Effect of alum-dispersed rosin system on water absorption, strength and optical properties of papers made from recycled fibers

In this study, the effect of alum- dispersed rosin sequence has been examined on different properties of papers made from recycled fibers. Therefore, reverse sizing recycled fibers with 0.5 consistency at pH6.5 was carried out by using 1 and 1.5 % alum, and 1, 1.5 and 2 % dispersed rosin, based on dry weight of pulp. Then, water absorption, optical and strength properties of papers with grammage (60±3 g/m2) were evaluated. Based on the results, to reduce the water absorption of papers, 1 % of both alum and dispersed rosin is required to achieve appropriate level of sizing. As a result, the water absorption of papers declined from 174±7.4 g/m2 to 36±0.4 g/m2, and the contact angle of water droplet with paper surface increased from 31.2 degree to 118.1 degree. Moreover, concurrent to the hydrophobicity of fibers surface formed by rosin molecules and its repellency impact of inter-fiber bonding, alum imparts an improvement of bonds in paper network owing to the neutralization of anionic trash and retention of cellulose fines. Paper opacity has been increased due to the development of filler retaining in fibrous web of paper.