Commonly used cleaning agents can be classified in different ways. For example, according to their chemical composition, they can be divided into inorganic chemical cleaning agents and organic chemical cleaning agents [2]; according to the possible different effects of some cleaning agents on different dirt, or having two or more effects on the same kind of dirt, they should be classified according to their important effects under general circumstances.
1. Water and non-aqueous solvents
The solvent of dirt refers to those substances that can strip off the dirt of the cleaning object in the form of dissolution or dispersion without generating new substances with stable and definite chemical compositions. It includes water and non-aqueous solvents.
(1) Water: Water is the most important solvent that exists in nature. In industrial cleaning, water is both the solvent for most chemical cleaning agents and the solvent for many kinds of dirt. In cleaning, wherever dirt can be removed with water, non-aqueous solvents and various additives will not be used.
(2) Non-aqueous solvents: Non-aqueous solvents include hydrocarbons and halogenated hydrocarbons, alcohols, ethers, ketones, esters, phenols, etc., and their mixtures. They are mainly used to dissolve organic dirt, such as oil dirt and certain organic compound dirt.
2. Surfactants
Its molecules simultaneously have hydrophilic polar groups and lipophilic non-polar groups. When a small amount is added, it can greatly reduce the surface tension of the solvent (usually water) and the interfacial tension, and has lubricating, solubilizing, emulsifying, dispersing and washing functions.
Surfactants have many classification methods. Widely based on its ionization state in the solvent and the type of hydrophilic group ions. The most commonly used are anionic surfactants, cationic surfactants, amphoteric surfactants, and non-ionic surfactants. The first three are ionic surfactants.
Surfactants have wide applications in household life and industrial production cleaning.
3. Acid-base cleaning agents
Cleaning agents that rely on acid-base reactions with dirt (sometimes accompanied by oxidation-reduction reactions), changing the dirt into substances that can be dissolved or dispersed in the cleaning solution, mostly organic acids, inorganic acids, alkalis, and salts that become acidic or alkaline after hydrolysis.
Most acid-base cleaning agents are composed of water solutions of acids and alkalis plus necessary adjuvants. Another type of acid or alkali that acts on dirt in a molten state under high temperature conditions, converting dirt that was originally insoluble or difficult to dissolve in the cleaning medium into easily soluble compounds, these acids and alkalis are usually called fluxes. This kind of cleaning agent has good results when dealing with dirt that is difficult to clean with solvents or solutions.
4. Oxidation-reduction agents
Preparations that mainly eliminate dirt through oxidation-reduction reactions with dirt are cleaning oxidants or reductants, including fluxes.
Oxidants are used to remove reducing dirt, such as many organic dirt. Reductants are used to clean oxidizing dirt, such as rust dirt.
5. Metal ion chelating agents
By cooperating with metal ions in dirt, making the dirt change into chelates that are easily soluble in cleaning agents, such cleaning agents or adjuvants are called chelating agents. They are commonly used in rust dirt and inorganic salt dirt cleaning.
6. Adsorbents
Substances that clear dirt through physical adsorption or chemical adsorption of dirt are cleaning adsorbents. Adsorbents with strong affinity for dirt should be selected for cleaning.
Membrane cleaning Antifouling agent Antifouling agent