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Tuesday, October 13, 2009

Bonding Broken Bones

In common with other resin adhesives, the polyurethanes have been investigated in the gluing of fractured bones. Special interest has been shown in mixtures that evolve a relatively large amount of carbon dioxide and thereby produce a foamed structure. In one paper on their use, the interesting statement is made that the polyurethane foam, in and during its formations, becomes an intimate part of the bone and that this distinguishes it from ordinary gluing.

Miscellaneous Uses

Apart from its use in the bonding of rubber to metal, triphenylmethane triisocyanate improve the adhesion to synthetic fibers such as rayon and nylon in the manufacture of rubber tyres. The particular use has now been discontinued in England, but diphenylmethane diisocyanate is still used as the active component in adhesives for bonding synthetic fibres in non tyre uses such as rubber belting. However, the use of two so-called "specialty" isocyanates has recently been described, polymethylene polyphenylisocyanate and dianisidine diisocyanate; improved adhesion between rubber and synthetic fibres is claimed when fabric is dipped in the isocyanate or when the isocyanate is incorporated in the rubber, including neoprene and nitrile rubber.

Polyurethane adhesives, at least those based on tolylene diisocyanate are not generally thought to give very good adhesion to copper and glass, although adhesion to glass can be improved by increasing the flexibility of the adhesive, so the type of polyol and the amount added are important.

A polyurethane adhesive of unspecified composition is, however, stated to develop strong bonds to a wide range of materials including both copper and glass; and with regard to the latter it is further stated that whereas aluminum test joints withstood many hours exposure to boiling water, glass-to-glass bonds failed in three hours. The reason is probably associated with the known affinity of water to glass, and is further evidence of the need to consider also the adherend in assesing resistance to liquids, especially to water.

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