Although cleaning using water is by far the cheapest method of laundering cloths, we know that rich and fine fabric has to be laundered by dry cleaning. Dry cleaning was formerly known as ‘French cleaning’ or Chemical cleaning. Dry cleaning is based on the fact that most of the dirt or soiling matter is held by grease. When this grease is removed, the dirt is removed along with it. Dirt in ordinary washing is removed by the emulsification and Saponification of grease whereas dry cleaning indicates the removal of grease by the solvent action of certain liquids and by dry powder which act as grease absorbents. Most of the dry cleaning solvents used for cleansing does not penetrate in the fabric as water does in ordinary washing. Normal cleaning by water is very much detrimental for the structured and delicate fabrics like corduroy, sateen, velvet, velveteen and similar pile fabrics. To restore the beauty of such beautiful delicate and structured fabrics, it is pervasive to dry clean them as it does not alter/ disturb the structure. Dry cleaning is necessary for fabrics which cannot be washed such as far, felt, dark-skin gloves crape fabrics can be easily dry cleaned. And this causes no shrinkage as water does. Velvet and other pile fabrics can be easily dry cleaned. The pile is flattened by washing, but not flattened by dry cleaning.
Fabrics finished by moir’s making, lacquered fabrics and imitation far can be dry cleaned. The surface marking may be affected by this treatment, but it causes less damage than washing. Dry Cleaning is the best method of cleaning garments with pleats. It does not remove the pleats as it does not wet the fabric. In this paper we have made an attempt to elaborate the dry cleaning process along with the pros and cons of the solvent.
Dry cleaning can be defined as the cleaning of fabrics in a substantially non-aqueous liquid medium. This process has evolved into a highly effective laundering process (the last 75 – 80 years) involving low cost and safe method for removal of soils from all types of textiles. The first dry cleaning business was established by Frenchman, Jean Baptist Jolly in 1825. Solvent cleaning was introduced in Perth, Scotland in 1866 and, dry cleaning began to be used extensively in the USA during the period of 1910 – 1920.
Two general types of cleaning fluids are used in the industry, petroleum solvents and synthetic solvents. Petroleum solvents are inexpensive and its combustible hydrocarbon mixtures are similar to kerosene. Synthetic solvents are nonflammable but more expensive, halogenated hydrocarbons like Perchloroethylene and trichlorotrifluoroethane are 2 synthetic dry cleaning solvents currently in use. Operations using these synthetic solvents are respectively called “perc” plants or fluorocarbon plants.
(a) Difference between Laundering and Dry cleaning
Both laundering and dry cleaning remove soil by similar mechanisms and operations. Garments are tumbled in the cleaning liquid in horizontal washers. Detergents are used in both cases to emulsify or solubilize the soils insoluble in cleaning liquid. In laundering bleaching agents are added and strong alkalis can be used to saponify fats. Saponification is not used in dry cleaning but techniques have been developed to permit the use of some bleach in dry cleaning.
(b) Difference between Dry and Wet Solvent
The primitive dry solvent technique removes majorly oil-soluble stains. Current methods remove oil, many water-soluble as well as insoluble materials with the help of detergents and various agents. The important distinct feature between dry and wet solvent is, in wet solvent the latter swell the hydrophilic textile fabrics while dry solvents do not. Dimensional changes of the fibres undergo as they swell and cause fabric swelling leading to shrinkage, wrinkles and colour bleeding. Dry cleaning solvents do not cause fibre swelling and so do not cause shrinkage, wrinkles and colour bleeding. Also oily stains are removed at low temperatures in dry-cleaning. While in laundering, high temperature are preferred. Hence dry cleaning is a safe method for cleaning delicate textiles. Fabrics sensitive to wet treatments can be cleaned effectively of oil stains by dry cleaning.
2. Dry cleaning Operations
A number of processes are involved in the dry-cleaning operations. These processes are explained in detail below
When the soiled garments are delivered at the laundry, they are first sent to marking department. Here a tag, a white piece of fabric with a number or some other code stamped on it with indelible marking ink, is securely attached to the garment. Each article is treated individually to facilitate identification.
The garments are then passed on to the sorting Department. At this point if there are any tears or seams that have ripped open the garment, it is sent to the seamstress for mending. Various types of garments are sorted out into different hampers so that each hamper contains only one class of garments and can hold a maximum load of about 45 kg. There are six major groups into which clothes are sorted. These are
- White and light coloured clothes.
- Dark coloured clothes.
- White and light coloured woolens.
- Dark coloured woolens.
- Draperies and furniture.
- Raincoats and windcheaters.
At this stage, pockets are checked and cleaned and other parts of the garment showing dust or dirt are brushed and fancy buttons, buckles etc. are removed.
2.3 Pre- Spotting
Heavily soiled areas of the garment are treated with solvents. Volatile dry solvents like amyl acetate are applied to remove oil-borne stains. While, non-volatile solvents are used on paint and varnish stains. Water soluble stains such as perspiration are spotted with emulsifying agents. Some pre-spotters are digestive agents. They are mixtures of enzymes capable of digesting food stains. Pre-spotters are applied using a spotting gun which uses compressed air and helps spray the solvents on to the stains or heavily soiled area. Special spotting tables are equipped with steam guns, compressed air and spot- removal chemicals.
The workload of approximately 45 kg is transferred to the dry-cleaning cylinder. Very delicate clothes are put in net bags. Appropriate solvent is circulated through the clothes. The contact time of the clothes with the solvent depends on the size and type of the workload. This can vary from 5 to 45 minutes depending on fabric composition and degree of soiling. The dry-cleaning machine is constructed in such a way as to provide mechanical agitation of the work-load. The horizontal drum has ribs built- in to help lift up the garments as the drum rotates. These garments are then dropped back into the solvents for repetition.
The excess solvent is removed from the garments by centrifugation or in a revolving perforated cylinder contained in a tumbler. Modern dry-cleaning machines have perforated cylinder contained in a tumbler that perform cleaning and extraction in the same cylinder. The operators are not exposed to solvent vapors.
After extraction of excess solvent, the garments are dried in a (performed drum) drier enclosed in a tumbler. Hot air is passed through the cloths and is sucked out by exhaust fan. The temperature is controlled around 70°C.
2.7 Filtering and distillation of the solvent
Solvents are expensive and therefore it is filtered, distilled and re-used. They are not allowed to evaporate into the atmosphere. This also reduces the fire hazard and health hazard to workers in the laundry. Dry-cleaning solvents are purified by two processes:
(a) Filtration: The first filter is a mechanical one that holds back all solids such as dust, dirt particles and lint. The solvent is then passed through a filter of activated carbon or diatomaceous earth which clears the colour of the solvent and also removes all grease, waxes and water.
(b) Distillation: The solvent is heated to its boiling point in an enclosed system. It evaporates and passed through condensers to obtain pure solvent. Oily and greasy soils which were dissolved by the solvent during the cleaning process remain behind and are removed. All traces of colour, detergents and remaining water are removed at this stage.
Dried garments are inspected to check whether they are perfectly clean. If necessary they are spot cleaned the second time. In this operation each item is inspected individually. If any spots or stains are seen; the garment is sent back to the spotting department for their removal. The spotters have to processes a good knowledge of textile fibres, fabric construction, dyes and chemicals to deal with these special stains. He should also have a special skills and knowledge of techniques to be used. This will help him to know which strains can be removed without damage to the fabric and how to do this.
The extent of finishing depends on the quality of the fabric, the dyes used and the quality of tailoring. Cleaned garments are pressed by steam air forms which are of two basic types the grid head press used on woolens and the hot head press for silk and silk like fabrics. Both these types of presses have performed bucks as the bottom plate. The grid head press has a perforated head, while the hot head press is smooth and non-porous. The heads are heated internally by steam to a surface temperature of 149°C. The garment is placed on the buck and pressure is exerted by lowering the head.
Proper use of these presses is a skilled art. Pressing is the most expensive operation in dry cleaning. Many dry cleaners provide special services. Besides garment repair, they also offer re-dyeing, water proofing, moth proofing, softeners application, sizing, etc. They also clean leather goods. Dyeing and application of finishes like water-proofing, moth-proofing, antistatic finish application, etc are done in separate departments.
Buttons and buckles that had been removed are stitched back. Finally the garments are packed in paper or suspended from clothes hangers, covered with polythene bags and are ready for delivery .
3. Solvents used for dry cleaning
A dry-cleaning solvent must be an effective solvent for fats and oils, sufficiently volatile to permit easy drying, easily purifiable and of low toxicity. It should not weaken, dissolve or shrink the textile fibres or cause bleeding of dyes. It must be non-corrosive to metals commonly used in the machinery and non-flammable. These severe requirements have restricted the commercially successful solvents to a few petroleum fractions, some chlorinated hydrocarbons and chloflurocarons.
3.1 Perchloroethylene (perc)
Perchloroethylene (perc) is the most widely used solvent in the UK for the dry cleaning of textile and leathers. Textile products suitable to be cleaned by perc are denoted by either the symbol for normal process or for
It has been in use since the 1940s. This is the strongest solvent and the most aggressive cleaner. It is generally suitable for cleaning most textiles goods, including leather in special processes. It can, however cause harm to some plastics used like beading and trims. It may also dissolve some adhesives and strip the plasticiser out of polyvinylchloride (PVC). Some dyes, finishes and resins may also not be fast to perc. Manufacturers should test the dimensional stability of textiles to dry cleaning using ISO 3175 Part 2:1998. They should also check for colour fastness using EN ISO 105-DO1: 1993. Ideally a composite including all components should be submitted for evaluation using ISO 3175. SITRA’s dry cleaning experts identified other potential problems that are often overlooked, such as fabrics that may become difficult to press after cleaning, or components that should be removed and replaced after cleaning .
Draw back: – A recent study conducted at Georgetown University shows perc, classified as carcinogenic to humans by the EPA, is retained in dry-cleaned clothes and that levels increase with repeat cleanings.
3.2 Halogenated Hydrocarbons
- The main advantage of the Chlorinated hydrocarbons over petroleum is non-flammability.
- Carbon tetrachloride was the first hydrocarbon to replace petroleum because of the high cost of petroleum. It has now been replaced by perchloroethylene because of its toxicity and corrosiveness.
- Trichloroethylene is less toxic and more stable than carbon tetrachloride. Its major disadvantage is that, it causes bleeding of many acetate dyes.
- Perchloroethylene is the most widely used dry cleaning solvent. It is not easily hydrolyzed and therefore under normal conditions it does not yield corrosive amounts of hydrochloric acid. Since it does not evaporate rapidly, hazardous vapor concentrations do not occur if equipment is mainted properly. It has fewer tendencies to bleed dyes than trichloroethylene.
- 1,1,1- trichloroethene has high solvent power. It is non- allergenic, but it has a low boiling point and is more easily hydrolyzed than perchloroethylene.
- Fluorinated chlorohydrocarbons. 1,1,2 – trichloro-1,2,2, trifluoroethane has several advantages over other dry cleaning solvents. It is compatible with fabrics, dyes and garment accessories. It has a short drying time, high stability and lower toxicity than perchloroethylene. However it is less effective in spotting and stain removal.
3.3 Petroleum-based dry-cleaning
Petroleum-based solvents are flammable; PERC is not. Petroleum-based solvent vapors are fuels that can burn if they are present in concentrations between the lower explosive limit (LEL) and the upper explosive limit (UEL) with sufficient oxygen. If the concentration of petroleum based solvents in air falls below approximately 8 percent, flames will extinguish. When sufficient petroleum-based solvent vapors and oxygen are present, a fire can begin in the presence of an ignition source such as a spark or static electricity. Petroleum-based dry cleaning machines have several technical advances to improve machine safety and reduce the risk of fire and explosion. These advances include vacuum technology, inerting with nitrogen, and better control of machine operating parameters. The following measures can be taken either in combination or separately:
- Use of an inert gas such as nitrogen or argon to displace oxygen and ensure that the oxygen concentration is sufficiently low to prevent combustion.
- Operation under vacuum to remove oxygen level and lower its concentration.
- Ensuring that the LEL is not exceeded,
- Ensuring that the vapor concentration remains below 50 percent of the LEL by controlling operating temperatures or providing sufficiently high airflow .
Table 1: Advantage & disadvantages of petroleum based dry cleaning.
3.4 Liquid carbon dioxide
- Liquid Carbon Dioxide (CO2) is a recently developed technology that became commercially available in 1998. Liquid carbon dioxide has been used for cleaning in other processes for several years. CO2 would be processed by a gas manufacturer and delivered to drycleaners in pressurized canisters.
- During the process, clothes are immersed in liquid CO2 in an enclosed cylindrical basket. The load is then agitated inside the basket by high velocity fluid jets or mechanical action to remove soils. Once the cleaning process is finished, the garments are removed and need no drying.
- Manufacturers indicate that because of liquid CO2 having low viscosity, better cleaning is possible because, smaller particles can be removed from the surface with less redeposition. Liquid carbon dioxide is a nonpolar solvent that is most effective at removing nonpolar soils such as oil and grease. Since water soluble soils are polar, they have a relatively low solubility in liquid carbon dioxide (as well as PERC). To remove common polar soils such as salt and glucose, liquid CO2 additives must be used, or the stains can be removed during pre-spotting .
Table 2: Advantages & Disadvantages of liquid carbon dioxide
3.5 Glycol Ethers
They are in many cases more effective than perchloroethylene (perc) and in all cases more environmentally friendly. Dipropylene glycol tertiary butyl ether (DPTB) has a flashpoint far above current industry standards, yet at the same time possesses a degree of solvency for water-soluble stains that is at least equivalent to, and in most cases better than perc and the other glycol ether dry cleaning solvents presently in commercial use. A particular advantage of the DPTB-water solutions of the Rynex product in dry cleaning is that they do not behave like a typical mixture but rather, their behavior is the same as a single substance. This permits a better-defined separation upon azeotropic distillation at a lower boiling point and facilitates reclamation more effectively (at a level of 99% or greater), and also enhances purification using conventional distillation techniques .
3.6 Liquid Silicone
It is gentler on garments than perc and does not cause color loss. Though considerably more environmentally friendly, the price of it is more than double that of perc. It degrades within days in the environment to silica and trace amounts of water and CO2. Liquid Silicon produces nontoxic, nonhazardous waste. Toxicity tests by Dow Corning shows the solvent to increase the incidence of tumors in female rats (no effects were seen in male rats), but further research concluded that the effects observed in rats are not relevant to humans because the biological pathway that results in tumor formation is unique to rats .
4. Dry cleaning Materials
Dry cleaning solvents remove oily stains and so detergents are not necessary. However, at times, addition of detergents helps removal of other soils that may be present. They also inhibit soil redeposition by englobing the soil particle. Dry cleaning detergents are not formulated products similar to household detergents but principally surfactants or a mixture of surfactants, with concentration of active ingredients ranging from 40% to 90%. The following classes have been identified in commercial dry cleaning detergents.
- Soap-fatty acid mixtures.
- Mahagany or petroleum sulphonates.
- Sulphosuccinic acid salts.
- Alkalarenesulphonates acid salts.
- Amine alkylarenesulphonates.
- Fatty acid esters of sorbitol.
- Ethoxylated alkanolamides.
- Ethoxylated phenols.
- Ethoxylated phosphate esters .
All dry-cleaning solvents are used at ambient temperature. There is no heater in a dry cleaning machine to warm the solvent during the cleaning cycle. The only heat used in the process is during the drying cycle to drive off the solvent and latter in the distillation unit. The used solvent is recycled via filter system into a distillation unit where it is heated and the clean solvent is evaporated. The solvent vapor is then led off and cooled in order to condense it back into liquid. A similar process condenses the solvent for further reuse after it has been removed from the textile during drying .
The symbols under dry cleaning operation are as follows
Figure No 5.1: Symbols of Dry Cleaning
6. Apparatus for Testing of Textile Material to Dry-Cleaning
6.1 Design and Constructional Requirements
The apparatus should consist of:
- Glass or stainless steel containers in which the test specimens or composite specimens, test solution and stain steel balls or stainless steel discs are to be contained together,
- A device to revolve the containers.
- A thermostatic water bath to maintain the temperature of test solution in the containers at a constant value as required in the test.
6.2 Glass or Stainless Steel Containers
The containers shall be made either from glass conforming to the relevant requirements given in IS 2619 : 1971 or form stainless steel conforming to IS 5522 : 1978, leak proofed and sealed. They shall be of 75 ± 5 mm diameter, 125 ± 10 mm height and 550 ± 50 ml capacity. They shall be able to withstand a revolving speed of 40 ± 2 rev/min without any damage. They shall have smooth surface and shall be free from rough edges. (The container should preferably be cylindrical in shape.)
6.3 Revolving Device
It shall consist of an electric motor, a revolving shaft and holders for containers fixed to the revolving shaft radially. It shall enable the containers to be fixed so that the centre line of holders may position in one line with the centre line of the containers. It shall be capable of rotating the shaft/ container assembly at a speed of 40 ± 2 rev/min. The distance between the centre line of the revolving shaft and the bottom of the containers shall be 45 ± 10 mm.
6.4 Thermostatic Water Bath
A heater capable of keeping the temperature of the test solution contained in the rotating containers at the specified temperature within ± 2° C.
6.5 Stainless steel Balls
They should be non-corrodible, made from stainless steel conforming to IS 6603: 1972 and shall have a diameter of 6 ± 0.4 mm.
6.6 Stainless steel Discs
They should be non-corrodible, made from stain steel conforming to IS 6603: 1972 and shall have a diameter of 30 ± 2 mm and mass of 20 ± 2 g. They shall be smooth and free from rough edges.
6.7 Inspection and Testing
The apparatus shall be checked for the following requirements are:
- All containers, holders, thermostatic water bath and stainless steel discs must be checked for defects like pin holes, cavities, etc.
- The entire apparatus should be checked for static and dynamic balancing for smooth working and any unbalance shall be removed.
- The electric circuit should be checked to avoid any short circuiting in operation.
- The temperature control mechanism should be checked for its proper working and the instrument should be calibrated to read accurate temperature.
- Te revolving device should be checked for proper working and periodic calibration of speed, preferably by speed indicator, should be done.
The entire apparatus assembly should be packed with strong and sturdy packing so as to avoid damage during transit.
The apparatus should be marked at appropriate place with the following:
- The name of the apparatus
- Indication of the source of manufacture, and
- The month and year of manufacture of the apparatus.
- The apparatus may also be marked with the standard Mark.
|1.||Glass or Stainless Steel Containers||IS 2619 : 1971 and IS 5522 : 1978|
|2.||Stainless steel Balls||IS 6603: 1972|
|3.||Stainless steel Discs||IS 6603: 1972|
Table No 6.1: ISO Standards
7. Dry Cleaning Waste
7.1 Cooked muck
Cooked powder residue is the name for the waste material generated by cooking down or distilling muck. It is a hazardous waste and will contain solvent, powdered filter material (diatomite), carbon, non-volatile residues, lint, dyes, grease, soils, and water. This material should be disposed of in accordance with environmental concerned factors.
The waste sludge or solid residue from the still contains solvent, water, soils, carbon, and other non-volatile residues. Still bottoms from chlorinated solvent dry cleaning operations are hazardous wastes. Still bottoms from machines using other solvents may also be hazardous due to toxic constituents in fabric dyes and notions.
Filters used in Perchloroethylene based machines are also regulated hazardous waste.
7.4 Separator water
Water will separate from the dry cleaning solvent, and must be removed. This waste water, from machines using Perchloroethylene, is a regulated hazardous waste.
Soiling of textiles creates an acute problem as it needs to be removed by employing various wet and dry methods. Each and every dry cleaning method has some advantages as well as disadvantages. In the age of 3E (energy, environment and economy) it is essential to have an efficient and cost effective one without disturbing environment. Solid waste generated due to dry cleaning is a big problem. Feature research should be aimed to over come this problem.
- Noemia D’ Souza, Fabric Care, New age international publishers, P 125-128.
- Christine Antrobus, Solvents used in dry-cleaning, SATRA Spotlight October 2007,
- Control of Exposure to Perchloroethylene in Commercial Drycleaning (Substitution), U.S. Department of health and human services, September 1997.
- Data for web links browsed from 8th to 10th of November 2013.
- http://wikipedia.org/wiki/Drycleaning (retrieved on 22nd November 2013.