Sodium carboxymethyl cellulose (CMC) is an important functional additive used in laundry detergents. Its primary function is to prevent soil redeposition and improve the cleanliness and whiteness of clothes after washing. Its quality specifications and dosage must be strictly controlled based on the detergent's formulation requirements and performance targets. The following are specific technical requirements and application points:
1. Specification Requirements for Sodium Carboxymethyl Cellulose (CMC)
The technical specifications for CMC used in laundry detergents generally follow national standards (such as GB/T 12028) or industry regulations. Core indicators include physical and chemical properties, purity, and safety to ensure its functional performance and stability during the washing process. The following are key specifications:
1.1 Degree of Substitution (DS) reflects the extent to which hydroxyl groups in the cellulose molecule are replaced by carboxymethyl groups. It directly affects CMC's water solubility, hard water resistance, and ability to prevent soil redeposition. The degree of substitution (DS) for CMC used in laundry detergents is typically required to be between 0.5 and 0.7 (i.e., each glucose unit has an average of 0.5 to 0.7 carboxymethyl groups), with uniform distribution to ensure rapid dissolution and colloidal stability in water. A low DS can result in poor solubility or insufficient antifouling properties; a high DS can increase costs or affect other properties (such as foam control).
1.2 The viscosity of CMC is related to its molecular weight and concentration and is typically measured as the viscosity of a 1% aqueous solution at 25°C. The viscosity of CMC for laundry detergents typically ranges from 5 to 40 mPa·s (measured using a rotational viscometer at a shear rate of approximately 850 s⁻¹). Lower viscosity CMC is more easily dispersed in laundry detergent particles and dissolves quickly in the wash liquid to form a colloid, effectively suspending dirt particles. High viscosity, on the other hand, can result in slow dissolution or affect the fluidity of the detergent.
1.3 The purity of CMC, expressed as the active ingredient content on a dry basis, is required to be ≥55%. High purity means fewer impurities (such as inorganic salts and unreacted cellulose), minimizing negative impacts on washing performance (e.g., impurities may adsorb surfactants or reduce transparency). Purity is measured through methods such as washing and separation with 80% ethanol to ensure consistent product quality.
1.4 The pH value of a CMC aqueous solution reflects its acidity and alkalinity. Detergents typically require a pH between 8.0 and 11.5 (measured as a 1% aqueous solution at 25°C). This range ensures compatibility with alkaline systems (such as sodium carbonate and sodium silicate) in detergent formulations, preventing acid-base neutralization and resulting in performance loss.
1.5 CMC is highly hygroscopic. Excessive moisture content can cause powder clumping, affecting mixing uniformity and storage stability during detergent production. Therefore, the moisture and volatile content must be strictly controlled to ≤10%.
1.6 For laundry detergents produced using the dry-mix method, CMC must be able to pass through specific sieves (e.g., a 0.45 mm sieve with a pass rate of ≥95% and a 0.80 mm sieve with a pass rate of 100%) to ensure uniform mixing with other ingredients and prevent large particles from affecting powder flowability or dissolution in the wash.
1.7 High-quality CMC for laundry detergents should exhibit excellent hard water resistance, maintaining colloidal stability in detergents containing calcium and magnesium ions and effectively suspending dirt. Furthermore, its solution should exhibit high transparency, without affecting the clarity of the detergent or the efficacy of other ingredients such as bleach.
1.8 As a detergent ingredient, CMC must comply with relevant safety standards, limiting the presence of harmful substances such as heavy metals (e.g., lead and arsenic), chlorides, and microorganisms, ensuring skin non-irritation and environmental friendliness.
2. Sodium Carboxymethyl Cellulose Addition Amount
The amount of CMC added to laundry detergents should be determined based on a comprehensive consideration of factors such as its functional positioning, formulation (e.g., whether enzymes or bleach are present), water hardness, and the intended washing target. The following are general recommended ranges and influencing factors:
2.1 Standard Addition Level Range
In conventional laundry detergents, the typical addition level of CMC is 0.5%–3% of the total formulation. This range balances anti-redeposition effectiveness with cost and the impact on other performance properties (such as foaming and detergency). For example, a 1%–2% addition level in regular synthetic laundry detergents can significantly improve whiteness retention.
In concentrated laundry detergents, low-foaming laundry detergents, or formulations designed for darker colors, the addition level may be adjusted appropriately (e.g., reduced to 0.3%–1.0% to control foaming or cost), or slightly increased in areas with high water hardness to enhance anti-redeposition performance.
2.2 Factors Influencing Addition Level
Regarding water hardness, hard water (high calcium and magnesium ions) reduces the colloidal stability of CMC, necessitating a moderate increase in the dosage (upper limit near 3%) to maintain anti-staining effectiveness.
Regarding surfactant types, anionic surfactants (such as LAS) work best with CMC, while nonionic or amphoteric surfactant systems may require careful dosage adjustments to avoid interference.
The presence of other additives, such as enzymes, bleaching agents (such as perborate), or anti-redeposition polymers (such as polyvinylpyrrolidone (PVP)), may affect CMC requirements, necessitating formulation optimization to balance functional overlap or competitive adsorption.
Regarding wash temperatures, CMC dissolves more slowly at low temperatures, potentially necessitating a higher degree of substitution or an appropriately increased dosage to rapidly form an effective colloidal layer.
2.3 Risks of Overdosage
Overdosage carries risks, such as foam suppression. Excessive CMC may over-thicken the detergent, indirectly inhibiting foam formation or reducing foam stability, thus affecting wash feel (especially in handwash formulations).
Increased costs: High-viscosity or high-purity CMC is more expensive, and adding more than necessary can significantly increase formulation costs.
Agglomeration tendency: When moisture control is poor, high CMC levels can exacerbate clumping in detergents, compromising product usability.
3. Application Considerations
To ensure optimal CMC performance in laundry detergents, the following key practical considerations should be observed:
3.1 Raw material selection: Based on the target market (e.g., household laundry, industrial laundry), water quality characteristics, and cost budget, select a detergent-specific CMC grade that complies with the national standard GB/T 12028. Prioritize products with moderate viscosity, uniform substitution, and good flowability.
3.2 Production process adaptation: During the laundry detergent manufacturing process (e.g., spray drying or dry blending), ensure that CMC and other powdered raw materials (e.g., sodium carbonate, sodium tripolyphosphate substitutes) are thoroughly mixed and uniformly to avoid localized agglomeration that affects dispersibility. For dry blending, particle size requirements are particularly important.
3.3 Formula optimization: CMC's anti-redeposition function can synergize with other anti-redeposition agents (e.g., PVP). However, it is important to note the incompatibility between anionic CMC and cationic softeners or biocides to prevent charge neutralization failure. Formula experiments should be conducted to verify the interactions and optimal dosages of the different ingredients.
3.4 Performance Testing and Verification: Before actual production, laundry detergents containing CMC should undergo detergency, whiteness retention, and anti-redeposition testing (e.g., through a standard soiled cloth wash test). This should be combined with stability testing (e.g., high-temperature, high-humidity storage) to ensure long-term effectiveness.
4. Summary
As an essential anti-soil redeposition agent in laundry detergents, sodium carboxymethyl cellulose (CMC) must meet stringent standards for core indicators such as degree of substitution (0.5-0.7), viscosity (5-40 mPa·s), purity (≥55%), pH (8.0-11.5), and moisture content (≤10%) to ensure dissolution rate, colloidal stability, and anti-fouling properties. The addition level is typically controlled between 0.5% and 3%, with fine-tuning based on water quality, formulation complexity, and cost targets. Through rational raw material selection, optimized production processes, and collaborative formulation design, CMC can significantly enhance the cleaning performance of laundry detergents, keeping clothes clean and bright, while maintaining economic efficiency and safety.
