Information about Soaps and Detergents
|Cleaning products play an essential role in our daily lives. By safely and effectively removing soils, germs and other contaminants, they help us to stay healthy, care for our homes and possessions, and make our surroundings more pleasant.
The Soap and Detergent Association of Canada (SDAC) recognizes that public understanding of the safety and benefits of cleaning products is critical to their proper use. To help foster this understanding, we’ve created a summary of key developments in the history of cleaning products, including the chemistry of how they work; the procedures used to evaluate their safety for people and the environment; the functions of various products and their ingredients; and the most common manufacturing processes.
This section is intended to be a valuable information resource about cleaning products for consumers, educators, students, media, government officials, businesses and others.
To understand what is needed to achieve effective cleaning, it’s helpful to have a basic knowledge of soap and detergent chemistry.
Water, the liquid commonly used for cleaning, has a property called surface tension. In the body of the water, each molecule is surrounded and attracted by other water molecules. However, at the surface, those molecules are surrounded by other water molecules only on the water side. A tension is created as the water molecules at the surface are pulled into the body of the water. This tension causes water to bead up on surfaces (glass, fabric), which slows wetting of the surface and inhibits the cleaning process. You can see surface tension at work by placing a drop of water onto a counter top. The drop will hold its shape and will not spread.
In the cleaning process, surface tension must be reduced so water can spread and wet surfaces. Chemicals that are able to do this effectively are called surface active agents, or surfactants. They are said to make water “wetter.”
Surfactants perform other important functions in cleaning, such as loosening, emulsifying (dispersing in water) and holding soil in suspension until it can be rinsed away. Surfactants can also provide alkalinity, which is useful in removing acidic soils.
Surfactants are classified by their ionic (electrical charge) properties in water: anionic (negative charge), non-ionic (no charge), cationic (positive charge) and amphoteric (either positive or negative charge).
Soap is an anionic surfactant. Other anionic as well as non-ionic surfactants are the main ingredients in today’s detergents. Now let’s look closer at the chemistry of surfactants.
Soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali.
First let’s examine the composition of fats, oils and alkalis; then we’ll review the soap-making process.
Fats and Oils
The fats and oils used in soap-making come from animal or plant sources. Each fat or oil is made up of a distinctive mixture of several different triglycerides.
In a triglyceride molecule, three fatty acid molecules are attached to one molecule of glycerine. There are many types of triglycerides; each type consists of its own particular combination of fatty acids.
Fatty acids are the components of fats and oils that are used in making soap. They are weak acids composed of two parts:
A carboxylic acid group consisting of one hydrogen (H) atom, two oxygen (O) atoms, and one carbon (C) atom, plus a hydrocarbon chain attached to the carboxylic acid group. Generally, it is made up of a long straight chain of carbon (C) atoms each carrying two hydrogen (H) atoms.
An alkali is a soluble salt of an alkali metal like sodium or potassium. Originally, the alkalis used in soap-making were obtained from the ashes of plants, but they are now made commercially. Today, the term alkali describes a substance that chemically is a base (the opposite of an acid) and that reacts with and neutralizes an acid.
The common alkalis used in soap-making are sodium hydroxide (NaOH), also called caustic soda; and potassium hydroxide (KOH), also called caustic potash.
How Soaps are Made
Saponification of fats and oils is the most widely used soap-making process. This method involves heating fats and oils and reacting them with a liquid alkali to produce soap and water (neat soap) plus glycerine.
The other major soap-making process is the neutralization of fatty acids with an alkali. Fats and oils are hydrolyzed (split) with a high-pressure steam to yield crude fatty acids and glycerine. The fatty acids are then purified by distillation and neutralized with an alkali to produce soap and water (neat soap).
When the alkali is sodium hydroxide, a sodium soap is formed. Sodium soaps are “hard” soaps. When the alkali is potassium hydroxide, a 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 oil and grease and repelled by water. It is known as the hydrophobic (water-hating) end.
How Water Hardness Affects Cleaning Action
Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts like calcium (Ca) and magnesium (Mg) and occasionally iron (Fe) and manganese (Mn). The mineral salts react with soap to form an insoluble precipitate known as soap film or scum.
Soap film does not rinse away easily. It tends to remain behind and produces visible deposits on clothing and makes fabrics feel stiff. It also attaches to the insides of bathtubs, sinks and washing machines.
Some soap is used up by reacting with hard water minerals to form the film. This reduces the amount of soap available for cleaning. Even when clothes are washed in soft water, some hardness minerals are introduced by the soil on clothes. Soap molecules are not very versatile and cannot be adapted to today’s variety of fibres, washing temperatures and water conditions.
SURFACTANTS IN DETERGENTS
A detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the hardness minerals in water and most will not form a film.
Detergent surfactants were developed in response to a shortage of animal and vegetable fats and oils during World War I and World War II. In addition, a substance that was resistant to hard water was needed to make cleaning more effective. At that time, petroleum was found to be a plentiful source for the manufacture of these surfactants. Today, detergent surfactants are made from a variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils).
Petrochemicals and Oleochemicals
Like the fatty acids used in soap-making, both petroleum and fats and oils contain hydrocarbon chains that are repelled by water but attracted to oil and grease in soils. These hydrocarbon chain sources are used to make the water-hating end of the surfactant molecule.
Chemicals, such as sulphur trioxide, sulphuric acid and ethylene oxide, are used to produce the water-loving end of the surfactant molecule.
As in soap-making, an alkali is used to make detergent surfactants. Sodium and potassium hydroxide are the most common alkalis.
How Detergent Surfactants Are Made
The chemical reacts with hydrocarbons derived from petroleum or fats and oils to produce new acids similar to fatty acids.
A second reaction adds an alkali to the new acids to produce one type of anionic surfactant molecule.
non-ionic surfactant molecules are produced by first converting the hydrocarbon to an alcohol and then reacting the fatty alcohol with ethylene oxide.
These non-ionic surfactants can be reacted further with sulphur-containing acids to form another type of anionic surfactant.
HOW SOAPS AND DETERGENTS WORK
These types of energy interact and should be in proper balance. Let’s look at how they work together.
Let’s assume we have oily, greasy soil on clothing. Water alone will not remove this soil. One important reason is that oil and grease present in soil repel the water molecules.
Now let’s add soap or detergent. The surfactant’s water-hating end is repelled by water but attracted to the oil in the soil. At the same time, the water-loving 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 grease and oil in soil. Washing machine agitation or hand rubbing helps pull the soil free.
The origins of personal cleanliness date back to prehistoric times. Since water is essential for life, the earliest people lived near water and knew something about its cleansing properties, or at least that it rinsed mud off their hands.
A soap-like material found in clay cylinders during the excavation of ancient Babylon is evidence that soap-making was known as early as 2800 B.C. Inscriptions on the cylinders say that fats were boiled with ashes, which is a method of making soap, but do not refer to the purpose of the “soap.” Such materials were later used as hair styling aids.
Records show that ancient Egyptians bathed regularly. The Ebers Papyrus, a medical document from about 1500 B.C., describes combining animal and vegetable oils with alkaline salts to form a soap-like material used for treating skin diseases, as well as for washing
At about the same time, Moses gave the Israelites detailed laws governing personal cleanliness. He also related cleanliness to health and religious purification. Biblical accounts suggest that the Israelites knew that mixing ashes and oil produced a kind of hair gel.
The early Greeks bathed for aesthetic reasons and apparently did not use soap. Instead, they cleaned their bodies with blocks of clay, sand, pumice and ashes, then anointed themselves with oil, and scraped off the oil and dirt with a metal instrument known as a strigil. They also used oil with ashes. Clothes were washed without soap in streams.
Soap got its name, according to an ancient Roman legend, from Mount Sapo, where animals were sacrificed. Rain washed a mixture of melted animal fat, or tallow, and wood ashes down into the clay soil along the Tiber River. Women found that this clay mixture made their wash cleaner with much less effort.
The ancient Germans and Gauls are also credited with discovering a substance called soap, made of tallow and ashes, that they used to tint their hair red.
As Roman civilization advanced, so did bathing. The first of the famous Roman baths, supplied with water from their aqueducts, was built about 312 B.C. The baths were luxurious, and bathing became very popular. By the second century A.D., the Greek physician, Galen, recommended soap for both medicinal and cleansing purposes.
After the fall of Rome in 467 A.D. and the resulting decline in bathing habits, much of Europe felt the impact of filth upon public health. This lack of personal cleanliness and related unsanitary living conditions contributed heavily to the great plagues of the Middle Ages, and especially to the Black Death of the 14th century. It wasn’t until the 17th century that cleanliness and bathing started to come back into fashion in much of Europe. Still, there were areas of the medieval world where personal cleanliness remained important. Daily bathing was a common custom in Japan during the Middle Ages. And in Iceland, pools warmed with water from hot springs were popular gathering places on Saturday evenings.
Soap-making was an established craft in Europe by the seventh century. Soap-maker guilds guarded their trade secrets closely. Vegetable and animal oils were used with ashes of plants, along with fragrance. Gradually more varieties of soap became available for shaving and shampooing, as well as bathing and laundering.
Italy, Spain and France were early centres of soap manufacturing, due to their ready supply of raw materials such as oil from olive trees. The English began making soap during the 12th century. The soap business was so good that in 1622, King James I granted a monopoly to a soap-maker for $100,000 a year. Well into the 19th century, soap was heavily taxed as a luxury item in several countries. When the high tax was removed, soap became available to ordinary people, and cleanliness standards improved.
A major step toward large-scale commercial soap-making occurred in 1791 when a French chemist, Nicholas Leblanc, patented a process for making soda ash, or sodium carbonate, from common salt. Soda ash is the alkali obtained from ashes that combines with fat to form soap. The Leblanc process yielded quantities of good quality, inexpensive soda ash.
The science of modern soap-making was born some 20 years later with the discovery by Michel Eugene Chevreul, another French chemist, of the chemical nature and relationship of fats, glycerine and fatty acids. His studies established the basis for both fat and soap chemistry.
Also important to the advancement of soap technology was the mid-1800s invention by the Belgian chemist, Ernest Solvay, of the ammonia process, which used common table salt, or sodium chloride, to make soda ash. Solvay’s process further reduced the cost of obtaining this alkali, and increased both the quality and quantity of the soda ash available for manufacturing soap.
These scientific discoveries, together with the development of power to operate factories, made soap-making one of North America’s fastest-growing industries by 1850. At the same time, its broad availability changed soap from a luxury item to an everyday necessity. With this widespread use came the development of milder soaps for bathing and soaps for use in the washing machines that were available to consumers by the turn of the century.
The chemistry of soap manufacturing stayed essentially the same until 1916, when the first synthetic detergent was developed in Germany in response to a World War I-related shortage of fats for making soap. Known today simply as detergents, synthetic detergents are washing and cleaning products without soap, “synthesized” or put together chemically from a variety of raw materials. The discovery of detergents was also driven by the need for a cleaning agent that, unlike soap, would not combine with the mineral salts in water to form an insoluble substance known as soap curd.
Household detergent production in North America began in the early 1930s, but did not really take off until after World War II. The war-time interruption of fat and oil supplies as well as the military’s need for a cleaning agent that would work in mineral-rich sea water and in cold water had further stimulated research on detergents.
The first detergents were used chiefly for hand dishwashing and fine fabric laundering. The breakthrough in the development of detergents for all-purpose laundry uses came in 1946, when the first “built” detergent (containing a surfactant/builder combination) was introduced in the United States. The surfactant is a detergent product’s basic cleaning ingredient, while the builder helps the surfactant to work more efficiently. Phosphate compounds used as builders in these detergents vastly improved performance, making them suitable for cleaning heavily soiled laundry.
By 1953, sales of detergents in the United States had surpassed those of soap. Now detergents have all but replaced soap-based products for laundering, dishwashing and household cleaning. Detergents (alone or in combination with soap) are also found in many of the bars and liquids used for personal cleansing.
Since those early achievements in detergent and builder chemistry, new product activity has continued to focus on developing cleaning products that are efficient and easy to use, as well as safe for consumers and for the environment. Here’s a summary of some of those innovations:
As consumer needs and lifestyles change, and as new manufacturing processes become available, the soap and detergent industry responds with new products. A commitment to safety is a top priority from the time a company begins working on a new product and continues as long as the product is in the marketplace. Companies evaluate the safety of existing cleaning products by talking with consumers, reviewing scientific developments and monitoring product use data that may affect the safety assessment process.
To determine the safety of a cleaning product ingredient, industry scientists evaluate the toxicity of the ingredient. Toxicity is generally defined as any harmful effect of a chemical on a living organism like a human, an animal, a plant or a microorganism. Since all chemicals, including water, are toxic under certain conditions of exposure, scientists must consider a number of factors affecting exposure. These include the duration and frequency of exposure to the ingredient; the concentration of the ingredient at the time of exposure; and the route and manner in which the exposure occurs (for example, eye, skin or ingestion). This information is essential whether assessing the effect on humans, animals, plants or microorganisms.
Because human safety and environmental evaluations consider different types of exposures, they are evaluated by different procedures. The principal steps in the assessment process are, however, the same. They involve:
This safety evaluation process enables scientists to predict the potential risk, if any, associated with the use of the ingredient or product, and determine if it is safe for consumers and the environment.
Medical science has long confirmed the important relationship between cleanliness and health. The regular use of cleaning products is fundamental to the health of our society and the well-being of its people.
Because cleaning products are part of our everyday lives, it is essential that they not present a significant risk to health. In considering the human safety of an individual ingredient or product, toxicologists (scientists who assess the safety of a chemical) are concerned with the effects from two types of exposures: intended and unintended. Intended exposures occur with use of a cleaning product according to the manufacturer’s directions. Unintended exposures can result from misuse, through improper storage or by accidental contact, such as when a liquid detergent is splashed in the eye.
Hazards from these types of exposures are evaluated from information obtained through acute (short-term) and chronic (long-term) tests and through a review of existing data. Expected exposure routes are considered as part of this evaluation.
Human safety evaluations begin with the specific ingredients and then move on to the whole product. The effects for all ingredients are considered as the product is formulated.
Toxicologists compare the expected exposure to the expected effect during both product manufacture and use. How will workers be exposed in the plant? What is the intended use of the product? Is it to be diluted? Undiluted? Used daily in the home? Weekly in the workplace? Toxicologists also consider the expected effect of an unintended exposure. What is the potential hazard, for example, if a child drinks a product directly from the bottle?
If this human safety evaluation indicates an unacceptable risk, it may be possible to make the risk smaller by changing the manufacturing process; reformulating to reduce or eliminate an ingredient contributing to the toxic effect; or using labelling or a child-resistant closure. If the risk cannot be reduced, the product will not be marketed.
Even though manufacturers formulate cleaning products to ensure that they are safe or have very low risk, human health effects can still result from unintended exposure. To warn consumers about a specific hazard, household cleaning products carry cautionary labelling whenever necessary. For consumers, this is one of the most important features of the label.
Federal regulations govern how precautionary statements related to human safety are used on household cleaning product labels. The regulations require that statements follow a standard format.
Along with the safety evaluation process and cautionary labelling, a consumer education program on the proper use, storage and disposal of cleaning products supports the human safety efforts of the soap and detergent industry. In addition, the industry works closely with poison control centres to assure that, should an accidental exposure occur, treatment information is available to health care providers. Together, these activities enable consumers to use cleaning products with confidence in both their safety and performance.
Most household cleaning products are formulated to be used with water and “go down the drain” into wastewater treatment systems (municipal sewage treatment plants or septic tank systems). To assure that products are safe for the environment, manufacturers evaluate the impacts of product ingredients in wastewater treatment systems, streams, rivers, lakes and estuaries. Scientific principles that are widely recognized by the technical and regulatory communities are used to assess the risk to the environment of these impacts.
Environmental risk assessment considers the exposure concentrations and effects of individual ingredients. Two sets of information are used in these assessments. One set enables industry scientists to predict the concentration of the ingredient from all sources, including cleaning products, at various locations in the environment (the predicted exposure concentration). The other set is used to find the highest concentration of the ingredient at which no harm will occur to animals, plants or microorganisms living in the environment (the no-effect concentration). Comparing the predicted exposure concentration and the no-effect concentration enables scientists to determine whether the use of an ingredient is safe for the environment. The planned use of a cleaning product ingredient is acceptable if the predicted exposure concentration is lower than the concentration that would harm animals, plants or microorganisms.
This information applies to ingredients processed through household septic tank systems as well as municipal treatment plants. Two basic steps occur in the treatment of wastewater in both systems. The first step, called primary treatment, consists of the removal of solid material, such as grit or grease, from the wastewater by physical means, like settling and flotation in tanks.
The second step, called secondary treatment, removes the dissolved material by biological means, like consumption by microorganisms. It is in the secondary treatment stage where the most important process in reducing the exposure concentration of detergent ingredients occurs. This is called biodegradation. Biodegradation describes how organic (carbon-containing) detergent ingredients, like surfactants, enzymes and fragrances, are broken down into carbon dioxide, water and minerals by the action of microorganisms such as bacteria. At this stage, biodegradation reduces the amount of detergent ingredients discharged into the environment to levels that do not present a risk to fish or other aquatic life. Any small amounts of chemicals which are not biodegraded or removed during sewage treatment are diluted in surface waters, soil and the ocean. They continue to biodegrade or be removed from water by attaching to solids, a process known as adsorption.
Some inorganic (not carbon-containing) detergent ingredients, such as phosphates, zeolites and some dyes, also attach to solids, and are further treated during processing of the biosolids (sludge) produced in primary and secondary treatment. Biosolids are often used as fertilizers and soil conditioners.
Because of modern treatment methods, only an insignificant amount of the ingredients used to clean clothes, dishes, home and workplace surfaces actually reaches the environment. And that amount is at such levels as to not cause any adverse effects.
Improving Environmental Quality
The soap and detergent industry is committed to understanding the impact of its products and packages on the environment. With this understanding comes the ability to reduce their impact and improve their environmental quality.
Manufacturers of cleaning products have been leaders in reducing packaging waste and encouraging sound waste disposal practices. Advances in technology have resulted in products that are more concentrated, products that combine two functions in one, products with refill packages and packages that use recycled materials. Concentrated products need less energy to manufacture and transport, and require less packaging. Multifunctional products eliminate the need for separate packages. Refill packages allow consumers to reuse primary packages many times, decreasing the amount of packaging used and the volume of trash generated. Plastic and paperboard that would otherwise be thrown away become usable materials through recycling.
Through education and community programs, the soap and detergent industry helps consumers learn how to reduce waste and how best to dispose of it. Consumers are reminded that the environmentally wise way of handling any household cleaning product is to buy only the amount that can be used; to use it all up or give it away; and, if it must be disposed, to dispose of it properly. As a rule of thumb, products designed for use with water should be disposed of by pouring down the drain; solid products such as scouring pads should be put into the trash.
A promising method under development for improving the environmental quality of a product is life cycle assessment (LCA). LCA describes a “cradle-to-grave” look at all the environmental impacts of a product and its package, from acquiring raw materials through manufacture and distribution to consumer use and disposal. One advantage of LCA is that it can determine whether reducing an environmental impact in one area, such as manufacturing, shifts the impact to another, such as disposal. LCA also helps to identify where environmental improvement efforts should be focused.
Sound scientific information provides the foundation for the soap and detergent industry’s commitment to safety. The industry maintains this commitment without compromising product performance, convenience or cost-effectiveness.
Products and Ingredients
Soaps and detergents are essential to personal and public health. Through their ability to loosen and remove soil from a surface, they contribute to good personal hygiene; reduce the presence of germs that cause infectious diseases; extend the useful life of clothes, tableware, linens, surfaces and furnishings; and make our homes and workplaces more pleasant.
Soaps and detergents found in the home can be grouped into four general categories: personal cleansing, laundry, dishwashing and household cleaning. Within each category are different product types formulated with ingredients selected to perform a broad cleaning function as well as to deliver properties specific to that product. Knowing the different products and their ingredients helps you select the right product for the cleaning job.
Personal Cleansing Products include bar soaps, gels, liquid soaps and heavy duty hand cleaners. These products get their cleaning action from soap, other surfactants or a combination of the two. The choice of cleaning agent helps determine the product’s lathering characteristics, feel on the skin and rinsability.
Laundry Detergents and Laundry Aids are available as liquids, powders, gels, sticks, sprays, pumps, sheets and bars. They are formulated to meet a variety of soil and stain removal, bleaching, fabric softening and conditioning, and disinfectant needs under varying water, temperature and use conditions.
Dishwashing Products include detergents for hand and machine dishwashing as well as some specialty products. They are available as liquids, gels, powders and solids.
Household Cleaners are available as liquids, gels, powders, solids, sheets and pads for use on painted, plastic, metal, porcelain, glass and other surfaces, and on washable floor coverings. Because no single product can provide optimum performance on all surfaces and soils, a broad range of products has been formulated to clean efficiently and easily. While all-purpose cleaners are intended for more general use, others work best under highly specialized conditions.
Surfactants and builders are the major components of cleaning products. Other ingredients are added to provide a variety of functions, such as increasing cleaning performance for specific soils/surfaces, ensuring product stability and supplying a unique identity to a product. Let’s examine how surfactants and builders work and then review other commonly used ingredients.
Surfactants, also called surface active agents, are organic chemicals that change the properties of water (see Chemistry.)
By lowering the surface tension of water, surfactants enable the cleaning solution to wet a surface (for example, clothes, dishes, countertops) more quickly, so soil can be readily loosened and removed (usually with the aid of mechanical action). Surfactants also emulsify oily soils and keep them dispersed and suspended so they do not settle back on the surface. To accomplish their intended jobs effectively, many cleaning products include two or more surfactants.
Surfactants are generally classified by their ionic (electrical charge) properties in water.
Builders enhance or maintain the cleaning efficiency of the surfactant. The primary function of builders is to reduce water hardness. This is done either by sequestration or chelation (holding hardness minerals in solution), by precipitation (forming an insoluble substance), or by ion exchange (trading electrically charged particles). Complex phosphates and sodium citrate are common sequestering builders. Sodium carbonate and sodium silicate are precipitating builders. Sodium aluminosilicate (zeolite) is an ion exchange builder.
Builders can also supply and maintain alkalinity, which assists cleaning, especially of acid soils; help keep removed soil from redepositing during washing; and emulsify oily and greasy soils.
Ingredient Key: The following key indicates the product category in which an ingredient may be used. The key letters appear below each ingredient.
PC – Personal Cleansing
Soap and detergent manufacturing consists of a broad range of processing and packaging operations. The size and complexity of these operations vary from small plants employing a few people to those with several hundred workers. Products range from large-volume types like laundry detergents that are used on a regular basis to lower-volume specialties for less frequent cleaning needs.
Cleaning products come in three principal forms: bars, powders and liquids. Some liquid products are so viscous that they are gels. The first step in manufacturing all three forms is the selection of raw materials. Raw materials are chosen according to many criteria, including their human and environmental safety, cost, compatibility with other ingredients, and the form and performance characteristics of the finished product. While actual production processes may vary from manufacturer to manufacturer, there are steps which are common to all products of a similar form.
Let’s start by looking at bar soap manufacturing and then we’ll review the processes used to make powder and liquid detergents.
Traditional bar soaps are made from fats and oils or their fatty acids which are reacted with inorganic water-soluble bases. The main sources of fats are beef and mutton tallow, while palm, coconut and palm kernel oils are the principal oils used in soap-making. The raw materials may be pre-treated to remove impurities and to achieve the colour, odour and performance features desired in the finished bar. The chemical processes for making soap, like saponification of fats and oils and neutralization of fatty acids, are described in the Chemistry section.
Soap was made by the batch kettle boiling method until shortly after World War II, when continuous processes were developed. Continuous processes are preferred today because of their flexibility, speed and economics.
Both continuous and batch processes produce soap in liquid form, called neat soap, and a valuable by-product, glycerine (1). The glycerine is recovered by chemical treatment, followed by evaporation and refining. Refined glycerine is an important industrial material used in foods, cosmetics, drugs and many other products.
The next processing step after saponification or neutralization is drying. Vacuum spray drying is used to convert the neat soap into dry soap pellets (2). The moisture content of the pellets will vary depending on the desired properties of the soap bar.
In the final processing step, the dry soap pellets pass through a bar soap finishing line. The first unit in the line is a mixer, called an amalgamator, in which the soap pellets are blended together with fragrance, colourants and all other ingredients (3). The mixture is then homogenized and refined through rolling mills and refining plodders to achieve thorough blending and a uniform texture (4). Finally, the mixture is continuously extruded from the plodder, cut into bar-size units and stamped into its final shape in a soap press (5).
Some of today’s bar soaps are called “combo bars,” because they get their cleansing action from a combination of soap and synthetic surfactants. Others, called “syndet bars,” feature surfactants as the main cleansing ingredients. The processing methods for manufacturing the synthetic base materials for these bars are very different from those used in traditional soap-making. However, with some minor modifications, the finishing line equipment is the same.
Powder detergents are produced by spray drying, agglomeration, dry mixing or combinations of these methods.
In the spray drying process, dry and liquid ingredients are first combined into a slurry, or thick suspension, in a tank called a crutcher (1). The slurry is heated and then pumped to the top of a tower where it is sprayed through nozzles under high pressure to produce small droplets. The droplets fall through a current of hot air, forming hollow granules as they dry (2). The dried granules are collected from the bottom of the spray tower where they are screened to achieve a relatively uniform size (3).
After the granules have been cooled, heat sensitive ingredients that are not compatible with the spray drying temperatures (such as bleach, enzymes and fragrance) are added (4). Traditional spray drying produces relatively low density powders.
New technology has enabled the soap and detergent industry to reduce the air inside the granules during spray drying to achieve higher densities. The higher density powders can be packed in much smaller packages than were needed previously.
Agglomeration, which leads to higher density powders, consists of blending dry raw materials with liquid ingredients. Helped by the presence of a liquid binder, rolling or shear mixing causes the ingredients to collide and adhere to each other, forming larger particles.
Dry mixing or dry blending is used to blend dry raw materials. Small quantities of liquids may also be added.
Both batch and continuous blending processes are used to manufacture liquid and gel cleaning products. Stabilizers may be added during manufacturing to ensure the uniformity and stability of the finished product.
In a typical continuous process, dry and liquid ingredients are added and blended to a uniform mixture using in-line or static mixers.
Recently, more concentrated liquid products have been introduced. One method of producing these products uses new high-energy mixing processes in combination with stabilizing agents.
The final step in the manufacture of soaps and detergents is packaging. Bar soaps are either wrapped or cartoned in single packs or multipacks. Detergents, including household cleaners, are packaged in cartons, bottles, pouches, bags or cans. The selection of packaging materials and containers involves considerations of product compatibility and stability, cost, package safety, solid waste impact, shelf appeal and ease of use.