Views: 0 Author: Site Editor Publish Time: 2023-02-24 Origin: Site
Abstract: This paper introduces the types, preparation methods, performance characteristics and application status of cellulose ethers in papermaking industry, puts forward some new varieties of cellulose ethers with development prospects, and discusses their application and development trend in papermaking .
Key words: cellulose ether; performance; paper industry
Cellulose is a natural polymer compound, its chemical structure is a polysaccharide macromolecule with anhydrous β-glucose as the base ring, and each base ring has a primary hydroxyl group and a secondary hydroxyl group. Through its chemical modification, a series of cellulose derivatives can be obtained. The preparation method of cellulose ether is to react cellulose with NaOH, then carry out etherification reaction with various functional reactants such as methyl chloride, ethylene oxide, propylene oxide, etc., and then wash the by-product salt and some cellulose sodium to obtain the product. Cellulose ether is one of the important derivatives of cellulose, which can be widely used in medicine and hygiene, daily chemical industry, papermaking, food, medicine, construction, materials and other industries. In recent years, foreign countries have attached great importance to its research, and many achievements have been made in applied basic research, applied practical effects, and preparation. In recent years, some people in China have gradually started to get involved in the research of this aspect, and have initially achieved some results in production practice. Therefore, the development and utilization of cellulose ether plays a very important role in the comprehensive utilization of renewable biological resources and the improvement of paper quality and performance. It is a new type of papermaking additives worth developing.
1. Classification and preparation methods of cellulose ethers
The classification of cellulose ethers is generally divided into 4 categories according to ionicity.
1.1 Nonionic Cellulose Ether
Non-ionic cellulose ether is mainly cellulose alkyl ether, and its preparation method is to react cellulose with NaOH, and then carry out etherification reaction with various functional monomers such as monochloromethane, ethylene oxide, propylene oxide, etc. , and then obtained by washing the by-product salt and cellulose sodium, mainly including methyl cellulose ether, methyl hydroxyethyl cellulose ether, methyl hydroxypropyl cellulose ether, hydroxyethyl cellulose ether, cyanoethyl Cellulose ether and hydroxybutyl cellulose ether are widely used.
1.2 Anionic cellulose ether
Anionic cellulose ethers are mainly sodium carboxymethyl cellulose and sodium carboxymethyl hydroxyethyl cellulose. The preparation method is to react cellulose with NaOH and then carry out ether with chloroacetic acid, ethylene oxide and propylene oxide. Chemical reaction, and then obtained by washing the by-product salt and sodium cellulose.
1.3 Cationic Cellulose Ether
Cationic cellulose ethers mainly include 3-chloro-2-hydroxypropyltrimethylammonium chloride cellulose ether, which is prepared by reacting cellulose with NaOH and then reacting with cationic etherifying agent 3-chloro-2-hydroxypropyl Trimethyl ammonium chloride or etherification reaction with ethylene oxide and propylene oxide, and then obtained by washing the by-product salt and sodium cellulose.
1.4 Zwitterionic Cellulose Ether
The molecular chain of zwitterionic cellulose ether has both anionic groups and cationic groups. Its preparation method is to react cellulose with NaOH and then react with monochloroacetic acid and cationic etherification agent 3-chloro-2-hydroxypropyl Trimethylammonium chloride is etherified, and then obtained by washing the by-product salt and sodium cellulose.
2. Performance and characteristics of cellulose ether
2.1 Film formation and adhesion
The etherification of cellulose ether has a great influence on its characteristics and properties, such as solubility, film-forming ability, bond strength and salt resistance. Cellulose ether has high mechanical strength, flexibility, heat resistance and cold resistance, and has good compatibility with various resins and plasticizers, and can be used to make plastics, films, varnishes, adhesives, latex And drug coating materials, etc.
Cellulose ether has good water solubility due to the existence of polyhydroxyl groups, and has different solvent selectivity for organic solvents according to different substituents. Methylcellulose is soluble in cold water, insoluble in hot water, and also soluble in some solvents; methyl hydroxyethyl cellulose is soluble in cold water, insoluble in hot water and organic solvents. However, when the aqueous solution of methylcellulose and methylhydroxyethylcellulose is heated, methylcellulose and methylhydroxyethylcellulose will precipitate. Methyl cellulose is precipitated at 45-60°C, while the precipitation temperature of mixed etherified methyl hydroxyethyl cellulose is increased to 65-80°C. When the temperature is lowered, the precipitate redissolves. Hydroxyethylcellulose and sodium carboxymethylcellulose are soluble in water at any temperature and insoluble in organic solvents (with a few exceptions). Utilizing this property, various oil repellants and soluble film materials can be prepared.
Cellulose ether is dissolved in water in the form of colloid, its viscosity depends on the degree of polymerization of cellulose ether, and the solution contains hydrated macromolecules. Due to the entanglement of macromolecules, the flow behavior of solutions differs from that of Newtonian fluids, but exhibits a behavior that changes with shear force. Due to the macromolecular structure of cellulose ether, the viscosity of the solution increases rapidly with the increase of concentration and decreases rapidly with the increase of temperature. According to its characteristics, cellulose ethers such as carboxymethyl cellulose and hydroxyethyl cellulose can be used as thickeners for daily chemicals, water-retaining agents for paper coatings, and thickeners for architectural coatings.
When cellulose ether is dissolved in the water phase, bacteria will grow, and the growth of bacteria will lead to the production of enzyme bacteria. The enzyme breaks the unsubstituted anhydroglucose unit bonds adjacent to the cellulose ether, reducing the relative molecular weight of the polymer. Therefore, if the cellulose ether aqueous solution is to be stored for a long time, preservatives must be added to it, and certain antiseptic measures should be taken even for cellulose ethers with antibacterial properties.
3. Application of cellulose ether in paper industry
3.1 Paper strengthening agent
For example, CMC can be used as a fiber dispersant and a paper strengthening agent, which can be added to the pulp. Since sodium carboxymethyl cellulose has the same charge as the pulp and filler particles, it can increase the evenness of the fiber. The bonding effect between fibers can be improved, and physical indicators such as tensile strength, bursting strength, and paper evenness of paper can be improved. For example, Longzhu and others use 100% bleached sulfite wood pulp, 20% talcum powder, 1% dispersed rosin glue, adjust the pH value to 4.5 with aluminum sulfate, and use higher viscosity CMC (viscosity 800~1200MPA.S) The degree of substitution is 0.6. It can be seen that CMC can improve the dry strength of paper and also improve its sizing degree.
3.2 Surface sizing agent
Sodium carboxymethyl cellulose can be used as a paper surface sizing agent to improve the surface strength of paper. Its application effect can increase the surface strength by about 10% compared with the current use of polyvinyl alcohol and modified starch sizing agent, and the dosage can be reduced by about 30%. It is a very promising surface sizing agent for papermaking, and this series of new varieties should be actively developed. Cationic cellulose ether has better surface sizing performance than cationic starch. It can not only improve the surface strength of paper, but also improve the ink absorption performance of paper and increase the dyeing effect. It is also a promising surface sizing agent. Mo Lihuan and others used sodium carboxymethyl cellulose and oxidized starch to conduct surface sizing tests on paper and cardboard. The results show that CMC has an ideal surface sizing effect.
Methyl carboxymethyl cellulose sodium has a certain sizing performance, and carboxymethyl cellulose sodium can be used as a pulp sizing agent. In addition to its own sizing degree, cationic cellulose ether can also be used as a papermaking retention aid Filter, improve the retention rate of fine fibers and fillers, and can also be used as a paper strengthening agent.
3.3 Emulsion stabilizer
Cellulose ether is widely used in emulsion preparation because of its good thickening effect in aqueous solution, which can increase the viscosity of emulsion dispersion medium and prevent emulsion precipitation and stratification. Such as sodium carboxymethyl cellulose, hydroxyethyl cellulose ether, hydroxypropyl cellulose ether, etc. can be used as stabilizers and protective agents for anionic dispersed rosin gum, cationic cellulose ether, hydroxyethyl cellulose ether, hydroxypropyl cellulose ether, etc. Base cellulose ether, methyl cellulose ether, etc. can also be used as protective agents for cationic disperse rosin gum, AKD, ASA and other sizing agents. Longzhu et al. used 100% bleached sulfite wood pulp, 20% talcum powder, 1% dispersed rosin glue, adjusted the pH value to 4.5 with aluminum sulfate, and used higher viscosity CMC (viscosity 800~12000MPA.S). The degree of substitution is 0.6, and it is used for internal sizing. It can be seen from the results that the sizing degree of the rosin rubber containing CMC is obviously improved, and the stability of the rosin emulsion is good, and the retention rate of the rubber material is also high.
3.4 Coating water retaining agent
It is used for coating and processing paper coating binder, cyanoethyl cellulose, hydroxyethyl cellulose, etc. can replace casein and part of latex, so that printing ink can easily penetrate and the edges are clear. Carboxymethyl cellulose and hydroxyethyl carboxymethyl cellulose ether can be used as pigment dispersant, thickener, water retention agent and stabilizer. For example, the amount of carboxymethyl cellulose used as a water-retaining agent in the preparation of coated paper coatings is 1-2%.
4. Development Trend of Cellulose Ether Used in Paper Industry
The use of chemical modification to obtain cellulose derivatives with special functions is an effective way to seek new uses of the world's largest yield of natural organic matter-cellulose. There are many kinds of cellulose derivatives and wide functions, and cellulose ethers have been applied in many industries due to their excellent performance. In order to meet the needs of the paper industry, the development of cellulose ether should pay attention to the following trends:
(1) Develop various specification products of cellulose ethers suitable for paper industry applications, such as series products with different degrees of substitution, different viscosities, and different relative molecular masses, for selection in the production of different paper varieties.
(2) The development of new varieties of cellulose ethers should be increased, such as cationic cellulose ethers suitable for papermaking retention and drainage aids, surface sizing agents, and zwitterionic cellulose ethers that can be used as reinforcing agents to replace coating latex Cyanoethyl cellulose ether and the like as a binder.
(3) Strengthen the research on the preparation process of cellulose ether and its new preparation method, especially the research on reducing the cost and simplifying the process.
(4) Strengthen the research on the properties of cellulose ethers, especially the film-forming properties, bonding properties and thickening properties of various cellulose ethers, and strengthen the theoretical research on the application of cellulose ethers in papermaking.