Effect of Ca2+-Pectates on Drainage and Paper Properties of Mechanical Pulp

The effect of Ca2+ and model pectic acids of different molar mass on drainage, sheet properties and heat-induced yellowing of TMP was studied. The aggregation of pectic acids by Ca2+ was strongly dependent on the molar mass of pectic acids. Ca2+-concentrations over 0.3 mmol/L induced strong retention of pectic acids with molar mass > 7.8 kDa. The retained Ca2+-pectates resulted in impaired drainage rate. The formed paper sheets were thicker and the grammage was slightly higher. Also brightness was decreased. Pectic acids are slightly coloured compounds, the yellowish colour becoming stronger at lower molar mass, and they showed some contribution to heat-induced brightness reversion.