Optimizing The Preparation Of Starch-Based Fixing Agents And Investigating Their Application Performances

The increasing utilization of closed white water in recirculation system results in the accumulation of dissolved and colloidal substances (DCS) in the wet-end of modern papermaking processes. DCS deposition has negative influences on the paper machine runnability, product quality and producing cost. Our previous studies have shown that the starch-based fixing agents (SBF) made in our laboratory have good affinities to the dissolved polysaccharides in the water phase of pulp suspension, thus they have unique propertes in controlling DCS as well as strengthening paper sheets. However, the cost of the SBFs is too high, since their degree of substitution is as high as0.65. Besides, to fully use the technologies, on-site devices to degrade the molecular weight of the cationized starches must be used. This will certainly increase equipment investment, moreover, it is necessary to add high performance control systems to maintain the stability of the process and the product. Therefore, it is necessary to do more research to reduce the production cost, as well as to develop new products which can be easily transported, stored, and applied.Thus, in this study, SBFs with much lower DS values were prepared according to the old method, i.e., starch etherification followd by acid hydrolysis for molecular weight degradation, and their effects of controlling DCS in a bleached chemithermomechanical pulp (BCTMP) were compared with a traditional polyamine (PA) fixing agent. The results showed that the two SBFs were easier to be adsorbed onto fibers, had better effect in agglomerating the colloidal substances, and better paper strengthening effects. The SBF with DS of0.22can be used as a good fixing agent in treating BCTMP.Due to the fact that following the etherification/acid hydrolysis method, the SBF products would be in liquid form, therefore, the stabilities of the liquid SBFs were investgated after adding some bacteriacides. The results showed that the SBFs would have good viscosity and pH stability after being stored after five days at room temperature.Next, a significantly different way was used to make SBFs. With corn starch as raw material, it was first degraded, and then etherified, among which there were three methods of degradation, i.e., by acid hydrolysis, by enzyme hydrolysis and by oxidation with hypochlorite. The new SBFs were used to treat a PRC-APMP, and their effects in the controlling DCS and paper strengthening were investigated. The results showed that under proper reaction conditions, starch degradation followed by etherification can produce SBFs with high reaction efficiency. With the same dosage of etherifying agent, the DS of the SBFs made from different degraded starches were close to each other. For SBFs with DS below0.32, it was found that the degradation degree did not have notable effects on their DCS controlling properties, but the less degraded SBFs had better retention and drainage effects. On the other hand, for the SBFs made by different methods of degradation, the acidically degraded and enzymatically degraded SBFs had better retention and drainage effects, and the acidically degraded and oxidatively degraded SBFs were more readily to be adsorbed to fiber. It was also found that the SBFs were significantly more effective than the PA in terms of strengthening the paper. SBFs with a higher degradation degree could improve the tensile strength better when the dosage of the SBFs were0.4%odp, especially the enzymatically degraded SBFs. With regard to bursting, interestingly it was found that the acidically degraded and enzymatically degraded SBFs were significantly superior to that by the oxidatively degraded one. However, for tearing, each kind of SBF was found to have some positive effect, however, the differences were niche.At last, three SBFs made by degradation followed by etherification, desinated as A-SBF, E-SBF and O-SBF correspondingly for that degraded by acid hydrolysis, enzyme hydrolysis and hypochlorite oxidation, having similar levels of DS as around0.32, and one SBF designated as S-SBF, which was made by peroxide degradation and cationic etherification alternatively, and having DS around0.28, were compared. The results showed that the enzymatically degraded SBFs (E-SBF) had better retention and drainage effects, and better DCS controlling effect than the acidically degraded SBFs (A-SBF), oxidatively degraded SBFs (O-SBF) and SBFs made by starch degradation and etherification simultaneously(S-SBF). E-SBF and A-SBF could improve the tensile strength and bursting obviously.