Bleached aspen kraft pulp was provided by Yinxing Paper Co., Ltd. (Jinan, China). Old newsprint deinked pulp, CPAM with molecular weight 1–4 million and CS were provided by Huatai Group (Dongying, China). Sulfuric acid (95–98%) for hydrolysis, and poly dimethyldiallylammoniumchloride (PDADMAC) standards for titration were all analytically pure.