Carbomer is a key acrylic-based polymer that, when neutralized to a pH between 5 and 9, transforms into a clear gel, acting as a powerful rheology modifier with a carboxylic acid content of 56% to 68%. Its versatile structure allows different types like the homopolymer Carbomer 980 for high-clarity gels and the copolymer U21, which boasts a rapid self-wetting time of just 1.5 minutes, to provide excellent thickening and suspension for a wide range of products from lotions to shampoos.
Chemical Structure
Carbomer is a long-chain polymer formed by countless Acrylic Acid monomers linked together, and the process of "cross-linking" involves using specific cross-linking agents (such as Pentaerythritol) to tigtly "nail" these long chains together at multiple points, thereby forming a stable three-dimensional network structure.
The core of this structure lies in the Carboxyl (-COOH) functional groups on its chain. In an unneutralized acidic environment, these carboxyl molecules entangle and attract each other through hydrogen bonds, causing the entire molecular chain to be in a relatively coiled state.
The magical transformation occurs during the neutralization process—when a base (such as triethanolamine or sodium hydroxide) is added to adjust the pH value to neutral or slightly alkaline (typically between 5.0-9.0), the carboxyl group (-COOH) ionizes into a negatively charged carboxylate radical (-COO⁻).
These groups with the same charge repel each other, forcing the originally coiled molecular chain to rapidly stretch and swell, completely opening up that huge "molecular fishing net."
This stretching process greatly constrains the water molecules in the system and significantly increases fluid resistance, which is the fundamental principle behind Carbomer's ability to achieve instantaneous thickening.
Its carboxylic acid content is as high as 56% to 68%, ensuring that each molecular chain has enough "switches" to respond to pH changes, thus generating powerful thickening efficiency.
Carbomer is mainly divided into two structural types:
Structure Type | INCI Name | Monomer Composition | Cross-linking Agent | Key Structural Feature |
Homopolymer | Carbomer | Acrylic Acid | Polyols like Sucrose or Pentaerythritol | Relatively uniform structure, high carboxyl density, produces extremely high viscosity after neutralization. |
Copolymer | Acrylate/C10-30 Alkyl Acrylate Crosspolymer | Acrylic Acid + C10-30 Alkyl Acrylate | Allyl ether cross-linking agents | Introduction of hydrophobic long-chain alkyl groups on the main chain, giving the product excellent ion resistance and unique rheological properties. |
Homopolymers represented by AC-Carbomer 940/980: Their "fishing net" mesh is relatively dense, thus capable of generating very high viscosity and excellent transparency, suitable for gel products with high transparency requirements.
Copolymers represented by AC-Carbomer U20/U21: The long-chain alkyl groups in their molecular structure are like many "oily small anchors" hanging on the "fishing net." These hydrophobic groups can associate through hydrophobic interactions when encountering electrolytes (such as salts) or other ions in the formulation, maintaining good network structure and viscosity even in high ion strength environments, whereas the viscosity of traditional homopolymers would significantly decrease in this environment. This "associative thickening" mechanism makes U20/U21 particularly suitable for complex formulations containing electrolytes, such as shampoos and sunscreens.
Carbomer is not a single chemical substance but a family of polymers whose different properties are obtained by precisely controlling the chemical structure (such as the type and amount of cross-linker, and the type of co-monomer).
From homopolymers to copolymers, the essence is a molecular design that has evolved from the classic "macroscopic" thickening mechanism triggered by pH-induced charge repulsion to a "microscopic" associative thickening mechanism that resists external interference.
Key Properties
Thickening and Suspension Ability
Carbomer, once neutralized in an aqueous system, can form extremely high viscosity. For example, at pH=7.5 and a concentration of only 0.2%, AC-Carbomer U20 demonstrates better viscosity stability and peak viscosity than competing products in the same category.
At the same time, the three-dimensional network structure can effectively lock insoluble particles (such as sunscreens, pigments, or active ingredients), preventing their settling or clumping, thereby ensuring the uniformity and stability of the product.
AC-Carbomer 980 and U20 perform particularly well in suspension ability, with better dispersion effects than competitors.
Rheological Characteristics
The Carbomer family offers diversified options here:
Short Rheology (Pseudoplastic Fluid): Representative products include AC-Carbomer 940, 981, and U21. This characteristic means that the product has very high viscosity when static, providing good suspension and stability; but when subjected to shear force (such as spreading, pumping), the viscosity instantly drops, making it easy to spread and apply, resulting in a very refreshing, non-sticky user experience. This is like a high-quality ketchup that doesn't move when left still, but flows smoothly when squeezed hard.
Long Rheology (Elastic Fluid): Representative product is AC-Carbomer U20. Its viscosity drops slower under external force, providing a luxurious, rich skin feel, and imparting certain structural elasticity to the product, often used in hair gels that require unique styling or creams that offer a rich texture.
Ion Resistance
Many personal care formulations inevitably contain electrolytes, such as salts (from raw materials or sweat), surfactants, etc.
These ions can interfere with the charge repulsion thickening mechanism of traditional Carbomers, leading to a severe drop in viscosity.
Products like AC-Carbomer U20 have strong ion resistance, maintaining a relatively high viscosity in the presence of ions, ensuring formulation stability.
In contrast, the ion resistance of AC-Carbomer 940 and 980 is moderate.
Shear Stability and Self-Wetting
Shear stability refers to the ability of the Carbomer gel to maintain its structure without being destroyed by mechanical forces such as stirring and pumping.
In this regard, AC-Carbomer 940 and 980 perform "better," while U20 and U21 are "normal" or "slightly weaker."
Self-wetting is a great convenience advantage. It refers to the ability of powdered Carbomer to penetrate, absorb water, and disperse by itself in water without forming difficult-to-stir "fish eyes" (where the exterior gels but the interior remains dry powder).
AC-Carbomer U21 and U20 perform exceptionally well in this regard, with wetting times of only 1.5 minutes and 3 minutes, respectively, much faster than traditional Carbomers 940 (60 minutes) and 980 (40 minutes).
Property | Evaluation Standard | Representative Models (from Excellent to Normal) | Practical Impact on Formulation and Production |
Thickening Efficiency | Viscosity value achievable at unit concentration | U20 > 980 > 940 > U21 | Determines dosage cost and richness of skin feel |
Suspension Ability | Effect of preventing particle sedimentation and stratification | 980, U20 > Competitors | Ensures product uniformity, stability, and appearance |
Rheology Type | Viscosity change behavior when subjected to shear force | 940/981/U21 (Short Rheology), U20 (Long Rheology) | Directly determines spreadability and product functionality (e.g., setting) |
Ion Resistance | Viscosity retention rate in the presence of electrolytes | U20 > U21 > 980, 940 | Determines the tolerance and scope of application of the formulation |
Shear Stability | Ability to resist mechanical shear from stirring, pumping, etc. | 940 ≈ 980 > U20 > U21 | Affects process selection and stability during production |
Self-Wetting | Speed of powder dispersion in water | U21 (1.5min) > U20 (3min) > 980 (40min) > 940 (60min) | Directly relates to production difficulty, time, and cost |
High Transparency
High-quality Carbomers such as AC-Carbomer 940, 980, U20, and U21 can form crystal-clear gels with minimal air bubbles after neutralization.
Application Scenarios
Skincare Field
For transparent gels, serums, and refreshing moisturizing products that seek a crystal-clear texture, AC-Carbomer 940 is the preferred choice.
It can provide extremely high viscosity and unparalleled transparency, with minimal air bubbles after neutralization, giving the product a premium visual appearance and a balanced, refreshing skin feel.
For lotions and creams requiring a moisturizing and smooth experience, AC-Carbomer 980 shines.
It still provides excellent viscosity at low pH values or low addition levels. The skin feel is between refreshing and rich, with slight elasticity, moisturizing and smooth, making it very suitable for cream systems that require long-term stable suspension of active ingredients.
When the formulation contains solvents such as alcohol, glycerin, or propylene glycol, acrylate copolymers like AC-SF-1 exhibit excellent compatibility. It can stably thicken these transparent systems and is widely used in products such as sunscreen sprays and rinse-free hand sanitizers.
Haircare and Cleansing Products
Products like shampoos and body washes are rich in surfactants and salts (electrolytes), which can easily destroy the network structure of traditional thickeners.
At this point, the strong ion resistance of AC-Carbomer U20 and U21 becomes crucial.
They can maintain stable viscosity in high electrolyte environments, ensuring the product has a pleasant use texture. In particular, AC-Carbomer U20 offers long rheology and an extremely refreshing, non-sticky skin feel, making it very suitable for transparent shampoos, body washes, and cleansing products that require quick drying.
Carbomer is also the core of hair styling products. Whether it's a strong hold hair gel or a natural hold pomade, Carbomer (such as 940, 980) can provide long-lasting and re-combable hold by forming a tough polymer film.
Application Category | Recommended Carbomer Model | Key Performance Requirements | Final Product Skin Feel/Experience |
Transparent Water-based/Alcohol-based Gels | AC-Carbomer 940, AC-SF-1 | Extremely high transparency, rapid gelation | Refreshing, crystal-clear, no residue |
Lotions, Creams | AC-Carbomer 980, AC-Carbomer U20 | High-efficiency thickening and suspension, emulsion stability, smooth skin feel | Moisturizing, hydrating, rich texture |
Shampoos, Body Washes | AC-Carbomer U21, AC-Carbomer U20 | Ion-resistant, surfactant-resistant, easy to disperse | Refreshing, easy to rinse, non-sticky |
Hair Styling Products | AC-Carbomer 940, AC-Carbomer 980 | Good film-forming ability, strong hold | Long-lasting hold, re-combable |
Home Care and Special Formulations
In scrubs containing abrasive particles or physical sunscreens containing zinc oxide, Carbomer effectively prevents particle sedimentation, ensuring consistent ingredient uniformity with every use, avoiding the awkwardness of "one pump is all water, one pump is all sand."
For serums or ampoules containing insoluble active ingredients (such as vitamin powders, botanical extracts), the three-dimensional network of Carbomer acts like a miniature "storage compartment," firmly fixing the active ingredients in the system, ensuring that every drop of the product, from opening to finishing, has the same efficacy.
