Are you still troubled by the fact that the sealants used in your product manufacturing process always turn yellow? Sealants turning yellow causes huge losses for the project. To help you prevent the sealants you used from yellowing, here is a complete guide for you.
What Does Sealant Yellowing Mean
Is the yellowing of the sealant merely a visual change, or does it affect your product itself? The answer is that it not only causes a change in color but also signals product aging. This means that some of its structures have also changed to a certain extent, making it more prone to cracking, breaking, or even detaching from the substrate, and the stability of the seal cannot be reliably guaranteed.
Therefore, the yellowing of sealants is a problem that needs to be taken seriously.
The Types of Sealants
Perhaps when people think of sealants, they always think of silicone sealants, but in reality, there are many different types of sealants. Yellowing is not just a problem with silicone sealants; almost all sealants will gradually yellow over time, but the degree to which they yellow varies depending on the type of sealant.
Common types of sealants include silicone sealants, polyurethane sealants (PU sealants), polysulfide sealants, acrylic sealants, butyl sealants, and MS polymer sealants. Among these, materials that are more prone to yellowing include PU adhesives, some low-quality silicone sealants, and acrylic sealants.
Why Does the Sealant Yellow
There is more than one reason that causes sealants turn yellow. Generally speaking, the reasons mainly fall into these four categories.
Raw material issues
To save costs, some inexpensive silicone sealants use industrial raw aterials that are not resistant to aging or are of insufficient purity, which makes them extremely prone to yellowing after prolonged use.
Formula issues
The formulation largely determines the sealant’s aging resistance. In inexpensive silicone sealants, low-quality additives result in insufficient UV resistance and stability, leading to a shorter service life.
Usage methods that accelerate aging
Incorrect application methods can sometimes cause sealants to yellow faster than expected. The most common problem is the mixing of different sealants, especially between neutral alcohol-based sealants and neutral oxime-based sealants. They will interact with each other and negatively impact your project.
Although some sealants are elastic, prolonged and repeated stretching can cause inconsistencies in their thickness, affecting both their physical structure and their appearance to the naked eye.
Sometimes, the materials that the sealant comes into contact with can also cause it to yellow. If used to seal the edges of certain types of rubber or metal, the parts that come into contact with these materials will turn yellow locally.
Environmental factors
Undoubtedly, environmental factors are also an important reason for the aging of sealants. High temperatures, UV radiation, surface contamination, and the type of contact materials can all cause sealants to soften. The most significant influence, however, comes from ultraviolet radiation.
UV radiation can cause autocatalytic degradation of sealants. The chromophores contained in the sealant absorb ultraviolet light and generate free radicals. These free radicals then react with oxygen, producing a substance that continuously damages the internal structure and generates more free radicals, thus causing your sealant to age continuously.
Unsuitable temperature environments, such as high temperatures, can produce similar effects on sealants as exposure to ultraviolet light. Therefore, sealants exposed to high heat are more likely to yellow.
External contamination is also a root cause of sealant aging. During use, oil stains and chemical substances on the sealant surface, as well as mold growth due to humid environments, can cause the sealant to change color. The threats come not only from visible substances but also from smoke or corrosive gases in the air.
The Suggestion Prevents Sealants From Yellowing
Choose a sealant that is resistant to yellowing
To prevent sealants from yellowing, one of the easiest solutions is to choose sealants that have good anti-aging or UV-resistant properties.
As a widely used sealant, High-quality silicone sealants have excellent resistance to UV radiation and high temperatures. Furthermore, manufacturers often add stabilizers and other substances to further enhance their durability. If used properly, they can even maintain their original color after 10 to 20 years.
MS-based sealants are also a good option. After improvements to their molecular structure, they offer superior resistance to yellowing compared to some other sealants.
Although ordinary PU performs poorly under ultraviolet light due to chemical bonds in its molecular structure that are sensitive to UV radiation, polyurethanes with aliphatic isocyanates have relatively good resistance to yellowing.
Professional sealant manufacturers conduct tests to assess their products’ UV resistance. When choosing a sealant for your project, you can refer to this data to make an informed decision.
The above are all solutions for typical situations. If your sealant will be applied to areas exposed to direct sunlight, a silicone sealant specifically designed for outdoor use can be an excellent solution.
If the yellowing of the sealant is mainly due to mold growth in a humid environment, you can choose a specialized anti-mold silicone sealant that contains a long-lasting anti-mold agent.
Furthermore, if you are particularly concerned about the aesthetic issues caused by the sealant changing color, using a darker-colored sealant can, to some extent, make the color change less noticeable.
Appropriate usage methods
Proper construction methods can prevent the sealant from becoming contaminated from the outset or developing potential problems that could accelerate its aging.
Before applying the sealant, thoroughly and carefully remove any contaminants and old sealant residue from the application area using a cleaning agent. This step is crucial, as contaminants trapped inside the sealant can leach out over time, leading to discoloration.
To ensure the compatibility of sealants and connecting materials, a small-scale compatibility test can be performed with the sealant to check for any potential interactions.
During construction, try to avoid factors such as high temperatures and ensure good ventilation. At the same time, avoid mixing neutral and acidic sealants, neutral alcohol-based sealants and neutral oxime-based sealants, or other sealants that may interact with each other.
Maintain a smooth and firm surface on the sealant. Use a spatula or other tool to smooth the surface of the sealant, which facilitates subsequent cleaning and prevents contaminants from accumulating on the sealant. If masking tape was used, remove it promptly.
Try to avoid environmental factors that accelerate the yellowing of sealants
Since various environmental pollutants, high temperatures, and ultraviolet radiation are the main culprits behind sealant yellowing, keeping the sealant away from these environmental factors is a simple and effective method.
Avoid exposing the sealant to corrosive substances and hot environments whenever possible. If the sealant is applied in a humid environment, such as a bathroom, wipe away moisture promptly and ensure proper ventilation to prevent mold growth.
Preventing direct exposure to ultraviolet light can significantly extend the time that the sealant retains its original color.
Ensure proper maintenance is performed after curing
Even the best sealants will gradually yellow and deteriorate due to a lack of maintenance. Therefore, regular cleaning after curing is crucial.
Keep your sealant clean. Regularly clean the sealant surface with water, a neutral detergent, and a soft cloth. Avoid using acidic, alkaline, or high-concentration cleaning agents that can damage the sealant. Also, do not use tools like steel wool that can damage the surface, making it easier for contaminants to adhere.
If using polyurethane sealant or similar materials, you can wait for it to fully cure and then apply a weather-resistant paint to help it better withstand ultraviolet radiation.
If your sealant has turned yellow, you’ll have to replace it.
FAQs:
Why does white and clear silicone sealant turn yellow faster than other colors?
In fact, white and clear silicone sealants don’t age any faster than other colors. The tendency to yellow is more of a visual effect. Once aged, the white and transparent base color makes any color change more noticeable. Furthermore, white sealants contain titanium dioxide, which, while providing UV protection, also undergoes autocatalytic degradation, producing yellowish-brown substances.
Therefore, if you need to use these two colors of silicone sealant, please choose a high-quality product.
What is the difference between silicone sealants and silicone adhesives?
Although similar in chemical composition, the two products have different focuses, and incorrect application could lead to financial losses for your project. Silicone sealants focus on elastic sealing, weather resistance, and preventing yellowing, while silicone adhesives emphasize bonding and fixing functions.
While there are products on the market that combine both sealing and bonding properties, they should never be used in critical applications requiring strong bonding or high elasticity in sealing. However, if you have both of these needs, 100% RTV silicone sealant is a good option.
How to remove yellowed silicone sealant?
Old silicone sealant can be removed using tools such as a utility knife, a specialized sealant removal scraper, a hairdryer, and alcohol. For stubborn old sealant, you can first heat it with a hairdryer, then pry up a corner with a knife and peel off the sealant. Any remaining adhesive residue can be removed with a silicone sealant remover. Finally, wipe the surface clean with alcohol.
Conclusion
The assurance of engineering and product quality comes from attention to every detail and every reliable seal. If you are looking for high-quality silicone sealants, Legensilico will give you peace of mind backed by proven reliability. As a Chinese manufacturer of silicone products, Legensilico provides you with a one-stop service for all your silicone product needs. Choose a reliable silicone sealant for your products!
