In order to improve the dyeing fastness of cotton fabrics, formaldehyde-based fixing agents are often used in the dyeing process. Although the fixing agent can cross-link and fix the cellulose fiber and the dye , the cross-linking or fixation reaction product of the fixing agent reacts with the fiber in a certain environment medium, especially sweat, during the course of taking. The final generation of formaldehyde is commonly referred to as the release of formaldehyde. It can be absorbed by the skin through sweat, and then immersed in the human body , seriously endangering human health. Regarding the release of formaldehyde from textiles, in the past, research focused on optimizing the preparation process of crease-resistant finishing fabrics to reduce the release of formaldehyde, and studies on the law of the release of formaldehyde from dyed and fixed fabrics in aqueous media have hardly been reported. Therefore, in this paper, the cotton fabrics were dyed and fixed using direct dye and fixing agent Y, and the dyed and fixed cotton fabrics were released in different pH values â€‹â€‹in aqueous solution to simulate the dyeing of cotton fabrics under human sweat conditions. The formaldehyde release from sweat on the human skin surface focused on the effect of fixation treatment on the amount of formaldehyde released from dyed fabrics in aqueous media, laying the foundation for the evaluation of the exposure risk of formaldehyde to human skin.
1.1 Materials and Reagents
After the scouring and bleaching of pure cotton fabrics, fixing agent Y, direct lake blue 5B and direct black G are industrial products. Sulfuric acid and sodium hydroxide are analytically pure reagents.
1.2 Instruments and Equipment
Model 723 Visible Spectrophotometer (Shanghai Precision Scientific Instrument Co., Ltd.), ACS-24 Ambient Temperature Sample Dyeing Machine (Tianjin Ryan Technology Co., Ltd.), PHS-25C Acidity Meter (Shanghai Precision Scientific Instrument Co., Ltd.), and Electric Thermostatic Water Bath (Beijing) Medical Equipment Plant) etc.
1.3 Fabric dyeing methods
The dyeing process is used to dye cotton fabrics. Process conditions: direct dye 3%, bath ratio 1:50, dyeing temperature 90Â°C, dyeing time 75min, dyed cotton fabric after washing.
1.4 Fabric Fixing Methods
The dyed cotton fabric is immersed in a fixing agent solution at a predetermined temperature and concentration for a certain period of time, and dried and taken out to obtain a dye-fixed and solid-colored fabric sample, which is put into a sealed plastic bag and put into a refrigerator for use.
1.5 Release of formaldehyde in fabrics and method of determination
First, accurately weigh 10g of the cut solid cotton fabric sample, place it in a volumetric flask, add 1000mL of distilled water, and then place it in a constant temperature water bath at a temperature of (40Â±1)Â°C to release the formaldehyde test. Time to remove 1 ~ 2mL solution, filtered and centrifuged after the determination of formaldehyde, the specific determination method see the national standard GB/T2912.1-1998.
1.6 Initial Release Rate Calculation Method
The initial release rate (V0) is the initial release rate in the first 60 minutes (Î¼gÂ·g-1min-1), ie the linear regression analysis of the formaldehyde release concentration and the corresponding release time at different time within the first 60 minutes of release. The initial release rate equation is obtained, where the slope is the initial release rate.
1.7 Calculation Method of Average Release Rate
The average release rate (Vave) is the average release rate (Î¼gÂ·g-1min-1) over the entire release period and can be calculated using the following equation.
Where: Qb is the equilibrium release, Î¼gÂ·g-1; T is the release time, min.
2 Results and Discussion
2.1 formaldehyde release process analysis
To examine the process of formaldehyde release from dye-fixed-colored cotton fabrics in human acidic and alkaline sweats, the dye-fixed-colored cotton fabrics were placed in distilled water with a pH of 5.0 and a pH of 8.0, respectively, to release the formaldehyde. The effect of pH on the release of formaldehyde from fabrics was investigated and the results are shown in Figure 1 and Table 1.
From Figure 1 and Table 1, it can be seen that the amount of formaldehyde released from the two dye-fixing fabrics increases rapidly at the initial stage as the release time increases, and then slowly increases. There was a good linear relationship between the amount of formaldehyde released (Q) and the release time (T) between the two fabrics during the initial release (60 min), and their initial release rates were significantly higher than their average release rates. This is mainly because the fixing agent contains a small amount of free formaldehyde, which is transferred to the fabric during the processing of the fabric, since it is not chemically bound to the fiber molecules and rapidly desorbs from the fabric into the aqueous solution after encountering water. In addition, during the initial release, the fixation reaction product of the fixing agent with the fiber and the self-condensation product can also undergo a hydrolysis reaction in the aqueous solution to generate formaldehyde, but these hydrolysis reactions proceed relatively slowly. After the initial release period, the formaldehyde released from the fabric mainly comes from the fixation reaction of the fixing agent with the fiber and the hydrolysis reaction of the condensate itself, so the average release rate is lower. It is worth noting that the amount of formaldehyde released, the initial release rate and the average release rate of the fixing cotton fabric in the distilled water medium having a pH of 5.0 are much higher than those of the distilled water medium having a pH of 8.0. The reason can be explained as fixing agent Y is a polymer compound, which produces a lake by a cationic group in a molecular structure and an anionic group in a dye molecule, and can also form a methylene bond fixed by intermolecular condensation. Fiber surface. This methylene linkage may be hydrolyzed in acidic and basic conditions to produce formaldehyde, see equation (1). And under acidic conditions this decomposition reaction may be more prone to occur, releasing more formaldehyde.
2.2 Fixing agent concentration effect
The dyeing fabrics were fixed with different fixing agents at a temperature of 70Â° C. for 30 min, and the dyed fixing cotton fabrics were then placed in distilled water with a pH of 5.0 and a pH of 8.0 for formaldehyde release to investigate the fixation. The effect of the concentration of the agent on the release of formaldehyde from the fabric is shown in Figure 2.
As can be seen from FIG. 2, the formaldehyde emission of the dye-fixed-colored cotton fabric increases linearly with the increase of the fixing agent concentration, and at the same fixing agent concentration, the formaldehyde releasing amount of the fabric in the medium of pH 5.0 is high. Formaldehyde release in medium with pH 8.0. This is because the increase in the concentration of the fixing agent causes a relatively large amount of fixing agent to adhere to the fiber surface. When the fabric is placed in water to release the formaldehyde test, there is a corresponding increase in the chance of hydrolysis of the fixing agent, resulting in release of the fabric. More formaldehyde. In addition, the release of formaldehyde was slightly increased when the release time was extended from 60 minutes to 120 minutes.
2.3 Fixing temperature effect
The dyeing fabrics were fixed at different temperature conditions using a 40 g/L concentration fixing agent for 30 minutes. The fixed color cotton fabrics were then placed in distilled water having a pH of 5.0 and a pH of 8.0 for formaldehyde release to examine the fixing temperature. The effect of formaldehyde on fabric release is shown in Figure 3.
As can be seen from FIG. 3, as the fixing temperature increases, the amount of formaldehyde released from the dye-fixed colored cotton fabric gradually increases, and especially the fabric fixed at 90Â° C. is particularly prominent, and when the release time is extended from 60 to 120 minutes. The amount of formaldehyde released has increased. This may be because the increase in temperature favors the adsorption of the fixing agent by the cotton fiber, so that the amount of the fixing agent adhered to the fiber surface increases, but the fixing agent occurs when the fabric is placed in water to release formaldehyde as described above. The chance of hydrolysis increases accordingly, which is conducive to the production of more formaldehyde.
2.4 Fixing time effect
The dye-fixed cotton fabrics were fixed at a temperature of 70Â° C. for different times using a 40 g/L concentration fixing agent, and the resulting fixed cotton fabrics were then placed in distilled water having a pH of 5.0 and a pH of 8.0, respectively. Formaldehyde was released to investigate the effect of fixing time on the release of formaldehyde from the fabric. The results are shown in Figure 4. As shown in Fig. 4, when the fixing time is prolonged from 10 minutes to 20 minutes, the amount of formaldehyde released from the dye-fixing fabric is significantly reduced, especially in the acidic condition with a pH of 5.0, but it is continued with the fixing time. Prolonged, the amount of formaldehyde released no longer significantly reduced. This may be due to the fact that when the fixing time is short (10 min), although only a small amount of the fixing agent is adsorbed on the surface of the cotton fiber, their reaction with the fiber and the dye is not sufficient. When the dye fixing fabric is placed in water to release the formaldehyde test, these fixing agents are prone to desorption into the water, which facilitates the hydrolysis reaction to release formaldehyde.
3.1 dye fixation cotton fabric at pH
Both 5.0 and pH 8.0 can release formaldehyde. During the initial release, there is a linear relationship between the amount of released formaldehyde and the release time, and the initial release rate is significantly higher than the average release rate.
3.2 The release parameters, such as equilibrium release, initial release rate and equilibrium release rate of the dye-fixed cotton fabric in distilled water medium with a pH value of 5.0 are larger than the corresponding release parameters in a distilled water medium with a pH of 8.0.
3.3 Increasing the fixing agent concentration and increasing the fixing temperature in the fixing treatment process can increase the amount of formaldehyde released from the dye-fixed-colored cotton fabric, and prolonging the fixing time is beneficial to the reduction of formaldehyde emission.
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