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Editor’s note: This article is featured in the Fall 2009 issue of SDL Atlas Update, the company’s quarterly newsletter. To sign-up to receive the newsletter, send us an e-mail at firstname.lastname@example.org.
Pilling of woolen knitted fabrics has been a problem for a long time. The development and wide use of man-made fibers in apparel has made it a more serious issue. This defect, which can develop and become worse as a consumer wears and launders a garment, is one that the industry has been trying to solve in a number of ways.
Starting at the fiber and yarn level, it is reported that high test yarns may have a lower pilling propensity. Ring spun cotton yarns often produce less pilling than open spinning. Enzymes are added to some laundry detergents to remove the fibrils before they become entangled with other lint and form an unsightly pill in the laundry process.
Some synthetic fibers are engineered with a special profile to have lower pilling. Pills are formed when fibers on a fabric surface “tease out” and become entangled during wear. Such surface deterioration is generally undesirable, but the degree of consumer tolerance for a given level of pilling depends on the garment type and fabric end use. The well-known EN ISO 12945-1 standard tells us, Generally the level of pilling which develops is determined by the rates of the following parallel processes:
a) fibre entanglement leading to pill formation;
b) development of more surface fibre;
c) fibre and pill wear-off.
The rates of these processes depend on the fiber, yarn, and fabric properties. Examples of extreme situations are found in fabrics containing strong fibers versus fabric containing weak fibers. A consequence of the strong fiber is a rate of pill formation that exceeds the rate of wear-off. This results in an increase of pilling with an increase of wear. With a weak fiber, the rate of pill formation competes with the rate of wear-off. This results in a fluctuation of pilling with an increase of wear. In other constructions, surface fiber wearoff occurs before pill formation. Each of these examples demonstrates the complexity of evaluating the surface change on different types of fabric.
The ideal laboratory test would accelerate wear processes a), b), and c) by exactly the same factor and would be universally applicable to all fiber, yarn, and fabric types.
No such test has been developed. However, test procedures have been established in which fabrics can be ranked in the same order of fuzzing and pilling propensity as is likely to occur in end-use wear. Regardless of the approach taken to improve fabrics by reducing pilling, a standard and objective laboratory test is needed to determine whether a proposed change in the fiber, yarn, or fabric is truly a positive change.
SDL Atlas provides a wide variety of industry standard and innovative instruments to predict and grade a fabric’s propensity to pill or fuzz.
M227A&B ICI/M&S Pilling and Snagging Tester is a universal pilling and snagging tester drive system available with 2 (M227A) or 4 (M227B) positions. This system allows a user to rapidly predict pilling or snagging of fabrics in a fraction of the time that it would occur in normal use. The controller allows the user to input test cycle and rotational speeds of 20, 30, 40, 45, 50, 60, 65, and 70 rpm. An automatic reversing function is available for 30 rpm speed.
A variety of pilling and snagging boxes and drums are available as options to meet ISO, BS, M&S and other retailer (predominately European) standards, including EN ISO 12945-1 and the new BS 8479. The pilling test in these devices has the specimen mounted on a polyurethane tube and tumbling against the cork-lined interior surface of the box. Interestingly, the authors of the EN ISO 12945-1 standard tell the user that generally, the frictional properties of the cork are not a major source of test result variation. This is in contrast to the widely used American method ASTM D3512 for the SDL Atlas M227R&S Random Tumble Pilling Tester, in which cork liners are used only 30 minutes per side within a cylindrical chamber and then discarded. Recent studies conducted in Australia by a group of wool testing laboratories have suggested that variation in the properties of the polyurethane tubes on which the specimens in EN ISO 12945-1 are mounted are statistically significant when studying between lab differences in pilling results.
The testing approach detailed in ASTM D3512 was originally developed in the E.I. DuPont fiber research labs in the 1950s to duplicate the type of pilling that was seen on Dacron/cotton blend shirting fabric. Their approach was to use unmounted specimens that are caused by spinning stainless steel rotors to freely tumble within a fixed corklined cylinder. This random tumbling motion is meant to imitate on an accelerated basis the abrasive wear the fabric would receive in actual use. In order to make the pills more visible, small amounts of cotton lint are added to the chamber prior to testing.
Cork surfaces are not the only abradant used for the mild abrasion that initiates pilling. Abrasion testers like the SDL Atlas M235 Martindale Abrasion and Pilling Testers are widely used for testing the abrasion and pilling resistance of all types of fabric structures. These testers are found in almost every textile laboratory. Specimens are rubbed against known and standardized abradants at low pressures and in continuously changing directions so the amount of abrasion or pilling is compared against standard parameters. The EN ISO 12945-2 Textiles—Determination of fabric propensity to surface fuzzing and to pilling— Part 2: is a modified Martindale test procedure in which a circular test specimen is passed over a friction surface comprising the same fabric or, when relevant, a wool abradant fabric, at a defined force in the form of a Lissajous figure. The test specimen is able to rotate easily around an axis through its center, perpendicular to the plane of the test specimen. Fuzzing and pilling are assessed visually after defined stages of this rub testing.
In 1974, a group of American textile experts meeting in an ASTM committee decided that a specific type of pilling was occurring on shirt collars and that this was caused by the fabric being abraded by the wearer’s skin. They designed a test using the predecessor to the SDL Atlas M282 Universal Wear Tester. This instrument was originally designed in U.S. Army Quartermaster laboratories for determining wear and abrasion resistance of fabrics used in clothing, footwear, and industrial applications. They equipped the Universal Wear Tester with a special silicone pad to simulate human skin and created the test now known as ASTM D3514 Standard Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Elastomeric Pad.
There is no single solution for pilling testing, but SDL Atlas offers the most complete range of instruments to meet whatever test standard our customers require.
However, the instrument used is only a part of the solution in pilling testing. Many in the standards development process have come to realize that interlab variability is often not due to differences in the instruments but rather in the Pilling Evaluation and Grading.
Visual evaluation of pilled fabrics may be specified by the standard that your laboratory must meet. Photographs or control fabrics are often used for these evaluations, but in either case, standardized lighting and viewing conditions are critical to reproducible ratings. SDL Atlas recommends the G210 60/120 Color Viewing Booths as high-specification and low-cost solutions for a laboratory.
M227C Pilliscope Assessment Viewer allows the user to assess pilling on tested fabrics against five standard photographs using Halogen high-incident illumination. These comparison photographs of either knitted or woven fabrics are mounted on a 5-sided drum and used sequentially to grade the samples. M&S suppliers may order a Holoscopic viewing system with holograms of knitted or woven fabrics on the 5-sided drum.
M227PAV Universal Pilling Assessment Viewer is designed for all standards where the assessment of pilling is necessary, whether grading against control fabrics or photographs. Note that photographs are not included and must be ordered separately as required by the individual standard. Visit the SDL Atlas website or see the current SDL Atlas catalog for details and ordering information.
M227G Pillgrade™ Automatic Pilling Grading System removes the subjective element from grading and improves interlaboratory reproducibility. The Pillgrade 3D fabric scanning system objectively and repeatably grades fabric specimens for surface properties and can ensure agreement on grading throughout the textile supply chain. The system outputs pilling and fuzziness data plus a 1.0 to 5.0 pilling grade according to ASTM and ISO standards. A user supplied computer running either Windows 2000 or Windows XP is needed. For more details on the computer requirements and data output, please visit the SDL Atlas website, www.sdlatlas.com, or see the current SDL Atlas catalog for details and ordering information.