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Wednesday, March 18, 2009

Glycidyl Ether Adhesives

The number of epoxide groups per molecule and the rigidity of the molecular structure are factors that effect hot strength of an adhesive. In the search, therefore, for higher hot strength, glycidyl ethers of certain polynuclear phenols including phenolic resins, and also those of some polyhydric mononuclear phenols such as resorcinol and hydroquinone, have been examined.

The preparation and properties of some these glycidyl ethers have been described in papers and patent specifications; and important one is the glycidyl polyester of tetraphenylolethanc; a tetraphenol made by reacting ordinary phenol with glyoxal, a di-aldehyde. The relationship between strength and temperature of this resin hardened with two different amines and two different anhydride is shown on the figure.

Attention has been given to the adhesive properties of this resin when cured with diaminodiphenyl sulphone and also when modified by the incorporation of a polyvinyl acetal.

Dearbors et al have compared certain di-, tri-, and tetra-glycidyl ethers cured with anhydrides. Although adhesion was not among the properties examined, much of the information given is important in considering the usefulness of these resin as adhesives.

In a patent describing epoxy resins from certain trisphenols, adhesive strengths on aluminum alloy have been quoted, using 4,4 – diaminodiphenyl sulphone as hardener. These, for the glycidyl ether of 1,2,2-tris (hydroxyphenyl) ethane are reproduced in certain condition. The glued joints in this test were 0.126 mm thick and the glued area 2.5 cm wide by 1.25 cm overlap. The lower strength of the trisphenol glycidyl ether at 21 oC compared with bisphenol A glycidyl ether results from the brittleness of the former adhesive being emphasized by the type of stress imposed in the testing of an overlap joints.