Epoxy damping prepreg resin of epoxy / amine dual-curing system and preparation method of epoxy damping prepreg resin

Abstract

The invention discloses epoxy damping prepreg resin of an epoxy / amine dual-curing system and a preparation method of the epoxy damping prepreg resin, and belongs to the technical field of prepreg resin preparation. The preparation method of the epoxy damping prepreg resin of the epoxy / amine dual-curing system comprises the following steps: grafting a polyurethane flexible chain segment to an epoxy resin side chain segment to prepare epoxy-terminated urethane resin; mixing the epoxy-terminated urethane resin with polyether triamine, and carrying out pre-curing, so as to obtain pre-cured resin; and mixing the pre-cured resin, dicyandiamide and a diaminoimidazole triazine complex, and carrying out final curing, so as to obtain the epoxy damping prepreg resin of the epoxy / amine dual-curing system. By regulating and controlling the curing degree, on the basis that the viscosity, viscosity and the like of the resin are freely adjusted to meet the requirements of a production process, the tensile strength, modulus, short-time bending creep and other mechanical properties of the prepreg resin cannot be greatly changed due to the adjustment of the viscosity and the viscosity, and meanwhile, the damping performance of the prepreg resin can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of prepreg resin preparation technology, and more specifically relates to an epoxy / amine dual-curing system epoxy damping prepreg resin and its preparation method. Background Technology

[0002] Composite materials, with their advantages of high specific strength, corrosion resistance, and strong functional designability, have been widely used in aerospace, vehicle engineering, and shipbuilding in recent years. During service, composite structures are subjected to various dynamic loads, leading to structural vibration instability and even component failure. Generally, increasing the loss factor and modal damping ratio of composite materials to effectively reduce the peak value of structural vibration is a recognized effective vibration reduction approach.

[0003] Currently, advanced composite material components are mostly high-stiffness and high-strength structures with excellent mechanical load-bearing performance, but poor damping and vibration reduction performance. Therefore, it is necessary to modify composite materials to increase damping and develop new damping composite materials. The damping mechanism of composite materials includes: viscoelasticity of the matrix and fibers, damping at the fiber-matrix interface, and damage-induced damping. However, the loss factor of the resin matrix is ​​much higher than that of the reinforcing fibers, so it can be considered that the damping of composite materials mainly originates from the resin matrix. Increasing the loss factor of the resin can effectively increase the damping of the composite material.

[0004] Prepregs, as raw materials in the production of high-quality advanced composite materials, are combinations of reinforcing fibers and specially formulated thermoplastic or thermosetting resins. As intermediates in composite material products, their properties directly affect the molding process and final performance of the composite material. Among various types of prepregs, epoxy prepregs are widely used due to their excellent mechanical properties, strong adhesion to various substrates, high corrosion and chemical resistance, and low curing shrinkage. The brittleness of epoxy resin is a major problem in its widespread application. The development of novel epoxy curing agents can improve the resin's toughness, the prepreg's resistance to humid heat aging, and its shelf life. Adding nanoparticles to the resin is also an effective technique to improve resin toughness. Studies have shown that adding end-epoxy nitrile butadiene rubber (ETBN) liquid rubber to the prepreg layer improves the interlaminar toughness of the composite material. Currently, research on epoxy prepregs mainly focuses on the curing kinetics, humid heat storage life, and epoxy toughening. However, there has been little research on the problem of low damping loss of epoxy prepregs, which makes it difficult to meet the design requirements of vibration reduction function of composite materials. Therefore, the development and research of new epoxy damping prepregs is particularly important. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy / amine dual-curing system epoxy damping prepreg resin and its preparation method, so as to solve the problems existing in the prior art, improve the damping loss of epoxy prepreg resin, and meet the needs of composite material vibration reduction design.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention is to provide a method for preparing an epoxy / amine dual-curing system epoxy damping prepreg resin, comprising the following steps:

[0008] A terminal epoxy urethane resin was prepared by grafting flexible polyurethane segments onto the side segments of epoxy resin.

[0009] The terminal epoxy urethane resin and polyether triamine are mixed and pre-cured to obtain a pre-cured resin;

[0010] The pre-cured resin, dicyandiamide, and curing accelerator are mixed and cured to obtain the epoxy / amine dual-curing system epoxy damping prepreg resin.

[0011] Preferably, the mass of the polyether triamine is 10-25% of the mass of the terminal epoxy urethane resin.

[0012] Preferably, the pre-curing temperature is 60–90°C and the time is 2–3 hours.

[0013] Preferably, the mass of the dicyandiamide is 3-4% of the mass of the terminal epoxy urethane resin; and the mass of the curing accelerator is 1.5-2% of the mass of the terminal epoxy urethane resin.

[0014] Preferably, the curing accelerator includes urea-based accelerators and / or modified imidazole-based curing accelerators, specifically including diaminoimidazolium triazine complexes. The curing accelerator mainly functions to reduce the curing temperature and time of dicyandiamide and adjust the shelf life of the prepreg resin, with minimal impact on resin properties.

[0015] Preferably, the curing temperature is 110–130°C, and the curing time is 2–3 hours. After curing, the product is removed and allowed to cool naturally to room temperature.

[0016] Preferably, the preparation steps of the terminal epoxy urethane resin include:

[0017] Toluene diisocyanate was added to polypropylene glycol for prepolymerization to obtain a polyurethane prepolymer.

[0018] Epoxy resin is added to the polyurethane prepolymer for grafting reaction to obtain the terminal epoxy urethane resin.

[0019] Preferably, during the prepolymerization, the molar ratio of -NCO in toluene diisocyanate to -OH in polypropylene glycol is 2 to 2.3:1.

[0020] Preferably, the prepolymerization temperature is 105–110°C and the time is 1–3 hours.

[0021] Preferably, the amount of epoxy resin used is determined by the amount of residual -NCO in the polyurethane prepolymer; the temperature of the grafting reaction is 105-110°C.

[0022] The second technical solution of the present invention provides an epoxy damping prepreg resin of an epoxy / amine dual-curing system prepared by the above preparation method.

[0023] The epoxy / amine dual-curing system epoxy damping prepreg resin provided by this invention solves the problem of low damping loss in prepreg resins. The specific mechanism is as follows:

[0024] This invention employs a pre-curing process using polyether triamine to terminally epoxy-terminated urethane resin, followed by final curing with a dicyandiamide and diaminoimidazolium triazine complex. By slightly adjusting the amount of polyether triamine as the curing agent, this invention can increase the degree of cure (DOC) of the resin during the pre-curing stage from 10% to 25% (e.g., ...). Figure 3 As shown in a), the content of epoxy groups only decreased slightly (as shown in a). Figure 3 (As shown in b). When the final curing was carried out under the condition that the amount of dicyandiamide curing agent and curing accelerator were kept consistent, the degree of cross-linking of the resin changed little. Although the degree of pre-curing of the resin changed, its strength and modulus did not fluctuate significantly. During this process, with the increase of polyether triamine dosage, the proportion of polyether soft segments in the resin cross-linking structure increased accordingly, and the content of freely moving molecular segments increased. This allows the resin molecular chains to slide freely between segments when subjected to dynamic loads, thereby enhancing the dynamic energy loss between resin segments. This improved the damping performance of the prepreg resin without significantly affecting tensile strength, modulus, and short-term flexural creep.

[0025] On the other hand, the product quality of prepreg resin is closely related to its viscosity-temperature characteristics and room-temperature viscosity. The viscosity-temperature characteristics of the resin determine the uniformity of the prepreg resin film and the wettability of the fibers, while the room-temperature viscosity mainly reflects the prepreg resin's layup processability. The ideal coating viscosity of prepreg resin is generally in the range of 10,000–20,000 mPa·s. High viscosity resin is difficult to form a uniform film, while low viscosity resin is prone to overflow during coating. For the commercial use of automated layup technology for large structures, the viscosity parameters of the prepreg resin layup process are crucial to the automated layup process. In particular, adjusting the program parameters of the coating equipment and the layup temperature during production to match the resin's hot-melt coating viscosity and layup tack often adds extra costs to composite material manufacturing. Therefore, customizing the required resin coating viscosity and layup tack according to the parameters in the production equipment can save costs and time for prepreg resin production and composite product manufacturing. This invention allows for the customization of prepreg resins with specific coating viscosities and adhesion properties by adjusting the amount of polyether triamine curing agent, thus meeting specific needs in actual industrial production processes. The specific mechanism is as follows:

[0026] This invention regulates the pre-curing degree of terminal epoxy-based urethane resin by adjusting the amount of polyether triamine curing agent, thereby enabling the pre-cured resin to form a network cross-linked structure of varying degrees (e.g., Figure 2 (As shown). During this process, as the degree of cross-linking increases, the molecular weight of the resin increases significantly, thereby changing the overall viscosity and viscousness of the liquid flexible end-epoxy urethane resin, which can meet the specific requirements of the prepreg resin production process.

[0027] The present invention discloses the following technical effects:

[0028] This invention provides a novel method for preparing epoxy damping prepreg resin based on a dual-curing system, solving the problem of low damping loss in prepreg resins. This invention uses polyether triamine to pre-cur an epoxy-terminated urethane resin, followed by final curing with a dicyandiamide and diaminoimidazolium triazine complex. The greatest advantage of this formulation design is that it not only has no significant impact on tensile strength, modulus, and short-term flexural creep, but also improves the damping performance of the prepreg resin. When the amount of polyether triamine relative to the epoxy-terminated urethane resin is increased from 10 wt% to 25 wt%, the loss factor of the prepreg resin increases from 0.09 to 0.14. Furthermore, this invention can also customize prepreg resins with specific coating viscosities and lay-up tack by adjusting the amount of polyether triamine curing agent to meet specific needs. Attached Figure Description

[0029] Figure 1 A diagram illustrating the specific synthesis reaction mechanism of terminal epoxy-based urethane resins;

[0030] Figure 2This is a diagram illustrating the pre-curing mechanism during the synthesis of prepreg resin.

[0031] Figure 3 The DSC exothermic peak curve (a) and FT-IR spectrum (b) of the precured resin obtained in Example 1 are shown.

[0032] Figure 4 The viscosity (a) and lay-up tack (b) of the prepreg resin obtained in Example 1;

[0033] Figure 5 The tensile stress-strain curve of the prepreg resin obtained in Example 1 is shown.

[0034] Figure 6 The curves showing the changes in storage modulus (a), loss modulus (b), and loss factor (c) of the prepreg resin obtained in Example 1 with temperature are shown.

[0035] Figure 7 The curves showing the changes in dynamic storage modulus (a), loss factor (b), and frequency of the prepreg resin obtained in Example 1 are shown.

[0036] Figure 8 The curve shows the effect of T403 dosage on the short-term bending creep of the prepreg resin obtained in Example 1. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0043] Unless otherwise specified, all raw materials used in the following embodiments and performance tests of this invention are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0044] The polypropylene glycol (PPG2000, molecular weight 2000) used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; toluene diisocyanate (TDI-80) was purchased from Shandong Baiqian Chemical Co., Ltd.; epoxy resin DGEBA (E44, epoxy equivalent EE = 227 g / mol) was purchased from Yuehua Organic Chemical Plant of Yueyang Petrochemical General Plant; polyether triamine (T403) was purchased from Zhongshan Ousbang New Materials Co., Ltd., brand name Huntsman T403; latent curing agent dicyandiamide (DICY, solid powder particle size of 5-10 μm) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; latent curing accelerator diaminoimidazolium triazine complex (GYHT110, solid powder particle size of 2-5 μm) was purchased from Guangdong Guyan Electronic Materials Co., Ltd.; and defoamer (Deform6800) was purchased from Dow Corning Inc.

[0045] Prepreg tape made of glass fiber / prepreg resin (256g / m) 2 The process was outsourced to Xianning Haiwei Composite Materials Co., Ltd., and the resin tack test was conducted using prepreg tape, i.e., the prepreg tack test.

[0046] Example 1

[0047] In this embodiment, six prepreg resins with different amounts of polyether triamine, dicyandiamide, and diaminoimidazolium triazine complex were prepared, as detailed below:

[0048] (1) Synthesis of epoxy-terminated urethane resin (EUR):

[0049] Polyurethane flexible segments were grafted onto epoxy resin side segments using molecular design. PPG2000 and TDI-80 were weighed at a molar ratio of -NCO to -OH of 2.1:1. PPG2000 was poured into a three-necked flask equipped with a stirrer and thermometer, and dehydrated under reduced pressure by distillation for 2 hours under nitrogen protection. Then, the temperature of the PPG2000 material was maintained at 80°C and stirred. TDI-80 was added dropwise to the three-necked flask using a constant-pressure dropping funnel, with the reaction temperature maintained between 85°C and 105°C during the dropwise addition. After the addition was complete, the reaction temperature was gradually increased to 105°C to continue the reaction. During the reaction, after 1 hour of reaction, samples were taken, and the -NCO content in the system was continuously measured using chemical analysis until the theoretical value of 3.2% was reached. After the polyurethane prepolymer cooled to 90°C, E44 was weighed and added to the prepolymer, ensuring a molar ratio of E44 to residual -NCO in the prepolymer of 1.1:1. The reaction temperature was then slowly increased to 105°C to continue the reaction, with high-speed stirring and continuous monitoring of the -NCO content until the -NCO content reached the theoretical value of 0% (actual values ​​ranged from 0.05% to 0.1%), indicating the synthesis reaction was complete. The epoxy equivalent EE of EUR was determined to be 350.87 g / mol according to GB / T4612-2008 standard.

[0050] The specific synthesis reaction mechanism of terminal epoxy urethane resins is as follows: Figure 1 As shown.

[0051] Synthesis of prepreg resin:

[0052] EUR and T403 were added to a three-necked flask according to the proportions in Table 1, and the pre-curing reaction was carried out at 80°C for 2 hours (500 r / min) to obtain pre-cured resin. Then, DICY and GYHT110 were added to the pre-cured resin at 80°C, and the mixture was stirred at 1000 r / min for 20 minutes using a mechanical stirring disc. The mixture was then poured into a mold for curing and cured at 120°C for 3 hours to obtain prepreg resin.

[0053] Table 1 Prepreg Resin Formulation

[0054]

[0055] The pre-curing mechanism during the synthesis of prepreg resin is as follows: Figure 2 As shown.

[0056] To investigate the relationship between curing agent dosage and degree of cure (DOC), i.e., the linear relationship between curing agent dosage and resin pre-curing degree, the pre-cured resin prepared above was tested using two methods (DSC exothermic peak peak area calculation and FT-IR epoxy stretching vibration peak intensity calculation) to evaluate the relationship between resin DOC and curing agent dosage.

[0057] Differential Scanning Calorimetry (DSC): The heat flux and total heat of reaction of the pre-cured resin were tested using a DSC (200F3 Maia, Netzsch, Germany). The pre-cured resin was weighed using a Mettler Toledo balance with an accuracy of ±0.01 mg. The sample chamber was purged with nitrogen at a rate of 50 mL / min. To determine the relationship between DOC and curing agent dosage, the pre-curing stages with different T403 contents were studied. A series of dynamic DSC tests were performed by heating the sample from 25 °C to 250 °C at a heating rate of 5 °C / min.

[0058] Fourier Transform Infrared Spectroscopy: The functional groups at each stage of resin preparation were characterized using a Fourier Transform Infrared Spectrometer (TENSORII, Bruker Beijing Technology Co., Ltd.). Test conditions: 4 cm⁻¹ resolution. -1 The number of scans was 16, and the test range was 400–4000 cm. -1 The degree of cure (DOC) is calculated using the following formula: 916 cm⁻¹ -1 The intensity of the stretching resonance peak at the epoxy group.

[0059] Among them, I0, I t I ∞ These represent the samples at 916 cm⁻¹. -1 Peak intensity at the beam location during the initial, B-level pre-curing, and C-level final curing stages of the sample. Note that formulation T403-100% is a stoichiometric dosage, belonging to the C-level final curing stage.

[0060] The results are as follows Figure 3 As shown in Table 2.

[0061] Table 2 shows the test results of DSC and FT-IR and the calculated values ​​of curing degree.

[0062]

[0063] Figure 3 The DSC exothermic peak curve (a) and FT-IR spectrum (b) of the precured resin obtained in Example 1 are shown.

[0064] Figure 3The table shows the DSC exothermic curves of the pre-cured resin under different T403 dosages, and Table 2 lists the specific data of the exothermic curves. The data in the table shows that the exothermic peak onset temperature gradually increases with decreasing T403 dosage. This is because the amine functional group content gradually decreases, and the epoxy groups and amine functional groups require higher activation energy for ring-opening, resulting in a stepwise polymerization reaction. Comparing the experimental DOC value calculated by peak area with the theoretical predicted DOC value, the error between the two is found to be within 10%. The data in the table shows that the transmission peak intensity of the epoxy group gradually increases, representing a larger base for the ring-opening reaction between the epoxy group and the amine functional group. Calculating the resin's DOC change using the epoxy group peak intensity shows that the difference between the calculated peak intensity DOC value and the theoretical predicted DOC value is within 10%, which also verifies the DSC test results. Furthermore, FT-IR spectra reveal that at 1100 cm⁻¹... -1 Under the beam, the stretching vibration peaks associated with ether bonds (-ROR-) did not disappear, suggesting that the pre-curing reaction mainly involves the stepwise three-dimensional polymerization of primary and secondary amines with epoxy groups (e.g., Figure 1 As shown in the diagram, etherification almost never occurs. This is because etherification requires a higher activation energy compared to the former reaction. DSC and FT-IR test results, along with theoretical predictions, show that the error between DOC values ​​is within 10%, indicating a good consistency between the T403 dosage and the degree of curing. When the amount of curing agent is reduced, the resin begins a self-limiting reaction after the reaction has progressed to a certain extent. This allows for precise design of the resin crosslinking network structure by adjusting the amount of curing agent, enabling adjustments to the resin's performance parameters within a certain range. Therefore, this invention demonstrates that by adjusting the amount of polyether triamine curing agent, it is possible to customize prepreg resins with specific coating viscosities and lay-up tack to meet specific needs.

[0065] Performance testing:

[0066] 1. Viscosity and tackiness test:

[0067] The viscosity-temperature characteristics of the prepreg resin were tested using a BROOKFIELD CAP 2000+ high-shear cone viscometer. The test temperature range was 50–120°C. The viscosity was tested once every 5°C increase in temperature. Each group of samples was tested three times, and the average value was taken.

[0068] The probe method adhesion test was used to test the adhesion of prepreg resin during installation. The probe used for the adhesion test had a diameter of 10 mm and was made of smooth stainless steel. The prepreg tape was left to stand at room temperature (25°C) for 24 hours. First, a force of 10 N was applied to the surface of the prepreg tape. Then, the probe was moved upwards at a speed of 2 mm / min, and the maximum resistance to this movement was taken as the adhesion force of the prepreg resin.

[0069] The results are as follows Figure 4 As shown.

[0070] Figure 4 The viscosity (a) and lay-up tack (b) of the prepreg resin obtained in Example 1 are shown.

[0071] Prepreg resin coating viscosity and lay-up tack are considered two important process parameters in the production of prepreg resins, and these two properties are strongly affected by the degree of pre-curing. Figure 4 Figure a shows that as the degree of pre-curing increases, the resin viscosity increases linearly. Compared with uncured EUR resin, it was found that when the amount of curing agent T403 was 10%, the viscosity at 50°C increased by about 400%. As the amount of curing agent T403 increased to 25%, the resin viscosity at 50°C increased linearly, nearly 10 times that of uncured EUR resin. This indicates that in the prepreg resin coating stage, the viscosity-temperature characteristics of the resin can be changed by adjusting the amount of curing agent T403, thereby adjusting the resin coating viscosity and customizing the required prepreg resin viscosity according to relevant coating parameters.

[0072] Figure 4 Figure b shows that when the amount of curing agent T403 is 5%, the prepreg resin is in a low-viscosity liquid state with certain fluidity, exhibiting a low viscous force. As the amount of curing agent T403 increases to 15%, the viscous force of the prepreg resin reaches its maximum. This is because during the pre-curing process, the terminal epoxy groups of EUR undergo a polycondensation reaction with the primary and secondary amines of T403. Since T403 contains triamine functional groups, at lower T403 dosages, the prepreg resin forms a branched cross-linked structure, reducing the number of freely moving chain segments, resulting in an almost linear increase in viscosity. However, when the amount of prepreg agent T403 exceeds 20%, the viscosity of the prepreg resin begins to decrease, mainly due to excessive cross-linking. The prepreg resin begins to exhibit a gel-like state. When the amount of prepreg agent T403 reaches 30%, the resin is almost initially cured, and the surface has almost no tackiness.

[0073] 2. Tensile property test:

[0074] The tensile strength of the prepreg resin specimens obtained in Example 1 was tested using a universal tensile testing machine (CMT4204, MTES Industrial Systems (China) Co., Ltd.) according to GB / T528-2009 standard. The loading rate was 2 mm / min, and each group of specimens was tested 5 times and the average value was taken.

[0075] The results are as follows Figure 5 As shown in Table 3.

[0076] Table 3. Tensile property data of the prepreg resin obtained in Example 1

[0077]

[0078] Figure 5 The tensile stress-strain curve of the prepreg resin obtained in Example 1 is shown.

[0079] Depend on Figure 5 As shown in Table 3, the higher the pre-curing degree of the prepreg resin, the higher its elongation at break. This is because the increased amount of long-chain polyether triamine T403, after partial cross-linking with the resin, causes a large number of long-chain segments to curl. When subjected to continuous tensile load, the curled segments are straightened, resulting in an increase in elongation. The increased pre-curing degree means that the tensile modulus and strength of the prepreg resin are almost unaffected. Generally, the properties of composite resins mainly exhibit the properties in the transverse tensile direction of the laminate. According to the theory of composite mixing ratio, a 5% change in the resin's modulus and strength has a negligible impact on the performance of the composite laminate. Within the DOC range of 0-25%, the change in modulus and strength is within 5%, which has a negligible impact on the static tensile properties of the composite material. Therefore, the change in tensile properties can be considered to be within an acceptable range, meaning that it has no effect on tensile strength and modulus.

[0080] 3. Viscoelasticity test:

[0081] The dynamic viscoelastic temperature spectrum and frequency spectrum of the prepreg resin sample obtained in Example 1 were tested using a dynamic thermomechanical analyzer (DMA1, METTLER TOLEDO, Switzerland). Both the temperature spectrum and frequency spectrum were tested in three-point bend mode. The temperature spectrum was tested at a frequency of 1 Hz, with a heating rate of 3 °C / min and a temperature scan range of -10 to 150 °C. The frequency spectrum was tested at a temperature of 25 °C, with a sweep frequency range of 1 to 1000 Hz.

[0082] The short-term creep behavior test was conducted in a three-point bend mode at a temperature of 25°C, with a stress load of 1.0 MPa and a scan duration of 21,000 s.

[0083] The results are as follows Figures 6-8 As shown.

[0084] Figure 6 The curves show the changes in storage modulus (a), loss modulus (b), and loss factor (c) of the prepreg resin obtained in Example 1 with temperature.

[0085] exist Figure 6 The storage modulus variation graph of α shows that in the range of 10-30℃, the dynamic modulus and static tensile modulus of the prepreg resin are almost the same. The dynamic modulus of the prepreg resin is the highest when there is no T403 pre-curing. As the degree of pre-curing increases, the dynamic modulus decreases slightly. Figure 6The loss modulus variation curve shows an opposite trend to that of the dynamic storage modulus. This is mainly due to the pre-curing of polyether triamine, which increases the flexibility of the molecular chains and reduces the density of the crosslinking network between molecular chains. In the final curing stage of DICY, the rigid curing agent begins to crosslink, leading to an increase in the rigidity of the resin chain segments and an increase in the crosslinking density. Figure 6 The curve in Figure c shows that as the amount of T403 increases, the glass transition temperature (T) of the prepreg resin decreases. g The temperature shifts towards lower temperatures, and the peak value gradually increases. This is because the increased use of T403 during the pre-curing stage leads to a higher content of soft segments in the prepreg resin, increased molecular chain flexibility, and a lower molecular chain freezing temperature, resulting in a higher T403 content in the prepreg resin. g Shifting towards lower temperatures. T403-25% compared to T403-10% T g The temperature shifted by 20°C towards lower temperatures. Furthermore, when the T403 content was 15%, the curve showed two distinct peaks, indicating that microphase separation occurred in the prepreg resin during T403 pre-curing and DICY final curing, broadening the glass transition region of the prepreg resin. This often leads to hysteresis and mechanical loss in the prepreg resin over a wide temperature range, which is related to… Figure 6 The loss modulus of b changes in a consistent manner.

[0086] To reduce the line spectral peaks at different resonant frequencies in composite material structures, the composite material needs to have a high loss factor over a wide frequency band. Therefore, the prepreg resin must possess wide-bandwidth high damping loss characteristics. In the vibration reduction design stage of composite material structures, the loss factor of the material is mostly frequency-dependent. Therefore, by using temperature-frequency conversion, the dynamic viscoelasticity of the prepreg resin as a function of temperature can be reflected in the frequency domain at a specific temperature. Figure 7 The curves showing the dynamic storage modulus (a), loss factor (b), and frequency domain variation of the prepreg resin obtained in Example 1 are shown.

[0087] Figure 7 The results in section a show that, within the test frequency band, the dynamic modulus decreases slightly with the increase of pre-curing degree, which is consistent with the variation law in the temperature spectrum of dynamic viscoelastic properties. Figure 7 The results in section b show that the loss factor increases with increasing degree of curing. Throughout the entire frequency range, the prepreg resin exhibits high damping loss characteristics, which is related to the large number of flexible coiled molecular chains present after cross-linking. The elongation deformation of the coiled segments exhibits a hysteresis effect under alternating loads; the elongated segments are difficult to quickly recover their original state, thus increasing the mechanical loss properties of the prepreg resin. When the T403 content is 10%, the loss factor of the resin across the entire frequency range is 0.09. When the T403 content increases to 25%, the loss factor increases to 0.14, an increase of nearly 50%.

[0088] Figure 8 The curve shows the effect of T403 dosage on the short-term bending creep of the prepreg resin obtained in Example 1.

[0089] Depend on Figure 8 It is known that the creep characteristics of prepreg resin exhibit three stages: instantaneous deformation, primary creep, and secondary creep. Prepreg resin does not show large deformations characteristic of tertiary creep; this type of creep typically occurs only under large stress loads and prolonged stress. As the pre-curing degree of the prepreg resin increases, the flexural creep increases significantly. Prepreg resin exhibits low creep characteristics without T403 pre-curing. When 10% T403 is introduced for pre-curing, the resin's creep increases, and the flexural strain increases by 17.1%. When the T403 content reaches 25%, the flexural strain increases by 69.3%. Prepreg resin fully cured with T403 exhibits the worst creep resistance, with a 98.3% increase in flexural strain compared to prepreg resin fully cured with DICY. Analysis of the increasing flexural strain trend suggests that the prepreg resin introduces flexible segments into the T403 pre-cured crosslinking network. Under prolonged load, these segments are prone to slippage, leading to increased flexural deformation. During the pre-curing stage, the triamine functional groups of T403 undergo ring-opening with the terminal epoxy groups, forming a dendritic cross-linked network. In the final curing stage, some of the uncured segments and the formed dendritic network constitute an interpenetrating polymer network, which to some extent restricts large deformation slip between segments and reduces the creep behavior of the resin. Therefore, the prepreg resin exhibits high damping loss characteristics without significantly increasing flexural creep.

[0090] The above test results demonstrate that this invention utilizes an epoxy / amine dual-curing system to prepare a novel damping prepreg resin with customizable viscosity and tack. Pre-curing the synthesized terminal epoxy urethane resin with polyether triamine allows for control of the resin's viscosity and lay-up tack by adjusting the amount of polyether triamine. Under secondary curing with dicyandiamide, the tensile modulus and strength of the prepreg resin are almost unaffected by the degree of pre-curing. After pre-curing, the prepreg resin forms a dendritic network structure, which, together with the dicyandiamide-cured chain segments, constitutes an interpenetrating network structure, increasing the microphase separation and loss factor of the prepreg resin. Compared to prepreg resin without T403 pre-curing, the loss factor of the prepreg resin increases by 10-50%, with a loss factor ranging from 0.09 to 0.15. Simultaneously, under a creep test lasting 21,000 s, the flexural strain of the resin increases by 17-70%. While exhibiting high damping loss characteristics, the prepreg resin did not significantly increase flexural creep.

[0091] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0092] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an epoxy / amine dual-curing system epoxy damping prepreg resin, characterized in that, Includes the following steps: A terminal epoxy urethane resin was prepared by grafting flexible polyurethane segments onto the side segments of epoxy resin. The terminal epoxy urethane resin and polyether triamine are mixed and pre-cured to obtain a pre-cured resin; The pre-cured resin, dicyandiamide, and curing accelerator are mixed and cured to obtain the epoxy / amine dual-curing system epoxy damping prepreg resin.

2. The preparation method according to claim 1, characterized in that, The mass of the polyether triamine is 10-25% of the mass of the terminal epoxy urethane resin.

3. The preparation method according to claim 1, characterized in that, The pre-curing temperature is 60–90°C, and the time is 2–3 hours.

4. The preparation method according to claim 1, characterized in that, The mass of the dicyandiamide is 3-4% of the mass of the terminal epoxy urethane resin; the mass of the curing accelerator is 1.5-2% of the mass of the terminal epoxy urethane resin; the curing accelerator includes urea accelerators and / or modified imidazole curing accelerators.

5. The preparation method according to claim 1, characterized in that, The curing temperature is 110–130°C, and the time is 2–3 hours.

6. The preparation method according to claim 1, characterized in that, The preparation steps of the terminal epoxy urethane resin include: Toluene diisocyanate was added to polypropylene glycol for prepolymerization to obtain a polyurethane prepolymer. Epoxy resin is added to the polyurethane prepolymer for grafting reaction to obtain the terminal epoxy urethane resin.

7. The preparation method according to claim 6, characterized in that, During the prepolymerization process, the molar ratio of -NCO in toluene diisocyanate to -OH in polypropylene glycol is 2 to 2.3:

1.

8. The preparation method according to claim 6, characterized in that, The prepolymerization temperature is 105–110°C, and the time is 1–3 hours.

9. The preparation method according to claim 6, characterized in that, The amount of epoxy resin used is determined by the amount of residual -NCO in the polyurethane prepolymer; the temperature of the grafting reaction is 105-110°C.

10. The epoxy / amine dual-curing system epoxy damping prepreg resin prepared by the preparation method according to any one of claims 1 to 9.

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