Surface Wear Analysis of Fabrics
Over the past several years, a task group of ASTM International’s Subcommittee D13.60 on Fabric Test Methods, Specific, has focused on improving the measurement and evaluation of fabric surface wear, specifically the problems of abrasion and pilling. The task group, which is composed of members from all segments of the textile industry, government, and academia, provides a forum for discussion of the many issues associated with standard test methods for measuring resistance to abrasion and pilling. With the introduction of computer-aided video image analysis techniques, the task group is guiding the development of this technology to provide quantitative measurements of fuzzing and pilling.
ASTM’s Subcommittee D13.60, part of Committee D13 on Textiles, is dedicated to the development of standards for evaluating the surface wear, strength and construction characteristics of textile materials. Of the 26 active standards maintained by D13.60, 10 are devoted to measuring and predicting abrasion and pilling resistance of consumer and industrial fabrics.
|Side view of textile surface showing fuzz and pills.
Changes in the surface of a fabric during processing, use, and care can be as obvious as loss of structural integrity due to abrasion or as subtle as fuzzing, pilling, or apparent changes in color and texture (see the photo above and the definitions sidebar below). These latter phenomena, although less likely to affect a textile’s functional performance, frequently result in consumer dissatisfaction and subsequent disposal of textile products long before they reach the end of their useful wear life.
||The wearing away of any part of a material by rubbing against another surface.
||Untangled fiber ends that protrude from the surface of a yarn or fabric.
||Bunches or balls of tangled fibers which are held to the surface of a fabric by one or more fibers.
| Pilling resistance
||Resistance to the formation of pills on the surface of a textile fabric.
Evaluating surface wear has been a challenging and contentious issue since the first standards for pilling and abrasion were developed in the late 1970s and early 1980s. A few standards have been developed more recently, but most of the theoretical and empirical research on surface wear dates back before the 1950s when durability of military uniforms was a priority. A major concern associated with all wear testing is the ability of accelerated laboratory instrumentation to simulate the surface wear that occurs during normal use. This concern is further complicated if antiquated instrumentation has poor reliability and the evaluation of results relies on subjective human ratings. An additional challenge unique to the textile industry is the inability to define “normal” wear since consumers’ expectations vary widely and typical performance for one product cannot necessarily be expected or specified for another.
These limitations have resulted in the development of a plethora of different abrasion and pilling testers (many whose reliability are currently in question), different evaluation procedures that rely on subjective human ratings, and photographic adjuncts that no longer represent contemporary textiles available to today’s consumers. Because of these limitations, most Committee D13 performance specifications do not include recommendations related to abrasion and pilling resistance a critical omission for many textile products. Periodic reapproval and upgrade of abrasion and pilling standards have been and continue to be crippled by these problems. With these issues in mind, Subcommittee D13.60 formed an abrasion and pilling task group to identify weaknesses of active wear-related standards and investigate new approaches to improve the evaluation of abrasion and pilling resistance.
Wear performance is of critical importance to manufacturers, distributors, and retailers from every segment of the international textile production chain. Consequently, representatives from these segments were included in the task group. Other task group members include manufacturers of testing equipment and calibration fabrics, representatives from independent testing laboratories, military research facilities, consulting firms, and academia. Ultimately, all task group members are consumers of textile products with a vested interest in improving surface wear testing and evaluation. The collegiality and cooperation within the abrasion and pilling task group transcends corporate competition and has contributed to its remarkable productivity and accomplishments.
Initial Efforts: Abrasion and Pilling Brainstorming Sessions
Subcommittee meetings are an important mechanism for conducting ASTM business. However, these meetings do not provide the time or flexibility for less structured group activities. Since 1999, the abrasion and pilling task group has scheduled informal meetings during the first evening of each committee week to discuss the improvement of related standards. Work items identified during these sessions are presented at regularly scheduled meetings of Subcommittee D13.60 to keep all members in the communication loop and to collectively develop an agenda for the next brainstorming session. ASTM headquarters assists with publicizing the agendas and coordinates the scheduling of the sessions. Subcommittee D13.60 approves and facilitates work items proposed by the task group.
Issues identified by the task group in their brainstorming sessions have provided a framework for defining subcommittee goals and prioritizing activities. Topics initially discussed by the task group have evolved into D13 seminars or industry-sponsored research projects. The goals and accomplishments of the task group are summarized below (see also the sidebar below).
|Strategies used by the abrasion and pilling task group to improve related standards
|• Informal brainstorming sessions
||• Working groups within the task group
|• Ruggedness testing
||• Group projects
|• Vendor exhibitions
|• Interlaboratory tests
||• New and revised standards
|• Changing test methods to guides
||• New and revised adjuncts
Goal 1: Improve Instrumentation and Test Methodology
ASTM standard E 456, Terminology Relating to Quality and Statistics, states, “A ruggedness test is a planned experiment in which environmental factors or test conditions are deliberately varied in order to evaluate the effects of such variation.” The abrasion and pilling task group identified related standards that were most problematic and gave them a priority ranking for ruggedness testing. The flex abrasion tester associated with D 3885, Test Method for Abrasion Resistance of Textile Fabrics (Flexing and Abrasion Method), was selected for the first ruggedness test because of the many reported problems with reproducibility.
A ruggedness test project, sponsored by Subcommittee D13.60, facilitated by the ASTM Contract and Project Management Services department and funded by a consortium of 16 corporate stakeholders, was organized in 1999. Industry participants included representatives from domestic and international fiber, yarn, and fabric manufacturers, instrument manufacturers, commercial testing laboratories, and trade organizations.
Research conducted at the University of Georgia revealed significant problems with tensioning the test specimens, variability of standard calibration fabrics, and inconsistent performance of the flex bar used to apply reciprocal force to the specimen. This information resulted in the redesign of the specimen clamps and stabilization of the flex block by instrument manufacturers. New specifications were developed for the calibration ribbon, and preconditioning the flex bar with a second fabric was discontinued.
Test Method D 3885 is currently undergoing major revisions, and interlaboratory testing is planned. In the interim, a significantly improved flex tester is commercially available, and instruction manuals have been revised. Results of this ruggedness test (1) are on file at the Information Center at ASTM headquarters. These will be further disseminated through textile journals and trade publications. At the start of the ruggedness project, the steering committee prioritized standards for evaluating abrasion and pilling machines, and they likely will recommend a second ruggedness test.
Below is a list of other activities of the abrasion and pilling task group related to improvement of instrumentation and test methodology.
1. Interlaboratory evaluation of five pilling and two abrasion test methods have been organized by task group members. Precision and bias statements have been completed or are in progress. Interlaboratory evaluation of other testers is planned as reapproval dates approach.
2. Rather than letting a test method languish in the subcommittee balloting process and endanger its active status, the abrasion and pilling task group has taken a proactive approach to the standards maintenance and reapproval process. If a test method is known to be deficient in methodology, instrumentation, and/or evaluation, it may be reballoted as a standard guide. This strategy allows the task group time to implement improvements and still retain the standard for active use. When revisions subsequently reach full consensus, the guides will transition back as significantly improved and more reliable test methods.
3. Adjuncts used with standards sometimes develop problems or become outdated. This situation has been the motivation for several projects undertaken by the task group. The cotton sliver and cork liner, which are integral components of D 3512, Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Random Tumble Pilling Tester, were evaluated, and new material specifications were developed. Task group members also have determined that the design and brand of viewing cabinets and the type and angle of illumination are not critical considerations when visually rating abraded fabrics. This information, obtained using fabrics from previous interlaboratory tests, led to a broadening of the viewing procedures required for six pilling and abrasion standards and provided the foundation for future consideration of alternative evaluation methods.
4. Development of new testing instrumentation also is of interest to the abrasion and pilling task group. A new pilling test method has been approved by Subcommittee D13.60 and, after determination of precision and bias, will be submitted to Committee D13 and the Society for approval.
Goal 2: Improve Visual Evaluation and Automate Evaluation Procedures Incorporating New Technology
The limitations of visual evaluation are well-known and include the variability and inconsistencies associated with most human activities. During brainstorming sessions, task group members identified specific problems with the photographic standards currently used to visually rate pilling resistance and proposed the following work items. Four working groups within the task group were formed to individually address these concerns.
1. Pilling and fuzzing are dynamic processes that start with the formation of fuzz. The next step is the entanglement of fuzz to form pills. These pills continue to mature and increase in density while either increasing or decreasing in size. Finally, it is possible that the pills will wear off through breaking of the anchor fibers or by untangling and reverting back into fuzz. This process is continuous throughout the wear life of a fabric. Consumers’ tolerance for fuzzing and pilling varies with the type of fabric and its intended end use.
The current photographic standards (originally developed for use with D 3512 and D 3514, Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Elastomeric Pad, but used in practice to evaluate pilling produced by any tester) do not include fuzz at its various stages of formation and represent only one stage in the pilling life cycle maturation. A working group within the abrasion and pilling task group is working to incorporate fuzz into the standard rating procedures used with all of the ASTM pilling test methods. Options under consideration are to incorporate fuzz, either together or separate from pilling, and to broaden the increments or rating steps to better encompass the dynamic process of surface wear.
2. Another working group has been formed to broaden the scope of ASTM photographic standards to include knit fabrics. The current photographic standards represent pilling only on woven fabrics. It is well known that a greater number of pills with different shapes form on knit fabrics than on woven. Originally developed in the late 1970s, the current photographic standards also do not represent contemporary fabrics commonly used by consumers. The evaluation of photographic standards used commercially and by other standards developing organizations is in progress and will provide direction for the working group assigned to this issue.
Until recently, visual ratings based on photographic standards were one of the few options for evaluating pilling resistance. With advances in computer and video technology, the ability to automate the analysis of abraded fabrics has become a reality. This transition to automated evaluation has raised a number of issues for the abrasion and pilling task group.
3. At the October 2004 committee week, a Surface Measurement Technology Exhibition was planned by the task group and hosted by Subcommittee D13.60. (2) The purpose of this event was to bring together software vendors of image analysis systems for measuring surface defects with specific emphasis on fuzzing and pilling. The exhibition included presentations from image analysis vendors, a summary of current imaging technology, and concurrent demonstrations by individual vendors.
The task group is currently sponsoring a subcommittee ballot that will broaden pilling evaluation methods to include automated procedures. (3) Interlaboratory tests incorporating image analysis software are in the planning stage and will be a cooperative effort among task group members, vendors, and users.
Initially, the transition to automated analysis probably will require correlation with visual ratings. Producers, instrument manufacturers, and laboratory personnel will need training in the use and meaning of automated ratings. Users of the abrasion and pilling standards will wonder how visual ratings correlate to the new system. Interlaboratory tests incorporating both systems will provide some of this information. Ultimately, the many advantages of an automated rating system will prevail, and its use will become accepted practice rather than theory.
Outlook for the Future
The activities and accomplishments described above are just some examples of how subcommittees within Committee D13 are working to improve and update their standards within the full consensus process. Surface wear testing and evaluation will always be a challenge for Subcommittee D13.60. However, many issues are being addressed by the abrasion and pilling task group, whose main source of inspiration has been informal brainstorming sessions held in conjunction with regular subcommittee meetings. Most members of Subcommittee D13.60 and its abrasion and pilling task group would agree that significant progress is on the horizon.
The author gratefully acknowledges all of the members of the abrasion and pilling task group who have worked so diligently to accomplish the goals set forth by Subcommittee D13.60. A special thanks also to James A. Knopp, North Carolina State University at Raleigh, and Randall R. Bresee, the University of Tennessee at Knoxville. //
(1) Annis, P.A. and Brewer, M.S. Subcommittee D13.60 Research Project (#1037) on Ruggedness Testing of Textile Abrasion and Pilling Machines: Flex Abrasion Testing (D3885-99) Final Report (Number D13-1107), sponsored by Subcommittee D13.60 on Fabric Test Methods, Specific, ASTM International, West Conshohocken, Pa., 2002.
(2) “Subcommittee on Fabric Test Methods to Host Surface Measurement Technology Exhibition,” ASTM Standardization News, September 2004, pp. 10-11.
(3) ASTM WK6804, Test Method for Pilling Resistance and Other Related Surface Changes of Textiles Fabrics (Martindale Pressure Tester Method); WK6805, Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Brush Pilling Tester; WK6806, Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Random Tumble Pilling Tester; and WK6807, Test Method for Pilling Resistance and Other Related Surface Changes of Textile Fabrics: Elastomeric Pad