märkäkirkkaustuminen

märkäkirkkaustuminen is a Finnish term that translates to "wet brightening" in English. It refers to a process used in the paper industry, particularly in the production of mechanical pulp, to improve the brightness of the pulp. This method is employed when the pulp is still in a wet state, hence the name.

The primary goal of märkäkirkkaustuminen is to increase the whiteness and brightness of paper. This is achieved by reducing or eliminating the colored impurities present in the wood fibers. These impurities can include lignin, a complex polymer that gives wood its rigidity but also contributes to yellowness in pulp.

This process typically involves the use of chemical bleaching agents. Common chemicals used include hydrogen peroxide or sodium dithionite. These chemicals react with the chromophores, which are the parts of molecules responsible for color, within the wood fibers, breaking them down or transforming them into colorless compounds. The pulp is kept wet throughout this chemical treatment.

Compared to dry brightening processes, wet brightening is often considered more efficient for certain types of pulp and can be carried out at lower temperatures. It is a crucial step in producing high-quality paper products where brightness is a key aesthetic and functional requirement, such as printing paper, writing paper, and tissue paper. The specific chemicals and conditions used can be tailored to the type of wood and the desired final brightness level.