Polyacrylamide used for paper making industry

Application of Polyacrylamide in Paper Industry

There are two main applications of polyacrylamide in the paper industry: one is to increase the retention rate of additives and pigments to reduce the loss of raw materials and environmental pollution; the other is to increase the strength of paper.

1. Improve the retention rate of raw materials, etc.

After PAM is added at the headbox or impeller pump of papermaking, through the flocculation of PAM, pigments, fillers and fibers are deposited to reduce their loss in white water. For example, after adding 0.25%-0.5% PAM to the pulp, the sedimentation speed of the paper is increased by 20-80 times. The solid content in white water is reduced by about 66%, the gray scale of paper is increased, and the retention rate of white water and other fillers is increased by 8%-18%. The filler retention rate can be increased from 50%-60% to 80%-90%. According to literature, after using PAM, 20kg of pulp can be saved per ton of paper, which not only increases production and saves, but also improves the structure of paper by improving the distribution uniformity of fillers, pigments, and fuels in the pulp, extending the length of the copper mesh. Long service life, reduce the clogging of the felt, and make the equipment easy to operate.

After using PAM, the turbidity of white water is also greatly reduced, reducing environmental pollution. According to the statistics of a kraft paper mill, adding PAM to the causticizing solution can improve the clarity of white water. If the inorganic flocculant is used alone, the effect is not as good as that of the combination of inorganic flocculant and polymer flocculant. For example, the chemical oxygen demand (COD) of sulfite papermaking waste liquid is 2500mg/l, and the COD can be reduced to below 200mg/l by using the formula of aluminum sulfate 25mg/l and hydrolyzed PAM 2mg/l. After the hydrolysis degree is 5%-10%, the relative molecular mass is 5.5 million-1 million PAM1mg/l and aluminum sulfate 500mg/l (adjusted to pH 7.5-8.5), white water can be turned into colorless and transparent liquid, the suspended solids are reduced to below 50mg/l.

2. Improve the dry strength and wet strength of paper

Polyacrylamide can be used as a dry strength additive for paper and paper cards. When PAM is added to paper, dry strength properties such as tensile strength, folding resistance, and burst resistance are all improved. In addition, the use of PAM can also improve tear resistance, porosity, modified visual and printing properties.

The PAM used can be hydrolyzed PAM, with a relative molecular mass of about 12 million. Polyacrylamide is used together with alum to achieve good results in adjusting the pH value. When PAM is used for refining, a higher dry strength refining pulp can be obtained.

3. As a dispersant for long fiber papermaking

In the past, long-fiber paper was made of plant mucus, such as shavings, water shield, green maple stems and waxy leaves. The supply of this kind of plant mucus is greatly affected by the seasons, and it is not suitable for the mechanized production of the paper industry, and often cannot meet the needs due to the large consumption. Using PAM instead of plant mucus has been applied in some paper mills in my country. Using PAM with a degree of hydrolysis of 20%-30% and a relative molecular weight of 7 million as a dispersant, all technical indicators have reached and exceeded the level of vegetable gum. Every 10,000 pieces of wax paper can save 42,500-117,100 yuan compared with the original process, and because of the use of PAM, the operating rate and speed can be increased by 10%.

4. Increase the stability of emulsion (or pulp liquid)

PAM has a greater stabilizing effect on natural latex than polyvinyl alcohol, so it is a good thickener for latex. When PAM is added to 60% latex and stored for two weeks, the viscosity can be increased by 1.5-2.0 times.

5. Pigment binder for paper coating

 Mix PAM and starch at a ratio of 1:2 and use it as a good binder for paper coating.

6. Paper finishing agent

The reaction of PAM and dialdehyde can obtain water insolubility, which can be used in paper finishing.

The PAM used in the paper industry has different requirements for the relative molecular weight and carboxyl content (degree of hydrolysis) of the polymer due to different purposes. The general rule is: the relative molecular weight used as a flocculant should be as high as possible, while the degree of hydrolysis should be lower; the relative molecular weight used as a dispersant should be smaller, and the carboxyl content should be more; used as a dry strength agent in between the above two.

In the paper industry, many small and medium paper mills use grass fiber or other fibers as raw materials. In order to improve product quality and increase output, various chemical reinforcing agents are often used. PAM is a widely used additive in the paper industry at home and abroad, but Due to the high price, it affects the scope of application. As a traditional papermaking additive, starch is not as effective as PAM, and grafted PAM just makes up for the shortcomings of the former two. Since the PAM branch chain is connected to the starch molecular skeleton, the relative molecular weight is greatly increased, and the countless amide groups on the graft branch chain form hydrogen bonds with the hydroxyl groups of the cellulose or hemicellulose molecules of the pulp, which has a strong adsorption effect. . Therefore, the use of starch-acrylamide and other graft copolymers as paper additives not only plays the role of retention and drainage, improves the strength of paper, but also reduces costs and increases economic benefits compared with general PAM.