How to solve the core burning problem of PU foam?


Polyurethane is mainly divided into molded flexible foam, block flexible foam, rigid foam, thermoplastic polyurethane elastomers(TPU), etc.. It’s widely used in household material (sofa, mattress), building materials, thermal insulation materials and automotive seat/ interior material.


>> What’s polyurethane core burning problem?

The oxidative stability of polyurethanes depends on the structure, especially the chemical structure of the polyol. Polyester-based polyurethanes usually have better thermal and oxygen stability than polyether-based polyurethanes.

During polyurethane foaming, a large amount of heat is released due to the reaction of the polyol with the isocyanate. In the presence of oxygen, methylene groups adjacent to the -O- group are oxidized to peroxide groups in a rapid reaction. When temperatures up to 160°C, it may result in a yellow/brown discoloration, also called as core burning problem.


>> Why does the core burning occur in the production process of PU foam? And how to solve?

> Problems with the quality of polyether polyol:

A. Excessive water in the product during production, storage or transportation. 

B. High content of peroxide or low boiling point impurities

C. High concentration of metal ions, and improper type and concentration of antioxidant.

> Formulation:

A. TDI index is too high

B. The proportion of water and physical blowing agent in the blowing agent is improper

> Climatic influences:

Too hot in the summer, heat dissipation becomes slow, reaction center temperature exceeds the antioxidant temperature. 


Therefore, choosing suitable antioxidants to prevent uncontrolled oxidative degradation is the most direct and effective way to solve the problem of PU foam core burning.

OMNISTAB AN6133 could quickly stabilize free radicals generated by oxidative degradation, reduces heat generation and decreases core yellowing.

More importantly, it's no phenol, low volatile and Eco-friendly. AN6133 also could be used in PU coating and adhesive, to improve the thermal stability, and slow down the yellowing problem.


>> How to solve the problem of yellowing of PU foam during storage and use?

Because the structure of polyurethane contains both amino group, which is easy to be oxidized and yellowed, and unsaturated bond which is easy to be yellowed by ultraviolet rays, so polyurethane products are very easy to be yellowed during storage and use. Therefore, the addition of UV absorber and light stabilizer to PU foam formula is critical. We’d like to recommend the solution of "OMNISTAB UV571+OMNISTAB LS292+ AN6133", which can effectively solve the problem of yellowing caused by UV oxidative degradation, so as to enhance the overall aesthetics and service life of PU foams!

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