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Monday, August 11, 2008

Polyamines Hardeners

This polyamine hardener can use of alkylene series. The amount of the alkylene series of polyamines which needs to be added is usually between 6 and 12 % of the weight of the resin depending on its epoxies content. Diethylenetriamine and triethylenetetramine react vigorously exothermally, a shortcoming that limits the amount of adhesive it is advisable to mix at one time unless steps are taken to dissipate the heat. These amines are hygroscopic, a property that should be borne in mind when working in conditions of high relative humidity. They are also liable to cause skin irritation and dermatitis in some persons, an effect that may be lessened to some extent by using an N-hydroxyalkyl derivative of these polyamines, such as N,N-bis (hydroxyethyl) diethylenetriamine.

Aliphatic amines react to form adhesives that five good strength with a variety of adherents including most metals, glass, wood and mainly plastics. In spite of the fact that certain types are cold curing, all give a higher bond strength if hot cured or post cured, for example, at a temperature of 80oC - 100 oC. In some cases hot curing increases hot strength even more than room temperature strength, but in making comparisons it is important not to overlook the fact that subjecting the glued joint to heat in the course of the test may be equivalent to deliberate post-curing.

Example of the bond strength obtainable with two aliphatic polyamines is given in the table. The effect of curing temperature is well emphasized, even in the case of the highly reactive triethylenetetramine. But a factor that also affects adhesive strength is the exothermic temperature rises (if any) that has been reached before the glue is applied.

Included in the large number of other aliphatic amines that are suitable as hardeners are amino ethers such as butanediol bis(aminopropyl) ether. There is evidence that some of these ethers cure more completely at low temperatures than the alkylenepolyamines.

Particularly valuable amine curing agents which contain both primary and secondary amino groups and also amido groups are the polyamides known as the ‘Versamids’. These polyamides are made be reacting a dimerized drying oil acid and a polyamines, particularly dilinoleic acid and ethylenediamine, and they react with epoxy resins to form versatile adhesives. The most useful Versamid hardener is those that are liquids as distinct from resinous solids, especially Versamid 115. In cases where the resultant viscosity of the adhesive is too high, solvent mixtures of the lower alcohol and hydrocarbons may be used a diluents.