Some reasons for epoxy resin yellowing

• Photo-oxidation reaction

Epoxy resin is susceptible to ultraviolet rays and oxygen in the sunlight caused by the oxidation of the aniline group in the epoxy resin, which in turn leads to the phenomenon of yellowing of epoxy resin glue;

• Thermal degradation

Long-term high temperature conditions, epoxy resin will find thermal degradation, which will lead to molecular chain breakage, yellowing phenomenon;

• Some chemical reactions

Epoxy resin adhesive and some substances in contact with chemical reactions, yellowing; for example, substances containing sulfide and epoxy resin contact;

• Curing agent and accelerator reasons

The free amine component in the amine curing agent directly polymerises with the epoxy resin, resulting in local heating of the glue and accelerated yellowing; In the heat aging process, the amine curing epoxy resin material surface has a large number of imine presence, thus easier degradation and yellowing. Tertiary amine accelerators, nonylphenol accelerators in the thermal oxygen, UV irradiation is also easy to yellowing;

How to avoid epoxy resin yellowing

• Reduce the irradiation of ultraviolet rays

In the production and application process of epoxy resin, must avoid the influence of high temperature and ultraviolet rays, prevent epoxy resin oxidation reaction.

• Add yellowing-resistant additives

Adding antioxidant and UV absorber can greatly delay the aging and oxidation of epoxy resin, thus prolonging its service life and preventing yellowing.

• Curing agent selection

Amine curing agent, try to choose the amine curing agent with less free amine content;

Anhydride curing agent, epoxy system in the anhydride curing agent is heat aging and light aging type of excellent.

The conclusion

The yellowing of epoxy resin is caused by a variety of factors. The most important is ultraviolet radiation, if it is an outdoor product, it is recommended to add a certain amount of ultraviolet absorber to delay the yellowing, and it is best to add some antioxidants together as well, to play a concordant effect.

Adding UV diluents and antioxidants can not fundamentally solve the epoxy resin yellowing, but only delay yellowing, so that the product transparency lasts for a period of time.