Paper-Recycling System: Part 3

In chemical pulping there are two prevailing process principles: the sulfate principle and the sulfite principle. These differ from each other by the type of cooking chemicals used to extract lignin from cellulose fibers. Until the 1960s sulfite technology had a major market share in pulp production, but during the past 20 years it has decreased rapidly and today represents less than 15% of the overall chemical pulp production in Western Europe. In Scandinavia, its share is not greater than 10% of the total chemical pulp. In Central Europe, the share is still about 18%. This process is considered more efficient in processing the main raw wood material in the region (spruce) than the sulfate process. Chemical fiber has a firm position as a raw material for printing - and writing-quality papers not only in Western Europe but also worldwide. One explanation for this position is that the majority of the pulp (about 80%) is bleached. Chlorine is the prevailing bleaching agent. On the other had, advanced cooking methods and substituting bleaching agents have substantially reduced chlorine use during the past 10 years.

Mechanical pulping is more widely used in Scandinavia than in Central Europe, due to a larger share of newsprint production for which mechanical pulp is the main raw material. Basically, there are two processing principles for mechanical pulping: grinding and refining the wood. For both technologies there are several modifications concerning utilization of heat, pressure, chemicals, and so on. A major part of the mechanical pulp is also bleached. Instead of chlorine, however, different peroxides are frequently used as bleaching agents in modern mechanical pulping mills.