Concentration of Anionic starch Solution in Paper Surface Sizing on Physical and Strength Properties of Recycled Paper

Surface sizing of paper by anionic starch were carried out with the aim of its concentration effect on physical and strength properties of recycled paper. For this, hand sheets (100 GSM) of mixed recycled pulp containing 1% cationic starch were prepared and were treated by the sizing agent on the sheet surface at various concentration (0, 3-10%). Application and concentration increment of the starch solution caused its higher retention on the surface and lesser penetration into the paper structure (Z direction), contributed to the better hydrophobicity of sized paper and significantly reduction in water absorption of the paper, with the highest reduction in the Cobb test up to the solution concentration of 5%. Also, the results revealed that regarding to absorption and its increment into the paper surface combined to penetration to the paper thickness, strength properties of bending stiffness, burst and tensile indices have been increased which the improvement rate were more predominant up to the 5% cons. Penetration of a part of sizing agent into the porous structure of paper and resulted improvement in fiber bonding are possible and probable, that higher concentration and viscosity of the starch solution contributed to the lesser penetration and bonding formation with higher retention on the paper surface which resulted in continuous improvement in paper smoothness. With the sizing solution thickening, tear index decreased due to starch film formation on the paper surface with brittle character. In general, increasing of the anionic starch solution up to the 5% could be reported as an optimum level.