Study On The Mechanism And Application Of DCS Deposition Controlled By Highly Cationic Starch

It is well known that colloidal and dissolved substances (DCS) built up in papermaking system is very harmful. According to previous studies, the DCS were mainly composed of lipophilic extracts from raw material, carbohydrate-derived materials, which may be the pectin from mechanical pulps and chemical mechanical pulps, the decomposed cellulose and hemicellulose in chemical pulping, or the oxidized starch, the interbonding starch, and the coating starch from brokes or waste papers. We also known that when compared with the traditional anionic trash catcher PA, the undegraded highly cationic starches (HCS) had no advantaged effects in controlling DCS. However, applying degraded HCS by acid hydrolysin into recycled pulps, the degraded HCS had more better effects in controlling DCS than PA, also maintainde or even increased the strengths of handsheets.In this study, normal, linear and branched starches were used to prepare HCS with substitution degree as high as around0.68. The HCSs were then degraded by acid hydrolysis in order to obtain lower molecular-weighted HCSs which were named as LHCSs. The effects of these LHCSs with different branching degrees on controlling recycled pulp were investigated by measuring the Zeta potential of the pulp, turbidity and cationic demand of the filtrate. The results showed that the branched LHCS had the best effects viewing from the effects of DCS controlling and paper strengthening.Applying the LHCS into APMP pulps showed that compared with PA, the LHCS had much better effects in removaling dissolved and colloidal substances than PA. At the same time, LHCS can be adsorbed onto fibers easier and promote the APMP pulps drainability, but formation and strength of the APMP handsheets were worse.A mixture of resin acid, oleic acid and palmitic acid were chosen as the model for fatty acids and resin acids, pectin, oxidized starch and degraded hemicellulose were chosen as the model for polysaccharides-based anionic trashes, and the mixture of the two models were used as a hybrid model for DCS. The different effects of branched LHCS and polyamine (PA) on controlling DCS were investigated by measuring the Zeta potential, size, cationic demand, and the changes of all kinds of chemical composition of the supernatants after the three kinds of model.The results showed that when compared with the traditional anionic trash catcher PA, the LHCS had much better effects in controlling resin and fatty acids in the first model syestem. The different effects of LHCS and PA on controlling the polysaccharides model were discovered to be that LHCS had better affinity to fibers and better selectivity in removing the hemicellulose-based dissolved and colloidal substances. The different effects of LHCS and PA on controlling the hybrid model were found to be that LHCS had better selectivity in removaling anionic trash than PA, and compared with the resin-based anionic trash, LHCS had preferential effect on the polysaccharides in the system.