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Tuesday, March 1, 2011

Polyethylene Adhesives

Polyethylene would appear to stick better to polyvinyl formal and butyral than to metals, and the application of a priming film of either of these is a method proposed for ensuring good adhesion of a polyethylene coating to metal. It is perhaps rather surprising that we are considering polyethylene here as an adhesive since it is a notoriously difficult material to bond unless the surface specially treated. Having made that comment, it is pertinent to mention an adhesive developed to bond to bond polyethylene. This adhesive, a partially hydrogenated polybutadiene with 8% unsaturation, is said to produce a vulcanized bond by heat sealing with the polyethylene.

The cross linking of a hot melt polyethylene adhesive in situ is possible by the addition of an organic peroxide having a suitable decomposition temperature. Furthermore, dicumyl peroxide has been utilised to bond with ethylenic polymer to an elastomer. It should be understood that polyethylene can be crosslinked to an extent where it may perhaps be classified as a thermosetting resin.

Returning to the use of polyethylene as hot melt adhesive, some very interesting work (under the slightly misleading title of "Making Polyethylene adhsionable") have been reported by Bikerman. From observation he had made, Bikerman reasoned that removal of low molecular weight polymers (probable also certain additives) from normal polyethylene would have a material having increased power of adhesion. He therefore removed the more soluble greatly increased adhesion in tension with bolt joined of steel and glass much greater in fact than the tensile strength of the polyethylene itself. However, it is not at all easy to find out just what one is removing by fractional precipitation. The commercially available polyethylene contain additives such as plasticizes and antioxidants, and the wide difference in the ratios of adhesive strength with fractioned and unfractioned polyethylene of different origin must be attributable, at least in part, to the removal of these substances during fractionation. The comparative strengths at room temperature for three sample of polyethylene.