Temperature resistance of epoxy

The answer depends on several factors. Each epoxy system has its own level of heat resistance. A frequently asked question we receive is: “What is the heat resistance of epoxy, and how can I increase it?” We’re happy to explain this in more detail. It’s important to know up to what temperature your epoxy can withstand heat and what you can do to improve this after curing. In this article, we’ll give you more information about the heat resistance of your epoxy product. In another article, we’ll discuss working with epxoxy at high temperatures.

1. Composition of epoxy (what happens during curing)

Epoxy is also called a plastic. It concerns so-called thermosetting plastics. That means that, once cured, the plastic can no longer be melted. In addition to thermosetting plastics, there are also thermoplastic plastics. These can be melted again after use, after which other products can be made from them. Epoxy must be weighed and mixed accurately. In case of an incorrect mixing ratio, resin or hardener will remain during the reaction. This results in the epoxy not curing (or not curing completely).

2. Temperature resistance for each epoxy system

Each thermoset has a certain heat resistance. This is called the “glass transition temperature” (Tg). Below the glass transition temperature, the material is hard and glass-like; above this temperature, it becomes rubber-like and somewhat flexible. In the table below, we indicate the heat resistance of the epoxy systems that you can order from us.

* after curing for 7 days at 21°C

3. Increasing the heat resistance of epoxy

As can be seen in the table, it is possible to increase the heat resistance of the product you have made, such as a table or a set of coasters, so that your epoxy product can better withstand heat. This can be done in several ways, which we explain one by one below.

• Option 1: applying a layer of heat-resistant epoxy
  A layer of heat-resistant epoxy helps to keep the surface looking good. If you want a transparent, glossy layer, the Eli-Chem UltraCast Epoxyhars is the best choice. This epoxy has a heat resistance of approximately 70 °C and is therefore well-suited for, for example, a hot cup of coffee or tea. This epoxy is also colourless, cures relatively quickly, and provides a nice surface. The epoxy is UV-resistant, which keeps the appearance intact. You can also use Motip Clear Coat to increase heat resistance. Read the instructions carefully for this. 

   

• Option 2: applying a layer of DD paint
  A layer of DD Paint can also help to increase the heat resistance of the surface. DD paint is a heat-resistant and UV-filtering two-component PU lacquer. It can be brushed, rolled or sprayed and is available in transparent or coloured versions. DD paint increases scratch resistance and the heat resistance of epoxy surfaces.
  
  
• Option 3: post-cure
  The heat resistance of most epoxy systems can be increased with a post-cure. This means allowing the epoxy to cure for several hours at a higher temperature. The required temperature and curing time can be found in the technical datasheet.
  
  Post-cure in a mould: place the mould in the oven after curing at a temperature around the maximum Tg (glass transition temperature).
                                                                                                                                                                                                                                                                                                                         Post-cure outside the mould: increase the temperature gradually. For small castings 10-15 degrees per hour to 15 degrees below Tg. Maintain this temperature for approximately 5 hours.

4. What happens if the temperature exceeds the heat resistance?

The heat resistance indicated in the table below is the so-called “glass transition temperature.” Below this temperature, the material behaves glass-like; above this temperature, it becomes rubber-like. If the temperature exceeds the glass transition temperature, effects can occur such as rings, streaks, bending, or the used glass fiber becoming visible as a relief on the surface.

Only at 200 to 250 °C will the epoxy truly become too hot and lose its chemical structure. At this point, the epoxy begins to char (burn).

More information about heat resistance

Do you have questions about heat resistance, post-cure, or related topics? Feel free to contac our specialists. We are happy to assist you with your project.

T: +31 (0)85 022 00 90
E: support@polyestershoppen.com