Adhesive, selection long term performance

There is a need for an accurate assessment of the mechanism of cathodic debonding of thick adherends. This would contribute to better control over the selection of formulations resistant to attack. One of the objectives of this work was to develop an accelerated screening test. The screening test was used to evaluate the relative performance profiles of a number of commercial adhesives which were recommended for marine applications. It is hoped that a screening test such as this one could be used to isolate measurable primer properties which can be related to the long term prospectus of the primer, and the variability of this prospectus under permutation of substrate type or additives. 

For cold-curing epoxides wide variations in adhesive material properties are possible, with different combinations of resin, hardener, filler, and the multitude of modifiers. Products which cure at ambient temperature cannot achieve the same performance as is obtained by curing at elevated temperature. For products cured at room temperature their TgS, at 40-50 °C initially, are relatively low and may be lowered even further by absorbed water, in liquid or vapour form. This may also be accompanied by a reduction in strength and modulus. Thus the use of materials with a slow and small water uptake is to be preferred, which implies a fairly highly cross-linked formulation. Such considerations do of course depend upon the performance and durability expectations in service. Whilst the environmental durability of joints can often be improved enormously by the surface pretreatment methods employed (see Chapters 3 and 4), the adhesive must be selected carefully to ensure long term durability in consideration of the modes and duration of loading, and the environmental conditions. Ideally the adhesive should be fairly tolerant of poor surface pretreatment procedures. 

These high performance polymers not only meet unusual requirements for long term durability at elevated temperatures, they may also have unique and diverse characteristics such as conductivity, insulating properties, chemical resistance, self extinquishing, selective gas barrier properties and are also used in normal applications as films, fibers, elastomers, adhesives, and coatings as well as injection moldable materials of construction. 

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