Synthesis And Applications Of The Cationic Starch With High Degree Of Substitution In The Wet-End Of Papermaking

Starches as the materials of chemical industry have more advantages such as cheap, regeneration, abundance, biodegradabiliry, green protection etc than the oil chemical materials. They are one of the most important reproduction resources. The cationic starch is one of Ihe most important derivations of starches. It is widely used in paper industry all over the world.Now the degree of substitution (DS) of cationic starch used in the wet-end of papermaking is ranged from 0.01 to 0.07. The DS of this kind of cationic starch is low. In order to make better use of starch and to enlarge the applied fields of cationic starch in paper industry, we studied the methods of preparation the cationic starch with high degree of substitution (HCS). Through probing into the influence factors, we obtained the optimum process conditions separately prepared by solvent-water system and half-dry process. We made use of Ihe cationic starch with high DS as retention, drainage aids and anionic trash catchers (ATC) in Ihe wet-end of papermaking to improve filler retention. At last we also discussed the reaction mechanism of the HCS with fibers, fillers and fines in the wet-end of papermaking.In the first part of this paper, the preparation of the HCS separately by solvent-water system and half-dry process was studied. In order to obtain the optimum process conditions, the effects of some factors, such as the dosage of etherifying agent, the dosage of alkaline, water content of the system, reaction temperature and reaction time were studied. Under the optimum process conditions, the HCS with DS at about 0.4 can be prepared by solvent-water system and the HCS with DS at about 0.5 can be prepared by half-dry process.Secondly, the HCS was characterized by Fourier transform infrared spectroscopy (FTIR) and its charge density was determined by colloid titration. All the results showed that preparation of the HCS were successful.Thirdly, the application of HCS in the wet-end of papermaking was studied. A series of HCS were used as filler retention and drainage aids for deinked pulp and bleached wheat straw pulp and also used as ATC in the deinked pulp. The experiments show that the HCS has the better effects on filler retention and drainage of the deinked pulp. When the DS of HCS is 0.501 and the dosage is 0. 1 %, the beating degree decreases about 11 SR and the filler retention improves about four times. The HCS has little effect on the drainage but remarkable effects on filler retention in the bleached wheat pulp. When the HCS used as ATC in the deinked pulp, the optimum dosage is 0.04% and it can improve the efficiency of the strengthening, filler retention and water drainage.At last, the reaction mechanisms of HCS in the wet-end of papermaking were discussed. The advanced technology of colloid titration with PCD, combined with the analysis of Zetapotential, was applied to measure the charge and Zeta potential of furnish systems. The reaction mechanisms of HCS used as filler retention, water drainage aids and ATC were explained theoretically.