Method for determining the degree of crosslinking of film-forming agents

Abstract

The present invention belongs to the technical field of film-forming agents, and specifically relates to a method for determining the degree of crosslinking of film-forming agents. The dried film-forming agent is used as a test sample, and the mass of the test sample is calculated as M1; the test sample is wrapped with filter paper and placed in a filter bag to obtain a filter bag containing the test sample, and the total mass of the test sample, filter paper and filter bag is calculated as M2; the filter bag containing the test sample and a composite extractant are added to a Soxhlet extractor for extraction, and after the extraction is completed, the filter bag containing the remaining test sample is taken out, naturally dried, and dried to obtain a filter bag containing the remaining test sample after drying, and the total mass of the filter bag containing the remaining test sample after drying is calculated as M3. The method of the present invention is environmentally friendly, highly accurate, simple to operate, repeatable, and saves time and cost.

Description

Technical Field

[0001] The invention belongs to the technical field of film-forming agents, and in particular relates to a method for determining the cross-linking degree of a film-forming agent. Background Art

[0002] Film formers are the main components of the sizing agents used in the high-speed drawing process of glass fibers. They can bond hundreds of glass fibers together, form a protective film on the fiber surface, and give the glass fibers good process properties such as wettability, stiffness, ribbonization, short-cutting and dispersibility. At present, there are five main types of film formers in the sizing agents for glass fibers: epoxy, polyester, PVAC, acrylate and polyurethane. These five categories are composed of hydrophilic components (containing hydroxyl groups, carboxyl groups, etc.) and lipophilic components (containing benzene rings, fatty chains, etc.); and the cross-linked film formers prepared by self-crosslinking or adding crosslinking agents can make the original linear structure form a three-dimensional network structure during the film-forming process, giving the glass fiber good solvent resistance and mechanical properties, and have the characteristics of strong raw fiber bundling, excellent high temperature performance, and fast penetration speed.

[0003] Usually, the methods for determining the degree of crosslinking of polymers mainly include extraction method, DSC test method and infrared method. Infrared spectroscopy mainly uses infrared spectroscopy to determine the residual amount of functional groups involved in the crosslinking reaction to calculate the degree of crosslinking. This method is relatively accurate, but it requires that the characteristic absorption peak of the functional group involved in the curing reaction must be clearly observed in the infrared spectrum, and the absorption peak cannot be interfered by other irrelevant absorption peaks; this method is troublesome to test and is easily interfered by miscellaneous peaks, and has poor repeatability. The DSC test method is complicated to operate, the instrument is expensive, and it cannot be popularized. Although the test time is fast, the sample preparation is cumbersome, the repeatability is poor, and the types of test samples are limited. It is impossible to test thin films and foaming materials. When the extraction method is used to determine the degree of crosslinking of crosslinked polymers, the extraction efficiency is low, and it usually takes more than 13 hours to reach the extraction equilibrium; and the extractants currently used to measure the degree of crosslinking by extraction are generally highly toxic extractants such as benzene, toluene, and xylene, which are harmful to the human body and the environment and are single, with low extraction efficiency, and a single extractant cannot play a synergistic role, which takes a long time, the extraction is incomplete, and the recovery cost is high.

[0004] Chinese patent CN106706458A discloses a method for testing the crosslinking degree of EVA in an electric heating sleeve. It uses xylene as a single extractant to extract EVA. The extraction time is as long as 5 hours, and the extraction efficiency is not high, the repeatability is poor, and it cannot be reused after being reused three times. In addition, xylene is highly toxic to humans and the environment. Since the film-forming agent contains hydrophilic and lipophilic components, the patented method can only extract the lipophilic component, while the hydrophilic component cannot be extracted. Therefore, the patented method is not suitable for the determination of the crosslinking degree of the film-forming agent.

[0005] Chinese patent CN105582691A discloses an extractant and its application and a method for determining the crosslinking degree of a polymer. The extractant contains aromatic hydrocarbon A, aromatic hydrocarbon B and alkane C. The aromatic hydrocarbon A is a C6 or C8 aromatic hydrocarbon, the aromatic hydrocarbon B is a C7-C9 aromatic hydrocarbon, the alkane C is a C5-C7 alkane, and the aromatic hydrocarbon A is different from the aromatic hydrocarbon B; the volume ratio of the aromatic hydrocarbon A, the aromatic hydrocarbon B and the alkane C is (1-15):(1-10):1. Although this patent utilizes three extractants, namely aromatic hydrocarbon A, aromatic hydrocarbon B and alkane C, for mixed extraction, the extraction time is as long as 4.5-6 hours, and benzene, xylene, etc. are used as extractants. The extractants are harmful to the human body and the environment, the extraction is incomplete, and the repeatability is poor. This patent does not make a detailed introduction to the principle of extraction. Moreover, since the film-forming agent is a polymer containing hydrophilic and lipophilic components, the extractant used in this patent can only extract the lipophilic component, but not the hydrophilic component. Therefore, it is not suitable for the extraction of cross-linked film-forming agents containing hydrophilic and lipophilic components.

[0006] The national standard GB / T 18474-2001 "Test method for crosslinking degree of cross-linked polyethylene (PE-X) pipes and fittings" is only applicable to the testing of EVA and lipophilic crosslinking agents. The test method is cumbersome and has low accuracy. General laboratories do not have the precision instruments required for the test.

[0007] Currently, there is no relevant literature involving the determination of the cross-linking degree of film-forming agents. Summary of the invention

[0008] The invention aims to provide a method for determining the cross-linking degree of a film-forming agent, which is environmentally friendly, highly accurate, simple to operate, has good repeatability, and saves time and cost.

[0009] The method for determining the crosslinking degree of a film-forming agent of the present invention comprises the following steps:

[0010] (1) The dried film-forming agent is used as a test sample, and the mass of the test sample is counted as M1;

[0011] (2) Wrap the test sample with filter paper and place it in a filter bag to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0012] (3) adding the filter bag containing the test sample obtained in step (2) and the composite extractant into a Soxhlet extractor for extraction; after the extraction is completed, taking out the filter bag containing the remaining test sample, air-drying it naturally, and drying it to obtain a filter bag containing the remaining test sample after drying; the total mass of the filter bag containing the remaining test sample after drying is calculated as M3;

[0013] (4) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0014] The film thickness of the film-forming agent described in step (1) is 0.5-1.5 mm, and the mass of the film-forming agent is 0.6-1.5 g.

[0015] The diameter of the filter paper described in step (2) is 6-10 cm.

[0016] The mesh size of the filter bag described in step (2) is 200-500 meshes.

[0017] The filter bag described in step (2) has a length of 5-9 cm and a width of 4-6 cm.

[0018] The composite extractant described in step (3) is a mixture of ketones, esters and cycloalkanes, wherein the ketone is one of acetone, butanone, methyl butanone or methyl isobutyl ketone, the ester is one of methyl formate, ethyl acetate, propyl acetate or butyl acetate, the cycloalkanes are one of cyclopentane, cyclohexane or cycloheptane, and the mass ratio of ketones, esters and cycloalkanes is 10-20:2-10:8-15.

[0019] The mass ratio of the test sample to the composite extractant in step (3) is 1:200-400, preferably 1:300.

[0020] The addition rate of the composite extractant described in step (3) is 20-50 drops / min.

[0021] The extraction temperature in step (3) is 80-160°C.

[0022] The extraction time described in step (3) is 1-3h.

[0023] The natural drying time in step (3) is 0.5-2h, preferably 1h.

[0024] The drying temperature in step (3) is 110-140° C., preferably 130° C.; the drying time is 1-3 h, preferably 1 h.

[0025] The film-forming agent measured in the present invention is a polyester, epoxy resin or polyvinyl acetate polymer. The lipophilic component in the polymer contains functional groups such as epoxy groups, ketone groups, aliphatic hydrocarbons and benzene rings, and the hydrophilic component contains functional groups such as hydroxyl groups, ester groups and carboxyl groups.

[0026] The method for determining the crosslinking degree of a film-forming agent of the present invention comprises the following specific steps:

[0027] (1) Prepare instruments and reagents: Soxhlet extractor, desiccator, constant temperature water bath with magnetic stirring, oven, 200-500 mesh filter bag, filter paper with a diameter of 6-10 cm, composite extractant which is a mixture of ketone, ester and cycloalkane, and electronic balance (accurate to 0.1 mg).

[0028] (2) taking a film-forming agent with a dried film thickness of 0.5-1.5 mm (preferably 0.8-1.2 mm) and a mass of 0.6-1.5 g (preferably 0.7-1.0 g) as a test sample, and the mass of the test sample is calculated as M1;

[0029] (3) Wrap the test sample with filter paper and place it in a 200-500 mesh filter bag (preferably a 300-400 mesh filter bag) to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0030] (4) Add the filter bag containing the test sample obtained in step (3) and the composite extractant into a Soxhlet extractor, heat the water bath to 80-160° C. for extraction for 1-3 h, control the dripping rate of the composite extractant to 20-50 drops / min (preferably 30-40 drops / min), take out the filter bag containing the remaining test sample, dry it naturally, and dry it to obtain the filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3.

[0031] (5) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0032] After Soxhlet extraction, the quality of filter paper and filter bag remains unchanged, and repeated use of filter bag will not affect the accuracy of this method. After 1-3h extraction, the cross-linking degree of film-forming agent is constant.

[0033] The present invention adopts a Soxhlet extractor to convert the composite extractant into a pure solvent after condensation and reflux, thereby increasing the dissolution efficiency and preventing the composite extractant from damaging the cross-linked network structure during continuous heating, thereby improving the repeatability and accuracy of test data.

[0034] The composite extractant used in the present invention can be used repeatedly for many times, and the composite extractant needs to be replaced after being used 10 times.

[0035] The present invention uses filter paper to wrap the test sample, and then puts the filter paper into a filter bag. The filter bag can be used repeatedly, saving costs.

[0036] Since the film-forming agent is a polymer containing hydrophilic and lipophilic components, a composite extractant containing hydrophilic and lipophilic components is required to completely extract the uncrosslinked part, so composite extractants with different polarities are selected to completely extract the dissolved matter. The present invention mixes low-toxic ketones, low-toxic esters and cycloalkanes in a certain proportion, and utilizes the principle of like dissolves like to achieve a synergistic effect of the three, thereby forming an environmentally friendly and low-toxic composite extractant, which can quickly extract, achieve complete extraction in 1-3 hours, has good repeatability, and can be repeatedly used. The composite extractant can achieve good results in testing the crosslinking degree of the film-forming agent.

[0037] Since ketones tend to be more hydrophilic (ketones can form hydrogen bonds with ester groups, amine groups and carboxyl groups, which are more conducive to extraction), esters are between hydrophilic and lipophilic, and cycloalkanes tend to be more lipophilic (such as epoxy groups, benzene rings and aliphatic hydrocarbons), using only one of ketones, esters or cycloalkanes as an extractant to extract film-forming agents containing hydrophilic and lipophilic components cannot achieve a good extraction effect.

[0038] The extraction principle of the composite extractant in the present invention is to use ketones, esters and cycloalkanes to extract in coordination. The ketone small molecules form hydrogen bonds with the hydrogen of the hydrophilic group in the film-forming agent through the oxygen in the ketone bond. The esters are both hydrophilic and lipophilic, and the cycloalkanes are more lipophilic. The ketones, esters and cycloalkanes play a bridging role, which can better extract the dissolved substances in the composite extractant. The cross-linked film-forming agent is insoluble in the composite extractant and therefore cannot be dissolved.

[0039] The beneficial effects of the present invention are as follows:

[0040] (1) The present invention adopts the Soxhlet extraction method to determine the crosslinking degree of the film-forming agent. The composite extractant is subjected to cyclic distillation to ensure that the pure extractant is in contact with the filter bag; the error caused by the small molecular polymer dissolved in the extractant adhering to the filter bag is avoided; and there is no need to add an antioxidant during the extraction process, and a new extractant is used to extract the sample each time.

[0041] (2) The testing method of the present invention is simple, has good generalizability, and is easy to operate.

[0042] (3) The composite extractant of the present invention is low-toxic and environmentally friendly, can be reused multiple times, and has a good extraction effect on film-forming agents containing hydrophilic components and lipophilic components; the determination method is easy to operate, fast, accurate, and has good repeatability. DETAILED DESCRIPTION

[0043] The present invention is further described below with reference to the embodiments.

[0044] The test samples in the embodiments and comparative examples are all commercially available PVAc film-forming agents purchased from the same batch, namely, cross-linked polyvinyl acetate emulsion film-forming agents. The cross-linking degree of the PVAc film-forming agent is 67.53% as measured by differential scanning calorimetry (DSC).

[0045] Examples 1-6

[0046] (1) Prepare the following instruments and reagents: Soxhlet extractor, desiccator, constant temperature water bath with magnetic stirring, oven, 500-mesh filter bag, 8-cm diameter filter paper, composite extractant which is a mixture of acetone, ethyl acetate and cyclohexane, with a mass ratio of acetone, ethyl acetate and cyclohexane of 10:10:15, and electronic balance (accurate to 0.1 mg).

[0047] (2) Take the dried PVAc film-forming agent as the test sample, and the mass of the test sample is calculated as M1;

[0048] (3) Wrap the test sample with filter paper with a diameter of 8 cm, fold it into a rectangle with a length of 3 cm and a width of 1.5 cm, and put it into a 500-mesh filter bag with a length of 7 cm and a width of 4 cm to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0049] (4) Add the filter bag containing the test sample obtained in step (3) and the composite extractant into a Soxhlet extractor, heat the water bath to 85° C. for extraction, control the dripping speed of the composite extractant, take out the filter bag containing the remaining test sample, dry it naturally for 1 hour, and dry it at 130° C. for 1 hour to obtain the filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3.

[0050] (5) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0051] The conditions and results of Examples 1-6 are shown in Table 1.

[0052] Table 1 Conditions and Parameters of Examples 1-6 and Results

[0053]

[0054] Examples 7-12

[0055] (1) Prepare the following instruments and reagents: Soxhlet extractor, desiccator, constant temperature water bath with magnetic stirring, oven, 500 mesh filter bag, 8 cm diameter filter paper, composite extractant which is a mixture of butanone, ethyl acetate and cyclopentane, with a mass ratio of butanone, propyl acetate and cyclopentane of 15:6:11, and electronic balance (accurate to 0.1 mg).

[0056] (2) Take the dried PVAc film-forming agent as the test sample, and the mass of the test sample is calculated as M1;

[0057] (3) Wrap the test sample with filter paper with a diameter of 8 cm, fold it into a rectangle with a length of 3 cm and a width of 1.5 cm, and put it into a 500-mesh filter bag with a length of 7 cm and a width of 4 cm to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0058] (4) Add the filter bag containing the test sample obtained in step (3) and the composite extractant into a Soxhlet extractor, heat the water bath to 108° C. for extraction, control the dripping speed of the composite extractant, take out the filter bag containing the remaining test sample, dry it naturally for 0.5 h, and dry it at 140° C. for 2 h to obtain the filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3.

[0059] (5) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0060] The condition parameters and results of Examples 7-12 are shown in Table 2.

[0061] Table 2 Condition parameters and results of Examples 7-12

[0062]

[0063] Examples 13-18

[0064] (1) Prepare the following instruments and reagents: Soxhlet extractor, desiccator, constant temperature water bath with magnetic stirring, oven, 500-mesh filter bag, 8-cm diameter filter paper, composite extractant which is a mixture of methyl butyl ketone, butyl acetate and cyclohexane, with a mass ratio of methyl butyl ketone, butyl acetate and cyclohexane of 13:7:9, and electronic balance (accurate to 0.1 mg).

[0065] (2) Take the dried PVAc film-forming agent as the test sample, and the mass of the test sample is calculated as M1;

[0066] (3) Wrap the test sample with filter paper with a diameter of 8 cm, fold it into a rectangle with a length of 3 cm and a width of 1.5 cm, and put it into a 500-mesh filter bag with a length of 7 cm and a width of 4 cm to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0067] (4) Add the filter bag containing the test sample obtained in step (3) and the composite extractant into a Soxhlet extractor, heat the water bath to 113° C. for extraction, control the dripping speed of the composite extractant, take out the filter bag containing the remaining test sample, dry it naturally for 2 h, and dry it at 110° C. for 3 h to obtain the filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3.

[0068] (5) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0069] The condition parameters and results of Examples 13-18 are shown in Table 3.

[0070] Table 3 Condition parameters and results of Examples 13-18

[0071]

[0072] Examples 19-23

[0073] In Example 19, the composite extractant is a composite extractant that has been used 3 times, in Example 20, the composite extractant is a composite extractant that has been used 5 times, in Example 21, the composite extractant is a composite extractant that has been used 7 times, in Example 22, the composite extractant is a composite extractant that has been used 9 times, in Example 23, the composite extractant is a composite extractant that has been used 10 times, and the other steps in Examples 19-23 are the same as in Example 1.

[0074] The condition parameters and results of Examples 19-23 are shown in Table 4.

[0075] Table 4 Conditions and Parameters of Examples 19-23 and Results

[0076]

[0077] It can be seen from Table 4 that the composite extractant that has been used 3-10 times can still be used for extraction, which does not affect the determination of the cross-linking degree of the film-forming agent and saves costs.

[0078] Embodiment 24

[0079] (1) Prepare the following instruments and reagents: Soxhlet extractor, desiccator, constant temperature water bath with magnetic stirring, oven, 500-mesh filter bag, 8-cm diameter filter paper, composite extractant which is a mixture of acetone, ethyl acetate and cyclohexane, with a mass ratio of acetone, ethyl acetate and cyclohexane of 10:2:8, and electronic balance (accurate to 0.1 mg).

[0080] (2) Take the dried PVAc film-forming agent as the test sample, and the mass of the test sample is calculated as M1;

[0081] (3) Wrap the test sample with filter paper with a diameter of 8 cm, fold it into a rectangle with a length of 3 cm and a width of 1.5 cm, and put it into a 500-mesh filter bag with a length of 7 cm and a width of 4 cm to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2;

[0082] (4) Add the filter bag containing the test sample obtained in step (3) and the composite extractant into a Soxhlet extractor, heat the water bath to 98° C. for extraction, control the dripping speed of the composite extractant, take out the filter bag containing the remaining test sample, dry it naturally for 1 hour, and dry it at 130° C. for 1 hour to obtain the filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3.

[0083] (5) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1*100%.

[0084] Comparative Example 1

[0085] The extractant is acetone, and the other steps are the same as Example 24.

[0086] Comparative Example 2

[0087] The extracting agent is ethyl acetate, and the other steps are the same as Example 24.

[0088] Comparative Example 3

[0089] The extractant is cyclohexane, and the other steps are the same as Example 24.

[0090] Comparative Example 4

[0091] The extractant is a mixture of acetone and ethyl acetate, the mass ratio of acetone to ethyl acetate is 18:2, and the other steps are the same as Example 24.

[0092] Comparative Example 5

[0093] The extractant is a mixture of acetone and cyclohexane, the mass ratio of acetone to cyclohexane is 12:8, and the other steps are the same as Example 24.

[0094] Comparative Example 6

[0095] The extractant is a mixture of ethyl acetate and cyclohexane, the mass ratio of ethyl acetate to cyclohexane is 10:10, and the other steps are the same as Example 24.

[0096] The condition parameters and results of Example 24 and Comparative Examples 1-6 are shown in Table 5.

[0097] Table 5 Condition parameters and results of Example 24 and Comparative Examples 1-6

[0098]

[0099]

[0100] As can be seen from Table 5, the present invention uses a composite extractant of acetone, ethyl acetate and cyclohexane to extract the film-forming agent, which has a better extraction effect than using acetone, ethyl acetate or cyclohexane alone or any combination of the two of them. This is because the use of the two alone or in combination cannot completely extract the uncross-linked components in the film-forming agent, resulting in a larger experimental result. Therefore, the film-forming agent can only be completely extracted by using the composite extractant of the present invention.

[0101] The crosslinking degree of the PVAc film-forming agent measured in Examples 1-24 is between 66.79% and 68.16%, while the crosslinking degree of the PVAc film-forming agent tested by the differential scanning calorimeter (DSC) method is 67.53%. By comparison, it can be seen that the crosslinking degree measured by the present invention is similar to the DSC test result, and the error is extremely small. It can be seen that the determination method of the present invention has high accuracy.

Claims

1. A method for determining the crosslinking degree of a film-forming agent, characterized in that The steps include: (1) The dried film-forming agent is used as the test sample, and the mass of the test sample is counted as M1; (2) Wrap the test sample with filter paper and place it in a filter bag to obtain a filter bag containing the test sample. The total mass of the test sample, filter paper and filter bag is calculated as M2; (3) adding the filter bag containing the test sample obtained in step (2) and the composite extractant into a Soxhlet extractor for extraction. After the extraction is completed, taking out the filter bag containing the remaining test sample, air-drying it naturally, and drying it to obtain a filter bag containing the remaining test sample after drying. The total mass of the filter bag containing the remaining test sample after drying is calculated as M3; (4) Cross-linking degree calculation formula: Q = (M1-(M2-M3)) / M1×100%; The composite extractant in step (3) is a mixture of ketones, esters and cycloalkanes, and the mass ratio of ketones, esters and cycloalkanes is 10-15:2-10:8-15.

2. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The film thickness of the film-forming agent in step (1) is 0.5-1.5 mm, and the mass of the film-forming agent is 0.6-1.5 g.

3. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The diameter of the filter paper in step (2) is 6-10 cm.

4. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The mesh size of the filter bag in step (2) is 200-500 meshes, and the length of the filter bag is 5-9 cm and the width is 4-6 cm.

5. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that In step (3), the ketone is one of acetone, butanone, methyl butanone or methyl isobutyl ketone, the ester is one of methyl formate, ethyl acetate, propyl acetate or butyl acetate, and the cycloalkane is one of cyclopentane, cyclohexane or cycloheptane.

6. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The mass ratio of the test sample to the composite extractant in step (3) is 1:200-400.

7. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The addition rate of the composite extractant in step (3) is 20-50 drops / min.

8. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The extraction temperature in step (3) is 80-160°C.

9. The method for measuring the crosslinking degree of a film-forming agent according to claim 1, characterized in that The extraction time described in step (3) is 1-3h.

10. The method for determining the crosslinking degree of a film-forming agent according to claim 1, characterized in that The natural drying time in step (3) is 0.5-2 hours, the drying temperature is 110-140° C., and the drying time is 1-3 hours.

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