Simulation method for analyzing flame retardant property change in aging process of polymer insulating material based on intermolecular force

Abstract

The invention provides a simulation method for analyzing flame retardant property change in an aging process of a polymer insulating material based on intermolecular acting force. The simulation method comprises the following three contents: 1) simulating and analyzing microscopic parameters related to the intermolecular acting force in the aging process of polymer insulating material molecules; 2) obtaining the evolution behavior of the intermolecular acting force in the molecular aging process of the polymer insulating material; and 3) constructing a structure-function relationship between the intermolecular force of the polymer insulating material and the flame retardant property. The method provides theoretical guidance for obtaining the influence rule of the intermolecular force on the performance of the polymer insulating material in the aging process of the polymer insulating material.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular simulation, and in particular relates to a simulation method for analyzing changes in flame retardant properties of polymer insulating materials during aging based on intermolecular forces. Background Art

[0002] Due to their excellent physical, chemical and electrical properties, polymer insulation materials such as resins and rubbers are widely used in power equipment. However, polymer insulation materials cannot avoid aging in complex environments, resulting in a decrease in performance. Power equipment is subject to a variety of stresses during operation, such as electrical stress and thermal stress. Under these stresses, the insulation material will continue to age as the operating time increases, causing a decrease in flame retardant properties, greatly increasing the risk of fire in power equipment.

[0003] At present, the aging analysis methods for polymer insulation materials mainly use macroscopic test methods such as infrared spectroscopy, gas chromatography and nuclear magnetic resonance. These methods can only obtain the change rules of specific groups, molecular bonds and atomic numbers of polymers before and after aging, and it is difficult to obtain the evolution behavior of the intermolecular forces of polymer insulation materials. At the same time, macroscopic test tests require a lot of manpower and material resources and are costly. There are few reports on the microscopic mechanism analysis of the influence of the evolution behavior of the intermolecular forces of polymer insulation materials on their flame retardant properties during aging. Summary of the invention

[0004] The purpose of the present invention is to provide a simulation method for analyzing the changes in flame retardant properties of polymer insulating materials during aging based on intermolecular forces. The simulation method of the present invention constructs a structure-activity relationship between intermolecular forces and flame retardant properties of polymer insulating materials, providing theoretical guidance for understanding the influence of intermolecular forces on the performance of polymer insulating materials during aging.

[0005] A simulation method for analyzing the change of flame retardant properties of polymer insulation materials during aging based on intermolecular forces comprises the following steps:

[0006] A) using Gaussian View software to construct the molecular structure of the polymer insulation material and optimize it, placing the optimized molecular model of the polymer insulation material in a periodic structure, using GULP software based on the ReaxFF force field to simulate the reaction kinetics of the polymer insulation material, extracting the polymer insulation material structures corresponding to different simulation times, and obtaining n molecular models of the polymer insulation material with different aging degrees;

[0007] B) geometrically optimizing n molecular models of polymer insulating materials with different aging degrees, placing n optimized molecular models of polymer insulating materials with the same aging degree in the same periodic system using Packmol software, obtaining TOP files required by the GAFFL force field in the molecular dynamics simulation process of n polymer insulating materials with different aging degrees using Sobtop software, calculating the RESP charge of the polymer insulating material using Multiwfn software, assigning the charge to the TOP file, performing molecular dynamics simulation using Gromacs software, and performing molecular dynamics simulation based on the NPT ensemble;

[0008] C) calculating the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius of the polymer insulating material molecules at different aging degrees based on the molecular dynamics simulation trajectories of the n polymer insulating material molecules at different aging degrees obtained in step B);

[0009] D) Based on the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius data of the polymer insulating material molecules with different aging degrees obtained in step C), combined with the change law of the flame retardant properties of the polymer insulating material with the aging degree, the structure-activity relationship between the intermolecular force and the flame retardant properties of the polymer insulating material is constructed.

[0010] Preferably, in the step A), the degree of polymerization of the polymer insulating material molecular model is not less than 10, and both ends of the polymer insulating material molecules are subjected to hydrogenation saturation treatment.

[0011] Preferably, in step A), the molecular structure of the polymer insulating material is geometrically optimized using Gaussian software M062X functional and 6-311G (d, p) basis set method.

[0012] Preferably, in the step A), the lowest temperature at which the polymer insulating material molecular model reacts is used as the reaction kinetics simulation temperature.

[0013] Preferably, the geometric optimization of the molecular models of the n polymer insulating materials with different aging degrees in step B) is performed using Gaussian software M062X functional and 6-311G (d, p) basis set method.

[0014] Preferably, in the step B), the simulation time of the molecular dynamics simulation based on the NPT ensemble is ≥20 ns, and the simulation trajectory after 10 ns is selected for data extraction.

[0015] Preferably, the free volume fraction FFV is calculated according to formula I:

[0016]

[0017] In formula I, FFV is the free volume fraction, V free is the total free volume of the polymer insulating material, V occ is the total occupied volume of the polymer insulating material.

[0018] Preferably, the self-diffusion coefficient D is calculated according to formula II:

[0019]

[0020] In formula II, D is the self-diffusion coefficient, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0, respectively, and N is the total number of atoms.

[0021] Preferably, the cohesive energy density CED is calculated according to Formula III and Formula IV:

[0022] E coh =- <E inter >= <E intra >- <E total > Formula III;

[0023]

[0024] In Formula III and Formula IV, E coh is the cohesive energy of the model, V is the volume of the model, E inter is the energy between the model molecules, E intra is the intramolecular energy, E total is the total energy of the model.

[0025] Preferably, the radius of rotation (R g ) is calculated according to formula V:

[0026]

[0027] In formula V, m i is the mass of atom i, r i is the coordinate of atom i, r c are the coordinates of the center of mass of the system, and m is the mass of atom j.

[0028] The present invention provides a simulation method for analyzing the change of flame retardant properties of polymer insulating materials during aging based on intermolecular forces, which includes three aspects: 1) simulation analysis of microscopic parameters related to intermolecular forces of polymer insulating material molecules during aging; 2) obtaining the evolution behavior of intermolecular forces during aging of polymer insulating material molecules; 3) constructing the structure-activity relationship between intermolecular forces and flame retardant properties of polymer insulating materials. The present invention provides theoretical guidance for obtaining the influence of intermolecular forces on the properties of polymer insulating materials during aging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0030] Figure 1 The structural change process of the silicone rubber under the damp heat aging conditions in the embodiment of the present invention;

[0031] Figure 2 It is the oxygen index of the silicone rubber at different aging times in the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention provides a simulation method for analyzing the change of flame retardant performance of a polymer insulating material during aging based on intermolecular forces, comprising the following steps:

[0033] Step 1: Simulate and analyze the microscopic parameters related to intermolecular forces during the aging process of polymer insulation materials.

[0034] Gaussian View software was used to construct the single molecular structure of the polymer insulating material. To ensure the accuracy of the simulation results, the degree of polymerization of the monomer model of the polymer insulating material was not less than 10, and both ends of the polymer were hydrogenated and saturated.

[0035] Based on density functional theory, the Gaussian software M062X functional and 6-311G (d, p) basis set method were used to perform geometric optimization on the constructed polymer insulating material monomer model to make the model closer to the actual structure. The M062X functional is very suitable for the combination optimization of organic matter, and the high-quality 6-311G (d, p) basis set ensures the accuracy of the results.

[0036] The optimized monomer model of polymer insulation material is placed in a periodic structure, and the reaction kinetics of polymer insulation material is simulated using GULP software based on the ReaxFF force field. The temperature during the simulation is higher than the actual temperature. Based on the target temperature of the actual use process, the temperature test during the simulation is performed in increments of 50K to obtain the lowest temperature at which the polymer insulation material model reacts, and the lowest temperature at which the reaction occurs is set as the simulation temperature. Water molecules and oxygen molecules are added to the model to simulate humidity and nutrient environment, and the electric field strength is set for the model to simulate the electric field environment.

[0037] Based on the reaction kinetics simulation process of the polymer insulation material model, the main structural evolution process of the polymer insulation material during the aging process is extracted, and the aging level of the polymer insulation material is named according to the degree of structural degradation, that is, molecular models of polymer insulation materials with n different aging levels are obtained.

[0038] The geometric optimization of polymer insulating materials with different aging levels was performed using Gaussian software M062X functional and 6-311G (d, p) basis set method. Packmol software was used to place n identical polymer insulating materials with the same aging level in the same periodic system, for example, 30 polymer insulating material molecules with aging level 1 were placed in a periodic box, and 30 polymer insulating material molecules with aging level 2 were placed in another periodic box, and so on, to carry out molecular dynamics simulation of polymer insulating materials with different aging levels.

[0039] In the molecular dynamics simulation of polymer insulation materials with different aging levels, GAFFL force field is used. GAFF force field is more accurate in simulating polymers. Sobtop software is used to obtain the TOP file required by GAFFL force field in the molecular dynamics simulation of polymer insulation materials with different aging levels. Based on the wave function file after geometric optimization of the polymer insulation material model with different aging levels, Multiwfn software is used to calculate the RESP charge of the polymer insulation material and assign the charge to the TOP file. The RESP charge of the polymer insulation material is better adapted to the GAFF force field, and more accurate molecular dynamics simulation results can be obtained.

[0040] The present invention uses Gromacs software to carry out molecular dynamics simulation of polymer insulating materials with different aging levels, and performs molecular dynamics simulation of no less than 20ns based on the NPT ensemble. The first 10ns is used for the balance of the model to achieve a more reasonable density, and the simulation after 10ns is used for various property analysis of the model. Gromacs software can complete molecular dynamics simulation at the ns scale, greatly reducing the randomness of molecular dynamics simulation and improving simulation accuracy.

[0041] Step 2: Obtain the evolution behavior of intermolecular forces during the aging process of polymer insulation materials.

[0042] Based on the molecular dynamics simulation trajectories of polymer insulation materials with different aging levels obtained in the first step, the changes in free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius of polymer insulation materials with different aging levels are calculated.

[0043] The total volume of the polymer insulating material is given by the occupied volume V occ and the free volume V free Composition, the free volume is dispersed in the entire polymer in the form of voids. The size, dimensions and density of different polymer insulating materials are different. The free volume fraction (FFV) is introduced to measure the free volume size of different types of insulating oil molecules. The free volume fraction is shown in Formula I.

[0044]

[0045] The mean square displacement (MSD) of polymer insulating material molecules can be calculated by the following formula:

[0046]

[0047] Among them, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0 respectively.

[0048] The self-diffusion coefficient of polymer insulating materials can be solved with the help of Einstein's formula, as shown in Formula II:

[0049]

[0050] Wherein, N is the number of total atoms. In order to make the calculation result of the self-diffusion coefficient more accurate, 10% to 90% of the MSD curve is selected for linear fitting.

[0051] The cohesive energy density of polymer insulation materials can be calculated using formulas III and IV:

[0052] E coh =- <E inter >= <E intra >- <E total > Formula III;

[0053]

[0054] Where E coh is the cohesive energy of the model, V is the volume of the model, E inter is the total energy of the model, Eintra is the intermolecular energy, E total is the total energy of the model.

[0055] The radius of gyration of the polymer (R g ) can be calculated by formula V, where mi is the mass of atom i, ri is the coordinate of atom i, rc is the coordinate of the center of mass of the system, and m j is the mass of atom j.

[0056]

[0057] Step 3: Construct the structure-activity relationship between the intermolecular forces and flame retardant properties of polymer insulating materials.

[0058] Based on the calculation results of the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius of polymer insulation materials with different aging levels in the second step, the change laws of the microscopic parameters of polymer insulation materials with different aging levels are summarized.

[0059] The flame retardant properties of polymer insulation materials at different aging stages are tested in accordance with "GBT 5169.16-2017 Fire hazard test for electric and electronic products Part 16: Test flame 50W horizontal and vertical flame test method".

[0060] Combining the changing patterns of flame retardant properties of polymer insulating materials with aging degree and the simulation results of microscopic parameters, the structure-activity relationship between intermolecular forces and flame retardant properties of polymer insulating materials is constructed.

[0061] The present invention provides a simulation method for analyzing the change of flame retardant properties of polymer insulating materials during aging based on intermolecular forces, which includes three aspects: 1) simulation analysis of microscopic parameters related to intermolecular forces of polymer insulating material molecules during aging; 2) obtaining the evolution behavior of intermolecular forces during aging of polymer insulating material molecules; 3) constructing the structure-activity relationship between intermolecular forces and flame retardant properties of polymer insulating materials. The present invention provides theoretical guidance for obtaining the influence of intermolecular forces on the properties of polymer insulating materials during aging.

[0062] In order to further illustrate the present invention, a simulation method for analyzing changes in flame retardant properties of polymer insulating materials during aging based on intermolecular forces provided by the present invention is described in detail below in conjunction with an embodiment, but it should not be construed as limiting the scope of protection of the present invention.

[0063] Example

[0064] This embodiment takes the change in the flame retardant performance of a silicone rubber polymer insulating material under the action of wet heat aging as an example.

[0065] According to the molecular structure of silicone rubber, the monomer model of silicone rubber polymer insulating material was constructed using Gaussian View software, and the degree of polymerization was 10. The constructed monomer model of silicone rubber polymer insulating material was geometrically optimized using Gaussian software M062X functional and 6-311G (d, p) basis set method.

[0066] A silicone rubber molecule is placed in a periodic structure. Considering the wet heat aging under the action of moisture and temperature, a water molecule is added to the model. According to the test, silicone rubber can decompose at a temperature of 500K. Therefore, the simulation temperature is set to 500K.

[0067] Based on the ReaxFF force field, GULP software was used to simulate polymer aging under wet and hot aging conditions, and the structural change process of silicone rubber under wet and hot aging conditions was extracted. Figure 1 As shown. Figure 1 The five silicone rubber structures shown in 0 to 4 are named aging degree 0 to aging degree 4 respectively.

[0068] Based on the above five silicone rubber results, density functional simulation was performed using the M062X-6-311G (d, p) method and Gaussian software to optimize the structures of these five silicone rubbers, and the RESP atomic charges of different silicone rubber structures were obtained by combining Multiwfn software. Packmol software was used to place 30 silicone rubbers of the same structure and aging level in the same periodic system, and the energy of the model was minimized using Gromacs software and the steepest gradient method. Then, a 20ns molecular dynamics simulation was performed under the NPT ensemble based on the GAFF force field, with the temperature set to 473K and the step size of 1.5fs. The simulation trajectory of the last 10ns was selected to calculate the changes in the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius of silicone rubber under different structures, and the results are shown in Table 1.

[0069] The results show that with the structural changes of silicone rubber during the wet-heat aging process, its microscopic parameters also change accordingly. The change trend of the microscopic parameters is not completely monotonically decreasing or increasing, but presents a fluctuating trend. This indicates that with the increase of the aging degree, the intermolecular force of silicone rubber shows a trend of first decreasing, then increasing, and then decreasing.

[0070] Table 1 Microscopic parameters of silicone rubber under different aging degree structures

[0071]

[0072] Conduct damp heat aging test on silicone rubber and test its flame retardant properties to further verify the simulation results. Refer to "Environmental Test Part 2: Test Method Test Cab: Constant Damp Heat Test" to conduct damp heat aging test on samples, the ambient temperature is set to 85±5℃, the ambient relative humidity is set to 90±10%, and the aging days are 0-56d. Flame retardant performance test is carried out on samples with different aging degrees, and vertical combustion test is carried out on silicone rubber test samples in accordance with "GBT 5169.16-2017 Fire Hazard Test for Electrical and Electronic Products Part 16: Test Flame 50W Horizontal and Vertical Flame Test Method", and the change of oxygen index during the test is obtained, such as Figure 2 As shown in Figure 2, it can be found that the flame retardant properties of silicone rubber show a trend of first decreasing and then increasing.

[0073] Combining the test and simulation results, it can be seen that the density and cohesive energy density of silicone rubber show a trend of first decreasing and then increasing, and the intermolecular force of silicone rubber on the surface shows a trend of first decreasing and then increasing with the increase of aging degree; the free volume fraction and self-diffusion coefficient first increase and then decrease, which indicates that the thermal stability of silicone rubber first decreases and then increases. During the test, the higher the oxygen index, the stronger the surface flame retardancy. The experimental results show that with the increase of aging days, the flame retardancy of silicone rubber first decreases and then increases, and the simulation results well reveal the experimental phenomenon.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A simulation method for analyzing the change of flame retardant properties of polymer insulation materials during aging based on intermolecular forces, comprising the following steps: A) using Gaussian View software to construct the molecular structure of the polymer insulation material and optimize it, placing the optimized molecular model of the polymer insulation material in a periodic structure, using GULP software based on the ReaxFF force field to simulate the reaction kinetics of the polymer insulation material, extracting the polymer insulation material structures corresponding to different simulation times, and obtaining n molecular models of the polymer insulation material with different aging degrees; B) geometrically optimizing n molecular models of polymer insulating materials with different aging degrees, placing n optimized molecular models of polymer insulating materials with the same aging degree in the same periodic system using Packmol software, obtaining TOP files required by the GAFFL force field in the molecular dynamics simulation process of n polymer insulating materials with different aging degrees using Sobtop software, calculating the RESP charge of the polymer insulating material using Multiwfn software, assigning the charge to the TOP file, performing molecular dynamics simulation using Gromacs software, and performing molecular dynamics simulation based on the NPT ensemble; C) calculating the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius of the polymer insulating material molecules at different aging degrees based on the molecular dynamics simulation trajectories of the n polymer insulating material molecules at different aging degrees obtained in step B); D) Based on the free volume fraction, self-diffusion coefficient, density, cohesive energy density and gyration radius data of the polymer insulating material molecules with different aging degrees obtained in step C), combined with the change law of the flame retardant properties of the polymer insulating material with the aging degree, the structure-activity relationship between the intermolecular force and the flame retardant properties of the polymer insulating material is constructed.

2. The simulation method according to claim 1, characterized in that: In the step A), the degree of polymerization of the polymer insulating material molecular model is not less than 10, and both ends of the polymer insulating material molecules are subjected to hydrogenation saturation treatment.

3. The simulation method according to claim 1, characterized in that: In the step A), the molecular structure of the polymer insulating material is geometrically optimized using Gaussian software M062X functional and 6-311G (d, p) basis set method.

4. The simulation method according to claim 1, characterized in that: In the step A), the lowest temperature at which the polymer insulating material molecular model reacts is used as the reaction kinetics simulation temperature.

5. The simulation method according to claim 1, characterized in that: The Gaussian software M062X functional and 6-311G (d, p) basis set method are used to perform geometric optimization on the molecular models of n polymer insulating materials with different aging degrees in step B).

6. The simulation method according to claim 1, characterized in that: In the step B), the simulation time of the molecular dynamics simulation based on the NPT ensemble is ≥20 ns, and the simulation trajectory after 10 ns is selected for data extraction.

7. The simulation method according to claim 1, characterized in that: The free volume fraction FFV is calculated according to formula I: In formula I, FFV is the free volume fraction, V free is the total free volume of the polymer insulating material, V occ is the total occupied volume of the polymer insulating material.

8. The simulation method according to claim 1, characterized in that: The self-diffusion coefficient D is calculated according to formula II: In formula II, D is the self-diffusion coefficient, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0, respectively, and N is the total number of atoms.

9. The simulation method according to claim 1, characterized in that: The cohesive energy density CED is calculated according to formula III and formula IV: E coh =- <E inter >= <E intra >- <E total > Formula II; In Formula III and Formula IV, E coh is the cohesive energy of the model, V is the volume of the model, E inter is the energy between the model molecules, E intra is the intramolecular energy, E total is the total energy of the model.

10. The simulation method according to claim 1, characterized in that: Radius of rotation (R g ) is calculated according to formula V: In formula V, m i is the mass of atom i, r i is the coordinate of atom i, r c is the coordinate of the center of mass of the system, m j is the mass of atom j.

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