As discussed in the introduction, textile items are routinely subjected to laundering or dry-cleaning in order to remove dirt and to restore their appearance. Laundering
138 Understanding and improving the durability of textiles
uses water, detergent, and agitation to accomplish dirt removal: subsequent drying and pressing restore appearance. Within those simple statements are a multiplicity of possible details. The AATCC Technical Manual (AATCC 2011) includes a monograph on home laundering conditions. Laundering practice has always varied widely from country to country. The situation is becoming ever more complex as regulations to promote efficient use of energy and water are introduced and enforced to different extents in different parts of the world. If a textile is to be washed in a laboratory as part of testing, it is vital that the conditions be carefully controlled and reported to maximize test precision. As washing machine design is now changing rapidly, testing organizations face a dilemma: should tests reflect machines being sold, or the majority of machines in actual use, or should a long-standing standard design be used so that new tests can be compared to old test results?
Some of the factors that need to be controlled in laundering are:
• water volume;
• total load/ballast;
• water temperature(s);
• type and amount of detergent (even if detergent is a given commercial name, it may be formulated differently in different locations; the use of a standard detergent is preferable);
• agitation (determined by specifying machine, although in ‘smart’ machines this may vary depending on load);
• wash time;
• rinse cycle.
Drying can be on a rack, a line, or in a tumble dryer, when the temperature and agitation should also be specified. Similar but less extensive considerations apply to dry-cleaning.
7.6.1 Testing for color loss and wear during refurbishment
Laundering can cause colors to fade. This can often be gradual. Realistic testing would require that items be washed several times before evaluation of color loss.
To avoid interference from other colors, each item would need to be washed with only white ballast in the laundry load. So the testing of several different colored items would involve an impossibly large number of full-scale washings. This has long been recognized as unrealistic so tests have been developed in which small samples are subjected to conditions that (by correlation testing) are known to generate comparable results to, say, five launderings in a single cycle. In a suitable piece of equipment, 20 or more items can be tested simultaneously. Thus AATCC’s TM61 uses rotating steel cylinders of differing sizes, and includes options with a number of steel or rubber balls, and specified temperatures, detergent concentra- tions and amounts, with and without chlorine bleach to simulate hand, home and vigorous launderings. ISO 105-C06 has a similar range of variations. Sadly it is
Testing textile durability 139 quite common for this accelerated color-loss test to be applied where it was never intended. Researchers wishing to demonstrate the durability of a fabric treatment will run such a test three times and suggest that their treatment will stand 15 washings when no such correlation has ever been demonstrated. Even staining, routinely measured on this test, does not correlate to the staining that would be experienced in repeated washing.
Full-scale laundering is used to assess colorfastness to launderings that include non-chlorine bleach (AATCC TM172) and chlorine bleach (AATCC TM188).
Laundering can also cause wear. Repeated washing (readily evidenced by the lint that builds up in a lint trap) wears fabrics. Indeed, it is likely that many textiles are
‘washed out’ rather than ‘worn out’! A number of proprietary tests recognize this phenomenon and use machines with an aggressive action to test the durability of prints, pleats, collars, quilted fabrics, and so on. The original twin tub domestic washing machines have been superseded by newer, purpose-built machines (SDL, 2011; Heal, 2011).
7.6.2 Testing for shrinkage and skewness during refurbishment
Laundering can change fabric dimensions, or can cause garments to become skewed. Continued dimensional change over several launderings can be inter- preted as a lack of durability. In contrast to testing for color loss, dimensional change can be tested on several items in the same laundry load and multiple (usually three to five) full-scale launderings are the norm (ISO 5077: AATCC TM 135, 150 for home laundering of garments and fabrics respectively, ISO 675TM 96 for commercial laundering). Skewness resulting from home laundering is assessed in AATCC TM179. AATCC TM158 assesses dimensional change after dry cleaning. Small-scale devices have been developed to assess shrinkage rapidly (AATCC TM187, ISO 23231).
Laundering and subsequent drying can affect the surface appearance of an item.
Excessive wrinkling (perhaps over time as a wrinkle-free finish is lost) is a problem. The appearance of fabrics and garments after home laundering is compared to a set of plastic wrinkle replicas in ISO 15487, AATCC TM124 and 143. The retention of creases and the puckering of seams can also be tested (AATCC TM88B and C). Several attempts have been made to automate the rating of these tests by image analysis techniques (e.g. Matsuoka et al., 2008), but have yet to be adopted.
7.6.3 Testing for soil repellency, release and redeposition during refurbishment
Laundering is designed to remove soil. A garment from which stains are not readily removed would become dingy and be thought unacceptable before its time. Soils
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can be repelled before becoming ingrained in a fabric, predicted by an oil repellency test (AATCC TM 118, ISO 14419) in which a series of oils are dropped onto a fabric to determine which of them fails to wet the fabric in 30 seconds. If a fabric does become soiled, the subsequent release of the soil in laundering is important. AATCC TM130 places five drops of corn oil onto a fabric. After being kept under a weight for one minute, the fabric is laundered and the remaining stain rated against a series of visual standards. The soil removed from one garment can be redeposited on other laundry items. A test of soil redeposition (AATCC TM 151) uses the launderometer to wash a presoiled fabric together with a test specimen, and the degree of redeposition is determined by spectrophotometric measurement.
7.6.4 Testing for loss of finish during refurbishment
Laundering can also cause the loss of a finish, or other applied substance such as a coating. Finishes are applied to achieve many different effects, and to determine the durability of a finish would usually involve repeated laundering and a compari- son between washed and unwashed specimens using a test of the appropriate property. The list of such tests is extensive, but would include those that determine resistance to water, flames, and microbes. Related are the more recently introduced moisture management finishes, designed to wick moisture away from the body, and tested in AATCC TM 195.
Loss of water repellency
The water resistance/repellency tests vary in severity and should be matched with the expectations of the end use. They include AATCC TM22 (Water Repellency:
Spray Test), TM 42 (Water Resistance: Impact Penetration Test), TM 35 (Water Resistance, Rain Test). AATCC TM127 (Suter test) measures the hydrostatic pressure required to force water through a fabric, while ASTM D751 (Mullen test) uses higher pressures to force water through coated fabrics. For severe outdoor conditions, the Bundesmann test (ISO 9865) rubs and rotates fabrics while they are being ‘rained’ on. The degree to which a fabric soaks up water while being agitated is tested in AATCC TM 70 (Tumble Jar). AATCC TM193 and ISO23232 measure water repellency by the use of water–alcohol mixtures in a parallel test to that used for oil repellency.
Flame resistance
Flame resistance applies to critical end uses. Flame resistant materials can be derived from inherently FR fibers (such as aramids), from additives or modified monomers in the case of manufactured fibers, or by the application of a finish, essential in the case of natural fibers. Such materials should obviously be durable
Testing textile durability 141 to laundering, and failure may derive from both the loss of a finish, or the build up (of lint or softeners, for example) over many laundry cycles. The multiplicity of agencies and standards makes listing test methods impracticable. ASTM D4723 (Standard Classification Index of and Descriptions of Textile Flammability Test Methods) contains more than 300 methods.
Antimicrobial effectiveness
The value of controlling the growth of microorganisms in both critical health industry applications, and in more mundane consumer items (socks that do not smell, shower curtains that do not mildew) has increased in recent years, and the durability of such finishes is an important issue. Whether the finish is leaching or non-leaching affects both its effectiveness and durability. Tests that would meas- ure the effectiveness of finishes before and after laundering include AATCC TM 30, 100 and 147.