Method for detecting molecular weight of VAE emulsion

Abstract

The invention discloses a method for detecting the molecular weight of a VAE (Vinyl Acetate Ethylene) emulsion, which comprises the following steps of: preparing a film from the VAE emulsion, soaking the film in an acetone or tetrahydrofuran solvent to dissolve a VAE polymer, adding water to precipitate and extract the VAE polymer, and finally detecting the molecular weight through high performance gel permeation chromatography (GPC). The method disclosed by the invention is simple, efficient and time-saving in sample treatment and high in measurement result accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer compound detection, and particularly relates to a method for detecting the molecular weight of a VAE emulsion. Background Art

[0002] Vinyl acetate-ethylene copolymer emulsion (VAE emulsion) is a polymer emulsion made by emulsion polymerization of vinyl acetate and ethylene as basic raw materials. It is widely used in adhesives, exterior wall insulation, coatings, textiles, paper processing and other fields.

[0003] The relative molecular mass of VAE is one of its most basic and important structural parameters, which directly affects the application properties of the emulsion product, such as rheology, adhesion, and impact strength. Therefore, the test of VAE molecular weight is of great significance to the quality control of VAE products. At present, there are few methods for detecting the molecular weight of VAE emulsion. The Ubbelohde viscometer is a commonly used instrument for detecting the molecular weight of polymers, but acetone, tetrahydrofuran and methanol, the good solvents of VAE polymers, are all volatile organic solvents, which can easily cause changes in the concentration of the test liquid during the measurement process. Therefore, it is necessary to explore a simple and easy-to-implement method to accurately detect the molecular weight of VAE emulsions. Summary of the invention

[0004] The present invention has found in experiments that the VAE polymer in the coating film can be extracted by directly immersing the VAE coating film in acetone or tetrahydrofuran solution at room temperature for 10 to 24 hours and then precipitating with water. Based on this, the present invention provides a simple, easy and highly accurate method for detecting the molecular weight of VAE emulsion.

[0005] The present invention solves the technical problem by adopting the following technical solution:

[0006] A method for detecting the molecular weight of a VAE emulsion comprises the following steps:

[0007] Step 1: Extraction of VAE polymer

[0008] Weigh 5-10g of VAE emulsion, use a film applicator to push the VAE emulsion into a thin film, and place it at room temperature for 10-24 hours to obtain a transparent coating film; take 1-2g of the transparent coating film, cut it into small pieces, add it into 50-100mL of acetone or tetrahydrofuran solvent, and place it at room temperature for 10-24 hours, then use a triangular funnel to separate the solid from the filtrate, pour the obtained clear filtrate into 2-4 times the volume of distilled water, stir it, and precipitate the VAE polymer; after washing the obtained precipitate with running water, place it in a vacuum drying oven at 70-80°C and dry it for 24 hours to obtain a dry VAE polymer;

[0009] Step 2: Use gel permeation chromatography to detect VAE molecular weight

[0010] The VAE polymer obtained in step 1 is added to acetone or tetrahydrofuran at a concentration of 2 to 6 mg / mL, dissolved at room temperature for more than 24 hours, and then subjected to gel permeation chromatography to determine the VAE molecular weight.

[0011] Furthermore, the thickness of the film coater used in step 1 is 100-400 μm.

[0012] Further, in step 2, three chromatographic columns were connected in series on the chromatograph, namely, styragel@HR5THF 7.8mm×300mm, styragel@HR4THF 7.8mm×300mm and styragel@HR3THF 7.8mm×300mm. The sample flow rate in the chromatographic detection was 0.5 μL / min. Polystyrene (Shodex S-47, Mn=4.54×10 4 , PDI=1.03) to calibrate the instrument.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] (1) The present invention directly immerses the coating film in acetone or tetrahydrofuran solvent. Compared with the Soxhlet extraction method, the extraction efficiency is comparable, the operation is simpler, easier to implement, and the detection cost is lower.

[0015] (2) The present invention uses high performance gel chromatography to measure the molecular weight of the VAE emulsion. Compared with using an Ubbelohde viscometer to measure the molecular weight, the present invention avoids the change in the concentration of the test liquid caused by the volatilization of acetone or tetrahydrofuran solvent during the measurement process, and the measurement result is more accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The NMR spectra of the VAE polymers extracted in Examples 1 to 3 are shown.

[0017] Figure 2 The NMR spectra of the VAE polymers extracted in Comparative Examples 1 to 3 are shown. DETAILED DESCRIPTION

[0018] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0019] Example 1

[0020] In this example, the molecular weight of the VAE polymer was determined as follows:

[0021] Step 1: Extraction of VAE polymer

[0022] Weigh 6 g of VAE emulsion (sample 1), use a 100 μm applicator to push the VAE emulsion into a thin film, and place it at room temperature for 24 hours to obtain a transparent coating film; take a transparent coating film with a mass of about 2 g (accurate to 0.01 g, recorded as m0), cut it into small pieces, add it to 80 mL of acetone, and let it stand at room temperature for 12 hours, then use a triangular funnel to separate the solid from the filtrate, pour the obtained clear filtrate into 2 times the volume of distilled water, and stir it with a glass rod to precipitate the VAE polymer; after rinsing the obtained precipitate with running water, place it in a vacuum drying oven at 70°C and dry it for 24 hours to obtain a dry VAE polymer, which is weighed (accurate to 0.01 g, recorded as m1).

[0023] Step 2: Use gel permeation chromatography to detect VAE molecular weight

[0024] The VAE polymer obtained in step 1 was added to tetrahydrofuran at a concentration of 5 mg / mL and dissolved at room temperature for more than 24 hours, and then subjected to gel permeation chromatography to determine the molecular weight of VAE. Three chromatographic columns were connected in series on the chromatograph, namely styragel@HR5THF 7.8mm×300mm, styragel@HR4THF 7.8mm×300mm and styragel@HR3THF7.8mm×300mm. The sample flow rate in the chromatographic detection was 0.5μL / min, and polystyrene (ShodexS-47, Mn=4.54×10 4 , PDI=1.03) to calibrate the instrument.

[0025] Example 2

[0026] In this example, the molecular weight of the VAE emulsion (sample 2) was tested in the same manner as in Example 1.

[0027] Example 3

[0028] In this example, the molecular weight of the VAE emulsion (sample 3) was tested in the same manner as in Example 1.

[0029] Comparative Example 1

[0030] The molecular weight of the VAE polymer was determined in the following steps:

[0031] Step 1: Extraction of VAE polymer

[0032] Weigh 6g of VAE emulsion (sample 1), use a 100μm film applicator to push the VAE emulsion into a thin film, and place it at room temperature for 24 hours to obtain a transparent coating. Take a transparent coating with a mass of about 2g (accurate to 0.01g, recorded as m0), wrap it with filter paper, place it in a Soxhlet extractor, then add 200mL of acetone to a flat-bottomed flask, set the water bath temperature to 80-85℃, and start extraction; the extraction time is 24h. After the extraction is completed, remove the device, cool the liquid in the flat-bottomed flask to room temperature, slowly pour it into distilled water, stir it with a glass rod, and precipitate it with water; take out the solid and wash it with water again. Place the solid in a vacuum drying oven at 70℃ and dry it for 24 hours to obtain a dry VAE polymer, which is weighed (accurate to 0.01g, recorded as m1).

[0033] Step 2: Use gel permeation chromatography to detect VAE molecular weight

[0034] Same as Example 1.

[0035] Comparative Example 2

[0036] In this comparative example, the molecular weight of the VAE emulsion (sample 2) was tested in the same manner as in comparative example 1.

[0037] Comparative Example 3

[0038] In this comparative example, the molecular weight of the VAE emulsion (sample 3) was tested in the same manner as in comparative example 1.

[0039] The extraction rate (ω) of the VAE polymer in step 1 of the above embodiment and comparative example was calculated according to the following formula:

[0040]

[0041] Table 1 Comparison of extraction rates of different extraction methods

[0042] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[m0 / g]]> 2.32 1.98 2.50 2.30 1.95 2.50 <![CDATA[m1 / g]]> 1.52 0.96 1.38 1.54 0.91 1.35 ω / % 65.5 48.5 55.2 67.1 46.7 54.0

[0043] From the extraction rate results of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, it can be seen that the extraction rate of the extraction method of the present invention is equivalent to that of the VAE polymer extracted by using a Soxhlet extractor.

[0044] In order to investigate the structure of the extracted substance of the present invention and the substance extracted by Soxhlet extractor, the structure of the extracted polymer was characterized by nuclear magnetic resonance spectroscopy. Figure 1 and Figure 2 It can be seen that the peak positions of the NMR spectra of Examples 1 to 3 and Comparative Examples 1 to 3 are the same, all of which are characteristic peaks of VAE, and no other impurity peaks appear, indicating that the extraction method of the present invention can achieve simple extraction of VAE polymer.

[0045] The test results of gel permeation chromatography in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2.

[0046] Table 2 Molecular weight results of GPC determination in Examples 1 to 3 and Comparative Examples 1 to 3

[0047]

[0048] As can be seen from Table 2, the errors of the number average molecular weight detection results of Examples 1-3 and Comparative Examples 1-3 are 6.6%, 3.8% and 1.4%, respectively, and the errors are small, indicating that the extraction method of the present invention has the advantages of reliable method, high accuracy and simple operation for detecting the molecular weight of VAE emulsion.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. All modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting the molecular weight of a VAE emulsion, characterized in that: The following steps are involved: Step 1: Extraction of VAE polymer Weigh 5-10g of VAE emulsion, use a film applicator to push the VAE emulsion into a thin film, and place it at room temperature for 10-24 hours to obtain a transparent coating film; take 1-2g of the transparent coating film, cut it into small pieces, add it into 50-100mL of acetone or tetrahydrofuran solvent, and place it at room temperature for 10-24 hours, then use a triangular funnel to separate the solid from the filtrate, pour the obtained clear filtrate into 2-4 times the volume of distilled water, stir it, and precipitate the VAE polymer; after washing the obtained precipitate with running water, place it in a vacuum drying oven at 70-80°C and dry it for 24 hours to obtain a dry VAE polymer; Step 2: Use gel permeation chromatography to detect VAE molecular weight The VAE polymer obtained in step 1 is added to acetone or tetrahydrofuran at a concentration of 2 to 6 mg / mL, dissolved at room temperature for more than 24 hours, and then subjected to gel permeation chromatography to determine the VAE molecular weight.

2. The detection method according to claim 1, characterized in that: The thickness of the film applicator used in step 1 is 100-400 μm.

3. The detection method according to claim 1, characterized in that: In step 2, three chromatographic columns are connected in series on the chromatograph, namely styragel@HR5THF 7.8mm×300mm, styragel@HR4THF 7.8mm×300mm and styragel@HR3THF 7.8mm×300mm. The sample flow rate in the chromatographic detection is 0.5 μL / min, and the instrument is calibrated with polystyrene.

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