Soap and Detergents

What is soap and detergent?

We use soap and detergent every day. Detergent is a cleaning agent that helps to remove dirt and grease from porous surface such as fabrics, clothes, non-treated wood) and non-porous surface (such as metals plastics and treated wood). On the other hands, soap helps to remove dirt from our body and keeps us clean.

Soaps

Soaps are water-soluble sodium or potassium salts of fatty acids.Soap is made from a fatty acid that is reacted with an alkali. The acid end of the fatty acid reacts with the alkali to form a salt that is water-soluble. The other end is the fatty end, which repels water, and is attracted to fats and oils. The process of making soap is called saponification. One kind of soap is sodium stearate. Beef fat reacting to alkaline wood ashes created the earliest soap, and it was the cleaning product of choice for millenia.

  

Detergents

Detergentsare usually sodium slats of sulphonic acid and are refers to a water-soluble cleansing agent that combines with impurities and dirt to make them more soluble. It differs from soap in not forming a scum with the salts in hard water.Detergents have molecules with one side that prefers water (hydrophilic), and another side that prefers oils and fats (hydrophobic). The hydrophilic side attaches to water molecules, and the hydrophobic side attaches to oil molecules. This action allows the oil droplets to break up into smaller droplets, surrounded by water. These smaller droplets are no longer stuck to the material to be cleaned, and are washed away.

 

What do soaps and detergents contain?

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 beat up on surfaces (fabric and others), 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.Surface tension must be reduced so water can spread and wet surfaces.

Soaps and detergents contain surfactants (surface active agents). Surfactants are saidto make water "wetter." This ability increases the contact between the soil and the detergent solution and allows it to penetrate the minute irregularities of the dirt more effectively. They contain a combination of fats (triglycerides) and alkali that create molecules with two unique chemical ends. The “hydrophilic” end is attracted to water and the “hydrophobic” end attracted to the grease and oil. The hydrophobic ends bond with the dirt and the hydrophilic ends lie up around them, encapsulating dirt and grease with a layers of molecules that allows to float through water.

Moreover, surfactants perform other important functions in cleaning, such as loosening, emulsifying sink dishes(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. In addition, it is also a substance that was resistant to hard water was needed to make cleaning more effective. Soap is an anionic surfactant. Other anionic as well as nonionic surfactants are the main ingredients in today's detergents. There are 4 typessurfactants are available, which are:

 

1.  Anionic - the active part is negatively charged and generally is a good foamer and has good wetting properties.

2. Cationic - the active part is positively charged and generally is biocidal. 

3. Amphoteric - which is cationic in acid medium and anionic in alkaline medium. Can sometimes be biocide.

4. Non-ionic surfactant, these have no overall charge but are very good emulsifying agents.

Some laundry detergents contain "optical brighteners". These are fluorescent dyes that glow blue-white in ultraviolet light. The blue-white color makes yellowed fabrics appear white. Moreover, laundry detergent may also contain phosphate and polyethylene glycol, a polymer that prevents dirt from re-depositing on the clothes. Another polymer used for this purpose is carboxyl methyl cellulose. This is derived from natural cellulose, but is very soluble in water.

Yet another ingredient in laundry detergents is Diethyl Ester Dimethyl Ammonium Chloride (DEEDMAC). It is a fabric softener. It is a cationic surfactant that is rapidly biodegradable. It works by reducing the friction between fibers, and between fibers and the skin. Cationic surfactants are those where the hydrophilic part (in this case the ammonium chloride) is positively charged, and is attracted to substrates that are negatively charged, such as proteins and many synthetic fabrics. Hair conditioners use this trick also. You can think of a hair conditioner as fabric softener for your head.

How do soaps and detergents work in cleaning?

Soaps and detergents are used frequently in our daily life, but we use without ever really paying attention to how they work. The cleansing action of both soaps and detergents results from their ability to lower the surface tension of water, to emulsify oil grease and to hold them in suspension in water.

The 3 most important energy needed in cleaning process are;

Chemical energy: which are provided by the soap and detergent.

Thermal energy: which are provided by the warm or hot water.

Mechanical energy: which are provided by the hand or washing machine

To know better let see the explanation below!

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. 

 What to do? 

Now let's add soap or detergent, which provide chemical energy in cleaning.In water, a sodium soap dissolves to form soap anions and sodium cations.  The soap anion consists of a long hydrocarbon chain with carboxylate group on one end. The hydrocarbon chain is hydrophobic, which is soluble in grease and oils. The ionic part is the carboxylate group which is hydrophilic (soluble in water). These opposing forces loosen the soil and suspend it in the water.

CH₃(CH₂)₁₄COO^-Na⁺àCH₃(CH₂)₁₄COO^- + Na⁺

On the other hand, detergent dissolves to form detergent anions and cations. Similarly, the anion part of detergent also consists of hydrophobic part and hydrophilic part.These opposing forces loosen the soil and suspend it in the water.

Warm or hot water (which is the thermal energy) helps dissolve grease and oil in soil. To speed up the cleaning process, we need mechanical energy which we need to use a washing machine agitation or hand rubbing helps pull the soil free.

Below shows some diagram of how soap and detergent work in cleaning.

 

  

Effectiveness of cleaning action of soaps and 

Detergents are better than soaps in hard water! Soaps are only suitable for the use in soft water. Soft water is water that contains little or no calcium and magnesium ions. Soaps do no form scum with soft water. Although soap is a good cleansing agent, but its effectiveness will reduce when use in hard water. Hard water is water that contains calcium and magnesium ions. These ions react with soap to form an insoluble precipitate known as soap scum. The formation of soap scum reduces the amount of soap available for cleaning, thus causes wastage of soap.

  

Detergents do not form scum with hard water, it form soluble subtances with calcium and magnesium salts. Thus it can perform its cleansing action in hard water and it is more effective then soap in hard water.

Soap in hard water…(RCOONa=Soap)

RCOONa(aq)+ Mg²⁺(aq) à (RCOO)₂Mg (s) (scum)+ 2Na⁺(aq)

RCOONa(aq) + Ca²⁺(aq) à (RCOO)₂Ca (s) (scum)+ 2Ca⁺(aq)

Detergent in hard water…(ROSO₃Na=Detergent)

ROSO₃Na (aq) + Mg²⁺ (aq) à (ROSO₃)₂Mg (aq) + 2Na⁺(aq)

ROSO₃Na (aq) +Ca²⁺ (aq) à(ROSO₃)₂Ca (aq) + 2Ca⁺(aq)

The effectiveness of the cleansing action of soap also reduced when used in acidic water. The hydrogen ions in acidic water react with the soap to form long chain fatty acid, which is insoluble in water due to their high relative molecular masses. This reduces the amount of soap available for cleaning. Detergent do not form precipitates in acidic water. Thus, their cleansing action is not affected.

Soap in acidic water…

RCOONa (aq) + H⁺(aq) à RCOOH (s) + Na⁺(aq)

Detergent in acidic water…

ROSO₃Na (aq) + H⁺(aq) à ROSO₃ H (aq) + Na⁺ (aq)

Difference between soap and detergent

Soap	Detergent
Made from neutral resources (animal fats and vegetables oils)	Made from synthesis resources (petroleum fraction)
Form scum in hard water	Do not form scum in hard water
Effective cleaners in soft water	Effective cleaners in both soft and hard water
Form precipitate in acidic water	Do not form precipitate in acidic water
Biodegradable (Do not cause pollution)	Non-biodegradable (produce thick foam that kills aquatic live)

What to use in the process of making soap?

1. Fats and Oils

2. Alkali

Fats and Oils…

The fats and oils are 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.

Alkali…

An alkali is a soluble salt of an alkali metal like sodium or potassium. Originally, the alkalis 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 soapmaking are sodium hydroxide (NaOH), also called caustic soda; and potassium hydroxide (KOH), also called caustic potash.

The process of making soap

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

Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap.In the industrial manufacture of soap, tallow (fat from animals such as cattle and sheep) or vegetable fat is heated with sodium hydroxide.

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.Once the saponification reaction is complete, sodium chloride is added to precipitate the soap. The water layer is drawn off the top of the mixture and the glycerol is recovered using vacuum distillation. Vacuum distillation is used to convert the neat soap into dry soap pellets (2). 

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, colorants 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 soapmaking. However, with some minor modifications, the finishing line equipment is the same.

Saponification reaction

The process of making detergent.

During the past century, the shortage of animal and vegetable fats during World War 1 and World War 2 lead to the development of detergents. During the preparation of detergents, a long chain of hydrocarbon obtained from petroleum fractions is converted into organic acid through a series of steps. The organic acid is then neutralized with sodium hydroxide solution to produce a neutral salt, which is detergent. Two commons detergents are sodium alkyl sulphate and sodium alkyl benzene sulphonate. These two detergents are prepared using different method. Let us see the preparation of sodium alkyl sulphate first.

First step, formation of organic acid (sulphonation). Concentrated sulphuric acid is added to the long chain alcohol. Then alkyl sulphonic acid and water is produced. The second step is neutralization. Sodium hydroxide solution is added to alkyl sulphonic acid to produce water and sodium alkyl sulphate.

*R = long chain hydrocabon

As for the preparation of sodium alkyl benzene sulphonate, the first step is sulphonation. Concentrated sulphuric acid is added to alkyl benzene to produce alkyl benzene sulphonic acid and water. The second step is neutralization. Alkyl benzene sulphonic acid is mixed with sodium hydroxide solution to produce sodium alkyl benzene sulphonate and water.