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Cleaning Agent BasicsArticle courtesy of Kärcher Academy: Basics of Cleaning
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The choice depends on:
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Types of dirt:
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Type of surface:
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Cleaning agents must…
1. General:
– Have good dirt dissolving and removing effect
– Have a good anti-redeposition effect
– Have a good emulsifying effect
– Be gentle on the skin
2. With respect to the equipment used and objects to be cleaned:
3. Reasonable selling price
4. There may be further requirements with respect to:
Reduction of the surface tension (cohesion – adhesion): The surface must be moistened to ensure uniform cleaning. For this purpose, the surface tension must be reduced first. The properties of the surfactant (tenside) molecules (these are the molecules in cleaning agents) accomplish this moistening. This is why they are also called surface-active molecules (more commonly called surfactant molecules).
Water drop on a smooth surface. No moistening (the water’s surface tension is too high) |
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Low dosage of cleaning agent. |
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Correct dosage of cleaning agent. Complete moistening (complete reduction of the surface tension). Optimum cleaning. |
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An emulsion is the fine distribution of one insoluble liquid in another:
The ability of two liquids to emulsify depends on the surface tension of the respective liquids. The emulsifying ability is increased by reducing (or eliminating) the surface tension. This is achieved with the help of an emulsifier. A surfactant can act as an emulsifier.
A cleaning agent is a weak emulsifier if it contains few surfactants and is a strong emulsifier if it contains many surfactants. During cleaning, grease or oil can be detached from the surface as very small droplets and dispersed in the water (emulsion).
Important: The liquids in an emulsion will separate after a certain time. If the cleaning agent is designed in such a way that this separation takes place after the dirt removal but before disposal in the sewers, i.e. in the oil and petrol trap, the wastewater contamination is very low. We call this separation-friendly.
A dispersion is the fine distribution of a solid in a liquid (for example, limescale in water). The ability to keep small particles in suspension is called the anti-redeposition capacity (antiredepositing power). This effect is also produced by the surfactants.
The term “surfactant” is a collective term for different chemical substances. They are divided into the following groups: Detergents, humectants, cleaning agents and rinsing agents.
This classification is based on the charges of the surfactant molecules. A surfactant molecule consists of a hydrophilic and a hydrophobic part.
It therefore wants to get out of the water and prefers to bond with oil and grease. This part is responsible for the emulsifying properties of the surfactant molecule. Due to these two properties, surfactants reduce the interfacial tension.
The hydrophobic part of the surfactant tries to get out of the water. The hydrophilic part immerses in the water. As a con sequence of this, all interfaces (water/air, water/wall, water/dirt) are very densely coated with surfactant molecules. This causes a considerable reduction in surface tension. In their efforts to occupy the most interfaces as possible, the surfactant molecules also penetrate areas cannot be accessed by water (between the dirt and the wall). The adhesion between the dirt and surface is thus eliminated. As a result, the dirt is loosened. The dirt particle is then quasi surrounded by surfactants and can be e.g. washed away with a high-pressure jet.
You can see how dirt is suspended in water by the addition of a surfactant-based cleaning agent on the following drawings.
Water with dirt without cleaning agent. | ![]() |
Water with dirt with cleaning agent. | ![]() |
Oil is emulsified. | ![]() |
Alkalis chemically react with vegetable and animal fats. This chemical reaction causes saponification of the fat. The soap produced by this reaction promotes the effect of the surfactants in the cleaning agent. Alkaline-based agents also enable strongly adhering/bonding dirt to be removed more easily because they swell up. The effect of alkaline-based agents on dirt and grease is also very dependent on the influence of the electrical charges existing between the dirt particles and the surface.
Application: Alkaline-based cleaning agents include degreasers and deep cleaners.
Caution:
Acids chemically react with mineral (limescale) and oxidised (rust) soiling. The soiling (dirt) is converted by a chemical reaction into water-soluble salts and gases.
Example: CaCO3 + 2 HCl > CaCl2 + CO2 + H2O (Calcium carbonate + hydrochloric acid > calcium chloride + carbon dioxide + water)
Application: Acids are used in sanitary cleaners as surface laitance removers and descalers.
Caution:
Water hardness stabilizers are also called complexing agents. Water contains calcium ions (Ca2+), magnesium ions (Mg2+) and other minerals. Together, these minerals cause so-called water hardness.
Water hardness is expressed in °dH (° German hardness). 1° dH equals 0.179 mmol calcium oxide (millimole per litre water). 0.179 mmol = 10 mg calcium oxide.
Water hardness has adverse effects on the cleaning effect, because Ca2+ and Mg2+ ions are bound to the surfactants. (See diagram to the right: Increasing cleaning agent consumption at higher water hardness). These bonded surfactants are then no longer available for the cleaning effect.
The following substances can be used as builders (or water hardness stabilisers):
Polyphosphates have the most advantages in a cleaning agent, but are currently often replaced by MGDA, because these are more environmentally compatible.
Fillers: These are used above all in powder products, solely for price reasons. Fillers are cheap salts, e.g. sodium sulphate.
Inorganic complexing agents: These are used to intensify the cleaning effect and to improve the anti-redepositing power (dispersing ability). Dirt is then held longer in the cleaning liquid and does not redeposit back on the cleaned surface too quickly.
Preservatives: These are substances that ensure that the cleaning agent can be stored for a longer period.
Colourants: These are important for the recognisability of a cleaning agent. They can help to prevent errors in use.
Perfumes: These mainly have a psychological effect when using a product. However, they may also have adverse effects, and therefore these substances must be used with great caution.
Bleaching agents: They are used mainly for textile cleaning and have a damaging effect on the laundry (sodium hypochlorite or chlorine bleach).
The pH value of a cleaning agent indicates the hydrogen ion concentration per litre water. Therefore, only water-based cleaning agents can be classified according to this pH value table.
The pH value can be checked using a pH meter or a pH test strip (litmus paper). |
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The pH value provides information about:
It is necessary to check the pH value of the dirty water before it can be discharged into the drains. If it is lower than 6.5 or higher than 9 it must be neutralized:
Some cleaning agents do not have a pH value. These products are solvent-based.
Solvent-based cleaning agents have a special position among cleaning agents. Organic solvents have a strong fat-dissolving effect. Several kinds of solvents must be mixed with water. hese are then used as additives in water-soluble products.
The most important groups of solvents:
– Aromatic; e.g. benzene
– Aliphatic; e.g. cleaner’s solvent (petrol-based), turpentine
– Petroleum
The vast majority of cleaning agents are water-based. Dirt containing minerals, e.g. limescale deposits or metal oxides (rust), can only be effectively removed with the help of acidic cleaning agents. Here you must also pay attention to the surface: if it contains calcium carbonate, like marble, then the surface may be damaged.
Acids:
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Used in:
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Advantages:
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Disadvantages:
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Use:
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Advantages:
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Lyes:
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Used in:
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Very alkaline cleaners - pH 14
Strong grease-removing but also caustic properties, dangerous for eyes and skin, attacks light metals (zinc, aluminium) and all kinds of other materials such as paint, linoleum and textiles.
Weaker alkaline cleaners - pH 9
Dirt and grease removal: No or almost no risk of attack, moderately hypoallergenic.
Neutral cleaners - pH 7
Less effective oil and grease removal properties, depending on surfactants used, no limescale or rust compounds, no risk of attacking anything.
Weaker acidic cleaners - pH 6
Limescale and rust removal; grease removal thanks to the influence of detergents and solvents; low risk of attacking metals and skin. Caution with stone containing calcium carbonate!
Very acidic cleaners - pH 1
Powerful limescale and rust removal, skin and eye irritant. There is a risk of metals, paint, glaze and stones containing calcium carbonate/limestone being attacked.
The cleaning agent must never damage the high-pressure cleaner or the surface to be cleaned. Acidic and alkaline agents can cause such damage.
Example
Acid: Attacks metals
Lye: Efflorescence on aluminium surfaces.
When using cleaning agents, environment issues must also be considered (if necessary, neutralise).
Surface damage due to cleaning agents:
Object Material | Is Attacked By | Note (How To Clean) |
Iron, Steel | Acidic cleaning agent, free chlorine in disinfectants |
Cleaning agent with inhibitor, phosphatise |
Aluminium | Alkaline cleaning agent | Clean with acid, use cleaning agents with inhibitors |
Sheet Metal, Zinc | Very alkaline and very acidic agents | Clean with neutral agent |
Copper and Alloys | Good cleaning agent resistance | |
Paint, Varnish | Very alkaline cleaning agent | Clean with mild alkaline agent |
Rubber | Solvents (e.g. petroleum) | Short reaction time (e.g. preservative removal) |
Stainless Steel | Free chlorine in disinfectants | Rinse thoroughly |
Excessive phosphates in our surface waters represent a risk to the environment. They promote algae growth. This phenomenon is called eutrophication.
Algae release oxygen during the day. However, they need plenty of oxygen at night. This reduces the level of oxygen in the water and there is a large risk of fish mortality. The microorganisms that consume the algae after they have died require oxygen too. This further reduces the water’s oxygen concentrations. This can cause extensive fish mortality especially in the autumn.
Problem: In order to prevent more extensive eutrophication, the total phosphorous load must be reduced to less than 1% of the
present day level. Phosphates in cleaning agents are difficult to replace because they are used for several reasons: Water softening, dirt-dissolving and anti-redepositing properties.
The pH values of the discharged water must lie between 6.5 and 9. If this is not the case, it must be neutralised.
If too many emulsifying agents are added to the cold degreaser, it is impossible to achieve good separation within the specified time.
Biological degradability:
Most water-based cleaning agents are biologically degradable. However, not only must the detergents be fully degradable; but also the degradation process may not produce or release any toxic intermediate products. Surfactants must be 90% degraded within a given time and under specific conditions. The degradation process for the remaining 10% can take place more slowly, but must actually take place.
Many cleaning agents can be used safely. Examples are neutral and weak alkaline-based cleaners for daily maintenance cleaning. To prevent allergies, it is also advisable to wear protective gloves when using such products.
However, aggressive agents must be used in some situations in order to clean efficiently.
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a) Flammability (Label: flame symbol) Only applies to solvent-based products.
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b) Toxic ingredients are very rarely found in cleaning agents (Label: Skull and crossbones) |
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c) Aggressive to the eyes, skin and mucous membranes – very acidic and alkaline cleaning agents (Label: Test tube with hand: ”Caustic”)
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It is mandatory to wear personal protective equipment when using such products. For details regarding transport and use, please refer to the corresponding safety data sheets containing the hazardous material and hazardous goods labels.
In the event of skin or eye contact: Rinse with plenty of water and consult a physician.
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