Curing silicone is a process that has been around for well over 100 years. It’s certainly not a process we invented but definitely one we feel we’ve perfected. At Eyce, our silicone products are made from a process called platinum curing. But silicone can be refined from its raw form in a number of different curing processes. The most common is known as peroxide curing. When setting out to create a silicone product, it’s important to understand the differences between the curing process and what that means for the quality of a final product.
What is silicone?
Silicone is an odorless polymer composed of carbon, hydrogen, oxygen, and primarily silicon - which is found naturally in sand, quartz, and rocks. It’s an incredibly flexible material that is durable and able to withstand exposure to high temperatures.
To create silicone, it must be cured. Silicone curing is defined as the fundamental chemical process used in polymer chemistry for crosslinking polymer chains - so basically it’s taking a liquid and making it a hardened solid in a desired shape and size. During production, a catalyst must be added to make silicone cure - once the catalyst is added the raw rubber will harden and set to the final product. Using a peroxide catalyst is the cheapest and most common catalyst. The type of catalyst used has serious effects on the outcome of the product - the catalyst can impact the products appearance, physical properties, and chemical properties.
When curing silicone, there are two curing systems that are most commonly used - platinum cure systems and peroxide cure systems. The different curing systems create silicone products with different properties with different pros and cons for each. Because of the very different products created by either cure system, it’s important to research which type of catalyst works best for specific silicone applications.
Platinum cured silicone is a relatively new way of curing raw silicone. In a platinum cure system, the only catalyst introduced to the raw silicone is platinum - a precious metal. Because in a platinum-cure system we’re adding platinum to the raw silicone to create a catalyst - it’s considered addition curing. Where peroxide curing uses a process called free radical curing.
When raw silicone is introduced to platinum, a hydride- and a vinyl-functional siloxane polymer react creating an ethyl bridge between the two. This bridge is what bonds the raw silicone giving it its increased strength and durability. It’s also because of this bridge that the reaction has no by-products, a huge advantage over peroxide cured silicone.
Platinum cured silicone is considered best for applications where purity is a concern like medical equipment, food and beverage goods, and in our case, smoking pipes. When comparing platinum cure products and peroxide cure products you can physically see the difference in products - because of the lack of by-products, platinum cured silicone is often clearer and less oily than peroxide cured products.
Platinum cured silicone is also considered to have the best elongation and tensile strength compared to other curing methods. It’s best for applications where the product may experience long term exposure to heat or tension and has the ability to be shaped into products with detailed customization and incredible hardness.
While platinum-cure silicone creates the highest quality silicone product, it does have a few cons. Platinum-cure systems tend to be more expensive and require a high temperature for curing. It also requires extreme care when handling - platinum cure systems are highly susceptible to contamination that would inhibit its ability to cure. Because of this, extreme care needs to be taken when curing with platinum. However the higher production cost and cleaner process from start to finish creates a higher quality product that in the long run is ready to stand the test of time.
Crosslinking, or curing, with peroxide has been around since the early 1900’s. It’s long been the customary approach to curing silicone because of it’s cost-effectiveness. The raw ingredients are often cheaper to acquire and the final product is often easier to produce thanks to lower temperatures required to cure the silicone. To stimulate crosslinking, raw silicone requires a very small amount of peroxide catalyst. The small amount and low costs often make peroxide cured silicone a favorable option for producers
The chemistry behind peroxide curing is a fairly straightforward process using just silicone resins and different kinds of peroxide to create a catalyst. A catalyst, by definition, is a substance that facilitates a forward chemical reaction without being depleted as the reaction takes place. In peroxide curing, the first step in the chemical reaction is the spontaneous formation of peroxide radicals. The radicals break down double bonds in the raw silicone structure which then allows the site where the double bond broke to form a single bond with groups on another silicone chain through a number of reaction pathways. The bonds that stretch between the various silicone chains form a crosslink. The crosslinking created between silicone chains is what causes an increase in strength while curing silicone.
While curing with a peroxide-cure system, the process can create by-products which gives the silicone an oily or greasy feel. This phenomenon is known as “blooming”. Blooming occurs when the left-over catalyst rises to the surface of the silicone, forming a powdery white substance - or the “bloom”. Unfortunately, the bloom typically consists of volatile organic acids and needs to be removed. To remove the bloom, the silicone must undergo a post-cure process where the silicone is heated in a controlled and ventilated environment to burn off the bloom. The process removes most of the remaining catalyst but is still considered unsuitable for food grade applications as trace amounts of remaining catalyst are undesirable due to the contamination concerns.
To stimulate crosslinking, raw silicone requires a very small amount of peroxide catalyst. The small amount and low costs often make peroxide cured silicone a favorable option for producers. Peroxide cured products are considered safe for mechanical and construction applications - situations where durability is a greater concern than purity. Peroxide cured silicone is not considered food or medical grade because there’s no way to guarantee trace amounts of the catalyst weren’t left behind.
While peroxide-cure systems have been commonplace for a long time, the newer platinum-cure systems have clear benefits despite the higher cost. We take pride in never cutting corners and creating the highest quality product we can for our customers. The use of platinum-cure systems is yet another way Eyce differentiates itself from other silicone products on the market. The Eyce Icon Collection is crafted from the highest quality platinum-cured silicone, which you now know is the most durable, cleanest, and safest silicone on the market.