Paper Additives in Non-wood Plant Fiber Pulp Paper Applications

Due to the shortage of long-fiber raw materials, people are trying hard to develop new fiber resources from various aspects, using waste paper, twigs, hardwoods, machine wood and other inexpensive grass fibers to make paper pulp instead of softwood pulp to produce fine paper. Therefore, non-wood plant fibers will undoubtedly play an increasingly important role in the global pulp and paper industry. Facts have proved that as long as the proportion of non-wood plant fiber raw materials and the pulping process are correctly selected, most grades of paper or paperboard can be produced. If the environment permits, all grades of paper can be added without any wood pulp. Make a copy. However, in most cases, non-wood plant fiber raw materials still need to be used in combination with a small amount of wood pulp. This is mainly because the use of non-wood fiber raw materials will cause the following problems for papermaking:

(1) Wet paper sheets are easily crushed and easy to stick the rollers.

(2) The fibers are short, the number of heterocytic cells is large, and the drainage of water is difficult. (3) Papermaking has low tearing. These are not conducive to papermaking, and the addition of additives in the wet end of the paper machine can significantly improve the above problems, and has become a problem that has attracted worldwide attention in recent years. With the continuous development of chemical additives at home and abroad, the application of additives in the paper industry is becoming wider and wider. Various types of internal sizing agents, wet and dry enhancers, retention aids, defoamers, resin control agents, fiber dispersants, and waste paper deinking agents are widely used in papermaking. The application of these auxiliaries improves the paper sheet making conditions, reduces the pulp consumption and energy load, and improves the physical properties of the paper sheets. It is adapted to the high speed of paper machines, light weight quantification, diversification of the variety of uses, and closure of paper machine water. Recycled various requirements. The addition of various polymers to make paper reinforced is a hot topic in today's papermaking.

In the early days, it was mainly natural products such as starch and vegetable gums, and later developed into semi-synthetic products such as starch derivatives and carboxymethyl cellulose. With the introduction of polymers into the paper industry, polyacrylamides and a series of single- and dual-component systems based on them have emerged. Most of these products have been modified by amine methylation or quaternary ammonium salts and have a strong positive charge for better fiber adsorption. In recent years, retention aid filtration has become a common concern for the paper industry. Apart from the reinforcing effect of starches and polyacrylamides, it can also speed up the drainage of paper materials to make them easier to dry and increase the retention of fine fibers and fillers. In order to promote sizing and reduce white water pollution and other issues. Currently used adjuvants are cationic starch and cationic polyacrylamide.

1 starch series

Starch is a complex and valuable raw material. The starch used in the paper industry is mainly modified starch. Commonly used are: oxidized starch, cationic starch, anionic starch, phosphate starch and dialdehyde starch. Used in four areas: wet end addition, interlayer spray, surface sizing, and coating application. Wet application is an important part of its application in the papermaking process. In the case of wet end additives, the use of starch derivatives will minimize their contamination.

Starch derivatives have the following characteristics: 1 good retention itself and can also increase the retention rate of fillers and fine fibers; 2 do not interfere with the clarification of sewage once as a precipitant; 3 non-toxic; 4 can be highly biological degradation. Ionic derivatives of starch are widely used for applications involving strength, retention, and drainage, and several commonly used types are discussed here:

1 1 Cationic Starch Cationic starch has been used in many paper grades, most of which are filled white paper due to its effects on strength, retention and drainage. These products have the advantages of high dispersibility (due to the repulsive effect of charged substituents) and high retention (high efficiency and low contamination). Cationic starches are economical, though they are more expensive but have a higher retention than unmodified starches. In addition, the reduction of the content of fine fibers and fillers in paper machine waste water has strongly stimulated the application of this product. Cationic starches are also used in other applications. For alkaline sizing agents, AKD and ASA are used with cationic starches to act as retention aids and emulsion stabilizers. Speakman recommends the use of cationic starch instead of natural undenatured starch or anionic starch to improve retention at the wet end. Rate. Other uses include what are commonly referred to as two-component systems, such as cationic starch and hydrolyzed polyacrylamide, to achieve higher retention levels than would be possible with a single polymer. Polymeric electrolytes of opposite charge are sequentially added to the slurries containing the fillers to form floes, which are referred to as "hard flocs" because they have excellent anti-flocculation action under high shear.

A remarkable feature of cationic starch compared to other wetted polymers is the high dosage in the pulp. This is caused by two reasons. On the one hand, the cationic starch is added in a high amount, usually 1% to 2%; on the other hand, the retention rate of cationic starch is not 100%, especially in the pulp containing more impurities. Accumulation in the wet end of the cycle, in which many of the starch's positive charge has been neutralized by highly active "hetero-anions" in the pulp, makes retention even more difficult. However, excessive use will cause gradual accumulation until excess cations cause system charge reversal, which will have an adverse effect.

1 1 1 Effect of Cationic Starch on Papermaking Production

(1) Effect on Pulp Filtration and Dewatering Cationic starch has a great difference between the filter effect and the reinforcement effect. The enhancement effect increases with the increase of starch in the pulp, but the filter aid effect is only at a low dosage. When it happens, the starch will hinder the filtration in high dosage. In practical applications, when the cationic starch achieves the best reinforcing effect, the amount thereof often exceeds the scope of the filter aid, and it may cause a cation system, which makes the operation of the paper machine difficult, the filler retention rate decrease, and the effect is reduced. Cationic starch also increases the water retention value of the pulp at high dosages and therefore has an adverse effect on dehydration. This effect is very important for cardboard production, because the cardboard is thicker, the speed of the paper machine is limited by the drying capacity, and the combined water of the pulp increases, which will inevitably reduce the drying efficiency of the drying section. In addition, the high pulp water retention value also has an adverse effect on the bonding between the layers.

(2) Influence on papermaking operations Cationic starch is lost in the papermaking wire and then recycled back into the papermaking system with white water. Due to the enhanced cationic nature of the system, charge reversal, especially the sensitivity of the balance of ionic charges in medium and alkaline papermaking, can cause the wet part to run out of control and the paper machine operation is poor.

(3) Effect on BOD and COD of papermaking wastewater Papermaking wastewater is mainly paper machine whitewater, and the starch remaining in it will become the main source of BOD and COD, which will increase the load of sewage treatment, leading to an increase in the dosage of flocculant and when the sewage treatment capacity When insufficient, BOD and COD that are likely to cause sewage discharge will be exceeded.

The retention of cationic starch retained by cationic starch is affected by the nature of the pulp and starch properties. The higher the pulp pH, the lower the negative impurity and the higher the retention rate of cationic starch. The higher the degree of substitution of starch cations, the higher the retention rate of cationic starch. In the range of dosage, the higher the starch addition, the lower the retention rate; The higher the amount, the lower the retention rate; polyacrylamide added pulp before the cationic starch also led to a decrease in the retention rate of starch.

1 1 3 Application of cationic starch and influencing factors (1) When the content of fine components and fillers in the paper stock is high, the degree of substitution of cationic starch is high, and the retention and filtration aid effect is better, but the strength may be reduced. For paper stock with less filler, the use of cationic starch with low degree of substitution can make the paper sheet stronger. (2) PH value had little effect on the retention effect of cationic starch, but the strength of paper sheet increased when the PH value was high. (3) The use of aluminum sulfate increases, retention increases, and sheet strength increases.

1 2 Anionic Starch Anionic starches include phosphate starch, starch with carboxyl groups and sulfonic acid groups, xanthate starch, and oxidized starch with both carboxyl and carbonyl groups. These derivatives have lower gelation temperatures, better dispersion properties, higher viscosities and anti-reduction effects than undenatured starches, and their solutions have good transparency and the like. For wet end addition, the only commercially effective anionic starch is phosphate starch. Addition of phosphate starch to the papermaking system requires at least 1% of alum (dry fiber) and a pH in the range of 4 to 60 in the pulper slurry. Phosphate starch provides better sheet strength and better filler retention in the wet addition and the traditional advantages of those cationic starches. 1 3 Amphoteric starch Amphoteric starch is more effective than cationic starch in improving the strength of sheet, the retention of fillers and fine fibers, and the filtration of the paper machine, thereby increasing the speed of the paper machine and greatly reducing the load of white water. Paper to neutral, alkaline paper change.

1 3 1 Effects of Amphoteric Starch on Wet End

(1) The anionic groups of amphoteric starch help to remove hetero-cations in the system that interfere with the adsorption of starch to the fibers. (2) The anion of amphoteric starch can reject "heteroanion" to reduce premature neutralization of cationic groups. (3) Recycled white water will not lose charge balance.

1 3 2 Application and Influence of Amphoteric Starch

(1) The 1% dosage of amphoteric starch with a pH of 7 to 7 5 has a good retention effect. (2) When the amount of aluminum sulfate is small, filler retention increases, but it decreases when it is excessive. (3) The increase of the degree of substitution of anion, filler retention increases first and then decreases. It is recommended that the anion substitution degree is 0 026. (4) The increase in the degree of substitution of cations leads to a gradual increase in filler retention. It is recommended that the degree of cation substitution be 0 047.

2 Polyacrylamides

Due to the lack of softwood resources, the amount of hardwood and grass materials is increasing, the recovery of waste paper and the amount of filler are also increasing. Therefore, the content of fine components in the slurry increases. Because of the worldwide shortage of water resources and the requirement to prevent pollution, papermaking must be closed to recycling water. In this case, from the aspects of energy conservation, reduction of pulp consumption, reduction of paper-making drainage, and processing load, it is necessary to keep the fine components and fillers in the pulp as much as possible, and at the same time, to maximize the dehydration of the wet end of the paper machine. Therefore, it is most economical. The solution is to use highly efficient retention and drainage aids, and amphoteric polyacrylamide has better efficacy in this regard.

2 1 Tianjin Institute of Light Industry research results in this respect (1) Amphoteric polyacrylamide has good retention and filter aids for bleaching wheat straw pulp and wood pulp, when the amount is 0 05%, the molecular weight is 2.02 million, and the degree of cationic amination At 218%, the degree of hydrolysis of 4% is better. (2) The above amphoteric polyacrylamide increases with the PH value, and the water content and retention of the paper stock decreases, and increases with the amount of aluminum sulfate.

2 2 Cationic polyacrylamide-starch graft copolymer (abbreviated as CAS) CAS is a cationic polymer flocculant. Its molecular chain contains both non-ionic functional groups and cationic functional groups. These functional groups are widely embedded in high-molecular polymers. Within the chain link, it can rely on the van der Waals force between non-ionic functional groups to bridge the microparticles and short fibers that are continuously dispersed in the aqueous phase, making them flocculate together as a group; and it is reliable for the electricity of the cationic functional group. The electrical double layer and the zeta potential of these microparticles, short fibers are destroyed, and they aggregate and aggregate. Therefore, it not only has the function of a high-molecular flocculant, but also has a dielectric-like agglomeration effect. After experimental research, CAS performance is stable, easy to use, there are significant retention, aiding filtration and enhancement effects in papermaking process. It can significantly reduce the consumption of pulp and filler, reduce production costs, and reduce white water pollution to the environment. It is a kind of papermaking auxiliary that has broad application prospects.

3 Polyethylene oxide (PEO)

In recent years, PEO has received more and more attention from people. The main reason is that many mixed waste paper mills have no effect on the use of conventional retention aids, and newsprint mills face similar problems. PEO is a high molecular weight nonionic polymer whose retention mechanism is effected by bridging and bonding, and PEO acts through the network with suspended solids present in the pulp. Its molecular weight, amount, place of addition, and use of synergist all affect retention. In general, the addition of certain second additives such as sulfonated phenolic polymers and lignin derivatives in PEO can significantly improve the retention effect. When the pH is from 4 to 10, these activators can form hydrogen bonds with the ether oxygen in the PEO to produce a synergistic effect and produce a copolymer linkage, which can increase the retention. When the PH value is greater than 10, the carboxyl group loses its linking effect due to dissociation, and the retention rate decreases. In addition, a small amount of PEO can have a good dispersion effect, often as a dispersant to make long fibers at a low beating degree to make a thin and uniform paper with good water absorption. This will be used to create toilet paper, napkins and other household papers.