Molecular simulation method for polyacrylonitrile fiber electron beam irradiation and heating coupling pre-oxidation process

Abstract

The invention provides a molecular simulation method for a polyacrylonitrile fiber electron beam irradiation and heating coupling pre-oxidation process. The molecular simulation method comprises the following steps: establishing a polyacrylonitrile trans-syndiotactic stereostructure model in a certain oxygen environment by adopting computer molecular material simulation software; inserting a temperature controller in a polyacrylonitrile pre-oxidation gradient heating process by using a molecular dynamics method, and creating a primary collision atom bombardment molecular system to simulate a coupling effect of irradiation and heating; continuing gradient heating to complete pre-oxidation molecular dynamics simulation; microcosmic result output is conducted on the simulation process. According to the method, electron beam irradiation is introduced in the polyacrylonitrile gradient temperature rise process by using a molecular dynamics method to simulate the electron beam irradiation and heating coupling effect in the polyacrylonitrile pre-oxidation process, and a set of controllable simulation parameters is provided for the introduction opportunity of electron beam irradiation in the pre-oxidation process; the method has guiding significance for exploring the pre-oxidation reaction mechanism of the polyacrylonitrile fiber electron beam irradiation and heating coupling effect.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials and carbon fiber processing, and specifically relates to a molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling. The technology aims to establish a trans-syndiotactic polyacrylonitrile (PAN) model and then simulate the influence of the electron beam irradiation and heating coupling on the PAN molecular chain during the pre-oxidation process. Background Art

[0002] PAN-based carbon fibers are widely used in aerospace, electronics, medical, sports and other fields due to their low density, high strength and high rigidity. Compared with other precursors such as cellulose and pitch that have been used for commercial fibers, PAN-based carbon fibers support more than 90% of commercial carbon fiber production with their excellent mechanical properties. The pre-oxidation process of PAN-based carbon fibers is a key link in determining the final carbon fiber performance, which directly affects the final fiber quality generated by subsequent carbonization and graphitization. The high cost and time-consuming pre-oxidation process under PAN experimental conditions has always been a major challenge for the carbon fiber industry.

[0003] In the study of PAN irradiation pre-oxidation process, the change of free radical concentration during pre-oxidation was used as a reference in the literature on the effect of high-dose rate electron beam irradiation of polyacrylonitrile fibers and their influence on pre-oxidation, and the pre-oxidation process of electron beam irradiation modified PAN fibers was optimized; in the literature, microfocus SR-SAXS reconstruction and molecular simulation revealed the heterogeneous microstructure of γ-irradiated pre-oxidized PAN fibers, and the structural evolution of different PAN structures introduced by irradiation after heat treatment was simulated using molecules; in the literature, the molecular simulation of the stabilization of PAN-based carbon fiber processing used a model combining random chemical reactions and molecular dynamics to simulate the PAN heat treatment process with atomic details; in the literature, the ladder structure chain of PAN was used in the molecular simulation of the evolution of microstructure during carbon fiber processing to simulate the microstructure evolution of PAN-based carbon fiber during carbonization and graphitization; in the PAN modeling study, the molecular dynamics study of the crystalline phase and pseudomorphic phase of polyacrylonitrile pointed out that the PAN molecular chain has more complex chain structures such as random structure, syndiotactic structure, isotactic structure, etc., and the PAN syndiotactic structure with a planar "Z"-shaped conformation has the lowest energy and highest stiffness among all chain conformations, and is one of the conformations with the most development potential.

[0004] In the current research, it is limited to the PAN irradiation pre-oxidation process or the pre-oxidation process of irradiation followed by heat treatment. There is a lack of molecular dynamics simulation technology for the PAN chain model for irradiation and heating coupling pre-oxidation. In addition, the introduction of electron beam irradiation during the PAN gradient heating period is also a problem that cannot be solved under laboratory conditions. Therefore, the molecular dynamics simulation method is used to combine the PAN trans-syndiotactic stereoisomer model with the pre-oxidation effect of electron beam irradiation and heating coupling, which can explore the best time to introduce electron beam irradiation in the future PAN fiber during the heat treatment process, which is of great significance for optimizing the pre-oxidation process of PAN fiber by electron beam irradiation and heating coupling. Summary of the invention

[0005] The present invention provides a modeling method for a PAN plane "zigzag" trans-syndiotactic molecular chain model with low energy and high rigidity, and then the model is subjected to irradiation and heating coupled pre-oxidation simulation calculation in a Lammps dynamic simulation calculation tool, and a temperature controller is used and electron beam irradiation is introduced during the PAN heat treatment process, and simulation calculation and output are performed. The molecular dynamics method is used to predict the influence of irradiation and heating coupling on the pre-oxidation process of PAN fibers and the structural evolution, filling the gap in the molecular dynamics simulation technology of PAN precursor from the establishment of a trans-syndiotactic stereoisomer model to the pre-oxidation effect of electron beam irradiation and heating coupling.

[0006] In summary, the present invention adopts the following technical solutions:

[0007] A molecular simulation method for a polyacrylonitrile fiber pre-oxidation process coupled with electron beam irradiation and heating, comprising the following steps:

[0008] (1) Using MaterialsStudio software, draw a PAN monomer, select the head and tail atoms using the Build Polymers module, and build a repeating unit consisting of two PAN monomers connected together;

[0009] (2) Using MaterialsStudio software, the PAN dimer is used as a new monomer molecule, and the degree of polymerization is set to establish a trans-syndiotactic molecular chain;

[0010] (3) Introducing the molecular chain obtained in step (2), using Materials Studio software, using the Movement module to replicate and combine the molecular chain, based on the PAN hexagonal lattice chain stacking mode, according to the PAN experimental density of 1.17-1.20 g / cm 3 , creating an ideal trans-syndiotactic PAN hexagonal unit cell model;

[0011] (4) Introducing the hexagonal unit cell model obtained in step (3), using the Crystal module in MaterialsStudio software to build a rectangular Amorphous Cell box with a chain length*width*height, placing the established PAN hexagonal unit cell model in the box, and adding a certain number of oxygen molecules;

[0012] (5) exporting the three-dimensional coordinate data file of the model in step (4) and converting the file format;

[0013] (6) Using Lammps software, import the data file obtained in step (5), set simulation parameters, select reactive force field, first perform energy minimization, then perform position constraint, and finally perform relaxation to allow the entire system to reach a preliminary equilibrium state;

[0014] (7) using Lammps software, introducing the stable structure obtained in step (6), setting the gradient heating range and simulation parameters, performing gradient heating simulation, and outputting various data files during the simulation system operation process;

[0015] (8) Using Lammps software, create PKA position areas during the gradient heating process, set the kinetic energy of PKA in the x, y, and z directions according to the irradiation dose to simulate irradiation energy transfer, monitor the PKA kinetic energy, perform irradiation simulation, and output various data files during the simulation system operation process;

[0016] (9) Using Lammps software, the three-dimensional coordinate data after irradiation obtained in step (8) is introduced, the gradient temperature is continued, and the simulation system conformation and various data files are output;

[0017] (10) Visually verify the simulation results obtained in step (8) and step (9), output the simulation flow chart, and perform species quantity and molecular weight statistics on the simulation process.

[0018] The conversion software used in step (5) is OVITO visualization software.

[0019] The energy minimization algorithm used in step (6) is the conjugate gradient method, and the relaxation method is the Nosé-Hoover thermostat method. The relaxation adopts the canonical (NVT) ensemble, and the simulation time is 20 ps;

[0020] The simulation parameters described in step (6) include simulation environment parameter settings, using a charge balance algorithm to dynamically adjust atomic charges in the simulation to meet the balance of charge distribution;

[0021] The gradient temperature rise interval described in step (7) selects a pre-oxidation temperature of about 300K to 600K, sets a temperature rise gradient, and performs a temperature rise and insulation treatment; the canonical (NVT) ensemble is used, and the simulation time of each temperature gradient is 10ps.

[0022] In step (8), the microcanonical ensemble (NVE) was used, and the temperature range was controlled by a Berendsenn temperature controller, and the simulation time was set according to the irradiation dose and PKA kinetic energy;

[0023] Step (8) monitors the PKA kinetic energy, uses the "compute" command in combination with the "variable" command to calculate the total PKA kinetic energy, and then outputs the PKA kinetic energy.

[0024] The conformations described in steps (7) and (8) were viewed using OVITO software.

[0025] The PKA kinetic energy expression obtained by deduction in step (8) is as follows:

[0026] Here, we assume that the velocity v is in the direction [h, k, l], the kinetic energy is NeV, the mass is M gram / mol, N A is Avogadro's constant.

[0027] Step (10) is to obtain simulation details by taking simulation snapshots using OVITO software, and to count the number of species and molecular weight of the species file output by the simulation process using Python software.

[0028] The present invention studies a systematic and complete method for simulating the pre-oxidation process of PAN by introducing electron beam irradiation from modeling to heat treatment. Through molecular dynamics simulation, the difficult problem of exploring the pre-oxidation process of PAN fiber by coupling irradiation and heating under current traditional experimental conditions is solved.

[0029] By adjusting the electron beam irradiation dose and irradiation introduction time, the molecular dynamics simulation of the microscopic reaction of PAN precursor under electron beam irradiation conditions during the gradient heating process is realized, and then the irradiation dose and temperature parameters of the PAN electron beam irradiation and heating coupling are optimized, and the optimal time for introducing electron beam irradiation into the trans-syndiotactic PAN fiber during the heat treatment process is explored, providing in-depth theoretical basis and support for the pre-oxidation process of PAN fiber irradiation and heating coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a PAN dimer with the head and tail atoms defined in Example 1.

[0031] Figure 2It is the trans-syndiotactic PAN chain with a degree of polymerization of 60 in Example 1.

[0032] Figure 3 This is the hexagonal lattice chain stacking diagram of PAN in Example 1.

[0033] Figure 4 This is the initial structure diagram of the PAN hexagonal unit cell in Example 1.

[0034] Figure 5 This is a flow chart of the pre-oxidation by electron beam irradiation introduced at the initial stage of heat treatment of the PAN model in Example 1.

[0035] Figure 6 This is a molecular weight diagram of the results of pre-oxidation by electron beam irradiation introduced at the initial stage of PAN heat treatment in Example 1.

[0036] Figure 7 It is the trans-syndiotactic molecular chain of the ternary copolymer PAN with a polymerization degree of 100 in Example 2.

[0037] Figure 8 This is the initial structure diagram of the hexagonal unit cell of the trans-syndiotactic stereoisomer of the ternary copolymer PAN in Example 2.

[0038] Fig. 9 This is a pre-oxidation flow chart of electron beam irradiation introduced at the later stage of heat treatment of the PAN model in Example 2.

[0039] Fig.10 This is a molecular weight diagram of the results of pre-oxidation by electron beam irradiation introduced into PAN at the later stage of heat treatment in Example 2. DETAILED DESCRIPTION

[0040] The specific technical solution of the present invention is explained with examples

[0041] Example 1

[0042] The first embodiment of the present invention provides a molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling, the method comprising the following steps:

[0043] (1) Using the software MaterialsStudio, based on the planar zigzag configuration of the PAN monomer molecule and the structure of all trans conformations, the probability of the two monomer molecules reacting is determined to be 0.5 each;

[0044] (2) Use the software MaterialsStudio to create a PAN monomer, use the Built Polymers module to select the head and tail atoms, create a repeating unit with two monomers, form a trans chemical bond connection site, and connect the two monomers into a dimer;

[0045] Figure 1It is a PAN dimer with the head and tail atoms defined in Example 1.

[0046] (3) Using the software MaterialsStudio, the dimer is regarded as a new monomer. Using the Build Polymers module, the dimer is a new monomer molecule and the degree of polymerization is set to 30, that is, each molecular chain has 60 monomers.

[0047] Figure 2 It is the trans-syndiotactic PAN chain with a degree of polymerization of 60 in Example 1.

[0048] (4) Using Materials Studio software, the molecular chain described in step (3) was replicated, and the PAN chain spacing formula a=√3b was obtained according to the hexagonal lattice stacking mode of polyacrylonitrile. According to the experimental density of 1.17-1.22 g / cm 3 , the molecular chain spacing of the hexagonal unit cell model is determined to be Set up a hexagonal cell PAN simulation box;

[0049] Figure 3 This is the hexagonal lattice chain stacking diagram of PAN in Example 1.

[0050] Step (4) The size of the PAN hexagonal unit cell simulation box is 12.5×12.5×9 nm. 26 oxygen molecules are added into the simulation box to simulate an oxygen concentration environment of 21%. The obtained simulation system is converted into a three-dimensional coordinate file that can be recognized by a dynamic simulation calculation tool.

[0051] Figure 4 This is the initial structure diagram of the PAN hexagonal unit cell in Example 1.

[0052] (5) Using Lammps software, import the initial three-dimensional coordinate file obtained in step (4), set the simulation unit to real unit, set the x, y, and z directions to periodic boundary conditions, set the atom type to charge, and set the simulation time step to 0.25 fs;

[0053] (6) Lammps software was used, the force field was selected as the reactive force field, the element types used in the simulation were specified, including hydrogen, carbon, nitrogen and oxygen elements, and the thermodynamic information was output every 100 steps to monitor the system status;

[0054] In step (6) of the reactive force field parameters, a charge balance algorithm is used, which is suitable for the reactive force field to dynamically adjust the atomic charges during the simulation to meet the balance of charge distribution.

[0055] (7) Using Lammps software, use the "variable" command to set the model area again in the x, y, and z directions of the simulation box and use the "fix" command to constrain the positions of the two ends of the model, fix the forces at both ends to 0, and perform energy minimization operations;

[0056] The energy minimization algorithm used in step (7) is the conjugate gradient method, and the damping value is set to 5000.

[0057] (8) Initial relaxation at 300 K to obtain a stable configuration;

[0058] The relaxation described in step (8) is the Nosé-Hoover thermostat method. The relaxation adopts NVT, the simulation time is 40ps, and the neighbor list is updated every 100 steps.

[0059] (9) Lammps software was used to introduce the stable configuration obtained in step (8), and six temperature gradients were set, namely 498 K, 528 K, 548 K, 568 K, 580 K, and 598 K. Electron beam irradiation simulation was introduced in the first gradient 300 K-498 K heating stage;

[0060] (10) Lammps software was used to create the PKA initial position region using the "create_atoms" and "region" commands, where the coordinates were set to (40, 2, 67). The oxygen atom was set as PKA, and the "velocity" command was used to set its kinetic energy in the x, y, and z directions according to the irradiation dose to simulate the irradiation energy transfer, while monitoring the PKA kinetic energy and outputting the simulation data file;

[0061] In step (10), kinetic energy is assigned to oxygen atoms according to the PKA electron volt and kinetic energy conversion formula. Here, the "velocity" command is used to set the y-direction kinetic energy to Perform dynamics calculations and use the "dump" command to output species, bond, dump, xyz and data type files.

[0062] In step (10), use the "compute" command to define the PKA velocity components, and use the "variable" command to sum the squares of each velocity component, and then use the "compute reduce" command to obtain the square sum. Finally, use the "variable" command to calculate the total PKA kinetic energy, output it every 100 steps, and monitor the changes in PKA kinetic energy.

[0063] In step (10), NVE was used, and the temperature during irradiation was adjusted to 300K-498K using a Berendsenn temperature controller. The temperature controller time scale was set to 2000 steps to slowly dissipate heat, and the irradiation simulation time was 100ps.

[0064] (11) Using Lammps software, import the data file obtained in step (10) and continue to analyze the 498K, 528K, 548K,

[0064] (11) Using Lammps software, import the data file obtained in step (10), continue to perform heating and insulation treatment at 498K, 528K, 548K, 568K, 580K, and 598K, and output species, bond, dump, and xyz data files;

[0065] In step (11), the NVT ensemble is continued to be used, and the simulation duration of each temperature gradient heating and insulation is 10 ps.

[0066] The total simulation duration is 230 ps.

[0067] During each gradient heating and heat preservation simulation process in step (11), the output file can be verified and analyzed by OVITO software, thereby obtaining a molecular-level reaction image of the trans-syndiotactic PAN model during the pre-oxidation process and performing image analysis.

[0068] Figure 5 This is a flow chart of the pre-oxidation by electron beam irradiation introduced at the initial stage of heat treatment of the PAN model in Example 1.

[0069] (11) importing the species file outputted in step (10), and using Python software to perform species type and molecular weight analysis on the final outputted heat treatment data;

[0070] Figure 6 This is a molecular weight diagram of the results of pre-oxidation by electron beam irradiation introduced at the initial stage of PAN heat treatment in Example 1.

[0071] Example 2

[0072] The second embodiment of the present invention provides a molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling. This embodiment is different from the first embodiment in that, in order to verify its beneficial effect, comparative data under the coupling effect of electron beam irradiation and heat treatment in the present invention are provided. The method comprises the following steps:

[0073] (1) Using the software MaterialsStudio, a PAN monomer was established based on the planar zigzag PAN trans-syndiotactic stereoisomer structure with a trans conformation, and the inter-monomer connection sites were determined;

[0074] (2) Using the software MaterialsStudio, use the Built Polymers module to select the head and tail atoms to connect the two monomers into a dimer to form a trans chemical bond connection site. The dimer is used as a new monomer and the degree of polymerization is set to 50, that is, each molecular chain has 100 PAN monomers;

[0075] (3) Using the software MaterialsStudio, a copolymer was added to the trans-syndiotactic PAN chain with a degree of polymerization of 100, where two methyl acrylate monomers and three itaconic acid monomers were added;

[0076] Figure 7 It is the trans-syndiotactic molecular chain of the ternary copolymer PAN with a polymerization degree of 100 in Example 2.

[0077] (4) Using MaterialsStudio software, the molecular chains described in step (3) are replicated and combined to determine the molecular chain spacing of the hexagonal unit cell model to be Establish a hexagonal unit cell PAN simulation box;

[0078] Step (4) The size of the hexagonal unit cell PAN simulation box is 21.5×21.5×12 nm. 84 oxygen molecules are added into the simulation box to simulate a 21% oxygen environment. The obtained simulation system is converted into a three-dimensional coordinate file that can be recognized by a dynamic simulation calculation tool.

[0079] Figure 8 It is the initial structure diagram of the hexagonal unit cell of the trans-syndiotactic stereoisomer of the ternary copolymer PAN in Example 2, and the three-dimensional coordinate conversion software is OVITO software.

[0080] (5) Using Lammps software, introduce the initial three-dimensional coordinate information obtained in step (4), set the simulation unit to real unit, set the x, y, and z directions to periodic boundary conditions, set the atom type to charge, and set the simulation time step to 0.25 fs;

[0081] (6) Lammps software was used, the reactive force field was selected as the force field, and the element types used in the simulation were specified, which included hydrogen, carbon, nitrogen, and oxygen elements. The thermodynamic information was output every 100 steps to monitor the system status.

[0082] (7) Lammps software was used to use the “fix” command to constrain the positions of both ends of the model, fix the forces at both ends to 0, and perform energy minimization operations.

[0083] (8) Initial relaxation at 300 K to obtain a stable configuration;

[0084] The energy minimization algorithm used in step (7) is the conjugate gradient method, and the damping value is set to 10000.

[0085] The relaxation method described in step (8) is the Nosé-Hoover thermostat method. The relaxation adopts NVT, the simulation time is 20 ps, ​​and the neighbor list is updated every 100 steps.

[0086] (9) Using Lammps software, import the relaxation data file obtained in step (8), and use the "fix" command to perform gradient heating processing;

[0087] In step (9), the temperature is selected as 300K-583K, and seven temperature rise gradients are set to 463K, 483K, 503K, 523K, 543K, 563K, and 583K, respectively. Each temperature gradient is heated and kept warm. The "fix" command is used to heat the gradient to the 563K-583K stage. The simulation duration of each gradient heating and keeping warm is 10ps.

[0088] (10) During the 583K holding stage, use the "create_atoms" and "region" commands to create five PKA initial position regions, set the coordinates to (30, 2, 65), (60, 2, 65), (108, 2, 65), (152, 2, 65), and (183, 2, 65), respectively, set the oxygen atom as PKA, and use the "velocity" command to set the kinetic energy of the primary collision atom in the x, y, and z directions according to the irradiation dose to simulate the irradiation energy transfer, while monitoring the PKA kinetic energy and outputting the irradiation data file;

[0089] Step (10) gives oxygen atoms kinetic energy to simulate radiation energy, and uses 5 PKAs to divide the energy of the incident particles. Here, the "velocity" command is used to set the y-direction kinetic energy of each primary collision atom to Perform dynamic calculations and use the "dump" and "fix" commands to output species, bond, dump, and xyz data files.

[0090] In step (10), the “compute” command is used to define the PKA velocity components, and the “variable” command is used to square and sum each velocity component, and then the “compute reduce” command is used to obtain the square sum. Finally, the “variable” command is used to calculate and output the total PKA kinetic energy, with a time step of once every 100 steps.

[0091] In step (10), NVE is used, and the Berendsenn temperature controller is used to control the temperature to 583K-583K and gradually dissipate the irradiation heat. The time scale of the temperature controller is set to 1000 steps to slowly dissipate the heat, and the irradiation simulation time is 20ps.

[0092] The total simulation duration is 170 ps.

[0093] During the gradient heating and heat preservation process in step (10), the simulation operation process can be verified and analyzed by OVITO software to obtain a molecular-level reaction image of the trans-syndiotactic PAN during the pre-oxidation process.

[0094] Fig. 9 This is a pre-oxidation flow chart of electron beam irradiation introduced at the later stage of heat treatment of the PAN model in Example 2.

[0095] (11) Import the species file output from step (10) and use Python software to perform statistical analysis on the species and molecules of the final output heat treatment data.

[0096] Fig.10 This is a molecular weight diagram of the results of pre-oxidation by electron beam irradiation introduced into PAN at the later stage of heat treatment in Example 2.

Claims

1. A molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling, characterized in that: The following steps are involved: (1) Using MaterialsStudio software, draw a three-dimensional ball-and-stick model of polyacrylonitrile (PAN) monomer, determine the PAN monomer connection site based on the molecular chain conformation of trans-syndiotactic PAN, and set the degree of polymerization to establish a trans-syndiotactic molecular chain; (2) Using MaterialsStudio software, a hexagonal unit cell PAN simulation box is established according to the PAN experimental density, a certain number of oxygen molecules are added into the simulation box to simulate the oxygen concentration conditions, and the obtained model is converted into a three-dimensional coordinate file that can be recognized by the dynamic simulation calculation tool; (3) using Lammps software, introducing the coordinate file obtained in step (2), setting simulation parameters, performing energy minimization operation and relaxation to obtain a stable configuration of the simulation system, so that oxygen molecules are randomly distributed in the simulation system; (4) using Lammps software, introducing the stable configuration obtained in step (3), constraining the positions of the two ends of the model, setting the gradient heating range, inserting a temperature controller during the gradient heating process, creating a primary collision atom (PKA) region, giving PKA kinetic energy to simulate radiation energy transfer, performing simulation calculations and outputting simulation results; (5) Using Lammps software, the model data obtained in step (4) is introduced, and the temperature is gradually increased to complete the pre-oxidation simulation; (6) Visually verify the simulation process and process and analyze the data files output by the simulation.

2. The molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling according to claim 1 is characterized in that Step (1) uses the Built Polymers module to select the head and tail atoms of the first monomer to polymerize and connect into a dimer, and uses the dimer as a new monomer molecule to establish a PAN trans-syndiotactic molecular chain. Step (2) uses the Crystal module to establish a rectangular Amorphous Cell box.

3. The molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling according to claim 1 is characterized in that The energy minimization algorithm used in step (3) is the conjugate gradient method, the relaxation algorithm is the Nosé-Hoover thermostat method, and the temperature controller used in step (4) is the Berendsenn temperature controller.

4. The molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling according to claim 1, characterized in that: Steps (3) and (5) use the canonical ensemble (NVT), and step (4) uses the microcanonical ensemble (NVE). The force field uses the reactive force field, and the simulation algorithm uses the charge balance algorithm, which is suitable for dynamically adjusting the atomic charge in the reactive force field to meet the balance of charge distribution: In step (3), the temperature is selected as 300K and the simulation time is 20ps; In step (4), 5 to 7 temperature ramps are set according to the pre-oxidation temperature, the PKA kinetic energy is set according to the irradiation dose and the PKA mass, and the irradiation simulation time is 20 to 100 ps; In step (5), the gradient heating is carried out according to the irradiation insertion temperature, and the gradient heating simulation time is 90 to 130 ps.

5. The molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling according to claim 1, characterized in that: The expression of PKA atomic kinetic energy is as follows: Here, we assume that the velocity v is in the direction [h, k, l], the kinetic energy is NeV, the mass is M gram / mol, N A is Avogadro's constant.

6. The molecular simulation method for the pre-oxidation process of polyacrylonitrile fiber by electron beam irradiation and heating coupling according to claim 1, characterized in that Step (6) Use OVITO software to take atomic snapshots of the simulation process to obtain simulation details, and use Python software to perform statistical analysis on the molecular weight output of the simulation.

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