What is the purpose of bleaching pulp?

　　Pulps obtained by chemical and mechanical processes are called natural pulps, and the natural pulps have a certain color (usually yellow or brown). In order to meet the requirements of the paper, the pulp must be bleached so that the paper has a high degree of whiteness. Bleaching is the use of a suitable bleaching agent to oxidize, reduce or decompose the reaction to dissolve the remaining lignin in the pulp, or discolor the colored matter while leaving the lignin.

　　What are the common ways to bleach paper pulp?

　　There are two commonly used bleached pulp methods:

　　One is the oxidative bleaching method, which uses an oxidizing bleach to destroy the structure of lignin and dissolve it so as to increase the purity and whiteness of the pulp. Such bleaches include Cl2, Clo2, and hypochlorite. Oxidative bleaching is still the main bleaching method. Oxidizing bleaches are bleached by chlorine and are heavily contaminated and will be gradually replaced by oxygen bleaching methods.

　　The other is the reduction bleaching method, which uses a reducing bleach to change the structure of the chromophoric groups and decolorize them. Because it does not cause the loss of fiber components, and can maintain the characteristics of the original slurry, it is particularly suitable for bleaching wood pulp, chemical mechanical pulp and other pulp slurry. Such bleaching agents include zinc dithionite, sodium hyposulfite, hydrogen peroxide and sodium peroxide. The paper bleached bleached pulp has poor whiteness stability and will return to its original color after being exposed to light in the air for a long period of time.

　　Of course, in the bleaching practice, one method cannot be used to float the pulp to a higher degree of whiteness, and a variety of bleaching methods are often used in combination, that is, so-called multi-stage bleaching, such as three-stage bleaching, five-stage bleaching, and the like. Pick up the picking of fresh peppers, picking and picking.

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