How Soap and Detergents are Made

Soap

For centuries, soap has been manufactured by means of the reaction between an alkali, nowadays caustic soda, and animal fats or vegetable oils such as tallow, coconut or palm kernel oil. This process is known as saponification, and in a modern soap-making plant it is carried out by mixing together the oils and alkali, and then heating them under pressure to around 130C.

As well as soap, the reaction also produces glycerine and this has to be extracted by adding hot brine. The glycerine dissolves in salty water more readily than the soap, which can then be removed using centrifugal extractors. The molten soap undergoes further processing to create various kinds of products:

Hard Soaps are made by spray-drying the molten soap, adding other ingredients such as perfumes and colourants, and moulding it into bars. Toilet Soaps are made using higher-quality fats than hard soaps, and are heated after drying to reduce their moisture content to around 10%, as opposed to 28% for hard soaps.
Traditional Soap Powder for washing fabrics is made by pumping molten soap and other ingredients to the top of a spray-drying tower. The mixture is then blown down high pressure nozzles into rising currents of air so that it solidifies into granules. Various additives are mixed into the molten soap before it dries.
Soap Flakes are made by forming the molten soap into ribbons, adding perfumes and preservatives and milling it until it forms a thick skin. This is then cut into diamond-shaped flakes.

Non-Soap Detergents

The development of powders and flakes, which dissolve easily in water, was a natural step for the soap industry. However in the 20th century, and particularly during the two world wars, supplies of animal and vegetable oils became harder to obtain and scientists sought alternative raw materials. They gradually developed detergents based on mineral oils, and today most of these synthetic or 'non-soap' detergents are made from a petroleum derivative. Non-soap detergents were originally produced as powders, but the last decade has also seen the development of liquids, and there are now a wide variety of products available in both forms. The main advantage of non-soap detergents is that they lather equally well in hard or soft water leaving no scum, whereas soap does not produce a lather until all the water hardness has been neutralised.

Manufacture

Powders can be made in one of two ways. Either by spray-drying as with their soap- containing counterparts (as described above), or using a relatively new method of manufacture that mixes the ingredients in their dry state. This new process uses 80% less energy than the spray-drying method and is seen as a big step forward in terms of environmental performance. Liquid non-soap detergents are produced by mixing the ingredients together in liquid form, with a hydrotrope to ensure that they do not separate. Concentrated detergents use less chemicals and packaging per wash than conventional detergents. They also save energy in production, distribution and use, and reduce the amount of waste passing into the environment. The creation of such detergents has been a complex process, requiring the development of weight-efficient and sometimes multifunctional ingredients to replace more traditional ones. They are generally manufactured using the new energy-saving manufacturing process.

'Light Duty'

Detergents designed for lightly soiled items or for delicate fabrics which would be affected by the action of a washing machine (eg woollens without a machine-washable finish) and which are mainly used for washing by hand, are sometimes called 'light duty'. These powders and liquids consist of a blend of surfactants, perfume, colouring and preservatives, and contain none of the bleach or various additional ingredients found in other 'heavy duty' powders. The simplest light duty products of all are soap flakes, which have no additives except perfume and preservatives.

'Heavy Duty'

Heavy duty detergents are designed to give excellent results in any kind of washing machine, removing all types of dirt from a whole range of modern fabrics, commonly in the same wash load. To meet all these needs, a number of ingredients are added along with the basic surfactants. These include:

Water softener - sometimes called builders - eg sodium tripolyphosphate (found mostly in conventional or 'big box' products) or zeolite with polycarboxylate (found mainly in concentrated formulations)
Anti-redeposition agent, to stop the dirt being deposited back onto the clothes Bleach, fabric-safe oxygen bleaching agents used are perborate or percarbonate (though neither are used in Colour care products)
Bleach activator, eg TAED (ie tetra acetyl ethylene diamine), which combines with the ordinary perborate bleach to form peroxyacetic acid or 'per-acid'. This is a different form of bleaching agent which starts to act much earlier in the wash cycle, at the lower temperatures often used today.
A special bleach stabilising ingredient has also been introduced to prevent the newly formed per-acid from destroying itself as the cycle proceeds. These are used to aid stain removal.

Enzymes, the 'biological' ingredient used to break down stains and make them easier to remove. Particularly effective at temperatures of 40-60?C, the first to be introduced was protease which breaks down protein stains such as blood and egg; lipase which breaks down fatty stains like mayonnaise; and amylase which is effective against starch based stains such as chocolate. (Not included in Non-Biological detergents)

Fluorescers or optical brighteners help reflect light, making whites look really bright white. (Only needed for white material, they are not included in Colour care products).

Other ingredients include sodium sulphate and sodium silicate, to stop the powder clogging; perfumes; colourants and preservatives.

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