With the use of coated broken paper, deinking waste paper, high-yield pulp and the improvement of the paper machine white water circulation closure, the concentration of interfering anionic impurities in the wet end of the paper machine is getting higher and higher, which is harmful to the operation of the wet end of the paper machine It becomes bigger and bigger, and makes some cationic additives less effective. Especially with the conversion of papermaking to alkaline systems, when aluminum sulfate is no longer added to the slurry as a sizing and fixing agent, the problem of anionic impurities becomes more prominent. Therefore, it is very necessary to understand the sources, hazards and countermeasures of anionic impurities. Sources and harms of anionic impurities 1.1 Source of anionic impurities Anionic impurities refer to all dissolved anionic oligomers or polymers and nonionic hydrocolloid substances present in the wet end of the paper machine. These anionic impurities have different properties and sources: (1) From pulp, such as lignin derivatives, hemicellulose, fatty acids, etc. If fresh grass is used to make pulp in grass pulp due to shortage of raw materials, the anion impurities content in grass pulp will also be increased because the pectin and starch in the grass are not removed by natural fermentation. In the pulping process, the pulping of wood and grass materials depends largely on the elution of lignin, hemicellulose, extracts, etc. from the raw materials. These dissolved substances constitute the most important organic anions in the papermaking system. Impurities. The amount of these organic anion impurities is closely related to the pulping and bleaching process conditions, process control, and the degree of washing of the bleached pulp. Generally speaking, paper mills using high-yield pulp and waste paper pulp contain the largest amount of anionic impurities.The anionic impurities from various mechanical pulps and semi-chemical pulps are mainly in the form of lignin sulfonate, humic acid and anionic gum. Soluble substances present. The anionic impurities from waste paper pulp are mainly large amounts of lignin derivatives and other anionic impurities related to waste paper grades. Among them, paper mills using coated damaged paper or waste paper have the highest amount and the most complex anionic impurities. Coated paper or waste paper, especially coated paper or waste paper using calcium carbonate and titanium dioxide, the coating contains a large amount of anionic dispersant (when starch is used as a binder than protein is used as a binder More dispersant makes the concentration of anionic impurities increase rapidly. For ordinary chemical bleached pulp, straw pulp contains more anionic impurities than wood pulp. Regardless of the pulp, the low degree of pulp cleanliness is the most direct cause of the concentration of anionic impurities in the pulp. In the manufacture of paper sheets, when using calcium carbonate as a filler and coating pigment, that is, when making paper under neutral or alkaline conditions, because an aluminum sulfate cannot be used as a fixing agent, the anionic impurities cannot be neutralized; At alkaline pH, anionic impurities will ionize more anionic groups; and under alkaline conditions, low molecular weight hemicellulose may also dissolve from the fiber cell wall (such substances include xylose and arabinose-based glycans ); Some colloidal substances enclosed in fiber cells under acidic conditions may also be released due to cell wall swelling under alkaline conditions. Therefore, papermaking under alkaline conditions will increase the concentration of soluble anionic impurities. In recent years, due to the increasing degree of closure of the white water system of the paper machine, and the anionic impurities are not adsorbed on the pulp, these anionic impurities accumulate more and more with the white water> cycle, and the problem of anionic impurities caused by closed cycle white water is far greater The pulp itself is serious. 1.2 The effect of anionic impurities on papermaking Anionic impurities can affect the making of paper sheets in many ways, such as: (1) Affect the operation of the paper machine: the formed agglomerates (resin, white resin, adherents) reduce the performance of the paper machine and increase the number of broken ends. In short, anionic impurities affect papermaking by two mechanisms.One is that its high negative electrical properties make the pulp's positive charge requirement very high. Adding cationic additives, such as retention aids, filter aids, enhancers, etc., anionic impurities first Neutralization reaction with these polymers consumes a large amount of cationic additives (generally cationic additives are not effective charge neutralizers), which may make cationic application technology. The production process additives completely fail, and their high negative charge also affects the pulp The flocculation of medium and small fibers affects the retention of pulp and drainage. Therefore, the content of anionic impurities is usually expressed by the positive charge requirement of the slurry filtrate. Furthermore, as the anionic impurities accumulate, they combine with other substances or form agglomerates or complexes and deposit from the aqueous solution. Reduced the bonding strength between the fibers and the brightness of the paper; if left in the wire section, pipe and blanket during paper copying, it will block the paper net and blanket, causing sticking rollers in the press section and increasing the paper break Times, and there are dark spots on the paper, which will also interfere with the sizing and dyeing of the paper.
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(2) From anionic additives, such as starch, CMC, organic acids, dyes, fungicides, etc.
(3) From filler dispersant, such as polyphosphate, polyacrylate, etc.
(4) From clean water, such as humic acid, fungicides, etc.
Most of the harmful anionic impurities come from pulp, so only the accumulation of anionic impurities from pulp is introduced here. Every link from preparation to papermaking involves the accumulation of anionic impurities. In the preparation, experience has shown that long-term storage of wood has an adverse effect on fiber strength and bleaching process, but shortening the storage time prevents volatile substances such as terpene compounds from being separated; sticky substances, such as esterified fatty acids Can not be oxidized and saturated, resulting in shortened storage time and increased the content of anionic impurities in the pulp.
(2) Affecting the performance of additives: It has an adverse effect on the effects of sizing agents, dry strength agents, wet strength agents, retention aids, dyes, etc.
(3) Affect the quality of the paper: reduce the uniformity of the paper, reduce the opacity and brightness of the paper, cause small holes and dark spots, and reduce the strength of the paper. 
Causes and Countermeasures of Anion Impurities in Wet End of Paper Machine