Peel Strength Properties of Adhesives

For various reasons, one of which concerns the surface treatment of the metal, peel strength is a property that is not as consistently reproduced in an adhesive as is tensile shear strength. This is the reason why the bend test of an overlap joint is often preferred to the peel test as a measure of flexibility. It is, however, certain that for two polymer adhesives the variation of peel strength with temperature depends largely on the behavior of the thermoplastic component. The usual effect of heat is first to create an increase and later a decrease in peel strength. A typical peel strength/temperature relationship of a polyvinyl acetal/phenolic adhesive is shown on the picture below. The curve shows the strength according to the Ciba (ARL) drum peel method, the climbing drum method gives a somewhat higher figure and an average value for this at 25^oC is shown.

Polyvinyl Acetal/phenolic Application

Where adhesive is used in some highly important application such as in an aeroplane, durability is a subject of more than usual importance. Test made in Nigeria on aluminum alloy joints glued with an acetal/phenolic adhesive (not openly exposed to weather but exposed to the tropical atmosphere), have shown no drop in strength after nearly 5 years. And in America tests made over a wide range of climates have given generally satisfactory results, but with one or two anomalies, which is not uncommon experience in such testing.