Why do plastic products change color?

Color change caused by automatic oxidation of additives

The automatic oxidation of phenolic stabilizers is an important factor in promoting the color change of white or light-colored products. This color change is often called "Pinking" in foreign countries. It is made up of anti-oxidants such as BHT (2-6). - Di-tert-butyl-4-methylphenol) oxidation product coupled and shaped like a 3,3',5,5'-stilbene quinone reddish reaction product, this discoloration is only in aerobic and water and no In the case of light, when exposed to ultraviolet light, the reddish stilbene oxime is rapidly decomposed into a yellow monocyclic product.

Coloration of pigments by tautomerism under photothermal heating

Partially colored pigments undergo tautomerization under the action of photothermal heat, such as the use of CIPig.R2 (BBC) pigments from azo type to 醌 type, which changes the original conjugate effect and causes the reduction of conjugated bonds. It causes the color to change from dark blue red to light orange; at the same time, under the catalysis of light, it decomposes with water, causing the co-crystal water to change and cause fading.

Color change caused by atmospheric pollutants

When the plastic products are stored or used, some reactive groups, whether they are resins or additives, or colored pigments, will react with the moisture or chemical pollutants in the atmosphere, such as acids and bases, under the action of light and heat. Causes a variety of complex chemical reactions that, over time, can lead to discoloration or discoloration, which can be avoided or mitigated by the addition of suitable thermo-oxygen stabilizers, light stabilizers, or the use of high-quality weathering aids and pigments.