Friday, November 12, 2010

Polyamide Resins and Nylons

A polyamide is a polymer obtained by reacting a di- or poly-carboxylic acid with a di- or polyamine. Two types of ployamide are of interest as adhesives one is the Versamid type of polyamide resin and the other is the Nylon type of polyamide plastic. The former is a relatively low molecular weight material prepared by the condensation of dimerised vegetable fatty acids and polyamines. It is largely the type of acid, for example, dilinoleic acid, that makes the product of the reaction different from the polymer of relatively high molecular weight called nylon. For interest, nylon is by definition a generic term for a long chain synthetic polymer amide capable of being formed into a filament in which the recurring amide elements can be oriented in the direction of the axis. It is no doubt possible to make a Versamid type of polyamide that would fit into the nylon definition, but some distinction must be made here because the products about to be considered are very different in non chemical respect.

Polyamide Resins (Versamids)
These resins vary from medium viscosity liquids to hard thermoplastic solids. The liquids are well-known as hardeners for epoxy resins. The solid forms, containing none or few reactive amine groups, have adhesive properties by themselves. With molecular weights from about 3000 - 9000 they have melting points (ball and ring) between 95oC and 190oC. A later development of the original product, containing reactive amino groups resulting from the use of polyalkylene polyamine, has been describe.

Although most solid grades of Versamid are soluble in a variety of organic solvent, and have limited use as solution adhesives, their relatively sharp melting point make them attractive as hot melt adhesives either by themselves or in admixture with other components. They stick to polyethylene and polypropylene, polymer film, celophane, cellulose acetate, polyvinylidene, chloride, nylon, and aluminum foil; and it specially interesting to see that they also stick waxed glassine.