Principles of Cleaning Agent Formulation Design

With the rapid growth of my country's industrial economy, the industrial cleaning sector has flourished. Industrial cleaning performance depends not only on the cleaning process but also on the choice of cleaning agent. Given the wide variety of cleaning agents available and increasingly stringent environmental regulations, the selection of raw materials has garnered significant attention. This article focuses on the selection of surfactants for water-based cleaning agents; by comparing various parameters, the most suitable surfactant for a given system can be selected to meet requirements for high efficiency and environmental friendliness.

As the name implies, industrial cleaning is the process of removing contaminants (soil) from the surface of a substrate—accumulated through physical, chemical, or biological processes—to restore the surface to its original state. Industrial cleaning is primarily influenced by three factors: cleaning technology, cleaning equipment, and cleaning agents.
I. Cleaning Technologies
(1) Chemical cleaning: This includes common methods such as acid cleaning, alkaline cleaning, and solvent cleaning. These methods typically require the use of cleaning equipment in conjunction with cleaning agents. In standard industrial cleaning operations, chemical cleaning has long held a dominant position due to its low cost, speed, and convenience.
(2) Physical cleaning: This encompasses methods such as high-pressure water jetting, air agitation cleaning, ultrasonic cleaning, electric pulse cleaning, shot blasting, sandblasting, dry ice cleaning, and mechanical scraping. These methods rely primarily on cleaning equipment using media like water or solid particles. While highly efficient, the equipment is often expensive, and operating costs are significant.
(3) Biological cleaning: This method utilizes the catalytic action of microorganisms. It is frequently used for textiles and pipeline cleaning; however, its application is somewhat limited due to specific requirements regarding the catalytic activity of the biological enzymes involved. Industrial cleaning agents are classified in various ways, with common categories including water-based, semi-aqueous, and solvent-based agents. With rising environmental awareness, solvent-based cleaning agents are gradually being phased out, while water-based agents are capturing a larger share of the market. Water-based cleaning agents can be further categorized by pH level into alkaline, acidic, and neutral agents. Cleaning agents are evolving towards being eco-friendly, highly efficient, energy-saving, and cost-effective. This trend imposes the following requirements: water-based cleaning agents should replace traditional solvent-based ones; formulations must be phosphorus-free, low-to-zero nitrogen, and free from heavy metals or environmentally harmful substances; they should move towards concentration (to reduce transport costs), multifunctionality, and specialization; application conditions should be convenient, ideally allowing for use at ambient temperature; and production costs should be low to minimize expenses for the end-user.

II. Principles of Water-Based Cleaning Agent Formulation Design. Before designing a formulation, contaminants are typically classified. Common contaminants can be categorized based on the cleaning method required:
(1) Contaminants soluble in acid, alkali, or enzyme solutions: These are easily removed; specific acids, alkalis, or enzymes can be selected to create a solution for direct removal. (2) Water-soluble contaminants: Examples include soluble salts, sugars, and starches; these can be dissolved and washed away from the substrate surface via water immersion, ultrasonic cleaning, or spraying.
(3) Water-dispersible contaminants: Examples include cement, gypsum, lime, and dust; these can be wetted, dispersed, and suspended in water for removal with the aid of mechanical force from cleaning equipment, water-soluble dispersants, and penetrating agents.
(4) Water-insoluble soils: Examples include oils, greases, and waxes; these require external force, additives, and emulsifiers to undergo processes such as emulsification, saponification, and dispersion under specific conditions, detaching them from the substrate surface and carrying them away as a dispersion. However, soils rarely exist in isolation; they often adhere to the substrate surface or penetrate deep into it as complex mixtures. Under external influences, they may undergo fermentation, decomposition, or mold growth, resulting in even more complex contaminants. Regardless of whether they are reactive contaminants formed via chemical bonding or adhesive contaminants formed via physical bonding, the cleaning process generally involves four key steps: dissolution, wetting, emulsification/dispersion, and chelation .

III. Approach to Water-Based Cleaning Agent Formulation Design
1. Selection of the System. Common water-based cleaning agent systems fall into three categories: neutral, acidic, and alkaline. Neutral cleaners are primarily used on surfaces sensitive to acids and alkalis; the cleaning process relies on a synergistic combination of cleaning auxiliaries and surfactants to remove soil from the substrate surface.
Acidic cleaning is typically employed for rust and scale removal on metals. Options for auxiliaries under acidic conditions are limited; the process primarily involves the reaction of the acid with rust or scale to detach the soil, while auxiliaries and surfactants emulsify and disperse the loosened contaminants to achieve the desired cleaning effect. Common acids include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, citric acid, oxalic acid, acetic acid, methanesulfonic acid, dodecylbenzenesulfonic acid, and boric acid. Alkaline cleaning is the most widely used method in industrial cleaning; because alkalis can saponify vegetable oils to form hydrophilic soap products, they are highly effective for removing oily soils.
Commonly used alkalis include sodium hydroxide, potassium hydroxide, sodium carbonate, aqueous ammonia, and alkanolamines. 

2. Selection of Auxiliaries: In industrial cleaning, additives that enhance cleaning performance are termed "cleaning auxiliaries." These include chelating and dispersing agents, corrosion inhibitors, defoamers, biocides/preservatives, enzyme preparations, and pH stabilizers. Commonly used additives fall into the following major categories: Chelating and dispersing agents: phosphates (sodium pyrophosphate, sodium tripolyphosphate, sodium metaphosphate, sodium phosphate, etc.), organophosphonates (ATMP, HEDP, EDTMP, etc.), alkanolamines (triethanolamine, diethanolamine, monoethanolamine, isopropanolamine, etc.), aminocarboxylates (NTA, EDTA, etc.), hydroxycarboxylates (citrates, tartrates, gluconates, etc.), polyacrylic acid and its derivatives (maleic-acrylic copolymers), etc.; Corrosion inhibitors: oxide film-forming types (chromates, nitrites, molybdates, tungstates, borates, etc.), precipitation film-forming types (phosphates, carbonates, hydroxides, etc.), adsorption film-forming types (silicates, organic amines, organic carboxylic acids, petroleum sulfonates, thiourea, urotropine, imidazoles, thiazoles, benzotriazole, etc.);
Defoamers: silicone-based, polyether-modified silicone, silicone-free defoamers, etc.

3. Selection of surfactants
Surfactants play a crucial role in industrial cleaning; they reduce the system's surface tension and enhance product permeability, allowing the cleaning agent to rapidly penetrate the soil. They also serve to disperse and emulsify the oil and grease removed during the cleaning process. Commonly used surfactants are categorized into the following major groups: Non-ionic: alkylphenol ethoxylates (NP/OP/TX series), fatty alcohol ethoxylates (AEO series), branched alcohol ethoxylates (XL/XP/TO series), secondary alcohol ethoxylates (SAEO series), polyoxyethylene-polyoxypropylene ethers (PE/RPE series), alkyl polyoxyethylene-polyoxypropylene ethers, end-capped polyoxyethylene ethers, fatty acid ethoxylates (EL), fatty amine ethoxylates (AC), acetylenic diol ethoxylates, alkyl polyglycosides, etc.; Anionic: sulfonates (alkylbenzene sulfonates/LAS, alpha-olefin sulfonates/AOS, alkyl sulfonates/SAS, succinate sulfonates/OT, fatty acid ester sulfonates/MES, etc.), sulfates (K12, AES, etc.), phosphates (alkyl phosphates, fatty alcohol ethoxylate phosphates, alkylphenol ethoxylate phosphates, etc.), carboxylates (fatty acid salts, etc.); Cationic: quaternary ammonium salts (1631, 1231, etc.); Zwitterionic: betaines (BS, CAB, etc.), amino acids; amine oxides (OB, etc.), imidazolines.

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