Textile News, Apparel News, RMG News, Fashion Trends
Testing & Standards

Practices and importance of testing and analysis of textiles

Introduction:

The primary purpose of textile testing and analysis is to assess textile product performance and to use test results to make predictions about product performance.  Product performance must be considered in conjunction with end use; therefore, tests are performed with the ultimate end use in mind.  Examples of testing for end-use performance include testing draperies for light fastness or tire cords for strength.  The key question in testing for end-use performance is, Does the textile meet the needs of the application for which it will be used?  One problem in this category of testing is that often one does not know specifically how a textile fabric will be used by consumers, and because of the variability of consumer behavior, even when the end use is known, the actual performance expectations may not be well understood.  However, organization and manufacturers establish performance specifications for various end uses, and use these specifications to assess the suitability of textile fabrics or products for the intended use. Manufacturers of apparel, home furnishings products, and industrial textile products also use specifications in acceptance testing of their suppliers’ products. For the majority of clothing items aesthetic factors provide the initial impulse of attraction and may be the only factors which influence the decision to buy.  The exception is the requirement that the item should fit.  But even fit may be a function of fashion and style.  Such aesthetic factors as handle, drape, colour and style all interact in a complex manner and are crudely and subtly influenced by social factors – a desire to be in fashion, a desire to present an image, for example.

Clearly there are exceptions where performance is an over-riding consideration, as in protective clothing, even if only for a leisure pursuit.  However, the comment by a customer that they do not consider performance when purchasing is quite frequently correct.  That does not of course mean that performance is unimportant to them.  Premature breakdown, whether of fabric, seam or simply a button falling off, may produce a customer complaint, and although the customer may not actually return the garment to the retailer, it may well result in an association in their mind of poor performance, which may influence their decision on another purchase.

Aesthetic and performance factors are, of course, inextricably linked with price.  The often-repeated statement that ‘you get what you pay for’ is generally associated with performance, but a customer’s concept of what the level of performance should be will vary considerably.  It is often influenced by aesthetic considerations.  Thus the concept of good quality is not a static issue operating at one level for all customers; it is influenced by aesthetics, performance and price, and is specific to an individual customer.

Aesthetic and performance factors are, of course, inextricably linked with price.  The often-repeated statement that ‘you get what you pay for’ is generally associated with performance, but a customer’s concept of what the level of performance should be will vary considerably.  It is often influenced by aesthetic considerations.  Thus the concept of good quality is not a static issue operating at one level for all customers; it is influenced by aesthetics, performance and price, and is specific to an individual customer.  An example of this is a silk tie.  To most customers this would represent good quality, but in performance terms silk is markedly inferior to polyester.  A polyester tie, however, would be considered of lower quality than a silk tie and, of course, would be cheaper.  In this situation aesthetic characteristics are dominating the opinion expressed.  This leads to a number of guidelines about the balance between aesthetics, performance and price:

  • For a given customer the balance required will change with the item being purchased.  A woman, for example, may apply very different criteria to the purchase of a dress for a social occasion from those applied to the purchase of a pair of school trousers for her son.
  • Balance is dependent on the socio-economic position of the customer.  Higher income group people will be willing to pay a high price for individuality in aesthetic terms and will be less concerned about durability, although they may expect high performance standards for the albeit short lifespan of the item.  Quality is not a single definable entity; it is a statement of the balance of actors which will satisfy an individual customer.
  • Overall economic factors may radically change the behavior of customers in terms of perceived requirements.  Credit restrictions and a harsh economic climate may not only lead to reduced purchase but also to greater attention to performance details such as durability.

An item of clothing is a summation of materials, starting with fibre, through yarn, fabric and trimmings which go to make it up.  The complexities of balancing aesthetics, performance and cost factors therefore apply to the selection and use of these materials.  Customers have perceptions of the aesthetic and performance values of all components of clothing items, although of course their judgment may be faulty and subject to misunderstood technical factors as well as ingrained social habits.  The classic example is the belief that wool is ‘warm’.  The act that wool garments constructed and designed in an appropriate way do give a high level of insulation does not mean that other fibres used in different constructions and with a wider variety of applications may not give insulation in a far more cost-effective way.  Nevertheless, the tradition of a wool overcoat remains and represents a level of social standing.

The main objective of testing and analysis are research & development, quality control, comparative testing, analyzing, product future, government regulation, selection of raw materials, product control, process control, process development, product testing etc,. They are elaborated as follows.

  1. Research and Development:

Textile products are evaluated during the development process.  This helps textiles scientists determine how to proceed at the each stage of product development.  This category also includes testing in order to study theories of fabric or fabric or fibre behavior.  With advances in research and development, new products and processes may require innovative testing procedures that are not provided through standard test methods.  Test methodologies developed for a specific research application within one laboratory often gain wider acceptance and eventually are developed into industry-wide standard test methods.

  1. Quality Control

Textile products are tested at various stages of production to assure quality processing and products.  For example, in dyeing processes, the fabric is evaluated to determine whether it is dyeing evenly.  Manufacturers may use quality-control testing as a marketing tool, in that trade names imply to the consumer that certain levels of quality are assumed to be standard for products produced by the manufacturer.  Quality-control testing aids the manufacturer in assuring that the expected level of quality is maintained.

  1. Comparative Testing

Comparative testing compares two or more products being considered by a company or government agency.  For example, a jeans manufacturer may perform a series of tests on denim fabrics from different suppliers prior to deciding which supplier to use for its product.  In selecting between competitive products, a fabric manufacturer also may test fibres or yarns from different suppliers.

  1. Analyzing Product Failure

Testing is done in this case to pinpoint defects in processing or design.  The example of the trouser pockets falls into this category.  Results from this type of test can be used to improve products, and are also used to determine liability in litigation.

  1. Government Regulations

Textile product testing is sometimes performed in order to meet government regulations.  Such regulations may require mandatory testing of products before they can be legally sold.  An example of this is the flammability testing of textiles.

  1. Selection of Raw Materials

‘Raw Materials’ is a relative term; the raw material of the spinner is the fibre, the raw material of the weaver is yarn, and that of the finisher is cloth.  One attribute common to most textile raw materials is their variation in quality.  Fibres vary in length, colour, and fineness; yarns vary in count, strength, and twist; fabrics vary in threads per inch, freedom from faults, and shrinkage.  Since prevention is better than cure it is sound policy to test the available raw materials to ensure the smooth running of production processes.  Unsuitable material can be rejected or perhaps put to another use.  The standards by which raw materials are accepted or rejected must be realistic, otherwise much will be rejected which in fact is good enough, or else a large amounts of inferior material will find its way into the flow of production and cause trouble.

The testing of fibres is generally not so important when dealing with manmade fibres and manmade continuous filament yarns, because they are supplied to customers’ requirements and their properties, including length, colour, and fineness are determined and controlled during their manufacture.

  1. Process Control

When processing goes out of control the amount of waste and their number of seconds increase, costs go up, and very often tempers too.  Higher end-breakages in spinning and winding departments and excessive looms stops due to warp or weft breaks affect the operatives as well as production.  A plan of production requires certain standard levels to which materials in process must conform.  Since it is impossible to maintain a chosen standard absolutely, limits on either side of the standard level are calculated and materials whose characteristics fall within these limits are allowed to pass forward to the next process.  In a spinning mill the most common characteristic measured is the weight per unit length of the lap, sliver, roving, or yarn.  The nominal hank or count is decided upon and control limits are calculated from test results.  In brief, a ‘quality control’ scheme is operated.

For maximum effectiveness the ‘process control’ test should be close to the processing machinery.  Quick answers are required to prevent excessive amounts of faulty material from getting through before detection.

  1. Process Development

Process development may be considered as a form of applied research.  The experimental work involved may be carried out in research, institutes, in pilot plants within the boundaries of the mill, or perhaps on the actual processing machinery.  In each case investigations into better, cheaper, and quicker methods of manipulating fibres and yarns are made.  The success achieved is often measured by the improvement in one or more characteristics of the material delivered after change in machine design or setting.  The effects of blending different materials may be the aim of the experiment.  Most trials of this nature require the testing of the material produced and it is important to be quite clear which properties are to be measured to avoid unnecessary waste of time and money.

  1. Product Testing

If we could be absolutely certain that our choice of raw materials was right and that our system of process control had maintained the stipulated standard levels, and then we could pack the end-products into cases with confidence, knowing that they would fulfil their intended purposes satisfactorily.  Mill managers would sleep better at night if this pipe dream were a reality.  Unfortunately our knowledge of the effect of the many variables possible in the structure of yarns and fabrics, including the effects of physical and chemical treatments, is limited.  The more we find out, the more we learn how much there is still to discover.  The testing of the product helps in the continual search for new knowledge.  Sometimes a forecast of the probable performance in a subsequent process is required.  A very old question of this type is ‘How well will this yarn weave?’ We are still looking for a simple test which will give us an answer near enough to the truth.

The performance of a finished article in actual service could be the object of a product test.  One thorny problem is the assessment of the resistance of a fabric to the ‘wear and tear’ of everyday use.  We could try to imitate the kind of treatment meted out to the fabric, rubbing it against abrasives, wetting it and drying it, bending it, stretching it, creasing it, and so on.  Such a test would indeed be complicated, and as someone once said, ‘Imitative tests are a snare and a delusion!’  Alternatively, we might subject the material to a series of laboratory tests, each of which tests only one property at a time.

2. Standard test methods and specifications:

The term standard is used often in regard to testing of products.  It may be ambiguous at times, as it can have several different meanings.  It can refer to the actual test method, or to the minimum acceptable level of performance on a particular test.  It is generally used as an adjective, in which we mean ‘uniform’, ‘controlled’, or ‘widely accepted’, as in a standard test method or a standard performance specification.  An exception is its use as a proper noun to refer to a specific, numbered, test method or specification.

  1. Standard Test Methods:

Development of Standard Test Methods

Test methods are developed for textiles and textile products by several different organizations.  They are typically developed in response to a need expressed by an individual manufacturer, a product user, or occasionally by a consumer group.  The example of the test for SA after laundering began as a widely perceived need to precisely define the degree of fabric wrinkling, at a time when there was a large research and development effort in the area of durable press (DP) finishes.  A similar situation paralleled the more recent introduction of inflatable restraints, or automotive air bags, resulting in the current development of tests for this product.  Another recent example is the urgent development of test methods for penetration of fabrics by blood-borne pathogens, largely a result of concern over transmission of the AIDS virus.  Test methods for blood-borne pathogens are addressed.

As explained in the section on Research and development, the initial development of a test method sometimes occurs within an individual lab or company, and the method is later adopted – perhaps in a modified form – by the industry-wide organization as a standard test method. An example is the wrinkle recovery angel test, which was originally developed by the Monsanto Company, but later modified and adopted by AATCC.

Whether the idea for a test method begins within an industry-wide organization or within an individual company, once the idea is adopted by the industry-wide organization, test method development typically takes place through committees composed of individuals representing companies or organizations that either will eventually use the test method or who have an interest in the objectives of the test method.  Committee members suggest approaches and laboratory trials are conducted within the various groups represented by the committee members.  Basically, through a process of trial and error, combined with committee members’ expertise in understanding the properties to be evaluated by the test method, the proposed test procedure is refined and the written, proposed method revised until it is acceptable to the working group actively involved in its development.

During this process, committee members are concerned with the validity of the test method, and the practically of following the test method in everyday use.  In this case, validity means whether the proposed method actually addresses the problem.  For example, if the purpose of the proposed test method were to evaluate the effects of abrasion on upholstery, then the questions of validity would center around whether the abrasion machine employed in the test provides the same forces that the upholstery would be subjected to in actual use as people repeatedly sit on the upholstered furniture.  The other concern that of the practically of conducting the test on a routine basis, involves considering the skill and training of the personnel who will perform the test, the cost of conducting the test, including the cost of time, equipment, supplies, and personnel, and the usefulness of the test results.  These are difficult consideration and often compromises and trade-offs must be made between validity and practicality.

In most organizations that develop standard test methods, once the test procedure is clearly defined, the proposed method then undergoes inter-laboratory trials.  Inter-laboratory testing can reveal problems with procedures that must be corrected, and they can also be used to determine whether the test method is applicable to a particular type of product; for example, does the method work only on woven fabrics, or can it also be sued for knits?  The primary purpose of the inter-laboratory test is to determine the precision of the test.  Precision indicates whether the test will repeatedly produce the same results on the same fabric specimen.  Inter-laboratory test determine the reproducibility of the test from one lab to another and from one operator to another.  A test which has a high level of precision has good inter-laboratory reproducibility and good between-operation reproducibility.

Following inter-laboratory testing and refinement of the method, the proposed test method is submitted to committee vote. When approved by the committee, the method must undergo balloting by other committees.  For example, in AATCC, after a proposed test method on weathering is approved by the weathering research committee, it must be approved by the Editorial Committee, and then by the Technical Committee on Research, which is composed of the chairs from many different research committees.  At each level of balloting, input from committee members is sought and is used to improve the test method.  At each level, attempts are made to resolve negative votes through written correspondence and conferences.

Finally, once a test method is approved as a standard test method for the organization (such as AATCC or ASTM), the method must undergo periodic reconsideration and re-approval in order to be retained as a standard test method.  This extensive development and review process is intended to assure that standard test methods meet the needs of users.  Test method development and revision are ongoing processes.  New test methods are introduced every year and older methods are dropped in response to the changing needs of the textile, apparel, and home furnishings industries and their consumers.

Format of Standard Test Methods

Test methods usually have a standard form, regardless of which organization developed them.  The sections of a test method include the following.
1. Test number and name – This usually also includes the year that the method was accepted or revised by the organization.
2.  Scope and purpose – This states what types of materials are covered by the test method and for what purpose the method was originally intended.
3. Definition of terms – Any terms that are not generally understood or that have definitions that are specific to the test method is defined.
4. Safety precautions – These are now required for most methods.  They prescribe special handling precautions for chemicals or equipment to be used during performance of the test.
5. Apparatus and materials – This section describes the instruments, devices, and materials that are required to conduct the test.
6. Test specimens – The size, number, and preparation of test specimens are explained.
7. Procedure – This section outlines in detail the steps to follow in performing the test, and any related factors that need to be controlled as the test is performed.
8. Evaluation or calculation of results – This explains how to acquire the data or result.  It includes explanation of any factors, such as ratings or formulas, needed to determine the results.
9. Report – This section indicates what information should be given in the report describing the test results.
10. Precision and bias – The precision to be expected from the test is outlined and may know biases in the test are identified.
11. Notes – Footnotes of additional information, including suppliers of instruments and material, as well as literature reference, are included in this section.

  • Test Criteria: Throughout this text and during your course in textile testing and analysis, you will learn the principles of numerous textile tests that are used to evaluate the performance of textile materials, and you will likely have the opportunity to conduct many of these tests yourself.  You will find that some standard textile test methods are easier that others to understand and interpret, and that some seem to be very applicable to end-use situations, while others do not.  In evaluating a textile material, you may be faced with a choice between two or more test methods that could be used to test a particular performance characteristic.  Textile test methods should meet three criteria, which can also be used when selecting among several standard methods.  These criteria are simplicity, reproducibility, and validity.
  • Simplicity: The criterion of simplicity means that a textile test method should be easy to read and understand.  It should provide enough information so as to leave no doubt as to how to perform the test, the procedure should be easily mastered with a minimum of practice, and the results should be easily obtained and interpreted.
  • Reproducibility: The results of a textile test should be reproducible with respect to user, time, and location.  Two individuals who perform the same test on the same specimen should obtain the same results.  Using the same test specimen, you should be able to obtain similar results from one day to the next.  It should be noted that a lack of reproducibility with respect to user to time may be associated with a lack of simplicity.  When a test is difficult to understand or perform or when it involves several steps or extensive handling of specimens, the results may also be difficult to reproduce.

Textile tests should also be reproducible with respect to location.  Using identical specimens, a student working in a laboratory in Athens, Georgia, should obtain the same results as a student performing the same test in Delhi, India, provided that the two students are correctly following the test procedure.
The ideal textile test method specifies how to control factors that could influence reproducibility.  In the wrinkling example presented, we noted the viewing distance, angle, lighting, and other such factors that could influence reproducibility in the determination of SA ratings.  In addition to these factors that are method-specific, environmental factors, (e.g., humidity and temperature) directly influence certain textile properties.  When not carefully controlled, these environmental factors can reduce the reproducibility of textile tests.  These factors are addressed.

  • Validity: The procedure followed in a textile test method should duplicate or closely simulate the actual end-use situation.  In other words, the test method should be applicable to the end use.

In selecting an appropriate test method, the criteria of simplicity, reproducibility, and validity should be considered in conjunction with the goal of a particular test.  For example, there are more sophisticated methods of evaluating fabric wrinkling than our example of SA ratings.  Highly accurate methods exist for counting the number of wrinkles, their depth, and angles. Such procedures can be useful in certain types of research, but for the shirt manufacturer whose goal is to provide a product with a wrinkle-free appearance that will be acceptable to consumers, the use of SA ratings represents a valid, and certainly a simpler approach that can be used in selecting shirting fabrics.

All three test criteria are rarely met simultaneously in one textile test.  Sometimes validity is partly compromised in order to achieve reproducibility, as in the case of weathering tests. Instrumental weathering tests cannot actually duplicate exposure to sun and changeable weather conditions, but they do offer reproducibility by allowing the user to control light exposure, temperature, and moisture, factors which would be impossible to control in actual outdoor exposure.  Most instrumental tests also enhance simplicity by providing accelerated conditions, and shorter test cycles than would be possible under real-life conditions.

In selecting and conducting any textile test, the basic goal of textile testing and analysis is to aid manufacturers, designers, and merchandisers in providing quality products that meet consumers’ performance expectations.

Several validity criterion problems are often associated with standard test methods.  Because they are ‘standard’ (i.e., uniform and controlled), the methods may not actually simulate realistic end-use conditions.  It is usually impossible for a standard test method to simulate the synergistic or antagonistic effects that may occur in actual use.  In the laboratory, we can usually test only one property at a time, for example, strength or abrasion resistance.  However, in actual use, a textile product is subjected to many forces at the same time.  It is difficult to simulate this combination of effects in one standard laboratory test.

Further, laboratory tests are continuous, and usually accelerated, whereas actual wear is intermittent and characterized by low degree of stress.  This makes it difficult to simulate wear in a single laboratory test.  For example, fabric abrasion over the life of a shirt may be due to a combination of bending and rubbing at the elbows, occasional low-stress rubbing against the fabric of a jacket worn over the shirt, gradual abrasion at the cuffs and collar, and contact with other fabrics and surfaces during laundering; however, most laboratory tests are not designed to simulate all of these components of the abrasion process.  Lastly, because people are different, they will subject products to different kinds and degrees of wear, and will care for them differently.  These factors present further problems in testing for performance in end-use conditions.

In testing, the term, validity may imply that a valid test gives the true value of a property.  However, this is rarely the case. Most textile tests do not purport to give the absolute or true value of a property; rather, they are most often used to compare the performance of different products.

3. Performance Specifications

Standard performance specifications are based on standard test methods. In other words, the statement of how a fabric must perform in a particular end use is designated in terms of results on standard tests.  Table 1 is a portion of the ASTM Standard Performance Specifications for men’s and boys’ woven dress shirt fabrics, ASTM D 3477.

The characteristics listed in the left-hand column of the table are performance characteristics that ASTM committees determined were important for men’s and boys’ dress shirt fabrics.  For each of these characteristics, there is a standard test method.  Some of these characteristics correspond with standard ASTM test methods, while others correspond with standard AATCC test methods. The center column of the table designates the requirements with respect to each characteristic, specifically the minimum acceptable level of performance on each of the tests.

Table 1 : ASTM D 3477 – Standard Performance Specifications for men’s and boys’ woven dress shirt fabrics

Characteristic Requirements Section
Breaking strength (load) 111 N (25 lbf), min 7.1
Yarn slippage 67 N (15 lbf), min 7.2
Tear strength 6.7 N (1.5 lbf), min 7.3
Dimensional change:
Pressing 1% max, in each direction 7.4.1
Pressing and laundering 2% max, in each direction 7.4.2
Dry cleaning 2% max, in each direction 7.4.3
Colorfastness to:
Laundering
Alteration in shade Class 4, minD 7.5.1
Staining Class 3,B minD
Dry cleaning 7.5.2
Alteration in shade Class 4,A minD
Burnt gas fumes 7.5.3
Alteration in shade: Class 4,A minD
1 cycle on Original, and after 1 washing or 1 dry cleaning, or both Crocking 7.5.4
Dry Class 4,C minD
Wet Class 3,C minD
Perspiration (acid phase) 7.5.5
Alteration in shade Class 4,A minD
Staining Class 4,B minD
Light (20 AATCC SFU) Class 4,A minD 7.5.6
(Xenon arc)
Fabric appearance DP 3.5, minD 7.6
Flammability Pass 7.7

The final column in the table refers the user to the section of the specification that further explains the test methods and requirements.  The requirements and test methods listed in this table are discussed in the various chapters that correspond with the particular characteristics.  Appendix F includes a summary of ASTM performance specifications.

In establishing performance specifications, agreement is first reached on the desired characteristics.  The requirements, or the specific performance level for each characteristic, are more difficult to establish.

Manufacturers’ experience with consumers and suppliers is often a factor in establishing the minimum performance levels.  When the minimum performance level is set too low, almost every product will meet the specification, or ‘pass the test’ and find its way to the marketplace; however, consumer complaints may result because the product does not meet the consumer’s minimum requirement!  In contrast, when the minimum performance level is set too high, most products will fail.  This could result in limited availability and/or higher prices for consumers.  Obviously, the goal in establishing standard performance specifications is to make them match consumers’ performance expectations for the product.  In particular, a difficulty in implementing performance standards is that there is often poor correlation between different operators in different laboratories performing the same test on the same fabrics.  This factor makes it difficult to see the performance criteria level.

In most cases, the use of standard performance specifications is voluntary.  However, the fact that a product meets a performance specification is an indication of a certain level of quality, and can be an important selling point for the product.

Many manufacturers will establish their own performance specifications that exceed the minimum levels indicated in the standard performance specifications developed by an industry-wide organization, such as ASTM.

Safety specifications are a special case of standard performance specifications.  Safety specifications are usually set by a regulatory agency to ensure the safety of consumer products, in which case, manufacturers are required by law to meet the safety specification.  However, some voluntary safety standards, such as the upholstered furniture manufacturers’ voluntary flammability standard, are being considered for release as a mandatory standard.

Those setting safety standards may compensate for the reproducibility or validity problem (i.e., lack of correlation or applicability to end use) by building in large safety factors.  For example, in a voluntary standard performance specification for textiles, a 95% confidence level is generally acceptable, but a higher level, perhaps 99%, may be required for meeting safety specifications.  In other words, the safety standard is set high enough to offset different results from different labs, and essentially all the products still will be safe.

References:

1. Textile Testing and Analysis, Billie J. Collier & Helen H. Epps, Merrill Prentice Hall, New Jersey, 1999, ISBN 0-13-488214-8.
2. Principles of Textile Testing, J.E. Booth, CBS Publishers & Distributors Pvt. Ltd., New Delhi, 3rd Ed., 1996, ISBN 81-239-0515-7.
3. Textile Testing, Jewel Raul, APH Publishing Corporation, New Delhi, 2005, ISBN 81-7648-748-1.
4.Fashion Design and Product Development, Harold Carr & John Pomeroy, Blackwell Science Ltd. London, 1996, ISBN 0-632-02893- London, 1996, ISBN 0-632-02893-9.
5.Physical Testing, P. Angappan & R. Gopalakrishnan, SSM Institute of Textile Technology, Komarapalayam, 1991.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

Related posts

M.B. Trade Corporation’s seminar shows path to overcome future challenges of textile industry

Textile Today

IDFL officially unveils another testing lab in Bangladesh

Textile Today

Latest Publications

View All