The yellowing and whitish phenomenon of silicone products is usually caused by the following reasons:
1. Material and formula factors
Influence of raw material impurities: If the purity of the silicone raw material itself is not enough and it contains more impurities, such as some metal ion impurities, these impurities may cause chemical reactions over time and under the influence of external environmental factors, causing the color of the silicone surface to change, yellowing, whitish, etc. In addition, if some additives added to the formula are of poor quality, insufficient purity, or have compatibility problems with each other, it may also affect the stability of the silicone product and cause the color to change.
Vulcanizer selection and dosage issues: Vulcanizer plays a key role in the vulcanization molding process of silicone. If the selected vulcanizer is not suitable, for example, some vulcanizers will leave colored substances inside the silicone after decomposition, which will easily make the product yellow over time. In addition, inaccurate dosage of vulcanizer will also have an impact. Excessive dosage may accelerate the aging of silicone, causing it to deteriorate faster, such as yellowing and whitish. Too little dosage may lead to incomplete vulcanization, affecting the performance and appearance stability of silicone.
2. Influence of processing technology
Improper vulcanization process: In the vulcanization process, poor control of parameters such as temperature, time, and pressure will affect the quality of silicone products. For example, if the vulcanization temperature is too high, it is easy to cause over-vulcanization of silicone, resulting in damage to its internal structure, accelerating the aging process, and then showing a yellow or whitish appearance; too long vulcanization time also has a similar effect, and insufficient vulcanization pressure may cause uneven product density and insufficient vulcanization in some areas, which may cause color changes in these parts during subsequent use.
Inadequate cleaning: Before and after the processing of silicone products, if the surface is not thoroughly cleaned, impurities such as oil, dust, and mold release agents will remain. These impurities will affect the appearance of silicone, and during long-term storage or use, they will interact with external environmental factors, which may cause the surface of silicone to turn yellow or white. For example, if there is too much mold release agent residue, the surface may deteriorate and discolor under the influence of the subsequent environment.
3. Effects of environmental factors
Impact of light: When silicone products are exposed to sunlight or strong artificial light sources (such as ultraviolet light) for a long time, the high-energy photons in ultraviolet light will destroy the molecular structure of silicone, trigger photo-oxidation reactions, break and reorganize the chemical bonds in silicone, and produce some chromophores, which will cause the product to turn yellow or white. Especially for transparent or light-colored silicone products, the color change caused by this light will be more obvious.
Influence of temperature and humidity: In a hot and humid environment, silicone is more likely to undergo chemical reactions such as hydrolysis and oxidation. High temperature will accelerate the movement of silicone molecules, making its internal structure unstable, while humidity provides moisture and promotes the occurrence of chemical processes such as hydrolysis. As these reactions proceed, the appearance of silicone will gradually deteriorate, and yellowing and whitening will occur. For example, in some humid and hot areas in the south, the probability of silicone products having such problems is relatively higher.
Contact with chemical substances: If silicone products come into contact with some corrosive chemicals, such as strong acids, strong alkalis, organic solvents, etc., their chemical structure will be destroyed, causing surface discoloration. For example, silicone products may be corroded and turn yellow or white after contact with certain chlorine-containing detergents. Even if they are no longer exposed to these substances, the color changes that have already occurred are difficult to restore.
4. Use and aging factors
Long-term use and wear: During long-term use, silicone products are constantly subjected to external forces such as friction, extrusion, and stretching. The microstructure of the surface will be destroyed, making the originally uniform appearance rough. Some internal components may also be exposed due to wear. Combined with the influence of external environmental factors, yellowing and whitening are prone to occur. For example, silicone mobile phone cases often have this color change after long-term daily use and friction.
Natural aging: As time goes by, silicone products themselves will naturally age, the intermolecular forces will weaken, the chemical bonds will gradually break and reorganize, and their performance and appearance will change accordingly. Yellowing and whitening are one of the common aging manifestations. Generally, silicone products with a longer service life are more likely to have such color changes.