POLYSACCHARIDES DISSOLVED FROM NORWAY SPRUCE IN THERMOMECHANICAL PULPING AND PEROXIDE BLEACHING

Methanolysis, followed by GC analysis, was used to determine the amoun t and composition of sugar units comprising the carbohydrates present in water samples from unbleached and peroxide bleached thermomechanica l pulp (TMP). Circulation experiments were carried out in the laborato ry to simulate white water system closure in mechanical pulp mills. Wa ter samples from simulated ''closed'' water systems were fractionated to determine the composition of the neutral and anionic polysaccharide s released from the TMP samples. Decreasing fresh water consumption fr om 100 to 10 m3/t, for both unbleached and peroxide bleached TMP, had little influence on the overall sugar composition of the carbohydrates in the water samples. Alkaline peroxide bleaching resulted in substan tial changes in the sugar composition of the carbohydrates comprising the dissolved and colloidal substances (DCS) in the water samples. The polysaccharides released from unbleached TMP were comprised of neutra l (88%) and anionic (12%) polysaccharides. The neutral polysaccharides were mostly O-acetyl-galactoglucomannans and the anionic polysacchari des were mostly arabinogalactans. The galactoglucomannans, partially a cetylated when dissolved in the unbleached suspension, were deacetylat ed by the alkaline conditions of peroxide bleaching, thereby causing t heir substantial adsorption onto the TMP fibers. The anionic arabinoga lactans probably originated from heartwood present in the TMP furnish. About half of the dissolved polysaccharides present after peroxide bl eaching were neutral, probably comprised mostly of galactoglucomannans . Anionic galacturonans and arabino-(4-O-methylglucurono)xylans were r eleased from the pulp in peroxide bleaching. Anionic arabinogalactans were also present after alkaline peroxide bleaching.