5 ways to help you identify common fibers

With the continuous advancement of textile production technology, more and more new fibers have become the raw materials of textiles, which has brought about the problem of identifying fibers for textiles. Commonly used fiber identification methods include microscopic observation, combustion, reagent color development, dyeing, dissolution, etc.

1 Microscopic observation method

Make longitudinal slices and cross-sectional slices of the fibers, observe the longitudinal and transverse morphology of the fibers under a microscope, and identify the fibers based on differences in morphological characteristics, see Table 1.

Table 1 Morphological characteristics of various fibers

Fiber types	Vertical form	Cross-sectional shape
Tencel fiber	smooth	More regular round or oval shape, with skin and core layer
Modal fiber	There are 1 to 2 grooves in the longitudinal direction	Irregular, similar to a round waist, smoother, with a skin core
Soy fiber	The surface has irregular grooves and island-like concavities	Flat dumbbell shape and round waist
Bamboo fiber	There are grooves on the surface	Zigzag type, with skin and core layer
Chitin fiber	There are obvious grooves on the surface	The edge is jagged and the core layer has obvious small gaps
Viscose fiber	There are grooves on the surface	Zigzag type, with skin and core layer
Cotton fiber	There are natural twists	The waist is round with a middle cavity
Silk	Smooth surface	Irregular triangle
Wool fiber	There are scales on the surface	Circle
Polyester fiber	Rod-shaped	Smooth round surface

2 Combustion method

Different fibers have different flames, smoke, odors, residues, etc. during the burning process. Therefore, fiber types can be distinguished according to the characteristics of the fibers during and after burning, as shown in Table 2.

Table 2 Characteristics of various fibers during and after combustion

Fiber types	Close to the flame	In flames	Leave the flame	Burning smell	Residue form
Tencel fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	Gray black gray
Modal fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	Gray black gray
Soy protein fiber	Shrink	It does not melt when burning, but has black smoke	Not easy to burn	Burning hair smell	Crunchy black ash
Bamboo fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	Gray black gray
Chitin fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	Gray black gray
Viscose fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	A small amount of off-white ash
Cotton fiber	Does not melt or shrink	Burn quickly	Keep burning	The smell of burning paper	A small amount of off-white ash
Silk	Shrink	Gradually burning	Not easy to burn	Burning hair smell	Crunchy black ash
Wool fiber	Shrink	Gradually burning	Not easy to burn	Burning hair smell	Crunchy black ash
Polyester fiber	Shrinkage melt	Melt first and then burn, with solution dripping	Can spread burning	Special aroma	Glassy dark brown hard ball

3 Reagent color development method

Since the structures of various fibers are different, they have different coloring reactions to iodine and potassium iodide solutions. The fibers can be identified by observing the color and swelling of the fibers after the action of the reagents. This identification only applies to white fibers, and colored fibers must fade before testing can be conducted. Reagent preparation: Dissolve 20 grams of iodine in 100 ml of saturated potassium iodide solution, mix thoroughly, and then soak the fiber for 1 minute. After sufficient washing, judge according to its color, see Table 3.

Table 3 Coloring reactions of various fiber burning to iodine solution

Fiber types	Tencel fiber	Modal fiber	Soy protein fiber	Bamboo fiber	Chitin fiber
Color development in iodine solution	Black, blue and green	Blue gray	Brown	Blue gray	Black
Types of fiber	Viscose fiber	Cotton fiber	Silk	Wool fiber	Polyester fiber
Color development in iodine solution	Black, blue and green	No staining	Light yellow	Light yellow	No staining

4 staining methods

The dyeing method is used to identify fibers, mainly based on the different color reactions of various fibers to dyes. There are two types of dyeing methods: cold dyeing and boiling dyeing. The recipe of the dyeing method is shown in Table 4.

Table 4 Dyeing method formula

Cold dyeing		Boiling dyeing method
Dyes	Weight (g)	Dyes	Weight (g)
Direct Indigo 2B	2.5	Acid fuchsin 6B	1
Acid fuchsin 6B	3	Salt base light yellow (thick)	1
Picric acid	5	Disperse blue GF	0.5
Tannin	5	Pancreas plus bleach T	0.5

Pour the formula in Table 4 into 50 ml of ethanol and stir until dissolved, then dilute to 500 ml with distilled water for later use. The cold dyeing method directly puts the fiber into the solution for dyeing, then rinses the fiber with cold water, squeezes out the water, and observes the color for identification; the boiling dyeing method puts the fiber into the solution for dyeing, boils it for 3 minutes, rinses it 3 times, and then puts it into 0.1 % of the pancreas plus bleaching T solution, squeeze out the water, and observe the color for identification. The dyeing reactions of various fibers are shown in Table 5.

Table 5 Dyeing reactions of various fibers

Fiber types	Cold dyeing method	Boiling dyeing method
Cotton fiber	Purple	Earthy yellow
Viscose fiber	Red purple	Light yellow
Vinyl	Light yellow-green	Dark olive green
Acrylic	No color	Light yellow
Polyester	No color	Light sky blue
Nylon	Light yellow	Dark grass green

5 Dissolution method

The dissolution method is an effective method to identify various fibers. The principle is to use the dissolution characteristics of various fibers in different chemical solvents and at different temperatures to determine their varieties. The fibers to be identified can be put into a test tube, inject a certain solvent, stir with a glass rod, and observe the dissolution of the fibers. If the amount of fiber is very small, you can also put the sample into the concave surface with a concave slide, add solvent, cover the slide, and observe directly under the microscope. Using dissolution method to identify fibersAt this time, the concentration of the solvent and the heating temperature should be strictly controlled, and the dissolution speed of the fiber should be paid attention to. Using the dissolution method requires an accurate understanding of the chemical properties of various fibers, and the inspection procedures are also complicated. The microscopic observation method and combustion method are more intuitive, but inspectors must have rich practical experience; the reagent colorimetric method and staining method are more complicated to operate and can be used under special circumstances.