Abstract
The main purpose of the study was to find ways of strengthening paper made from old corrugated containerboard (OCC) using the addition of cationic polyacrylamide (cPAM) and starch (CS) in conjunction with anionic PAM (aPAM) and starch (AS). Through modifying the wet-end conditions and modes of addition, we searched for optimal conditions to enhance paper strength, while in the meantime considering estimates of the drainage performance, production cost, and machine runnability. The results indicated that Percol 182, a cPAM, had the best enhancing efficacies on the tensile, burst, and folding strengths of the resulting paper. The amphoteric PAMs, Hercobond 6350 and PS 1280, had slightly inferior performances. While the aPAM, Percol 155, contributed to the tensile strength that was only better than an anionic starch, which had the worst burst strength. The tearing strength was highest when PS 1280 was used. Drainage effects of the additives differed according to the type and dose of the polyelectrolyte. Percol 182 significantly increased the freeness of the pulp, allowing water to drain faster. Hercobond 6350 was next, while Percol 155 significantly decreased the freeness of the pulp. When applying a fixed cPAM and CS to moderate the doses of an amphoteric PAM or aPAM, paper strengths varied with the polyelectrolyte complex used. For paper tensile strength, a pulp concentration of 1.00% and a tensile index Percol 182 dose of 1.00% were optimal, and the tensile indices of the resulting handsheets were optimized. However, when the cost factor was considered, then sequential CS/Percol 155 addition at a 0.75/0.25% dose was effective in elevating the tensile performance. For tearing strength, the sequential addition of CS with PS 1280 at doses of 0.25/0.75% and 0.50/0.50% was better. When cost was considered, adding CS and AS sequentially at a 0.75/0.25% or 0.50/0.50% dose was optimal for strength enhancement.