Toughening and forming method of high-performance PEI plate for high-heat-resistance structural member

Abstract

The invention discloses a toughening forming method of a high-performance PEI plate for a high-heat-resistance structural part, and particularly relates to the technical field of high-performance composite material forming. Pre-embedding a PEI toughening layer between thermosetting prepreg layers, and controlling the temperature, the pressure, the pressure maintaining time and the heating rate in the hot pressing process; carrying out infrared spectrum or solid nuclear magnetic resonance testing on the interface area sample subjected to hot press molding, and calculating the chain segment residual rate Rp; determining the interface penetration depth Di through a transmission electron microscope in combination with energy spectrum analysis; inputting the Rp and the Di into an interface coupling model, and outputting an interface combination quality factor Q by the model in a form of combining weighted linearity and logarithmic functions; the interface bonding grade is judged according to the Q value, and when the Q value is lower than a threshold value, hot-pressing process parameters are backtracked for optimization; according to the method, quantitative evaluation of the interface performance and process closed-loop optimization are realized, and the interface bonding strength and service reliability of the composite material can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-performance composite material forming technology, in particular to a high-performance PEI plate toughening forming method for high-heat-resistant structural parts. BACKGROUND

[0002] High-performance PEI plate toughening forming refers to modifying polyetherimide (PEI) material through specific processes and formulations to improve its toughness while maintaining excellent properties such as high strength and high heat resistance, making it more suitable for processing into plates. This process typically includes adding toughening agents, optimizing processing parameters, and other technical means to improve the material's crack resistance, impact resistance, and overall structural stability during the forming process, thereby meeting the stringent application requirements of high-performance engineering plastics in aerospace, electronics, and other fields.

[0003] In the high-performance composite material hot pressing forming process, to improve the overall performance of the material, the temperature needs to be raised to 330-360°C, which is close to or exceeds the melting temperature range of polyetherimide (PEI). In this temperature range, the PEI toughening layer melts and interpenetrates with the thermosetting resin interface, helping to form a stable physical interlocking structure. However, if the hot pressing temperature is further increased to close to 400°C or above, it may cause thermal degradation of PEI, leading to molecular chain rupture and the generation of low molecular weight fragments. These degradation products disperse in the interface, weakening the bonding strength between the toughening layer and the thermosetting resin, ultimately causing interlayer debonding. Therefore, to ensure interface stability, a thermosetting resin system with a curing temperature above 330°C should be selected, such as bismaleimide resin or polyimide resin, to achieve temperature matching and interface synergy with the PEI toughening layer.

[0004] In addition, due to the difficulty in identifying the initial interlayer debonding problem through conventional detection methods, it often shows serious interface failure under the combined action of high temperature environment and mechanical vibration during service, which may cause catastrophic structural damage. SUMMARY

[0005] The purpose of the present application is to provide a high-performance PEI plate toughening forming method for high-heat-resistant structural parts to solve the problems in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a high-performance PEI plate toughening forming method for high-heat-resistant structural parts, comprising:

[0007] Obtaining a thermosetting prepreg as the base material, stacking the layers in the designed order, and pre-embedding a polyetherimide toughening layer between adjacent layers;

[0008] The hot-pressing temperature, pressure, pressure holding time and heating rate are controlled in a fixed preset interval, and a composite sample is prepared according to the set parameters based on the ether imide toughening layer;

[0009] After hot-pressing, the interface region sample of PEI and thermosetting resin is obtained by focused ion beam or ultrathin sectioning technology for microstructure test;

[0010] The interface region is analyzed by infrared spectroscopy or solid-state nuclear magnetic resonance to obtain the characteristic absorption peak intensity of PEI main chain, calculate the polymer chain segment residual rate Rp, and judge the thermal degradation degree;

[0011] Based on transmission electron microscopy combined with energy spectrum analysis technology, the penetration depth Di of PEI phase in the thermosetting resin is obtained for characterizing the interface physical fusion ability;

[0012] The chain segment residual rate Rp and the interface penetration depth Di are input into the constructed interface coupling model, the model is: Q = a·Rp + b·ln(Di + 1); Wherein a and b are the weight coefficients preset according to the material system, Q is the interface bonding quality factor;

[0013] According to the value of the interface quality factor Q, the interface strength grade is determined, and when the Q value is lower than the set threshold, the hot-pressing temperature, pressure holding time or PEI toughening layer thickness parameters are traced back to optimize the hot-pressing process.

[0014] Preferably, the ether imide toughening layer is in a film, powder or gel state, and the layer thickness is controlled between 1-25 μm.

[0015] Preferably, the hot-pressing temperature, pressure, pressure holding time and heating rate are controlled in a fixed preset interval, including: setting the hot-pressing temperature to 220-260℃, the pressure to 0.3-0.7MPa, the pressure holding time to 30-90 minutes, and the heating rate to 2-5℃ / min.

[0016] Preferably, the calculation of the polymer chain segment residual rate Rp includes:

[0017] The interface region sample of PEI and thermosetting resin extracted from the hot-pressed composite sample is dried, and the Fourier transform infrared spectrometer is used for spectrum scanning to obtain the characteristic carbonyl stretching vibration peak intensity in the wave number interval of 1775cm-1 to 1720cm-1;

[0018] The characteristic peak intensity value of the PEI sample before hot-pressing is taken as the reference standard, and the absorption peak area or peak height of the corresponding characteristic peak in the sample after hot-pressing is measured;

[0019] The formula is: The residual rate Rp of the polymer chain segment is calculated, wherein A_after is the characteristic peak area of the sample after hot pressing, and A_before is the characteristic peak area of the standard sample before hot pressing.

[0020] Preferably, the penetration depth Di of the PEI phase in the thermosetting resin includes:

[0021] A sample containing the interface region of the PEI toughening layer and the thermosetting resin is cut from the composite material after hot pressing;

[0022] High-resolution imaging is performed on the interface region to observe the morphology, distribution and penetration path of the PEI phase in the interface region, and the structural boundary of the transition of the PEI phase to the thermosetting matrix is identified;

[0023] Energy spectrum analysis is performed on multiple points in the TEM imaging region to detect the concentration gradient change of the PEI characteristic elements in the interface layer;

[0024] According to the spatial variation range of the element distribution concentration from high to low, combined with the extension distance of the PEI phase morphology in the image, the maximum effective diffusion distance of the PEI to the thermosetting resin is determined as the penetration depth Di.

[0025] Preferably, the chain segment residual rate Rp and the interface penetration depth Di are input into the constructed interface coupling model, including:

[0026] The chain segment residual rate Rp obtained by infrared spectroscopy or solid-state nuclear magnetic resonance test and the interface penetration depth Di obtained by transmission electron microscopy combined with energy spectrum analysis are used as input items of the interface coupling model, and the model is constructed in the form of weighted linear and logarithmic function;

[0027] The interface bonding quality factor is used as an output item, and the obtained Q value is used to evaluate the overall bonding performance of the composite material interface under the hot pressing process condition.

[0028] Preferably, the interface strength grade is determined according to the interface quality factor Q value, including: when Q is greater than or equal to 110, the interface bonding performance is high grade; when Q is between 90 and 110, the interface bonding performance is medium grade; and when Q is less than 90, the interface bonding performance is low grade, and the process condition needs to be adjusted.

[0029] In the above technical solutions, the present application provides technical effects and advantages:

[0030] 1. The application establishes an interface coupling model, takes the segment residual rate Rp and the interface penetration depth Di as double input parameters, introduces the mixed operation form of weighted linear and logarithmic function, and outputs the interface bonding quality factor Q, so as to realize the quantitative characterization of the interface performance of the composite material. Compared with the existing evaluation method which only depends on a single physical or chemical parameter, the application can comprehensively reflect the synergistic effect of the stability of PEI molecular chain and the interface physical embedding, and significantly improve the accuracy and reliability of the interface performance evaluation. Through clear threshold division, the interface bonding performance grade can be quickly determined, and the subjectivity and uncertainty existing in the traditional detection method can be avoided.

[0031] 2. The application takes Q value as a feedback signal, introduces a process backtracking and optimization mechanism, so that the hot pressing temperature, holding time and PEI toughening layer thickness and other key process parameters can be self-adaptively corrected according to the interface performance results, thereby forming a closed-loop control system. This not only can effectively reduce the interface peeling and failure risk, but also improves the long-term service reliability of the composite material in high temperature and high load environment, and has good implementability and popularization value, and is suitable for wide application in the fields of aerospace, rail transportation and high-end equipment manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art based on these drawings.

[0033] Figure 1 The method flowchart of the present application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0035] Embodiment, please refer to Figure 1 As shown in the figure, the high-performance PEI plate toughening forming method for high-heat-resistant structural parts described in the embodiment includes:

[0036] The thermosetting prepreg is taken as the matrix material, and the layers are stacked in the designed order, and the polyetherimide toughening layer is pre-embedded between adjacent layers;

[0037] Based on the ether imide toughening layer, the hot pressing temperature, pressure, holding time and heating rate are controlled in a fixed preset interval, and the composite sample is prepared according to the set parameters;

[0038] After hot pressing, the sample is obtained by focused ion beam or ultrathin section technology to obtain the interface region sample of PEI and thermosetting resin for microstructure test;

[0039] The interface region is analyzed by infrared spectroscopy or solid nuclear magnetic resonance to obtain the characteristic absorption peak intensity of PEI main chain, calculate the polymer chain segment residual rate Rp, and judge the thermal degradation degree;

[0040] Based on transmission electron microscopy combined with energy spectrum analysis technology, the penetration depth Di of PEI phase in thermosetting resin is obtained for characterizing the interface physical fusion ability;

[0041] The chain segment residual rate Rp and the interface penetration depth Di are input into the interface coupling model constructed, the model is: Q = a.Rp + b.ln(Di + 1); Wherein a and b are the weight coefficients preset according to the material system, Q is the interface bonding quality factor;

[0042] According to the value of interface quality factor Q, the interface strength grade is determined, and when the Q value is lower than the set threshold, the hot pressing temperature, holding time or PEI toughening layer thickness parameters are traced back to optimize the hot pressing process.

[0043] In the present application, the thermosetting matrix material used is in the form of prepreg, the reinforcing body is high-strength carbon fiber or glass fiber, and the matrix resin is epoxy resin, bismaleimide (BMI) or benzoxazine thermosetting resin. The above-mentioned thermosetting prepreg is in B-stage state at room temperature, has a certain processing time, and can complete the curing reaction by hot pressing or vacuum forming.

[0044] As an interface reinforcing phase, polyetherimide (PEI) material is selected because it has the following advantages:

[0045] The glass transition temperature (Tg) is as high as 215-240℃, which is suitable for high-temperature hot pressing;

[0046] It has certain chemical compatibility with various thermosetting resins;

[0047] It can be processed into various states such as film, powder, gel, etc., which is convenient for interface construction;

[0048] Microscopic phase separation structure can be formed during processing, which can effectively absorb interface fracture energy.

[0049] The morphology of PEI toughening layer can be selected as:

[0050] High purity PEI film (recommended thickness: 3-15 μm);

[0051] Microspheric PEI powder (particle size: 1-5 μm, dispersion density: 10-30 g / m 2 );

[0052] Gel state interface adhesive layer prepared by PEI / solvent system.

[0053] The following are the specific implementation steps of embedding PEI toughening layer into the structure of thermosetting composite prepreg:

[0054] Select thermosetting carbon fiber prepreg tapes with consistent specifications (such as 250 gsm, 150 μm thickness), store them in an environment below -18°C, restore them to room temperature (about 1-2 hours) before use, and cut them into predetermined shapes and sizes.

[0055] According to different structures and target performance requirements, the following three ways can be used to prepare PEI toughening layer:

[0056] PEI film method: select commercially available PEI film (such as 1000, 1010, etc.), thickness control in 3-15 μm; use laser cutting or hot knife cutting to cut into equal area sheets as prepreg sheets; the surface can be treated by plasma or solvent immersion to improve the interface wettability.

[0057] PEI powder dispersion method: use ball milling method to prepare PEI micro powder with particle size of 1-5 μm; uniformly disperse in the interface area to be enhanced, the reference mass control standard is 20±5 g / m 2 ; it is suggested to match with hot melt adhesive spraying to fix and avoid position deviation before hot pressing.

[0058] PEI gel state interface adhesive layer method: dissolve PEI in NMP or DMAc and other polar organic solvents, the mass concentration is 10-20%; use screen printing or blade coating method to coat on the surface of prepreg, form a gel layer of about 5-10 μm; pre-dry for 30 minutes at room temperature to remove part of the solvent, facilitate stacking.

[0059] Stack the interface sheet with PEI toughening layer and thermosetting prepreg alternately, use the following lamination strategy: symmetric lamination method: mirror image configuration from top to bottom, improve the overall stability; local reinforcement design: selectively arrange PEI layer in key areas of the structure (such as opening, edge, hole edge); layer thickness control requirement: the total thickness of PEI layer should not exceed 3% of the total composite board thickness, to ensure that the overall structure rigidity is not weakened. It is suggested to use a press roller to compact each layer when stacking, to exclude air and prevent the formation of initial voids.

[0060] To prevent the sliding between the stacked layers or the displacement of the PEI film, short-time preheating (10 minutes) at 80-100°C can be performed before vacuum bagging; at the same time, standing and pressure weighting for 1 hour at room temperature can make the initial interface fit more closely.

[0061] In this step, to ensure the full play of the function of the PEI toughening layer, the following parameters need to be controlled:

[0062] The thickness of the PEI layer is controlled in the range of 1-25 μm, and too thick PEI layer is easy to cause resin enrichment or phase discontinuity;

[0063] Adhesion uniformity: through thermal imaging or laser scanning, it is ensured that there is no empty area in the distribution of PEI;

[0064] Adhesion stability: the film method needs to have anti-slippage treatment, and the gel method needs to be cured and bonded;

[0065] Compatibility of thermosetting matrix and PEI: the interface structure stability is determined by the preliminary small sample test.

[0066] In the present application, hot pressing not only completes the curing process of the thermosetting resin, but more importantly, realizes the following two functional goals:

[0067] On the one hand, the PEI film or particles are melted and penetrated into the adjacent thermosetting resin layer by heating;

[0068] On the other hand, while keeping the temperature and pressure stable, the resin completes the spatial network crosslinking and is shaped into a plate structure.

[0069] The functionality of the PEI toughening layer depends on its softening, diffusion and interfacial embedding performance in the hot pressing environment, so the hot pressing parameters are optimized in the present application to ensure the realization of structure and performance.

[0070] According to the thermal properties of PEI, the curing curve of the thermosetting matrix and the interfacial penetration characteristics, the present application proposes the following key hot pressing parameter ranges as the preferred intervals:

[0071] Table 1 Key hot pressing parameter range intervals

[0072]

[0073] As shown in Table 1, the hot pressing temperature should be controlled in the range where PEI does not undergo thermal degradation (<260°C), and the pressure and holding time need to be adjusted according to the thickness of the product and the rheological properties of the resin. The heating rate has a great influence on the time window of PEI softening and the interfacial thermal balance, and is an important variable affecting the interface quality.

[0074] The hot pressing process described in the present application can be completed in the following equipment:

[0075] Hot press with flat platens (temperature and pressure can be precisely controlled);

[0076] Vacuum hot press (suitable for large size and complex components, ensuring consistent degassing and temperature control);

[0077] Programmable temperature control molding device (convenient for segmented heating and constant temperature control).

[0078] During the entire hot pressing cycle, it is recommended to use a segmented temperature control curve, that is, to set the following three key stages:

[0079] Preheating stage (room temperature to about 120°C): resin flow is started, and PEI begins to soften;

[0080] Main hot pressing stage (220-250°C): ensure that PEI is fully melted and interfacial penetration occurs;

[0081] Curing stage (constant temperature + pressure holding): resin completes curing and crosslinking, and the structure is shaped.

[0082] Choose a metal mold with appropriate size, and line the mold cavity with polytetrafluoroethylene film or release cloth to prevent the product from sticking to the mold wall.

[0083] Place the stack with PEI toughening layer arranged in the mold, apply initial pressure (0.05-0.1 MPa), remove excess air and stress, and stand for 10 minutes.

[0084] Slowly heat up to 220°C at a set rate (e.g. 3°C / min), then increase the pressure to a set pressure (e.g. 0.5 MPa), and enter the pressure holding stage.

[0085] Maintain the hot pressing temperature (220-240°C) and pressure for 30-90 minutes to ensure that PEI interfacial penetration occurs and the thermosetting resin completes crosslinking.

[0086] Slowly cool down (≤5°C / min) to below room temperature, release the pressure, take out the molded plate sample, and number it for storage.

[0087] To ensure that the composite material sample has good interlaminar bonding and thermal stability, the following points need to be controlled:

[0088] Temperature stability: the temperature difference during hot pressing should be controlled within ±2°C to avoid local overheating and decomposition of PEI;

[0089] Pressure uniformity: the pressure distribution on the plate surface should be uniform to avoid air inclusions;

[0090] PEI softening window matching: when the temperature rises to 230°C, PEI is in a flowable state, and the resin has not yet rapidly cured, which is beneficial for interfacial penetration;

[0091] Degassing design: the mold or equipment needs to have a vacuum channel to discharge residual gas in time to prevent air bubbles.

[0092] In the composite material using PEI as the interfacial toughening material, the final interfacial performance strength depends not only on the macroscopic physical parameter control, but also on the structure morphology and distribution state at the microscale. In particular, whether the PEI effectively penetrates into the thermosetting matrix, whether a continuous or semi-continuous phase is formed, and whether a good interfacial adhesion state is possessed, all need to be confirmed by means of high-resolution imaging.

[0093] The resolution of conventional optical microscopy is limited and cannot obtain the interface evolution information at the nanoscale, therefore, the following two advanced methods are used for microscale sample extraction of the interface in the present application: focused ion beam (FIB) section preparation technology and ultramicrotomy.

[0094] The above two methods have high-precision slicing capability, and can obtain complete and representative PEI-resin interface zone structure samples, which are used for subsequent transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) or nano-infrared spectroscopy (nano-FTIR) analysis.

[0095] FIB uses accelerated Ga+ ion beam to accurately etch the sample, and can cut and polish to nanoscale flatness at the specified position, which is the most commonly used high-precision sample preparation method for microelectronic and material interface analysis at present. The advantages of FIB are:

[0096] Accurate positioning: can lock specific microstructure regions such as interface crack initiation points;

[0097] Imaging synchronization: can cut while observing to obtain complete structure images;

[0098] Supporting subsequent TEM analysis: can directly prepare ultrathin sections below 100 nm.

[0099] Ultramicrotomy is suitable for large-area interface structure analysis, and the sample is cut into continuous sections with a thickness of 50-100 nm by using a glass knife or a diamond knife. The characteristics are as follows:

[0100] High throughput: multiple regions can be continuously sectioned, which is beneficial for statistical analysis;

[0101] Low cost and simple operation;

[0102] Can be used with TEM or atomic force microscopy.

[0103] The present application preferably uses FIB sample preparation when high spatial resolution or complex interface identification is required, and uses ultramicrotomy in large sample statistical research.

[0104] Select the composite sample after hot pressing, cut 5x5mm or 10x10mm small size sample along the thickness direction;

[0105] Use sandpaper or precision grinding equipment to flatten the cross section;

[0106] According to the test area requirements, the interface distribution is observed by microscope and the interface layer to be extracted is marked.

[0107] Fix the sample block on the FIB sample holder and use high vacuum pumping;

[0108] Low current electron beam is used for preliminary imaging and positioning;

[0109] Ga+ ion beam is used to strip the surrounding material according to the set path, and only the target interface area (usually about 100nm thick) is reserved;

[0110] Prepare a flat cross section by cross section cutting + ion polishing;

[0111] Transfer the prepared thin slice to a copper mesh or support for TEM, EDS or AFM testing.

[0112] Pre-soak the sample block in epoxy embedding agent to form an embedded block;

[0113] Use an ultramicrotome with a diamond knife to cut the target area into 50-100nm thick sections;

[0114] Use water bath transfer method to collect the sections on the support net, dry and develop;

[0115] Transfer to TEM or infrared nanospectroscopy equipment for imaging and spectrum acquisition.

[0116] The interface structure samples obtained by the above method can be used for the following analysis:

[0117] Table 2 analysis means

[0118] Analysis means Objectives TEM imaging Observation of PEI penetration structure, phase separation morphology EDS energy spectrum analysis Element distribution, chemical compatibility analysis Nano-FTIR Identification of PEI and resin interface functional group distribution SEM / AFM Surface roughness, interface stress concentration area detection Pull-out / broken cross-section analysis Interface peeling morphology, crack initiation mechanism verification

[0119] As shown in Table 2, further extraction can be performed, such as: interface penetration depth D i (unit: nm); phase structure type (island, interpenetration, double continuous); adhesion failure mode (adhesion failure / material bulk failure); these data will be used as the basis for subsequent establishment of interface quality model input, and can be associated with process parameters regression.

[0120] Polymer chain segment residual rate (Rp) refers to the degree of integrity of key functional groups (such as imide group, aromatic nucleus, etc.) in polyetherimide main chain during hot pressing process, which is defined as:

[0121] The ratio of the characteristic absorption peak area or peak height of the target main chain functional group in the interface region sample after hot pressing treatment to the same functional group absorption peak in the standard sample before hot pressing is usually expressed in percentage.

[0122] In the present application, Rp is mainly used to quantitatively evaluate whether PEI has undergone significant thermal degradation or chain scission reaction.

[0123] Combined with previous experimental and literature data verification, when the Rp value of PEI is lower than 90%, it can be considered that it has undergone mild molecular chain degradation; when Rp is lower than 70%, it indicates that the material has undergone significant thermal degradation, which may affect the interfacial mechanical properties.

[0124] The imide structure in the PEI main chain has a clear carbonyl (C=O) stretching vibration absorption peak between 1775 and 1720 cm-1; the aromatic core skeleton also has characteristic absorption in the range of about 1500 to 1600 cm-1. By measuring the peak height or integral area of these characteristic peaks, it can be determined whether the main chain structure has been broken or degraded.

[0125] Using cross-polarization magic angle spinning (CP / MAS) technique for 13C nuclear magnetic resonance analysis, the signal intensity of the main chain structure carbon atoms can be obtained at two chemical shift points of 165 ppm (imide carbon) and 125 ppm (aromatic core carbon). The decay of signal intensity can also characterize the integrity of the molecular chain structure.

[0126] Select the interface region sample of the composite material after hot pressing treatment (which can be obtained by focused ion beam or ultrathin sectioning);

[0127] Dry in a vacuum oven at 60°C for 12 hours to remove moisture and volatile components to prevent interference with the absorption signal;

[0128] The comparative sample is the original PEI film sample before hot pressing, which is treated in the same way.

[0129] FTIR analysis:

[0130] Use ATR-FTIR mode to press the surface of the dried sample against the germanium crystal;

[0131] Set the scanning range to 4000 to 400 cm-1, resolution 4 cm-1, and repeat the scan 64 times to reduce noise;

[0132] Extract the carbonyl peak intensity in the range of 1775-1720 cm-1, record the peak area or peak height (A);

[0133] Repeat the measurement of the corresponding peak intensity in the comparative sample (PEI before hot pressing), denoted as A.

[0134] SSNMR analysis:

[0135] CP / MAS 13 C NMR device, rotation rate set to 5 kHz;

[0136] Record the integral intensity of the absorption peak corresponding to δ = 165 ppm and δ = 125 ppm;

[0137] Integrate the hot-pressed sample and the standard sample respectively, and calculate the intensity ratio.

[0138] By comparing the characteristic absorption peaks before and after hot pressing, the residual rate Rp of the polymer chain segment is calculated, and the calculation expression is as follows:

[0139] The area A of the characteristic absorption peak corresponding to the functional group in the hot-pressed sample is compared with the corresponding peak area A in the standard sample before hot pressing, that is,

[0140] When Rp≥90%, it is considered that the molecular chain integrity is good and no obvious degradation occurs;

[0141] When 70%≤Rp<90%, it indicates that there is a certain degree of degradation, and the hot pressing parameters should be checked;

[0142] When Rp<70%, it indicates that the PEI main chain structure is obviously broken, and the temperature or pressure holding time needs to be re-evaluated.

[0143] In the high-performance PEI toughened composite material of the application, the interface physical fusion ability is the key factor to determine the interlayer toughness and long-term reliability. Polyetherimide (PEI) needs to be partially melted and penetrated into the thermosetting resin during hot pressing, so as to form a nanoscale physical embedding layer. The thickness of the embedding layer is defined as the interface penetration depth Di.

[0144] Di is an important physical quantity describing the interface fusion ability. When Di is too small, it indicates that PEI cannot fully penetrate into the matrix, resulting in insufficient interface strength; when Di is large and uniformly distributed, it indicates that a stable interpenetrating network is formed, which helps to improve the interface fracture toughness. In order to accurately determine Di, the application proposes an interface quantitative testing method based on transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS).

[0145] The interface penetration depth Di is defined as: in the hot-pressed composite material, from the boundary of the obvious PEI phase, to the spatial distance at which the PEI element concentration decreases to the background level of the matrix, with the unit of nanometers.

[0146] The concentration distribution data of the target element is obtained by energy spectrum analysis, and the concentration curve is established along the interface direction. The concentration values are normalized from high to low, and the concentration change interval of 90% to 10% is set as the effective diffusion range, and the spatial distance corresponding to this range is Di.

[0147] When Di < 20 nm, the interface chimeric ability is insufficient, belonging to low fusion level;

[0148] When Di is between 20 to 100 nm, the interface fusion ability is at a medium level, which can meet the needs of most structural parts;

[0149] When Di > 100 nm, the interface forms a clear interpenetrating network, with excellent fusion performance, belonging to high fusion level.

[0150] Cut a sample block with a size of about 5 mm x 5 mm x 1 mm from the composite material after hot pressing;

[0151] Prepare a thin sample with a thickness of 50 to 100 nm using focused ion beam (FIB) cutting or ultrathin sectioning;

[0152] Transfer the sample to a copper mesh or carbon film support sheet, ensuring that the interface area is exposed and the structure is intact.

[0153] Use a transmission electron microscope with an acceleration voltage of 120 to 200 kiloelectron volts (keV);

[0154] Perform high-resolution imaging at a magnification of 10,000 to 50,000 times;

[0155] Confirm the interface position of the PEI phase and the thermosetting resin, and record the interface topography characteristics.

[0156] Perform energy dispersive spectroscopy (EDS) scanning in the interface area, using line scanning mode to collect data along the normal direction of the interface;

[0157] Select nitrogen as the characteristic identification element of PEI, and simultaneously collect the carbon element distribution as a comparison;

[0158] Obtain the distribution curve of nitrogen element concentration with distance, and perform data smoothing processing.

[0159] Normalize the nitrogen element concentration data, with the highest concentration value on the PEI side of the interface defined as 100%, and the background level of the matrix defined as 0%;

[0160] Determine the interval range where the concentration drops from 90% to 10%;

[0161] Measure the spatial distance corresponding to this interval, which is the interface penetration depth Di.

[0162] For example: If the concentration curve shows that the concentration is 100% at a distance of 0 nm from the interface boundary, and drops to 10% at a distance of 80 nm, then the penetration depth Di = 80 nm.

[0163] When Di is less than 20 nm, it indicates that the interface physical chimeric is insufficient, and the hot pressing temperature or the holding pressure time needs to be adjusted;

[0164] When Di is 20 to 100 nanometers, it is considered that the interface fusion is in a stable state;

[0165] When Di is more than 100 nanometers, the interface shows a highly interpenetrating structure, which can significantly improve the fracture toughness.

[0166] In the present application, the calculation process of Di is realized by the following algorithm:

[0167] Input: element concentration and corresponding position data obtained by energy spectrum scanning;

[0168] Processing: normalize the concentration value and remove noise using the Gaussian smoothing algorithm;

[0169] Determination: search for the points of 90% and 10% on the concentration curve;

[0170] Output: the spatial distance between the two points, which is defined as the penetration depth Di.

[0171] In the composite material using polyetherimide (PEI) toughening layer, the interface performance not only depends on whether the material is degraded during hot pressing, but also depends on the degree of interface fitting and mutual penetration. A single indicator cannot fully characterize the interface bonding performance, therefore the present application proposes an interface coupling model, taking the chain segment residual rate (Rp) and the interface penetration depth (Di) as input parameters, combining the weighted linear and logarithmic functions, outputting the interface bonding quality factor Q, so as to quantitatively evaluate the overall interface bonding performance of the composite material under the hot pressing process conditions.

[0172] The interface coupling model is used to comprehensively calculate Rp and Di, and the output quantity is defined as the interface bonding quality factor Q. The size of Q directly reflects the degree of interface bonding. The model is constructed by combining the weighted linear and logarithmic functions, and the specific calculation method is: Q = a Rp + b ln (Di + 1); wherein a and b are the weight coefficients preset according to the material system, and Q is the interface bonding quality factor.

[0173] The chain segment residual rate Rp of the sample is determined by infrared spectroscopy or solid-state nuclear magnetic resonance method;

[0174] The interface penetration depth Di is determined by transmission electron microscopy combined with energy spectrum analysis technology;

[0175] Rp and Di are input into the data processing module as model input items.

[0176] A series of standard samples obtained under different hot pressing temperatures, pressures and holding times are prepared;

[0177] Rp and Di of these samples were measured respectively, and the interfacial shear strength was obtained through mechanical test;

[0178] The function relationship between Rp, Di and interfacial shear strength was established by using the least square fitting method, and the optimal weight coefficients α and β were fitted.

[0179] The operation logic was realized in a computer or data processing software (such as MATLAB or Python environment);

[0180] Rp and Di were substituted into the model formula, and the natural logarithm function was called to calculate the β term;

[0181] The interfacial bonding quality factor Q value calculated was output.

[0182] The grade threshold of Q value was set: when Q was greater than or equal to 110, the interfacial bonding performance was high grade;

[0183] When Q was between 90 and 110, the interfacial bonding performance was medium grade;

[0184] When Q was less than 90, the interfacial bonding performance was low grade, indicating that the hot pressing parameters might be unreasonable, and the process conditions needed to be adjusted.

[0185] The process parameter backtracking optimization process included: reading the historical records of temperature, pressure, pressure holding time and PEI toughening layer thickness in the hot pressing process; comparing the parameters corresponding to low Q value with the standard parameters corresponding to high Q value; identifying the key process variables that caused the decline of interfacial bonding performance; and outputting the recommended parameter correction range for subsequent hot pressing process optimization.

[0186] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for toughening and molding high-performance PEI sheets for high heat-resistant structural components, characterized in that: include: Obtain a thermosetting prepreg as the base material, stack the layers in the design sequence, and pre-embed a polyetherimide toughening layer between adjacent layers; Based on the etherimide toughening layer, the hot pressing temperature, pressure, holding time and heating rate are controlled within a fixed preset range, and composite material samples are prepared according to the set parameters. After the sample is hot-pressed, the interface region between PEI and thermosetting resin is sampled by focused ion beam or ultrathin sectioning technology for microstructure testing. Infrared spectroscopy or solid-state nuclear magnetic resonance analysis was performed on the interface region to obtain the intensity of the characteristic absorption peak of the PEI main chain, calculate the polymer chain segment retention rate Rp, and determine its degree of thermal degradation. Based on transmission electron microscopy combined with energy dispersive spectroscopy, the penetration depth Di of the PEI phase in thermosetting resin was obtained to characterize the physical fusion capability of the interface. The chain segment survival rate Rp and the interface penetration depth Di are input into the constructed interface coupling model, which is: Q=α·Rp+β·ln(Di+1); where α and β are weight coefficients preset according to the material system, and Q is the interface bonding quality factor; The interface strength level is determined based on the Q value of the interface quality factor, and when the Q value is lower than the set threshold, the hot pressing temperature, holding time or PEI toughening layer thickness parameters are backtracked to optimize the hot pressing process.

2. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 1, characterized in that: The etherimide toughening layer is in the form of a film, powder, or gel, with a thickness controlled between 1 and 25 μm.

3. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 1, characterized in that: The control of hot pressing temperature, pressure, holding time, and heating rate within a fixed preset range includes: setting the hot pressing temperature to 220-260℃, the pressure to 0.3-0.7MPa, the holding time to 30-90 minutes, and the heating rate to 2-5℃ / min.

4. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 3, characterized in that: The calculation of the polymer chain segment retention rate Rp includes: The PEI and thermosetting resin interface region sample extracted from the composite material sample after hot pressing was dried and then scanned with a Fourier transform infrared spectrometer to obtain the intensity of the characteristic carbonyl stretching vibration peak in the wavenumber range of 1775 cm-1 to 1720 cm-1. Using the characteristic peak intensity value of the PEI sample that has not degraded before hot pressing as a reference standard, the absorption peak area or peak height of the corresponding characteristic peak in the sample after hot pressing is measured. Through formula Calculate the polymer chain segment retention rate Rp, where A_after is the characteristic peak area of ​​the sample after hot pressing, and A_before is the characteristic peak area of ​​the standard sample before hot pressing.

5. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 4, characterized in that: The method of obtaining the penetration depth Di of the PEI phase in the thermosetting resin includes: A sample of the interface region containing the PEI toughening layer and the thermosetting resin was taken from the composite material after hot pressing. High-resolution imaging of the interface region was performed to observe the morphology, distribution and penetration path of the PEI phase in the interface region, and to identify the structural boundary of the transition from the PEI phase to the thermosetting matrix. Multi-point elemental scanning was performed within the TEM imaging region using energy dispersive spectroscopy (EDS) analysis to detect changes in the concentration gradient of PEI characteristic elements in the interface layer. Based on the spatial variation range of elemental concentration from high to low, and combined with the expansion distance of the PEI phase morphology in the image, the maximum effective diffusion distance of PEI towards the thermosetting resin is determined as the penetration depth Di.

6. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 5, characterized in that: The chain segment survival rate Rp and the interface penetration depth Di are input into the constructed interface coupling model, including: The chain segment retention rate Rp obtained by infrared spectroscopy or solid-state nuclear magnetic resonance testing, and the interface penetration depth Di obtained by transmission electron microscopy combined with energy dispersive spectroscopy analysis are used as input terms of the interface coupling model, which is constructed in the form of a combination of weighted linear and logarithmic functions. The interface bonding quality factor is used as an output term, and the resulting Q value is used to evaluate the overall bonding performance of the composite material interface under hot pressing conditions.

7. The method for toughening and molding high-performance PEI sheet for high heat-resistant structural components according to claim 6, characterized in that: The determination of interface strength level based on the interface quality factor Q value includes: when Q is greater than or equal to 110, the interface bonding performance is high; when Q is between 90 and 110, the interface bonding performance is medium; when Q is less than 90, the interface bonding performance is low, and process conditions need to be adjusted.

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