Sulfittmasse

Sulfittmasse, or sulfite pulp, is a type of chemical pulp produced by the sulfite pulping process. In this method, wood chips are cooked in an acidic solution containing sulfurous acid and bisulfite, which promotes the hydrolysis and solubilization of lignin while preserving most of the cellulose fibers. The cooking liquor may use different counterions (such as sodium, calcium, magnesium, or ammonium bisulfite), giving rise to slightly different sulfite pulps. The process typically operates under low pH, and the spent liquor contains lignin sulfonates that are removed with the waste stream.

The resulting pulp generally has higher residual lignin content than kraft pulps and a different fiber morphology, often with lower tear strength and distinct drainage properties. Sulfite pulps tend to bleach more easily and can produce very bright papers, which historically made them favorable for fine printing papers and for dissolving pulps used in regenerated cellulose fibers. Yields are commonly high, but the mechanical strength of sulfite pulps is usually lower than that of kraft pulps. Some variants are used to produce dissolving pulp for viscose and other regenerated fibers.

In modern industry, kraft pulping has largely supplanted sulfite pulping in many regions due to stronger pulps and more efficient chemical recovery, but sulfite pulps remain in use for specific grades, especially dissolving pulps and certain high-bleach, high-brightness papers. Environmental considerations center on acidic effluents from the cooking liquor and the management of sulfur-containing compounds, which require proper treatment and recovery.