Removal of dirt – the cleaning process

Removal of dirt – the cleaning process Dirt is the term applied to grease, grime and dust jammed between the fabric structure. There are two types of dirt. One, which is held loosely onto the fabric and can be removed easily and the other, which is held tightly by means of sweat and grease. The loose dirt can be simply brushed or shaken off or will be removed by steeping in water.

The tightly held grease can be loosened in steeping process, but requires reagents that will act upon the grease to loosen the dirt. There are three main methods of removing grease – by the use of solvents, absorbents or emulsifiers. When cleaning is done by solvents or absorbents it is called dry cleaning . Normal cleaning – washing is done in water with the help of soaps and detergents, which emulsify the grease (break it in to very small particles).

This is then rinsed with water. (i) Water is the most valuable agent used for laundry work. There is a certain adhesion between fabrics and water. During steeping water penetrates into the fabric and cause wetting.

Pedesis or the movement of water particles helps to remove the non-greasy dirt from the fabric. Washing in water alone, with agitation provided by hand or machine, will remove some loose dirt and particulate soils. Increase in temperature of the water increases its pedesis and its penetrating power. It is further beneficial when the dirt is greasy.

However, water alone cannot remove the dirt that is not soluble in water. It also does not have the ability to keep the dirt suspended resulting in the removed dirt getting redeposited on fabric. Redeposition of dirt is the major cause of fabric graying over repeated launderings. (ii) Soaps and detergents are the most important cleansing agents used in laundry work.

Soap result from a reaction between natural oils or fats and alkali. If alkali is used in excess it is released when soap is used on the fabric. Synthetic detergents are synthesised from chemicals. Both soaps and detergents are sold in powder, flake, bar and liquid forms.

The type of soap or detergent to be used depends on the fibre content, colour and the type of dirt on the fabric. Both soaps and detergents share a critical chemical property – they are surface–active agents or surfactants. In other words, they reduce the surface tension of water. By reducing this effect water soaks more easily in clothes and removes stains and dirt faster.

Surfactants and other ingredients in laundry detergents also work to keep the removed soils suspended in the wash water so they do not redeposit on to the clean fabrics. This prevents graying of fabrics. There are some differences in soaps and detergents. Soaps possess a number of qualities that make them preferable to detergents.

As mentioned earlier, they are natural products and less harmful to the skin and environment. Soaps are biodegradable and do not create pollution in our rivers and streams. On the other hand, soap is not effective in hard water, which results in wastage. Another shortcoming of soap is that it is less powerful than synthetic detergent and tends to lose its cleaning power over time.

An added benefit of detergent is that they can be specifically engineered for each cleaning task and for use in different types of washing machines. (iii) Methods of washing: Once the soap or detergent has emulsified the grease holding the dirt, it has to be held in suspension till it is rinsed out. Some parts of the fabric may have dirt, which is closely adhering to the fabric. The methods employed for washing assist in these two tasks – disassociating the dirt adhering to the fabric and holding it in suspension.

The method selected depends on the fibre content, the type of yarn and fabric construction and the size and weight of the article being washed. The methods of washing are classified as follows: Friction washing Kneading and squeezing Suction Washing by machines Let us now discuss these methods in detail. (a) Friction: This is the most commonly used method. This method of cleaning is suitable for strong fabrics like cottons.

Friction may be caused by rubbing one part of the garment against another part of the garment with hands. Alternately using a brush over the dirty parts kept on the palm of the hand or on a scrubbing board if the article is big are also examples of friction washing. Friction is not applied on delicate fabrics like silk and wool and on surfaces like pile, looped or embroidery. (b) Kneading and squeezing: As the name suggests, this method involves gently rubbing with hands of the article in soap solution.

Since the pressure applied in this is very low, it does not harm the texture, colour or weave of the fabric. Thus the method can be easily used to clean delicate fabrics like wool, silk, rayon and coloured fabrics. This method would not be effective for heavily soiled articles. (c) Suction washing: This method is used for articles like towels where brush cannot be used and when it is too big or heavy to be handled by kneading and squeezing technique.

The article is placed in soap solution in a tub and the suction washer is pressed down and lifted repeatedly. The vacuum created by pressing loosens dirt particles. (d) Machine washing: Washing machine is a labour saving device especially useful for large institutions, like hotels and hospitals. These days a variety of washing machines are available in the market by different companies.

The principle behind each is the same. This is to create agitation in the clothes to loosen the dirt. For washing in these machines, pressure is provided by the movement of either the tub in the machine or a central rod attached to the machine. The washing time varies with type of fabric and amount of soiling.

Washing machines can be manual, semi-automatic and fully automatic.