Identification of coatings
The reagents and methods used to remove the coating depend on the type of coating. ATR (Attenuated Total Reflection, Attenuated Total Reflection) Fourier Transform Infrared Spectroscopy (FTIR) was used to conduct ATR-FTIR analysis on the two coatings, and good results were achieved in their qualitative identification. Since carbon-oxygen double bonds, hydroxyl groups, amino groups, etc. all have different characteristic absorption peaks, the main components of the coating can be determined based on the standard infrared spectrum, which provides a good basis for removing the coating on the sample. This method has high qualitative accuracy for the coating, but the equipment cost is high and it takes a long time.
What makes textile testing competitive today is time, that is, the inspection cycle. The shorter the cycle, the more competitive it is. Therefore, the above methods are of great significance in the field of scientific research, but their operability and practicality are relatively insufficient in daily large-scale inspections. According to experience and data, in terms of feel, compared to polyurethane (PU) coating, PA coating, also known as polyacrylate coating, has a relatively astringent feel, while PU coating is smoother; PU coating The elasticity of the coating layer is better than that of the PA coating; in terms of appearance gloss, the PA coating has no luster, while the PU coating is glossy and relatively bright; and the PU coating has a good film feel and feels like a film to the touch. To put it simply, PU coating is brighter and PA coating has a drapey feel. The hand-visual method of identifying these two coatings is fast and low-cost, but the accuracy is relatively low and requires higher experience of the inspectors. However, this method is more operable and practical in daily large-scale inspections.
Coating Removal
Removal of polyacrylate coating
Using GB/T 2910.1-2009 “Quantitative Chemical Analysis of Textiles Part 1: General Testing Principles”, soak the sample in a solution containing 2g/L soap flakes or other suitable detergent and 2g/L at 70~75°C. In the solution of sodium hydroxide, the liquor ratio is 1:100, stir for 30 minutes, rinse with 85 ℃ deionized water 3 times, 15 minutes each time, wring out and dry. Data show that in dimethylacetamide (DMAC) and dimethyl sulfoxide (DMSO), water bath heating and oscillation conditions also have good results. Special attention should be paid to the selection of reagents when wool, silk, acetate, triacetate, acrylic and spandex fibers are present.
Removal of polyurethane coating
The above-mentioned national standard points out that a completely satisfactory method is not easy to obtain. You can choose to soak the sample in dimethyl sulfoxide or methylene chloride and rinse it multiple times with clean reagents. Without affecting the fiber components, some polyurethanes can be hydrolyzed and removed in a boiling aqueous solution containing 50g/L sodium hydroxide, or an aqueous solution containing 50g/L sodium hydroxide and 100g/L ethanol above 50°C. replace. Experience and data show that the same effect can be achieved using tetrahydrofuran (THF) and N’N-dimethylformamide (DMF) under water bath heating and shaking conditions. Similarly, special attention should be paid to the selection of reagents when wool, silk, acetate, triacetate, acrylic and spandex fibers are present.
Notes
It is not advisable to use alkaline reagents for fabrics made of wool, silk and acrylic; DMF and DMAC are soluble in acetate, triacetate, acrylic and spandex fibers, and THF is recommended; for ramie, modal, lyocell, vinylon and other other There are few fiber-related reports, and the relevant parameters need further experimental verification. Table 1 shows the mass compensation coefficients (d values) of several common fibers in commonly used organic reagents DMF, THF and DMAC.
Experience shows that if the coating is removed by manual splitting first, and then the next step of dissolution and removal is performed, the effect will be better; when the coating is difficult to remove, it is necessary to increase the temperature or extend the dissolution time to achieve complete removal.
Conclusion
In summary, coatings can not only improve the appearance and style of fabrics, but also increase the functionality of fabrics, but this brings difficulties to inspection work. The existence of the coating has a great influence on the chemical dissolution method. It will cause the dissolution reagent used to dissolve the soluble fiber. Determining the type according to the appearance and the reagent according to the composition are important tasks before removing the coating. Due to the influence of the reagents used on the fiber composition of the sample, the fiber composition should be characterized first in actual inspection, and then the removal experiment should be performed. Pay special attention when wool, silk, acetate, triacetate, acrylic or spandex fibers appear in the fiber composition, choose appropriate reagents and methods, and avoid using reagents such as sodium hydroxide solution or DMF to avoid damaging the fiber composition of the sample. Since there are still many fiber-related parameters that need further testing and verification, such as ramie, modal, etc., it is very difficult to remove the coating during the actual inspection process. How to enhance the simplicity, accuracy, and speed of coating removal operations requires in-depth research and standard improvement.
Article source: Woolen Technology
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