Recovery of water-soluble acetylgalactoglucomannans from mechanical pulp of spruce.

Application: The method described in this paper enables mills producing mechanical pulp and wood-containing paper to improve runnability and paper strength and produce valuable by-products for commercialization.

This paper presents a method for recovering acetylgalactoglucomannans from mechanical pulp at a yield of 5 kg/ton pulp, at 95% purity. The acetylgalactoglucomannans can be obtained in dry state for later use or as a concentrate for targeted use in the wet end of the paper machine. Possible benefits of using mannans in the wet end include improved paper machine runnability and better paper strength. This method also provides a convenient means of interstage washing in a mechanical pulp mill, with the additional benefit of possible recovery of valuable substances such as wood resin and aromatic substances, including lignans. In the method, TMP water, containing dissolved and colloidal substances, is prepared from mechanical pulp. A cationic organic coagulant, followed by filtration, serves to remove dispersed colloidal wood resin. Dissolved aromatic substances, mainly lignans and lignin, are then removed by sorption to polyacrylate resin. Further purification is accomplished by membrane filtration using a 20 kDa filter, giving a concentrate enriched in acetylgalactoglucomannans that can be used as such in the wet end of the paper machine. Pure acetylgalactoglucomannans are recovered for later use by precipitating the acetylgalactoglucomannans in ethanol. We also discuss some alternative purification and drying steps.

Willfor, Rehn, Anna Sundberg and Holmbom are with the Abo Akademi University, Process Chemistry Group, c/o Laboratory of Forest Products Chemistry, Porthansgatan 3, FIN-20500 Turku, Finland; Kenneth Sundberg is with Raisio Chemicals Oy, P.O. Box 101, FIN-21201 Raisio, Finland Email Willfor at [e-mail].