Industrial Cleaning Agent Formulation Design Guide

Introduction

Industrial cleaning, as the name suggests, is the process of using physical, chemical, or biological actions to remove contaminants (soils) from the surface of a substrate. The ultimate goal is to restore the surface to its original state.

The success of industrial cleaning is primarily influenced by three major factors: cleaning technology, cleaning equipment, and cleaning agents.

Primary Cleaning Technologies

Cleaning technologies are generally categorized into three types:

1. Chemical Cleaning: This includes common methods such as acid washing, alkaline washing, and solvent cleaning. These methods typically require cleaning equipment to work in tandem with chemical agents. In conventional industrial cleaning, this remains the dominant method due to its low cost, speed, and convenience.

2. Physical Cleaning: This includes high-pressure water jetting, air turbulence, ultrasonic cleaning, electric pulse cleaning, shot blasting, sandblasting, dry ice cleaning, and mechanical scraping. These methods rely on equipment paired with water or solid particles. While highly efficient, the equipment is often expensive, and operating costs are relatively high.

3. Biological Cleaning: This involves the use of microbial catalytic actions. It is commonly used for textiles and pipeline cleaning. However, its application is narrow because it requires specific catalytic activity from biological enzymes.

Classification of Industrial Cleaning Agents

There are various ways to classify industrial cleaning agents. Common types include water-based, semi-aqueous, and solvent-based cleaners. Due to rising environmental awareness, solvent-based cleaners are gradually being replaced, allowing water-based cleaners to occupy more market space. Based on pH levels, water-based cleaners are further divided into alkaline, acidic, and neutral types.

The industry is moving toward green, efficient, energy-saving, and economical solutions. This transition sets specific requirements for modern cleaners:

• Replacing traditional solvents with water-based systems.

• Formulating products that are phosphate-free, low-nitrogen to nitrogen-free, and free of heavy metals or environmentally harmful substances.

• Developing concentrated formulas to reduce transportation costs.

• Ensuring convenience, ideally for use at ambient temperatures.

• Maintaining low production costs to reduce the end-user's expenses.

Principles of Water-Based Formulation Design

Before designing a cleaning agent formula, we must classify the contaminants based on the appropriate washing method.

Common Contaminant Categories:

1. Contaminants soluble in acid, alkali, or enzyme solutions: These are easily removed. We can select specific acids, alkalis, or enzymes to prepare solutions for direct removal.

2. Water-soluble contaminants: Examples include soluble salts, sugars, and starches. These can be dissolved and carried away via water immersion, ultrasonics, or spraying.

3. Water-dispersible contaminants: Examples include cement, gypsum, lime, and dust. These require the mechanical force of cleaning equipment combined with water-soluble dispersants and penetrants to wet, disperse, and suspend them in water.

4. Insoluble soils: Examples include oils and waxes. These require external force, additives, and surfactants to undergo emulsification, saponification, or dispersion. This allows the soil to detach from the substrate and form a dispersion liquid to be washed away.

In reality, soils rarely exist in isolation. They are usually mixed together and adhered to the surface or deep within the substrate. Environmental factors can also cause fermentation, decomposition, or mold, creating complex pollutants. Regardless of whether the bond is a reactive chemical force or a physical adhesive force, the cleaning process must follow four critical steps: Dissolution, Wetting, Emulsification/Dispersion, and Chelation.

1. Water-Based Cleaning Agent Design Logic

1.1 System Selection

Common water-based cleaning systems are categorized into three types: neutral, acidic, and alkaline.

• Neutral Cleaners: Used primarily for substrates that cannot tolerate acids or alkalis. The process relies on the synergistic effect of additives and surfactants.

• Acidic Cleaning: Generally used for metal rust and scale removal. There are fewer additives available for acidic conditions. It relies on the reaction between the acid and the rust/scale to peel off the soil. Surfactants then emulsify and disperse the debris. Common acids include nitric, hydrochloric, sulfuric, phosphoric, citric, oxalic, acetic, methanesulfonic, dodecylbenzenesulfonic, and boric acid.

• Alkaline Cleaning: The most widely used in industrial settings. Since alkalis can undergo saponification with vegetable oils to form hydrophilic soaps, they are ideal for grease removal. Common alkalis include NaOH, KOH, sodium carbonate, ammonia water, and alcohol amines.

1.2 Selection of Additives

In industrial cleaning, additives that enhance the cleaning effect are called "builders" or auxiliaries. These include chelating dispersants, corrosion inhibitors, defoamers, preservatives, enzymes, and pH stabilizers.

Common categories include:

• Chelating Dispersants: Phosphates (Sodium pyrophosphate, STPP, etc.), organic phosphonates (ATMP, HEDP, etc.), alcohol amines (TEA, DEA, MEA, etc.), aminocarboxylates (NTA, EDTA, etc.), hydroxycarboxylates (citrates, tartrates, gluconates, etc.), and polyacrylic acid derivatives.

• Corrosion Inhibitors: Oxidizing film types (chromates, nitrites, etc.), precipitation film types (phosphates, carbonates, etc.), and adsorption film types (silicates, organic amines, imidazolines, triazoles, etc.).

• Defoamers: Silicone-based, polyether-modified silicone, and non-silicone defoamers.

1.3 Selection of Surfactants

Surfactants play a vital role in industrial cleaning. They reduce the surface tension of the system and improve the penetration of the product. This allows the cleaning agent to quickly penetrate deep into the soil. Furthermore, surfactants provide dispersion and emulsification for the removed oil.

Common categories of surfactants include:

• Non-ionic: Alkylphenol ethoxylates (NP/OP/TX series), fatty alcohol ethoxylates (AEO series), isomeric alcohol ethoxylates (XL/XP/TO series), secondary alcohol ethoxylates (SAEO series), EO/PO block copolymers (PE/RPE series), fatty acid methyl ester ethoxylates (FMEE), fatty acid ethoxylates (EL), fatty amine ethoxylates (AC), acetylenic diol ethoxylates, and alkyl polyglycosides (APG) series.

• Anionic: Sulfonates (LAS, AOS, SAS, OT, MES, etc.), sulfates (K12, AES, etc.), phosphate esters (alkyl phosphates, alcohol ether phosphates, alkylphenol ether phosphates), and carboxylates (fatty acid salts).

• Cationic: Quaternary ammonium salts (1631, 1231, etc.).

• Amphoteric: Betaines (BS, CAB, etc.), amino acids, amine oxides (OB, etc.), and imidazolines.

When selecting surfactants, we typically evaluate four critical parameters based on their molecular structure: Surface Tension, HLB Value, CMC (Critical Micelle Concentration), and Cloud Point (or Krafft Point).

• Surface Tension: Adding surfactants lowers the surface tension of the cleaning agent. Common surfactants can reduce it to approximately 30 mN/m. Since surface tension represents the contraction force of the liquid surface, a lower value allows the cleaner to spread more easily on the substrate and better wet the solid surface.

• HLB Value: This represents the Hydrophilic-Lipophilic Balance. A higher HLB indicates better hydrophilicity, while a lower value indicates poorer hydrophilicity.

  • HLB 1–6: Lipophilic properties dominate; used as defoamers or W/O emulsifier aids.

  • HLB 7–9: Balanced properties; commonly used as wetting and penetrating agents.

  • HLB > 10: Hydrophilic properties dominate; commonly used as emulsifiers in cleaning.

• CMC: The Critical Micelle Concentration is the lowest concentration at which surfactant molecules associate to form micelles. Below the CMC, molecules exist in a free state, and surface tension decreases as concentration increases. Once the CMC is reached, surface tension hits its minimum. Further increases in concentration only increase micelle density, enhancing the capacity to dissolve oil.

• Cloud Point (Krafft Point): For ionic surfactants, solubility increases sharply at a specific temperature called the Krafft point. Therefore, ionic surfactants should be used at temperatures above their Krafft point. Non-ionic surfactants behave oppositely; their solubility drops sharply as temperature rises, causing turbidity or precipitation. This temperature is the Cloud Point. Non-ionic surfactants should generally be used below or near their cloud point.

Application Example

Case Study: Aluminum Alloy Degreaser Formulation Design

Establishing the System:
For industrial degreasing, alkaline systems (such as Sodium Hydroxide) are preferred because fatty substances saponify more easily under alkaline conditions.

Various auxiliaries are available for alkaline systems, including sodium gluconate, sodium silicate, STPP, and EDTA-2Na. however, when cleaning aluminum alloys, corrosion is a primary concern. Aluminum is an amphoteric metal that corrodes in both acidic and alkaline conditions. Therefore:

1. Alkali content must be strictly controlled.

2. A suitable corrosion inhibition system must be selected.

Surfactant Selection:
The core of degreasing lies in selecting surfactants based on the four key parameters:

• Surface Tension: Most surfactants can meet the requirement of not exceeding 30 mN/m.

• HLB Value: A value greater than 10 is required. If using isomerized alcohol ethoxylates as the primary surfactant, the EO (Ethylene Oxide) count should be 5 or higher.

• Temperature & Cloud Point: In ultrasonic cleaning, temperatures can reach approximately 50°C. Therefore, a surfactant with a cloud point above 50°C is necessary, requiring an EO count of 7 or higher.

• Ease of Use: Generally, higher EO values result in higher pour points. For convenience, it is ideal for the pour point not to exceed 30°C. This ensures the surfactant remains in a liquid state at room temperature for maximum efficiency. Consequently, an EO range of 7 to 12 is chosen for the primary surfactant.

Synergy and Penetration:
While primary surfactants provide excellent emulsification and detergency, their wetting and penetration power weakens as the EO count increases (due to higher hydrophilicity). Therefore, a wetting penetrant is required for the blend. Surfactants with an HLB of 7–9 are ideal for this. For alcohol ethers, an EO count between 4 and 6 is typically selected.

Lipophilic Structure Considerations:

• Straight-chain: Stronger emulsification power.

• Branched-chain: Superior penetration power.

• Molecular Size: Larger structures hinder penetration, while excessively small structures may lose surface activity.
  Therefore, surfactants with a lipophilic chain of 8 to 10 carbon atoms are generally preferred as penetrants.

Final Formulation Composition:

• Sodium Hydroxide: 1–2%

• Sodium Silicate: 2–3%

• Sodium Gluconate: 1–2%

• EDTA-2Na: 1–2%

• Penetrant QH-7: 0.1–0.5%

• Lutensol TO-8: 3–5%

• Corrosion Inhibitor FS-11: 0.1–0.5%

• Preservative/Bactericide: As needed

• Water: Balance

Cleaning Process:
Dilute 10–20 times. Use for room temperature immersion cleaning (ultrasonic assistance is recommended for best results).