Bonding joints must bear the role of external forces, but also subject to the use of environmental factors test, such as temperature, humidity, chemical media, outdoor climate and so will affect the bonding strength. Adhesive if used in harsh environments, should do the simulation test of environment.
Moisture and soaking
Moisture affects the bonding strength in two ways. Some polymer materials, especially those containing ester bonds, in the hot and humid environment will be the loss of strength and hardness, even when the liquefaction. Water will also penetrate the adhesive layer, to replace the adhesive interface of the adhesive, which is in the wet environment, the most common reason for the reduction of adhesive strength.
The rate of hydrolysis depends on the chemical structure of the binder base, the type of catalyst, the amount used, and the flexibility of the adhesive. Some chemical bonds, such as esters, urethanes, amides and ureas, can be hydrolyzed. Some types of polyurethane and anhydride-cured epoxy resins have the fastest hydrolysis rate of ester bonds. In most cases, the hydrolysis stability of the amide-cured epoxy resin is better than that of the anhydride. The hydrolysis rate of the hydrolyzable material is also related to the amount of catalyst used in the formulation. Appropriate choice of base material and the amount of catalyst, can get better.
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