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Types, development and synthesis methods of wet enhancers

the wet strength of paper refers to the strength of paper when it meets water or in a wet environment. Under normal circumstances, when the paper is wetted without additives, its strength is only 5%-10% of that when it is dry. After adding wet enhancers, most of the paper can maintain 20%-40% of its original dry strength. Wet strength agents are functional additives, most of which are hydrolysis resistant synthetic resins. Adding them to pulp before paper forming can not only improve wet strength, but also create favorable conditions for the operation of high-speed paper machines

I. types and development of wet strength agents

long ago, people used sulfuric acid to treat the base paper to sheepskin, sprayed and covered the surface of the paper with waterproof paint, plastic film or metal foil, or used white gelatin and animal glue to size the surface of the paper, and then made the sizing paper contact with bauxite, formaldehyde or Glyoxal at high temperature to form a protective layer. These methods are quite expensive and inefficient, and this method itself can only play the role of water resistance, and does not substantially improve the wet strength of paper

in 1935, people first found that using urea formaldehyde resin (UF resin for short) as surface sizing agent can make paper have a certain wet strength after heat treatment. Subsequently, UF resin can be developed to be directly added to the pulp, but because it has negative charge and is not easy to combine with loaded fibers, the retention rate is low, and the wet strength effect is very poor. In 1942, melamine formaldehyde resin (referred to as MF resin) was developed, which can be directly added to the pulp, and the paper can obtain good wet strength after heating and drying. In 1946, the cationic modified UF resin was successfully trial produced. The retention rate and wet strength paper efficiency of the resin were similar to those of MF, but the price was low, creating conditions for mass production of wet strength paper. After using urea formaldehyde resin and melamine resin as wet strength agents, not only the treatment process is simplified, but also the wet strength can be as high as 50%. While improving the wet strength, it can also improve some dry strength indexes (such as breaking length, bursting resistance, folding resistance, etc.) and sizing degree of the paper

at the same time, people have also developed some other compounds that can make paper and paperboard have a certain wet strength. For example, phenolic resin, polyethyleneimine (PEI), synthetic latex (styrene butadiene latex, nitrile latex, etc.), dialdehyde starch (DAS), etc., but phenolic resin has a very deep color and needs to be matured at a high temperature of about (150 ℃), so synthetic latex is expensive and needs to be made into latex when applied; Polyethylene sizing is usually only suitable for the preparation of wet strength paper without sizing and absorption; Although dialdehyde starch has the advantages that it does not change the absorption property of the paper and the wet strength has nothing to do with the drying temperature, it can only give the paper a temporary wet strength. Therefore, these wet strength agents are rarely used except for some special purposes

in 1960, polyamide polyamine epichlorohydrin resin (abbreviated as PPE or PAE resin) with medium alkaline curing was developed. PPE resin has many advantages that MF resin and UF resin cannot be simulated. It is not only a high-efficiency wet enhancer cured under medium alkaline conditions, but also improves the wet strength without losing the softness and absorption of the paper. It is especially suitable for medical and sanitary paper. And in the production process, the foam is small, the whiteness of the paper is small, and it has good regeneration and pulping performance

on the basis of PPE resin, researchers have developed PPA, CPAM, PA and other wet strength agents. Polyamide polyamine resin (PAA) is a cationic water-soluble polymer, which is mainly used in carton paper and paper materials for liquid packaging such as milk and fruit juice. The effect is better than UF resin and MF resin. Cationic polyacrylamide (CPAM) is a strengthening agent with dry and wet strengthening effects. It is a strategic emerging industry with added value, and can make paper have high whiteness. It is easy to disperse into pulp after the recovery of damaged paper. The curing time is short and the price is moderate. Its suitable pH range is 4 5。 Its main disadvantage is that the wet strength of its enhanced paper will lose 40% about a minute after it is wetted, so it is not suitable for papers requiring persistent wet strength. American paper mills use it to produce handkerchiefs, face towels and other high-grade papers. Polyamine (PA) wet strength agent is the lowest cost of the three water-soluble polymers. This kind of product has good storage stability and dry strengthening performance. It has higher wet strength and durability than CPAM, but it is not as good as PPE resin. It is used in the production of toilet paper and corrugated paper in the United States

it can be seen that the wet strength agent has been developed so far, mainly into two categories of products, namely, the acidic curing resin represented by MF resin and UF resin and the alkaline curing resin represented by PPE resin. Alkaline curing resin has more advantages than acid curing resin, and will become the development trend of agents in paper industry

II. Synthesis method of wet reinforcement

(I) synthesis method of PPE resin

polyamide polyamide epichlorohydrin resin is abbreviated as PPE, also known as polyamide polyamide epichlorohydrin resin or polyamide epichlorohydrin resin. PPE is a water-soluble, cationic, thermosetting resin, non formaldehyde polymer, non-toxic and tasteless. It can be used in the pH range and has a good wet strength effect. It is characterized by low dosage, suitable for neutral papermaking, and easy to treat paper damage. It can also be used as a flocculant for treating factory wastewater

1. Quality index of PPE resin: appearance: light amber particulate liquid, solid content: 12.5% ± 0.3%, specific gravity: 1.03kg/l, viscosity: CPS, freezing point: -1 ℃, pH4 9。

2. The chemical synthesis method of PPE resin is mainly divided into two steps. The first step is to synthesize polyamide, and the second step is to use polyamide as raw material to generate PPE resin. When synthesizing polyamide, diethylenetriamine or triethylenetetramine can be used

3. Raw materials: diethylenetriamine 103G (triethylenetetramine 146g)

oxalic acid 146g

epichlorohydrin 80g (when using triethylenetetramine, epichlorohydrin takes 76.4g)

appropriate amount of water

10% hydrochloric acid (or sulfuric acid) appropriate amount

10% sodium hydroxide appropriate amount

4. Utensils: open enamel barrel (or three neck flask), mixer, glass rod, alcohol lamp (or electric heater), balance (platform scale), measuring cylinder, beaker Viscometer

5. Process conditions: normal temperature and pressure

6. Synthesis method:

step 1. Take 103G of diethylenetriamine (or 146 of triethylenetriamine), put it into an open enamel barrel (or three neck flask), start the mixer, and add 31G of water. Then add 146g of oxalic acid slowly. At this time, the temperature rises to C by itself. After mixing evenly, start heating and warming up. When it reaches 130c, foam will appear. At this time, pay attention to keeping the temperature for about half an hour to prevent foam from overflowing. After the foam disappears, continue to heat up to 190 ℃ -200 ℃, and moisturize for about 1 Whether the piston of the hour overflow valve is dead or installed reversely. Stop heating. When the temperature drops below 160 ℃, slowly add water to make the total amount of 400g. At this time, the solid content of the resin is about 50%. After stirring evenly, the resin yield is about 85%

step 2. Add 600g of water to the polyamide liquid prepared in the first step, stir and add 80g of epichlorohydrin drop by drop, and add it in about minutes. Start heating, stop heating when the temperature rises to 75c, keep stirring, and when the viscosity reaches centipoise (solid content 19%), immediately add 10% hydrochloric acid (or sulfuric acid) to adjust the pH, and then store it for standby

step 3. When using, first adjust the pH value with 10% sodium hydroxide solution, add an appropriate amount of water to dilute, and then add it to the slurry pool after stirring

7. Precautions:

(1) diethylenetriamine (or triethylenetetramine) reacts with acetic acid at 160 ℃ -210 ℃ under normal pressure for 0 The molar ratio of amine to acid is 0.8: 4:1, preferably 0.9: 2:1, less than 0.8:1 will appear gelation, more than 1.4:1 will produce small molecular weight polyamide

(2) when polyamide reacts with epichlorohydrin, the temperature is about 45 ℃ -70 ℃, and the viscosity is greater than 0.85 centipoise. It is best to let the reaction be carried out in aqueous solution to ease the reaction. Usually, the pH value is not adjusted, but the pH value will decrease during the reaction. If necessary, add the acid generated in the neutralization part of alkali, which is conducive to the conversion of chlorohydrin group to epoxy group. When the required viscosity has been reached, dilute it with water to make the content of resin solution about 10%, cool it to 25 ℃, and then add acid to adjust the pH to make it stable, preferably as high as ph=5. Use 1 Satisfactory results can be obtained with 5 grams of epichlorohydrin

(3) when using PPE resin, the pH should be adjusted to 10% sodium hydroxide to activate it. PPE resin can be directly added to the slurry, with the addition range of 0.1% - 5% (for dry fiber)

(4) avoid contact with concentrated acid when using PPE resin

8. Storage method: PPE resin should be stored in a cool, ventilated and dry place to avoid ice and high temperature (>32 ℃). The storage temperature should be higher than 4.4 ℃. If the product is solidified and melted, it should be mixed evenly and used immediately; It can be stored for 3 months under the environment of lower than 32 ℃, and the wet strength effect decreases after more than 3 months. Generally, the storage period is 6 months

(II) synthesis method of cationic UF resin

urea formaldehyde resin is abbreviated as urea formaldehyde resin, which is formed by the polymerization of urea and formaldehyde. UF resins are divided into anionic and cationic types. Anionic UF resin is not easy to combine with negatively charged fibers, with low retention and poor wet strength. Cationic UF resin is modified by anionic UF resin. The wet strength of the modified cationic UF resin can reach more than 50% of the dry strength. While improving the wet strength, it does not affect other properties of the paper. At the same time, it can also correspondingly improve the breaking length, bursting resistance, folding resistance and sizing degree of the paper

uf resin is a colorless (or straw yellow) transparent, uniform, syrupy liquid, which can be mixed with water in any proportion without precipitation. It has ionic properties, including cationic and anionic types. When added to the pulp, the resin will be absorbed by the fiber and retained on the fiber. Cationic UF resin is commonly used in industry

1. Synthesis method of ethylenediamine modified urea formaldehyde resin

(1) characteristics: ethylenediamine modified urea formaldehyde resin is a cationic resin. Because it is cationic, it has significantly stronger humidification effect than unmodified urea formaldehyde resin. In addition, it has the characteristics of good water solubility, not easy to gel, convenient manufacture and low price. It is made by the first action of urea and formaldehyde, with the addition of ethylenediamine and other auxiliary chemicals

(2) raw material: urea (95%-100% crystallization) 1mol

formaldehyde (51% aqueous solution) 2.5mol

ethylenediamine (%) 0.1mol

hydrochloric acid (38%) 0.1mol

sodium hydroxide (25%), which is used to control the pH value of resin solution

formic acid (90%), which is used to control the pH value of tree fat solution

(3) equipment: measuring cylinder, balance, pH test paper, burette, heater (50 ℃ -100 ℃), with thermometer Vessels of agitators and reflux condensers, etc

(4) synthesis steps: A. first, 9.5ml of acid reacts with 6.1ml of ethylenediamine to form ethylenediamine salt, and then 147ml of formaldehyde solution is put into a container equipped with a thermometer, stirrer and reflux condenser

b, control the pH value at 7 0, then 60g urea was added, and the pH value of the reaction solution was still controlled above 7.0

c, then raise the temperature. When the temperature gradually rises to 95 ℃, adjust the pH value to 4.2 with formic acid. After measuring the reduction of density (or the reduction of coating thickness) before and after friction, because ethylenediamine is alkaline, then the pH value of the reaction solution is increased to 6.2, and then formic acid is used to reduce it

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