Sodium carboxymethylcellulose is widely used in industry, pharmaceuticals and food production. This compound is made from wood and is a biologically inert material, that is, it does not participate in physiological processes. Due to the special properties of solutions with this component, the viscosity of substances and other technical parameters can be adjusted.
Description
Sodium carboxymethylcellulose (CMC) is the sodium salt of cellulose glycolic acid. The chemical name of the compound according to the IUPAC nomenclature is sodium poly-1,4-β-O-carboxymethyl-D-pyranosyl-D-glycopyranose.
The empirical formula of technical sodium carboxymethylcellulose is: [C6H7 O 2 (OH) 3- x (OCH 2 COONa) x ] n. In this expression, x is the degree of substitution for CH 2 -COOH groups, and n is the degree of polymerization.
The structural formula is shown in the figure below.
Properties
In appearance, commercial sodium carboxymethylcellulose is a powdery, fine-grained or odorless fibrous material with a bulk density of 400-800 kg/m 3 .
Na-CMC has the following characteristics:
molecular weight of the compound - n;
quickly dissolves in both hot and cold water, insoluble in mineral oils and organic liquids;
forms films that are resistant to oils, greases and organic solvents;
increases the viscosity of solutions and gives them thixotropy - with an increase in mechanical impact, a decrease in flow resistance occurs;
absorbs water vapor from the air well, so the substance must be stored in dry rooms (under normal conditions it contains 9-11% moisture);
the compound is non-toxic, non-explosive, but in a dusty state it can ignite (self-ignition temperature +212 °C);
in solutions exhibits the properties of an anionic polyelectrolyte.
When the temperature changes, the laboratory viscosity of sodium carboxymethylcellulose in solutions varies greatly. This is one of the most important characteristics of this compound, which determines the scope of its application. A high degree of polymerization provides greater viscosity and vice versa. At pH<6 или более 9 снижение сопротивления потоку значительно падает. Поэтому данную соль целесообразно применять в нейтральных и слабощелочных средах. Изменения вязкости при нормальных условиях являются обратимыми.
Sodium carboxymethylcellulose also has chemical compatibility with many other substances (starch, gelatin, glycerin, water-soluble resins, latexes). When heated to temperatures above 200 °C, the salt decomposes to sodium carbonate.
The main factor influencing the characteristics of this compound is the degree of polymerization. Solubility, stability, mechanical properties and hygroscopicity depend on molecular weight. The substance is produced in seven grades according to the degree of polymerization and two grades according to the content of the main substance.
Receipt
Sodium carboxymethylcellulose has been produced on an industrial scale since 1946. CMC production currently accounts for at least 47% of the total volume of cellulose ethers.
The main raw material for the synthesis of this compound is wood cellulose, the most common organic polymer. Its advantages are low price, biodegradability, lack of toxicity and simplicity of the processing technology.
Sodium carboxymethylcellulose is produced by reacting alkali cellulose with C₂H₃ClO₂ (monochloroacetic acid) or its sodium salt. In recent years, work has been underway to find new sources for the extraction of raw materials (flax, straw, cereals, jute, sisal and others), as the demand for this material is constantly growing. To improve the quality of the substance, the finished salt is washed from impurities, cellulose is activated, or it is exposed to microwave radiation.
Sodium carboxymethylcellulose: industrial applications
Due to its special properties, CMC is used for the following purposes:
thickening of various compositions, gelatinization;
binding of fine particles in paint films (film formation);
use as a water-retaining agent;
stabilization of physical and chemical properties;
increasing the viscosity of solutions to ensure uniform distribution of their ingredients;
modification of rheological characteristics;
protection against coagulation (sticking together of suspended particles).
One of the largest consumers of sodium carboxymethylcellulose is the oil and gas industry, where this compound is used to improve the performance of drilling fluids.
The substance is also used in the manufacture of the following technical products:
detergents;
printing products;
solutions for construction finishing works;
adhesives, sizing materials;
dry construction mixtures, cement (to prevent the formation of cracks);
paints and varnishes;
cutting fluids;
rail hardening media;
coating of welding electrodes and others.
To stabilize foam, sodium carboxymethylcellulose is used in fire fighting, the food industry, and in the manufacture of perfumes and ceramics. Technicians estimate that this compound is used in more than 200 fields of technology and medicine.
Protective coatings
One of the promising directions is the introduction of nanoparticles synthesized from CMC suspensions as stabilizer additives in corrosion-resistant coatings. This allows you to increase adhesion to the base material, improve the physical and mechanical properties of the coating without significantly increasing the cost of the composition. Nanoparticles form microclusters, making it possible to obtain composites with valuable technical properties.
The advantage of this additive is also that it is environmentally friendly and biodegradable. Its production does not require the use of organic solvents, therefore reducing the risk of pollution of wastewater and the atmosphere; there is no need to use specialized equipment and a high temperature range.
Food supplement
Sodium carboxymethylcellulose is used as a food additive (E-466) in a concentration of no more than 8 g/kg. The substance performs several functions in products:
thickening;
properties stabilization;
moisture retention;
extension of shelf life;
preservation of dietary fiber after defrosting.
Most often, this compound is added to fast food, ice cream, confectionery, marmalade, jelly, processed cheese, margarine, yogurt, and canned fish.
Medicine and cosmetology
In the pharmaceutical industry, sodium salt of carboxymethylcellulose is used in such groups of drugs as:
eye drops, injection solutions - to prolong the therapeutic effect;
tablet shells - to regulate the release of the active substance;
emulsions, gels and ointments - to stabilize formative substances;
antacid drugs - as ion-exchange and complexing components.
In the production of hygiene and cosmetic products, this compound is used in toothpastes, shampoos, shaving and shower gels, and creams. The main function is to stabilize properties and improve texture.
Effect on the human and animal body
Sodium carboxymethylcellulose is hypoallergenic, biologically inactive, non-carcinogenic and does not impair the reproductive function of living organisms. Use as food additives in safe concentrations does not lead to negative consequences. Dust from the compound can cause irritation if it comes into contact with the eyes and upper respiratory tract (the aerosol MPC is 10 mg/m3).
ST. PETERSBURG STATE TECHNOLOGICAL UNIVERSITY OF PLANT INDUSTRIES
POLYMERS
REPORT ON ENGINEERING PRACTICES
Methylcellulose and carboxymethylcellulose: properties of solutions and films
Checked by: senior researcher, doctor of chemical sciences
Alexander Mikhailovich Bochek
Completed: Art. gr. 144
Tatishcheva Valentina Aleksandrovna
SAINT PETERSBURG 2003
Introduction
Methylcellulose is the first member of the homologous series of 0-alkyl cellulose derivatives (ethers). According to the degree of substitution, cellulose methyl ethers can be divided into low-substituted, soluble in aqueous solutions of strong alkalis of a certain concentration, and highly substituted, soluble in both water and organic solvents. Cellulose methyl ethers can be obtained by reacting cellulose with various alkylating reagents: dimethyl sulfate, methyl chloride (or methyl iodide and bromide), diazomethane, benzenesulfonic acid methyl ester. Currently, methylcellulose (mainly water-soluble) is an industrial product.
Preparations of 0-carboxymethylcellulose, depending on the degree of substitution, as well as other 0-alkyl derivatives, can be divided into low-substituted and highly substituted. The preparation of CMC preparations with a degree of substitution γ greater than 100, however, is very difficult due to the electrostatic effects of repulsion of similarly charged groups (chloroacetate ion and carboxymethyl group). Therefore, practically “highly substituted” CMC preparations are products that have a degree of substitution γ = 50-100 and are water-soluble.
Obtaining methylcellulose
In industry, the most commonly used method for producing methylcellulose is the alkylation of alkali cellulose with methyl chloride.
The alkylation process with alkyl halides occurs at temperatures of 353-373 K. Since methyl chloride has a boiling point of 248 K, the alkylation reaction is carried out in autoclaves under high pressure.
During the alkylation process, side reactions occur between methyl chloride and alkali to form alcohol and salt, and between alcohol and methyl chloride to form dimethyl ether:
NaOH+CH 3 Cl+CH 3 OH→CH 3 OCH 3 +NaCl+H 2 O
CH 3 Cl+NaOH→CH 3 OH+NaCl
Therefore, it is necessary to use an excess of methyl chloride and a significant amount of solid alkali, since with increasing alkali concentration the decomposition of methyl chloride decreases.
The iodine atom is the easiest to exchange (the most mobile), which is due to its greater polarizability; however, alkyl iodides are relatively expensive. Chlorides and bromides differ little in reactivity, so in industrial syntheses they prefer to use more accessible alkyl chlorides.
The rate of reaction through the transition state is proportional to the concentration of each reactant. It should be assumed that the reaction of cellulose with methyl chloride occurs according to the above scheme, i.e., it is a bimolecular reaction of nucleophilic substitution –S N 2.
The production of methylcellulose is associated with certain difficulties due to the high consumption of reagents, the need to work under pressure, etc. Therefore, finding new ways to synthesize methylcellulose is of great practical importance. From this point of view, the works seem interesting. The authors used esters of aromatic sulfonic acids as alkylating agents, namely esters of p-toluenesulfonic acid, toluene disulfonic acid, benzene sulfonic acid and naphthalene sulfonic acid.
Alkylation with these ethers proceeds according to the following scheme:
C 6 H 7 O 2 (OH) 3 + xRSO 2 OR "→ C 6 H 7 O 2 (OH) 3 (OR") x + xRSO 2 OH,
where R= -C 6 H 5, -CH 3 C 6 H 4, -C 10 H 7; R"= -CH 3, -C 2 H 5, etc.
It was found that as the length of the alkylating radical increases, the reaction rate decreases. Based on experimental data, sulfonic acid esters can be arranged in the following series according to reactivity:
C 6 H 5 SO 2 OCH 3 > C 6 H 5 SO 2 OS 2 H 5 > C 6 H 5 SO 2 OS 6 H 7.
Most often, dimethyl sulfate (CH 3) 2 S0 4 is used for alkylation of cellulose in laboratory conditions, which has a boiling point of 461 K and allows one to obtain products at normal pressure. But, despite this, its use in production is limited due to its high toxicity. The formation of cellulose ether in the case of dimethyl sulfate can be expressed in general form by the following equation:
C 6 H 7 O 2 (OH) 3 + x(CH 3) 2 SO 4 → C b H 7 O 2 (OH) 3- x (OCH 3) x + xCH 3 OSO 3 Na + xH 2 O.
Simultaneously with the main alkylation reaction of cellulose, a side reaction of dimethyl sulfate decomposition also occurs according to the following scheme:
(CH 3) 2 SO 4 + 2NaOH → Na 2 SO 4 + 2CH 3 OH.
Methyl sulfuric acid formed during the main reaction can react with methyl alcohol, giving dimethyl ether and, in the presence of excess alkali, Na sulfate:
The methylation reaction occurs only in an alkaline environment, which is obviously due to the predominant reaction of cellulose in the form of a dissociated alkaline compound.
Obtaining fully substituted products by methylating cellulose using this method encounters significant difficulties. Thus, after 18 - 20 operations of methylation of cotton, Denham and Woodhouse obtained a product containing 44.6% OCH 3 (theoretical value for trimethylcellulose 45.58% OCH 3), and Irvine and Hirst - with a content of 42 - 43% OCH 3; After 28-fold methylation, Berl and Schupp obtained an ester containing 44.9% OCH 3 .
The existence of the above-described side reaction is one of the reasons why it is difficult to obtain a highly substituted product. The decomposition of dimethyl sulfate during the production of methylcellulose requires the use of a large excess of it, which, in turn, leads to the need to use a large excess of alkali, because the reaction of the medium must always remain alkaline.
It was found that at a higher alkali concentration it is possible to obtain a higher degree of substitution of methylcellulose. This fact is explained by various reasons. First, it has been shown that the degree of decomposition of dimethyl sulfate decreases with increasing alkali concentration. Secondly, it can be assumed that with increasing concentration of NaOH, the equilibrium in the system shifts to the right
C 6 H 7 O 2 (OH) 3 + Na + + OH − → C 6 H 7 O 2 (OH) 2 O − + Na + + H 2 O.
However, in some cases it is possible to obtain highly substituted methylcellulose without repeated repetitions of methylation.
Thus, Haworth et al., having previously crushed filter paper to a fine powder and suspended it in acetone, obtained a methoxyl content of 45% after 2-fold methylation. The simplest way to obtain a high methoxyl content is by dissolving recycled cellulose acetate in acetone and gradually adding dimethyl sulfate and aqueous alkali. In this way, a methoxyl content in the reaction product of close to 45% can be achieved in one operation.
Preparation of carboxymethylcellulose
Low-substituted Na-carboxymethylcellulose was obtained by reacting alkali cellulose with monochloroacetic acid under various conditions. Due to the fact that chloroacetic acid is a solid, crystalline substance and for the production of low-substituted products it is required in small quantities compared to cellulose, the uniform distribution of the reacting components of the mixture is of particular importance. In one of the methods, the reaction was carried out by treating air-dried cellulose with a solution of the sodium salt of monochloroacetic acid in a 17.5-18% NaOH solution at a liquid modulus of 5 (the ratio of the amount of liquid in ml to the mass of cellulose in g). The salt solution was prepared before the reaction by dissolving the appropriate portion of monochloroacetic acid in an alkali of such a concentration that after neutralization it remained within the specified value.
The degree of substitution of the low-substituted Na-salt of carboxymethylcellulose is determined by its Na content. The sodium content in carboxymethylcellulose can be determined by the gravimetric method in the form of sulfate, by ashing the sample in a crucible, treating the ash with sulfuric acid and calcination at 973 K, or by the volumetric method by back titrating excess sulfuric acid alkali in the presence of bromophenol blue as an indicator (the transition region must be in an acidic environment so that the alkali does not bind back to the carboxyl groups).
The solubility, viscosity of solutions and other properties of carboxymethylcellulose largely depend on the method of its preparation.
There are several known methods for producing Na-CMC, based on the same reaction:
Cell(OH) n + 2mNaOH + mCH 2 C1COOH →
Cell(OH) n - m (OSH 2 COONa) m + mNaCl + 2mH20,
but made in various modifications. Therefore, it is of interest to compare Na-CMC samples obtained from the same cellulose, but using different methods.
The following methods for obtaining CMC were used.
1. Cellulose mercerized with a 17.5% NaOH solution was pressed to 3 times its mass and processed in a Werner and Pfleiderer type grinder with dry sodium salt of monochloroacetic acid (CH2C1COONa) at a temperature of 313 K for 30 minutes. Then the reaction mixture was kept under stationary conditions at 295 K for 24 hours in a closed vessel. During this time, oxidative-alkaline destruction of cellulose occurs: the degree of polymerization decreases from 1200 to 300-400 and the solubility of CMC samples in water improves. According to this method, alkylation occurs at maximum concentrations of the active masses (cellulose and monochloroacetic acid), resulting in a high degree of alkylation. However, the conditions for mixing the reaction components are not favorable for obtaining uniformly alkylated Na-CMC samples.
P. Air-dried cellulose was treated with a solution of sodium salt of monochloroacetic acid in 18% NaOH solution at a liquid module of 5 and a temperature of 313 K. Oxidative-alkaline destruction was carried out in the above-described method 1 after squeezing the reaction mixture to
3 times the mass relative to cellulose. This method is characterized by the uniform penetration of the alkylating reagent - monochloroacetic acid - into the cellulose fibers during swelling, which makes it possible to obtain uniformly substituted products. However, as has been shown, most of the taken amount of CH 2 ClCOOH goes to the side reaction of its saponification.
III. Cellulose was mercerized with an 18% NaOH solution. Alkalicellulose, pressed to 5 times its mass, was washed on a Buchner funnel with propanol (with infusion) to remove excess NaOH and water. Propanol was added to the desired modulus and the pulp was placed in the grinder. After 10 minutes of grinding, dry salt CH 2 ClCOONa was added. The reaction was carried out at constant temperature. Using this method, the size of the side reaction of saponification of CH 2 ClCOONa is reduced to a minimum, thereby increasing the efficiency of using the alkylating reagent. In all cases, CMC samples were washed with hot 70% ethanol in a Soxhlett apparatus until a negative reaction for NaOH with phenolphthalein and for Cl – with AgNO 3 solution.
As you can see, the highest degree of substitution with the same amount of CH 2 C1COOH is achieved using method III - in a propanol environment. This is obviously explained by a decrease in the consumption of CH 2 ClCOOH for the side saponification reaction.
Properties of methylcellulose solutions
The solubility of low-substituted methylcellulose in water at room temperature and below and the composition of the fractions that go into solution depend on its degree of substitution, homogeneity and degree of polymerization.
In table Table 1 presents data on determining the solubility of various methylcellulose preparations in water. When analyzing the data in the table, the following circumstance first of all attracts attention: the solubility of methylcellulose in water is very low, even with a relatively high content of methoxyls (for methylcelluloses with a high degree of polymerization). Methylcelluloses, which have a lower degree of polymerization, are more soluble.
The method of producing methylcellulose is a significant factor that determines the solubility limits of methylcellulose in a particular solvent.
When producing methylcellulose in solution, the original crystalline structure is destroyed, and a new lattice is not immediately built when regenerated from solution (under special conditions), so the product turns out to be amorphous and, therefore, more easily soluble. Of great importance is the varying availability of cellulose, due to which a mixture of reaction products is obtained, the degree of substitution of which is different. This heterogeneity leads to a decrease in the amount of soluble substance.
A very interesting effect is the freezing effect, which manifests itself in a significant increase in solubility.
Table 1.
Solubility of methylcellulose in water
Sample number |
Solubility, % of absolutely dry sample |
Solubility, % of the original sample |
OSSN3 content in the undissolved part,% | Content of OCH3 in the dissolved part, % | |||
| Before freezing | Before freezing | After freezing and thawing | |||||
| 1 | 11,4 | 0,5 | 3,5 | - | 10,8 | - | 29,1 |
| 2 | 20,75 | 0 | 5,3 | - | 20,25 | - | 29,6 |
| 3 | 21,7 | 3,6 | 9,8 | 21,5 | 20,60 | 30,5 | 31,8 |
| 4 | 22,3 | 5,3 | 11,1 | 21,8 | 21,3 | 32,0 | 30,3 |
| 5 | 28,10 | 9,3 | 25,8 | 27,9 | 27,4 | 30,0 | 30,0 |
| 6 | 19,8 | 16,9 | 22,3 | 17,8 | 17,2 | 29,5 | 29,1 |
| 7 | 26,3 | 51,5 | 58,7 | 22,2 | 20,6 | 30,0 | 30,3 |
In table Table 2 presents data on the solubility of low-substituted methylcellulose in 6.5% NaOH. In contrast to dissolution in water, methylcellulose already at a degree of substitution of about 5 dissolves by 95% after freezing in a 6.5% NaOH solution. When freezing low-substituted methylcellulose, the average degree of its polymerization (in the case of relatively high-molecular products DP = 1100-1200) decreases to approximately 1000. Products obtained from previously degraded cellulose (by oxidative-alkaline destruction) and having a DP of about 400, after freezing, almost do not change its molecular weight.
Solutions of low-substituted methylcellulose with a concentration of 1-2% were studied. which can be classified as concentrated solutions. It should be noted that the concept of “concentrated” solutions of high-molecular substances in the sense of concentration is conditional and significantly differs from the usual concept of concentrated solutions.
table 2
Solubility of low-substituted methylcellulose in 6.5% NaOH solution
| Sample number | Degree of substitution | OCH3 content in methylcellulose, % | Solubility, % of the original sample | |
| At 291 K | After freezing and thawing | |||
| 1 | 68,6 | 12,4 | 3,4 | 100,0 |
| 2 | 66,9 | 12,1 | 3,4 | 97,8 |
| 3 | 64,5 | 11,66 | 2,8 | 100,0 |
| 4 | 50,3 | 9,1 | 2,3 | 99,3 |
| 5 | 47,5 | 8,6 | Not defined | 98,0 |
| 6 | 30,4 | 5,5 | Not defined | 99,2 |
| 7 | 24,3 | 4,4 | 0,5 | 99,0 |
| 8 | 22,7 | 4,1 | Not defined | 98,5 |
| 9 | 16,6 | 3,0 | Not defined | 96,0 |
| 10 | 11,6 | 2,1 | Not defined | 95,3 |
| 11 | 9,4 | 1,7 | Not defined | 95,1 |
| 12 | 6,6 | 1,2 | Not defined | 48,0 |
| 13 | 1,3 | 0,25 | Not defined | 35,6 |
| 14 | 21,5 | 3,9 | 7,6 | 100,0 |
| 15 | 29,9 | 5,4 | 9,57 | 100,0 |
| 16 | 32,1 | 5,8 | 11,87 | 100,0 |
In the chemistry of high-molecular compounds, concentrated solutions are those in which there is interaction between individual particles of a dispersed substance. As a result of this interaction, solutions of high-molecular substances show a number of deviations from the laws characteristic of normal liquids. These deviations already occur in relatively diluted 0.3-0.5% solutions.
The studied solutions of low-substituted methylcellulose had a concentration significantly higher than the indicated values and a fairly high degree of polymerization of chain molecules, so they can be classified as concentrated solutions.
As a rule, concentrated solutions of cellulose ethers are quite stable over time. This or that change in the viscosity of such solutions over time is determined by the influence of a number of factors, namely: a change in the degree of esterification of the dissolved product, a change in the degree of solvation and the possibility of the formation of three-dimensional structures.
We will consider in more detail the properties of water-soluble methylcellulose.
Properties of water-soluble methylcellulose
With an increase in the degree of methylation to γ = 50, the hygroscopicity of the resulting ester increases. This is explained by the fact that in cellulose macromolecules there is mutual saturation of most hydroxyl groups with the formation of hydrogen bonds.
When a higher degree of substitution in the region of 26.5-32.5% of the content of methoxyl groups is reached, methylcellulose dissolves in water. With a further increase in methoxyl groups to 38% and above, it loses its solubility in water (at room temperature and above). Highly methylated products are also soluble in organic solvents.
Aqueous solutions of methylcellulose (γ = 160-200), as in the case of low-substituted methylcelluloses, are not stable.
When solutions are heated, solubility deteriorates until the polymer precipitates. The upper limit of temperature stability of the solution is 313-333 K for such a product (depending on the DP and concentration). This phenomenon is explained by the formation of a “hydroxonium compound” of the alkoxy group with water, which is destroyed when the temperature rises, leading to the precipitation of the polymer.
The possibility of transferring tri-substituted methylcellulose into a solution (aqueous) was shown (trimethylcellulose was previously reprecipitated with petroleum ether from a solution in chloroform). The upper limit of temperature stability of a solution of trimethylcellulose in water at a concentration of about 2% is 288 K. Such solutions have good film-forming properties. Films formed in a desiccator over P 2 0 5 at low temperature have tensile strength (5-7). 10 7 N/m 2.
The fact that trimethylcellulose can be dissolved in water directly indicates the ability of OCH 3 groups to hydrate. The loss of trimethylcellulose from solution with a slight increase in temperature indicates a very low
the strength of these connections. With an increase in the proportion of hydroxyl groups in the ether, i.e., with a decrease in γ to 160, the upper limit of the temperature stability of the solution increases to 313-333 K. These conclusions were confirmed by studies of the homologue of methylcellulose - ethylcellulose. Highly substituted ethylcellulose (γ=200) behaves similarly to trimethylcellulose in terms of solubility in water. Under normal conditions, it dissolves in water only slightly - by 9%.
Re-precipitated EC is practically insoluble at room temperature, but at 273 K its solubility in water is 50-60%. Thus, fractionation of “highly substituted” EC was carried out, as a result of which the following fractions were obtained: reprecipitated, soluble and insoluble in water. To characterize the part of EC dissolved in water and to explain the reasons for the transition of only part of the substance into an aqueous solution, all fractions were characterized by the content of OC 2 H 5 groups, by the value of intrinsic viscosity, as well as by IR spectroscopy methods. The results are shown in table. 3.
Table 3
Characteristics of ethylcellulose fractions
Aqueous solutions of EC with γ = 220 can be obtained at a concentration of no more than 1.4%. Solutions with a concentration of no higher than 0.8% are transparent and stable over time at low temperatures. The turbidity of a 0.82% solution begins to increase extremely at temperatures above 279 K. In the case of a more concentrated solution, a sharp increase in turbidity occurs at a lower temperature.
Thus, EC is characterized by the same pattern as MC: with an increase in the degree of substitution, the limit of temperature stability of the solution decreases (as is known, ordinary water-soluble EC with γ = 100, like MC, coagulates when heated to 323-333 K) . Therefore, it is most likely to assume that -OS 2 H 5 groups take part in the interaction of EC with water.
In aqueous solutions, methylcellulose exhibits the properties of nonionic high-molecular substances. The intrinsic viscosity in these solutions is related to the molecular weight by the Kuhn-Mark relationship:
To determine the change in intrinsic viscosity depending on molecular weight and determine the constants of this equation, Vink carried out the destruction of methylcellulose by acid hydrolysis.
Methylcellulose was preliminarily purified by precipitation from an aqueous-ethanol solution with ether. The degree of substitution of the original cellulose was 1.74 and the degree of polymerization was 2000.
Based on measurements of absolute molecular weight values using osmometry and determination of end groups, the dependence of the intrinsic viscosity of the resulting methylcellulose fractions on its molecular weight (or degree of polymerization Py) was established:
Vincom found that the characteristic viscosity of methylcellulose does not depend on the presence of a foreign electrolyte - acid - in the solution.
It should be noted that other authors (who determined absolute molecular weights using sedimentation in an ultracentrifuge and light scattering) obtained slightly different values for the exponent “a” in the Kuhn-Mark equation for methylcellulose. Thus, in the work a = O.63 and in a = 0.55.. The authors themselves explain these discrepancies by the high ability of methylcellulose to aggregate in aqueous solutions.
Properties of carboxymethylcellulose solutions
Data on the solubility of various carboxymethylcellulose preparations show that low-substituted CMC after freezing almost completely dissolve even at a low γ value (about 2).
Thus, the effect of very small substitution and low temperatures on the solubility of these cellulose derivatives is fully confirmed.
The solubility of low-substituted carboxymethylcelluloses in alkali and the efficiency of sodium monochloroacetate can be increased by dry grinding the cellulose before reaction. The solubility of low-substituted carboxymethylcellulose preparations can also be increased by reducing the degree of polymerization by oxidative destruction in an alkaline environment. In this case, after the end of the reaction, which is carried out for 4 hours at 313 K, the CMC is squeezed out to 2.6-2.8 times its mass, crushed and subjected to “ripening,” i.e., oxidative-alkaline destruction. After a certain “maturation” time, Na-CMC is washed with water until neutral and dried. In this way, Na-CMC can be obtained, which has complete solubility in alkali at γ = 10-12 and gives 6-8% solutions.
The stability of solutions of low-substituted carboxymethylcellulose upon dilution was studied.
CMC solutions prepared by freezing in 4 and 6% caustic soda were diluted several times with distilled water, after which the minimum alkali concentration was noted, corresponding to the appearance of turbidity or the release of a precipitate. The data from these experiments showed that solutions of low-substituted Na-carboxymethylcellulose behave quite stable even when diluted to a very low alkali concentration, up to 0.5%. This circumstance is very important when preparing solutions of Na-salt of carboxymethylcellulose for practical purposes, for example, for finishing fabric.
The work investigated the effect of temperature on the viscosity of aqueous solutions of Na-CMC, as well as methylcellulose, hydroxyethylcellulose and methylcarboxymethylcellulose.
Temperature-viscosity relationships for aqueous solutions of cellulose ethers are of great practical importance, since their use in many cases depends on this.
Savage obtained a linear dependence of viscosity on temperature for Na-CMC solutions on a semi-logarithmic coordinate scale. The dependence of viscosity on temperature during reverse cooling of such solutions is expressed by a straight line lying slightly lower than the first one. These experiments confirm the hysteretic nature of changes in the viscosity of Na-CMC solutions under the influence of temperature.
The decrease in viscosity is obviously a consequence of the very low relaxation rate in such high-molecular systems as an aqueous solution of Na-CMC. The time it takes to establish equilibrium in them can be very long, so that during the measured period of time the system does not have time to return to its original state. The possibility of some degradation of molecules upon heating cannot be ruled out, which should, of course, lead to irreversible changes in viscosity.
Modern ideas about solutions of cellulose derivatives in various solvents are based on the fact that these substances form true solutions in which macromolecules are kinetically free. However, this does not exclude the fact that if the industrial product of cellulose esterification is extremely heterogeneous in the degree of esterification, then its individual fractions will be poorly soluble. As a result, the solution, along with most of the molecularly dispersed substance, may also contain remnants of the structure of the original cellulose.
Concentrated solutions of carboxymethylcellulose, like solutions of many other high-molecular compounds, are not Newtonian liquids.
Na-CMC solutions have a significant viscosity anomaly. A characteristic feature of its real solutions is also the presence of various non-molecular dispersed particles and aggregates of macromolecules, especially in the presence of multivalent cations. Therefore, both in viscometric and osmometric measurements of the degree of polymerization (DP), it is necessary to take into account these features and the actual composition of the solution and, before such measurements, separate the fractions that interfere with obtaining correct results.
When studying aqueous solutions of Na-CMC with a concentration from 0.0025 to 0.1 g/l, the work obtained data indicating a significant polarity of its molecules. The above data characterize carboxymethylcellulose as a substance that has a number of properties inherent in many polyelectrolytes. The presence of a large electric torque, it would seem, should determine in a number of cases the possibility of the manifestation of electrostatic adsorption. However, if we take into account the aggregation of CMC molecules with increasing its concentration in solution and the screening of its charges, it should be noted that electrostatic adsorption can manifest itself mainly in dilute solutions.
Properties of methylcellulose (films) regenerated from solutions
Dissolved in water and in aqueous-alkaline solutions, methylcellulose of varying degrees of substitution can be regenerated from them in the form of films. The production of films of low-substituted methylcellulose, soluble in alkali, is carried out by the “wet” method - by coagulation in specially selected precipitation baths. Satisfactory results were obtained with precipitation baths consisting of a solution of ammonium sulfate (NH 4) 2 SO 4 (100 g/l).
The effect of the ammonium sulfate precipitation bath can be expressed as follows:
2NaOH + (NH 4) 2 SO 4 =Na 2 SO 4 + 2NH 3 + 2H 2 0.
Due to a change in the composition of the solvent and partial dehydration of dissolved methylcellulose, its chains come closer together and undergo glass transition, i.e., the formation of a highly swollen film.
When a film is formed on a solid substrate, due to a certain tension (as a result of adhesive forces), a plane-oriented structure appears in it. At the same time, in a freshly formed film, due to its highly swollen state, some mobility of the chains is possible due to thermal movement. All this entails relaxation processes, i.e., the return of the film structure to the most stable position, corresponding to the isotropic state. Due to the above circumstances, when a methylcellulose film is formed on glass from its alkaline solution, the dimensions of the film decrease along the plane and its thickness increases.
In terms of mechanical strength, alkali-soluble films are close to conventional plasticized cellophane films, since they have
tensile strength in the longitudinal direction (6.8-8.8). 10 7 N/m 2, elongation at break about 20%.
Data on hygroscopicity and water absorption of films of low-substituted methylcellulose, presented in table. 4 show that
Table 4
Hygroscopicity and water absorption of methylcellulose films
the hygroscopicity and water absorption of methylcellulose films reach large values, which largely depend on the degree of esterification of the original methylcellulose; An increase in the content of OCH 3 groups in the initial product entails an increase in the hygroscopicity and swelling properties of methylcellulose films in water.
The structure of regenerated methylcellulose and its relationship with the physical and mechanical properties of films was studied in the work. For comparison purposes, films of low-substituted methylcellulose and high-substitution methylcellulose, up to 3, were studied. Films of the same high-substitution methylcellulose were obtained from such dramatically different solutions as water and organic solvents. This comparison is of particular interest, because it allows us to draw a conclusion about the structure of the methylcellulose lattice during regeneration from solution, depending not only on the degree of substitution, but also on the solvent. For this purpose, methylcellulose with a high degree of substitution (close to 3) was obtained, capable of dissolving both in water and in the organic solvent chloroform. Films from aqueous solutions and solutions in chloroform were obtained by casting on glass and evaporating the solvent.
Films from an aqueous solution of methylcellulose (γ = 180), obtained by slow evaporation of the solvent at room temperature, have an amorphous structure. However, with such a high degree of substitution under certain conditions, the possibility of ordering the structure of methylcellulose in the finished films is quite likely. Such conditions turned out to be heating of the films in an environment that causes swelling. Thus, already boiling the film in water (methylcellulose is insoluble in hot water) for 30 minutes causes a noticeable increase in the order. Heating the film in glycerol at a temperature of 473 K causes even greater ordering.
Of particular interest is the formation of films from aqueous solutions of methylcellulose at elevated temperatures. When a film is boiled in water, in addition to ordering, the structure is compacted and various internal defects are destroyed, which apparently explains the increase
film strength.
Forming films at 343 K leads to a significant increase in elasticity, which can be explained by a more folded configuration of macromolecules, since hot water is not a solvent for methylcellulose.
Moving on to a consideration of the structure of trimethylcellulose films, we should note an interesting feature of this ether. Trimethylcellulose is able to dissolve not only in organic solvents, but also in cold water (T = 273 K). The structure of trimethylcellulose films as a stereoregular polymer is characterized by high crystallinity. Water is a v-solvent for trimethylcellulose, so films formed from an aqueous solution are less crystalline.
Electron microscopic examination of the surface of MC films and the surface of chips obtained as a result of film fracture along the drawing axis at liquid nitrogen temperature made it possible to establish smaller-scale details of the film structure. At draw ratios λ≤2.0, the surface of the oriented films remains quite smooth and even. The fibrillar structure, visible in an optical microscope, is not detected by electron microscopy. At λ≈2.2-2.5, a relief appears on the surface of the films, formed by fairly regular and extended grooves 0.2-0.4 µm wide, directed perpendicular to the drawing axis. When scanning perpendicular to the hood axis (Fig. 1), transverse folds 0.3-0.5 µm wide are visible, and in some areas delaminations are found in the form of microcracks with a width of 0.1-0.2 µm and a length of 1.0-1.5 µm, directed parallel to the hood axis. When scanning parallel to the stretch axis, in addition to the folded structure, irregularities with a predominant orientation along the stretch axis become visible. Examination of the chipped surface reveals the presence of a porous structure; the pore size ranges from 0.1 to 1.0 µm.
Properties of regenerated from alkaline solution Na -KMC (in the form films)
Due to the possibility of obtaining viscous solutions of low-substituted carboxymethylcellulose with a sufficiently high degree of polymerization, films were prepared and their properties were studied.
Film formation was carried out according to the technique used for methylcellulose solutions. In table Figure 5 shows data on the mechanical strength of the films. Films made from low-substituted carboxymethylcellulose had good mechanical strength, but low elasticity; The elongation at break of these films was only 5-6%.
Table 5
Tensile strength of low-substituted carboxymethylcellulose films
| Sample number | Degree of substitution γ | Solution concentration, % | Tensile strength σ. 10 -7 , |
Tension at break % |
| 1 | 5,0 | 2,0 | 9,0 | 5,3 |
| 2 | 10,4 | 2,0 | 9,3 | 6,0 |
| 3 | 9,8 | 2,0 | 7,9 | 5,0 |
| 4 | 9;8 | 4,0 | 11,8 | 6,0 |
| 5 | 9,2 | 2,0 | 8,3 | 5,0 |
| 6 | 9,2 | 4,0 | 11,3_ | - |
Data on hygroscopicity and water absorption of films made from low-substituted carboxymethylcellulose are presented in Table 6. Hygroscopicity was determined by keeping the films in an atmosphere with a relative humidity of 80%; water absorption was measured by soaking the films in distilled water for two days at 293 K.
Table 6
Hygroscopicity and water absorption of films made from low-substituted
carboxymethylcellulose
As can be seen from table. 6, the hygroscopicity and water absorption of low-substituted carboxymethylcellulose films increase rapidly as
increasing the degree of product substitution. The influence of the degree of substitution on the water absorption of films is especially noticeable.
The effect of increasing the hydrophilic properties of cellulose with the introduction of a small amount of bulky radicals into it is explained, as already mentioned, by the fact that in the initial stage of esterification there is a redistribution of the strength of hydrogen bonds in the transverse structure of the fiber, characterized by the accumulation of weaker bonds.
Applications of methylcellulose
Highly substituted water-soluble methylcellulose preparations (γ = 150-200) received the greatest importance. These products have a complex of valuable technical properties and are produced industrially in the form of small granules or white or slightly yellowish powder. They are practically odorless and tasteless. At a temperature of 433 K they become colored and decompose. Aqueous solutions of methylcellulose give a neutral reaction.
In most cases, methylcellulose is used to thicken the aqueous medium. The effectiveness of thickening depends on the viscosity (i.e., the degree of polymerization). Methylcellulose allows water-insoluble substances to be converted into a stable finely dispersed state in an aqueous environment, since it forms hydrophilic monomolecular protective layers around individual particles.
Valuable properties of methylcellulose are its high binding effect for pigments, high dry adhesion and ability to form films. These interesting properties are used in the preparation of water-based paints and adhesives. Methylcelluloses with a low viscosity are especially suitable for this purpose, since they can be applied to a wide variety of substrates.
In the textile industry, methylcellulose is used as a sizing agent for wool warps and for soft finishing of fabrics to achieve an elegant feel and gloss.
Methylcellulose is successfully used in the soap industry. In pharmaceutical practice, it is used as a fat-free base for so-called mucous and oil/water emulsion ointments, which serve to protect the skin from light burns and for the treatment of wounds. In addition, methylcellulose serves as an independent drug.
In cosmetics, water-soluble cellulose ethers are used to produce toothpastes and elixirs, protective emulsions and low-fat skin creams.
In all kinds of emulsions, methylcellulose is used as emulsifiers and stabilizers for vegetable oils.
It is also widely used in the food industry.
Thus, in the production of ice cream, its use provides the necessary fluffiness, stability and taste. Methylcellulose is used in flavor emulsions, gravies, fruit juices, canned food, etc.
An interesting application in the food industry is the ability of methylcellulose solutions to gelatinize when heated. For example, adding methylcellulose to fruit pie fillings or sweet jam fillings prevents these components from leaking out during baking, which significantly improves the appearance and preserves the taste of the products.
In pencil factories, methylcellulose is used instead of gum tragacanth for color and copying leads, for pastel leads, school crayons and paints, etc.
Thus, the applications of water-soluble methylcellulose, although smaller in scale than CMC, are extremely diverse.
As for low-substituted (alkali-soluble) methyl cellulose, it has not yet received significant use.
Applications of carboxymethylcellulose
Films consisting of 100% H-CMC are soluble starting only from pH=11. Films of the specified composition can be used in cases where it is desirable to limit their solubility within small pH ranges, for example, in pharmaceutical coatings. Such a shell should not dissolve, for example, in the slightly acidic environment of gastric juice, but dissolves well in the slightly alkaline environment of the intestine.
Sodium salt of carboxymethylcellulose with a degree of substitution from 0.5 to 1 −1.2 is produced by industry in large quantities, as it is widely used in petroleum, textile, food, pharmaceutical technologies, in the production of detergents, etc. as a stabilizing, thickening, adhesive, film-forming agent etc. substance. This salt is highly soluble in water.
A number of studies conducted testing Na-CMC as an additive to detergents have shown that this product significantly improves their cleaning properties.
Literature
1.Prokofieva M.V., Rodionov N.A., Kozlov M.P.//Chemistry and technology
cellulose derivatives. Vladimir, 1968.S. 118.
2. Nesmeyanov A.N., Nesmeyanov N.A. The beginnings of organic chemistry. M., 1969.T.1.
663s.
3. Plisko E.A.//ZHOKH.1958. T. 28, No. 12. S, 3214.
4. Plisko E.A.//ZHOKH.1961. T. 31, No. 2. P. 474
5. Heuser E. The Chemistry of Cellulose. New York, 1944. 660 p.
6. Gluzman M.X., Levitskaya I.B. //ZHPH. 1960. T. 33, N 5. P. 1172
7. Petropavlovsky G.A., Vasilyeva G.G., Volkova L.A. // Cell. Chem.
Technol. 1967. Vol. 1, N2. P. 211.
8. Nikitin N.I., Petropavlovsky G.A. //ZHPH. 1956. T. 29. P. 1540
9. Petropavlovsky G.A., Nikitin N.I. //Tr. Institute of Forests of the USSR Academy of Sciences. 1958. T.45.
P. 140.
10. Vasilyeva G.G. Properties of alkali-soluble carboxymethylcellulose and
Possibility of its use in the paper industry: Dis. Ph.D.
tech. Sci. L. 1960.
11. VinkH. //Macromoleculare Chemie. 1966. Bd. 94. S. 1.
12. Vole K., Meyerhoff G. // Macromoleculare Chemie. 1961. Bd. 47. S. 168.
13. NeelyW.B.//J. Organ. Chem. 1961. Vol. 26. P. 3015.
14. Savage A.B. //Ind. Eng. Chem. 1957. Vol. 49. P. 99.
15. Allgen L. //J. Polymer Sci. 1954. Vol. 14, N 75.P. 281.
16. Podgorodetsky E.K. Technology for the production of films from
high molecular weight compounds. M: Art, 1953. 77 p.
Introductionp. 2
Obtaining methylcellulose page 2
Preparation of carboxymethylcellulose page 4
Properties of methylcellulose solutions pp. 6
Properties of water-soluble methylcellulosep. 8
Properties of carboxymethylcellulose solutions pp. eleven
Properties of methylcellulose regenerated from solutions
(films)p. 12
Properties of Na-CMC regenerated from an alkaline solution
(in the form of films) p. 15
Application of methylcellulose 16
Application of carboxymethylcellulosep. 18
For many years, wallpaper has been one of the most common materials for interior decoration. And the most popular means of installing them remains CMC glue. It not only firmly and permanently attaches the canvas to the wall surface, but also has one important quality: it is diluted in water of almost any temperature, which is not typical for other similar compositions. It is noteworthy that in this case lumps, clots and sediment do not form in the adhesive liquid. This is predetermined by its technical, performance characteristics and chemical structure features.
Compound
The name of the glue comes from its chemical composition. The basis is a substance called carboxymethylcellulose. For the purpose of ease of pronunciation and abbreviation of the name, the manufacturers created an abbreviation from the first letters of each of the three components of the word - KMC. Externally, the glue is a white powder, the particles of which are small granules.
Recently, CMC wallpaper adhesive with auxiliary antiseptic properties has gained popularity. Special additives endowed it with this property. Now the adhesive layer actively prevents the formation and growth of mold.
So, the time has come to consider in more detail all the technical characteristics of the CMC adhesive composition:
- the amount of dry matter in the structure is from 57%;
- the total volume of dry matter contains at least 69% of the active element;
- sodium chloride content in dry matter is 21%;
- product humidity - 12%;
- the period of thorough swelling of the particles until a homogeneous mixture is formed is no more than two hours;
- the working properties of the finished solution are maintained for 7 days.
It is important that the composition of CMC wallpaper glue includes special additives that give it insecticidal properties and also prevent it from rotting. However, the glue is absolutely harmless to our health, since its components are non-toxic.
It is often added to the mixture for installing tiles, as well as to cement and chalk putties, which significantly increases their adhesive qualities and strength.
Types, how to choose
The color of a product is an important characteristic; you should pay attention to it when choosing a product in a store. Glue powder, produced in accordance with GOST standards, is pure white. This product is characterized by excellent quality; when combined with water, it forms a homogeneous mixture without sediment or lumps.
A yellow tint is not acceptable. He usually says that the glue is made in a homemade way by unscrupulous manufacturers. A product like this has the same quality. They usually do not meet the standards of adhesive work, so the result can be very disappointing. For example, after drying, unpleasant yellow stains will appear on paper wallpaper, which can no longer be removed, and you will have to repeat all the work of gluing the wallpaper.
Advice! Despite the large selection of this glue in hardware stores, be sure to carefully study the product before purchasing. Pay special attention to its color.
If we approach the description of CMC glue from the point of view of its purpose, then it is divided into three main groups:
- for installation of light thin wallpaper;
- for medium weight wallpaper;
- for thick, heavy wallpaper.
The thickness and stickiness of the mixture and, as a result, the ability to firmly attach heavy webs, directly depends on the amount of the main substance in the powder - carboxymethylcellulose. If there is a lot of it, then the solution is more viscous, and even heavy vinyl wallpaper will hold securely on the wall.
Advantages and main manufacturers of CMC
In addition to the already mentioned advantages (versatility, extreme simplicity in diluting the powder, reliability, protection against microbes and mold), CMC wallpaper adhesive has the following advantages:
- the appearance of stains and stains on the surface of the wallpaper is excluded;
- the repulsive odor is completely absent;
- the glue is very easy to prepare and use;
- the product is successfully combined with other chemical compounds.
Products of this kind, both domestic and foreign, are widely represented on the building materials market. Russian CMC glue has distinctive features, such as an affordable price and satisfactory characteristics. At the same time, it usually swells in 2 hours, which is acceptable from the point of view of the GOST standard.
The cost of foreign-made products is much higher. At the same time, the solution is prepared faster; after 15 minutes after dilution, it can already be used for wallpapering.
Undoubtedly, one of the most popular manufacturers of KMC wallpaper adhesive in Russia is Vympel Trade Center LLC, operating in the Moscow region. All its products are provided with the necessary certificates.
Features of using CMC glue
Let's look at what you need to know about preparing the adhesive mixture. It has already been verified by experience that there is nothing tricky in this procedure, and everyone is able to perform all the actions with their own hands.
- First of all, you need to prepare an enamel container: a bucket, basin or something similar. Take the packaged glue and look on the wrapper for instructions for preparation.
- Each package contains special information about the amount of dry glue and water that needs to be taken in order to properly prepare the adhesive solution. Typically, when working with thin wallpaper, 8 liters of water are taken per 500 g of powder. To glue thick canvases to the same amount of dry glue, you need to take 7 liters of water.
- The water should be at room temperature.
- Having looked at the ratio contained in the instructions, we begin to gradually pour the adhesive powder into the water, continuously stirring the liquid intensively.
- Leave the solution alone for the time specified in the instructions, wait until it is completely ready.
Advice! Information on the consumption of the finished adhesive composition is indicated by the manufacturer in the corresponding leaflet on the packaging.
As a rule, a package weighing 500 g is enough to cover a surface area of approximately 50 square meters.
As we said earlier, you should select the type of CMC glue with such technical characteristics that are optimally suited to the type of wallpaper that you plan to paste.
Where else is CMC glue used?
In addition to carrying out renovation work in homes, this composition is suitable for finishing offices, industrial premises, as well as for production purposes:
- foundry;
- construction, production of finishing and building materials;
- chemical industry;
- mining industry.
The popularity of KMC wallpaper glue does not decrease from year to year; knowing the specifics of working with it, you are protected in advance from possible errors and shortcomings when performing renovations in an apartment.
Sodium carboxymethyl cellulose (CMC) is the most versatile chemical reagent from the group of water-soluble colloids. CMC is the sodium salt of cellulose-glycolic acid, obtained by reacting alkali cellulose with sodium monochloroacetate.
The finished CMC is a fine-grained, fibrous or powdery material that is white or cream in color. NaCMC technical does not have a toxic or irritating effect.
CMC has the following properties:
Water retention
Viscosity increase
Can be used as a binding agent
Modification of rheological properties
Suspension and stabilization of dispersion solutions
Surface absorption capacity of minerals and other particles
Areas of use:
As an artificial substitute for natural water-soluble colloids (eg starch), NaCMC is used in many industries. This prevalence is due to its almost unique property of forming viscous homogeneous solutions in both cold and hot aqueous environments.
The largest volumes of CMC are consumed in the following activities:
- Production of synthetic detergents
A small addition of CMC to washing powder or washing paste prevents dirt particles from returning to the surface of the fabric during washing, providing a high degree of cleanliness (increases resorption properties).
- Oil and gas industry
In this industry, CMC is used as a protective colloid-stabilizer in highly mineralized clay suspensions during drilling.
- Mining and processing industry
CMC is used in the flotation concentration of copper-nickel and sylvinite ores.
- Textile industry
Using CMC, the base of the fabric is sized. Threads treated with CMC solution are less prone to breakage during the weaving process, which in turn reduces the number of stoppages, increasing the efficiency of weaving production.
- Construction industry
CMC is used as an adhesive material in the production of various adhesive solutions, putties, and in the production of sand-lime bricks as a suspending and binding agent.
- Paint industry
CMC is used as a thickener
- In the paper industry
In this area, CMC is used as an adhesive base for wallpaper pastes, in the manufacture of coatings on paper, and as an additive to paper pulp to increase the strength of paper.
- In foundry
CMC is used as a rod fastener.
- For biological research
CMC is used in its free acid form as a sorbitol ion exchanger.