The main applications of Paper retention aid in the paper industry are twofold:-To increase the retention rate of additives, pigments, etc., to reduce the loss of raw materials and environmental pollution; Second, to increase the strength of paper.
1. Improve the retention rate of raw materials, etc. After PAM is added in the paper headbox or impeller pump, through the flocculation of PAM, the pigment, filler and fiber are deposited to reduce their loss in white water. For example, adding 0.25% to 0.5% PAM to the pulp increases the paper sedimentation speed by 20 to 80 times. The solid content in white water is reduced by about 66%, the grayscale of the paper is increased, and the retention rate of fillers such as white water is increased by 8% to 18%. The retention rate of filler can be increased from 50%~60% to 80%~90%. According to the literature, after using PAM, 20 kg of pulp per ton of paper can be saved, which not only plays a role in increasing production and saving, but also improves the structure of the paper due to the improvement of the distribution uniformity of fillers, pigments, and dyes in the pulp, and extends the copper mesh. The service life of the machine reduces the clogging of the blanket and makes the equipment easy to operate.
After using Paper retention aid, it also greatly reduces the turbidity of white water and reduces environmental pollution. According to statistics of a kraft paper factory, after adding PAM to causticizing solution, it can improve the clarity of white water. If the inorganic flocculant is used alone, the effect is not as good as that of the inorganic flocculant combined with the polymer flocculant. For example, the papermaking waste liquid with sulfurous acid method has a chemical oxygen consumption (COD) of 2500mg/L. Using aluminum sulfate 25mg/L and hydrolyzed PAM 2mg/L formula treatment, COD can be reduced to below 200mg/L. After the hydrolysis degree is 5% ~ 10%, the relative molecular weight is (550 ~ 1000) x10* PAM 1mg/L and aluminum sulfate 500mg/L. The combined treatment (adjusted pH value to 7.5~8.5) can make white water It becomes a colorless and transparent liquid, and the suspended matter drops below 50 mg/L.
2. Improve the dry and wet strength of the paper
Polyacrylamide can be used as a thousand-strength additive for paper and paper cards. When PAM is added to human paper, the tensile strength, folding resistance, bursting resistance, etc. are improved. In addition, the use of PAM can also improve the tearability, porosity, modified vision and printing performance.
The PAM used may be hydrolyzed PAM with a relative molecular mass of about 1200x 10'. The brand name commonly used abroad is Accdstrenth. Resin 2386 (American cyanamide company). It can be used together with alum to obtain good results under the adjustment of pH. When PAM is used for scouring selection, it can obtain scouring pulp with higher dry strength.
3. Used as a dispersant for long-fiber papermaking. In the past, long-fiber papermaking used plant mucus, such as Phoebe sylvestris, Nan Li, green maple stem and waxy leaves. The supply of this plant mucus is greatly affected by the seasons, and it is not suitable for the mechanized production of the paper industry. It is often unable to meet the demand due to the large consumption. Replacing plant mucus with PAM has been used in some paper mills in my country. Using PAM with a degree of hydrolysis of 20% to 30% and a relative molecular weight of 700x10* as a dispersant, various technical and economic indicators have reached and exceeded the level of vegetable gum. Every 10,000 sheets of wax paper can save RMB 4.25-1117 million compared with the original process, and due to the use of PAM, it can increase the operating rate and vehicle speed by 10%.
4. Increase the stability of emulsion (or pulp)
PAM can play a greater role in stabilizing 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 to 2.0 times.
5. Pigment binder for paper coating PAM and starch are mixed in a ratio of 1:2 and used as a good binder for paper coating.
6. Paper finishing agent
The reaction between PAM and dialdehyde can obtain water insolubility, this property can be used in paper finishing.
The PAM used in the paper industry has different requirements for the relative molecular mass and carboxyl content (degree of hydrolysis) of the polymer due to different purposes of use. -The general rule is: the relative molecular mass used as a flocculant should be as high as possible, and the degree of hydrolysis should be lower; the relative molecular mass used as a dispersant should be smaller, and the carboxyl content should be more than one point; use The dry strength agent is between the two.
In the paper industry, many small and medium-sized paper mills use grass fibers or other fibers as raw materials. In order to improve product quality and increase output, various types of chemical reinforcing agents are often used. PAM is a large amount of additives used in the paper industry at home and abroad, but Because of the high price,
Affect the scope of application. As a traditional papermaking additive, starch is not as effective as PAM, and grafted PAM makes up for the deficiencies of the first two. Because the PAM branch chain is connected to the starch molecular skeleton, the relative molecular mass is greatly increased. Numerous amide groups on the graft branch chain form hydrogen bond with the hydroxyl group of the cellulose or hemicellulose molecule of the pulp, which has a strong adsorption effect. . Therefore, the use of starch-acrylamide and other graft copolymers as papermaking additives not only plays a role in retention and filtration, improves the strength of the paper, but also reduces costs and increases economic benefits compared with ordinary PAM .