Textile Notes related to fiber, yarn, fabric knowledge, spinning, weaving, processing, projects, knitting, Indian Traditional Textiles and denim manufacturing
Fibers represent one of the forensic evidences known as trace evidence.
The forensic examiners must handle a victim with care, to minimize fiber loss. Retrieving the victim's clothing as soon as possible is very necessary to prevent as much fiber loss as possible. Fibers are typically collected using adhesive tape.
The following details are particularly noted when analysing fibers. This helps to determine the source of the fibers.
1. Fiber Type: The presence of less common fibers at a crime scene or on the clothing of victim or suspect increases its significance.
2. Fiber Colors: It greatly influences the significance of fiber comparison. Fading and discoloration further adds significance to a fiber association.
3. Number of Fibers: The greater the number of fibers on the body of a suspect or victim, the more is the likely hood of a direct contact between individuals, however converse may not be true.
4. Fabric type: Loosley knit or woven fabric or new fabric shed more fibers.
The Following are the basic differences on the basis of which we can distinguish Linen from cotton:
1. Linen is about 20% more heavy than cotton.
2. It has a leathery feeling that is absent in cotton .
3. Cotton feels warmer(about 15-30% warmer) and holds heat better than linen.
4. On holding linen against light, the threads and the fibers composing the threads appear uneven and streaked as it is not possible to make linen yarn as uniform as cotton yarn.
5. On burning a linen thread, the fibers lie in the same position as before with no change except the scorched appearance. Burning a cotton thread causes the fibers to spread like a tuft.
6. Linen absorbs oil much better than cotton. To distinguish Linen with cotton in a piece of fabric, first remove all the impurities by washing and boiling. Then when if the fabric is dipped in oil, the linen fibers look transparent if held against the light. The Cotton remains nearly opaque.
7. Linen stands the action of sulphuric acid better than the cotton. To check a blend, first remove all the impurities then dip in con. sulphuric acid for a minute or two. Wash in water and dry on a blotting paper. All that remains on the blotting paper is linen. The cotton almost immediately dissolves in acid.
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All viscose including High Wet Modulus scorch and ignite quickly when brought near the flame. Like cotton they burn quickly with yellow flame when in the flame. When removed from the flame they continue to burn. There is no afterglow unlike cotton. The smell is that of burning paper. They leave a light gray and feathery ash.
When brought near the flame, it fuses away from flame turning black. When in the flame, it flames quickly. The fabric puckers, sputters and melts. It drips like burning tar. When removed from the flame, it continues to burn and melt. It smells like vinegar. It leaves a brittle hard, irregular black ash which is difficult to crush.
Nylon fuses and shrinks away from the flame when brought near the flame. In flame, it burns slowly without melting. When removed from flame the flame diminishes and tends to die out. It has somewhat pungent odor. It leaves a hard, round, tough and gray bead.
When brought near the flame, it shrinks away from the flame. When in the flames it puckers and chars. When removed from flame, it extinguishes by itself. It has no smell and it leaves a hard black bead.
Polyester fuses and shrinks away from flame. When in flame, it burns slowly with melting. When removed from the flame, it burns with difficulty. It has slightly sweetish smell. It leaves a hard round brittle, black bead.
Orlon, Acrilan and Creslan and Zefran fuse and melt away from Flame when brought near the flame. When in flame Orlon flames rapidly. The fiber puckers, sputters and melts. Acrilan flames rapidly and melts. Creslan flames and melts and Zefran sputters slightly and flames. When removed flame all of acrylics continue to burn and melt. Orlon has a slightly burning meat-like smell. Acrilan has a buring steak smell. Creslan has sharp sweet smell and Zefran has a turmeric like smell. Orlon, Acrilan and Cresla have hard, brittle and irregular black bead. Zefran has irregular black ash that can be crushed easily.
Modacrylics
Verel and SEF fuse and shrink away from the flame when approached near a flame. When in flame, Verel burns very slowly with melting. SEF shrinks, melts and smolders. When removed from flames, all modacrylics are self extinguishing. Verel has a gunpower smell whereas SEF has a sharp sweet smell. Verel leaves a hard and irregular black bead whereas SEF leaves a hard and irregular black bead.
Fuses but doesn’t shrinks away from the flame when approached near the flame. When in flame, it burns with melting. It has an acrid smell. It leaves a soft, fluffy black bead.
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Blend of Acrylic with Wool, Silk, Cotton, Viscose, Polyester or Nylon
1. Dissolve the acrylic fibres with (Dimethyl Formamide - DMF). Acrylic Fibres will dissolve in DMF.
2. Filter, rinse and weigh carefully to get the ratio of Acrylic Fibres.
Blend of Protein Fibres ( Wool or Silk) with cotton, polyester, nylon or acrylic
1. Take the blended fibres ( Carefully weighed) in a conical flask.
2. Add a solution of 5% (w/w) solution of Sodium Hydroxide or Potassium Hydroxide and boil for 10 minutes. Protein fibres will dissolve in Sodium Hydroxide or Potassium Hydroxide.
3. Rinse the leftover fibres with water and neutralise with dilute Acetic Acid.
4. Weigh the fibres after drying and find the ratio of protein fibres.
Blend of Polyester with Cotton or Viscose
1. Weigh the blend and heat it with Meta cresol. Polyester fibres will dissolve.
2. Weigh the residual fibres after rinsing thoroughly and drying and find the percentage of polyester fibres.
Blend of Elastane ( Spandex or Lycra) with Cotton or Viscose
1. Treat the blend with DMF. Elastane will dissolve in DMF.
2. Filter, Rinse, dry and get the weight of residual fibres to get the percentage of elastane.
How to Identify Constituent Fibre Percentage in a Textile Blend
Textile fabrics are often made from blends of two or more fibres. A polyester-cotton shirt, a polyester-viscose fabric, or a cotton-viscose blend may look like a single material to the eye, but its behaviour during dyeing, finishing, washing, shrinkage, comfort, strength, and costing depends heavily on the actual fibre composition.
For this reason, textile laboratories use quantitative fibre analysis to determine how much of each fibre is present in a blend. In simple terms, one fibre component is dissolved using a suitable chemical reagent, while the undissolved residue is filtered, washed, dried, and weighed. From the change in weight, the percentage of each fibre can be calculated.
Visual 1: A simple schematic showing a blended textile sample, selective chemical dissolution, filtration, residue drying, and final weighing.
Why Fibre Percentage Identification Matters
Knowing the fibre composition of a textile blend is important for production, merchandising, dyeing, quality control, costing, product labeling, and customer communication. A fabric declared as polyester-cotton, for example, may behave very differently depending on whether the blend is 65:35, 80:20, or 50:50.
Polyester and cotton also require different dyeing and finishing approaches. Polyester is hydrophobic and is commonly dyed with disperse dyes, while cotton is hydrophilic and is commonly processed with dye classes suitable for cellulosic fibres. Viscose is also cellulose-based, but it has different wet strength and chemical behaviour compared with cotton.
Basic Principle of Chemical Fibre Analysis
The basic principle of quantitative chemical analysis is selective dissolution. A known weight of the blended sample is treated with a reagent that dissolves one component while leaving the other component mainly unaffected. The remaining fibre residue is then separated, washed, neutralised if required, dried, cooled, and weighed.
The percentage of the undissolved fibre can be calculated as:
\[
\text{Percentage of residue fibre} =
\frac{\text{Dry weight of residue}}{\text{Original dry weight of sample}} \times 100
\]
The dissolved fibre percentage can then be calculated as:
\[
\text{Percentage of dissolved fibre} =
100 - \text{Percentage of residue fibre}
\]
In actual laboratory practice, correction factors may be required because the fibre remaining as residue may still lose a small amount of weight during chemical treatment. These correction factors should be applied according to the relevant standard method or laboratory procedure.
General Precautions Before Testing
Before quantitative analysis, the fibres present in the blend should first be identified by suitable qualitative methods such as microscopic examination, burning behaviour, solubility behaviour, or other standard fibre identification methods. Quantitative analysis should not be started blindly on a completely unknown sample.
The sample should also be free from non-fibrous material such as size, oil, wax, dirt, resin, finishing chemicals, coatings, or other additives. These substances can affect the sample weight and may lead to incorrect percentage calculation. If present, they should be removed by a suitable pre-treatment method before chemical analysis.
1. Polyester/Cotton or Polyester/Viscose Blend
In a polyester/cotton or polyester/viscose blend, the cellulosic component can be dissolved using sulphuric acid under controlled conditions, while polyester remains as the residue. Cotton and viscose are cellulose-based fibres, whereas polyester is more resistant to this treatment.
Method
Take approximately 0.5 to 1.0 gram of the blend sample and weigh it accurately.
Place the sample in a clean flask and add 75% by weight sulphuric acid.
Maintain a material-to-liquor ratio of about 1:200 so that the sample is properly immersed.
Keep the flask in a water bath for about one hour at approximately \(50 \pm 5^\circ C\).
Filter the contents carefully. The residue left on the filter is polyester.
Wash the polyester residue thoroughly with water and neutralise it using dilute ammonia solution.
Dry the residue at approximately \(110^\circ C\), cool it in a desiccator, and weigh it accurately.
The dried residue gives the polyester content. The remaining percentage represents the cellulosic component, either cotton or viscose depending on the original blend.
Calculation
\[
\text{Polyester %} =
\frac{\text{Dry weight of polyester residue}}{\text{Original dry weight of sample}} \times 100
\]
Therefore, the blend is approximately 65% polyester and 35% cotton or viscose.
Visual 2: Flow diagram for polyester/cotton or polyester/viscose analysis, showing cellulosic dissolution and polyester residue calculation.
2. Cotton/Viscose Blend
Cotton and viscose are both cellulose-based fibres, but their chemical behaviour is not identical. Viscose is regenerated cellulose and is generally more easily attacked by certain reagents than cotton. In this method, viscose dissolves and cotton remains as the residue.
Method
Take approximately 0.5 to 1.0 gram of accurately weighed sample.
Place the sample in a flask and add 60% by weight sulphuric acid.
Maintain a material-to-liquor ratio of about 1:100.
Stir the solution mechanically for about 30 minutes.
During this treatment, viscose dissolves and cotton remains.
Filter the cotton residue and wash it thoroughly with water.
Neutralise the residue with dilute ammonium hydroxide solution, wash again, dry, cool, and weigh.
A correction factor is important in this method because cotton may lose some weight during the treatment. A commonly used correction mentioned for this process is about 5% weight loss for cotton. Therefore, the observed cotton residue weight should be corrected before calculating the final blend percentage.
Calculation With Cotton Correction
If cotton loses approximately 5% during the process, the corrected cotton weight can be calculated as:
After applying the correction factor, the blend is approximately 50% cotton and 50% viscose.
3. Polyester/Cotton/Viscose Blend
A polyester/cotton/viscose blend contains one synthetic fibre and two cellulosic fibres. The analysis is done in stages. First, viscose is dissolved using 60% sulphuric acid. The remaining fibres are cotton and polyester. Then cotton is dissolved using stronger sulphuric acid, leaving polyester as the final residue.
This step-by-step separation allows the three components to be estimated separately. The first weight loss gives viscose, the final residue gives polyester, and cotton can be calculated by difference.
Method
Take an accurately weighed dry sample of the polyester/cotton/viscose blend.
Treat the sample with 60% by weight sulphuric acid. Viscose dissolves under this treatment.
Filter, wash, dry, cool, and weigh the remaining cotton and polyester residue.
Treat this residue with 75% sulphuric acid. Cotton dissolves under this treatment.
Filter the final residue carefully. Wash thoroughly, neutralise if required, dry, cool, and weigh.
The final residue is polyester. Cotton is calculated by difference after accounting for viscose and polyester.
Calculation
Let:
\[
W_0 = \text{Original dry sample weight}
\]
\[
W_1 = \text{Dry weight after dissolving viscose}
\]
Suppose the original dry sample weight is 1.000 gram, the dry weight after dissolving viscose is 0.700 gram, and the final polyester residue is 0.400 gram. The blend percentages are calculated as follows:
Therefore, the blend is approximately 40% polyester, 30% cotton, and 30% viscose.
Visual 3: Three-stage analysis chart for polyester/cotton/viscose blend, showing viscose removal, cotton removal, and polyester residue.
Quick Calculation Table
Blend
First Dissolved Component
Residue Obtained
Main Calculation
Polyester/Cotton
Cotton
Polyester
Polyester % = residue weight ÷ original weight × 100
Polyester/Viscose
Viscose
Polyester
Polyester % = residue weight ÷ original weight × 100
Cotton/Viscose
Viscose
Cotton
Corrected cotton weight may be required before percentage calculation
Polyester/Cotton/Viscose
Viscose first, cotton second
Polyester final residue
Viscose by first loss, polyester by final residue, cotton by difference
Practical Points to Remember
The accuracy of fibre percentage analysis depends on careful sampling, accurate weighing, complete dissolution, complete washing, correct neutralisation, and proper drying. Even a small error in drying or weighing can affect the final percentage, especially when the sample weight is small.
Chemical analysis is different from a simple burning test. A burning test can help identify the probable fibre type, but it cannot reliably provide the percentage of each fibre in a blend. For blend percentage, controlled quantitative analysis is required.
Correction factors should not be ignored. The fibre left as residue may still lose a small amount of weight during the chemical process. If a standard method prescribes a correction factor, it should be applied before reporting the final blend composition.
Related Reading on Fibre Identification and Textile Testing
ISO 1833-1:2020. Textiles — Quantitative chemical analysis — Part 1: General principles of testing. International Organization for Standardization. https://www.iso.org/standard/74881.html
Bureau of Indian Standards. IS 3416:1988 / IS 3416 Part 1: Method for quantitative chemical analysis of binary mixtures of polyester fibres with cotton or regenerated cellulose.https://law.resource.org/pub/in/bis/S12/is.3416.1988.pdf
This article is intended for textile learning and general technical understanding. It is not a substitute for an accredited laboratory test report, official standard method, or professional chemical safety training. The procedures mentioned involve strong chemicals such as sulphuric acid and should be performed only by trained personnel in a properly equipped laboratory with suitable safety precautions, ventilation, neutralising arrangements, and personal protective equipment.
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