Yellowing, oily residue, white powder on the surface, and unpleasant odors are some of the most common quality issues found in silicone rubber products. These problems don't just affect the product's appearance and feel—they can also raise concerns about product quality and safety.
In most cases, these issues are related to the curing system, raw material quality, and post-processing methods. Let's take a closer look at the main causes.
Yellowing is usually caused by chemical reactions inside the material or by long-term environmental exposure.
Silicone rubber cured with peroxide generates small-molecule by-products, such as ketones, during the crosslinking process. These compounds can oxidize over time, causing transparent or light-colored silicone products to turn yellow.
In comparison, platinum-cured addition silicone produces a much cleaner reaction with virtually no by-products, offering significantly better resistance to yellowing.
Long-term exposure to sunlight or high temperatures accelerates photo-oxidation and thermal aging of the silicone polymer, which can gradually lead to discoloration.
Contact with strong acids, strong alkalis, chlorine-based cleaners, or even formaldehyde released from certain packaging materials (such as MDF boards) may also cause silicone products to discolor.
An oily film or white powder on the surface is usually the result of low-molecular-weight compounds migrating out of the silicone.
If the curing temperature is too low or the curing time is too short, the silicone network will not fully develop. As a result, uncrosslinked polymer chains remain inside the material and gradually migrate to the surface, creating an oily appearance.
Additives such as phenyl silicone oil, which are often used to improve flexibility or yellowing resistance, may separate from the base polymer if used in excessive amounts or if compatibility is poor. This can result in oil bleeding on the surface.
If molded silicone parts are not properly post-cured, residual oligomers and volatile compounds remain inside the material. During storage or long-distance transportation—especially when temperature and humidity fluctuate—these substances can migrate to the surface and crystallize, leaving behind a white powder.
High-quality food-grade and medical-grade silicone should be virtually odorless.
If a silicone product has a strong chemical smell, it's usually a sign that something went wrong during manufacturing.
Using recycled silicone or low-purity raw materials may introduce unreacted monomers, low-molecular-weight polymers, or volatile organic compounds (VOCs), all of which can continue releasing unpleasant odors over time.
Some manufacturers reduce costs by adding phthalate plasticizers. Besides producing unpleasant odors, these additives may also present potential health concerns.
As mentioned earlier, peroxide curing creates reaction by-products. If these compounds are not completely removed during post-curing, they can leave a noticeable chemical odor in the finished product.
The most effective way to eliminate yellowing, surface residue, and unwanted odors is to switch from traditional peroxide curing to a high-purity platinum-cured addition system.
To meet the needs of high-end silicone applications, IOTA Silicone Oil has developed the IOTA 81 Series High-Purity Platinum Catalysts.
Manufactured using highly purified platinum sources and produced under strict quality control, the IOTA 81 Series offers several key advantages:
Cleaner curing process: Addition curing produces virtually no volatile by-products, helping prevent odors and yellowing at the source.
Stable crosslinked network: High catalytic efficiency creates a dense and uniform silicone network, significantly reducing the migration of low-molecular-weight compounds that cause oil bleeding or blooming.
Excellent batch consistency: Designed to meet the demanding purity and low-volatility requirements of medical-grade silicone, food-contact silicone, and precision electronic encapsulation materials.
If you'd like to learn more about the IOTA 81 Series High-Purity Platinum Catalysts, request technical data sheets (TDS), or receive formulation recommendations for solving yellowing, odor, or blooming issues in silicone rubber products, feel free to contact IOTA Silicone Oil.
Website: www.siliconeoil.net
Email: zyf@siliconeoil.cn
Our technical team is ready to provide technical support, formulation recommendations, and product selection guidance tailored to your application.
