The pulp obtained by chemical method and mechanical method is called the color paste, usually yellow or brown, in order to meet the requirements of the paper we use and the aesthetic effect, we need to bleaching the pulp, bleaching is to use the appropriate bleach through oxidation, reduction or decomposition requirements, the lignin in the pulp precipitation, or fade, so that the pulp becomes white.
Next let's look at some of the ways bleaching is commonly used.
1, oxidative bleaching method, the use of oxidative bleach, such as hypochlorite, etc., to destroy the structure of lignin, dissolve it, to achieve the purpose of improving the whiteness of the pulp, but this chlorine bleach pollution to the environment is relatively large, so gradually replaced by oxygen bleaching method.
2, reduction bleaching method, the use of reducing bleach to change the structure of the color base group, so that it is more suitable for grinding wood pulp, chemical machinery and other high pulp pulp bleaching use, because it will not cause the loss of fiber components, and can maintain the characteristics of the original pulp. However, the stability of the whiteness of the paper made by this bleaching method is relatively poor, and the original color will be restored after a period of light.
