PAM
is the most commonly used auxiliary chemical in the paper industry. It can be used as a retention aid for filler, fiber, and dye in board making and also as a drainage aid, dry and wet strength aid, dispersant of long fiber, glue, and flocculant to recover fiber from white water. Below is a table of typical PAM products used in the pulp and paper industry followed with brief discussions of each application:

Trade Name
Cationicity in molecule
(%)
Anionicity(%)
Molecular Weight
x106
Form
Solids Content
Residual Monomer
(%)
Application
PAM-3
/
3
4-8
White Powder
90
0.03
Retention & Drainage Aid
PHPAM-2
/
25-30
10-20
White Powder
90
0.03
Pulp Dispersant
PHPAM-4
/
25-30
6-9
White Powder
90
0.03
Retention & Drainage Aid, Flocculant
PHPAM-1
5
20-25
6-10
White Powder
90
0.03
Paper Strength Agent
PDCA-1
10
/
4-10
White Powder
90
0.03
Paper Strength Agent
PDCA-3
20
/
4-10
White Powder
90
0.03
Paper Strength Agent
PDCA-5
50
/
4-10
White Powder
90
0.03
Paper Strength Agent
PDCA-5A
80
/
4-6
White Powder
90
0.03
Paper Strength Agent


1. Retention and drainage aid: Through electric neutralization, adsorption and a bridging effect, the PAM produced by our company can flocculate the particles in the pulp, so the particles are retained on the screen. The formation of folcs is beneficial to water drainage from the pulp. Thus, PAM is added prior to the sheet-forming box or at the vane pump. Through flocculation more filler, dye, and fiber are settled on the screen, and their loss into the white water is reduced. PAM can also speed up the de-watering of pulp, enable solids to settle in the waste water, and reduce the pollution caused by the waste water. The optimum pH range in which our PAM works is 4.5 to 6.0. For instance, when 0.25% to 0.5% PAM is added in the pulp, the setting rate will increase by the factor of 40 to 80, solids contained in the white water will be lowered by 66%, ash content in the pulp will increase, and retention of the filler, such as clay, will increase by 8% to 18%. Through application of our PAM, approximately 20 kg of pulp can be saved per ton of paper. Besides increased production and decreased cost, the paper texture will be improved by more evenly distributed filler, dye, and pigment in the pulp. Also, the paper machine is easier to operate, with high utilization efficiency thanks to longer life of the copper screen and less plugging of openings.

2. Dry and Wet Strength Aid: Paper is composed of cellulose containing hydroxyl groups. The oxygen and hydrogen atoms on those groups can form hydrogen bonds (with 5Kal/mole energy), which is the main factor giving paper its strength. If PAM is added in the paper, the amino groups on PAM molecules will create new hydrogen bonds with hydroxyl groups on the cellulose. Thus, with the number of hydrogen bonds increased, stronger paper is obtained.

For the majority of pulp, PAM homopolymer (i.e., nonionic PAM) is only slightly adsorbed by the cellulose molecules. As a paper strength aid, PAM frequently contains some anionic or cationic groups. This will help the adsorption of PAM on paper, and promote the formation of new hydrogen bonds. In recent years, there is a trend in the paper industry to move to neutral and alkaline paper-making processes. Anionic PAM is not applicable to these processes. So, cationic or amphoteric PAM tends to be used more. In pulp they display a positive charge and can automatically be retained on the cellulose. For this reason they work more efficiently in the pulp without aluminum sulfate content. They can not only bring about higher strength to the paper over a wider pH range, but also be adapted to many kinds of pulp from different raw materials. Sometimes anionic groups are needed on cationic PAM molecules to balance the electrical charge. This will help maintain a certain pH value of the pulp and enable the cationic groups to perform better at such pH conditions. PAM used as strength aids are mainly from copolymers of modified PAM, acrylamide monomer, and other cationic monomers. For example, if PAM reacts with urea-formaldehyde resin modified by dimethylamine, a strength aid product is obtained. If such product is added to the pulp at a 0.5% dosing rate, the anti-breaking factor of the paper will increase by 40%. In the pH range of 3 to 7, the copolymer of acrylamide and dimethylamidoethlymethacrylate (DM) will provide over 90% retention. If 0.4% copolymer of acrylamide/methylacrylate/DM chloride is added in the pulp, the anti-breaking factor of the paper will increase by 37%. The copolymer of acrylamide and dimethyldiallyamide chloride (DMDAAC) is frequently used as a wet strength aid. For example, if we chlorinate the copolymer of acrylamide and DMDAAC (75:25) at 0~2, a product with 26.2% Nacrylamide chloride is obtained. If such product is added in pulp at a 1.5% dosing rate, the wet strength of the paper will increase by a factor of 4.5. If a copolymer of acrylamide and DMDAAC is reacted with glyoxal and the resulting product is added in the pulp at pH 9.6, at the dosing rate of 15 1b/t, the dry and wet strength of paper will reach 29.39 1b/M2 and 4.07 1b/M2 respectively. After 30 minutes the wet strength will drop to 62.9% of the original one.

3. Dispersant for Long-fiber Sheet-forming: Previously plant mucilage has been used as a dispersant for long-fiber sheet-forming. The supply of such mucilage is greatly influenced by the weather. So it is not suitable for continuous production. Now, PAM has successfully replaced plant mucilage. Using a wax paper mill as an example, when it used a 20-30% hydrolyzed, 10million molecular weight PAM as the dispersant, all the technical and economical indices improved. The operation rate and speed of the paper machine was increased by 10%. The equivalent of US$1.0-1.5 can be saved per 10,000 sheets of wax paper manufactured. As a dispersant, a PAM with higher molecular weight will give better performance.

4. Dye-fixation Agent in Sizing: If PAM is mixed with starch at the ratio of 1:2, the resulting mixture is a good fixation agent in sizing.

5.Flocculant in Waste Water Treatment: PAM contains amido groups, which has affinity for many substances and can adsorb on them through hydrogen bonding. High molecular-weight PAM bridges between adsorbed particles to form flocs, facilitating the particle to settle.
Waste water from paper-making contains a lot of organic impurities, which are difficult to treat with a conventional inorganic flocculant. It is one of the main pollution sources in many places. By using PAM, the turbidity and color of the waste water from paper-making can be greatly reduced. One facility uses 25ppm aluminum sulfate followed by 1ppm PAM was used to treat a milk-like pulp waste water with 3000ppm suspended solids and 6.8 pH, the milky water became clear and colorless, and suspended solids dropped to less than 50ppm.

In the paper industry, PAM can also improve gluing, upgrade the surface property of paper, and improve stability of the pulp and emulsions. At present, the paper industry is in an innovative period. More and more paper mills have shifted from the traditional acidic sheet-forming process to neutral or alkaline ones. In some cases raw materials are also changing from wood pulp to straw pulp. The assortment and volume of paper is growing continuously. Sheet-forming machines are developing towards high-speed and high-temperature. Because of this, all areas in the paper-making procedure require large amounts of auxiliary chemicals. Thanks to its special characteristics, PAM will certainly play more important roles in the paper industry. In the United States, the consumption of PAM in paper-making is growing at the rate of 6-7% each year. And in Japan, PAM used in paper-making accounts for 45.3% of all PAM consumption.

 

 
 

 


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