What is involved in pulp bleaching?

As an important element of paper products creation is a bleaching pulp by a multi -stage process in which the residual lignin is destroyed or removed to visually brightens the final product. Lignin, an organic compound that serves to rigidate tree cells, plays an important role in the color of the pulp. Thus, whitening pulp involves breaking the lignin into smaller molecules to achieve brightness. In general, the more lignin remains in the final product, the more likely it is to gradually be yellow due to exposure to air or light. The act of delignification tends to include several different steps of processing, because the whitening process on one step would probably adversely affect the overall power of the pulp.

There are two possible approaches to the chemical process whitening. If the final product is desirable to maintain a high percentage of pulp and reach up to 70 percent of potential brightness, the best approach is to break lignin to minimize its effects on ULP pzolor. For brightness 90 pRocent or higher with certain fiber losses must be almost completely removed. The brightness is defined as the degree of ability to reflect light. In both process, the dissolved lignin is washed out of the pulp between the processing phases.

Traditionally, the common whitening process was referred to as Cehded or Ceded in which letters indicate the order of use of specific chemicals. The CEHDED process included the following steps: chlorine (C); Alkaline extraction (E); Hypochlorate (H); chlorine oxide (D); More alkaline extraction (E); and more chlorine oxide (D). For the assignment, the Hypochlorat (H) step (H) was removed.

processes used in mechanical pulp bleaching were not considered to be a negative environmental effect, since the chemicals usually used in these processes tend to produce by -products that Azn's relatively benign. On the other hand, a whitening chemical pulp may lead to damage to lifeThe environment, especially due to organic materials released into neighboring water bodies. The 30th century before the 20th century was a bayonet of household or sodium hypochlorite usually a means of whitening; Later, the chlorine was a bleaching element. Since 1990, demolition of pulp has been more commonly used by newer processes that do not use chlorine. These processes are commonly known as without an element (ECF) that may contain a certain amount of chlorine oxide and completely chlorine (TCF), which uses chemicals such as hydrogen peroxide, oxygen or ozone instead of chlorine.