Analysis and Fate of Lipophilic Extractives in Sulphite Pulps

One of the major requirements of sulphite pulps, particularly those used in the manufacture of dissolving grades, is that their extractives content must not exceed certain levels, as specified by the customer. Since these levels are generally very low, the accuracy and reproducibility of extractives measurements can be poor, which in turn can lead to disagreements between pulp suppliers and their customers. In an effort to improve the reliability of extractives measurements, we have evaluated several methods for the determination of lipophilic extractives in sulphite pulps, using Soxhlet and Soxtec solvent extraction and various modes of drying the extracts including hot plate, infrared lamp, and freeze drying. Analysis of the extracts by size exclusion chromatography showed that a significant portion of the extracts was polymerized during the production process. Lipophilic extractives from ammonium sulphite pulps contain more polymerized matter than the extractives from the magnesium process.