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Carbomer Excipient | Uses, Suppliers, and Specifications
Carbomers are a family of chemically related, synthetic, high molecular weight, nonlinear polymers of polyacrylic acids cross-linked with a polyalkenyl polyether. They are an important class of pharmaceutical excipient and ingredient in personal care formulations. Different grades can be distinguished by their molecular weight, polymerization solvent or side groups. They are, however, all supplied as white-coloured, fluffy, acidic, hygroscopic powders with a characteristic odour.
Synonyms and Trade Names: Carbomer; Carbomer Type A/B/C; Acrylates/C10-30 Alkyl Acrylate Copolymer; Carbomer Copolymer; Polyacrylic acid; Acrylates/C10-30 Alkyl Acrylate Crospolymer, Acrypol; Acritamer; Acrylic Acid Polymer; Carbopol®; Carboxy Polymethylene; Carboxyvinyl Polymer; Pemulen®; Tego® Carbomer; Acrypol® Carbomer
Pharmacopoeial Compliance: USP-NF; Ph.Eur; JP; IP
Uses and Applications: Thickening Agents; Rheology Modifiers; Bioadhesive Polymers; Controlled-Release Agents; Emulsifying Agents; Stabilizing Agents; Suspending Agents; and Tablet Binders (Matrices)
Description
Carbomers are a group of synthetic, high molecular weight, nonlinear polymers of polyacrylic acids cross-linked with a polyalkenyl polyether. All Carbomers are chemically related to each other, only differing in molecular weight, polymerization solvent or side-groups. The amount of carboxylic acid groups in different Carbomer molecules varies between 56 and 68% w/w.
Originally developed by BF Goodrich and trademarked CARBOPOL® in 1958 (US patent 2798503), Carbomers (Carbopol 940, 941, and 934) revolutionised topical products by enabling formulators to create new types of products previously not possible. Even after several decades, they still remain highly relevant and should be on the shortlist for every new product development project.
Various pharmacopoeias use different approaches in the way they define Carbomers. The Ph.Eur, which is harmonised with the B.P, has a single monograph that covers Carbomer excipients that are official in these compendia. The J.P.E, Ch.P and I.P similarly have single monographs, respectively titled Carboxyvinyl Polymer, Carbomer Homopolymer, and Carbomer.
In the USP-NF, there are multiple monographs for five carbomers, namely Carbomer 934, Carbomer 934P, Carbomer 940, Carbomer 941, and Carbomer 1342, which are polymerised in benzene. In addition, the USP-NF includes three broad monographs, Carbomer copolymer, Carbomer homopolymer, and Carbomer interpolymer which are further split into three products (A, B, C) solely on the basis of viscosity.
Carbomers occur as white-coloured, low bulk density, hygroscopic powders with a perceptible odour of acrylic acid.
Chemical Structure & Identifiers
| Chemical Name | Carbomer |
| CAS Registry Number | Several CAS Registry number are used for carbomers:
[9003-01-4] [19007-16-31] [19007-17-41] [19062-04-081] [19007-20-91] |
| Molecular Weight | Molecular weight of Carbomers is estimated to be 7×105 to 4×109 Da. |
| EC Number | 618-347-7 |
| UNII Code (FDA) | 4Q93RCW27E |
Regulatory Status
Carbomers are approved pharmaceutical excipients and cosmetic ingredients. They are listed in all the main pharmacopoeia, including the USP-NF, Ph.Eur, JPE, IP and Ch.P. Carbomers are also included in the US FDA Inactive Ingredients Database (covering oral suspensions, tablets; ophthalmic, rectal, topical. transdermal preparations; vaginal suppositories).
Physicochemical Properties
| Physical form | Solid, powder |
| Appearance | White, fluffy powders |
| pH value (0.2% w/v aqueous dispersion) | 2.5 – 4.0 |
| Bulk density | 0.3 g/ml (powder)
0.4 g/ml (granular) |
| pKa (Dissociation constant) | 6.0 ±0.5 |
| Glass transition temperature | 100 oC – 105 0C |
| Melting point | Decomposition occurs within 30 minutes at 2600C |
| Moisture content | Carbomers are hygroscopic. Equilibrium moisture content at 25oC and 50% relative humidity is 8 – 10% w/w |
| Particle size distribution | Primary particles average about 0.2 µm diameter. Granular carbomer grades has a particle size in the range 150-425 µm |
| Solubility | Carbomers swell in water, ethanol, water, propylene glycol and glycerin to form gels |
| Relative density | 1.41 |
| Viscosity | Carbomers disperse in water to form acidic colloidal dispersions.
When neutralised, viscosity increases significantly to form highly viscous gels. Viscosity values (depend on concentration and grade) but are typically range 100 to 120,000 mPa.s |
Pharmacopeoeal Specifications
| USP-NF | PhEur | |
| Official name | Carbomer | Carbomer |
| Authorised use | Excipient | Excipient |
| Definitions | specified | specified |
| Identification | specified | Infra red spectrum
Dispersion at pH 7.5 Orange colour with Thymol Blue Viscosity |
| Description | White, fluffy hygroscopic powders, swelling in water and other polar solvents | White, fluffy hygroscopic powders, swelling in water and other polar solvents |
| Aqueous Viscosity (mPas) | n/a | 300 – 115,000 |
| Carbomer 934
934P (0.5% w/v) 940 (0.5% w/v) 941 (0.5% w/v) Carbomer 1342 (1% w/v) Carbomer Copolymer Type A Type B Type C Carbomer Copolymer (1% w/v) Type A Type B Type C Carbomer Interpolymer Type A (0.5% w/v) Type B (1% w/v) Type C (0.5% w/v) Loss on Drying |
30,500 – 39,400
29,400 – 39,400 40,000 – 60,000 4,000 – 11,000 9,500 – 26,500
4,500 – 13,500 10,000 – 29,000 25,000 – 45,000
4,000 – 11,000 25,000 – 45,000 40,000 – 60,000
45,000 – 65,000 47,000 – 77,000 8,500 – 16,500 ≤2.0% |
n/a |
| Sulphated Ash | – | ≤4.0% |
| Residue on Ignition | ≤4.0% | n/a |
| Heavy Metals | ≤0.002% | ≤20ppm |
| Benzene | + | ≤2ppm |
| Carbomer 934
934P (0.5% w/v) 940 (0.5% w/v) 941 (0.5% w/v) Carbomer 1342 Carbomer Copolymer Carbomer Copolymer Carbomer Interpolymer |
≤0.5%
≤0.01% ≤0.5% ≤0.5% ≤0.2% ≤0.0002% ≤0.0002% ≤0.0002% |
n/a
– – – – – – – |
| Free acrylic acid | ≤0.25% | ≤0.25% |
| Ethylacetate
Carbomer Copolymer Carbomer Copolymer Carbomer Interpolymer Cyclohexane Carbomer Copolymer Carbomer Copolymer Carbomer Interpolymer |
≤0.5% ≤0.5% ≤0.35%
≤0.3% ≤0.3% ≤0.15% |
n/a n/a |
| Assay (COOH content) | 56% – 68.0% | 56% – 68.0% |
| Labelling | specified | n/a |
Key: n/a Specification is not listed
*All claims with respect to conformity are subject to our Terms and Conditions. No express or implied warranty is made for specific properties or fitness for any particular application or purpose.
Applications in Pharmaceutical Formulations or Technology
Carbomers are used as bioadhensives, controlled-release agents; emulsifying agents; emulsion stabilizers; rheology modifiers; stabilizing agents; suspending agents or occasionally, as tablet binders.
In liquid and semi-solid pharmaceutical formulations, Carbomers find the greatest utility as rheology modifiers. These types of formulation include creams, gels, lotions and ointments for use in ophthalmic, rectal, topical and vaginal preparations.
Note that carbomer grades with residual benzene content greater than 2 ppm do not meet the specifications of current pharmacopoeia monographs. Carbomers with low residuals of other solvents other than the ICH-defined ‘Class 1 – 2 solvents may he used in the EU.
Carbomers with low residuals of ethyl acetate, such as Carbopol 971P NF, are permitted to be used in oral preparations, e.g in suspensions, capsules or tablets. In tablet formulations, carbomers are used as controlled release agents and/or as binders.
A quick run-through of the properties, functions and benefits of Carbomers is below:
Key Physicochemical Properties
- Molecular weight 700 kDa to 4 000 000 kDa
- Powdered carbomers have a dry particle agglomerated size of 2-7µm.
- Do not dissolve but swell in ethanol, water, propylene glycol and glycerin to form microgels.
- Dispersions are acidic with a pH ~3. Upon neutralization (pH 7), particles swell to around 1000 times their initial volume and the viscosity dramatically increases due to charge repulsion.
- Can produce clear gels in water and ethanol due to refractive index matching.
- Highly crosslinked carbomers are commonly used as super absorbers in disposable diapers.
- Salts can decrease viscosity by reducing the charge repulsion.
Applications
- Carbomers are listed in the USP-NF, PhEur, BP; JP, IP and ChP.
- Grades with residual benzene content > 2 ppm do not meet the specifications of current pharmacopoeia monographs.
- Carbomers with low residuals of other solvents other than the ICH-defined Class 1 – 2 solvents may be used in Europe.
- Carbomers with low residuals of ethyl acetate, such as Carbopol 971P NF, are permitted for use in oral preparations, e.g suspensions, capsules or tablets.
- For topical products, carbomers can be used as gelling agents (0.1 – 2.0%), controlled-release agents (5 – 30.0%), emulsifying agents (0.5 – 1.0%), eulsion stabilizers (<1.0%), rheology modifiers (0.5 – 1.0%) and stabilizing and suspending gents (0.5 – 1.0%).
- Carbomers are also employed as emulsifying agents in the preparation of oil-in-water emulsions for external administration.
- Carbomers can be used as bioadhesive polymers (0.1 – 0.5%), tablet binders (0.75 – 3.0%) and controlled release agents.
- Carbomers can aTopical medical devices (Ultrasound adhesive gel and personal and medical lubricants, and artificial tears)
Advantages
- Versatile and multifunctional excipients for oral (solids and liquids) and topical formulations.
- Synthetically derived, hence free from irregularities of natural products.
- Available in multiple grades and properties to meet different formulation or product performance requirements.
- Highly efficient thickeners at very low levels (<1% polymer). Suspensions and emulsions are efficiently stabilised due to the high yield value gels.
- Can make aqueous or alcoholic clear gels.
- Can make emulsifier free oil in water crème gel formulations.
- Can make stable water in oil in water emulsions.
- Excellent skin feel (<.5%) and shear-thinning rheology.
Formulating Tips
- Lightly cross-linked carbomers (lower viscosity) are more efficient at controlling drug release compared with highly cross-linked carbomers (higher viscosity).
- If used in wet granulation processes, water, solvents or their mixtures can be used as the granulating fluid. To control the tackiness of the wet mass include talc in the formulation.
- Carbomers from different manufacturers or grades produced via different manufacturing processes may not have identical properties. Therefore, grades should not be interchanged without performance equivalency ascertainment.
- When preparing carbomer gels, powders should first be dispersed into vigorously stirred water, taking care to avoid the formation of agglomerates. The dispersion should then be neutralized by the addition of a suitable base.
- Use granulated grades to reduce dusting issues during manufacturing.
- Carbomers can easily be added to emulsions by addition to the oil phase prior to emulsification.
- Adding electrolyte or small amounts of acid to the water phase prior to Carbomer addition significantly improves its dispersion by reducing solution viscosity. Up to 5% dispersions of Carbomer in water can typically be made with this approach.
- Agitation of the dispersion should be done carefully and gently with a broad, paddle-like stirrer to avoid introducing air bubbles.
- The viscosity of gels is significantly reduced at pH values less than 3 or greater than 9, or in the presence of strong electrolytes.
- Suitable neutralising agents include amino acids, potassium hydroxide, sodium bicarbonate, sodium hydroxide, and organic amines such as triethanolamine. One gram of carbomer is neutralized by approximately 0.4 g of sodium hydroxide.
- A number of manufacturers have introduced grades to overcome the challenges of dispersing powders in aqueous solvents, e.g Lubrizol’s Carbopol Ultrez.
- Gels rapidly lose viscosity on exposure to UV light. To minimise this add a suitable antioxidant.
Safety and Precautions
Carbomers are widely used in topical liquid and semisolid pharmaceutical products. They are also used in many personal care and hygiene products as viscosity modifiers and thickeners. Currently, only grades polymerized in Ethyl acetate can be included in oral products.
Carbomers are generally deemed as effectively nontoxic and non-irritant excipients. There is currently no data that supports hypersensitivity reactions when Carbomers are used in topical products. Carbomers are also not known to be absorbed systemically following oral intake. Acute oral toxicity studies in animal models have shown that Carbomer 934P has a low oral toxicity, with no fatalities reported when doses of up to 8 g/kg were administered to canine models.
Toxicology: LD50 (rat, oral): LD50 (rat, oral): 2.5g/kg for carbomer 934P and LD50 (rat, oral): 2.5 g/kg for carbomer 940
Stability and Storage Conditions
Carbomers are stable excipients, although they exhibit hygroscopicity. They remain stable when heated at temperatures below 104 oC for up to 2 hours. Prolonged exposure to heat stress can lead to discolouration, which reduces their stability. Complete decomposition occurs when Carbomers are heated for more than 30 minutes at 260 oC. However, aqueous gels can be autoclaved without significant changes in viscosity or pH, as long as oxygen is excluded from the system.
Carbomers in dry form (powders) are not able to support mold and fungi growth. However, unpreserved aqueous dispersions are susceptible to attack. Thus, a suitable antimicrobial preservative (e.g Methylparaben at 0.18% w/v or Propylparaben at 002% w/v) should be added. The use of certain antimicrobial agents, such as Benzalkonium chloride or Sodium benzoate, especially in high concentrations (0.1% w/v) is not recommended due to the tendency to cause cloudiness and reduction in viscosity of Carbomer gels.
Carbomer gels can maintain their viscosity during storage for long periods. Exposure to light can trigger oxidation that results in the lowering of viscosity. Stability to light may be improved by the addition of 0.05 – 0.1% w/v of a water-soluble UV absorber (for instance, bensophenone-2 or bcnzophenone-4 in combination with 0.05—0.1% w/v edetic acid).
It is recommended that bulk Carbomer powders be stored in airtight, corrosion-resistant containers. The material should be protected from moisture. Glass, plastic, or resin-lined containers are ideal options for the storage of formulations that contain carbomers.
When handling bulk Carbomer powders, observe SHEQ protocols appropriate to the institutional circumstances and quantity of material being processed. Excessive dust generation should be avoided to minimise the risk of explosion. Since Carbomer dust can irritate eyes, mucous membranes, and respiratory tract, the use of appropriate PPE is necessary.
Sustainability and Environmental Impact
A sustainability assessment of this material has not been conducted.
Manufacturers & Suppliers
- Carbopol® 71G
- Carbopol® 971P
- Carbopol® 974P
- Carbopol® 980
- Carbopol® 981
- Carbopol® 5984
- Carbopol® ETD 2020
- Carbopol® Ultrez 10
- Permulen™ TR-1
- Permulen™ TR-2
Evonik Corporation
- TEGO® Carbomer 134
- TEGO® Carbomer 140
- TEGO® Carbomer 141
- Acrypol® 971
- Acrypol® 974
- Acrypol® 980
- Acrypol® 981
Additional Resources (Downloads)
References and Literature Used
FAQS
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