Saturday, January 29, 2011

Miscellaneous Thermoplastic Adhesives

Most thermoplastic polymers can be used as hot melt adhesive for bonding one material or another. The poly carbonates (which are really unconventional polyesters), and the formaldehyde linear polymers, known as the polyacetals, are examples of two that have been examined as adhesives, although better known as plastic molding of their strength is shown in other tables.

The effect of priming the surface of the adherents with a phenolic resin follows the nylon pattern of behavior in the case of the polycarbonate and brings about an increase in adhesive strength. The decrease in the case of the polyacetal used with a phenolic resin is unusual and probably indicates extreme incompatibility.

Polyethylene can be applied as a coating on paper, cloth, cellophane or even certain metal foils, and the polyethylene surface hot welded. This naturally demands some measure of adhesion between the polyethylene and the paper, cellophane, etc, and although the bond strength is not high it is adequate for many applications. The degree of adhesion shown by polyethylene to most adherents can be greatly increased by oxidizing the polyethylene; a small degree of oxidation, such as that incidental to the failure to the spraying process has a marked effect on adhesion.