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Monday, March 9, 2009

Impact Structural Adhesives

Versatile as the bisphenol A adhesives are, they cannot yet be used satisfactorily to provide what may termed an impact structural adhesive. This type of adhesive requires initially the property of a pressure sensitive adhesive, but should subsequently cure and develop the resistance to creep expected of a structural adhesive. The difficulties are clearly very great but with the variety of rubbery and sticky polymers available, hardly inuperable. One approach has been through the use of other glycidyl ethers, and progress has been reported with the epichlorohydrin derivatives of the bisphenol of cashew nut shell oil, which is mainly 1,8-bis(hydroxyphenyl) pentadecane.

Durability
There is much everyday evidence on which to form the opinion that the durability of epoxy resin is excellent, but the most material, organic and inorganic, they suffer to some extent from exposure to weather, they do not, however, degrade rapidly or badly.

The durability of bisphenol A epoxy adhesives is under investigation in weathering tests being made by the Wright Air Development Center, and with tests still in progress it appears that epoxy phenolic adhesives are performing well. But question of the permeability of thin adhesive layers, as mentioned in the article before is always an important factor. The effect of permeability is such that water may penetrate a thin film of adhesive and cause separation at its interface is dependent in part on the type of metal, and so supports the axiom that the behavior of an adhesive depends on the adherent.