Sodium carboxymethyl cellulose (CMC-Na) plays a core supporting role in detergents (such as laundry detergents and multi-purpose cleaners). Its role and dosage need to be adjusted dynamically based on product type and formulation requirements, as follows:
Sodium carboxymethyl cellulose (CMC-Na) firstly exhibits anti-redeposition properties, significantly improving cleaning performance. The carboxyl groups (-COO⁻) on its molecular chain electrostatically attract and encapsulate oily particles (such as sebum and dust) removed during washing, forming a stable dispersion. This "soil-polymer" complex is negatively charged and repels the surface of clothing, effectively preventing reattachment. It is particularly effective in preventing yellowing of white fabrics and preserving the color of colored fabrics. In practice, laundry detergents containing CMC-Na can reduce the probability of "re-contamination" of clothing by 30%-50%, and can maintain the original color of fabrics after multiple washes. Secondly, the precise thickening function can optimize the user experience. CMC-Na can control the viscosity of the detergent at 500-2000 mPa·s (ordinary type) or 2000-5000 mPa·s (concentrated type) by forming a three-dimensional network structure, ensuring that the product is "easy to squeeze and does not drip". For example, a certain brand of laundry detergent uses 0.8% CMC-Na and NaCl for synergistic thickening, which can increase the viscosity from 300 mPa·s to 1200 mPa·s while maintaining good fluidity; and in the range of -10℃ to 45℃, CMC-Na can prevent the detergent from "thinning at high temperature and solidifying at low temperature" due to temperature fluctuations, making it suitable for all seasons. Secondly, it has a dispersing and emulsifying effect, which can stabilize the formula system. For complex formulas containing silicone oil, fragrances, enzyme preparations and other ingredients, CMC-Na can disperse the oil phase particles to a particle size of 1-5 μm through emulsification to avoid stratification or precipitation. For example, in a laundry detergent containing 2% silicone oil, 0.5% CMC-Na can increase the dispersion uniformity of the silicone oil by 70%; at the same time, it can also slow down the degradation rate of active ingredients such as proteases and amylases through adsorption. After adding 0.6% CMC-Na to a certain enzyme-added laundry detergent, the enzyme activity retention rate after 6 months of storage increased from 60% to 85%. CMC-Na also aids in stain removal and enhances penetration. When combined with anionic surfactants (such as AES), it can reduce surface tension to 30-35 mN/m (72 mN/m for pure water), promoting penetration of detergent into fabric fibers. For example, in a laundry detergent containing 15% AES, 0.7% CMC-Na can increase stain removal by 18% (JB standard soiled cloth test). Furthermore, CMC-Na reduces soap scum formation by chelating calcium and magnesium ions (Ca²⁺ and Mg²⁺). In hard water with a hardness of 200 ppm, detergent containing CMC-Na reduces stain removal by 50% compared to the control.
In terms of the dosage, the general range needs to be adjusted according to the product type. Ordinary laundry detergent most commonly uses 0.5%-1.5%. For example, a best-selling brand of laundry detergent adds 0.8% CMC-Na and compounded with 1% NaCl to achieve a balance between viscosity and detergency. Concentrated laundry detergent has a high concentration of active ingredients, so the dosage is usually 0.3%-1.0%. For example, a concentrated laundry detergent (active ingredient 45%) only adds 0.6% CMC-Na and can still maintain a viscosity of 1800 mPa·s. In special scenarios, the addition amount of low-foam laundry detergent is 0.3%-0.6% (to avoid excessive foam affecting rinsing), and that of children's laundry detergent is 0.2%-0.5% (to reduce the risk of irritation). The dosage should also be adjusted dynamically. From a formulation synergistic perspective, when compounded with nonionic surfactants (such as fatty alcohol polyoxyethylene ethers), the CMC-Na dosage can be reduced by 20%-30% (due to hydrogen bonding synergy). In formulations containing high-molecular-weight polymers (such as sodium polyacrylate), the dosage should be reduced to 0.3%-0.8% (to avoid gelation caused by excessive cross-linking). Regarding raw material purity, cosmetic-grade CMC-Na (purity ≥99.5%) can be safely used in detergents at up to 2%. Industrial-grade CMC-Na (purity ≤95%) is recommended to be below 1.5% due to the presence of impurities. Regarding pH, CMC-Na maintains a viscosity retention rate of ≥90% at pH 6-8. If the formulation pH is <5 (such as in acidic toilet cleaners), a buffer (such as sodium citrate) should be added or acid-resistant CMC should be used; otherwise, the viscosity may drop by more than 50%.
There are many typical examples in industry practice. For example, high-end color-protecting laundry detergents often incorporate 1.2% CMC-Na + 0.3% sodium polyacrylate, which improves anti-redeposition effectiveness by 40%. Microencapsulation of fragrances also extends the fragrance's longevity to 72 hours. Low-foaming laundry detergents specifically for machine washes use 0.5% CMC-Na + 0.2% defoamer (silicone). While maintaining detergency, they reduce rinse cycles by one or two times, saving 20% water. However, risk control is crucial in application. Adding more than 2% can cause pump blockage or clothing residue. This can be mitigated by adding the solution in stages (dissolving it in warm water before mixing with other ingredients) or by adding a low-viscosity cellulose (such as hydroxyethyl cellulose). Furthermore, CMC-Na solutions are susceptible to bacterial growth, so 0.1%-0.3% preservatives (such as phenoxyethanol) are required, and the total bacterial count in the production environment must be controlled to ≤100 CFU/g.
Regarding regulatory and standard references, China's "Safety Technical Specifications for Cosmetics (2015 Edition)" does not set specific limits for CMC-Na, but does require toxicology testing (such as skin irritation testing). Industrial detergents must comply with GB/T 13171-2023 (the standard for laundry detergents), and are indirectly constrained by an overall formula safety assessment. EU Regulation EC No. 1223/2009 requires CMC-Na to pass an SCCS safety assessment, with concentrations in leave-on products ≤ 0.65% and in rinse-off products (such as laundry detergents) ≤ 2%. The US FDA allows CMC-Na as an indirect food additive (21 CFR 172.872). Its use in daily chemical products must comply with GMP regulations and label the product with the INCI name (SODIUM CARBOXYMETHYL CELLULOSE).
In summary, CMC-Na is a functional additive rather than a core ingredient in detergents. Its function and dosage must adhere to the principle of "precisely matching needs": its core functions include anti-redeposition (critical), thickening, dispersion and emulsification, and formula stabilization. The recommended dosage is 0.5%-1.5% for ordinary laundry detergents and 0.3%-1.0% for concentrated types, and dynamic adjustment is required for special scenarios. In practice, it is recommended to verify viscosity, detergency, and stability through small-scale tests (500 mL batches), combined with toxicology testing to ensure safety, ultimately achieving a balance between "performance, cost, and compliance."
