As people’s requirements for the performance of fiber products increase, popular fabrics at home and abroad use a large number of Tencel, Modal, Viloft, bamboo pulp fiber, bamboo original fiber, soy protein fiber, and chitin, which are mainly comfortable and environmentally friendly. fiber etc. However, there are also some products on the market that are mixed with fish, and accurately understanding and identifying new textile fibers has become an important issue today. The author tested, analyzed and compared the identification methods of several new textile fibers, and proposed a more practical, simple and easy systematic identification method.
1. Combustion identification method
The combustion identification method uses the different chemical compositions of various fibers , the difference in combustion characteristics produced can be used to identify the type of fiber. The method is to take a small bundle (about 50 to 100 mg) of fiber sample and burn it on fire, carefully observe the fiber burning characteristics and the shape, color, softness and hardness of the residue, and smell the smell of smoke produced by it. The combustion characteristics of several new textile fibers are shown in Table 1.
The combustion method mainly observes and identifies fibers from three aspects: (1) Characteristic differences in fiber combustion states. For example, the difference between fibers that do not melt or shrink when close to the flame and curl and melt; how fast the fiber burns in the flame, and whether it has burning properties after leaving the flame. (2) The smell produced when fibers are burned.
This mainly depends on the differences in the internal chemical structure of the fibers. It is easier to distinguish cellulose fibers (smell of burning paper or burnt ashes), protein fibers (smell of burning hair) and synthetic fibers. (3) Differences in the morphology of the residue after fiber burning.
The first type is complete combustion ash, which is characterized by loose, soft, small, irregular shape, gray-black or gray-white color, such as Tencel, Modal, etc. in cellulose fibers. Viloft, bamboo pulp fiber, cotton, viscose, linen, etc.;
The other type is incomplete combustion residue, which is characterized by hard, brittle, regular shape and black color , such as wool, silk, milk protein fiber, soybean fiber, chitin fiber, etc. among protein fibers;
The third category is a melting, highly cohesive solid, which is characterized by hard lumps , hard balls, most of the colors are black, dark brown, brown, milky white, etc., such as polyester, vinylon, nylon, polypropylene, etc. among synthetic fibers.
The combustion method has its limitations. It is only suitable for the identification of single-component fibers, yarns and fabrics. It is not suitable for composite fibers, chemically modified fibers and chemical finishing agents. Treated fibers (such as flame retardant treatment). In addition, due to the differences in people’s perception of the combustion state and the color, taste and shape of the residue, as well as the influence of factors such as the surrounding environment (such as air flow velocity, dimness of light, etc.), it is difficult to detect fibers with no obvious difference in combustion characteristics. Accurately identify the specific type of fiber.
2. Microscopic observation method
Microscopic observation method is to use a microscope to observe the longitudinal and cross-sectional morphology of various fibers, and compare the standard microscopic photos and photos of fibers according to their morphological characteristics. Standard data for identification of fibers. The longitudinal and transverse microstructural morphological characteristics of several new textile fibers are shown in Table 2 and Figures 1~15.
Microscopic observation is a widely used identification method that can accurately identify specific varieties of natural fibers. Fibers of the same type (such as cellulose fibers and protein fibers) with the same or similar combustion characteristics have greatly different longitudinal and transverse morphological characteristics. Microscopic observation is an effective method to identify them. Among the new textile fibers, Tencel, Modal, Viloft, and bamboo pulp fibers are all cellulose fibers like cotton and linen. Their combustion characteristics and solubility properties are the same, but their longitudinal and transverse shapes have obvious differences and differences. They can be observed with a microscope first. method for identification. However, with the rapid development of chemical fibers, there are many types of special-shaped fibers. After preliminary identification of fibers using a microscope, other methods must be used to confirm them.
3. Dissolution method
The dissolution method is to identify fibers based on the different chemical compositions of various fibers and the differences in their solubility properties in different chemical reagents. During the test, a small amount of fiber sample can be placed in a test tube and a certain reagent (ratio of sample to reagent)For example, 1:100), under certain conditions, observe its solubility properties, that is, dissolution, rapid dissolution, partial dissolution or no dissolution, etc. See Table 3.
The dissolution method is a very widely used method. This method is simple to operate, easy to prepare reagents, has high accuracy, and is not affected by blending and dyeing. . Not only used for qualitative analysis of textile fibers, but also for quantitative analysis of blended products. However, when using this method to identify fibers, it must be noted that the solubility performance of fibers is not only related to the type of reagent, but also to the concentration of the reagent, the temperature during dissolution, and the time of action, etc.
To accurately identify the type of fiber, dissolution conditions must be strictly controlled. At the same time, it can be seen from Table 3 that one reagent can often dissolve a variety of fibers. If the dissolution method is used to identify a fiber alone, several different reagents need to be used for dissolution tests. For these reasons, under normal circumstances, the author recommends that the dissolution method be used to verify test results after preliminary identification by microscopic observation and combustion methods.
There are many methods for identifying textile fibers. In addition to the above three identification methods, there are also melting point method, density method, fluorescence method, etc. Modern testing methods, such as infrared absorption spectroscopy and X-ray diffraction, are methods to study the internal structure of fibers. Since the internal structures of various fibers have different characteristics, they can also be used to identify fibers. However, these methods require certain instruments and analytical techniques, and are rarely used in actual production.
4. Conclusion
The qualitative identification of textile fibers is a detailed and complex task, and each identification method has its own characteristics and scope of application. In actual identification, a single method cannot generally be used. Instead, several methods must be reasonably selected, appropriately combined, correctly used and comprehensively analyzed in order to draw the correct conclusion. Through the experimental demonstration and comparative analysis of several new textile fibers by the above three identification methods, a simple, intuitive, fast, accurate and easy-to-operate systematic identification method was established.
(1) First choose a simple and easy combustion method to divide fibers into three categories, namely cellulose fiber, protein fiber and synthetic fiber.
(2) Among cellulose fibers, by observing the longitudinal shape of the fiber, cotton is the one with natural twists; there are three types of fibers with horizontal knots and vertical lines, namely hemp, bamboo fiber, and flax. Among them, the cross-section is polygonal, with a small middle cavity, which belongs to flax; the waist-round one has a middle cavity and cracks, and the cross-section is thicker and uneven in thickness, which is ramie; the waist-round one has a middle cavity and cracks, and the cracks are deep and dense, and the thickness The more uniform one is bamboo fiber.
(3) Among Tencel, Modal, Viloft and bamboo pulp fibers, Viloft’s cross-section has a unique wall stack shape and shallow sawtooth, with continuous and multiple longitudinal fine grooves in the longitudinal direction, which is easy to It can be identified from among them that although the cross section of bamboo pulp fiber has a zigzag shape similar to that of viscose fiber, it has no obvious skin-core structure (different from viscose), and the zigzag shape is not as obvious as that of viscose fiber; Tencel and Modal fibers The cross-sectional shapes are similar, but under the microscope, the cross-section of Modal fiber is close to a round or waist-round shape, with a skin-core layer, black spots on the skin-core layer, and a thicker skin. If you look closely, you will find 1 or 2 grooves on the longitudinal surface. The cross-section of Tencel fiber is relatively regular and circular, with a thin cortex, smooth, thin and consistent longitudinal surface. The fiber is straight.
(4) Among protein fibers, when chitin fiber burns, it not only has the characteristics of cellulose fiber that does not melt, does not shrink, and burns rapidly, but also has the fishy smell of protein fiber hair, and in 88% formic acid solution It can be dissolved by boiling at medium; the milk fiber has no scales in the longitudinal direction (different from wool), the cross section is nearly round (different from silk), and has a protein smell when burned (different from non-protein fibers such as cotton, linen, chemical fibers, etc.), and can be used with 2.5 % NaOH is dissolved for 30 minutes, and the fiber swells into a jelly-like form for further confirmation; the cross section of the soybean fiber is irregular, flat, dumbbell-shaped or approximately waist-round, with an island structure and fine pores. There are obvious and irregular longitudinal cracks. The uneven features of grooves and flat islands can be confirmed by the expansion phenomenon of 88% formic acid at room temperature. </p
