Bleaching sequences can be divided into two segments depends on their function such as delignification segment and brightening segment. The function of delignification agent is to remove the lignin. Normally the initial stages of a sequence are delignification segment; the oxygen and chlorination stages are included in this segment. The main function of brightening agent is to raise the brightness of the pulp. The hypochlorite, Chlorine dioxide, hydrogen peroxide etc stages are included into this segment. Usually, the most of the brightening segment chemicals are highly selective chemicals (such as Chlorine dioxide and hydrogen peroxide) and that are used in later stages when the lignin content are low and the cellulose is vulnerable to degradation.