Textile fibre combustion identification method is a simple and easy to use, commonly used, fast and at the same time more accurate identification method, by observing the fibre in the combustion process of different performance, such as shrinkage, melting, burning speed, flame colour, smoke, smell and ash characteristics, etc., you can initially identify the type of fibre.

Combustion identification method is through the fibre burning on the fire, carefully observe the fibre close to the flame, burning in the flame and away from the flame combustion; smell; the colour of the smoke; the colour shape and hardness of the ash after combustion and so on. Record these characteristics, and fibre combustion should have the characteristics of comparison, you can roughly determine the type of burning fibre.

The basis of combustion identification method

Researchers base the combustion identification method on a variety of textile fibre combustion phenomena and characteristics, such as combustion speed, melting contraction, flame colour, burning smell, and ash state.

For pure spinning fabrics and pure spinning yarn interwoven fabrics using combustion identification method, the burning phenomenon is very obvious, showing the characteristics of a single raw material, it is easier to identify.

For blended fabrics and blended yarn interwoven fabrics, the phenomenon of mixed raw materials when burned, the characteristics are not obvious, especially when the multi-fibre blending, it is difficult to accurately determine the composition of the raw materials. When the blending ratio of fibres is different, it mainly shows the burning characteristics of fibres with higher content, while the weak characteristics of fibres with less content are often easily ignored, which may make the judgement result inaccurate.

For some of the fire, the anti-flammable and antibacterial treatment of fabrics will create a greater difference in the combustion phenomenon, and thus one should not use it to identify the combustion method.

Therefore, to ensure accuracy, we can carry out the combustion identification method based on the sensory identification method, as we can apply different treatment methods to the identified pure spinning, blending, and interweaving fabrics.

Burning characteristics of common textile fibres

Cellulosic fibres (cotton, hemp, viscose, modal, lyocell)

Burning state:

When close to flame: no melting or shrinking

In contact with the flame: rapid burning

When leaving the flame: continues to burn

Odour when burning: burnt paper smell

Characteristics of the residue: grey-black ash

1.Cotton fibre

Burns when exposed to flame, burns quickly, produces a yellow flame and has an odour.

Slightly grey-white smoke, can continue to burn after leaving the fire, after blowing out the flame there are still sparks in the continuation of combustion, but the continuation of time is not long.

After burning can maintain the original shape of the fleece, hand touch easily broken into loose ash, ash is grey fine soft powder, the burnt part of the fibre is black.

2. Hemp fibre

Burns quickly, softens, does not melt, does not shrink, produces a yellow or blue flame, has the smell of burning grass.

Leave the flame to continue to burn rapidly.

Ash less, light grey or off-white ash powder.

3. Viscose fibre

Burning properties are basically similar to cotton, but viscose fibre burns slightly faster than cotton fibre, less ash.

Sometimes it is not easy to keep the original shape, viscose fibre combustion will emit a slight sizzle.

Protein Fibre (Mulberry Silk, Quercus Silk, Sheep Wool, Cashmere, Rabbit Hair, Mohair)

Burning state:

When close to flame: melting and shrinking

In contact with the flame: rapid combustion

When leaving the flame: not easy to prolong combustion

Smell when burning: burning hair smell (hair loss young people can pick up your hair and smell it)

Characteristics of residue: grey-black ash

1. Wool

Contact with the flame does not immediately burn, first curled, then smoke, and then fibre blistering combustion.

The flame is orange, the burning speed is slower than cotton fibre.

Leave the flame immediately stop burning, not easy to continue to burn, there is a burning hair and feather odour.

Ash can not maintain the original shape of the fibre, but an indefinite or spherical glossy black-brown brittle pieces, with a finger pressure is crushed, the number of ashes is more, there is the smell of burning.

2. Silk

Burning slower, melting and curling, burned when shrinking into a ball, there is a burning hair odour.

Slightly flash when leaving the flame, slow burning, sometimes self-extinguishing.

The grey is a small black-brown crunchy ball, crumbles when pressed with a finger.

Synthetic fibres (polyamide, polyester, acrylic, polypropylene, polyethylene)

1. Nylon

Close to the flame caused by fibre contraction, the fibre quickly coiled and melted into a transparent gel after contacting the flame. While small bubbles formed, you can pick them with a needle while it is hot, and you can pull the gel into a fine wire.

When burning, it has no flame or a weak orange flame, the edge of the flame is blue, leaving the flame stops burning, it has an amine or celery flavour.

After burning, the tip of fibre is light brown glass sphere, hard and not easy to crush.

2.Acrylic

Melting and melting while burning, fast burning speed.

The flame is white, bright and powerful, sometimes slightly black smoke.

Has a fishy or pungent odour similar to that of burning coal tar.

Continues to burn away from the flame, but burns slowly.

Ash is black brown irregular brittle ball, easily twisted with fingers.

3. Polypropylene, polyethylene

One side curls up, melts at the same time, burns slowly.

There is a bright blue flame, black smoke, a gelatinous substance dripping down.

Smells like burnt paraffin.

Continues to burn away from the flame, sometimes self-extinguishing.

The ash is irregular hard lump, transparent, not easy to twist with fingers.

4.Acetate fibre

Burning fast, with sparks, melting and burning at the same time, burning with pungent acetic acid smell.

When leaving the flame, it melts and burns at the same time;

You can crush the grey, which is black with glossy irregular lumps, by hand.

5. Copper ammonia fibre

Burns rapidly, does not melt, does not shrink, has the odour of burning paper;

Leaving the flame continues to burn rapidly;

Little ash, light grey or off-white.

6. Polyester

When burning, the fibre first curls up, melts and burns slowly, with yellowish-white flame, blue flame edge and black smoke at the top of the flame;

Leave the flame continues to burn, sometimes will stop burning and self-extinguishing.

Burns with an aromatic or sweet odour.

Ash is black brown hard ball, not easy to twist with fingers.

7.Vinylon

Fibre shrinks rapidly when burning, burns slowly, flame is very small, almost smokeless.

When a large number of molten fibres will produce a large dark yellow flame, with small bubbles.

Burning with the special odour of calcium carbide gas.

Continue to burn away from the flame, sometimes self-extinguishing.

Black brown irregular brittle beads make up ash, which fingers can twist.

8.Chloride

Difficult to burn; melting and burning in the flame, black smoke; immediately extinguished away from the flame.

Do not let the flame stay extinguished; you cannot renew it.

Burning with an unpleasant pungent chlorine odour.

Ashes are irregular black-brown hard lumps, not easy to twist with fingers.

9. Spandex

Close to the flame first swells into a circle, and then shrinks and melts.

Melt and burn in the flame, the burning speed is slow, the flame is yellow or blue.

Leave the flame while melting and burning, slow self-extinguishing.

Burning with a special irritating odour; ash for the white sticky lumps.

Through these combustion characteristics, you can more accurately identify the type of textile fibres. Experts recommend that you pay attention to safety in practical operation to avoid the risk of fire caused by fibre combustion.

How to perform the cotton fibre combustion test?

The method of cotton fibre combustion test is as follows:

Test device check:

Open the valve of the gas supply section, select the gas mixture concentration, and control the flow rate at about 10L/min. Close the outlet and inlet valves and leave it for 30 minutes, observe the values of the manometer and flow meter to make sure that there is no gas leakage in the device.

Test temperature and humidity:

The team should carry out the test in an environment with a temperature of 10-30°C and a relative humidity of 30%-80%.

Specimen Preparation:

Mount the specimen in the middle of the specimen clamp and fix it. Then, vertically insert the specimen clamp along with the specimen onto the specimen support in the burning glass, ensuring that the upper end of the specimen is no less than 100mm from the mouth of the cylinder.

Test operation:

Open the oxygen and nitrogen valves, adjust the corresponding oxygen and nitrogen flow, keep the total flow of the gas mixture between 10-11.4L/min. Let the regulated gas flow flow to flush the combustion cylinder for at least 30 seconds before ignition of the specimen.

Ignite the igniter, point the igniter tube upwards, adjust the flame height to 15-20mm, ignite at the top end of the specimen, and control the ignition time within 10-15 seconds.

When the upper end of the specimen is fully ignited, immediately begin to determine the time of renewed ignition and negative ignition, followed by the determination of the length of the damage.

Oxygen concentration test:

Conduct the test by the ‘rising-falling method’, gradually adjust the oxygen concentration, observe the combustion of the specimen, and record the minimum oxygen concentration that enables the specimen to continue to burn.

Results Report:

Describe the burning characteristics of the sample, such as charring, melting, shrinkage, curling, etc., and provide the temperature and humidity conditions during the test.

The above steps allow you to perform a combustion test on cotton fibres to assess their burning characteristics. Please note that we should adhere to safety regulations during the test, as the combustion of textile materials may produce harmful gases.

Scope of application of the AATCC 20 fibre characterisation method

The following two main types of fibres include:

Natural fibres:

Producers obtain this type of fibre directly from nature, which includes plant sources (e.g. cotton, flax, bamboo, etc.), animal sources (e.g. wool, silk, cashmere, etc.), and mineral sources (e.g. asbestos). Natural fibres usually have good breathability, moisture absorption and comfort and are a common type of fibre used in textiles.

Man-made fibres:

Manufacturers produce man-made fibres from natural raw materials (e.g. wood, cotton staple, etc.) through chemical or mechanical processes. Such fibres include viscose fibres (rayon), acetate fibres, lyocell fibres, etc. Man-made fibres are widely used in the production of textiles due to their low production cost, plasticity and controllable properties.

AATCC 20 Fibre Qualitative Analysis Method Testing Principle

1. Microscopic observation:

Observation of the transverse and longitudinal morphology of the fibres through a microscope allows the identification of the natural characteristics of the fibres, such as shape, size and surface texture. These characteristics help to differentiate between natural and man-made fibres and the different types of fibres between them.

2. Solubility test:

Researchers can use the solubility of fibres in different solvents to identify fibre types. For example, certain fibres may be soluble in specific solvents while others are insoluble. This solubility test allows researchers to differentiate and identify various fibres.

3. Specific physical properties:

Other physical properties of fibres, such as twisting (how much a fibre twists), combustion tests (observing the behaviour of a fibre as it burns and the odour it produces), etc., can provide additional information that can help to further identify the type of fibre.

AATCC 20 Fibre Characterisation Method Equipment

1. The UL94 Horizontal Vertical Burning Tester TF328 tests fabric flammability. It also tests the burning of plastic, rubber, or film under a specified fire source to determine their fire resistance. This Flammability Testing Equipment is also used for lighting, appliances, motors, tools, and instruments. We typically use this flammability chamber for research, production, and quality inspection.

2.Microscope with objective and eyepieces at 100-500x magnification and fitted with a polarising analyser

3. Analysing needle

4. Sectioning device, stainless steel plate, measuring 2.54cm x 7.62cm x 0.0254cm (1 x 3 x 0.01in), drilled with several small holes of 0.09cm (0.04in) diameter. Soft copper magnetic wire AWG34; special slicer for microscope.

5. Thermostatic water bath

6.Blade

7. Electric oven

8. 100 ml glass beaker, test tube, etc.

9. Scissors and tweezers

10. The design features a glass density gradient tube that measures about 2.5cm (1in) in diameter and approximately 45cm (18in) in length. They seal the bottom, and a glass cap closes the 24/40 standard top, allowing for elevated humidity and reduced solvent volatilization. You can use calibrated fine glass spheres as density standards.

11. Melting point instruments contain a heat-resistant temperature measuring device, e.g., a thermometer, and can control the rate of temperature increase as well as allow observation of the sample at multiples of the method. The instrument has a temperature range of at least 100-300°C or greater and an accuracy of ±1°C over the entire temperature range.

12. Micro FTIR spectrometer.

13. Differential scanning calorimeter.

14. Slides and coverslips

Sampling for combustion test

We take fibres, yarns, or fabrics representative of the total sample as specimens.

1. If the sample is a bulk fibre or yarn, it may contain only one fibre, or it may be a blend of two or more fibres.

2. The yarn may be a single yarn, strands of two or more yarns. These yarns may be the same, may be different, or may include blends of more than one fibre.

3. Woven or knitted fabrics may be woven from the same or different yarns in different constructions, and these yarns may contain one or more fibres.

4. You can dye different fibres the same colour. Conversely, you can dye the same fibre to a different colour by using fibre dyeing, yarn dyeing, or by altering the dyeing properties of the fibres.

Note: Different yarns in various forms of construction may contain one or more fibres. Examiners should examine yarns of different colours separately. In the case of woven fabrics, you should check the warp and weft yarns separately even if they are of the same colour. In the case of a combined yarn, you should take it apart and examine the individual yarns separately.

Preparation of specimen for combustion test

1. In most cases, researchers can identify unknown fibres qualitatively without pretreatment.

2. Pre-treatment of specimen

If the examination reveals that starch, wax, grease, or other coverings blur the appearance of the specimen, we pre-treat the specimen.

2.1. Remove these foreign substances by treatment with warm or hot water.

2.2. If the method in 2.1 does not work, try extraction with an organic solvent, 0.5% hypochlorite HC1 solution or 0.5% sodium hydroxide NaOH solution.

2.3. To separate the cellulose fibre bundles, you can treat them with a 0.5% sodium hydroxide NaOH solution, then wash them with water and dry them.

2.4. When you require decolourisation (especially for cellulosic fibres), you may heat a solution of sodium hypochlorite at 50°C for 30 minutes.

3. Size and shape:

The supplier should provide the sample in the form of a sheet with dimensions of 125±5mm × 13.0±0.5mm and a minimum thickness of 3mm (-0.0, 0.2). If the minimum thickness of the sample is greater than 3mm or the maximum thickness is less than 3mm, a 3mm sample is not required. The maximum thickness of the sample shall not exceed 13mm, the maximum width shall not exceed 13.5mm, and the corner radius shall not be greater than 1.3mm.

4.Quantity:

You need at least 2 sets of samples, with each set containing 3 samples.

Combustion test visual and microscopic observation

1. If the sample under test is a fabric by splitting or cutting to disperse the yarns. If it is a woven fabric, separate the warp and weft yarns. If the yarns are significantly different in colour, lustre, size or other forms, take these yarns apart and identify them separately.

2. Separate a small amount of fibre from the yarn with a needle and place it on a slide.

3. Comb out the fibres, add a drop of glycerine and cover with a coverslip.

4. Examine the fibres under a 100x microscope.

5. Observation of fibre properties

Observe the properties of the fibres in the longitudinal direction and compare them with reference standards of textile fibres. Based on the fibre appearance characteristics, researchers can classify them into four categories for further examination.

5.1. Fibres with a scaly layer on the surface

These are animal fibres. According to the external characteristics of the fibres listed in the standards, they can be further identified by comparing them with known samples of hair-like fibres and by performing successive detailed microscopic analyses including cross-sectional analyses.

5.2. Fibres with transverse knots on the surface

These are in addition to cotton, plant fibres, according to the standards listed in the external characteristics of the fibre, and the known plant fibre samples for comparison, continuous and detailed microscopic analysis, including cross-sectional analysis, can be further identified.

5.3. Fibres with a twist

This category includes cotton and silk. They are easily identified by cross-sectional analysis. Comparison with known plant fibre samples allows further identification.

5.4. Other fibres

(a) Metal fibres, mulberry silk and asbestos are further identified by microscopy including cross-sectional identification. You can identify metallic fibres by their distinctive shiny appearance.

(b) Man-made fibres The same fibre may have different cross-sectional shapes. Man-made fibres may be further identified by their solubility.

Burning test microscope cross-section identification

1. Take a neat bundle of fibre or yarn.

2. Take a piece of sewing thread and make a loop through a small hole in the copper sheet.

3. Place the bundle of fibres or yarn in the loop of thread and pull it through the small hole. Stuff the hole with enough fibre to fill it.

4. Use a razor blade to cut the fibres flat on both sides of the copper sheet.

5. Observe with a microscope at 200x-500x and compare to a cross section of known fibres.

Test Procedure for UL94 Horizontal and Vertical Flammability Tester Fabric Combustion Test:

Test Procedure:

Scribing:

Mark 25±1mm and 100±1mm lines on the sample.

Clamping:

Clamp the tail end of the sample close to 100mm, keeping it horizontal in the lengthwise direction and 45°±2° from the horizontal in the widthwise direction, with the screen fixed 100±1mm below the sample.

Combustion setup:

Researchers used a combustor with a methane flow rate of 105 ml/min and a back pressure of 10 mm water column, achieving a flame height of 20 ± 1 mm.

Combustion:

The technician tilted the flamer at 45° and placed it into the flame at a depth of 6mm, allowing it to burn for 30±1 seconds, or the technician removed the flamer when it burned to 25mm.

Timing:

We started timing from the point where the flame burned to 25±1mm, and we recorded the length burned (L) and the burning time (t).

 

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