CMC, very commonly known as carboxymethyl cellulose is basically a derivative of cellulose while having carboxymethyl groups that are bonded with the hydroxyl groups of a compound known as glucopyranose. These are the building blocks of the cellulose backbone. Their preparation method is quite hard and takes up a lot of essentials for carrying out the purpose.

All the different sources of carboxymethyl cellulose are listed in this article which tells us about the whereabouts of this particular compound. In addition to all the excellent characteristics, there is a wide range of applications which are carried out by the carboxyl methylcellulose compounds fairly making an excellent mark in the industries of the whole world.

Introduction

Cellulose gum or Carboxymethyl cellulose (CMC) is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the glucopyranose monomers’ hydroxyl groups which makes up the backbone of cellulose. Carboxymethyl cellulose (CMC) is an anionic, water-soluble cellulose derivative. Most often, it is utilized as its sodium carboxymethyl cellulose, sodium salt. It is utilized for being marketed under the SE Tylose’s registered trademark, named Tylose.

The substitution distribution's uniformity and the degree of substitution determine the CMC's solubility. Its solubility also depends on the DP. With increased carboxymethyl substitution, substitution uniformity, and decreased DP, there would be an increase in CMC's water solubility. With an increase in concentration and DP of the solution, the solution’s viscosity also increases.

At any temperature, CMC is soluble in water. Carboxymethyl cellulose hydrates fast due to its extremely hygroscopic nature. When introduced into water, the CMC powder’s rapid hydration may result in the agglomeration and the formation of lumps. Lumps would not be created if high agitation is applied while the powder is added into the water or pre-blending the CMC powder with other dry ingredients like sugar, before its addition into the water.

Preparation of Carboxymethyl Cellulose

Cellulose’s alkali-catalyzed reaction with chloroacetic acid synthesizes carboxymethyl cellulose. Cellulose is chemically reactive and soluble because of the polar (organic acid) carboxyl groups.

After the first reaction, about 60% of CMC along with 40% of salts (sodium glycolate and sodium chloride) will be produced by the resultant mixture. This product is utilized in detergents and is the famous technical CMC. To create the pure CMC, a purification process is further utilized for removing these salts so that the pure CMC can be utilized for dentrifice (toothpaste), pharmaceutical, and food applications. Another production that happens is of an intermediate "semipurified" grade, which is utilized typically in paper applications, for instance, restoration of archival documents. Cellulose structure’s degree of substitution (how many hydroxyl groups in the substitution reaction), cellulose backbone structure’s chain length, and carboxymethyl substituent's degree of clustering are the three main components that determine the functional characteristics of carboxyl methylcellulose

Source of Carboxymethyl Cellulose (CMC)

After the first World War, Jansen discovered Carboxymethyl cellulose (CMC) for the first time. It was attained by him in a reaction between mono chloroacetic acid, or its sodium salt in an alkaline medium with an organic solvent’s presence, for instance, the hydroxyl group substituent. When World War II was about to end, carboxymethyl cellulose started. Carboxymethyl cellulose is extracted from cellulose which is a simple polymer based on sugar and present in the plant materials. The process is of 2 steps for the formation of carboxymethyl cellulose in commercial quantity;

Cellulose’s suspension in an alkaline medium. The suspension results in the opening of the chains of cellulose and paving the way for the water to enter.

After the suspension, the cellulose can give sodium carboxymethyl cellulose by reacting with sodium monochloroacetate.

The Functionality of Carboxymethyl Cellulose

The following factors determine several functions of carboxymethyl cellulose:

• Cellulose’s backbone.
• Carboxy methylcellulose chain’s length
• Amount of carboxymethyl cellulose and homogeneity of the substitution of sodium ions

For example, smooth flow potential will be improved by carboxymethyl cellulose with homogeneity substituent and it will function well in icing too. However, carboxymethyl cellulose with non-homogeneity replacement species is called thixotropic. Carboxymethyl cellulose produces a firm gel which transforms into extra molten when it is disturbed and thereby with time, enhances the gel.

Carboxymethyl Cellulose Solid Polymer Electrolytes

The development of a new polymer electrolyte system in the past three decades has been a significant part of research because of the need of searching electrolytes of new types for applications in numerous electrochemical devices. In 1975, after the discovery of ionic conductivity in a PEO/Na+ complex by Wright, SPE got more concern by the researcher, specifically because of the improvement of ionic conductivity. In comparison with gel and liquid polymer electrolytes, individual characteristics are possessed by solid polymer electrolytes (SPE), for instance, easy to fabricate, flexibility, low self-discharge in batteries, no leakage, and good compatibility with electrolytes.

Due to their remarkable electrical and mechanical characteristics, a huge amount of attention has been currently gained by the polymer electrolytes that are obtained from natural polymers like cellulose and starch derivatives like carboxymethyl cellulose (CMC), methylcellulose (MC), and hydroxyl ethyl cellulose (HEC). CMC displays amphiphilic properties. CMC also possesses many hydrophilic carboxyl groups and a hydrophobic polysaccharide backbone. One of the earth's most abundant organic substances is CMC.

Solid Polymer Electrodes

OA- and CMC-based solid polymer electrolytes were made and they occurred to be a transparent film. At room temperature (303 K), the highest ionic conductivity of 2.11 x 10-5 S cm-1 was possessed by sample OA20. Non-Debye behavior is showed by the samples in this study according to the Dielectric study. As compared to the value of the activation energy of conduction, the activation energy of relaxation is more, implying the fact that while conducting and also relaxing, the charge carrier has to overcome the higher energy barrier.

Cellulose-The Organic Material

One of the planet's most abundant organic materials is cellulose. All plants have cellulose as its integral part. For the packaging, paper, and textile industry, the most preferred raw material is cellulose. One of the most significant commercial cellulose ether is carboxymethyl cellulose (CMC). CMC is a cellulose derivative with sodium carboxymethyl group substitution to some of the glucopyranose monomers’ hydroxyl groups. The cellulose backbone is made up of the glucopyranose monomers’ hydroxyl groups. The structure is based on the cellulose’s (1→4)-d-glucopyranose polymer. A different degree of substitution is possessed by different preparations, but generally, it is in the range of 0.6-0.95 derivative per monomer unit.

CMC is used as a film former, stabilizer, binder, rheology control agent, and an effective thickener. Due to such usages, CMC also finds applications in the oil drilling fluids, adhesives, textile, pharmaceutical, food, cosmetics, and other industries. Recently, a huge amount of interest is gained in grafting polymerize vinyl and acryl monomers onto the cellulose backbone. When the monomer is grafted, some of the cellulose’s drawbacks like low strength against microbial degradation, high moisture transmission, and low tensile strength are eliminated.

To get more information about carboxymethyl cellulose (CMC),

you can read our blog post here.

The Graft Copolymers

According to its definition, graft copolymers are made up of one polymer’s long sequence (known as the backbone polymer) with another polymer’s one or more grafts (branches) which are chemically different from each other (Gowariker, Viswanathan, & Sreedhar, 1986; Odian, 2002). The synthesis of graft copolymer starts taking place with a polymer that’s preformed (in the grafted polysaccharide's case, it's the polysaccharide). Free radical sites are created on this preformed polymer by using an external agent which should be effective and sufficient enough for forming the desired free radical sites on the preformed polymer, and at the same time, the agent should not be too drastic that it may rupture the preformed polymer chain’s structural integrity. After the formation of free radical sites on the polymer backbone, the grafted chains are formed when the monomer (acrylic or vinyl compound) gets added up through the chain propagation step.

Synthesis of graft copolymer can be done via different methods, all of which are different from each other, for instance, there is a difference between them in the ways of formation of the free radical sites on this preformed polymer. Conventionally, UV rays in photosensitizers presence, high energy radiation (electron beam or gamma rays), or chemical-free radical initiators are utilized for this purpose. According to earlier studies, the most effective technique of synthesizing graft copolymer involves the usage of microwave radiations for starting the grafting reactions. Selective excitation of only the polar bonds is caused by the microwave radiations, therefore causing their cleavage/rupture, and thus resulting in the production of free radical sites.

The ‘C-C’ backbone

The microwave radiation doesn’t affect the preformed polymer’s ‘C–C’ backbone as it is comparatively non-polar. Synthesis methods like the microwave-based synthesis of graft copolymers have inherent benefits, as they are highly reproducible, simple, fast, and have great control over percentage grafting. Also, no inert atmospheric conditions are required by the microwave-based methods but many conventional synthesis methods do require that (for instance, ceric ammonium nitrate initiated methods). In conclusion, the most suitable method for the commercialization of these materials is the microwave-based method of graft copolymer synthesis as it has all the desired qualities.

Synthesis of CMC-g-PAA by Microwave Initiated Method

Microwave initiated method also synthesized CMC-g-PAA. There were variations in the time of microwave irradiation and concentration of acrylic acid (monomer) during the synthesis of graft copolymer’s various grades. The concentration of monomer and time of irradiation optimizes the synthesis. Its intrinsic viscosity and higher percentage grafting determine its optimized grade. The requirements are approximately 10 g concentration and 5 minutes of irradiation time when the microwave power is 800W. When the microwave radiation irradiates small polar molecules like water, the complete molecule rotates and heat is formed in the process. Due to the rotation of the whole molecule, there is no bond breakage (no free radicals are formed).

Polysaccharides Solution

No response is shown by the not so polar bonds (C-C bonds) when the macromolecules like polysaccharides are being irradiated with microwave radiation but at the same time, the polar bonds (O–H bonds) rotates in response. The polar bonds break because of the molecule's such partial rotation, which therefore results in the formation of free radical sites. Thus, microwave radiations cause selective excitation of the polar bonds unlike thermal energy and high energy radiations. The backbone polymer’s structural integrity remains intact because C-C bonds are not affected. After the formation of free radical sites on the backbone polymer, chain propagation is used to add the monomer up until the chain termination step terminates the free radical sites.

Uses of Carboxymethyl Cellulose

CMC is utilized as a thickener or viscosity modifier in food under the name E466 or E469 (when it is hydrolyzed, enzymatically). CMC is also used for stabilizing emulsions in numerous products, for instance, ice cream. CMC is a component of many of the non-food products too, for instance, reusable heat packs, textile sizing, detergents, water-based paints, diet pills, laxatives, toothpaste, and numerous paper products.

Due to its nontoxicity and high viscosity, CMC is primarily utilized and is considered to be hypoallergenic as cotton linter or softwood pulp is the major source fiber. In reduced-fat and gluten-free food products, CMC is broadly utilized. It is also used as a soil suspension polymer made for depositing onto cotton and other cellulosic fabrics in laundry detergents, forming a negatively charged barrier to soils in the wash solution. In artificial tears, CMC acts as a lubricant.

As a Thickening Agent

Carboxymethyl cellulose is utilized as a thickening agent too. It acts as a drilling mud ingredient in the oil-drilling industry, where it functions as a water retention agent and a viscosity modifier too. For instance, in rabbits, sodium CMC (Na CMC) is utilized for alopecia as a negative control agent.

Cellulose-made knitted fabric (for instance, viscose rayon or cotton) can be converted into CMC and can be utilized in numerous applications in medicine.

1. A device for nose bleeding (epistaxis). CMC knitted fabric covers a poly-vinyl chloride (PVC) balloon. The fabric is reinforced by nylon. A gel is formed when the device is soaked in water. The device is inserted inside the nose and the balloon is then inflated. Due to the balloon’s inflation and the CMC’s therapeutic effect, the bleeding stops.
2. It is used after the surgical procedures of the throat, nose, and ear as a fabric dressing.
3. A gel is made by adding water. After the surgery, the gel is inserted into the sinus cavity.

For purification of proteins in ion-exchange chromatography, insoluble micro granular CMC is utilized as a cation-exchange resin. The derivatization’s level is apparently much lower, so the micro granular cellulose's solubility characteristics are retained while adding enough negatively charged carboxylate groups for binding them to the positively charged proteins.

If you are interested in the applications of cellulose nanocrystals (CNC),

you can read our blog post here.

CMC in Ice Packs

CMC is utilized in ice packs for forming a eutectic mixture leading to a lower freezing point, and thus the cooling capacity of CMC is more than ice.

CMC in Aqueous Solutions

CMC’s aqueous solutions have been utilized for dispersing carbon nanotubes. Nanotubes are wrapped with the long CMC molecules, and dispersed in water. CMC is utilized as a fixative (commercially known as Walocel, Klucel) or as an adhesive in conservation-restoration.

CMC in Wine

In wine, CMC is utilized for obtaining tartrate or cold stability. In warm climates, wine is chilled by using megawatts of electricity which can be saved by this innovation. CMC is more stable as compared to metatartaric acid and CMC is also extremely effective in preventing tartrate precipitation.

According to reports, in CMC’s presence, the KHT crystals grow slower and their morphology is changed. Their shapes turn flat and flat as they lose 2 faces out of 7, altering their dimensions. Negatively charged at wine pH, the CMC molecules interact with the crystals' electropositive surface, and the potassium ions are contained at that surface. Due to the competition between the bitartrate ions and CMC molecule to bind to the KHT crystals, the result is the crystal's slower growth and shape modification. (Cracherau et al. 2001).

CMC in Veterinary Medicine

In large animals like horses, CMC is utilized in veterinary medicine, abdominal surgeries, and also for preventing the creation of bowel adhesions.

CMC as an Electrode Binder

In advanced battery applications (Li-ion batteries), particularly with graphite anodes sometimes, CMC is utilized as an electrode binder. The water solubility of CMC allows for less toxic and less expensive processing as compared to the non-water-soluble binders, for instance, the traditional polyvinylidene fluoride (PVDF). Toxic n-methyl pyrrolidone (NMP) is required by the PVDF for processing. For the electrodes which require extra flexibility, CMC is used often in conjunction with styrene-butadiene rubber (SBR).

Culinary Uses

In the ice cream industry, the need for salt ice mixes or conventional churners is eliminated as the CMC powder is utilized broadly in the ice cream industry for making ice creams without very low temperatures or churning. CMC is also utilized in making bakery products, for instance, cake and bread. CMC economizes on the fat component and provides a loaf to the baker in a much-enhanced quality but less cost. In biscuits of high quality, CMC acts as an emulsifier. CMC uniformly disperses fat in the dough, improving the dough’s release from the cutters and molds, thus attaining biscuits of good shape with no distorted edges.

CMC can achieve economy by helping in lessening the amount of fat or egg yolk that’s utilized in the production of biscuits. CMC can be used in the preparation of candies as it enhances the quality and texture of candies and guarantees smooth dispersion in flavor oils. CMC is utilized as an emulsifier in peanut butter, kinds of margarine, and chewing gums. CMC is used in leather crafting too for burnishing the edges.

Construction Industry

In the compositions of most of the cement and building materials, CMC is utilized and it functions as a hydrophilic agent and a stabilizer. CMC enhances sand’s dispersion in the cement and intensifies the adhesive action of the sand. In upholstery, CMC is also utilized as glue.

Detergents

CMC’s largest consumer is the detergent industry. Most often, the technical grade CMC compositions are utilized for detergents and soaps. After the detergent removes the grease, CMC redeposits the grease in the fabric by acting as an inhibitor.

Adhesives

Carboxyl methylcellulose is added to numerous compositions of adhesives and glues that are utilized for most of the materials. CMC is broadly utilized in the industry of leather. If CMC is combined with phenol-formaldehyde and starch, the adhesives that combine wood with other wood will be formed.

Enzymology

The usage of CMC is also extensively done for characterizing the enzyme activity from endoglucanases (cellulose complex’s part). For endo-acting cellulases, CMC is a highly specific substrate, as the structure of CMC is made for de-crystallizing cellulase and forming amorphous sites that are suitable for endoglucanase action. Carboxyl methylcellulose is required because the reducing sugar assay can be used to measure the catalysis product (glucose) easily, for instance, dinitrosalicylic acid.

If screening for cellulose enzymes, one of the significant methods is utilizing CMC in enzyme assays as the cellulase enzymes are desired for the conversion of cellulosic ethanol more efficiently. Although, earlier, CMC has been used with cellulase enzymes due to the association of complete cellulase activity with CMC hydrolysis. After completely understanding the cellulose depolymerization’s mechanism, it is understood that exo-cellulases are dominant in crystalline degradation (Avicel) and cellulose that’s not soluble (CMC).

Conclusion

Carboxyl methylcellulose is an excellent compound particularly because of all the excellent things that it brings along in the market and evolves the whole phenomenon of this very compound. The excellent nature of CMC has been made quite evident through all the researches that have been carried out in this regard. All the characteristics, properties, and wide range of uses have been mentioned here to prove that indeed CMC is an excellent and very beneficial product for all industries.

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References

https://www.celotech.com/about-celotech/carboxymethyl-cellulose-overview-and-applications.html

https://pubs.acs.org/doi/abs/10.1021/ie50430a015

https://cutt.ly/vKAH3Jk

https://link.springer.com/article/10.1007%2Fs13197-015-2060-4