🧪 Non-toxic insulating foams

Polyurethane foams are found in many everyday objects. A study published in Chemical Engineering Journal shows how to produce similar foams without using isocyanates.

Polyurethane foams are widely used to insulate buildings, make mattresses, or protect objects during transport. Their lightweight structure, filled with small bubbles, gives them excellent insulating properties. To manufacture them, industries typically use two main ingredients: a polyol and a polyisocyanate.


When these two substances react, they form a solid molecular network that constitutes the foam's framework. At the same time, isocyanates also react with water and produce carbon dioxide. This gas creates the bubbles that cause the material to expand while the polymer solidifies.

Thus, isocyanates play two essential roles: they participate in forming the solid material and produce some of the gas that creates the foam. However, these compounds are also known for their toxicity before reacting, particularly to the skin and respiratory tract. Therefore, their use is increasingly regulated.

To find an alternative, researchers from the Charles Sadron Institute (CNRS), in collaboration with the company SOPREMA, studied another chemical reaction called the aza-Michael reaction. It is based on the reaction between two types of molecules: an amine and an acrylate.

These two liquids react easily together without a solvent or catalyst. Their reaction gradually forms a solid polymer network, comparable in function to that of polyurethane foams. The advantage is that no isocyanate is required.

However, this reaction does not produce carbon dioxide. To create the bubbles characteristic of a foam, the researchers therefore use a blowing agent called cyclopentane. Under the effect of the heat from the chemical reaction, this compound evaporates and creates cavities in the material.

The entire challenge then lies in synchronizing two phenomena. The chemical reaction must release enough heat to evaporate the blowing agent, but not too quickly, so that the structure has time to solidify and trap the bubbles.

To solve this problem, the researchers conceived a two-step manufacturing process. They start with a pre-reaction using an excess of amine. This step allows better control of the mixture's viscosity, the reaction speed, and the heat produced.

By adjusting this first step, the team managed to produce a rigid foam capable of recovering up to 95% of its height after being heavily compressed. The resulting structure consists mostly of open cells.

The insulating performance is still slightly inferior to that of the best commercial foams. But the researchers believe that optimizing the internal structure and blowing agents could improve these results.

This approach shows that it is possible to manufacture rigid polymer foams without using isocyanates. In the long run, it could enable the production of insulating materials that are safer for health and more sustainable.