Introduction Identification of textile fibre composition is an important part of textile testing and quality evaluation. A textile product may contain natural fibres, regenerated fibres, synthetic fibres or blends of two or more materials. Correct identification is necessary for product classification, quality assessment, labelling, selection of appropriate processing methods and determination of conformity with specified requirements. Traditional fibre identification methods include visual examination, microscopic analysis, burning behaviour, solubility tests and other chemical methods. While these techniques remain useful, modern instrumental techniques can provide additional information rapidly and with greater chemical specificity. Fourier Transform Infrared Spectroscopy (FTIR) is one such analytical technique. It identifies materials based on the interaction of infrared radiation with chemical bonds within the material. The resulting spectrum provides characteristic information about the molecular structure of the textile material. What is FTIR Technology? FTIR stands for Fourier Transform Infrared Spectroscopy. It is an analytical technique in which infrared radiation is directed towards a sample and the interaction between the infrared radiation and the molecular bonds of the material is measured. Different chemical bonds absorb infrared radiation at characteristic frequencies. As a result, each material produces a characteristic pattern of infrared absorption known as its infrared spectrum. The spectrum can be considered a chemical fingerprint of the material. By comparing the spectrum obtained from an unknown textile sample with spectra in a reference library, the material can be identified or its composition can be assessed. In textile laboratories, ATR-FTIR (Attenuated Total Reflectance FTIR) is particularly useful because many textile specimens can be examined directly with minimal sample preparation. Principle of FTIR The basic principle of FTIR is based on the absorption of infrared radiation by molecular bonds. When infrared radiation interacts with a textile material, specific chemical bonds absorb particular wavelengths or frequencies of infrared radiation. These absorptions correspond to molecular vibrations such as stretching and bending. The instrument records the infrared response and converts the measured signal into a spectrum using a mathematical process called Fourier transformation. The resulting spectrum contains characteristic absorption bands that can be used to identify the chemical nature of the material. For example, fibres based on cellulose, protein and synthetic polymers exhibit different spectral patterns because their molecular structures are different. FTIR in Textile Material Identification FTIR is particularly useful for identifying the chemical nature of textile fibres. Common textile materials that can be examined include: 4.1 Natural Fibres FTIR can assist in the identification of natural fibres such as: Cotton Linen/flax Hemp Jute Wool Silk Cellulosic fibres such as cotton and flax show characteristic spectra associated with cellulose, whereas protein fibres such as wool and silk show spectral features associated with proteins. 4.2 Regenerated and Man-Made Cellulosic Fibres FTIR can assist in identifying materials such as: Viscose rayon Modal Lyocell Other regenerated cellulosic fibres Although these materials are cellulose-based, differences in their chemical processing and structure can produce variations in their spectra. 4.3 Synthetic Fibres FTIR is widely useful for identifying synthetic polymeric fibres, including: Polyester Polyamide/nylon Acrylic Polypropylene Polyethylene Polyurethane/elastane Other polymer-based fibres Each polymer generally produces a characteristic infrared spectrum that can be matched against reference spectra. FTIR for Identification of Silk FTIR is particularly useful as a supporting technique for silk identification because silk is a protein-based fibre primarily composed of fibroin. The spectrum of silk contains characteristic absorption regions associated with peptide bonds and protein structures. These spectral features can help distinguish silk from cellulosic and many synthetic fibres. However, FTIR results should be interpreted carefully because silk may undergo degumming, dyeing, finishing, coating or chemical treatment, which can influence the spectrum. Therefore, FTIR identification is preferably supported by microscopic examination and other appropriate fibre identification techniques when required. Importance of FTIR in Textile Testing FTIR provides several advantages for textile laboratories. Rapid Identification - FTIR can provide an identification result within a short time compared with some conventional chemical identification procedures. Small Sample Requirement- Only a small quantity of textile material may be sufficient for analysis, particularly when using ATR accessories. Minimal Sample Preparation - Many textile specimens can be tested directly or with very limited preparation. Chemical Fingerprinting - The infrared spectrum provides characteristic chemical information that can be compared with reference materials. Identification of Unknown Materials - FTIR is particularly valuable when the composition of an unknown textile sample is not known. Supporting Blend Analysis - FTIR can help identify the major polymeric components in textile blends, although quantitative blend determination may require complementary techniques and appropriate calibration. Detection of Finishes and Coatings - FTIR can assist in identifying certain surface finishes, coatings, binders, adhesives and chemical treatments present on textiles. Investigation of Contamination - Unexpected chemical substances or contaminants present on textile surfaces may sometimes be detected through their characteristic infrared spectra. FTIR for Textile Classification and Categorisation FTIR can support textile classification based on the chemical nature of the fibre or polymer. At a broad level, textile materials can be categorized as: Natural fibres → cellulose-based and protein-based fibres Regenerated fibres → regenerated cellulose and other regenerated materials Synthetic fibres → polyester, polyamide, acrylic, polypropylene and other polymers This chemical classification can support laboratory identification and verification of declared fibre composition. However, FTIR should not be regarded as a substitute for the complete regulatory or standard-based classification of a textile product. Product classification may also depend on fibre percentage, construction, processing, intended use and applicable legal or technical requirements. FTIR and Fibre Blend Identification Many textile products are manufactured using blends such as: Cotton/polyester Cotton/viscose Wool/polyester Silk/cotton Silk/viscose Polyester/elastane Polyamide/elastane FTIR can provide evidence of the chemical components present in such blends by identifying characteristic spectral features. However, when accurate percentage composition is required, FTIR results may need to be combined with quantitative chemical analysis, microscopy, gravimetric methods or other validated techniques, depending on the material and applicable standard. ATR-FTIR in Textile Laboratories ATR-FTIR is one of the most convenient configurations for textile testing. In ATR analysis, the textile specimen is brought into contact with an ATR crystal, and infrared radiation interacts with the surface region of the sample. This configuration is particularly suitable for textile laboratories because yarns, fibres, fabrics, coatings and other textile specimens can often be examined with little sample preparation. The technique is especially useful for rapid screening and identification of unknown textile materials. FTIR Testing Method - Testing method: A small textile specimen is placed directly on the FTIR/ATR sampling interface and its infrared spectrum is recorded; the obtained spectrum is then compared with reference spectra or a spectral library to identify the material. Interpretation of FTIR Spectra - FTIR identification is based on the presence, position, intensity and pattern of absorption bands in the spectrum. A trained analyst generally considers: Characteristic absorption bands. Functional groups. Overall spectral pattern. Peak positions. Relative intensity of peaks. Similarity with reference spectra. Quality of spectral match. Possible effects of dyes, finishes and coatings. Modern FTIR instruments may include spectral databases that automatically compare an unknown spectrum with reference materials and provide possible matches. Nevertheless, automated library matching should be considered an analytical aid rather than the sole basis for final identification. Professional interpretation and, where necessary, confirmation using another method remain important. FTIR for Identification of Textile Finishes and Coatings Textile materials may contain substances other than the primary fibre, including: Water-repellent finishes Resin finishes Softening agents Polymer coatings Adhesives Printing binders Surface treatments FTIR can sometimes identify the chemical groups associated with these materials. This makes FTIR useful not only for fibre identification but also for investigating why a textile exhibits particular surface or performance characteristics. FTIR for Quality Control and Failure Investigation FTIR can be used as a supporting tool in textile quality-control investigations. For example, it may assist in determining whether an unexpected chemical material is present on a fabric or whether a coating or finish differs from the intended formulation. It can also be useful in investigating: Unknown residues. Surface contamination. Chemical degradation. Changes after processing. Differences between supplied and specified materials. Identification of polymeric deposits. Changes in finishing treatments. Advantages of FTIR The major advantages of FTIR in textile testing include: Rapid analysis. Small sample requirement. Minimal sample preparation. Useful for a wide range of textile materials. Provides chemical-specific information. Useful for unknown material identification. Suitable for fibres, yarns and fabrics. Useful for polymer identification. Can support blend identification. Useful for finishes, coatings and contaminants. Spectral libraries enable rapid comparison. Can complement conventional textile identification techniques. Limitations of FTIR Despite its advantages, FTIR has certain limitations. It primarily provides chemical information rather than complete physical characterization. Identification can be affected by dyes, finishes, coatings and contaminants. Similar chemical compositions may produce similar spectra. Very small amounts of minor components may be difficult to detect. Surface-sensitive techniques such as ATR may not represent the composition of the entire textile if the surface differs from the bulk. Accurate quantitative blend analysis may require calibration and complementary methods. Interpretation requires suitable reference spectra and trained personnel. FTIR alone may not always provide definitive identification of every textile fibre. Therefore, FTIR should be used as part of a comprehensive analytical approach, particularly when the result has regulatory, commercial or dispute-resolution implications. FTIR Compared with Conventional Fibre Identification FTIR complements, rather than completely replaces, conventional textile testing methods. Microscopy - Fibre morphology and physical appearance Burning behaviour - Preliminary fibre classification Solubility/chemical tests - Chemical response and fibre identification FTIR - Molecular/chemical fingerprint Thermal analysis - Thermal behaviour and polymer characteristics Chromatographic techniques -Detailed chemical composition in suitable applications Using more than one technique can provide greater confidence in the identification of an unknown textile material. Importance in Textile Testing Laboratories For a modern textile testing laboratory, FTIR can serve as an important screening, identification and investigative tool. It can reduce the time required for preliminary identification and provide chemical evidence to support conventional testing. In cases involving suspected misdeclaration of fibre content, unknown textile materials, unusual finishes or polymeric components, FTIR can provide valuable preliminary information before more extensive confirmatory testing is undertaken. The reliability of the result depends on appropriate instrument calibration, sample handling, spectral quality, reference libraries, validated procedures and competent interpretation. Conclusion FTIR spectroscopy is a powerful analytical technique for the identification, classification and characterization of textile materials. Its ability to generate a characteristic chemical fingerprint makes it particularly useful for distinguishing natural, regenerated and synthetic fibres and for investigating textile blends, finishes, coatings and contaminants. For silk textiles, FTIR can provide valuable supporting evidence for identifying the proteinaceous nature of silk and differentiating it from other textile materials. However, the effect of degumming, dyes, finishes and other treatments must be considered during interpretation. The combination of FTIR with microscopy, physical examination and appropriate chemical or quantitative methods provides a more reliable approach to textile material identification. With its rapid analysis, small sample requirement and minimal preparation, FTIR is an important modern tool for quality control, research, product verification and forensic textile analysis.