Application of polyaluminum chloride in papermaking

Polyaluminium chloride is used in the paper industry except for some sewage and clean water treatment (in paper making),Its main use is as a neutral sizing precipitant for rosin and as a retention and filter aid. In addition, it can also be used to control resin barriers and serve as a capture agent for anionic impurities.

1.Polyaluminum chloride is used as rosin neutral sizing precipitant

Due to global resource shortages, raw materials for papermaking are becoming increasingly valuable,It becomes more practical to replace as much fiber as possible with cheaper CaCO fillers,Therefore, in the mid-1980s, Europe took the lead in using rosin neutral sizing technology to produce neutral paper. CaCO can be used as a filler in this production process.One of the keys to the success of this technology is the use of polyaluminium chloride instead of traditional alum as the sizing precipitant.Because polyaluminum chloride can maintain high electropositivity in the neutral or even alkaline range, it does not form Al(OH) precipitation as quickly as Al(SO).And due to the pre-hydrolysis of polyaluminium chloride,It does not lower the pH of the system as much as Al(SO).Therefore, polyaluminium chloride is an ideal new aluminum source for neutral sizing, and its sizing pH can reach 7.5.Following Europe, paper mills in North America and many other regions have adopted this technology to change acidic papermaking into neutral papermaking.Using this method for neutral sizing not only greatly reduces production costs, but also overcomes some unavoidable shortcomings (such as slippage and difficulty in sizing) when using synthetic rubber materials (such as AKD, etc.) for neutral sizing. control, etc.).Even so, since polyaluminum chloride is a complex inorganic polymer in a metastable state,Therefore, there are still many problems such as reasonable selection and the stability of the product itself during use, which have yet to be further solved in future research and development.

2. Polyaluminum chloride is used as a retention and filter aid

Retention aids:

At present, many theories believe that the retention of fine fibers and fillers in paper sheets is mainly achieved through two methods, namely mechanical entrapment and colloidal flocculation. With the continuous in-depth research on the retention mechanism, it is believed that The latter role is more important.Mechanical interception mainly means that particles are mechanically retained in the gradually formed paper structure. This mechanism is similar to filtration. It is only applicable to the longer fiber part in the paper material and cannot explain the high retention rate of fine components. The reason cannot explain the retention effect of retention aids.Currently, more and more research is focusing on the retention mechanism of fine fibers and fillers. These studies have established many different concepts and models, providing a theoretical basis for explaining and developing the retention mechanism and optimizing the process. Colloidal flocculation includes coagulation and flocculation.Coagulation refers to the use of inorganic salts or polymers with small molecular weight and high charge density to cause the colloidal suspension to lose stability and cause flocculation. The resulting flocs are small and tightly aggregated precipitates. This is mainly achieved through charge neutralization, heterogeneous condensation and patching.Flocculation refers to the use of a long-chain polymer to bind colloids together, causing the colloidal suspension to lose stability and flocculate. The resulting flocs are coarse, loose, and porous masses. Flocculation is mainly achieved through two forms: bridge flocculation and network flocculation.

Filter aid:

Since the dehydration process of paper stock will directly affect the quality of the paper and the operating performance of the paper machine,Moreover, the improvement of water filtration performance can improve productivity,Improve paper sheet formation, reduce energy consumption in the dryer section, etc. Therefore, improving the water filtration performance of paper stock is one of the important contents of wet end chemistry research.Under normal circumstances, almost all retention aids and charge neutralizers have filter aid functions, so aluminum sulfate, polyaluminum chloride, anionic starch, polyelectrolytes and particulate retention systems can all play a role in filter aids.