Adhesion relative humidity epoxy resin

The tertiary amine salts are claimed to provide epoxy formulations with very good adhesion to metal. The cured resins also show a hydrophobic effect when in contact with water or at high humidities. The strength, toughness, and elongation (4.7 percent) of the cured epoxy resin are very good. However, heat distortion temperature is only in the range of 70 to 80°C, and chemical resistance is relatively poor for an epoxy. The physical properties fall off rapidly with any rise in temperature. 

A filled epoxy resin used as a structural adhesive and based on the diglycidyl ether of bisphenol A cured with dicyandiamide was subjected, in its bulk form, to ageing at 40, 55 and 70C and about 100% relative humidity. Gravimetric viscoelastomeric and FTIR studies were effected after various times of exposure to monitor water ingress and to link variations in mechanical behaviour with chemical modifications occurring in the polymer. 34 refs. 

Moisture resistance of epoxy adhesives is always a topic of some importance. Significant improvements in moisture resistance of a solid DGEBA-resin-based adhesive have been achieved by the addition of 1-50% of <100-/i average diameter colloidal silica. Strength retention of ferrite bonded assemblies after 670 h at 95% relative humidity/50°C was 83% for a composition containing 3-4 weight % colloidal silica, compared to 39% for a composition containing no silica. 

The durability of epoxy-aluminium joints that used a homopolymerised epoxy resin was studied by researchers based in Spain [15], and the effects of relative humidity, temperature, and salt concentration analysed. The homopolymerised epoxy resin absorbed little water (1.5 wt%) because of its non-polar network structure. Increasing relative humidity and temperature enhanced water uptake, but the joint strength remained constant because of epoxy plasticisation. A saline environment was damaging to the adhesive joints because of metal corrosion, but was not significantly harmful to the epoxy resin because of the lower diffusion coefficient of salt water. The decrease in glass transition temperature of the epoxy adhesive due to water absorption was dependent upon only the amount of absorbed water and was independent of hydrothermal ageing conditions. The durability of epoxy adhesive joints made underwater has been studied [16]. 

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