those adhesive that are organic and synthetic, since important development are taking place with inorganic adhesives, a reference to organic/inorganic adhesive system seems justified. Under development and of potential interest is the condensation polymer of cyclic phosphonitrile chloride and a polyhydric aromatic, compound, which when blended and polyhydric aromatic compound, which when blended with synthetic elastomers has possibilities as an aircraft structural adhesive for operation at 200 o – 315 oC. More particularly, cyclic phosphonitrilic chlorides, principally the trimer and tetramer, are condensed with hydroquinone or resorcinol, and adhesives produced either by blending with a polar rubber such as polycrylonitrile rubber, or by reacting with polyepoxides, polyisocyanates or polyester.

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