The yellowing of polyurethane foam sponge has been a problem that has perplexed sponge manufacturers and polyol manufacturers for a long time.

Many sponge manufacturers, especially some high-grade sponge manufacturers, try to improve the anti-yellowing performance of sponge by adding antioxidants and light stabilizers, but the effect is not significant.

Ciba Jinghua, as a world-famous supplier of anti-aging additives, has developed IRGASTAB series of antioxidants, especially its revolutionary production of IRGASTAB PUR 68, which fundamentally provides a set of solutions for sponge yellowing. This paper will systematically analyze the causes of sponge yellowing based on the characteristics of polyol and sponge production upstream and downstream, and explain the corresponding solutions.

Generally speaking, from the point of view of additives, the yellowing of sponges includes the following four types:-yellowing of thermal oxygen aging caused by high temperature during sponge foaming / processing，

Gas fumigation caused by exposure to nitrogen oxides in the air (NOx).

Fabric pollution caused by sponge.

Yellowing caused by sponge exposure to ultraviolet rays.

These yellowing are often directly related to antioxidants.

In other words, the presence of antioxidants may have a positive inhibitory effect on some of the above yellowing, for example, the yellowing of thermal oxygen aging caused by high temperature during sponge foaming / processing is inhibited by the addition of antioxidants.

However, it may also play a negative role and promote the occurrence of other kinds of yellowing, for example, amine antioxidants can promote sponge yellowing when exposed to nitrogen oxides in the air (NOx, mainly from automobile exhaust), or ultraviolet rays, while antioxidant BHT is the main cause of fabric contamination.

Usually, polyol manufacturers will add a certain amount of antioxidants to polyols in order to ensure the safe production of downstream foaming manufacturers in the foaming process of polyols.

At present, the main types of antioxidants used by domestic polyether manufacturers are BHT and amine antioxidants or phenothiocyanate compound antioxidants, while international well-known polyether manufacturers mainly choose some high molecular weight hindered phenolic antioxidants, such as Ciba's IRGANOX 1135 (high molecular weight hindered phenolic antioxidants) and IRGANOX 5057 (amine antioxidants).

As a sponge market manufacturer, when getting a polyol, except for safety, cost and foaming performance, it is rare to evaluate the effect of antioxidant system in polyol on sponge yellowing.

However, this factor, which is often overlooked, hides the important reasons that affect the yellowing of the sponge.

Usually in the ideal condition, the antioxidant existing in polyol can inhibit the aging and degradation of polymer caused by the high temperature produced by foam itself, which ensures the safe production of sponge foaming process. it also effectively prevents the core yellowing in the process of sponge foaming.

However, with the completion of sponge foaming, the antioxidants left in the sponge are easy to cause the yellowing of many sponges.