1 Why Sulfonic Acid Is Frequently Used in Household Cleaning Formulations

In the household and daily chemical industry, the term “sulfonic acid” usually refers to linear alkylbenzene sulfonic acid (LABSA). It is a basic surfactant raw material commonly used in laundry powder, liquid laundry detergent, dishwashing liquid, hard-surface cleaners, and certain industrial cleaning agents.

LABSA is an acid-form raw material. In most neutral or mildly alkaline washing and cleaning products, it does not perform its main cleaning function directly in a strong-acid state. Instead, after being neutralized with sodium hydroxide, potassium hydroxide, or organic amines, it forms linear alkylbenzene sulfonate (LAS). LAS is one of the common anionic surfactants used in household cleaning systems.

In household cleaning products, raw material selection must consider cleaning performance, foam behavior, production cost, supply stability, and production compatibility at the same time. Sulfonic acid is widely used mainly because the LAS formed after neutralization offers a good balance among these factors.

2 How Sulfonic Acid Is Converted into an Active Cleaning Ingredient in Formulations

2.1 The key change after sulfonic acid enters the formulation is neutralization

LABSA is an acid-form substance and has strong acidity when added directly to the water phase. Most household cleaning products need to be close to neutral or mildly alkaline, so neutralization is usually required first in the formulation.

The neutralization process can be understood as:

LABSA + alkali → alkylbenzene sulfonate + water

When sodium hydroxide is used for neutralization, the main product is the sodium salt of LAS. When potassium hydroxide is used, the potassium salt is formed. When organic amines such as triethanolamine are used, the corresponding amine salts are formed. Different neutralization methods affect the formulation’s pH, solubility, viscosity, low-temperature stability, and skin feel.

2.2 In common neutral or mildly alkaline systems, the neutralized surfactant structure is the main contributor to cleaning performance

Neutralized LAS has a typical surfactant structure: one end is a hydrophobic alkyl chain that tends to approach oily soil, while the other end is a hydrophilic sulfonate group that disperses readily in water.

This structure enables LAS to interact with both oily soil and water, and to act among the oily soil, the surface being cleaned, and the water phase. It does not simply “dissolve” oil. Instead, it changes the interactions between oil and water, and between oil and the surface, making the oily soil easier to detach from the surface and enter the water phase.

3 What Happens to the Cleaning System After Sulfonic Acid Is Added

3.1 The cleaning liquid spreads more easily over the soil surface

When there is not enough surfactant, water often beads up when it contacts an oily surface and cannot spread sufficiently. As a result, the water phase has difficulty entering the interface between the oily soil and dishes, fabrics, or hard surfaces, leading to lower cleaning efficiency. After sulfonic acid is added and fully neutralized, LAS is formed in the system. LAS can reduce the surface tension of the water phase, allowing the cleaning liquid to spread more easily over the oily surface. The more fully the cleaning liquid spreads, the larger the contact area with the soil, and the easier the subsequent penetration, detachment, and emulsification processes become.

This is especially important in dishwashing liquids. Oily residues on tableware are usually distributed across plate surfaces, bowl walls, chopsticks, spoons, and other utensils. If the cleaning liquid cannot spread quickly, more mechanical rubbing is required to clean them effectively. After an appropriate amount of sulfonic acid is added, the cleaning liquid can more easily cover oily areas, improving both cleaning speed and the user experience.

3.2 Oily soil becomes easier to loosen from the surface

Oily soil is difficult to remove because it adheres strongly to the surface being cleaned. Rinsing with water alone usually removes only a small amount of loose soil, while thicker or stickier oily residues remain on the surface.

The hydrophobic chain of LAS tends to approach the oil, while the hydrophilic sulfonate group remains in the water phase. When enough surfactant molecules accumulate at the oil-water interface, the adhesion between the oily soil and the surface decreases. With rubbing, wiping, or water flow, the oily soil can then be detached more easily.

3.3 Oily soil is dispersed into the water phase and is less likely to redeposit

After oily soil is loosened from the surface, it still needs to enter the water phase in a stable manner. If it is merely wiped or pushed away without being emulsified and dispersed, the oily soil may redeposit on tableware, fabrics, or hard surfaces.

LAS can adsorb at the oil-water interface, reduce oil-water interfacial tension, and help oily soil form smaller oil droplets under the action of rubbing, wiping, or water flow. These droplets then disperse in the water phase. In this way, oily soil can be more easily carried away with rinse water through emulsification, dispersion, and micellar solubilization. This step is also important for liquid laundry detergents. After sebum, dust, and particulate soil detach from fabric fibers, they must remain dispersed to reduce redeposition.

3.4 Foam reflects the washing process but does not represent detergency

Sulfonate-type anionic surfactants usually have noticeable foaming ability. Foam allows users to visually observe the washing process. In some hand-washing or vertical-surface cleaning scenarios, foam can also improve the sense of coverage and residence time.

However, foam is not equivalent to cleaning power. A formulation with high foam does not necessarily have strong grease-removal ability, while a low-foam formulation may still have good degreasing performance. Formulation evaluation should be based on actual grease removal, soil removal, rinsability, and stability tests, rather than foam height alone.

4 How Formulation Performance Differs With and Without Sulfonic Acid

4.1 Differences in dishwashing liquids

The main soils encountered by dishwashing liquids include animal fats, vegetable oils, seasoning residues, and food particles. If a dishwashing liquid formulation lacks sufficient anionic surfactant, it may still have some grease-removal ability, but its spreading, foam, rinsing performance, and overall user experience are often insufficient.

4.2 Differences in liquid laundry detergents

Liquid laundry detergents deal with more complex soils than dishwashing products, including sebum, sweat stains, dust, particulate soil, and some food stains. LAS formed after neutralization of sulfonic acid can provide a basic cleaning framework, helping to wet fibers, disperse sebum soils, and reduce redeposition.

If a sulfonic acid system is not used, liquid laundry detergents can still achieve cleaning performance through alcohol ether sulfates, nonionic surfactants, enzymes, chelating agents, and builders. However, the formulation structure, cost, foam behavior, and soil-removal speed will change.

4.3 Differences in kitchen cleaners

Kitchen grease is usually more complex than oil residues on tableware. It may contain aged grease, dust, protein residues, and carbonized matter. Water alone has difficulty wetting greasy surfaces, while alkali alone may have insufficient spreading, poor rinsing, or high irritation.

After sulfonic acid is added and neutralized, the LAS in the system can help the cleaning liquid spread over the greasy surface and promote grease detachment and emulsification. When combined with nonionic surfactants, an appropriate amount of alkali, or solvents, the degreasing efficiency becomes more complete. Without sulfonic acid or other effective anionic surfactants, kitchen cleaners may need to rely on higher levels of solvents, alkalis, or nonionic surfactants to compensate. This may affect cost, odor, irritation potential, or rinsing performance.

5 Which Products Are Suitable for Sulfonic Acid

5.1 Products suitable for sulfonic acid

Sulfonic acid is more suitable for cleaning products with clear cleaning-performance requirements, high cost-control requirements, and large-scale production needs. These products usually do not focus only on mildness or transparent appearance, but instead place more emphasis on soil-removal efficiency, user experience, cost, and production stability.

5.2 Products where blind high-level use of sulfonic acid is not suitable

Sulfonic acid should not be used at high levels in all cleaning products without careful consideration. For the following product requirements, the dosage should be carefully controlled, and risks should be reduced through formulation blending.

5.3 When to consider LAS sodium salt or SDBS

The salt-form products discussed here mainly refer to anionic alkylbenzene sulfonate surfactants such as LAS sodium salt or sodium dodecylbenzene sulfonate (SDBS). They can serve as the salt-form surfactant after LABSA neutralization or as experimental references. The advantage of sodium sulfonate is greater ease of use. It is already in salt form, so after entering the water phase, it does not require acid-base neutralization. Its pH is easier to control, making it suitable for laboratory trials, small-batch production, or production conditions without neutralization equipment.

In large-scale household chemical production, sulfonic acid still has advantages in cost and formulation flexibility. In R&D sampling or simplified production, sodium sulfonate can reduce operational difficulty.

6 How to Select Sulfonic Acid Products

The quality of sulfonic acid directly affects neutralization, odor, color, viscosity, transparency, low-temperature stability, and finished-product consistency. Selection should be based on a comprehensive assessment of active matter, acid value, free oil, free sulfuric acid, color, and batch-to-batch stability.

Different products place different levels of emphasis on sulfonic acid indicators.

7 How to Use Sulfonic Acid Stably

7.1 Estimate the neutralization amount first, then confirm it through laboratory trials

When using sulfonic acid, alkali should not be added at a fixed amount based only on experience. A more reliable approach is to first estimate the theoretical neutralization amount based on the acid value of the sulfonic acid, and then correct it through laboratory titration and finished-product pH testing.

The acid value is usually expressed as the number of milligrams of KOH required to neutralize 1 g of sulfonic acid sample, with the unit mg KOH/g. If NaOH is used for neutralization, the amount can be converted based on the molar masses of KOH and NaOH.

Theoretical amount of pure NaOH = Actual LABSA dosage × acid value × (40.00 ÷ 56.11) ÷ 1000

Where:

① Actual LABSA dosage: the actual amount of commercial sulfonic acid raw material added;

② Acid value: unit is mg KOH/g;

③ 40.00: molar mass of NaOH;

④ 56.11: molar mass of KOH;

⑤ ÷1000: used to convert the mass unit in the acid value from mg KOH/g.

The actual LABSA dosage and the calculated theoretical amount of pure NaOH should use the same mass unit. For example, if LABSA is measured in kg, the NaOH result is in kg. If LABSA is measured in g, the NaOH result is in g.

If liquid caustic soda is used, further conversion is required:

Liquid caustic soda dosage = theoretical amount of pure NaOH ÷ mass fraction of NaOH in the liquid caustic soda

For example, when 32% liquid caustic soda is used:

32% liquid caustic soda dosage = theoretical amount of pure NaOH ÷ 0.32

It should be noted that the acid value reflects the total acidic components in the sample that can be neutralized by KOH, and is not completely equivalent to the active matter content of LABSA. The actual neutralization amount should also be corrected based on the target pH, free sulfuric acid, other acid-base components in the formulation, temperature, and laboratory titration results.

Calculation example:

Assume the LABSA dosage is 100 kg and the acid value is 180 mg KOH/g:

Theoretical amount of pure NaOH = 100 × 180 × (40.00 ÷ 56.11) ÷ 1000 ≈ 12.83 kg

If 32% liquid caustic soda is used:

32% liquid caustic soda dosage = 12.83 ÷ 0.32 ≈ 40.09 kg

This result is only the theoretical neutralization amount. In actual production, it still needs to be adjusted based on the target pH, other acid-base components in the formulation, temperature, raw material batch differences, laboratory trials, and finished-product testing.

7.2 Control temperature and local concentration during neutralization

Neutralization of LABSA is an exothermic process. If alkali is added too quickly, stirring is insufficient, or the local alkali concentration is too high, problems such as color darkening, uneven pH, abnormal viscosity, or reduced system stability may occur.

Key operational controls include:

① Add the alkali solution slowly;

② Maintain sufficient stirring;

③ Control the system temperature;

④ Avoid local strong-acid or strong-alkali zones;

⑤ Recheck pH after neutralization;

⑥ Add other surfactants, additives, fragrance, and preservatives afterward.

LABSA is a corrosive raw material. During use, the requirements in the safety data sheet should be followed, and appropriate protection and ventilation should be provided.

7.3 Formulation blending should be designed around specific problems

Sulfonic acid can provide basic cleaning power, but stable, mild, and user-friendly formulations usually require blending with other components.

Blending allows each raw material to solve a specific problem. Sulfonic acid provides the basic cleaning framework; nonionic surfactants enhance grease removal; amphoteric surfactants improve foam and mildness; chelating agents and builders improve performance in hard water and help manage complex soils.

7.4 Identify the thickening peak when adjusting viscosity with salt, and avoid thinning caused by excessive salt

In dishwashing liquids and some liquid laundry detergents, sodium chloride is commonly used to adjust viscosity. LAS-containing surfactant systems usually have a salt-thickening curve: with an appropriate amount of salt, viscosity may increase; beyond the suitable range, the formulation may become thinner again, turn cloudy, precipitate, or show reduced low-temperature stability. Therefore, salt should be added in stages, and the viscosity and appearance changes at different salt dosages should be recorded to identify the thickening peak of the system and avoid adding a fixed percentage all at once.

7.5 Finished-product verification should focus on actual use performance

After a sulfonic acid-containing system is completed, at least the following items should be verified:

8 Common Problems and Adjustment Directions

9 Classification Table of Representative Sulfonic-Acid-Related Chemicals Commonly Used in Cleaning Formulations

Note: The following products are representative products intended for laboratory research, small-scale formulation development, performance evaluation, and model formulation construction. They do not imply regulatory suitability for end-use household chemical products or recommendations for industrial-scale production. Before use in commercial formulations, the product grade, regulatory compliance, SDS, COA, impurity limits, usage restrictions, and requirements of the target market should be confirmed.

Table 1 Core Sulfonic Acid and Surfactant Products

Table 2 Neutralizers, Acid-Base Adjusters, and Alkaline Builder Products

Table 3 Chelating Agents, Solubilizers, Viscosity Modifiers, and Stabilizing Additives

Table 4 Solvents, Degreasing Enhancers, and Formulation Auxiliaries

Note: The above are representative Aladdin products related to scientific research and formulation studies. More product specifications, grades, and COA information can be found on the Aladdin website by searching by “product name/CAS/catalog number.”

References

[1] HERA. Human and Environmental Risk Assessment on Ingredients of Household Cleaning Products: Linear Alkylbenzene Sulphonate, LAS. Revised April 2013.

[2] OECD SIDS. Linear Alkylbenzene Sulfonate, SIDS Initial Assessment Report.

[3] GB/T 8447-2008, Industrial Linear Alkylbenzene Sulfonic Acid.

[4] Ittehad Chemicals. Technical Data Sheet for LABSA 96%.

[5] Cosmetic Ingredient Review Expert Panel. Amended Safety Assessment of Dodecylbenzenesulfonate, Decylbenzenesulfonate, and Tridecylbenzenesulfonate Salts as Used in Cosmetics. International Journal of Toxicology, 2010.

[6] Rosen M. J., Kunjappu J. T. Surfactants and Interfacial Phenomena. 4th Edition. John Wiley & Sons, 2012.

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