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Abstract: With the rapid development of the washing industry towards non phosphating, concentration, low-temperature energy saving, and green low residue, traditional phosphate detergents have been gradually restricted in use due to eutrophication of water bodies. Polymer dispersants have become an indispensable core functional additive in modern detergent formulations. Polymer dispersants, with excellent charge adsorption, particle dispersion, resistance to dirt re deposition, scale and crystal inhibition, and metal ion chelation ability, can significantly improve detergent cleaning efficiency, improve hard water adaptability, inhibit clothing ashing and vessel scaling. They are widely used in civilian laundry detergents, laundry powders, industrial linen cleaning agents, and automatic tableware washing systems. This article provides a systematic review of the types, molecular structure characteristics, and washing aid mechanisms of commonly used polymer dispersants in detergents. It analyzes the dispersion stability of different structural dispersants in inorganic clay stains, organic oil stains, calcium soap complexes, and scale systems, summarizes the application characteristics, formula compatibility, and existing technical problems of dispersants in different washing products, and looks forward to the development trend of green, multifunctional, low-temperature and high hard water resistant polymer dispersants for detergents, providing theoretical reference for the research and engineering application of new phosphorus free washing formulas.

Keywords: polymer dispersant; Phosphate free detergent; Anti redeposition; Dispersion mechanism; Scale inhibition; Formula application

1 Introduction

Washing and decontamination are complex physical and chemical processes at the solid-liquid interface. The dirt on the surface of clothing and tableware mainly includes inorganic clay sediment, metal oxides, sebum and oil, protein starch dirt, and calcium soap precipitates generated during the washing process. In traditional washing systems, surfactants mainly undertake wetting, emulsification, solubilization, foaming and cleaning functions. However, single surfactant systems have obvious shortcomings: they are easily combined with calcium and magnesium ions in high hardness water to form insoluble calcium soap precipitates; The peeled dirt particles are prone to re aggregation and re adsorption on the surface of the fabric, causing the clothes to become gray, hard, and lose luster after repeated washing; At the same time, carbonates and silicates in the washing water are prone to crystallization and precipitation, forming scale, water spots, and mist on the surfaces of fabrics, tableware, and equipment, seriously affecting the cleanliness and appearance of the washing.

To solve the above problems, the washing formula must introduce polymer dispersing agents. Early detergents commonly used sodium tripolyphosphate (STPP) as a detergent aid, which has excellent chelating, dispersing, and buffering pH capabilities. However, phosphorus containing wastewater is prone to eutrophication, algal blooms, and water quality deterioration. Currently, phosphate free washing standards have been fully implemented both domestically and internationally. In this context, polymer dispersants represented by carboxymethyl cellulose, sodium polyacrylate, acrylic acid maleic anhydride copolymer, and comb type polyether polycarboxylate have gradually become the core functional components of phosphate free detergents. Compared with traditional small molecule additives, polymer dispersants have advantages such as long molecular chains, stable adsorption, strong steric hindrance, excellent hard water resistance, low residue, and biodegradability. They can fundamentally solve the problems of dirt aggregation, re deposition, and scale crystallization, and are key materials for upgrading and iterating modern concentrated and green detergents.

Types and structural characteristics of commonly used polymer dispersants in detergents

Dispersants used in detergents are mostly anionic water-soluble polymers, which generally contain anchoring adsorption groups and hydrophilic solvation chains in their molecular structure. The anchoring groups are mainly polar groups such as carboxyl, hydroxyl, and ether bonds, which can firmly adsorb on the surfaces of dirt particles and mineral crystals; The hydrophilic long chain fully extends in the aqueous phase, forming a stable hydration layer, achieving dual stabilization effects of electrostatic repulsion and steric hindrance. At present, the mainstream industrial detergent dispersants are mainly divided into four categories.

2.1 Carboxymethyl cellulose (CMC)

CMC is a natural modified polymer dispersant that was first applied in the washing industry. Its molecules are rich in carboxyl and hydroxyl groups and ionize negatively in alkaline washing solutions. It can adsorb onto clay dirt and cotton fabric surfaces, forming a protective layer that effectively prevents dirt from re depositing. The material has low cost, good compatibility and moderate foam, and is widely used in traditional detergent systems. However, CMC has obvious performance shortcomings. In high hardness water, calcium and magnesium ions are prone to shield charges, resulting in a significant decrease in dispersion ability and anti redeposition effect. In addition, its high-temperature washing stability is poor, making it unsuitable for modern concentrated laundry detergents and industrial high-temperature washing systems.

2.2 Sodium polyacrylate (PAAS)

Sodium polyacrylate is a homopolymer formed by the polymerization of monomer acrylic acid, with molecular chains rich in high-density carboxyl groups and high negative charge density after ionization. It has strong dispersibility and depolymerization ability for hard dirt such as inorganic sediment and iron oxide dust, and can effectively inhibit particle aggregation and sedimentation. This type of polymer has good temperature resistance, excellent solubility, and outstanding cost-effectiveness, making it the main dispersant for phosphate free laundry detergent. However, its molecular structure is single, its side chains are short, its steric hindrance ability is limited, and its ability to chelate calcium and magnesium ions is weak. When used alone, its scale inhibition effect is average, and it usually needs to be used in combination with 4A zeolite, silicate and other detergents.

2.3 Acrylic acid maleic anhydride copolymer

Acrylic maleic anhydride binary copolymer is currently the most comprehensive and widely used detergent dispersant. By introducing polar monomers of maleic anhydride, the carboxyl density and charge uniformity of the molecular structure are significantly improved, while optimizing the flexibility of the molecular chain. Compared to homopolymers, it has multiple functions such as strong dispersion, strong chelation, microcrystal distortion, and anti redeposition. It can stabilize suspended inorganic dirt and chelate calcium and magnesium ions in water, interfere with the growth of calcium carbonate crystals, and inhibit scale formation. This copolymer is resistant to hard water, high temperature, and has strong compatibility. It can be adapted to all scenario systems such as laundry detergent, concentrated laundry detergent, dishwasher cleaning agents, and industrial linen washing.

2.4 Comb type polyether polycarboxylate dispersant

Comb shaped polycarboxylates are a new generation of high-end detergent dispersants, with the main chain consisting of acrylic acid carboxyl anchoring segments and side linked long-chain polyoxyethylene ether hydrophilic groups, forming a unique comb shaped three-dimensional structure. This structure breaks through the limitations of traditional linear polymers, while possessing high-density electrostatic repulsion and super strong steric hindrance effect, and has excellent dispersion stability for ultrafine clay and aged oil calcium soap composites. At the same time, the dispersant has good low-temperature solubility, no thickening, no layering, and excellent compatibility with non-ionic surfactants, enzyme preparations, and softening components. It is suitable for modern low-temperature concentrated laundry detergents and high activity enzyme composite washing systems, and is currently a research hotspot in green detergents.

The Core Mechanism of Polymer Dispersants in Washing Systems

The function of dispersants in detergents is no longer a single dispersing effect, but a multiple synergistic mechanism that integrates wetting dispersion, electrostatic stability, steric hindrance shielding, anti redeposition, chelation scale inhibition, and microcrystalline modification.

3.1 Particle wetting and depolymerization dispersion mechanism

The inorganic dirt on the surface of clothing is mostly aggregated particles with a large specific surface area and high surface energy, which are easily aggregated into large particles and settle in water. Polymer dispersants can quickly wet and aggregate particle pores, reduce solid-liquid interfacial tension, and promote the disintegration of large particles into small single particles under mechanical stirring, achieving uniform dispersion of dirt and greatly improving the cleaning efficiency of surfactants.

3.2 Stability mechanism of electrostatic repulsion

Anionic polymer dispersants are completely ionized in alkaline washing solutions, and negatively charged carboxyl groups are directionally adsorbed on the surface of dirt particles, causing all dirt particles to uniformly carry negative charges. The strong electrostatic repulsion generated between particles due to the same charge effectively prevents particles from colliding, flocculation, and agglomeration, allowing dirt to remain suspended in the washing solution for a long time and not settle back onto the fabric surface.

3.3 Spatial impedance redeposition mechanism

After the long polymer chains are adsorbed on the surface of the dirt, the hydrophilic segments fully extend into the aqueous phase, forming a thickness stable hydration polymer protective layer. This three-dimensional barrier can physically block the contact between dirt particles, while competing to adsorb on the surface of fabric fibers, occupying adsorption sites, preventing suspended dirt from reattaching to fibers, significantly improving the ability to maintain clothing whiteness, and preventing fabric ashing, darkening, and hardening after multiple washes.

3.4 Chelation and Microcrystalline Distortion Scale Inhibition Mechanism

Polycarboxylate dispersants can chelate Ca ² ⁺ and Mg ² ⁺ in water through carboxyl groups, reducing water hardness and minimizing the formation of calcium soap. At the same time, polymer chains can adsorb on the surface of calcium carbonate and calcium silicate microcrystals, interfering with normal crystal growth, disrupting lattice regularity, and transforming hard coarse crystals into soft amorphous microcrystals that cannot deposit and form scales. They can be discharged with rinsing water flow, effectively preventing water stains on tableware, glass fog film, and equipment pipeline scaling and blockage.

Application characteristics of dispersants in different washing products

4.1 Phosphate free laundry detergent system

Laundry powder has high solid content and stable formula system, mainly using sodium polyacrylate and acrylic acid maleic anhydride copolymer. The powder system mainly removes inorganic clay dirt, and dispersants can significantly enhance the powder’s cleaning power, prevent storage agglomeration, and inhibit the settling of washing dirt. In industrial formulations, 4A zeolite is usually used in combination. Zeolite is responsible for chelating calcium and magnesium ions, while polymer dispersants are responsible for dispersing suspended dirt. The two work together to achieve high-efficiency phosphorus free washing effects.

4.2 Concentrated liquid laundry detergent system

Concentrated laundry detergent has a high water content and a complex system, containing various components such as non-ionic surfactants, biological enzymes, softeners, preservatives, etc., which require extremely high compatibility with dispersants. Traditional linear dispersants can easily cause thickening, layering, and enzyme activity deactivation in the system, so high-end laundry detergents commonly use comb type polyether polycarboxylates. It has a stable structure, good low-temperature fluidity, does not affect enzyme activity, and has strong resistance to hard water. It can stably suspend oil stains and clay composite dirt for a long time, meeting the needs of low-temperature energy-saving washing.

4.3 Industrial linen detergent

Hotel and hospital linen washing has the characteristics of high water temperature, high water hardness, and multiple washing cycles. Linen is prone to accumulate calcium soap and mineral deposits, leading to a decrease in whiteness and a hard hand feel. Acrylic maleic anhydride copolymer has become the preferred dispersant for industrial washing due to its high temperature resistance, strong resistance to hard water, and excellent scale inhibition performance. It can maintain the whiteness of fabrics for a long time and extend their service life.

4.4 Automatic Dishwashing Auxiliary System

Dishwashers are prone to producing scale, water stains, and glass fogging due to high temperatures, high alkalinity, and high hardness. The core function of dispersants in this system is no longer decontamination, but scale and crystal inhibition. By interfering with mineral crystallization and dispersing micro precipitates, it prevents hard scale from adhering to tableware and equipment liners, and maintains the transparency and cleanliness of glass and stainless steel surfaces.

Common problems and defect mechanisms in the application of 5 formulas

5.1 Insufficient dosage of dispersant added

When the addition amount is too low, the dirt cannot be completely wrapped and stabilized, and the particles are prone to agglomeration and sedimentation, resulting in insufficient anti redeposition ability. After washing, the dirt will stick back to the fabric, causing the clothes to become gray, dull, and rough to the touch; Calcium soap cannot be effectively dispersed in hard water environments and is prone to soap scale accumulation.

5.2 Side effects of excessive addition of dispersants

Excessive free polymers will remain in the washing solution and the fabric surface, resulting in increased foam, difficulty in rinsing, and sticky clothing; At the same time, excessive anionic polymers can alter the rheological properties of the system, resulting in abnormal viscosity of the laundry detergent and cloudy storage stratification; Some systems may reduce the emulsifying and cleaning ability of surfactants.

5.3 Compatibility conflicts of additives

Anionic polycarboxylate dispersants have charge conflicts with cationic softeners and fungicides, which can lead to flocculation and system instability when used together; Some polymers will adsorb and encapsulate enzyme proteins, reducing the activity of proteases and lipases, leading to a decrease in cleaning power.

5.4 Shortcomings in Environmental Adaptability

Traditional CMC and low molecular weight polyacrylic acid salts exhibit significant performance degradation under high hardness water and low temperature conditions, with insufficient dispersion stability, making it difficult to adapt to modern low-temperature water-saving and high hardness washing conditions.

6 Development Trends and Prospects

With the continuous promotion of national policies on green washing, low-carbon environmental protection, and water conservation and energy conservation, the detergent industry is comprehensively upgrading towards phosphate free, low-temperature, concentrated, and bio composite directions, and polymer dispersants are showing a clear development trend. Firstly, green bio based dispersants are gradually replacing traditional petroleum based polymers, improving biodegradability and reducing residual pollution; The second is precise molecular structure design, by regulating molecular weight, acid value, and side chain grafting rate, to develop comb shaped multifunctional dispersants with low additives, high efficiency, high hardness water resistance, and low temperature resistance; The third is the development of multifunctional integrated additives, which integrate functions such as dispersion, scale inhibition, foam inhibition, enzyme stabilization, and anti-static, simplifying the washing formula system; The fourth is to adapt to low-temperature water-saving washing technology to solve the industry pain points of difficult dirt dispersion and weak crystallization inhibition at low temperatures. In the future, high-performance polymer dispersants will continue to lead the technological upgrading and green industrialization development of phosphate free detergents.

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