The level of modern manufacturing technology has improved, and coated fabrics have become a consumer hotspot
The PU coating finishing agent for fabrics is a polymer compound that is evenly applied to the surface of the fabric. It forms one or more films on the surface of the fabric through adhesion, which can improve the appearance of the fabric and increase the repellency, such as Fabric styles with extremely functional functions such as water, breathability, fire resistance, and UV resistance have opened up new uses for fabrics.
GB5296.4-1998 “Consumer Goods Instructions for Use of Fabrics and Work Clothes” clearly stipulates that the instructions for use of fabrics and work clothes sold domestically should indicate the name of the ingredients and their content of the raw materials used in the product, and the fiber content of the fabric. Labeling should comply with the regulations of FZ/T01053. PU coated fabrics have certain difficulties in component analysis, which can easily lead to inaccurate qualitative and large quantitative errors. The removal of PU coating is not only related to the type of PU coating agent, but more importantly, the fibers of the base fabric cannot be damaged or melted in a small amount during the removal process.
my country has certain research on the method of removing PU coating from polyurethane PU coated fabrics. Existing literature reports that the research on PU coating removal method is based on the premise that the base fabric is polyester (polyester), nylon, or cotton. The obtained PU coating removal method is limited in scope of application due to a single research object, and the damage and correction coefficient of the corresponding reagent to other types of fibers are not given, so the operability is not strong. Therefore, this article takes polyurethane PU coated fabric as the research object to explore the effectiveness of using tetrahydrofuran to remove PU coating.
1 test
1.1PU coating removal test
1.1.1 Test equipment and instruments
Biological microscope: magnification is 500-2000 times; constant temperature water bath oscillator: maintaining temperature at (25±2)℃, (50±2)℃, (60±2)℃; suction filtration device; with stopper triangle Flasks, glass sand core crucibles, measuring cylinders, etc.
1.1.2 Test samples
Polyurethane PU coated fabric.
1.1.3 Test reagents
Tetrahydrofuran (analytical grade), tertiary water.
1.1.4 Test steps
Put the polyurethane PU coated fabric into a stoppered Erlenmeyer flask, add 100mL tetrahydrofuran to each gram of sample, shake the Erlenmeyer flask to submerge the solution and fully wet the sample, then place it into the corresponding temperature (25℃, 50℃, 60 °C) in a water bath shaker for 30 min.
Watch and record the melting of the PU coating during the shaking process. After the shaking, use tweezers to take out the fabric, observe the changes in the PU coating on the surface of the fabric, and record them one by one. Then move the fabric into a glass sand core crucible, vacuum to drain the liquid, and rinse thoroughly with cold water. Finally, the crucible and fabric are vacuumed to drain, dried and cooled.
Observe whether there is any residual PU coating on the surface of the fabric after drying and cooling, and in the gaps between the spinning yarns. Use tweezers to pick out certain fibers in the fabric and place them on a glass slide. Add 1 to 2 drops of transparent medium and cover with a lid. View the glass slide under a microscope and record whether the surface of the fiber is clean and whether there are flakes or granular foreign matter adhering to it.
1.2 Research on d value of base fabric fiber
1.2.1 Equipment and instruments
Biological microscope: magnification is 500~2000 times; analytical balance: accuracy is 0.0002g; constant temperature water bath oscillator: maintaining temperature is (25±2) ℃, (50±2) ℃; drying oven: can maintain temperature is (105±3)℃; suction filtration device; capacity is 30mL~40mL, pore diameter is 90µm~150µm sintered round filter crucible; stoppered Erlenmeyer flask: capacity is 250mL; desiccator equipped with silica gel, weighing Dishes, slides, coverslips, tweezers, scissors, etc.
1.2.2 Test samples
Single fiber interlining (cotton, wool, mulberry silk, ramie, polyester, nylon, viscose, polyacrylonitrile fiber), vinylon, lyocell, modal, spandex.
1.2.3 Test steps
This test mainly tests cotton, wool, mulberry silk, ramie, polyester, nylon, viscose fiber, polyacrylonitrile fiber, vinylon, lyocell, modal and spandex respectively at (25±2)℃, (50 Mass change under the action of tetrahydrofuran solvent at ±2)℃. Conduct repeatability tests on 10 samples for each fiber under each condition (20 samples for samples with quality damage), and find the average value of d value (quality correction coefficient).
Process each fiber according to the PU coating removal method. Place each accurately weighed sample into an Erlenmeyer flask, add 100 mL of tetrahydrofuran per gram, shake the Erlenmeyer flask until the solution is immersed and fully wet the sample, then place it in (25±2)℃ and (50±2) respectively. Shake vigorously in a water bath shaker at ℃ for 30 minutes. After shaking, move the fabric into a glass sand-core crucible with a known dry weight, drain the liquid by vacuum suction, and wash it thoroughly with cold water. After each cleaning, drain the liquid by gravity first, and then use vacuum suction to drain the liquid. Finally, vacuum the crucible and fabric to drain the liquid, then dry, cool and weigh. Calculate the average of 10 fiber correction coefficients of the same component.
2 Results and Discussion
2.1PU coating removal test results
The removal conditions of polyurethane PU coating in tetrahydrofuran solvent are shown in Table 1.
Table 1 Removal effects of polyurethane PU coating in tetrahydrofuran solvent and various temperatures
As can be seen from Table 1, the use of tetrahydrofuran can better dissolve the polyurethane PU coating under the conditions of test temperatures of (25±2)℃, (50±2)℃, and (60±2)℃. It can achieve no PU coating residue on the fabric surface, and the yarn and fiber can be spun.�The surface is clean and no flake or granular foreign matter adheres, which meets the qualitative requirements of fiber composition analysis; at the same time, as the temperature increases, the PU coating melts faster, which is beneficial to improving efficiency. Therefore, (25±2)℃ and (50±2)℃ can be selected as the test temperatures for the next experiment.
2.2 D value of base fabric fiber
D value = (total weight before test – crucible weight) / (total weight after test – crucible weight). The effect of tetrahydrofuran on cotton, wool, mulberry silk, ramie, polyester, nylon, viscose fiber, polyacrylonitrile fiber, vinylon, lyocell, modal and spandex under the conditions of (25±2)℃ and (50±2)℃ The values are shown in Table 2.
Table 2 Summary table of d values of various base fabric fibers
According to the above test results, it can be seen that the d value of tetrahydrofuran on cotton, ramie, wool, mulberry silk, viscose fiber, modal, lyocell, polyester, nylon, vinylon, and polyacrylonitrile fiber at (20±2)℃ is 1.00, and has a correction coefficient of 1.04 for spandex; at (50±2)℃, the d value for ramie, wool, mulberry silk, viscose fiber, modal, lyocell, polyester, nylon, vinylon, and polyacrylonitrile fiber is 1.00 , there is a correction coefficient of 1.01 for cotton, and a correction coefficient of 1.06 for spandex. The above two experiments have proved that the use of tetrahydrofuran to remove polyurethane PU coating not only has good removal effect, but also is conducive to the qualitative analysis of fiber components; it also causes little damage to the base fabric fiber and has little impact on the quantitative analysis of fiber components. Therefore, in actual work, tetrahydrofuran, melting temperature (25±2)°C, and melting time of 30 minutes can be selected to remove the polyurethane PU coating.
3Conclusion
The traditional method of removing polyurethane PU coating is to use dimethylformamide. Because dimethylformamide will dissolve spandex and polyacrylonitrile fiber, this method is used when the base fabric fiber contains polyacrylonitrile fiber and spandex. Not applicable, and dimethylformamide is highly toxic. The PU coating removal method using tetrahydrofuran as the dissolving reagent, the test temperature is (25±2)°C, and the test time is 30 minutes has the advantages of low test temperature, wide application range, and low toxicity, and its test results fully meet the fiber composition analysis The pretreatment conditions provide an important guarantee for the accurate quantitative analysis of fiber components in the next step.
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