Puolikemiallisia

Puolikemiallisia is a Finnish term that translates to "semi-chemical" in English. It is most commonly used in the context of paper manufacturing and refers to a pulping process that falls between mechanical and fully chemical pulping. In semi-chemical pulping, wood chips are treated with a pulping liquor, but the process is less severe than in fully chemical methods like the Kraft process. This means that while some of the lignin binding the wood fibers together is dissolved, a significant portion remains.

The goal of semi-chemical pulping is to achieve a balance between fiber yield and paper strength. Mechanical pulping produces high yields of fiber but results in weaker paper due to the presence of most of the wood's lignin and shorter fiber fragments. Fully chemical pulping removes almost all lignin, producing strong fibers but at a lower yield. Semi-chemical pulping offers a compromise, yielding more fiber than chemical pulping while producing stronger paper than purely mechanical pulping.

The resulting pulp from semi-chemical processes typically has a higher burst strength and tensile strength compared to mechanical pulps. This makes it suitable for a range of paper products, including corrugated board, packaging papers, and some types of printing paper where a balance of strength and cost-effectiveness is desired. The specific chemicals and cooking conditions used in semi-chemical pulping can vary, influencing the properties of the final pulp.