Puolikemialliset

Puolikemialliset, also known as semichemical pulping, is a method used in the pulp and paper industry to produce paper from wood. It falls between purely mechanical and purely chemical pulping processes. In semichemical pulping, wood chips are first treated with a chemical solution, typically a mild alkaline solution, which softens the lignin that binds the wood fibers together. This chemical pre-treatment helps to reduce the amount of mechanical energy required in the subsequent pulping stage.

Following the chemical treatment, the softened wood chips are subjected to mechanical defibration, usually in a refiner. This mechanical action separates the wood into individual fibers. The result is a pulping process that yields a higher proportion of usable fiber compared to purely mechanical methods, while also retaining more of the wood's lignin than purely chemical methods. This balance allows for the production of pulps with properties that are intermediate between those of groundwood and fully chemically pulped fibers.

The primary advantage of semichemical pulping is its ability to produce a strong pulp with a good yield. The resulting paper often exhibits better strength characteristics, such as tear strength and tensile strength, than paper made from purely mechanical pulp. However, it may not achieve the same level of brightness or printability as papers made from fully bleached chemical pulps. This makes semichemical pulping a versatile option for producing a range of paper grades where a balance of strength, yield, and cost-effectiveness is desired, such as for packaging materials, corrugated board, and some printing papers.