1、 Tactile visual measurement

It is to identify the fiber according to its appearance, color, feel, stretching and other characteristics. It can be divided into natural fiber and chemical fiber. For example, natural fiber has poor length uniformity, while chemical fiber generally has regular length. In natural fiber, cotton fibers are short and thin, often with various impurities and defects. The hemp fiber feels rough and hard. Wool fibers are curly and elastic. Silk is a long and slender silk with a special luster.

Among chemical fibers, viscose fibers have significant differences in wet and dry strength, while spandex has high elongation and elasticity. By utilizing these features, they can be distinguished. Other chemical fibers are difficult to distinguish by tactile and visual methods due to their similar appearance characteristics and to a certain extent, they can be determined by human factors.

2、 Combustion experiment method

The combustion method is a fast and simple method for identifying textile fiber categories. He roughly distinguishes fibers based on their combustion characteristics. The method of identification is to take a small bundle of unknown fibers, clamp them with tweezers, slowly approach the flame, observe the combustion state of the fibers when they approach, come into contact with, and leave the flame, as well as the characteristics of the odor emitted during combustion and the residue after combustion, to roughly identify the fibers.

Acetate fiber: Melts and contracts near fire. Burning occurs when exposed to fire, with a slower burning speed. Although acetate fiber is also a regenerated cellulose fiber, it is already a semi synthetic fiber after esterification, so it has a pungent vinegar taste when burned. The ash is black, not only loose but also brittle. The unburned parts become hard lumps.

Polyester: When burned, it curls, melts, and emits smoke, resulting in a yellow flame. When burning, it emits a fragrant aroma, and the ashes are black brown glass balls that can be crushed by hand.

Nylon: When exposed to fire, it melts on one side and burns slowly on the other. When burning, there is no smoke or a slight white smoke, and the flame is very small and blue. When burning, it has a celery aroma. The ash is in the shape of a light brown glass ball, which is not easily crushed.

Chloroprene: Shrinks quickly when approaching the flame, and extinguishes immediately after leaving the flame. There is a pungent smell of chlorine when burning. The ashes are amorphous black hard lumps.

Vinylon: Shrinks quickly during combustion, but burns slowly. There is little flame and black smoke. There is a smell of formaldehyde during combustion. The ash is a brown amorphous hard lump that can be crushed.

Acrylic fiber: When exposed to fire, it melts and burns slowly. The flame is white and very bright. Sometimes there is a hint of black smoke and a fishy smell. The ash is a small black hard ball, very fragile and fragile.

The combustion method is simple and easy to identify fibers, but it is not easy to determine blended products. The interwoven fabric takes one yarn from each warp and weft direction (i.e., straight and horizontal directions) and burns it separately

The combustion method is only applicable to single component fibers, yarns, and fabrics, while for mixed component fibers, yarns, and fabrics, as well as fibers and textiles that have undergone flame retardant or other finishing, it is often difficult to distinguish them by combustion due to changes in combustion characteristics.

3、 Microscopic observation method

Microscopic observation method is a commonly used method in fiber identification, which uses ordinary biological microscopes to observe the transverse and longitudinal morphology of unknown fibers.

Natural fiber have unique morphological characteristics, such as scales on the surface of wool, natural twist on cotton fibers, transverse and vertical lines on hemp fibers, triangular cross section on silk, and nearly circular cross section on chemical fibers, which must be verified by other methods.

Identification Methods for Several New Textile Fiber Fabrics

At present, several new types of recycled fibers developed and utilized in textile production are blended and interwoven with various other textile fibers to produce various new textile fabrics. To identify the composition of these fabrics, we usually remove the warp and weft yarns of the fabric, and then untwist the yarns to remove the fibers. The identification analysis is as follows:

(1) Firstly, make longitudinal fiber slices and observe the longitudinal morphology of the fibers under a microscope to clearly distinguish whether they contain cotton and wool. The longitudinal morphology of soybean protein fibers has irregular grooves and island like concavities, and the surface is not smooth. The grooves on the surface are different from the longitudinal morphology of Tencel fibers, Modal fibers, bamboo fibers, and viscose based chitin fibers, and can also be preliminarily distinguished.

(2) Using a slicer to slice the yarn, observe the cross-section of the yarn under a microscope and easily determine whether it contains cotton fiber, silk, Tencel fiber, Modal fiber, and soybean protein fiber.

(3) The cross-sectional shape of Modal fiber is similar to a waist circle and relatively smooth with a skin core layer. It is significantly different from the waist circle with a central cavity in the cross-sectional shape of cotton fiber, and is also significantly different from the waist circle with a skin core layer in the cross-sectional shape of vinylon fiber, which can be distinguished.

(4) The cross-sectional shape of Tencel fiber is circular, similar to polyester and acrylic; The cross-sectional shape of soybean protein fibers is flat, dumbbell shaped, and waist circular, similar to vinylon; The cross-sectional shape of silk is triangular, similar to that of chemical fibers with a triangular cross-section; These can be distinguished by combustion and dissolution methods to determine whether cellulose fibers, plant protein fibers, or chemical fibers.

(5) Although the cross-sectional morphology of bamboo fibers and viscose fibers is relatively similar, they are both serrated and difficult to distinguish. Therefore, they can be distinguished by coloring and burning methods, or by comparing their tensile properties. Bamboo fiber has a higher tensile breaking strength than viscose fiber, and a lower elongation at break than viscose fiber; Although the cross-sectional morphology of viscose based chitin fibers and viscose fibers is relatively similar, with serrated edges, the core layer of viscose based chitin fibers has obvious small voids, while the cross-sectional morphology of viscose fibers is serrated with a skin core layer. Using the combustion method to verify, the ash color is slightly different. The ash of bamboo fiber and viscose based chitin fiber is gray black, while the ash of viscose fiber is gray white.

4、 Method of solubility experiment

The dissolution method utilizes the principle of different dissolution characteristics of fibers in different chemical reagents to identify fibers. It is suitable for various fibers and their products, and has a wide range of applications. It can not only qualitatively analyze fiber varieties, but also quantitatively analyze various blended yarns, fabrics, and bicomponent fibers. This method is relatively accurate and reliable, and other methods are commonly used for preliminary identification before being confirmed by dissolution method. However, in the experiment, it is necessary to strictly control the concentration, treatment temperature, and time of chemical reagents in order to obtain more accurate experimental results.

Based on the above situation, the identification procedure for fibers is to first sort out the unknown fibers, and then use the combustion method to preliminarily divide the fibers into three categories: cellulose fibers, protein fibers, and synthetic fibers. Cellulose fibers and protein fibers have their own distinct morphological characteristics, which can be distinguished by microscopy. Synthetic fibers are generally identified by dissolution method.

Some of the fibers we come into contact with are two or three component fiber blend products, which requires us to first conduct fiber qualitative identification and pre-treat the sample with appropriate methods. Then, use appropriate solvents to dissolve one type of fiber from the blend variety, clean, dry, weigh, and calculate the remaining fibers.

For example, if polyester cotton fabric weighs 1.0g and is dissolved in 75% sulfuric acid to remove cotton, and polyester is insoluble, weighing 0.6g, then this fabric contains 40% cotton and 60% polyester.