Method for determining crosslinking conditions of polymer

Abstract

The invention relates to the field of material crosslinking density testing, and discloses a method for determining the crosslinking condition of a polymer, and the method comprises the following steps: S1, mixing the polymer and a crosslinking initiator, and carrying out open milling and hot pressing treatment to prepare an uncrosslinked polymer doped with the crosslinking initiator; s2, carrying out a cross-linking reaction on the non-cross-linked polymer under a first cross-linking condition, and carrying out in-situ testing on the cross-linking densities at different times to form a first cross-linking reaction kinetic curve formed by the cross-linking densities at different times; s3, repeating the step S2 to form respective crosslinking reaction kinetic curves under a plurality of crosslinking conditions; and S4, obtaining the slope and the maximum crosslinking density of each crosslinking reaction kinetic curve, and selecting crosslinking conditions according to the slope and the maximum crosslinking density. According to the method, the analysis and research on the influence of the crosslinking condition on the crosslinking polymerization process can be realized.

Description

Technical Field

[0001] This invention relates to the field of material crosslinking density testing, and more specifically to a method for determining the crosslinking conditions of a polymer. Background Technology

[0002] As a key structural material in the field of advanced materials, the macroscopic physical properties of cross-linked polymers (including mechanical strength, thermal stability and resistance to media) are closely related to the cross-linking density.

[0003] At the research level, in-situ testing of crosslinking density can quickly reveal the crosslinking reaction rate, the formation and disappearance of intermediate products, and help to explore the kinetic mechanism of crosslinking reactions in depth, providing a basis for building more accurate reaction models. Simultaneously, it can clarify the relationship between crosslinking density and material properties, helping researchers to precisely control the amount of crosslinking agent and add auxiliary components according to material performance requirements, obtain the best crosslinking effect and material properties, and even explore new crosslinking systems and conditions to develop novel materials.

[0004] In the production process, real-time monitoring of the crosslinking reaction progress and changes in crosslinking density allows for the determination of optimal reaction time and process parameters, preventing crosslinking anomalies, shortening production cycles, and improving production efficiency. In-situ testing can also promptly detect reaction anomalies, facilitating process adjustments by operators, ensuring stable product quality, reducing defect rates, and consequently lowering raw material and energy consumption as well as after-sales costs, thus achieving cost reduction and efficiency improvement.

[0005] Therefore, in-situ testing of changes in crosslinking density during the crosslinking reaction is of great significance. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of existing technologies lacking in-situ direct testing methods for crosslinking density, and to provide a method for determining the crosslinking conditions of polymers. This method enables the analysis and study of the influence of crosslinking conditions on the crosslinking polymerization process.

[0007] To achieve the above objectives, the present invention provides a method for determining the crosslinking conditions of a polymer, wherein the method comprises: S1. Mix the polymer and crosslinking initiator and perform open milling and hot pressing to prepare an uncrosslinked polymer doped with the crosslinking initiator; S2. The uncrosslinked polymer is subjected to a crosslinking reaction under the first crosslinking condition, and the crosslinking density is tested in situ at different times to form the first crosslinking reaction kinetic curve of the crosslinking density at different times; S3. Repeat step S2 to form cross-linking reaction kinetic curves under multiple cross-linking conditions. S4. Obtain the slope and maximum crosslinking density of each crosslinking reaction kinetic curve, and select crosslinking conditions based on the slope and maximum crosslinking density.

[0008] The beneficial effects of the present invention through the above technical solution are as follows: (1) The method can directly test the crosslinking density in the crosslinking reaction process without damaging the sample, and can explore the effects of different reaction temperatures, different crosslinking initiators, different crosslinking initiator contents and different polymer types on the crosslinking reaction kinetics; (2) The method is applicable to any kind of crosslinkable polymer and crosslinking initiator, has good versatility, is simple to operate, does not require chemical modification, and is suitable for large-scale promotion and application. Attached Figure Description

[0009] Figure 1 These are the crosslinking reaction kinetic curves at different temperatures; Figure 2 These are the crosslinking reaction kinetic curves under crosslinking initiators with different doping ratios; Figure 3 These are the cross-linking reaction kinetic curves under different types of cross-linking initiators; Figure 4 These are the crosslinking reaction kinetic curves of different types of polymers. Detailed Implementation

[0010] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0011] As previously stated, the present invention provides a method for determining the crosslinking conditions of a polymer, wherein the method comprises: S1. Mix the polymer and crosslinking initiator and perform open milling and hot pressing to prepare an uncrosslinked polymer doped with the crosslinking initiator; S2. The uncrosslinked polymer is subjected to a crosslinking reaction under the first crosslinking condition, and the crosslinking density is tested in situ at different times to form the first crosslinking reaction kinetic curve of the crosslinking density at different times; S3. Repeat step S2 to form cross-linking reaction kinetic curves under multiple cross-linking conditions. S4. Obtain the slope and maximum crosslinking density of each crosslinking reaction kinetic curve, and select crosslinking conditions based on the slope and maximum crosslinking density.

[0012] The inventors of this invention discovered that by conducting in-situ tests of crosslinking density during the crosslinking reaction, crosslinking reaction kinetic curves formed at different times based on crosslinking density can be established, thereby enabling the investigation of the effects of different reaction temperatures, different crosslinking initiators, different crosslinking initiator contents, and different polymer types on the crosslinking polymerization process.

[0013] According to the present invention, the crosslinking reaction kinetic curve is constructed through the following steps: S2-1. Under the preset crosslinking conditions, test the crosslinking density in situ at different times and record the crosslinking density data at different times; S2-2. Using time as the x-axis and crosslinking density as the y-axis, the crosslinking reaction kinetic curve under the crosslinking conditions is obtained by fitting the data using data processing software such as Origin or Excel.

[0014] According to the present invention, the range of polymers is relatively broad. In this invention, it can be selected from one or more of polyethylene, polypropylene, and natural rubber, preferably polyethylene. More preferably, the polyethylene has a weight-average molecular weight of 10,000 g / mol to 500,000 g / mol and a density of 0.910-0.970 g / cm³. 3 .

[0015] According to the present invention, the crosslinking initiator is a free radical initiator. Preferably, the initiator may be selected from one or more of peroxide initiators, azo initiators and oxynitride initiators. More preferably, the initiator may be dicumyl peroxide (DCP) and / or 2,5-dimethyl-2,5-di-tert-butylperoxide (DHBP).

[0016] According to the present invention, the length × width of the uncrosslinked polymer film is ≥1cm × 0.5cm.

[0017] According to the present invention, in step S1, an uncrosslinked polymer film doped with a crosslinking initiator is prepared, comprising the following synthesis steps: A certain amount of polymer powder or granules and a crosslinking initiator are heated and mixed in a two-roll mill for a period of time to obtain a polymer doped with the crosslinking initiator. The resulting polymer is then hot-pressed in a flat vulcanizing mill, and after cooling, an uncrosslinked polymer film doped with the crosslinking initiator is obtained. Preferably, the types of crosslinkable polymer and crosslinking initiator can be arbitrary; the mass ratio of crosslinking initiator to polymer can be arbitrary; the mixing temperature in the two-roll mill is 2-5°C lower than the melting temperature of the polymer, and the mixing time is 3-8 min; the hot-pressing temperature in the flat vulcanizing mill is ±3°C of the melting temperature of the polymer, the pressure is 10-20 MPa, and the hot-pressing time is 10-20 min.

[0018] According to the present invention, in step S2, the crosslinking density of the uncrosslinked polymer film is tested in situ to establish the crosslinking reaction kinetics at different times, including the following steps: (S2-1) First, cut the polymer film doped with crosslinking initiator into multiple strips with a length × width ≥ 1 cm × 0.5 cm, and then load the cut strips into the NMR tube of the NMR crosslinking density analyzer. (S2-2) Place the NMR tube containing the sample to be tested in the test chamber of the NMR crosslinking density analyzer and preheat it for a period of time. After the equipment temperature stabilizes, set the NMR crosslinking density analyzer to measure the NMR parameters of the crosslinking density. Then, the uncrosslinked polymer film undergoes a crosslinking reaction under crosslinking conditions, and the crosslinking density is tested in situ at different times. (S2-3) The crosslinking density is tested once at the same time interval using a nuclear magnetic resonance crosslinking density analyzer, and the data is recorded and processed using the instrument's data analysis software to obtain a series of crosslinking density values.

[0019] (S2-4) Using the crosslinking density values ​​measured at different temperatures and times, we will study the changing trend of the degree of crosslinking reaction with temperature, crosslinking initiator content, crosslinking initiator type, or polymer type, and explore the crosslinking reaction kinetics under different reaction temperatures, crosslinking initiator content, crosslinking initiator type, or polymer type.

[0020] According to the present invention, in step S2, the crosslinking reaction can be carried out for different reaction temperatures, different crosslinking initiators, different crosslinking initiator contents, and different polymer types. The conditions for the crosslinking reaction include: the temperature being higher than the initiation temperature of the crosslinking initiator, and the time being 300s-7200s.

[0021] In this invention, the optimal initiation temperature range of the crosslinking initiator dicumyl peroxide (DCP) is 160-200°C, and the optimal initiation temperature of the crosslinking initiator 2,5-dimethyl-2,5-di-tert-butylperoxide (DHBP) is 150-190°C.

[0022] According to the present invention, in step S2, the instrument used for the in-situ test is a nuclear magnetic resonance crosslinking density analyzer. In the present invention, the nuclear magnetic resonance crosslinking density analyzer includes VTMR20-010V-I (Shanghai Newmai Electronic Technology Co., Ltd.) or Minispec mq20 (Germany Bruker).

[0023] According to the present invention, the process of in-situ testing of crosslinking density using an NMR crosslinking density meter includes: The specific instrument test parameters include: (1) Sampling bandwidth: 100-500kHz (actual test point value: 333.333kHz); (2) Number of sampling points: 10,000-50,000 (actual test point value: 45,364); (3) Waiting time: 500-5000ms (actual test point value: 3000ms); (4) Number of echoes: 20-60 (actual test point value: 46); (5) Start time: 0.01ms-0.1ms (actual test point value: 0.068ms); (6) End time: 5-40ms (actual test point value: 20ms); (7) The magnetic field strength is 0.3-1.0T (actual test point value: magnetic field strength 0.49T); (8) The frequency is 10-30MHz (actual test point value: frequency 21MHz); (9) The cumulative number of times is 5-20 times (actual test point value: cumulative number of times 10 times).

[0024] According to the present invention, in step S2, a crosslinking density analyzer is used to perform tests at equal time intervals, and the data is recorded and processed using instrument data analysis software to obtain a series of crosslinking density values. Preferably, the time interval is 20-40 seconds, and the total test time is 300-7200 seconds.

[0025] According to the present invention, in step S2, the NMR tube containing the uncrosslinked polymer film to be tested is placed in the test chamber of the NMR crosslinking density analyzer and preheated for a period of time; preferably, the stabilization period is 1-2 minutes.

[0026] According to the present invention, in step S3, establishing the crosslinking reaction kinetics formed by crosslinking density at different times includes: plotting the crosslinking reaction kinetics curve by drawing data curves with crosslinking density as the vertical axis and reaction time as the horizontal axis.

[0027] The present invention will be described in detail below through embodiments.

[0028] In the following embodiments: The raw material is dicumyl peroxide (DCP), a commercially available product from Sigma Corporation with the brand name 329541.

[0029] The feedstock for 2,5-dimethyl-2,5-di-tert-butylperoxide (DHBP) is a commercially available product from McLean Company, brand name T819468.

[0030] The low-density polyethylene raw material is a commercially available product from Qilu Petrochemical Company, brand name J182B.

[0031] Polypropylene is a commercially available product from Maoming Petrochemical Company, brand name HT9025NX.

[0032] Example 1 This embodiment aims to illustrate the effect of different temperatures on the crosslinking polymerization process.

[0033] The preparation of uncrosslinked polyethylene films doped with the crosslinking initiator dicumyl peroxide (DCP) includes the following synthesis steps: S1. First, weigh out 10g of low-density polyethylene (LDPE, density 0.918g / cm³). 3 LDPE and 50 mg DCP (0.5 wt%) were weighed and mixed in a two-roll mill for 5 min (115 °C) to obtain an initiator / polyethylene blend doped with a crosslinking initiator; the initiator / polyethylene blend was hot-pressed for 15 min at 120 °C and 15 MPa using a flat vulcanizing machine, and after cooling, an initiator / polyethylene blend film was obtained. S2. In-situ testing of the crosslinking density of the uncrosslinked polymer film was conducted to establish the crosslinking reaction kinetics at different times, including the following steps: (S2-1) First, cut the initiator / polyethylene blend film into multiple strips with a length × width of 1cm × 0.5cm, and then load the cut strips into the NMR tube; (S2-2) The change in crosslinking density during the crosslinking reaction was tested in situ using a nuclear magnetic resonance crosslinking density analyzer of model VTMR20-010V-I (Shanghai Newmai Electronic Technology Co., Ltd.). The nuclear magnetic parameters were set, including magnetic field strength of 0.49T, frequency of 21MHz, and a total of 10 tests. (S2-3) Set the equipment temperature to 180℃. After the equipment temperature stabilizes, place the NMR tube containing the sample to be tested in the NMR crosslinking density analyzer and stabilize it for 1 min. (S2-4) The crosslinking density of the sample was tested once every 20 seconds using a nuclear magnetic resonance crosslinking density analyzer. The test lasted for a total of 10 minutes. The data was recorded and processed using the instrument's data analysis software to obtain a series of crosslinking density values. (S2-5) Following the steps above, set the equipment temperature in step (S2-3) to 160℃ and 200℃ respectively, and test the crosslinking density of the crosslinking reaction at different temperatures; S3. Plot crosslinking density on the ordinate and reaction time on the abscissa to investigate the effect of different temperatures on the crosslinking reaction process by drawing data curves; for example... Figure 1As shown, the DCP-initiated polyethylene crosslinking reaction has a slow reaction rate at 160℃, and the fastest reaction rate at 200℃, but the crosslinking density is low at equilibrium. Considering the combined effects of temperature on the reaction rate and conversion rate, the reaction kinetic curves demonstrate that the optimal temperature for the DCP-initiated polyethylene crosslinking reaction is around 180℃. The crosslinking reaction kinetic curves at different temperatures clearly reflect the influence of reaction temperature on the crosslinking process.

[0034] Example 2 This embodiment illustrates the effect of different amounts of crosslinking initiators on the crosslinking polymerization process.

[0035] The preparation of uncrosslinked polyethylene films doped with different amounts of the crosslinking initiator dicumyl peroxide (DCP) includes the following synthesis steps: S1. Following the same method as step S1 in Example 1, prepare initiator / polyethylene blends with crosslinking initiator mass fractions of 0.5 wt%, 2 wt%, and 5 wt%, respectively. S2. Following the same method as step S2 in Example 1, the crosslinking density of the crosslinking reaction at 180°C with DCP mass fractions of 0.5wt%, 2wt%, and 5wt% was tested respectively. S3. Following the same method as step S3 in Example 1, plot data curves with crosslinking density as the ordinate and reaction time as the abscissa to investigate the effect of different amounts of crosslinking initiator on the crosslinking reaction process; for example... Figure 2 As shown, the DCP-initiated polyethylene crosslinking reaction exhibits a slow reaction rate and low crosslinking density at reaction equilibrium when the DCP mass fraction is 0.5 wt%. The reaction rate is fastest at a DCP mass fraction of 5 wt%, but the crosslinking density at reaction equilibrium is similar to that at a DCP mass fraction of 2 wt%. Considering the combined effects of crosslinking initiator content on reaction rate and conversion rate, as well as the cost of the crosslinking initiator, the reaction kinetic curves demonstrate that the optimal initiator mass fraction for DCP-initiated polyethylene crosslinking is around 2 wt%. The crosslinking reaction kinetic curves under different crosslinking initiator contents clearly reflect the influence of the crosslinking initiator content on the crosslinking process.

[0036] Example 3 This embodiment aims to illustrate the effect of different initiators on the crosslinking polymerization process.

[0037] The preparation of uncrosslinked polyethylene films doped with crosslinking initiators dicumyl peroxide (DCP) or 2,5-dimethyl-2,5-di-tert-butylperoxide (DHBP) includes the following synthetic steps: S1. Following the same method as step S1 in Example 1, prepare initiator (DCP) / polyethylene blends with a crosslinking initiator mass fraction of 2 wt%, and initiator (DHBP) / polyethylene blends with a crosslinking initiator mass fraction of 2 wt%. S2. Following the same method as step S2 in Example 1, test the crosslinking density of the crosslinking reaction at 180°C when the mass fractions of DCP and DHBP are both 2wt%. S3. Following the same method as step S3 in Example 1, plot data curves with crosslinking density as the ordinate and reaction time as the abscissa to investigate the effect of the type of crosslinking initiator on the crosslinking reaction process; for example... Figure 3 As shown, at 180℃, the polyethylene crosslinking reaction initiated by DCP has a faster reaction rate and a higher crosslinking density at reaction equilibrium. The polyethylene crosslinking reaction initiated by DHBP has a slower reaction rate and a lower crosslinking density at the same reaction time. The reaction kinetic curves demonstrate that at 180℃, DCP initiator is more suitable for initiating the polyethylene crosslinking reaction. The crosslinking reaction kinetic curves under different types of crosslinking initiators clearly reflect the influence of the type of crosslinking initiator on the crosslinking process.

[0038] Example 4 This embodiment aims to illustrate the influence of different polymer types on the crosslinking polymerization process.

[0039] The preparation of uncrosslinked polyethylene films and uncrosslinked polypropylene films doped with the crosslinking initiator dicumyl peroxide (DCP) includes the following synthesis steps: S1. Prepare an initiator (DCP) / polyethylene blend with a crosslinking initiator mass fraction of 2 wt% according to the same method as step S1 in Example 1.

[0040] The preparation of a crosslinking initiator / polypropylene blend with a crosslinking initiator mass fraction of 2 wt% is carried out according to the following steps: First, weigh 10 g of polypropylene (PP, density 0.895 g / cm³). 3 PP and 200 mg DCP (2 wt%) were weighed and mixed in a two-roll mill for 5 min (150 °C) to obtain an initiator / polypropylene blend doped with a crosslinking initiator; the initiator / polypropylene blend was hot-pressed for 15 min at 150 °C and 15 MPa using a flat vulcanizing machine, and after cooling, an initiator / polypropylene blend film was obtained. S2. Following the same method as step S2 in Example 1, test the crosslinking density of the crosslinking reaction at 180°C with 2wt% DCP. S3. Following the same method as step S3 in Example 1, plot data curves with crosslinking density as the ordinate and reaction time as the abscissa to investigate the effect of polymer type on the crosslinking reaction process; for example... Figure 4 As shown, at 180℃, the DCP-induced crosslinking reaction of polyethylene has a faster reaction rate and a higher crosslinking density at reaction equilibrium. The DCP-induced crosslinking reaction of polypropylene has a slower reaction rate, a lower crosslinking density at the same reaction time, and the crosslinking density gradually decreases with increasing crosslinking time due to the degradation of polypropylene. The crosslinking reaction kinetic curves for different polymers clearly reflect the influence of polymer type on the crosslinking process.

[0041] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for determining crosslinking conditions for a polymer, characterized by, The method includes: S1. Mix the polymer and crosslinking initiator and perform open milling and hot pressing to prepare an uncrosslinked polymer doped with the crosslinking initiator; S2. The uncrosslinked polymer is subjected to a crosslinking reaction under the first crosslinking condition, and the crosslinking density is tested in situ at different times to form the first crosslinking reaction kinetic curve of the crosslinking density at different times; S3. Repeat step S2 to form cross-linking reaction kinetic curves under multiple cross-linking conditions. S4. Obtain the slope and maximum crosslinking density of each crosslinking reaction kinetic curve, and select crosslinking conditions based on the slope and maximum crosslinking density.

2. The method according to claim 1, wherein, The crosslinking reaction kinetics curve was constructed through the following steps: S2-1. Under the preset crosslinking conditions, test the crosslinking density in situ at different times and record the crosslinking density data at different times; S2-2. Using time as the x-axis and crosslinking density as the y-axis, the crosslinking reaction kinetic curve under the crosslinking conditions is obtained by fitting the data using Origin or Excel data processing software.

3. The method according to claim 1, wherein, The polymer is selected from one or more of polyethylene, rubber, and polypropylene; And / or, the crosslinking initiator is a free radical initiator.

4. The method according to claim 1, wherein, The uncrosslinked polymer has a length × width ≥ 1cm × 0.5cm.

5. The method according to claim 1, wherein, In step S1, the conditions for open milling include: the open milling temperature is 2-5°C lower than the melting temperature of the polymer, and the mixing time is 3-8 minutes. And / or, in step S1, the conditions for the hot pressing treatment include: the hot pressing temperature is initially the melt temperature of the polymer ±3°C, the pressure is 10-20 MPa, and the hot pressing time is 10-30 min.

6. The method according to claim 1, wherein, In step S2, the conditions for the in-situ test include: placing the uncrosslinked polymer film in a nuclear magnetic resonance (NMR) tube, and then placing the NMR tube in the test chamber of the NMR crosslinking density meter for stable preheating.

7. The method according to claim 1, wherein, In step S2, the conditions for the crosslinking reaction include: a temperature higher than the initiation temperature of the crosslinking initiator, and a time of 300s-7200s; And / or, in step S2, the instrument used for the in-situ test is a nuclear magnetic resonance crosslinking density analyzer.

8. The method according to claim 7, wherein, The NMR parameters of the NMR crosslinking density analyzer are set as follows: magnetic field strength of 0.3-1.0T, frequency of 10-30MHz, and cumulative number of times of analysis of 5-20.

9. The method according to claim 8, wherein, The crosslinking density analyzer is used to perform tests at equal time intervals, and the data is recorded and processed using the instrument's data analysis software to obtain a series of crosslinking density values.

10. The method according to claim 9, wherein, The interval is 20-40 seconds; And / or, the stable preheating time is 1-2 minutes; And / or, the total time for the in-situ test is 300s-7200s.

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