Non-destructive testing (NDT) methods include a wide range of analytical techniques that can evaluate various kinds of materials, elements, welds, systems, etc., without rendering any damage or harm to the samples. This article focuses on the different NDT methods that are used in the textile industry.
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Textile producers conduct toxicological and other analytical tests, using various NDT methods, to analyze hazardous materials such as allergens, heavy metals, or even carcinogens in their products. Several toxic metals such as cadmium antimony, lead, chromium, mercury, zinc, etc. can either exist in the natural textile fibers or penetrate during the dyeing process or are present in the protection agents used for storing textiles.
Vibrational spectroscopy has been a commonly used NDT method because when light interacts with molecules present on the textile surface, it creates vibrations specific to the functional groups or chemical bonds present in the material. These vibrations generate unique spectral fingerprints which can be used to identify the material or elements present in the textile product.
NDT Techniques: a Brief Overview
NDT techniques have been in use for over thirty years, and their primary goal has been to detect flaws without affecting the operation of the equipment. NDT methods have several advantages over conventional testing methods that, most importantly, include a reduction in sample wastage. Additionally, imaging-based testing methods have enabled the design of optimal production processes, which result in a better quality and quantity of products.
Some of the most commonly used NDT methods are eddy current, microwave ultrasonic, and acoustic emission. A particular method selected for analysis is based on the type of object that needs to be inspected or the type of defect that needs to be identified.
Recent advancements in optical NDT methods provide higher detection accuracy and sensitivity. One of the common types of optical NDT includes infrared thermal imaging. Recently, optical fiber sensors are also being used for measuring the dynamic properties of materials.
NDT methods are powerful tools to detect deterioration of silk, which is characterized by splits and tears that progresses to powdery and friable surfaces. A deteriorated silk is difficult to restore. It is difficult to analyze silks using conventional methods because deterioration accelerates when treated with metallic salts, and many times these samples become difficult to identify. NDT techniques have overcome these difficulties and helped curators and conservators to preserve both technical art history as well as the condition of the objects.
NDT Methods in the Textile Industry
Spectroscopic techniques, such as Raman spectroscopy and polarised attenuated total reflectance infrared spectroscopy (pol-ATR), are commonly used to analyze the condition and composition of silks. In the textile industry, generally, Raman or infrared spectroscopy techniques are used to characterize textiles and fabrics, and to inspect the quality of raw materials. Two of the NDT techniques that are used to understand the condition and composition of silks are X-ray fluorescence (XRF) and near-infrared (NIR) spectroscopy. As stated above, several NDT methods are used in the textile industry, among which some are described below.
Infrared thermography (IRT) has been recently used as an NDT method to analyze adhesively bonded textile structures. In the manufacturing of apparel, textile bonding with adhesive has become a popular construction method. Researchers reported that
the spatial homogeneity of the temperature distribution in the bonded area is linked with the Peel Strength of that bond. IRT can be used to detect in-homogeneity in the thermal distribution and, thereby, can differentiate between a good and bad bond.
Scientists stated that the IRT result can reveal a two-step glue distribution pattern, during thermal treatment, of the sample which affects the Peel Strength of the bond. Additionally, the Fast Fourier Transform (FFT) technique can also elucidate the temperature distribution pattern within the bonded seam of a textile material.
Further Reading: Food Waste Reduction with Non-Destructive Testing
XRF and NIR Spectroscopy
In textile industries, XRF spectroscopy has been used for the identification of mineral dyes, weighting agents, and mordants. The advancements in analytical tools from larger-scale laboratory-based equipment to hand-held portable XRF devices have helped evaluate historic textiles.
These instruments are battery-powered and are connected to a computer where the data is analyzed. Total Reflection XRF (TXRF) is used for the detection of arsenic, chromium, lead, cadmium, cobalt, nickel, copper, mercury, and zinc in various cloth samples. Scientists have reported that the element pattern of textile samples is analogous to “fingerprints” which can be determined in TXRF-spectra.
Therefore, this technique is also used in a forensic investigation for the identification of textile samples. NIR spectroscopy has been used to identify a variety of natural and synthetic fabrics. This technique has been useful to analyze the strain areas in silks material. Similar to XRF spectroscopy, NIR spectroscopy is also used to study historic silk samples.
PE inspection method introduces a sound beam to the textile sample, which travels through the raised divider portion of the fabric and returns to the transducer. The sound travels back to the transducer upon encountering discontinuities inside the sample. The dispersed signals or sound waves are processed for the fast identification of textile fabrics.
Terahertz (THz) Technology
The electromagnetic waves whose frequency range from 0.1 THz to 10 THz are known as THz waves. THz wavelength occurs in between microwave and infrared. In the THz NDT method, THz radiation with a known wavelength is introduced on the textile sample and the reflected radiation is captured. The internal structure of the sample is determined by analyzing the changes in the THz signal. One of the advantages of this method is that, unlike IR thermography, THz waves can penetrate opaque materials.
References and Further Reading
Kumpati, R. et al. (2021) Current Trends in Integration of Nondestructive Testing Methods for Engineered Materials Testing. Sensors (Basel, Switzerland), 21(18), pp. 6175. https://www.mdpi.com/1424-8220/21/18/6175
Fernando, W.D. et al. (2019) Infrared thermography as a non-destructive testing method for adhesively bonded textile structures. Infrared Physics and Technology. 98. 10.1016/j.infrared.2019.03.001. https://www.sciencedirect.com/science/article/pii/S1350449518306467
Zhu, Y. K., et al. (2011). A review of optical NDT technologies. Sensors (Basel, Switzerland), 11(8), pp. 7773–7798. https://www.mdpi.com/1424-8220/11/8/7773
Non-Destructive Testing of Silks: Problems and Possibilities. (2011). [Online] Available at: https://www.english-heritage.org.uk/siteassets/home/learn/conservation/collections-advice--guidance/ndt-silk-1810-47-luxford-paper-en.pdf
Dogan, M. et al. (2002) Application of Total Reflection X-Ray Fluorescence Spectrometry in the Textile Industry. Microchimica Acta. 138. pp. 77-82. 10.1007/s006040200012. https://www.semanticscholar.org/paper/Application-of-Total-Reflection-X-Ray-Fluorescence-Do%C4%9Fan-Soylak/f327955942a518347db2b81965bb594c3cd31b22