Recovery of water-soluble acetylgalactoglucomannans from mechanical pulp of spruce

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 wet-end of the paper machine. Possible benifits 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 benifit of possible recovery of valuable substances such as wood resin and aromatic substances, including lignans. In the method, TMP water, containing dissolved and colloidal sucstances, 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 poly-acrylate resin. Futher purification is accomplised 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.