Weakening of paper strength by wood resin

The effects of retained wood resin and polysaccharides on paper strength, o ptical properties and friction were studied. Wood resin, glucomannans and p ectic acids were extracted from TMP. The wood resin was added in colloidal form to the fibre suspensions and aggregated by the addition of cationic po lymers or electrolytes. In part of the tests, polysaccharides isolated from TMP were also added. Hand sheets were made and tested. The amounts of resi n and polysaccharides in the sheets were determined by extraction and gas c hromatography. The strength properties of the sheets weakened when the amount of wood resi n was increased up to 2 mg/g fibres. Above 2 mg/g, no significant further d ecrease in strength properties was obtained. The static friction was lowere d when the amount of wood resin was increased in the sheets. However, the o ptical properties were not significantly affected, even at high resin conte nts. When polysaccharides were added to fibre suspensions, together with wood re sin, the strength properties were higher compared, at the same resin conten t, to sheets without added polysaccharides. Glucomannans and pectic acids e specially diminished the negative effect on paper strength caused by high r esin content. Some of the polysaccharides were probably adsorbed onto the s urface of the TMP fibres or wood resin droplets, which increased the hydrop hilicity of the surfaces, thereby promoting the formation of the hydrogen, or other, bonds between fibres. Aggregates of polysaccharides, wood resin a nd cationic polymer could also be retained in the fibre network.