1. Experimental principle In the textile industry, formaldehyde is widely used in the dyeing and finishing processes of pure or blended products (including some silk products) due to its use. The main function is to improve the durability of the auxiliary agent on the fabric. However, because formaldehyde has a strong stimulus to the protoplasm of biological cells, it can cause respiratory inflammation and dermatitis. Therefore, it has been identified as a carcinogen and teratogenic substance by the World Health Organization. The laws and standards of various countries all regulate the free formaldehyde content of textile products Strictly control . This article is based on the spectrophotometric method in GB/T2912.1-2009 'Determination of Formaldehyde in Textiles Part 1: Free and Hydrolyzed Formaldehyde (Water Extraction Method)The details have been experimentally studied and analyzed. 2. Test Procedure 1. Instruments and Reagents Cary 50 UV-Vis Spectrophotometer (Varian, USA); ZHWY-110X50 Water Bath Constant Temperature Shaker (Shanghai Zhicheng); Electronic Balance (0.001g); Iodine Measuring Bottle (250 mL) ; Color test
tube (10 mL); measuring cylinder (100 mL). Formaldehyde standard solution: the concentration is 11.0 mg/L (National Standard Material Research Center); tertiary water (or distilled water); color reagent (Nessler's reagent): in a 1000 mL volumetric flask, add 150 g of ammonium acetate, use 800 Dissolve in mL tertiary water, then add 3 mL glacial acetic acid and 2 mL acetylacetone, dilute to the mark with tertiary water, and store in a brown bottle for more than 12 h. Ammonium acetate, glacial acetic acid, and acetylacetone are all analytically pure. 2. Test principle The principle of the water extraction method to determine the content of formaldehyde in textiles is to extract the textile fabric in an aqueous solution at about 40°C , the formaldehyde in the extract reacts with the acetylacetone in Nessler's reagent, and the reaction equation is It is: CH2O+(CH3CO)2CH2→(CH3CO)2Cu003dCH2+H2O. The methylene group of acetylacetone is active because it has two carbonyl groups. It becomes a carbanion under the action of alkali, attacking formaldehyde, and first becomes 3- Hydroxymethyl-2,4-pentanedione ((CH3CO)2CH-CH2OH), and then dehydrated into 3-methylene-2,4-pentanedione (yellow) product. Then use a spectrophotometer to measure the absorbance value at a specific wavelength (412 nm), and then obtain the formaldehyde content by referring to the formaldehyde standard working curve. 3. Experimental method Take two samples from the sample and cut them into small pieces. Weigh 1g each, accurate to 0.001g, and put them into a 250 mL iodine measuring flask, add 100 mL tertiary water, close the lid, and put in (40± 2) Oscillate at a constant temperature of ℃ for (60±5) min, filter the extract, pipette 5 mL of filtrate and 5 mL of color developer into the color developing tube, place in a (40±2) ℃ water bath for color development (30±5) ) Min, then take it out, cool it at room temperature (30±5) min, measure the absorbance value with a spectrophotometer at the wavelength of 412 nm . 3. Results and analysis 1. The influence of whether the sample is completely infiltrated during extraction on the test results of formaldehyde content. Different textile fabrics are selected for the formaldehyde content test. 1# and 3# are the same sample, 2# and 4# are the same sample, 1 #Sample and 2# samples are floating on the water surface without hand shaking after adding water, 3# and 4# samples are artificial hand shaking (about 30 s) after adding water to make the cloth sample completely immersed in water, put 4 samples into the water at the same time In the constant temperature water bath oscillator, under the same other test conditions, the test results of the formaldehyde content of the same fabric due to the different degree of infiltration are shown in Table 1. Table 1 The formaldehyde content test of fabrics with different degrees of infiltration can be obtained from Table 1. Polyester cloth and nylon cloth (including coating) are mostly non-hydrophilic fabrics, so whether they are completely immersed in tertiary water during extraction has little effect on the test results of formaldehyde content; while flocking that is completely immersed after manual shaking The cloth fabric is nearly half higher than the result without soaking; the denim fabric is usually immersed in the water after adding water, and there is almost no possibility of floating on the water surface, so whether it is manually shaken has no significant effect on the result. It is comprehensively recommended that after adding 100 mL of tertiary water, relevant testers should try to completely immerse the tested sample in tertiary water (especially flocking cloth or woolen cloth), and then perform constant temperature shaking extraction to ensure the test results Accuracy. 2. The effect of the cooling time after shaking extraction on the test results of formaldehyde content. Under the same other test conditions, take 4 samples of different formaldehyde content grades (fabrics with the same composition analysis) and go through (40± 2) After shaking at a constant temperature for (60±5) min, the same sample was placed at room temperature and cooled for 10 min, 25 min, 35 min, 45 min, 60 min, and then subjected to the color test . The results are shown in Table 2. Table 2 Tests of formaldehyde content at different cooling times after extraction. As can be seen from Table 2, (1) Samples 1#～4# have different results in formaldehyde content with different storage time. The 1# and 2# samples have low formaldehyde content, and their influence with the storage time is also small, while the 3# and 4# samples have higher formaldehyde content, and their influence with the storage time is more significant. (2) It is not that the longer the storage time, the higher the formaldehyde content. The formaldehyde content in a short period of time (within about 60 minutes) is an increasing trend. When the storage time continues to extend (after 6 hours), the formaldehyde content gradually decreases with the volatilization of water and formaldehyde itself. (3) From the data in Table 2, it can be seen that the formaldehyde content within 30 minutes is quite close to the standard value, and the result will be far away from the standard value after 45 minutes. Therefore, it is recommended that after shaking extraction, the color test should be performed after appropriate cooling, but the cooling time should not be too long, preferably (30 ± 5) min.
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