Cleaning products play an important role in our daily lives. By safely and effectively removing dirt, bacteria and other contaminants, they help us stay healthy, care for our homes and property, and make our surroundings more pleasant.
We recognise that public understanding of the safety and benefits of cleaning products is essential for their proper use. To help deepen this understanding, we have summarised key developments in the history of cleaning products, including the chemistry of how they work; the processes used to assess their safety for people and the environment; the functions of various products and their ingredients; and the most common manufacturing processes.
I. Chemistry.
To understand what is needed to achieve effective cleaning, it is helpful to know the basics of soap and detergent chemistry.
Water, the liquid commonly used for cleaning, has a property known as surface tension. In a body of water, each molecule is surrounded and attracted by other water molecules. However, at the surface, these molecules are surrounded by other water molecules only on the water side. Tension occurs when water molecules at the surface are pulled into the body of water. This tension causes water to bead up on the surface (glass, fabric), which slows down the wetting of the surface and inhibits the cleaning process. You can observe the effect of surface tension by placing a drop of water on a countertop. The droplet will retain its shape and will not spread.
During the cleaning process, surface tension must be reduced so that water can diffuse and wet the surface. Chemicals that do this effectively are called surfactants or surfactants. They are said to make water ‘wetter’.
Surfactants also perform other important functions in cleaning, such as loosening, emulsifying (dispersing in water) and keeping dirt in suspension until it can be rinsed away. Surfactants also provide alkalinity, which helps remove acidic dirt.
Surfactants are classified according to their ionic (charge) properties in water: anionic (negatively charged), nonionic (uncharged), cationic (positively charged), and amphoteric (positively or negatively charged). Soap is an anionic surfactant. Other anionic and nonionic surfactants are the main ingredients in today's detergents. Now let's take a closer look at the chemistry of surfactants.
II. Soap water.
Soap is the sodium or potassium salt of water-soluble fatty acids.
Soap is made from fats and oils or their fatty acids by chemical treatment with a strong base.
First we will look at the composition of fats, oils and alkalis; then we will review the process of soap making.
1. Fats and oils
The fats and oils used in soap manufacturing come from animal or vegetable sources. Each fat or oil consists of a unique mixture of several different triglycerides.
In a triglyceride molecule, three fatty acid molecules are attached to one glycerol molecule. There are many types of triglycerides; each type consists of its own specific combination of fatty acids.
Fatty acids are components of fats and oils used in soap making. They are weak acids and consist of two parts:
A carboxylic acid group consisting of one hydrogen (H) atom, two oxygen (O) atoms, and one carbon (C) atom, and a hydrocarbon chain attached to the carboxylic acid group. Typically, it consists of a long straight chain of carbon (C) atoms with two hydrogen (H) atoms per carbon (C) atom.
2. Alkali
Alkalis are soluble salts of alkali metals such as sodium or potassium. Originally, the alkalis used in soap manufacture were obtained from the ashes of plants, but they are now produced commercially. Today, the term alkali describes a substance that is chemically a base (as opposed to an acid) and reacts with and neutralises acids.
The bases commonly used in soap making are sodium hydroxide (NaOH), also known as caustic soda, and potassium hydroxide (KOH), also known as caustic potash.
3. How soap is made?
Saponification of fats and oils is the most widely used process for making soap. The method involves heating fats and oils and reacting them with liquid lye to produce soap and water (pure soap) as well as glycerin.
The other major soap-making process is the neutralisation of fatty acids with lye. The fats and oils are hydrolysed (broken down) by high-pressure steam to produce crude fatty acids and glycerol. The fatty acids are then purified by distillation and neutralised with an alkali to produce soap and water (pure soap).
When the base is sodium hydroxide, sodium soap is formed. Sodium soap is ‘hard’ soap. When the base is potassium hydroxide, potassium soap is formed. Potassium soaps are softer and are found in some liquid hand soaps and shaving creams.
The carboxylate end of the soap molecule is attracted to water. It is called the hydrophilic (water-loving) end. The hydrocarbon chain is attracted to oils and fats and repelled by water. It is called the hydrophobic (water-hating) end.
4. How water hardness affects cleaning results？
Although soap is a good cleaning agent, it is less effective when used in hard water. Water hardness is caused by mineral salts such as calcium (Ca) and magnesium (Mg), as well as the occasional presence of iron (Fe) and manganese (Mn). The mineral salts react with soap to form an insoluble precipitate called soap film or scum.
Soap film does not rinse off easily. It tends to linger and create visible deposits on clothing and makes fabrics feel stiff. It can also be installed in bathtubs, sinks and the inside of washing machines.
Some soaps are consumed by reacting with hard water minerals to form a film. This reduces the amount of soap available for cleaning. Even when clothes are washed in soft water, some hardness minerals are carried by the soil on the clothes. Soap molecules are not very versatile and cannot be adapted to today's wide range of fibres, washing temperatures and water conditions.
III. Surfactants in detergent.
Detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical composition, the surfactants used in detergents can be designed to perform well under a variety of conditions. Such surfactants are less sensitive to hardness minerals in water than soap and most do not form a film.
Detergent surfactants were developed in response to shortages of animal and vegetable fats and oils during World War I and World War II. In addition, a substance resistant to hard water was needed to make cleaning more effective. At that time, oil was found to be a rich source for the manufacture of these surfactants. Today, detergent surfactants are made from a variety of petrochemicals (derived from oil) and/or oleochemicals (derived from fats and oils).
1. Petrochemicals and grease chemicals
Like the fatty acids used in soap manufacture, petroleum and fats contain hydrocarbon chains that repel water but are attracted to oils and fats in the soil. These hydrocarbon chains are used to make the water-repellent ends of surfactant molecules.
2. Other chemicals
Chemicals like sulphur trioxide, sulphuric acid and ethylene oxide are used to produce hydrophilic ends of surfactant molecules.
3. Alkalis
As in soap manufacture, alkalis are used to make detergent surfactants. Sodium hydroxide and potassium hydroxide are the most common bases.
4. How Detergent Surfactants Are Made
Anionic Surfactants
The chemical reacts with hydrocarbons from petroleum or fats and oils to produce new acids similar to fatty acids.
A second reaction adds a base to the new acid to produce an anionic surfactant molecule.
Nonionic surfactants
Nonionic surfactant molecules are prepared by first converting hydrocarbons to alcohols and then reacting the fatty alcohols with ethylene oxide.
These nonionic surfactants can be further reacted with sulfur-containing acids to form another type of anionic surfactant.
5. How Soaps and Detergents Work?
These types of energies interact with each other and should be in proper balance. Let's see how they work together.
Suppose there are oil stains on your clothes. Water alone will not remove these soils. A major reason for this is that the oil and grease present in the soil repels the water molecules.
Now let's add soap or detergent. The hydrophobic end of the surfactant is repelled by water but is attracted by the oil in the soil. At the same time, the hydrophilic end is attracted to the water molecules.
These opposing forces loosen the soil and suspend it in the water. Warm or hot water helps dissolve the oil in the soil. Washing machine agitation or rubbing by hand helps to remove the soil.
IV. Safety
The soap and detergent industry introduces new products as consumer needs and lifestyles change, and as new manufacturing processes emerge. Commitment to safety is a top priority from the time a company begins to develop a new product until the time the product is released to the market. The Company evaluates the safety of existing cleaning products by talking to consumers, reviewing scientific developments and monitoring product usage data that may influence the safety assessment process.
To determine the safety of a cleaning product ingredient, industry scientists evaluate the toxicity of the ingredient. Toxicity is commonly defined as any harmful effect of a chemical on living organisms such as humans, animals, plants or microorganisms. Since all chemicals, including water, are toxic under certain exposure conditions, scientists must consider many factors that affect exposure. These include the duration and frequency of exposure to the constituent; the concentration of the constituent at the time of exposure; and the route and manner in which the exposure occurs (e.g., eyes, skin, or ingestion). This information is essential whether assessing effects on humans, animals, plants or microorganisms.
Because human safety and environmental assessments consider different types of exposures, they are conducted through different processes. However, the main steps of the assessment process are the same. They involve:
This safety assessment process allows scientists to predict the potential risks, if any, associated with the use of an ingredient or product and determine whether it is safe for consumers and the environment.
Medicine has long confirmed the important relationship between cleanliness and health. Regular use of cleaning products is essential to the health of our society and the well-being of our people.
Since cleaning products are part of our daily lives, it is critical that they do not pose a significant risk to health. When considering the human safety of an individual ingredient or product, toxicologists (scientists who assess the safety of chemicals) focus on the effects of two types of exposure: intentional and unintentional. Intentional exposure occurs when cleaning products are used according to the manufacturer's instructions. Unintended exposures can occur from misuse, improper storage, or accidental contact (e.g., splashing liquid cleaners in the eyes).
The hazards of these types of exposures are assessed based on information obtained through acute (short-term) and chronic (long-term) testing and a review of available data. Anticipated routes of exposure are considered as part of this assessment.
The human safety assessment begins with the specific ingredient and then moves to the entire product. Products are formulated with the effects of all ingredients considered.
Toxicologists compare the expected exposures during the manufacture and use of the product with the expected effects. How will workers in the plant be exposed? What is the intended use of the product? Is it to be diluted? Undiluted? Daily use at home? Weekly in the workplace? Toxicologists also consider the expected effects of accidental exposure. For example, what is the potential hazard if a child drinks the product directly from the bottle?
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