The natural colour of lignin is about that of wood, but during the pulping process it tends to darken in colour. Consequently, the lignin must be removed if the user requires a product that is white and bright and resists the effects of aging. Chlorine dioxide and hydrogen peroxide are now the most common bleaching agents used by pulp mills in Canada. Transition in bleaching Canadian bleaching technology has undergone a profound transition as producers and researchers search for the best ways to satisfy customer demands and maintain quality while minimizing the effects on the environment.
ECF pulp refers to pulp bleached without chlorine gas.
Its manufacture is an extension of dioxin control technology. All chlorine is replaced by chlorine dioxide and the lignin content of pulp is reduced to as low a level as possible before bleaching. Research with ozone has been conducted on a laboratory and pilot scale in Paprican and around the world for many years. Ozone's effectiveness is hampered by the rapid, non-selective nature of its reactions which can cause losses in pulp strength and uniformity Activated oxygen. A novel form of activated oxygen is very effective at delignifying and brightening chemical pulps.