Method for determining free formaldehyde in solvent-based adhesives and use thereof

Abstract

This invention discloses a method and its application for determining free formaldehyde in solvent-based adhesives. The method includes the following steps: weighing the solvent-based adhesive sample to be tested, adding dichloromethane for extraction to obtain an extract; adding water to the extract, shaking, allowing it to stand and separate into layers, collecting the aqueous phase to obtain the aqueous phase to be treated; adding a derivatization reagent to the aqueous phase to be treated, and carrying out a derivatization reaction in the dark at a derivatization temperature of 35℃~45℃ and a derivatization time of 2h~4h to obtain a derivatized solution; detecting the derivatized solution using high-performance liquid chromatography (HPLC) to obtain the peak area of ​​the formaldehyde derivative, and calculating the content of free formaldehyde in the sample according to a standard curve. This invention solves the problems of inaccurate results and poor anti-interference in the determination of free formaldehyde in solvent-based adhesives by introducing a two-step dichloromethane-water layered extraction and precisely defined derivatization conditions.

Description

Technical Field

[0001] This invention relates to the field of free formaldehyde detection, and in particular to a method and application for determining free formaldehyde in solvent-based adhesives. Background Technology

[0002] Currently, the standard for determining free formaldehyde in solvent-based adhesives (such as GB18583-2008 and GB33372-2020) mainly recommends the acetylacetone spectrophotometric method. This method typically involves complex pre-distillation treatment steps, collecting the distillate at high temperatures for colorimetric determination. However, existing acetylacetone spectrophotometric methods show significant deviations between formaldehyde detection results and the actual formaldehyde content in unstable formaldehyde-containing solvent-based adhesive samples. Furthermore, the parallelism of detection data between different testing institutions is poor, easily leading to distorted results and a risk of misjudgment. In addition, while high-performance liquid chromatography (HPLC) is mature in water-based adhesives, for solvent-based adhesives, the insolubility in water and tendency to aggregate and precipitate in the aqueous phase result in extremely low extraction efficiency, making it difficult to directly apply the detection schemes for water-based adhesives. Moreover, in practical testing, it has been found that when the same solvent-based sample is tested using different standardized methods, data incoherence and poor reproducibility often occur.

[0003] Therefore, it is of great significance to develop a detection method that can effectively extract solvent-based adhesives and accurately lock free formaldehyde under mild conditions. Summary of the Invention

[0004] This invention provides a method and application for determining free formaldehyde in solvent-based adhesives. It provides an accurate and highly sensitive detection method by introducing a two-step layered extraction with dichloromethane and water, combined with precisely defined derivatization conditions, to solve the problems of inaccurate formaldehyde determination results and poor anti-interference in solvent-based adhesives.

[0005] The technical solution of the present invention is as follows:

[0006] A first aspect of the present invention provides a method for determining free formaldehyde in solvent-based adhesives, the method comprising the following steps:

[0007] S1. Sample extraction: Weigh the solvent-based adhesive sample to be tested, add dichloromethane for extraction, and obtain the extract;

[0008] S2, Back-extraction: Add water to the extract, shake, let stand to separate the layers, and collect the aqueous phase to obtain the aqueous phase to be treated;

[0009] S3. Derivatization reaction: Add derivatization reagent to the aqueous phase to be treated, and carry out a light-protected derivatization reaction at a derivatization temperature of 35℃~45℃ and a derivatization time of 2h~4h to obtain a derivatized solution;

[0010] S4. Detection: The derivatized solution was detected using a high-performance liquid chromatograph to obtain the peak area of ​​the formaldehyde derivative, and the content of free formaldehyde in the sample was calculated based on the standard curve.

[0011] According to the aforementioned method for determining free formaldehyde in solvent-based adhesives, in step S1, 1.0 g of sample is weighed, 20 mL of dichloromethane is added, and the mixture is first vortexed for 1 min, and then ultrasonically extracted for 15 min.

[0012] According to the aforementioned method for determining free formaldehyde in solvent-based adhesives, in step S2, the back-extraction process includes: adding 10 mL of water to the extract and sonicating for 15 min.

[0013] According to the aforementioned method for determining free formaldehyde in solvent-based adhesives, in step S3, the derivatizing reagent is a 10 g / L solution of 2,4-dinitrophenylhydrazine, the solvent is a phosphoric acid solution, and the volume ratio of the derivatizing reagent to the aqueous phase to be treated is (0.08~0.12):1.

[0014] Further, the specific operation of step S3 is as follows: 4.0 mL of the aqueous phase to be treated, 4.0 mL of water and 0.4 mL of derivatization reagent are transferred, mixed evenly and then the derivatization reaction is carried out.

[0015] Furthermore, in step S3, the derivatization temperature is 40℃ and the derivatization time is 2h.

[0016] According to the aforementioned method for determining free formaldehyde in solvent-based adhesives, in step S4, the high-performance liquid chromatography (HPLC) detection conditions are as follows: the chromatographic column is a C18 reversed-phase column; the column temperature is 30℃; the flow rate is 0.6 mL / min; the injection volume is 20 µL; the detection wavelength is 355 nm; and the mobile phase is a mixed solution of acetonitrile and water in a volume ratio of 60:40.

[0017] Furthermore, in step S4, the sample needs to be filtered through an organic phase microporous membrane before detection.

[0018] According to the aforementioned method for determining free formaldehyde in solvent-based adhesives, the solvent-based adhesives to be tested include adhesives containing unstable aldehyde-containing polymers, colored adhesives, or adhesives containing non-formaldehyde aldehyde substances.

[0019] A second aspect of the present invention provides an application of the determination of free formaldehyde in solvent-based adhesives in the evaluation of environmental indicators or quality testing of solvent-based adhesives, using the method for determining free formaldehyde in solvent-based adhesives according to the first aspect of the present invention.

[0020] Compared with the prior art, the method and application for determining free formaldehyde in solvent-based adhesives provided by the present invention have at least the following beneficial effects:

[0021] This invention utilizes dichloromethane for physical swelling and dilution, followed by back-extraction with water, to achieve the microscopic transfer of formaldehyde from the organic phase to the aqueous phase. Combined with precise derivatization conditions, this method significantly outperforms existing acetylacetone spectrophotometry and conventional liquid chromatography in terms of sensitivity, repeatability, and anti-interference capabilities. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for determining free formaldehyde in solvent-based adhesives. Detailed Implementation

[0023] To make the technical problems, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0024] Figure 1 This is a flowchart of a method for determining free formaldehyde in solvent-based adhesives. The method includes the following steps:

[0025] S1. Sample Extraction: Weigh the solvent-based adhesive sample to be tested, add dichloromethane for extraction, and obtain the extract. Specifically, weigh 1.0 g of the sample, add 20 mL of dichloromethane, vortex for 1 min, and then perform ultrasonic extraction for 15 min. The solvent-based adhesive to be tested includes adhesives containing unstable aldehyde polymers, colored adhesives, or adhesives containing non-formaldehyde aldehydes.

[0026] S2. Back-extraction: Water is added to the extract, and the mixture is shaken, allowed to stand for separation, and the aqueous phase is collected to obtain the aqueous phase to be treated. Specifically, the back-extraction process includes: adding 10 mL of water to the extract and sonicating for 15 min. The back-extraction is repeated at least twice, and the collected aqueous phases are combined and diluted to a final volume to obtain the aqueous phase to be treated.

[0027] S3. Derivatization Reaction: A derivatization reagent is added to the aqueous phase to be treated, and a derivatization reaction is carried out in the dark at a derivatization temperature of 35℃~45℃ and a derivatization time of 2h~4h to obtain a derivatized solution. Specifically, the derivatization reagent is a 10g / L solution of 2,4-dinitrophenylhydrazine, the solvent is phosphoric acid solution, and the volume ratio of the derivatization reagent to the aqueous phase to be treated is (0.08~0.12):1. The specific operation of step S3 is as follows: 4.0mL of the aqueous phase to be treated, 4.0mL of water, and 0.4mL of derivatization reagent are mixed evenly and then the derivatization reaction is carried out. Preferably, the derivatization temperature is 40℃ and the derivatization time is 2h. Because formaldehyde is volatile and chemically reactive, after the derivatization reaction, formaldehyde is converted into a structurally stable non-volatile substance. At the same time, formaldehyde reacts with 2,4-dinitrophenylhydrazine to form formaldehyde-2,4-dinitrophenylhydrazone, which introduces a chromophore with strong ultraviolet absorption, increasing the detection sensitivity.

[0028] S4. Detection: The derivatized solution was detected using high-performance liquid chromatography (HPLC) to obtain the peak area of ​​the formaldehyde derivative. The content of free formaldehyde in the sample was calculated based on the standard curve. The HPLC detection conditions were as follows: C18 reversed-phase column; column temperature 30℃; flow rate 0.6 mL / min; injection volume 20 µL; detection wavelength 355 nm; mobile phase was a mixture of acetonitrile and water at a volume ratio of 60:40. Optionally, the sample should be filtered through a 0.22 μm organic phase microporous membrane before detection, and the filtrate should be retained for HPLC analysis. The HPLC analysis method is conventional, and the calculation method is also existing technology, which will not be elaborated here.

[0029] Solvent-based adhesives are mostly high-molecular-weight polymers such as SBS and chloroprene rubber. Polar solvents such as water or acetonitrile can cause them to encapsulate formaldehyde. This invention utilizes the strong swelling and dissolving properties of dichloromethane for these solvent-based adhesives, allowing the encapsulated formaldehyde molecules to diffuse fully from between the polymer chains. Furthermore, dichloromethane has a higher density than water. During back-extraction, the dichloromethane layer (containing the solvent-based adhesive) is located at the bottom, and the water layer (containing formaldehyde) is located at the top. This greatly facilitates pipetting operations and avoids contamination of the HPLC system by the aspiration of viscous resin during sampling. This invention uses dichloromethane extraction followed by back-extraction with water. The partition coefficient of formaldehyde in water is much higher than its partition coefficient in dichloromethane, overcoming the technical obstacle of easy agglomeration and encapsulation of solvent-based adhesives in traditional polar solvents.

[0030] The method for determining free formaldehyde in solvent-based adhesives of the present invention can be applied in the evaluation of environmental indicators or quality testing of solvent-based adhesives.

[0031] The following specific embodiments illustrate the technical effects of the present invention.

[0032] Experimental Example 1:

[0033] To demonstrate the inventiveness and necessity of the present invention's limitation on the derivation temperature, a solvent-based adhesive sample (sample A) containing a small amount of unstable urea-formaldehyde resin monomer was selected and extracted according to the method of the present invention.

[0034] Weigh 1.0g of sample A, add 20mL of dichloromethane, vortex for 1min to dissolve / disperse the sample, and then sonicate for 15min.

[0035] Add 10 mL of ultrapure water to the above extract, sonicate for 15 min, let stand to separate the layers, take the upper aqueous phase, repeat the back-extraction twice, combine the aqueous phases and make up to 25 mL to obtain the aqueous phase to be treated.

[0036] In the derivatization step, a 10 g / L solution of 2,4-dinitrophenylhydrazine was used as the derivatization reagent, and phosphoric acid solution was used as the solvent. The volume ratio of the derivatization reagent to the aqueous phase to be treated was 0.10:1. A gradient interval of 5°C was set, and the change in formaldehyde content was observed within the range of 25°C to 65°C. The derivatization time was uniformly set to 2 hours.

[0037] The derivatized solution was detected using high performance liquid chromatography (HPLC). The chromatographic column was a C18 reversed-phase column; the column temperature was 30℃; the flow rate was 0.6 mL / min; the injection volume was 20 µL; the detection wavelength was 355 nm; and the mobile phase was a mixture of acetonitrile and water in a volume ratio of 60:40.

[0038] The experimental results are shown in Table 1:

[0039] Table 1 Formaldehyde content measured at different derivatization temperatures

[0040]

[0041] As shown in Table 1, this invention, through a detailed comparison at a 5℃ gradient, reveals that the derivatization temperature exhibits extremely stringent selectivity for the detection of free formaldehyde in solvent-based adhesives. Within the 25℃~35℃ range, the derivatization reaction, being an exothermic chemical reaction, suffers from limited kinetics in this low-temperature range, failing to complete quantitative coupling with sufficient 2,4-dinitrophenylhydrazine within 2 hours, resulting in low detection values. Within the 35℃~45℃ range, a significant plateau exists. Experiments demonstrate that the energy at around 40℃ is sufficient to overcome the activation energy barrier of the derivatization reaction (reaction completion >99%), yet not yet reaches the breaking energy of the main chemical bonds in the unstable urea-formaldehyde resin monomer, thus strictly limiting the detection target to the "free formaldehyde" range. Above 50℃, the measured values ​​show a sharp increase, which is not due to improved derivatization efficiency, but rather because the high temperature causes physical structural damage and chemical bond breakage in the solvent-based adhesive, forcing the release of formaldehyde that was not originally in a free state. If the traditional acetylacetone method is used (which usually requires a boiling water bath or high-temperature distillation), the measured value will exceed 1500 mg / kg, leading to serious misjudgments. Strictly limiting the derivatization temperature to 35~45℃ (preferably 40℃) is a comprehensive consideration of the stability and derivatization efficiency of specific solvent-based adhesives, ensuring the accuracy of the test results.

[0042] By precisely limiting the derivatization temperature to 35~45℃ and combining it with a mild dichloromethane extraction technique, this method can effectively avoid the decomposition and release of bound formaldehyde caused by high-temperature distillation or high-temperature color development in traditional detection methods. This allows the test results to more accurately reflect the downstream release risks of the product during room temperature storage and use, ensuring the accuracy of the test results.

[0043] Experimental Example 2:

[0044] This embodiment investigates the effect of derivatization time on the test results of solvent-based adhesives (containing unstable resins). A commercially available solvent-based adhesive containing urea-formaldehyde resin residue, similar to that used in Example 1, was selected and extracted according to the method of this invention. Tests were conducted at different derivatization times, with a derivatization temperature of 40°C. In the table, "h" represents hours.

[0045] Table 2 Formaldehyde content measured at different derivatization times

[0046]

[0047] As shown in Table 2, the data further demonstrates the scientific validity of 40℃ as the derivatization temperature. At 40℃, the derivatization reaction reaches completion within 2 hours (the measured value plateaus), and the measured values ​​remain almost constant over the subsequent 4 to 24 hours. This indicates that at 40℃, there is no continuous resin degradation process releasing formaldehyde (if degradation occurred, the value would increase linearly with time). The fact that saturation is reached in 2 hours, with no significant change from 4 to 24 hours, proves that 2 hours is a critical value that balances efficiency and accuracy.

[0048] The combination of derivatization conditions—40℃ and 2h—ensures both detection efficiency (eliminating the need to wait for the long room-temperature reaction required by traditional methods) and accuracy. This represents not only an optimization of experimental parameters but also a deep application of the unique properties of solvent-based adhesives, solving the industry's technical challenge of inconsistent detection data for solvent-based adhesives containing unstable resins.

[0049] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A method for determining free formaldehyde in solvent-based adhesives, characterized in that, Includes the following steps: S1. Sample extraction: Weigh the solvent-based adhesive sample to be tested, add dichloromethane for extraction, and obtain the extract; S2, Back-extraction: Add water to the extract, shake, let stand to separate the layers, and collect the aqueous phase to obtain the aqueous phase to be treated; S3. Derivatization reaction: Add derivatization reagent to the aqueous phase to be treated, and carry out a light-protected derivatization reaction at a derivatization temperature of 35℃~45℃ and a derivatization time of 2h~4h to obtain a derivatized solution; S4. Detection: The derivatized solution was detected using a high-performance liquid chromatograph to obtain the peak area of ​​the formaldehyde derivative, and the content of free formaldehyde in the sample was calculated based on the standard curve.

2. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, In step S1, 1.0 g of sample was weighed, 20 mL of dichloromethane was added, and the mixture was first vortexed for 1 min, and then ultrasonically extracted for 15 min.

3. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, In step S2, the back-extraction process includes: adding 10 mL of water to the extract and sonicating for 15 min; repeating the back-extraction at least twice, combining the collected aqueous phases and adjusting the volume to obtain the aqueous phase to be treated.

4. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, In step S3, the derivatization reagent is a 10 g / L solution of 2,4-dinitrophenylhydrazine, the solvent is a phosphoric acid solution, and the volume ratio of the derivatization reagent to the aqueous phase to be treated is (0.08~0.12):

1.

5. The method for determining free formaldehyde in solvent-based adhesives according to claim 4, characterized in that, The specific operation of step S3 is as follows: Take 4.0 mL of the aqueous phase to be treated, 4.0 mL of water and 0.4 mL of derivatization reagent, mix them evenly and then carry out the derivatization reaction.

6. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, In step S3, the derivatization temperature is 40℃ and the derivatization time is 2h.

7. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, In step S4, the high-performance liquid chromatography (HPLC) detection conditions are as follows: the chromatographic column is a C18 reversed-phase column; the column temperature is 30℃; the flow rate is 0.6 mL / min; the injection volume is 20 µL; the detection wavelength is 355 nm; and the mobile phase is a mixed solution of acetonitrile and water in a volume ratio of 60:

40.

8. The method for determining free formaldehyde in solvent-based adhesives according to claim 7, characterized in that, In step S4, the sample needs to be filtered through an organic phase microporous membrane before detection.

9. The method for determining free formaldehyde in solvent-based adhesives according to claim 1, characterized in that, The solvent-based adhesives to be tested include adhesives containing unstable aldehyde polymers, colored adhesives, or adhesives containing non-formaldehyde aldehyde substances.

10. The application of determining free formaldehyde in solvent-based adhesives in the environmental performance evaluation or quality testing of solvent-based adhesives, characterized in that... The method for determining free formaldehyde in solvent-based adhesives as described in any one of claims 1 to 9 is employed.

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