FIBRE TEST
Fiber Identification Tests
Recognition and identification of fiber content in fabrics has become extremely difficult because of the growing variety of types of fibers, the blending techniques in yarn and fabric construction, and the finishes that affect the appearance and hand of the fabrics. Therefore, certain tests are used for identification and verification.
The non-technical tests The consumer has the greatest handicap in identifying fiber content of fabrics. Should the identification and/or care labels be mutilated or lost from a textile product, one may not know the composition of the fabric and therefore not know what to expect of it. Because one is usually not in a position to make a laboratory analysis, reliance must be placed upon certain non-technical tests.
These non-technical tests do not require any special equipment for identifying textile fibers. Although these methods have certain limitations, they are useful because they are simple to perform and, under certain circumstances, provide ready identification.
Feeling Test The feeling test requires perception if it is to be of any value. Skilled perception is acquired only after handling many different fabrics over a period of time. To understand the feeling test, place your finger on a sample of wool. The heat generated by the finger remains in the area because wool is a nonconductor of heat. Consequently, wool fabric feels warm to the touch. If your finger is placed on a sample composed of the vegetable fibers-that is, cotton, linen, or even rayon-the heat of the finger passes off because such fibers are conductors of heat. These fabrics, therefore, feel cool to the touch. Limitations of this test become apparent when examining and comparing fabrics of different fiber contents.
Burning Test To recognize the composition of fabrics by the burning test, the sample of fiber, yarn, or fabric should be moved slowly toward a small flame and the reaction to the heat carefully observed. One end of the sample should then be put directly into the flame to determine its burning rate and characteristics. After it is removed from the flame, the burning characteristics should continue to be observed and the burning odor noted. After the sample has cooled, the ash should be examined for characteristics such as amount, form, hardness, and color.
The burning test is a good preliminary test for identifying categories of textile fibers, but it does not identify specific fibers themselves. It offers valuable data regarding appropriate care and indicates general fiber groupings. Problems arise when yarns or fabrics composed of two or more fibers are tested. The test will usually give the reaction of the fiber that burns most easily. But if a thermoplastic (heat-sensitive) fiber is involved, it might melt or withdraw from the flame and pull the other fibers with it.
Many fabrics either do not have a visible yarn structure or the yarns are difficult to remove, such as in knitted fabrics. When this occurs the use of the sliver of fabric is acceptable. However, if yarns have been used, it is always desirable to obtain single yarns for the burning test. As noted, if more than one type of fiber has been used in forming the product, the burning test will not give a meaningful result.
The technical tests
Where laboratory equipment is available, much more reliable testing techniques may be employed. However, these require technical knowledge and skill, particularly in handling many chemicals.
Microscope Test It is possible to be quite specific in fiber identification of several fiber types through the use of microscopes. For this test fibers should be mounted to obtain views of both the lengthwise and the crosswise dimensions, this test provides some degree of specificity and for some fibers is a positive identification. However, several of the man-made fibers are so similar that microscopic evaluation does not give a specific identification.
Identification by microscope with a magnification of at least 100 power is a reliable test that can be used to distinguish the fibers. This is particularly true of natural fibers. Manmade fibers are sometimes more difficult to identify because some are very similar in appearance and variants can complicate matters further. Knowing what the fibers look like under the microscope will also help you understand other identification tests. Certain manufacturing and finishing processes, such as mercerizing and delustering, affect the appearance of a fiber under the microscope. Besides, a very dark-colored fabric cannot be identified under the microscope because light, which is necessary for identification, cannot pass through a dark substance. The dyestuff must be removed, or stripped, by the use of bleach, which is determined by the suspected composition of the fabric. When stripping is essential and there is considerable doubt as to the composition of the fabric, chemical tests are advisable. Chemical Tests In addition to the microscope, chemical tests are another technical means of identifying fibers. But chemical tests are not intended for the general consumer. Their value is demonstrated, however, by the fact that some consumer magazines and commercial firms have their own laboratories for testing fabrics.
There are two chemical testing methods that may effectively be used: stain and solvent. One stain technique is the double-barreled fiber identification (DBFI). Every commonly known fiber has its own distinct two-color reactions when treated with the stain. A fiber stained at the boil in the presence of dilute acetic acid will turn to a color specific only to that fiber; when that fiber is stained in the presence of a mild alkali, such as carbonate of soda, that fiber will turn to an entirely different color that is also specific only to that fiber. For example acetate turns light green in acetic acid, but orange in dilute carbonate of soda: nylon stains light brown in one bath, bright red in the other.
The solvent method of identification become increasingly difficult, as fibers that are chemically similar have been developed and more fibers are blended and mixed in fabrics. There is no individual solvent or chemical identification for each fiber and no single solvent procedure for separating and identifying fibers in combinations. However, testing by solvents is very effective when it is used for eliminating or crosschecking.
In order to obtain accurate results, the fabrics to be tested should be thoroughly cleaned and finishing agents should be removed. The fabric should be un-raveled, yarns untwisted, and the fibers put in as loose a form as possible.
Recognition and identification of fiber content in fabrics has become extremely difficult because of the growing variety of types of fibers, the blending techniques in yarn and fabric construction, and the finishes that affect the appearance and hand of the fabrics. Therefore, certain tests are used for identification and verification.
The non-technical tests The consumer has the greatest handicap in identifying fiber content of fabrics. Should the identification and/or care labels be mutilated or lost from a textile product, one may not know the composition of the fabric and therefore not know what to expect of it. Because one is usually not in a position to make a laboratory analysis, reliance must be placed upon certain non-technical tests.
These non-technical tests do not require any special equipment for identifying textile fibers. Although these methods have certain limitations, they are useful because they are simple to perform and, under certain circumstances, provide ready identification.
Feeling Test The feeling test requires perception if it is to be of any value. Skilled perception is acquired only after handling many different fabrics over a period of time. To understand the feeling test, place your finger on a sample of wool. The heat generated by the finger remains in the area because wool is a nonconductor of heat. Consequently, wool fabric feels warm to the touch. If your finger is placed on a sample composed of the vegetable fibers-that is, cotton, linen, or even rayon-the heat of the finger passes off because such fibers are conductors of heat. These fabrics, therefore, feel cool to the touch. Limitations of this test become apparent when examining and comparing fabrics of different fiber contents.
Burning Test To recognize the composition of fabrics by the burning test, the sample of fiber, yarn, or fabric should be moved slowly toward a small flame and the reaction to the heat carefully observed. One end of the sample should then be put directly into the flame to determine its burning rate and characteristics. After it is removed from the flame, the burning characteristics should continue to be observed and the burning odor noted. After the sample has cooled, the ash should be examined for characteristics such as amount, form, hardness, and color.
The burning test is a good preliminary test for identifying categories of textile fibers, but it does not identify specific fibers themselves. It offers valuable data regarding appropriate care and indicates general fiber groupings. Problems arise when yarns or fabrics composed of two or more fibers are tested. The test will usually give the reaction of the fiber that burns most easily. But if a thermoplastic (heat-sensitive) fiber is involved, it might melt or withdraw from the flame and pull the other fibers with it.
Many fabrics either do not have a visible yarn structure or the yarns are difficult to remove, such as in knitted fabrics. When this occurs the use of the sliver of fabric is acceptable. However, if yarns have been used, it is always desirable to obtain single yarns for the burning test. As noted, if more than one type of fiber has been used in forming the product, the burning test will not give a meaningful result.
The technical tests
Where laboratory equipment is available, much more reliable testing techniques may be employed. However, these require technical knowledge and skill, particularly in handling many chemicals.
Microscope Test It is possible to be quite specific in fiber identification of several fiber types through the use of microscopes. For this test fibers should be mounted to obtain views of both the lengthwise and the crosswise dimensions, this test provides some degree of specificity and for some fibers is a positive identification. However, several of the man-made fibers are so similar that microscopic evaluation does not give a specific identification.
Identification by microscope with a magnification of at least 100 power is a reliable test that can be used to distinguish the fibers. This is particularly true of natural fibers. Manmade fibers are sometimes more difficult to identify because some are very similar in appearance and variants can complicate matters further. Knowing what the fibers look like under the microscope will also help you understand other identification tests. Certain manufacturing and finishing processes, such as mercerizing and delustering, affect the appearance of a fiber under the microscope. Besides, a very dark-colored fabric cannot be identified under the microscope because light, which is necessary for identification, cannot pass through a dark substance. The dyestuff must be removed, or stripped, by the use of bleach, which is determined by the suspected composition of the fabric. When stripping is essential and there is considerable doubt as to the composition of the fabric, chemical tests are advisable. Chemical Tests In addition to the microscope, chemical tests are another technical means of identifying fibers. But chemical tests are not intended for the general consumer. Their value is demonstrated, however, by the fact that some consumer magazines and commercial firms have their own laboratories for testing fabrics.
There are two chemical testing methods that may effectively be used: stain and solvent. One stain technique is the double-barreled fiber identification (DBFI). Every commonly known fiber has its own distinct two-color reactions when treated with the stain. A fiber stained at the boil in the presence of dilute acetic acid will turn to a color specific only to that fiber; when that fiber is stained in the presence of a mild alkali, such as carbonate of soda, that fiber will turn to an entirely different color that is also specific only to that fiber. For example acetate turns light green in acetic acid, but orange in dilute carbonate of soda: nylon stains light brown in one bath, bright red in the other.
The solvent method of identification become increasingly difficult, as fibers that are chemically similar have been developed and more fibers are blended and mixed in fabrics. There is no individual solvent or chemical identification for each fiber and no single solvent procedure for separating and identifying fibers in combinations. However, testing by solvents is very effective when it is used for eliminating or crosschecking.
In order to obtain accurate results, the fabrics to be tested should be thoroughly cleaned and finishing agents should be removed. The fabric should be un-raveled, yarns untwisted, and the fibers put in as loose a form as possible.