A common undesirable effect of degradation is discoloration.
Both natural polymer materials and synthetic polymers in
adhesives and sealants undergo induced discoloration as an
effect of degradation. Typically observed by an increase in
yellowness or darkening, discoloration often appears prior to
any measurable loss in physical properties. It is usually the
first critical indicator of damage that is observed, which
determines the useful service life of the product. Although
color development occurs at widely differing degrees in various
adhesives and sealants and may not directly correspond to a
decrease in the mechanical properties, a change in appearance is
often unacceptable in many adhesive applications. Adhesive
without AO Adhesive with AO-1 Adhesive with AO-2 The photo above
illustrates the positive effect of antioxidant systems on the
color stability of an adhesive after heat aging at 170°C.
Although not illustrated, additional benefits of antioxidants
may include improved initial color of the adhesiv