Garment washing

In addition to improving or softening the hand-feel of products, garment washing affects the aesthetic of the product, often by imparting a "worn in" or "aged" appearance. Garment washing has become an indispensable tool for apparel designers to manipulate garment aesthetic and to impart unique decorative effects, particularly for denim.

The umbrella terms "garment wet processing," "garment wet and dry processing," "garment finishing" or just "garment processing" can be used interchangeably to describe many different techniques, all designed to alter the garment's hand-feel or aesthetic in some fashion. "Garment washing" generally entails those specific treatments involving water and chemicals.

Dry procedures are used primarily for localized or even "patterned" abrasion effects and include techniques such as sandblasting, hand sanding, brushing, grinding, cutting (holes/patches), etc.

Wet garment washing processes involve the use of numerous chemicals depending on the exact nature of the process. Most wet processes are designed to abrade, decolourize, and/or soften the garments. Although the techniques are generally intended as an all-over treatment, the degree of abrasion, decolourization, and/or softening can and does vary significantly within and between garments in a typical load. For example, thick and/or more exposed areas of the garment (such as hems/seams) absorb more of the mechanical or kinetic energy during tumbling, and may therefore be more abraded and/or decolourized (faded) than flat areas. Conversely, tightly constructed areas of the garments may end up less decolourized than less-dense areas, since their ability to absorb chemicals (e.g., bleach) may be hindered.

By far, the most involved and intensive wet treatments are applied to denim products, although many of these same treatments are now applied to other woven bottoms, woven tops and even knit garments.

Two basic types of equipment are used for garment washing: 1) side-loading horizontal washers (commonly referred to as belly washers), and 2) front-loading rotary washer/extractors. There are numerous variants of each machine type.

Rotary washer/extractors, the more expensive of the two, generally provide many more options to control/optimize wet treatments, including advanced liquor ratio (water to fabric ratio) control, heating, and colourant/chemical add systems. As a rule, they provide more opportunities for waste minimization than belly washers.

After garment washing, large open-pocket tumble dryers are typically used to dry apparel. Smaller units may be heated electrically, while larger units are typically steam- or gas-heated. Modern tumble dryers have relatively sophisticated controls (e.g., moisture sensors), which help to minimize energy use.

Desizing/scouring

Woven denim products must be desized before further garment washing since they still contain sizing agents applied to the warp yarns. The most common sizing agent is starch, and amylase enzymes are commonly used to break down the starch molecules into water-soluble sugars to ease their removal. Another common sizing agent is polyvinyl alcohol (PVA). PVA is relatively water soluble, provided it is the right "grade." No enzymes or oxidizing agents are necessary to remove water-soluble sizing agents; they can be rinsed from the garments simply by using adequate washing temperatures and times, and a good detergent. PVA can create a high chemical load in the wastewater and should be reclaimed for reuse. In addition to sizing agents, other "top finishes" are sometimes applied to fabrics, mainly for purposes of lubrication (e.g., sewing lubricants, sanforizing lubricants). Garment scouring removes these top finishes, largely accomplished by rinsing with an appropriate detergent. Light scouring and desizing softens denim garments drastically.

Wet abrasion

Wet abrasion techniques are used to create a natural-looking (uneven) worn and faded effect, ranging from slightly to very uneven. Wet abrasion increases seam contrast, since thicker regions of the garment tend to abrade more readily than flatter regions. In its most basic form, wet abrasion entails tumbling wet garments in the presence of pumice stones (or an appropriate substitute). Commonly known as “stonewashing,” this technique can create a wide array of effects by adjusting the amount of water or stones, the size or shape of the stones, the tumbling time, and the mass ratio of stones to garments. Sometimes, stones are pre-soaked in an oxidative chemical solution (i.e., bleach) prior to tumbling with the garments. This increases the decolourizing potential of the stones, enabling the release of bleach to specific areas of the fabric and the garment as the stones collide. Common oxidizing agents used for this purpose include chlorine derivatives (e.g., sodium or calcium hypochlorite) and potassium permanganate. In fact, the once-popular "acid wash" was achieved by tumbling garments with stones that had been pre-soaked in potassium permanganate. Cellulase enzymes can also be used to accelerate wet abrasion effects (by removing, or at least weakening, the surface fibre), and can reduce, or in some cases, eliminate the need for stones altogether. Wet abrasion is usually followed by a quick rinse intended to remove any remaining loose dye-stuff and/or residual dust from stones or other abrasive materials, and to deactivate remaining cellulase enzymes if necessary.

Bleaching

Bleaching is often used to lighten the colour of garments overall, to brighten the indigo dye used on denim products and to remove indigo dye-stuff that may have deposited on the (undyed) filling yarns during the wet abrasion process. Most garment bleaching is done with chlorine derivatives (usually sodium or calcium hypochlorite). Hypochlorite is a strong bleach, reactive enough to work well at cooler temperatures, and is effective at removing certain dye-stuffs from garments.

Brightening

Sometimes referred to as "top brightening," this garment washing technique may be utilized after bleaching to further whiten, or brighten, the decolourized areas of the garment, thereby enhancing the contrast between the light (or white) and dark areas in the fabric. This is sometimes accomplished using a milder bleaching agent (e.g., hydrogen peroxide), or may be accomplished by using an optical brightener. Optical brighteners (also known as fluorescent whitening agents or FWAs) are colourless dye-stuffs that have the ability to absorb invisible UV radiation and retransmit it as visible (white) light.

Tinting/over-dyeing

The application of additional colourant to garments that have already been dyed and/or printed is known as tinting or over-dyeing. If any areas of the garment are white (e.g., filling/weft yarns in denim garments), these will fully absorb the colourant, but dyed or printed areas will also pick up a degree of colour. All types of colourants (e.g., dyes, pigments, metal salts) may be used to tint fabrics, depending on the substrate. Over-dyeing with one colour changes the hue of the pre-existing colours and tends to "unify" the look of the print, often imparting a more vintage or dusty appearance to the fabric. For example, over-dyeing with a blue shade will turn browns into warm, deep grays, and will turn grays into soft blues. Over-dyeing with a red shade will turn browns into deep rust, and will turn greys into soft reds. Over-dyeing with secondary shades can result in even softer and more complex effects.

Softening

The final step of most garment washing operations is softener application, which can enhance the garment's hand, drape, abrasion resistance and even tear strength. There are many different types of chemicals that can function as softeners, including sulfates and sulfonates, amines and quaternary amines, ethylene oxide derivatives, and hydrocarbon waxes. Softener selection is primarily a function of the desired hand-feel: dry (petrochemical/polyethylene), greasy (organic/fatty derivatives), or slick (silicone). Roughly one-third of the chemicals used as softeners are silicone-based. Softeners work by reducing the coefficient of friction of fibres and yarns.

Although dry processing techniques involve no chemicals, they do create environmental impacts, including extraction of abrasive media from natural habitats, the transport of material to the processing facility (often surprisingly long distances) and the landfilling of spent abrasive media. Dry techniques, such as sandblasting, can also involve considerable occupational health and safety hazards for operators, and proper safety precautions, such as appropriate personal protective equipment and adequate ventilation, must be in place—must not always is. Although sandblasting in Europe has been banned for decades, the practice is still abundant in Bangladesh and China, countries with a high likelihood of lack of enforcement for proper safety precautions.1, 2 Garment washing is a relatively water-intensive process, and may also be energy- and chemical-intensive, depending on the nature of the wash used. The environmental impacts of garment washing include the discharge of chemicals (surfactants, chelating agents, acids, alkalis, oxidizing agents, reducing agents, heavy metals, etc.) and colourants into water systems, which contributes to aquatic toxicity and/or high biological demand (BOD) or chemical oxygen demand (COD). High BOD and COD create environments that are hostile to aquatic plants and animals and may create problems with water reuse. Any colour removed from the garments during the garment washing process is also dispelled to the wastewater and may create problems with photosynthesis for aquatic plant life. In order to promote the permanence of colour on a textile substrate or garment, colourants and other chemicals used in textile and garment dyeing and printing are developed to be resistant to environmental influences. This durability sometimes limits the biodegradability of colourants and makes them difficult to remove from wastewater generated by dyeing or printing processes. In terms of its environmental impact, hypochlorite used in bleaching breaks down into table salt, oxygen and water. But if hypochlorite is exposed to organic material before it breaks down, it can react with that material to form halogenated organic compounds (organochlorines). Halogenated organic compounds are persistent, toxic compounds, may bioaccumulate in the food chain, are known teratogens/mutagens and suspected human carcinogens, and may cause reproductive harm. Toxicity and biodegradability of chemicals used as softeners are primary considerations. As a rule, fatty derivatives are highly biodegradable, whereas petrochemicals are not. Silicone is highly resistant to biodegradation by microorganisms (such as those used in biological wastewater treatment), but will degrade once it is in soil (e.g., in a landfill).

Fabric selection

One of the keys to reducing the environmental impact of garment washing processes is to select fabrics with desired garment hand-feel and aesthetic qualities engineered into the construction. If fabrics are physically engineered to exhibit desired qualities, the intensity (and by extension, the environmental impact) of many garment washing treatments can be minimized. For example, the hand-feel of garments can be dramatically altered by modifying fibre diameter and cross-section, fibre length, fibre tenacity and modulus, yarn twist, yarn count, yarn hairiness, fabric stitch density, etc., thereby minimizing the need for hand-feel modification in garment washing. In many cases, only slight physical modifications are necessary (i.e., they are visually undetectable). Similarly, the impacts of garment washing can be reduced significantly by selecting colours close to the desired final hue. Fifty percent or more of the colourant for deep shades is removed via abrasion or bleaching in garment washing. Selecting a colour closer to the desired garment shade after wash reduces the degree of decolourization (and associated energy, dye-stuff and waste) necessary.

Water reuse

In addition to minimizing the amount of water coming into a textile mill, water conservation can also occur after the wet processing is complete. A typical garment washing process may involve several wash cycles (e.g., desizing, wet abrasion, bleaching) as well as an assortment of rinses between cycles. This requires the garment washing machine to be drained and refilled numerous times. It's not unusual, for example, to use 35 or more gallons of water per garment during the garment washing process. In order for this water to be recycled and/or reused, it must contain little or no chlorine, and have low metal content and low salt concentration (e.g., chloride and sulfate). Alkalinity, pH and residual dyes are also of concern. Some garment washers have reduced water consumption by 50% or more by reusing process water. Some municipalities have even started marketing recycled water (e.g., water treated via reverse osmosis) to industrial customers. In fact, treated and recycled water is sometimes more consistent in terms of its impurities than potable water.

Frequency of machine cleanings

Total water consumption in garment washing is also affected by the frequency of machine cleaning. In general, scheduling machines to process progressively darker shades—from light to dark—minimizes the need to clean the machine between each colour batch.

LOW-LIQUOR-RATIO WASHING

One of the most important considerations, from a water and energy consumption perspective, is liquor ratio. Liquor ratio is the weight of the chemical bath (including the water) divided by the weight of the material (garments) being processed. Garment washing machines are available in a variety of sizes, and loads can vary widely depending on the nature and scale of the order. If the load size is small, and a large garment washing machine is used, the liquor ratio, the water volume and the energy used to heat that water will all be higher than necessary. Liquor ratio also affects the speed and level of fabric abrasion. In higher liquor ratio machines, garments and abrasive materials come into contact with each other less than in low-liquor-ratio circumstances. High liquor ratios therefore require more time (and energy) to achieve similar abrasion levels than low liquor ratios. As a rule, front-loading rotary washer/extractors have more flexible controls to accommodate various load sizes, enabling optimal water and energy use and minimizing waste.

PROPER CHEMICAL SELECTION

Another important element of pollution prevention is chemical selection. A wide variety of surfactants, chelating agents, oxidizing agents, reducing agents, enzymes, lubricants, colourants and other chemical types are routinely used in garment washing. Vendors generally elect chemicals based on their performance characteristics (effectiveness) and price, but must also factor environmental considerations such as toxicity, BOD, and COD into chemical selection decisions. In addition, the biodegradability of each chemical is of prime importance. For example, alkyl phenol ethoxylates (commonly referred to as APEO), a common class of surfactant used in garment washing, are undesirable due to their poor biodegradability, their toxicity (including that of their phenolic metabolites) and their potential to act as endocrine disrupters. APEO are banned in Europe, and there are a host of wetter/scour alternatives readily available. Overseas garment washing operations may still use APEO surfactants because of their low cost and good performance characteristics. In general, chemicals and their processes should be selected to be the most benign. For some processes, enzymes can replace chemicals and include: amylases used for desizing, cellulases used for wet abrasion and laccases used for bleaching.

LASERS

Another alternative to traditional processes of decolourizing fabrics is the use of lasers. Depending on its wavelength, the laser can either: 1) be absorbed by and decompose the colourant, or 2) be absorbed by and alter the surface chemistry of the fabric. The latter technique in particular has great potential to replace traditional wet abrasion and mechanical abrasion techniques such as hand sanding because it closely emulates the results these traditional abrasion processes achieve. Lasers for this purpose are already commercially available and several are in use in laundries around the world.

BLEACHING ALTERNATIVES

There are two technologies designed to replace chlorine derivative bleaches: ozone and enzyme-based processes. Ozone can be used with no water at all and is very effective at fading pre-dyed/pre-printed fabrics and garments. Laccase is an enzyme that has proven effective at decolourizing or fading pre-dyed/pre-printed apparel products. Enzymes are biodegradable (no-waste products) and typically work well at low temperatures, thereby minimizing energy consumption.

COMBINATION/ELIMINATION OF GARMENT WASHING PROCESSES

Another possibility for pollution prevention is the combination, or even the elimination, of specific garment washing processes. For example, denim desizing and wet abrasion have long been performed using two completely separate garment washing treatments, each with its own environmental impact. Desizing is performed using an amylase enzyme or oxidizing agent, followed by a wet abrasion treatment using stones, cellulase enzymes or both. It is sometimes possible to combine these two cycles into one, which significantly reduces process time as well as water, energy and chemical consumption. However, combining desizing and wet abrasion processes can present specific technical issues, such as severe streaking and back staining from the large amounts of dye present in the desizing bath. These issues can be overcome by using two specific types of cellulase enzyme in combination—one designed for abrasion assistance, and the other designed for streak reduction/prevention. Enzymes are added to the processing bath in a specific sequence or are selected to have an appropriate "dormant" period (i.e., the enzyme is not activated until the proper time during the washing cycle). This strategy is sometimes called a “combi-process.”

WASTE MINIMIZATION/SOURCE REDUCTION

Strong consideration should be given to whether a garment washing process is truly warranted. On certain products (e.g., denim), some form of garment washing is necessary—to remove the sizing agents present on the warp yarns, for example. On other products, such as knit tops, garment washing may not always be required. For example, where garment washing is performed to reduce the hairiness/pilling propensity of knit garments, fibre selection (e.g., less short fibre or lower-tenacity fibre) and/or modifications to the yarn (less twist) can sometimes eliminate that need. Where garment washing is performed to reduce the torque/skew or shrinkage in garments, some procedures in the manufacture of the fabric, such as Sanforizing, may suffice. And where garment washing is used to achieve a faded aesthetic, starting with a fabric shade closer to the desired garment shade after wash can significantly reduce the degree of decolourization (and associated energy, dye-stuff and waste) necessary.

ECO-AGING

Eco-aging is an alternative to sandblasting created by Fimatex in Italy. It’s a fading process that uses a vegetable mix composed of waste from food and is said to be biodegradable.3

1. Water conservation (gallons of water saved per item) when ozone bleaching is used.

2. non-chlorine bleached: If alternative bleach is used.

3. Laser treatments replacing conventional wet abrasion finishes could appeal to an increasingly tech-savvy consumer base.

4. Providing educational information on the social responsibility or brand website could detail information about lower impact processes for washing, finishing and bleaching.

1. blog.stylesight.com/denim/sandblasting-ban-update 2. www.mercurynews.com/business/ci_24407198/retailer-sandblasting-bans-have-changed-little-garment-industry 3. www.fimatexgroup.it/