Factors Affecting The Yellowing Of Sponges
The yellowing of polyurethane soft foam sponge has always been a question that has puzzled sponge manufacturers and polyol manufacturers for a long time. Many sponge manufacturers, especially some high-end sponge manufacturers, try to improve the anti-yellowing function of sponges by adding antioxidants and light stabilizers, but the effect is not obvious.
Generally, it is analyzed from the viewpoint of the additive. The yellowing of sponges includes the following four types:
1. In the process of foaming and processing of sponge, yellowing due to thermal oxygen aging caused by high temperature;
2. Yellowing caused by touching nitrogen oxides (NOx) in the air;
3. Fabric contamination caused by sponge;
4. Yellowing caused by the sponge touching the UV light.
These yellowing changes 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, such as: sponge foaming, thermal oxidative aging yellowing caused by high temperature during processing is inhibited by adding antioxidants. However, it can also have a negative effect and promote the occurrence of other types of yellowing, such as: amine antioxidants in contact with nitrogen oxides (NOx, mainly from car exhaust) in the air, or ultraviolet rays, will promote the yellowing of sponges; The antioxidant BHT is the primary cause of fabric pollution.
Generally speaking, polyol manufacturers will add a certain amount of antioxidants to polyols in order to ensure the safe production of downstream foam manufacturers in the process of using polyol foaming. At present, the main type of antioxidant used by domestic polyether manufacturers is the compound antioxidant system of BHT and amine antioxidants or phenthianine. As a sponge market manufacturer, when getting a polyol, in addition to thinking about safety, cost and foaming function, it seldom evaluates 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 the sponge.
