Why is the sponge yellowing

Release time：2018/5/14 17:41:20

For you to explain why the sponge is yellow, the yellowing of the polyurethane foam sponges has been a problem that has long been a perplex for the manufacturers of sponges and polyols. Many manufacturers of sponges, especially some high-grade sponge manufacturers, try to improve the anti yellowing properties of sponges by adding antioxidants and light stabilizers, but the effect is not significant. Based on the characteristics of polyols and sponge production, this paper systematically analyzes the causes of sponge yellowing and expounds the corresponding solutions.

Generally speaking, from the perspective of additives, the yellowing of sponges includes the following four kinds:

1, Fabric pollution caused by sponges

2. The yellowing caused by the exposure of the sponge to ultraviolet light

3, Sponge foam / processing process, due to high temperature caused by thermal oxidative aging yellow.

4, Contact with air nitrogen oxides (NOx) caused by fumigation yellow.

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 yellow variations, for example, the heat oxygen aging yellow caused by high temperature in the foam / processing process is suppressed by adding antioxidants; however, it may also play a negative role and promote the occurrence of other types of yellowing, such as amines. Antioxidants in contact with the air (NOx, mainly from automobile exhaust), or ultraviolet light, can promote the transformation of the sponge, and the antioxidant BHT, the main cause of the fabric pollution.

As a sponge Market manufacturer, in addition to the safety, cost and foaming performance of a polyol, the effect of antioxidant system in polyol on the change of sponge yellowing was rarely evaluated. This factor, which is often ignored by everyone, hides the important cause of sponge yellowing.

Usually in the ideal state, the antioxidant in the polyol, in the foam process, can inhibit the aging and degradation of the polymer due to the high temperature produced by the foaming itself, which not only ensures the safe production of the foam foaming process, but also effectively prevents the problem of the core yellowing during the foam foaming process. However, with the completion of sponge foaming, the antioxidants remaining in the sponge can easily cause the yellowing of many sponges.

Usually, polyol manufacturers will add a certain amount of antioxidant in polyol, the purpose is to ensure the downstream foaming manufacturers, in the use of polyol foaming process in the process of safe production. At present, the main types of antioxidants used in domestic polyether producers are the compound antioxidant system of BHT and amine antioxidants or phenothiano, while one of the famous international polyether producers is mainly selected with some macromolecular blocking phenolic antioxidants and amine antioxidants.

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