Dry cleaning


Dry cleaning is any cleaning process for clothing and textiles using a chemical solvent other than water. The modern dry cleaning process was developed and patented by Thomas L. Jennings.
Despite its name, dry cleaning is not a "dry" process; clothes are soaked in a liquid solvent. Tetrachloroethylene (perchloroethylene), which the industry calls "perc", is the most widely used solvent. Alternative solvents are trichloroethane and petroleum spirits.
Traditionally, the cleaning process was carried out at centralized factories. Small, local 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.
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 laundering. 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.
Garments are also checked for foreign objects. Items such as plastic pens that may dissolve in the solvent bath, damaging the textiles. Some textile dyes are "loose" and will shed dye during solvent immersion. Fragile items, such as feather bedspreads or tasseled rugs or hangings, may be enclosed in a loose mesh bag. The density of perchloroethylene is around 1.7 g/cm3 at room temperature (70% heavier than water), and the sheer weight of absorbed solvent may cause the textile to fail under normal force during the extraction cycle unless the mesh bag provides mechanical support.