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 advanced sponge manufacturers have tried to improve the anti-yellowing function of the sponge by adding antioxidants and light stabilizers, but the effect is not obvious. Generally, analyzing the yellowing of sponge from the viewpoint of increasing agent includes the following four types:
1. During the foaming and processing of the sponge, the yellowing due to thermal oxidative aging caused by high temperature;
2. The fume yellowing caused by touching the nitrogen oxides (NOx) in the air;
3. Fabric pollution caused by sponge;
4. Yellowing caused by the sponge touching 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: sponge foaming, thermal oxidative aging and yellowing caused by high temperature in the processing process are suppressed by adding antioxidants. However, it can also have a negative effect and promote the yellowing of other varieties. For example, when amine antioxidants touch the nitrogen oxides in the air (NOx, mainly from automobile exhaust), or ultraviolet rays, they will promote yellowing of the sponge; and the antioxidant BHT is the primary cause of fabric pollution.
Generally speaking, polyol manufacturers will add a certain amount of antioxidants to polyols, the intention is to ensure the safe production of downstream foaming manufacturers in the process of using polyol foaming. As a sponge market manufacturer, when getting a polyol, in addition to thinking about safety, cost and foaming function, it rarely 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 for the yellowing of the sponge.
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