Thermoplastic Resin Adhesives

A thermoplastic resin is one which melts or softens on heating and rehardens o cooling without (within certain temperature limits) undergoing any chemical change. At temperature above the melting point an irreversible chemical change such as depolymerisation or oxidative degradation may take place.

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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Varnishes

A varnish is an unpigmented colloidal dispersion or solution of synthetic and/or natural resins to oils and/or thinners used as a protective and/or decorative coating for various surface and which dries by evaportion, oxidation, and polymerization of portions of its constituents. Not being pigmented varnishes are less resistant to damage by light than paints, enamels, and pigmented lacquers. They furnish, however, a transparant film, which accentuates the texture of the surface coated. Varnishes are frequently oleoreinous; there are two minor classes, spirit varnishes and japans. Oleoresinous varnishes are solutions of one more natural or synthetic resins in a drying oil and a volatile solvent.

The oil reduces the natural brittleness of the pure resin film. Spirit varnishes are solutions of resins, but the solvent is completely volatile and nonfilm forming. Oleoresinous varnishes were formaly of major importance, but alkyd and urethane varnishes have largely replaced them because of greater durability, less yellowing, ease of application, and beauty. Pressure to reduce the amount of air-polutting solvent in varnishes and paints, coupled with the desire for water cleanup of tools and spills, has led to the development of water thinned varnishes.

Spirit resin varnishes are solution of resins in volatile solvents only, such as methanol, alcohol, hydrocarbons, ketones, and the like. Spirit varnishes dry most rapidly but are likely to be brittle and eventually crack and peel off unless suitable plasticizers are added. The preparation of these products involves active stirring and sometimes heating, to bring about the desired solution. An important example of a spirit varnish is shellac or a solution of the resin shellac in methanol or alcohol. Japans are rarely used now. They are opaque varnishes to which asphalt or some similar material has been added for color and luster. They may be subdivided into baking, semibaking, and air-drying japans, according to their method of application.

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