Generally, from the perspective of additives, the yellowing of sponges includes the following four types:
1. During the sponge foaming/processing process, thermal oxidation yellowing due to high temperature
2. Gas fumigation and yellowing caused by touching nitrogen oxides (NOX) in the air
3. Fabric pollution caused by sponge
4. The yellowing of the sponge caused by exposure to ultraviolet rays
These yellowings are often directly related to antioxidants. In other words, the presence of antioxidants can have a positive inhibitory effect on some of the above yellowing. For example, the anti-aging yellowing caused by high temperature in the foaming sponge/processing process is suppressed by adding antioxidants. However, it can also have a negative effect and promote the occurrence of other types of yellowing, for example: amine antioxidants in contact with nitrogen oxides (NOX, mainly from automobile exhaust) in the air, or ultraviolet rays, will promote the yellowing of sponges, Antioxidant BHT is the primary cause of fabric pollution
Generally, polyol manufacturers add a certain amount of antioxidants to polyols, the purpose of which is to ensure the safe production of downstream foaming manufacturers in the process of using polyols for foaming. At present, the main type of antioxidant used by domestic polyether manufacturers is the compound antioxidant system of BHT and amine antioxidant or phenothiazine, while some world-renowned polyether manufacturers mainly use some large molecular weight antioxidants. Hindered phenolic antioxidants, and amine antioxidants.
As a sponge manufacturer, when getting a polyol, in addition to considering safety, cost and foaming function, seldom evaluate the effect of the antioxidant system in the polyol on the yellowing of the sponge. And this factor, which is often overlooked by us, hides an important reason that affects the yellowing of sponges. Generally ideally, the antioxidants present in polyols can inhibit the aging and degradation of polymers due to the high temperature generated by the foaming itself during the sponge foaming process, which not only ensures the safe production of the sponge foaming process , and effectively avoid the problem of yellowing of the core during the foaming process of the sponge. However, as the foaming of the sponge is completed, the antioxidants remaining in the sponge can easily cause the yellowing of many sponges. The anti-yellowing solution for auditorium chairs and theater chair sponges we recommend is: "Select high-performance polyethers that do not contain BHT and amine antioxidants"
