4.5.5 UV Resistance

The adhesive used in external applications or applications in transparent or translucent substrates may be exposed to UV light. Exposure to sunlight and some artificial lights can have adverse effects on the performance life of adhesives or sealants. UV radiation can break the chemical bonds in a polymer. This process is called photodegradation and can ultimately cause cracking, scaling, colour changes and loss of the physical properties of an adhesive. Where resistance to UV light is a concern, absorbers and inhibitors of UV radiation may need to be added as surface coatings or additives.

The important aspect is that once photodegradation has started, it triggers a circular chain reaction that accelerates degradation, unless stabilisers are used to interrupt the oxidation cycle.

Figure 103 UV radiation may cause degradation of properties
Table 15 Summary of adhesive environmental conditions resistance
Temperature resistance Moisture Chemical UV
2C Epoxy High -55°C to 121°C (-67°F to 250°F) Excellent Excellent Good
1C Polyurethane Medium -40°C to 80°C (-40°F to 176°F) Moderate Good Poor
2C Polyurethane Medium -40°C to 130°C (-40°F to 266°F) Moderate Excellent Moderate
Reactive Hotmelt Polyurethane Medium 130°C (266°F) Moderate Good Moderate
Modified Silicone Polymer Medium 80°C (176°F) Moderate Good Excellent
1C and 2C Silicone Very High 200°C (392°F) Good Excellent Excellent
Anaerobic High -55°C to 121°C (-67°C to 250°F) Good Excellent Excellent
Acrylic High -55°C to 120°C (-67°F to 248°F) Good Good Good
Cyanoacrylate High -55°C to 120°C (-67°F to 248°F) Poor Moderate Good

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