Say you’re planning to use epoxy to glue, coat, or insulate something. You’ve used it on several materials, except for silicone. So now you’re wondering – will this resin work on this surface and what else can I use instead?
Epoxy will not stick to silicone because of silicone’s low surface energy. The molecular force between these two surfaces is weak, which is why epoxy doesn’t adhere to silicone surfaces.
Apart from explaining why epoxy doesn’t stick with silicone, I’ll also discuss the workarounds to this issue. Additionally, I’ll provide you a list of the best epoxy alternatives to work on a silicone surface.
Why Epoxy Doesn’t Stick to Silicone
Epoxy is a resin borne by the reaction of two chemical compounds. It’s tough and chemically resistant, which is why many use it for various projects. Although epoxy adheres to most surfaces, it doesn’t stick to silicone because of the latter’s low surface energy.
Surface energy refers to the force between the molecules of each surface, which allows products to attract or stick to one another. Materials with low surface energy – less than 36 dynes/cm – will not bond well with other materials.
Silicone only has a surface energy of 24 dynes/cm, which is why epoxy slides off it.
Think about Teflon, the material used to coat frying pans, which has a low surface energy of 24 dynes/cm. This surface energy prevents the food from sticking to the pan.
How Do You Make Epoxy Stick to Silicone?
Although epoxy slides off silicone, there are workarounds to this problem. You can make both surfaces ‘cling’ to one another with the help of the following:
Silicone Primer
Also known as silane primer, it makes silicone more adherent to silicone adhesives, acrylates, and of course, epoxies. It works just like paint primer, which helps paint stick better to the surface. Silanes do this by creating a compatible interface that promotes adhesion.
Corona Treatment
This process applies an electric discharge on the surface, which helps form an oxidizing layer and increasing the silicone’s low surface energy value. Additionally, corona treatment promotes wetting.
It helps liquids (epoxy in this case) to maintain firm ‘contact’ with a solid surface (silicone).
What Else Sticks to Silicone?
No time or budget for a silicone primer or treatment? No problem. You don’t have to abandon your project for good. All you need to do is use these adhesives that stick to silicone better than epoxy.
Pressure-Sensitive Adhesives
As the name suggests, this requires pressure to make things stick with each other. Compared to epoxies that solidify, pressure-sensitive adhesives remain tacky. They help wet the surface, which, as mentioned, keeps firm contact between two surfaces.
Heat-Cured Silicone Adhesives
Such products make use of platinum catalysts for neutral and non-corrosive adhesion. While this works well enough on silicone, you may strengthen its adhesive property further by:
- Curing the adhesive longer or at higher temperatures.
- Keeping the cured adhesive in a high-temperature area.
- Using a specialist primer.
Room Temperature Vulcanization Silicone
Also known as RTV silicone, it uses a tin or platinum compound to cure at room temperature.
Since it produces fine details, RTV silicone is perfect for artistic silicone projects (i.e., making sculptures or furniture).
What Sticks to Epoxy – and What Doesn’t
If you don’t have access to the primers and treatments stated above, you might think about replacing the silicone instead. Should you do so, don’t just go out and buy anything else. Many other materials, like silicone, don’t stick to epoxy.
You can prevent the same issue by avoiding these non-epoxy-sticking materials:
- Vinyl
- Rubber
- High-density polyethylene
- Wax Paper
- Parchment Paper
- Sheathing Tape
- Plastic bags and other containers
- Hot glue
Like silicone, these materials have low surface energies. As a result, epoxy slips off them.
On the other hand, if you’re looking for materials that adhere well to epoxy, then you should pick any of these:
- Wood
- Metal
- Cured polyester fiberglass
- Some plastics
Conclusion
Epoxy doesn’t stick to silicone because of the latter’s low surface value, as it’s just like Teflon, meaning epoxy will slide off the silicone’s surface. Although this is the case, you can make epoxy stick to silicone with the help of a primer or corona treatment.
Sans these options, you can go for adhesives that stick better to silicone. Excellent choices include pressure-sensitive adhesives, heat-cured silicone adhesives, and room-temperature vulcanization silicone.
Likewise, you can replace silicone with other products that adhere better to epoxy. These include wood, metal, cured polyester fiberglass, and some plastic materials.
