Five fabric components most easily misidentified during testing

Fiber content testing is crucial in all textile testing. Almost every batch of samples needs to have its component content tested. The test data is related to both the costs for manufacturers and distributors, and the health of consumers.

According to GB/T 29862-2013 “Labeling of Fiber Content in Textiles,” “each product should be labeled with its fiber content,” and this is a mandatory test item in all levels of random inspections. However, all inspections have errors, especially those that rely heavily on manual labor. Therefore, improving the accuracy of test data is particularly important. This article summarizes common missed detections in textile fiber content testing based on testing experience, aiming to improve the accuracy of test data.

Misjudgment and missed detection caused by different types of fabrics

1. Denim Fabric: Analysis of nearly 100 batches of denim fabric testing data revealed that samples containing 1% to 2% (or even lower) regenerated cellulose fibers are most prone to false negatives. After ruling out the influence of personnel experience and physical condition, the reasons for these false negatives are related to the darker dyeing of the denim fabric itself, making microscopic observation unclear. However, based on experience, the primary reason lies in the abnormal morphology of the regenerated cellulose fibers. The longitudinal section of these regenerated cellulose fibers in denim fabrics often appears ribbon-like and transparent, unlike the typical viscose fiber form. Furthermore, in some cases, not every fiber exhibits this morphology; often, only one out of three or four fibers will show this characteristic, requiring meticulous attention from inspectors.
2. Pure Mercerized Cotton Fabric: Currently, the composition of pure mercerized cotton fabrics on the market is more complex, but the overall visual appearance and feel are not significantly different. In recent years, similar fabrics have been found to contain lyocell, linen, and silk fibers. In most cases, the content of linen and silk fibers is very low. Given the similar morphologies of mercerized cotton, lyocell, and silk, false negatives are easily detected.
3. Fabrics with Indistinguishable Appearance and Pattern To increase strength and comfort, some garments use fabrics with different fibers in different areas. If these fabrics differ significantly in areas such as sleeves, body, cuffs, and collars, it has little impact on inspectors. However, if they exist in the same area and have no obvious differences in appearance, they are easily missed during inspection. For example, the upper and lower parts of the front panel of a knitted sweater may have different fiber compositions; two samples with identical jacquard patterns may have different fabric compositions. This requires inspectors to have a systematic understanding of the entire fabric before inspection, and for fabrics with no obvious differences in appearance, multiple samples should be taken for inspection.
4. Fiber Scraps

For garments made from fiber scraps, special attention needs to be paid to low-content and trace fiber content. It is recommended to use a dyeing method to qualitatively characterize the fabric. This provides an accurate determination of the fiber composition and a general understanding of its content, offering a reference for subsequent quantitative dissolution tests.

5Yarn-dyed Jacquard Fabrics

For yarn-dyed fabrics with irregular jacquard patterns, different colored yarns should be tested separately, and test data should be provided separately for each color. Experience shows that if the composition of each colored yarn varies significantly, the data obtained from testing different parts will differ greatly, seriously affecting the test results.

Error caused by changes in the solubility of the reagent in the fiber

With changes in textile materials and advancements in spinning technology, the solubility of conventional fibers has also changed. However, most solubility test methods in relevant inspection standards were established many years ago, which may affect the accuracy of current testing.

Due to improvements in spandex production processes and differences in raw materials, the solubility of different types of spandex varies significantly. When using DMF to dissolve spandex, some types are difficult to completely dissolve even after shaking in a 95°C water bath for 1 hour. This requires inspectors to carefully observe the dissolved fibers; if abnormalities are found, other methods should be used for testing. The splitting method should be the preferred method for spandex content testing.

For certain acetate fibers, lyocell, and multi-component samples of mulberry silk, sequential dissolution methods should be avoided as much as possible. Instead, the splitting method or a splitting followed by dissolution method should be used for testing. Tests show that alkaline sodium hypochlorite solution is soluble in some acetate fibers, and acetone may be soluble in some mulberry silk fibers, but the extent of solubility needs further experimental verification.

For blended fabrics of dark-colored cotton and lyocell fibers, a formic acid/zinc chloride solution dissolution test is required. Experience shows that it is better to bleach the fibers in an alkaline environment before testing. Following standard methods alone, lyocell fibers are difficult to dissolve completely, leading to unnecessary repeated testing and prolonging the inspection cycle.

When dissolving wool and silk blend samples, using the 75% sulfuric acid method, even with standard-compliant partial shaking dissolution, complete dissolution is difficult. Experience indicates that vigorous shaking at room temperature is more reasonable.

Misjudgment caused by novel or uncommon fibers

In recent years, new and functional fibers have emerged in large numbers, such as seaweed fiber, chitosan fiber, glass fiber, and certain special modified acrylic fibers. However, the corresponding testing standards for these fibers are either recently published or still in the drafting stage. This places higher demands on the technical skills of testing personnel. Therefore, it is essential to strengthen the understanding of new fibers and study relevant literature.

The Influence of Pretreatment on Quantitative Results: Dark-colored fabrics generally require bleaching treatment before formic acid/zinc chloride solution dissolution tests; denim, due to its dark color, sometimes has a significant impact on test results and also requires bleaching treatment; greige fabrics with high sizing content and a stiff hand feel generally require desizing treatment before testing. Composite fabrics are often used in windproof jeans, windbreakers, etc., where the inner and outer layers are generally bonded together with adhesive. Without desizing pretreatment, the quantitative test results will be greatly affected.

Although GB/T 2910.1-2009, “Quantitative Chemical Analysis of Textiles – Part II: General Test Rules,” clearly specifies the chemical reagents and methods used for degumming or desizing, these non-fibrous substances are often difficult to identify. The removal methods used are generally selected based on the experience of the inspectors, making standardization difficult. Different reagents and methods result in different removal effects, which will more or less affect the quantitative results. This requires inspectors to be adept at summarizing experience, carefully observing the removal status of treated samples, and noting the pretreatment details in the test report when necessary to avoid unnecessary disputes and controversies. For samples containing extremely difficult-to-remove non-fibrous substances, it is advisable to communicate with the client and perform only qualitative testing on that sample.

In Conclusion

Textile fiber content testing is a largely manual process, heavily reliant on personnel experience and utilizing limited equipment. This necessitates that personnel diligently summarize their experience during routine inspections, regularly review the latest literature, and minimize the probability of missed detections and misjudgments, thereby reducing the accident rate and preventing unnecessary economic losses for clients.

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