Studies On Composites Of Polyaluminum Chloride-Organic Polymers And Its Application In Papermaking Industry

In order to promote the stability of sizing effect and sizing degree of sheet with the neutral sizing system of anionic dispersed rosin size (DRS) and polyaluminium chloride (PAC) used in non-wood fiber pulp, a new series of composite polyaluminium chloride (PACP) with PAC and organic polymer (OP) were developed as neutral rosin sizing precipitant for replacing PAC.The combination of PAC with OP was achieved by two different combination methods. One is adding OP directly into preproduced PAC; the other is adding OP into aluminum chloride solution, with subsequent polymerization conducted by titration of basic solution. Studies showed that the factors affecting combination include the structure and charge type of OP, the basicity and concentration of PAC, organic polymer/aluminum (O/A) ratio (mass ratio), reaction temperature and stirring condition, and so on. Also, catonic organic polymer (COP) is easier to combine with PAC than anionic OP (AOP) or amphoteric organic polymer (AmOP).The study on speciation and the conversion law of PACP by Al-Ferron timed complexation spectrophotometry and infrared spectroscopy showed that PAC speciation is dependent on the structure, charge and molecular weight of OP, with AOP additive having more significant effect than COP. The higher the O/A ratio is, the stronger the influence is. Nevertheless, Alb is still the controlling component of the PACP system.The morphology of PACP was studied by Transmission ElectronMicroscope (TEM). Compared to PAC, the aggregating clusters of PACP are larger in size and more branched. The larger the O/A ratio and the higher the molecular weight of OP are, the bigger the size of PACP and the higher the extent of branch are.According to the streaming current measurement on the charge of PACP and the colloid titration measurement on the charge character of pulp in wet end adding PACP, it is also found out that the charge neutralizing ability of PAC can be greatly improved by COP combination, but decreased a little with AOP. Therefore, the colloid titration ratio (CTR) of wheat straw pulp shows a sequence of CTR value from high to low as PACPOPAC>PACPa, and the value increases with the increase of quantity of PACP.On the basis of above research, the optimum condition of neutral rosin sizing in the system of DRS/PACP with bleached wheat straw pulp was researched as: DRS 1%, PACP 0.8%, O/A ratio 0.05, amphoteric starch 1%, drying temperature 85-90癈, back sequence sizing. Comparing with PAC/DRS, neutral rosin sizing with PAC/DRS could be significantly improved and the stability of sizing could also be raised.The sizing mechanism of DRS/PACP was further studied. It was shown that the retention of DRS and aluminum increases with the increase of the charge of DRS, PAC or PACP, but gradually decreases with the increase of pH value. Also, calcium carbonate additive was detrimental to the retention, while amphoteric starch additive is beneficial. Accordingly, the sizing effects of these three sizing systems of DRS/PACPc, DRS/PACPa and DRS/PAC are also different. Scanning Electron Microscope (SEM) images confirmed that the sequence of sizing effect from good to bad is: DRS/PACPODRS/PACPa> DRS/PAC, as predicated by the different retention of DRS and aluminum.Studies also showed that PACP is better than PAC on the retention of pulp and the retention was improved with the increase of O/A ratio. However, an good retention and drainage effect could be all attained in the presence of PACP and PAC on neutral or slight alkali scope .