Generally, discoloration is not a critically important criterion for adhesives since the bond line is often unseen and hidden within a joint design. However, in certain applications discoloration is very detrimental and a difficult challenge to overcome. These applications are often those aimed at the consumer markets such as food packaging, clothing and footwear, sporting equipment, and so forth. However, discoloration is also detrimental in various industrial applications such as building and automotive sealants, graphic decoration and lamination, and wood joining.
Adhesives and sealants based on both natural and synthetic polymers can undergo induced discoloration as a result of degradation. There are a number of reasons why discoloration occurs. The most predominant are exposure to ultraviolet (UV) light and thermal oxidation, but other sources can also dominate in certain uses. This article will review the following origins of discoloration as related to adhesives and sealants.Discoloration is noticed by an increase in yellowness or darkening, and this is an aesthetic problem.