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    Home > Coatings News > Paints and Coatings Market > Determination of free formaldehyde content in fabric emulsions

    Determination of free formaldehyde content in fabric emulsions

    • Last Update: 2020-12-05
    • Source: Internet
    • Author: User
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    0 Introduction
    Formaldehyde is an important organic raw material, because of its low price and widely used in industrial production, in the textile printing and dyeing industry, formaldehyde is mainly used to improve the performance of fabric anti-wrinkle, anti-shrink, flame retardant and other aspects and to maintain the durability of printing, dyeing, but formaldehyde has a high toxicity, has been identified by the World Health Organization as carcinogenic and malformed substances, so the content of fabric residue formaldehyde should be strictly controlled.
    In the textile field, the state stipulates the limit of formaldehyde content in textiles (GB 18401-2003) as follows: infant supplies ≤ 20 mg/kg, direct contact with skin products ≤ 75 mg/kg, non-direct contact with skin products ≤ 300 mg/kg. The residual amount of formaldehyde in fabric is closely related to the content of formaldehyde in fabric emulsion, therefore, measuring how much formaldehyde content in fabric emulsion can provide a strong basis for the control of formaldehyde in textiles, so it is of good practical value and practical significance to study the measurement method of free formaldehyde in fabric emulsion
    China
    .
    formaldehyde content of many methods, commonly used spectrolight, high-efficiency liquid chromatography, electrochemical method, but the determination of formaldehyde content in fabric emulsion is not an effective method. High-efficiency liquid chromatography is often used for testing using the ISO/TS 17226 Leather-Chemical Test-Design of Formaldehyde Content standard.
    This standard is mainly used for the determination of free formaldehyde content in leather, test sample pre-treatment is: (1) the pre-called good leather quantitatively added to a conical bottle containing a mass concentration of 0.1% sodium tranium sulphate solution, covered with glass plugs; After heating the oscillation (60±2)min in a water bath (40±0.5) degrees C, the extract solution is immediately filtered in a hot vacuum with a filter of 0.45 m, the cooling filter is cooled to room temperature, and the high-efficiency liquid chromatography is used. Fabric emulsions are generally small in size and are filtered with a filter of 0.45 m, allowing the lotion to pass through.
    If the emulsion contains certain additives, and formaldehyde peak time is consistent or similar to the interference, then the method will produce a large error, and the instruments used are expensive, difficult to promote the application in the general enterprise. Fabric emulsion often uses hydroxymethyl acrylamide as crosslinker, if the content of free formaldehyde in fabric emulsion is determined by GB 18582-2008, it will have a great impact on the determination results of free formaldehyde due to the release of formaldehyde during high temperature distillation. In this study, the experimental device in GB 18582-2008 was improved, the free formaldehyde in the sample was steamed by decompression distillation, a stable yellow convection was produced with acetyl acetone under 60 degrees C constant temperature water bath conditions, and the absorbance test was carried out at its maximum absorption wavelength of 412 nm after cooling.
    the content of free formaldehyde in the sample is calculated according to the regression linear equation in the standard working curve. Through the study, it is found that the measured data are similar to the results measured by the high-efficiency liquid chromatography. Although the operation of this method is more cumbersome, but the instrument used is simple, low cost, and acetyl acetone color stability, repeatability and reproducibility are better, is worth promoting the application of the method.1 Test
    1.1 Reagents and Instruments
    Reagents used in the experiment can be found in Table 1, and the instruments used in the experiment are in Table 2.
    the drawing of the standard curve by the reagent
    experimental instrument
    1.2 standard curve
    and the drawing of the standard curve according to the requirements of GB 18582-2008: take 8 50 mL color tubes and move them into 0.00, 0.0. 20 mL, 0.50 mL, 1.00 mL, 3.00 mL, 5.00 mL, 8.00 mL formaldehyde standard solution (1 μg/mL), diluted with water to scale. Add acetyl acetone with a volume fraction of 0.25% of 2.5 mL, heat 30 min in a heated water bath at 60 OC, remove and cool to room temperature, and use water as a score to measure the absorbance at 412 nm using a UV-visible phosphorescometer.
    1.3 Sample Test
    With reference to the requirements in GB 18582-2008: (1) take the well-stirred sample 2 g (accurate to 1 mg), place in a 50 mL capacity bottle, shake with water, dilute to the scale. (2) Remove the 10 mL sample aqueous solution from a piped pipe and place it in a distillation bottle that has been pre-added with 10 mL of water, as shown in Figure 1. Pre-add 40 mL of distilled water to the distillation receiver, immerse the distillate receiver outlet and cool the exterior with an ice bath. Open the condensate, vacuum pump, while adjusting the capillary tube placed below the distillation surface, and fine-tune the capillary switch to control the bubble rate and vacuum degree, reach the specified vacuum level before starting to heat the distillation. When the sample is steamed to near dry, stop heating, turn on the capillary switch, turn off the vacuum pump, remove the fractional receiver, dilute with water to a scale of 100 mL, to be measured. For fabric emulsions with high formaldehyde content, it should be diluted and then measured to prevent its absorbance from exceeding the linear range, the operation steps are as follows: the fixed-capacity distillate with a pipe transfer a certain volume to 50 mL color tube, dilute it to determine the capacity, and after the fixed-capacity color tube to add 0.25% Acetyl acetone solution 2.5 mL, shake well, heat 30 min in a heated water bath at 60 degrees C, remove, cool to room temperature, in the ultraviolet hydrophosometer 412 nm to determine the absorbance A, while the water as a blank sample, measured blank absorption A0. Subtract the absorbance A of the sample from the blank absorbance of A0 and find the corresponding formaldehyde mass on the standard curve. The content of free formaldehyde in the emulsion is calculated according to the following formula:
    free formaldehyde content: w smfm'
    which: m - formaldehyde quality found on the standard curve, sg;
    m' - sample mass, g;
    f - total dilution factor.
    2 Results and discussion
    2.1 Standard Curve Drawing
    Standard Curve Drawing is the key to the quantitative analysis of formaldehyde content of UV-visible hydrometers, and the quality of the standard curve is directly related to the accuracy of the test results. Through experiments, the absorbance value of the known formaldehyde content sample is measured, the formaldehyde content is the horizontal coordinate, the absorbance value is the ordinate plot, and a straight line is achieved, that is, the standard curve, as shown in Figure 2.
    the standard curve equation: y -0.003 9x-0.004 3, the linear correlation coefficient is R2-0.999 4, the standard curve is good linear, which provides a strong guarantee for the accuracy of the test results.
    2.2 Normal pressure distillation method to determine the content of free formaldehyde in fabric emulsion

    data from Tables 3 and 4 show that: directly according to the GB18582-2008 method to determine the fabric emulsion free formaldehyde content repeatability difference, relative deviation is large, can not meet the GB 18582-2008 reproduction requirements (when the test results ≤100 mg/kg ≤10 mg/kg for the difference between the two test results of the same operator, and when the test results ≥100 mg/kg, the relative deviation ≤5%) from the results of the two tests of the same operator is far from the HPLC (Efficient Liquid Chromatography) test results (Table 8). The deviation of the data is mainly due to the higher direct heating temperature of the electric heating sleeve, which not only steams free formaldehyde out of the fabric emulsion, but also releases hydroxymethyl acrylamide in the fabric emulsion, which affects the accuracy of the measurement results. Therefore, it is not appropriate to determine the free formaldehyde content in fabric emulsion in full accordance with national standard GB 18582-2008. In order to reduce the error caused by the release of formaldehyde by hydroxymethyl acrylamide, this study attempted to determine the free formaldehyde content in fabric emulsion by decompression distillation.
    2.3 Decompression distillation to determine the free formaldehyde content in fabric emulsion
    In using decompression distillation to determine the free formaldehyde content of fabric emulsion, the effect of different distillation conditions, such as distillation time, distillation temperature, etc., on the test results was studied, and the repeatability of the experiment was verified under the best test conditions, and the results of this method were compared with the test results of the authoritative authorities.
    Effect of
    2.3.1 Distillation Time
    Under conditions of a constant vacuum of 0.05 MPa (at a certain bubble speed) and a distillation temperature of 120 degrees C, the effect of distillation time on the measurement results is examined, as shown in Figure 3.
    can be seen from Figure 3: when the sample distillation time is below 60 min, the formaldehyde content remains basically the same, and when the distillation time exceeds 60 min, the formaldehyde content increases sharply. This is mainly due to prolonged heating, resulting in the release of formaldehyde by hydroxy methyl acrylamide. It can be seen that in order to accurately determine the content of formaldehyde, distillation time must be controlled below 60 min. From Figure 3 can also be seen: even if the distillation of 30 min, the measurement results are longer than the authorities with HPLC test results, this is due to the distillation temperature of 120 degrees C, still higher, hydroxymethyl acrylamide easy to release formaldehyde; Considering that distillation takes too long, takes a long time, and is less efficient, and that the distillation time is too short, the free formaldehyde in the emulsion cannot be distilled completely, the optimal distillation time is determined to be 30 min.
    2.3.2 distillation temperature
    when examining the effect of distillation time on the measurement results, the distillation temperature was selected to be 120 degrees C. The temperature is higher, and hydroxymethylene acrylamide still releases formaldehyde. So on this basis, the effect of distillation temperature on the measurement results is examined. The effect of distillation temperature on the measurement results is examined under the premise of controlling a vacuum of 0.05 MPa (at a certain bubble speed) and a distillation time of 30 min, as shown in Table 5.
    can be seen from Table 5: the higher the distillation temperature, the greater the measurement results, the measured free formaldehyde content increases with the distillation temperature. At a temperature of 120 degrees C, it is edgy compared to HPLC test results due to the high distillation temperature and the easier release of formaldehyde by hydroxymethylene acrylamide. When the temperature is controlled at 97 degrees C, the measurement results are similar to those of HPLC, but the measurement results are low when the temperature is controlled at 86 degrees C, which is due to the low temperature, the free formaldehyde in the emulsion cannot be steamed out in 30 min, resulting in low results. Determine the optimum distillation temperature at 97 degrees C.
    2.3.3 Repetitive Test
    by exploring the distillation conditions, it is determined that the content of free formaldehyde in the fabric emulsion can be determined more accurately by decompression distillation of 30 min at 97 degrees C. To this end, this experiment is tested for repeatability under these conditions to verify the rationality of this condition. First, sample 1 is distilled at (97±2) degrees C decompression distillation of 30 min for repetitive testing, the results of which are shown in Table 6.
    As can be seen from Table 7, the measured results are stable, the measurement results are below 100 mg/kg, and the difference of the same operator's measurement results is ≤ 10 mg/kg, the repetition is very good, and the HPLC test results are similar. In addition, the maximum error of fabric emulsion samples 1 and 2 meets the requirements in GB 18582, so it is feasible to determine the free formaldehyde content in fabric emulsion samples under these conditions.
    2.3.4 Comparison of the measurement results of this method with the authoritative body HPLC
    through the above measurement condition analysis, it can be clearly seen from the data: in a certain vacuum degree (0.05 MPa), distillation time of 30 min, distillation temperature (97±2) degrees C, the measurement results are repetitive and the error is small. Compare the results of multiple measurements with errations with errations measured by HPLC, as shown in Table 8.
    From Table 8, it can be seen that decompression distillation determines the content of free formaldehyde, which is similar to the results of HPLC determination by the authority, indicating that it is feasible to determine the content of free formaldehyde in fabric emulsion with decompression distillation sample under these conditions.
    2.4 Analysis of the source of experimental error
    In the process of determining the free formaldehyde content in fabric emulsion by this method, there are many error sources, among which the condition of distillation is the main factor affecting the error, so the vacuum, distillation temperature and time must be strictly controlled in the test process. In the preparation of formaldehyde standard solution and calibration of its concentration, the judgment of titration end point must be strictly controlled. In the use of dlight chromodometer, the cuvette must be paired for use, after use must be cleaned in a timely manner, and regularly washed with erthyhexane and acetone, to minimize the impact of the cuvette on test results. Standard solutions used as standard curves must not be placed longer than 7 d and must be re-provisioned if they are exceeded. Acetyl acetone reagents (Nash reagents) are color-showing agents for determining formaldehyde content and must be stored in brown glass bottles to prevent chemical reactions between light and reagents, affecting color-showing effects. With the extension of the placement time, the color of acetylacetone gradually deepened, after placing 30 d must be re-provisioned to reduce the effect of color agent on the experimental results. 3 Conclusion
    According to GB 18582-2008 normal pressure distillation sample to determine the free formaldehyde content in fabric emulsion there is a large error, and the normal pressure distillation will be changed to decompression distillation, and in the vacuum of 0.05 MPa, Under the condition of distillation with a distillation temperature of 97 degrees C and a distillation time of 30 min, the stability of the measurement results is good, the repeatability is high, and the error compared with the HPLC test results of the authoritative body is small, the measured data is more reliable, and can be determined by the fabric emulsion manufacturer, which provides favorable conditions for controlling the content of formaldehyde in textiles.
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