Dry cleaning

Dry cleaning

1.     Dry cleaning is any cleaning process for clothing and textiles using a chemical solvent other than water. It is used to clean fabrics that degrade in water, and delicate fabrics that cannot withstand the rough and tumble of a washing machine and clothes dryer. It can eliminate labor-intensive hand washing.

2.     Unlike what its name implies, dry cleaning is not a 'dry' process. Clothes are soaked in a solvent other than water. Tetrachloroethylene (perchloroethylene), which the industry calls "perc," is the most widely used solvent. Alternative solvents are trichloroethane and petroleum spirits. Dry cleaning can be controversial because it uses chlorocarbons, which are of concern for their potential toxicity and environmental impact

3.     Modern dry cleaning's use of non-water-based solvents to remove soil and stains from clothes was reported as early as 1855.

4.     By the mid-1930s, the dry cleaning industry had adopted tetrachloroethylene (perchloroethylene), or PCE for short, as the solvent. It has excellent cleaning power and is nonflammable and compatible with most garments. Because it is stable, tetrachloroethylene is readily recycled

5.     Traditionally, the cleaning process was carried out at centralized factories. High street cleaners' shops received garments from customers, sent them to the factory, and then had them returned to the shop for collection by the customer. This cycle minimized the risk of fire or dangerous fumes created by the cleaning process. At this time, dry cleaning was carried out in two different machines—one for the cleaning process, and the second to remove the solvent from the garments.

6.     Machines of this era were described as vented; their drying exhausts were expelled to the atmosphere, the same as many modern tumble-dryer exhausts. This not only contributed to environmental contamination but also much potentially reusable PCE was lost to the atmosphere. Much stricter controls on solvent emissions have ensured that all dry cleaning machines in the Western world are now fully enclosed, and no solvent fumes are vented to the atmosphere. In enclosed machines, solvent recovered during the drying process is returned condensed and distilled, so it can be reused to clean further loads or safely disposed of. The majority of modern enclosed machines also incorporate a computer-controlled drying sensor, which automatically senses when all detectable traces of PCE have been removed. This system ensures that only small amounts of PCE fumes are released at the end of the cycle.

7.     In terms of mechanism, dry cleaning selectively solubilizes stains on the article. The solvents are non-polar and tend to selectively extract compounds that cause stains. These stains would otherwise only dissolve in aqueous detergents mixtures at high temperatures, potentially damaging delicate fabrics.

8.     Non-polar solvents are also good for some fabrics, especially natural fabrics, as the solvent does not interact with any polar groups within the fabric. Water binds to these polar groups which results in the swelling and stretching of proteins within fibers during laundry. Also, the binding of water molecules interferes with weak attractions within the fiber, resulting in the loss of the fiber's original shape. After the laundry cycle, water molecules will dry off. However, the original shape of the fibers has already been distorted and this commonly results in shrinkage. Non-polar solvents prevent this interaction, protecting more delicate fabrics.

9.     The usage of an effective solvent coupled with mechanical friction from tumbling effectively removes stains.

Drycleaning Machines

A drycleaning machine consists of four basic components:

1.     Holding or base tank

2.     Pump

3.     Filter

4.     Cylinder or wheel

5.     The holding tank holds the drycleaning solvent. A pump is used to circulate the solvent through the machine during the cleaning process. Filters are used to trap solid impurities. A cylinder or wheel is where the garments are placed to be cleaned. The cylinder has ribs to help lift and drop the garments.

6.     The operation of the drycleaning machine is easy to understand. The solvent is drawn from the tank by the pump. The pump sends the solvent through the filters to trap any impurities. The filtered solvent then enters the cylinder to flush soil from the clothes. The solvent leaves the cylinder button trap and goes back to the holding tank. This process is repeated throughout the entire cleaning cycle, ensuring that the solvent is maintained to give effective cleaning at all times.

7.     After the cleaning cycle, the solvent is drained and an extract cycle is run to remove the excess solvent from the clothes. This solvent is drained back to the bare tank. During extraction, the rotation of the cylinder increases in order to use centrifugal force to remove the solvent from the clothes

8.     Once the clothes have finished extracting, the cylinder stops. At this time, clothes are either transferred to a separate dryer or, on most machines, dried in the same unit, a closed system. The drying process uses warm air circulated through the cylinder to vaporize the solvent left on the clothes. The solvent is purified in a still. Here the solvent is heated. The vapors are then condensed back to a liquid leaving behind all impurities in the still. This clean solvent is then pumped back into the holding/base tank.

9.     Drycleaning machines are rated in pounds of fabric (dry weight) the machine can hold. Machine sizes vary from very small (20 pounds) to large (100 pounds) capacity of clothes cleaned per cycle.

10.  Before cleaning, garments are inspected and classified. The length of the cleaning cycle is dependant upon the type of article cleaned and the degree of soiling.

11.  Some heavily stained garments may go through a stain removal process prior to cleaning to aid in better soil and stain removal. A stain removal technician will treat specific items just prior to cleaning. A lot of effort goes into the process, and there are many skilled technicians involved in caring for your garments.