Degradable epoxy resin curing process regulation and control method based on dielectric parameter real-time monitoring

Abstract

The invention relates to a degradable epoxy resin curing process regulation and control method based on dielectric parameter real-time monitoring, and the method specifically comprises the following steps: S1, weighing raw materials according to a ratio, and mixing the raw materials to obtain an epoxy resin prepreg; s2, pouring epoxy resin prepreg in the electric field module, and connecting a power supply to monitor dielectric parameters; s3, placing the epoxy resin prepreg with the sensor in a set curing process environment, carrying out a curing procedure, and calculating to obtain a change curve of dielectric parameter values of different materials along with time; s4, regulating and optimizing a curing process to obtain an optimized curing process; and obtaining a change curve of the conductivity value along with time. A more reasonable heating rate and a temperature platform are set, so that the curing process is more uniform, the stress concentration in the material is reduced, the formation probability of microdefects is reduced, the cross-linking reaction is more sufficient, the internal structure of the material is more stable, the density of a formed cross-linked network is higher, and the overall mechanical property and dielectric property are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical insulation materials, and in particular relates to a method for controlling a degradable epoxy resin curing process based on real-time monitoring of dielectric parameters. Background Art

[0002] Since traditional epoxy resins are difficult to degrade in the natural environment, the current research hotspot is to introduce dynamic reversible bonds into epoxy resins to achieve accelerated degradation under specific conditions, mainly involving dynamic covalent bonds such as ester bonds, disulfide bonds and imine bonds. Taking the transesterification reaction as an example, the esters and alcohols in the epoxy resin will undergo a reversible reaction. Unlike traditional epoxy resins, during the curing reaction of the degradable epoxy resin, the catalyst will not only induce the ring-opening polymerization reaction of the anhydride, but also catalyze the reversible reaction of the ester group. The breaking and bonding of the dynamic reversible bonds will affect the molecular chain migration and cross-linking in the curing reaction, resulting in significant differences in the curing process of the degradable epoxy resin and the traditional epoxy resin.

[0003] Due to the introduction of dynamic reversible bonds and catalysts, the activation energy barrier of the epoxy resin curing process is reduced, which significantly improves the activity of the cross-linking reaction, speeds up the reaction rate and shortens the curing time. This not only shortens the process operation window, but also affects the processing performance and stress release process of the resin, thereby affecting the mechanical strength and dielectric properties of the material. This dynamic curing behavior of degradable epoxy resin needs to be finely controlled through process parameter optimization, which is not suitable for traditional curing processes and requires further research and optimization to balance the relationship between curing rate and material properties.

[0004] Therefore, it is necessary to develop a method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters, so as to improve the material properties of degradable epoxy resin by optimizing the curing process. Summary of the invention

[0005] The purpose of the present invention is to provide a method for controlling the curing process of a degradable epoxy resin based on real-time monitoring of dielectric parameters. In view of the problem that traditional curing process methods for degradable epoxy resins are not applicable, a real-time monitoring platform for dielectric parameters in the curing process of degradable epoxy resins is established, the curing process is optimized, and the material properties of the degradable epoxy resins are improved.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is that the method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters specifically comprises the following steps:

[0007] S1 Preparation of epoxy resin prepreg: weigh raw materials according to the ratio and mix them, and put the mixture into a mechanical stirrer in a vacuum environment to obtain epoxy resin prepreg;

[0008] S2 Curing Process Monitoring Platform Construction: Pour epoxy resin prepreg into the electric field module and connect it to the power supply to monitor the dielectric parameters;

[0009] S3 curing real-time dielectric parameter monitoring: The epoxy resin prepreg equipped with sensors is placed in the environment of the set curing process, and the curing process is carried out by controlling the heating rate through the heating platform, and the change curve of the dielectric parameter values ​​of different materials over time is calculated;

[0010] S4 curing process control and optimization: the epoxy resin prepreg prepared according to step S1 is subjected to real-time dielectric parameter monitoring according to steps S2 and S3. On the basis of adopting the set epoxy resin curing process, the curing process parameters (such as temperature or time) are dynamically and real-time adjusted through the temperature control unit according to the change trend of the dielectric parameters to obtain an optimized curing process; and then the conductivity value change curve over time under the optimized curing process is calculated.

[0011] Preferably, the method further includes a sample performance comparison test in step S5: pouring the epoxy resin prepreg prepared in step S1 into a mold, and then putting it into an oven for curing according to the process set in step S3 and the optimized curing process obtained in step S4, respectively, to ensure that the epoxy resin is completely cured, and then performing a performance test on the epoxy resin composite material sample to verify the optimized curing process. By preparing epoxy composite samples with a dynamic control process for performance test comparison, the optimized curing process of the degradable epoxy resin is verified.

[0012] Preferably, the raw materials in step S1 include epoxy resin matrix, epoxy resin curing agent, accelerator and dynamic catalyst, and the formula of the raw materials is as follows: 100 parts of bisphenol A epoxy resin, 84.66-88.7 parts of curing agent, and 0.5-1.0 parts of degradation catalyst.

[0013] Preferably, in the step S1, the epoxy resin matrix is ​​a pure epoxy resin matrix or a degradable epoxy resin matrix, and the degradable epoxy resin matrix includes a TBD-catalyzed epoxy resin matrix and a bio-based epoxy resin matrix.

[0014] Preferably, in step S1, the ratio of epoxy resin to bio-based in the bio-based epoxy resin matrix is ​​3:1 to 5:1.

[0015] Preferably, in step S1, the mixture mixed according to the proportion is put into a mechanical stirrer, maintained at room temperature of 25° C., and stirred at a speed of 300 rad / min for 1 hour, and the vacuum degree is maintained at ≤100 Pa.

[0016] Preferably, in step S1, the curing agent is methyltetrahydrophthalic anhydride; and the degradation catalyst is N,N-dimethylbenzylamine (BDMA) or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0017] Preferably, the specific steps of step S2 are: the built curing process monitoring platform is divided into a voltage module, a current monitoring module, a heating module and an electric field module, wherein the voltage module adopts a Tesman TRC2020 positive polarity high voltage power supply, and the current monitoring module adopts a Keithley 6517B electrometer current, with a measurement range of 10aA-20mA; the heating platform provides a constant temperature or constant rate heating environment to achieve the curing of the epoxy resin, and the epoxy resin resistance volume in the electric field module is 10×10×1.5cm; epoxy resin prepreg is poured in the electric field module until the container is fully immersed, with a height of 1.5cm, and then a positive power supply and a grounding wire are applied at both ends respectively, a constant electric field is provided by a positive polarity DC current generator, and then the voltage and current changes are calculated by a formula to monitor the dielectric parameters.

[0018] Preferably, in step S3, the curing process monitoring platform performs pressure testing on different temperature points, and the ambient temperature is set to a heating rate of 10°C / min, that is, the current value and voltage value are recorded every time the temperature rises by 10°C until the predetermined maximum test temperature is reached, and the change curve of the dielectric parameter values ​​of different materials over time is calculated.

[0019] Preferably, the curing process set in step S4 is a two-stage curing process, wherein the first stage is cured at 80°C for 4 hours; the second stage is cured at 140°C for 12 hours; the optimized curing process is a four-stage curing process, including a pre-curing temperature T p , intermediate curing temperature T m , complete curing temperature T f , post-curing temperature T s .

[0020] Preferably, in step S4, the curing process is optimized by using the Arrhenius equation to describe the effect of temperature on the chemical reaction rate, and the formula is:

[0021]

[0022] Where k is the curing reaction rate, A is the pre-exponential factor (or frequency factor), Ea is the activation energy, R is the ideal gas constant, and T is the temperature;

[0023] In the dielectric parameter-based curing monitoring platform, the curing reaction rate can be approximately equivalent to the slope of conductivity change; further optimization calculations are performed for the stage of significant conductivity change in the set traditional curing process stage. Combined with the temperature influence formula, the conductivity change rate is expressed as:

[0024]

[0025] Among them, f(σ) is a relationship function that describes the relationship between conductivity and reaction rate. Assuming that the change in conductivity is directly related to the curing reaction rate, f(σ) is a linear relationship. In order to ensure the stress release of the casting process and post-curing, the pre-curing temperature T p and post-curing temperature T s Still maintaining 80℃ and 140℃, calculate the intermediate curing temperature T when the slope is constant according to the conductivity rate formula m and complete curing temperature T f The temperatures are 90°C and 110°C respectively, and the optimized curing process is calculated as follows:

[0026] The first stage: maintain 80℃ for 3 hours; the second stage: heat up to 90℃ within 0.5 hours and maintain 90℃ for 2 hours; the third stage: heat up to 110℃ within 0.5 hours and maintain 110℃ for 2 hours; the fourth stage: heat up to 140℃ within 0.5 hours and maintain 140℃ for 7.5 hours. A constant heating rate of 0.5 hours is set to heat up to the temperature of the next stage.

[0027] Preferably, in step S4, the optimized process is used to perform a pressure test on the epoxy resin prepreg through a curing process monitoring platform, and the current and voltage values ​​are recorded until a predetermined maximum test temperature is reached, and monitoring is performed every 0.5 hours for a set time; during the entire curing process, a curve of the change in conductivity value over time under the optimized curing process is calculated.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) In view of the complexity of the curing behavior of degradable epoxy resin, the present invention builds a real-time monitoring platform for dielectric parameters of the curing process of degradable epoxy resin, and analyzes the curing process by real-time monitoring of the dielectric property curve of the curing system;

[0030] (2) The present invention optimizes the curing process of the degradable epoxy resin based on real-time monitoring of dielectric parameter changes, prepares epoxy composite samples with dynamic control process for performance testing and comparison, and verifies the optimized curing process of the degradable epoxy resin;

[0031] (3) In the process of optimizing the curing process of biodegradable epoxy resin, a more reasonable heating rate and temperature platform are set to make the curing process more uniform, reduce the stress concentration inside the material, and reduce the probability of forming micro defects; the cross-linking reaction is more complete, the internal structure of the material is more stable, and the cross-linking network density formed is higher, thereby improving the overall mechanical properties and dielectric properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the transesterification process in the epoxy resin material in the method for controlling the curing process of the degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0033] Figure 2 It is a wiring diagram for real-time monitoring of epoxy resin curing process in the method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0034] Figure 3 A diagram of a real-time monitoring platform for epoxy resin curing process in a method for controlling a degradable epoxy resin curing process based on real-time monitoring of dielectric parameters according to the present invention;

[0035] Figure 4 It is the charge migration process at different stages of epoxy resin curing in the method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0036] Figure 5 The conductivity-temperature curve of epoxy resin and degradable epoxy resin in the degradable epoxy resin curing process control method based on real-time monitoring of dielectric parameters of the present invention;

[0037] Figure 6 It is a traditional curing process and conductivity monitoring curve in the curing process control method of degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0038] Figure 7 It is an optimization curve of the curing process of the degradable epoxy resin in the curing process control method of the degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0039] Figure 8 It is a conductivity monitoring comparison curve before and after the curing process is optimized in the method for controlling the curing process of a degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0040] Fig. 9 It is a stress variation curve before and after the curing process is optimized in the method for controlling the curing process of a degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention;

[0041] Fig.10 The performance test comparison curves before and after the curing process is optimized in the method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters of the present invention; a) bending strength before and after process optimization; b) tensile strength before and after process optimization; c) bending strength stress-strain curve; d) breakdown strength before and after process optimization. DETAILED DESCRIPTION

[0042] The technical solution is further described below in conjunction with the accompanying drawings.

[0043] Embodiment: The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters specifically comprises the following steps:

[0044] S1 Preparation of epoxy resin prepreg: weigh the raw materials according to the ratio and mix them, put the mixture into a mechanical stirrer in a vacuum environment, keep the room temperature at 25°C, stir the mixture at a speed of 300 rad / min for 1 hour, and maintain the vacuum degree ≤100Pa to obtain epoxy resin prepreg;

[0045] The raw materials in step S1 include epoxy resin matrix, epoxy resin curing agent, accelerator and dynamic catalyst, and the formula of the raw materials is as follows: 100 parts of bisphenol A epoxy resin, 84.66-88.7 parts of curing agent, and 0.5-1.0 parts of degradation catalyst;

[0046] In the step S1, the epoxy resin matrix is ​​a pure epoxy resin matrix or a degradable epoxy resin matrix, and the degradable epoxy resin matrix includes a TBD-catalyzed epoxy resin matrix and a bio-based epoxy resin matrix;

[0047] In step S1, the ratio of epoxy resin to bio-based in the bio-based epoxy resin matrix is ​​3:1 to 5:1;

[0048] In step S1, the curing agent is methyltetrahydrophthalic anhydride; the degradation catalyst is N,N-dimethylbenzylamine (BDMA) or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD);

[0049] Taking transesterification as an example, the esters in epoxy resin and alcohols will undergo a reversible reaction, such as Figure 1 As shown;

[0050] S2 Curing Process Monitoring Platform Construction: Pour epoxy resin prepreg into the electric field module and connect it to the power supply to monitor the dielectric parameters;

[0051] The specific steps of step S2 are as follows: the built curing process monitoring platform is divided into a voltage module, a current monitoring module, a heating module and an electric field module, wherein the voltage module adopts a Tesman TRC2020 positive polarity high voltage power supply, and the current monitoring module adopts a Keithley 6517B electrometer current, with a measurement range of 10aA-20mA; the heating platform provides a constant temperature or constant rate heating environment to achieve the curing of the epoxy resin, and the epoxy resin resistance volume in the electric field module is 10×10×1.5cm; Figure 3 As shown, epoxy resin prepreg is poured into the electric field module until the container is fully immersed, with a height of 1.5 cm. Then, a positive power supply and a grounding wire are applied to both ends respectively, and a constant electric field is provided by a positive polarity DC current generator. Then, the voltage and current changes are calculated by the formula to monitor the dielectric parameters. The real-time monitoring connection diagram is shown in Figure 2 As shown;

[0052] S3 curing real-time dielectric parameter monitoring: Place the epoxy resin prepreg equipped with sensors in the environment of the set curing process, control the heating rate through the heating platform to perform the curing program, and calculate the change curve of the dielectric parameter values ​​of different materials over time; specifically: place the prepreg equipped with dielectric parameter sensors in the set curing environment to ensure that the sensor is in close contact with the material surface to avoid measurement errors caused by poor contact; use standard solutions to calibrate the curing process monitoring platform; different curing stages of epoxy resin will have a significant impact on charge migration and dielectric parameters. In the viscous flow stage, the movement of molecular chains is relatively free, ion migration is faster, and the conductivity is higher; in the gel state stage, the molecular chains gradually form a three-dimensional network, and ion migration is hindered; in the glass state stage, the movement of molecular chains almost stops, and the conductivity changes rapidly; such as Figure 4 shown.

[0053] In step S3, the curing process monitoring platform performs pressure testing at different temperature points, and the ambient temperature is set to a heating rate of 10°C / min, that is, the current value and voltage value are recorded every time the temperature rises by 10°C until the predetermined maximum test temperature is reached, and the change curve of the dielectric parameter values ​​of different materials over time is calculated;

[0054] S4 curing process control optimization: the epoxy resin prepreg prepared according to step S1 is subjected to real-time dielectric parameter monitoring according to steps S2 and S3. On the basis of the set epoxy resin curing process, the curing process parameters (such as temperature or time) are dynamically and real-time adjusted through the temperature control unit according to the change trend of the dielectric parameters to obtain an optimized curing process; then the conductivity value over time curve under the optimized curing process is calculated; the curing process set in step S4 is a two-stage curing process, wherein the first stage is cured at 80°C for 4 hours; the second stage is cured at 140°C for 12 hours;

[0055] In step S4, the curing process is optimized by using the Arrhenius equation to describe the effect of temperature on the chemical reaction rate, and the formula is:

[0056]

[0057] Where k is the curing reaction rate, A is the pre-exponential factor (or frequency factor), Ea is the activation energy, R is the ideal gas constant, and T is the temperature;

[0058] In the dielectric parameter-based curing monitoring platform, the curing reaction rate can be approximately equivalent to the slope of conductivity change; further optimization calculations are performed for the stage of significant conductivity change in the set traditional curing process stage. Combined with the temperature influence formula, the conductivity change rate is expressed as:

[0059]

[0060] Among them, f(σ) is a relationship function that describes the relationship between conductivity and reaction rate. Assuming that the change in conductivity is directly related to the curing reaction rate, f(σ) is a linear relationship. In order to ensure the stress release of the casting process and post-curing, the pre-curing temperature T p and post-curing temperature T s Still maintaining 80℃ and 140℃, calculate the intermediate curing temperature T when the slope is constant according to the conductivity rate formula m and complete curing temperature T f The temperatures are 90°C and 110°C respectively, and the optimized curing process is calculated as follows:

[0061] The first stage: maintain 80℃ for 3 hours; the second stage: heat up to 90℃ within 0.5 hours and maintain 90℃ for 2 hours; the third stage: heat up to 110℃ within 0.5 hours and maintain 110℃ for 2 hours; the fourth stage: heat up to 140℃ within 0.5 hours and maintain 140℃ for 7.5 hours. A constant heating rate of 0.5 hours is set to heat up to the temperature of the next stage;

[0062] In step S4, the optimized process is used to perform a pressure test on the epoxy resin prepreg through a curing process monitoring platform, and the current and voltage values ​​are recorded until a predetermined maximum test temperature is reached, and the set time is monitored every 0.5 hours; during the entire curing process, a curve of the change in conductivity value over time under the optimized curing process is calculated,

[0063] S5 sample performance comparison test: Pour the epoxy resin prepreg prepared in step S1 into the mold, and then put it into the oven for curing according to the process set in step S3 and the optimized curing process obtained in step S4 to ensure that the epoxy resin is completely cured. Then, perform a performance test on the epoxy resin composite material sample to verify the optimized curing process.

[0064] Specific Example 1, Specific Example 2 and Specific Example 3 respectively use three different formulas to prepare three different epoxy resin prepregs, and then use three different epoxy resin prepregs to build a curing process monitoring platform, and perform real-time monitoring of curing dielectric parameters. Through the curing process monitoring platform, set the traditional curing process: the first stage: 80°C curing for 4h; the second stage: 140°C curing for 12h, calculate the change curve of the conductivity value of the three different epoxy resin prepregs over time, and then test the mechanical properties and electrical properties of the samples of the three different epoxy resin prepregs. Specifically:

[0065] (1) Preparing epoxy resin prepreg: The specific formula is shown in Table 1. The raw materials are weighed and mixed according to the ratio. The mixture is placed in a mechanical stirrer in a vacuum environment. The mixture is kept at a room temperature of 25° C. and stirred at a speed of 300 rad / min for 1 hour. The vacuum degree is maintained at ≤100 Pa to obtain epoxy resin prepreg;

[0066] Table 1 Pure epoxy resin (traditional epoxy resin) and degradable epoxy resin material formula

[0067]

[0068] (2) Construction of curing process monitoring platform The platform is mainly divided into four parts: voltage module, current monitoring module, heating module and electric field module. The voltage module uses Tesman TRC2020 positive polarity high voltage power supply, and the current monitoring module uses Keithley 6517B electrometer with a current measurement range of 10aA-20mA; the heating platform provides a constant temperature or constant rate heating environment to achieve the curing of epoxy resin. The volume of epoxy resin resistance in the electric field module is 10×10×1.5cm, such as Figure 3 As shown;

[0069] (3) pouring the epoxy resin prepreg prepared in step (1) into the electric field module until the container is fully soaked to a height of 1.5 cm, applying a positive power supply and a grounding wire at both ends, respectively, and a positive polarity DC current generator providing a suitable voltage to generate a constant electric field;

[0070] (4) Real-time monitoring of curing dielectric parameters:

[0071] 1) Place the prepreg equipped with the dielectric parameter sensor in a set curing environment to ensure that the sensor is in close contact with the material surface to avoid measurement errors caused by poor contact; use standard solutions to calibrate the curing process monitoring platform; different curing stages of epoxy resin will have a significant impact on charge migration and dielectric parameters. In the viscous flow stage, the movement of molecular chains is relatively free, ion migration is faster, and the conductivity is higher; in the gel state stage, the molecular chains gradually form a three-dimensional network, and ion migration is hindered; in the glass state stage, the movement of molecular chains almost stops, and the conductivity changes rapidly; such as Figure 4 As shown;

[0072] 2) The ambient temperature is set to a heating rate of 10°C / min, and the current and voltage values ​​of different formulations are recorded until the predetermined maximum test temperature is reached. The conductivity value of different materials is calculated over time, such as Figure 5 shown; from Figure 5 It can be seen that the traditional epoxy resin in Specific Example 1 and the degradable epoxy resin (TBD, bio-based) in Specific Example 2 and Specific Example 3 reach lower viscosity points at 100°C, 80°C and 90°C, respectively, and the conductivity reaches a maximum value of 10-7.62S / m, 10-7.58 and 10-7.61S / m, respectively. The conductivity corresponding to the gel point is 10-8.70S / m, 10-8.36 and 10-8.54S / m, respectively. The conductivity peak value and gelation starting temperature of the degradable epoxy resin are significantly reduced. Under relatively low temperature conditions, the degradable epoxy resin can start and accelerate its curing reaction process, and enter the gel state and glass state more quickly. The difference in slope change before and after the gel point is obvious, and the monitoring curve of the degradable resin shows greater volatility, lacking the smooth transition characteristics of traditional resins;

[0073] 3) Through the curing process monitoring platform, set the traditional curing process: the first stage: 80℃ curing for 4h; the second stage: 140℃ curing for 12h, pressurize the epoxy resin prepreg, record the current and voltage values ​​until the predetermined maximum test temperature is reached, monitor once every 0.5h for the set time, and the conductivity monitoring curve is as follows Figure 6 shown; from Figure 6 It can be seen that in the traditional curing process, the curing temperature rises rapidly to 140°C after 4 hours. The conductivity drops sharply at this stage, from about 10-8S / m to about 10-15S / m. The rapid curing reaction will cause the internal stress of the resin to increase, and the molecular chains will quickly form a three-dimensional network in a short time, which will cause large residual stress and affect the mechanical properties and structural integrity of the material. In addition, too fast a curing rate may lead to inconsistent curing degrees in different areas, forming a non-uniform cured layer and shortening the process operation window. Therefore, it is necessary to optimize and adjust the curing temperature and time according to the dielectric parameter monitoring data, adopt a multi-stage curing process, gradually increase the temperature, and control the curing speed to reduce the formation of defects;

[0074] In order to solve the problem of too fast curing rate of biodegradable epoxy resin under traditional curing process, a multi-stage temperature increase strategy is adopted. After 3 hours of constant temperature at 80℃, the conductivity of the resin drops significantly, indicating that the curing process has reached the gel point. During the liquid-solid transition, the ambient temperature is still at 80℃, and there will be a significant turning point in the curing rate and post-curing stage, which will cause stress fluctuations. Therefore, it is necessary to add an intermediate temperature platform Tm after the pre-curing temperature Tp reaches the gel point. The post-curing temperature of 140℃ in the traditional process is mainly to eliminate thermal stress and improve the degree of curing, but in Figure 6 It can be found that the conductivity drops too fast after 4 hours, which will cause stress concentration. Therefore, it is also necessary to add a temperature platform. Combining the traditional curing process and the conductivity monitoring curve, the traditional two-stage curing process is optimized to a four-stage curing process: pre-curing temperature T p , intermediate curing temperature T m , complete curing temperature T f , post-curing temperature T s .

[0075] Specific embodiment 4: A method for controlling the curing process of a degradable epoxy resin based on real-time monitoring of dielectric parameters, specifically comprising the following steps:

[0076] S1 Preparation of epoxy resin prepreg: weigh the raw materials according to the ratio and mix them, put the mixture into a mechanical stirrer in a vacuum environment, keep the room temperature at 25°C, stir the mixture at a speed of 300 rad / min for 1 hour, and maintain the vacuum degree ≤100Pa to obtain epoxy resin prepreg;

[0077] The raw materials in step S1 include an epoxy resin matrix, an epoxy resin curing agent, an accelerator and a dynamic catalyst, and the formula of the raw materials is as follows: 100 parts of pure bisphenol A epoxy resin, 84.66 parts of curing agent methyltetrahydrophthalic anhydride, and 1.0 parts of degradation catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD);

[0078] S2 Curing Process Monitoring Platform Construction: Pour epoxy resin prepreg into the electric field module and connect it to the power supply to monitor the dielectric parameters;

[0079] The specific steps of step S2 are as follows: the built curing process monitoring platform is divided into a voltage module, a current monitoring module, a heating module and an electric field module, wherein the voltage module adopts a Tesman TRC2020 positive polarity high voltage power supply, and the current monitoring module adopts a Keithley 6517B electrometer current, and the measurement range is 10aA-20mA; the heating platform provides a constant temperature or constant rate heating environment to achieve the curing of epoxy resin, and the epoxy resin resistance volume in the electric field module is 10×10×1.5cm; epoxy resin prepreg is poured in the electric field module until the container is fully immersed, with a height of 1.5cm, and then a positive power supply and a grounding wire are applied at both ends respectively, a constant electric field is provided by a positive polarity DC current generator, and then the voltage and current changes are calculated by a formula to monitor the dielectric parameters;

[0080] S3 curing real-time dielectric parameter monitoring: Place the epoxy resin prepreg equipped with sensors in the environment of the set curing process, control the heating rate through the heating platform to perform the curing process, and calculate the change curve of the dielectric parameter values ​​of different materials over time; for the optimization of traditional processes, when the conductivity changes too fast, it is necessary to lower the temperature or reduce the curing stage time to slow down the curing reaction. The curing rate can be adjusted by controlling the temperature, and multi-stage curing is used, that is, gradually increasing the temperature, to smooth the curing process of the degradable epoxy resin, allowing stress relaxation to reduce residual stress;

[0081] The multi-stage curing process is divided into several key steps: pre-curing, intermediate curing, full curing and post-curing. The curing rate is affected by many factors, including resin type, temperature and curing time. The Arrhenius equation is commonly used to describe the effect of temperature on chemical reaction rate:

[0082]

[0083] Among them, k is the curing reaction rate, A is the pre-exponential factor (or frequency factor), Ea is the activation energy, R is the ideal gas constant, and T is the temperature. In the dielectric parameter curing monitoring platform, the curing reaction rate can be approximately equivalent to the slope of conductivity change. Further optimization calculations are mainly carried out for the stage of significant conductivity change in the traditional curing process. Combined with the temperature influence formula, the rate of change of conductivity can be expressed as:

[0084]

[0085] Among them, f(σ) is a relationship function that describes the relationship between conductivity and reaction rate. Assuming that the change in conductivity is directly related to the curing reaction rate, f(σ) is a linear relationship. In order to ensure the stress release of the casting process and post-curing, the pre-curing temperature T p and post-curing temperature T sStill maintaining 80℃ and 140℃, calculate the intermediate curing temperature T when the slope is constant according to the conductivity rate formula m and complete curing temperature T f 90℃ and 110℃ respectively. Figure 7 As shown, the specific curing process is calculated as follows:

[0086] The first stage: maintain 80℃ for 3 hours; the second stage: heat up to 90℃ within 0.5 hours and maintain 90℃ for 2 hours; the third stage: heat up to 110℃ within 0.5 hours and maintain 110℃ for 2 hours; the fourth stage: heat up to 140℃ within 0.5 hours and maintain 140℃ for 7.5 hours;

[0087] Through the curing process monitoring platform, the epoxy resin prepreg is pressurized and tested, and the current and voltage values ​​are recorded until the predetermined maximum test temperature is reached. The monitoring is set every 0.5 hours. During the entire curing process, the conductivity value change curve under different processes with time is calculated; the conductivity change curve of the traditional and optimized curing processes is obtained as follows Figure 8 As shown, from Figure 8 It can be seen that when the traditional curing process is used, the conductivity shows a significant decrease, mainly because the time zone in the curing process is the heating stage, the temperature rise is 60°C and the heating time is very short. The heating rate is set between the original temperature platforms and the intermediate temperature platform is added. After the curing process is optimized, the conductivity curve declines more smoothly and stably, without obvious inflection points. The log (conductivity) change rates within 3-3.5 hours, 5-5.5 hours, and 8-8.5 hours are 1.91, 1.39, and 0.507, which are significantly lower than the change rate of the traditional curing process. After the process is optimized, the curing process can be better controlled, the change of dielectric parameters is more uniform and stable, and the reduction in the curing rate is conducive to the formation of a more uniform cured layer, which can promote the gradual dissipation of stress and avoid stress concentration.

[0088] S5 sample performance comparison test: stir the mixture according to the formula of specific embodiment 2 in step S1 for 5-6 minutes to ensure that the catalyst is evenly dispersed, maintain room temperature at 25°C, and continue stirring the mixture at a speed of 300rad / min for 1 hour, maintain vacuum ≤100Pa, to obtain epoxy resin prepreg; pour the prepared epoxy resin prepreg into a pre-cleaned mold, and then put it into an oven for curing according to the obtained optimized curing process, namely, the first stage: maintain 80°C for curing for 3h; the second stage: heat to 90°C within 0.5h and maintain 90°C for curing for 2h; the third stage: heat to 110°C within 0.5h and maintain 110°C for curing for 2h; the fourth stage: heat to 140°C within 0.5h and maintain 140°C for curing for 7.5h, to ensure that the epoxy resin is completely cured. After curing, take out the mold from the oven and cool it to room temperature, demold it to obtain a degradable epoxy resin composite material sample under the traditional process. The mechanical properties and electrical properties of the degradable epoxy resin composite material samples obtained in Specific Example 2 and Specific Example 4 were compared and tested to obtain the performance data of the control group. Figure 9-10 The figure shows the changes in various properties before and after the curing process. By optimizing the curing process, the various properties of the degradable epoxy resin have been improved. In the stress change of the curing process, the stress after multi-temperature gradient heating has a significant decrease from 12.68MPa to 6.56MPa in the post-curing stage, and the stress change trend is slower. The optimized bending strength increased from 105.34MPa of the traditional process to 114.92MPa, an increase of 9.09%; the tensile strength increased from 61.22MPa to 69.17MPa, an increase of 12.98%. In addition, the optimized stress-strain curve shows that the elongation at break increased from 3.81% to 5.62%. The breakdown voltage range under the optimized process is 33.8kV, and that under the traditional process is 34.9kV, an increase of about 3.56%. At the same breakdown voltage, the breakdown probability of the optimized process is significantly lower than that of the traditional process.

[0089] From the performance test results, it can be seen that in the process of optimizing the curing process, the biodegradable epoxy resin sets a more reasonable heating rate and temperature platform, making the curing process more uniform, reducing the stress concentration inside the material, and reducing the probability of micro-defects. The cross-linking reaction is more complete, the internal structure of the material is more stable, and the cross-linking network density formed is higher, thereby improving the overall mechanical properties and dielectric properties.

[0090] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention, such as changes in certain materials or reaction conditions, should be included in the scope of protection of the present invention.

Claims

1. A method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters. It is characterized in that The specific steps include: S1 Preparation of epoxy resin prepreg: weigh raw materials according to the ratio and mix them, and put the mixture into a mechanical stirrer in a vacuum environment to obtain epoxy resin prepreg; S2 Curing Process Monitoring Platform Construction: Pour epoxy resin prepreg into the electric field module and connect it to the power supply to monitor the dielectric parameters; S3 curing real-time dielectric parameter monitoring: The epoxy resin prepreg equipped with sensors is placed in the environment of the set curing process, and the curing process is carried out by controlling the heating rate through the heating platform, and the change curve of the dielectric parameter values ​​of different materials over time is calculated; S4 curing process control and optimization: the epoxy resin prepreg prepared according to step S1 is subjected to real-time dielectric parameter monitoring according to steps S2 and S3, and the curing process parameters are dynamically and real-time adjusted through a temperature control unit according to the changing trend of the dielectric parameters, so as to obtain an optimized curing process; and then a curve of the change of the conductivity value over time under the optimized curing process is calculated.

2. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 1, It is characterized in that The method also includes step S5, which is a sample performance comparison test: pouring the epoxy resin prepreg prepared in step S1 into a mold, and then putting it into an oven for curing according to the process set in step S3 and the optimized curing process obtained in step S4, respectively, to ensure that the epoxy resin is completely cured, and then performing a performance test on the epoxy resin composite material sample to verify the optimized curing process.

3. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 1, It is characterized in that The raw materials in step S1 include epoxy resin matrix, epoxy resin curing agent, accelerator and dynamic catalyst. The formula of the raw materials is as follows: 100 parts of bisphenol A epoxy resin, 84.66-88.7 parts of curing agent, and 0.5-1.0 parts of degradation catalyst.

4. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 3, It is characterized in that In the step S1, the epoxy resin matrix is ​​a pure epoxy resin matrix or a degradable epoxy resin matrix, and the degradable epoxy resin matrix includes a TBD-catalyzed epoxy resin matrix and a bio-based epoxy resin matrix; in the step S1, the ratio of epoxy resin to bio-based in the bio-based epoxy resin matrix is ​​3:1 to 5:

1.

5. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 3, It is characterized in that In step S1, the curing agent is methyltetrahydrophthalic anhydride; and the degradation catalyst is N,N-dimethylbenzylamine or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

6. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 3, It is characterized in that The specific steps of step S2 are as follows: the built curing process monitoring platform is divided into a voltage module, a current monitoring module, a heating module and an electric field module, wherein the voltage module adopts a positive polarity high voltage power supply, and the current monitoring module adopts an electrometer current, and the measurement range is 10aA-20mA; the heating platform provides a constant temperature or constant rate heating environment to achieve the curing of the epoxy resin, and the epoxy resin resistance volume in the electric field module is 10×10×1.5cm; the epoxy resin prepreg is poured in the electric field module until the container is fully immersed, and then a positive power supply and a grounding wire are applied at both ends respectively, a constant electric field is provided by a positive polarity DC current generator, and then the voltage and current changes are calculated by a formula to monitor the dielectric parameters.

7. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 6, It is characterized in that In step S3, the curing process monitoring platform performs pressure testing on different temperature points, and the ambient temperature is set to a heating rate of 10°C / min, that is, the current value and voltage value are recorded every time the temperature rises by 10°C until the predetermined maximum test temperature is reached, and the change curve of the dielectric parameter values ​​of different materials over time is calculated.

8. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 7, It is characterized in that The curing process set in step S4 is a two-stage curing process, wherein the first stage is cured at 80° C. for 4 hours; The second stage is cured at 140°C for 12 hours; the optimized curing process is a four-stage curing process, including a pre-curing temperature T p , intermediate curing temperature T m , complete curing temperature T f , post-curing temperature T s .

9. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 8, It is characterized in that In step S4, the curing process is optimized by using the Arrhenius equation to describe the effect of temperature on the chemical reaction rate, and the formula is: Where k is the curing reaction rate, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and T is the temperature; In the dielectric parameter-based curing monitoring platform, the curing reaction rate can be approximately equivalent to the slope of conductivity change; further optimization calculations are performed for the conductivity change stage in the set curing process stage. Combined with the temperature influence formula, the conductivity change rate is expressed as: Among them, f(σ) is a relationship function that describes the relationship between conductivity and reaction rate. Assuming that the change in conductivity is directly related to the curing reaction rate, f(σ) is a linear relationship. In order to ensure the stress release of the casting process and post-curing, the pre-curing temperature T p and post-curing temperature T s Still maintaining 80℃ and 140℃, calculate the intermediate curing temperature T when the slope is constant according to the conductivity rate formula m and complete curing temperature T f The temperatures are 90°C and 110°C respectively, and the optimized curing process is calculated as follows: The first stage: maintain 80℃ for 3 hours; the second stage: increase the temperature to 90℃ within 0.5 hours and maintain 90℃ for 2 hours; the third stage: increase the temperature to 110℃ within 0.5 hours and maintain 110℃ for 2 hours; the fourth stage: increase the temperature to 140℃ within 0.5 hours and maintain 140℃ for 7.5 hours.

10. The method for controlling the curing process of degradable epoxy resin based on real-time monitoring of dielectric parameters according to claim 9, It is characterized in that In step S4, the optimized process is used to perform a pressure test on the epoxy resin prepreg through a curing process monitoring platform, and the current and voltage values ​​are recorded until a predetermined maximum test temperature is reached, and monitoring is performed every 0.5 hours for a set time; during the entire curing process, a curve of the change in conductivity value over time under the optimized curing process is calculated.

Images