Low-temperature toughened hydroxyl branched polymer modified epoxy resin composite material as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature toughened hydroxyl branched polymer modified epoxy resin composite material and a preparation method and application thereof, and belongs to the technical field of composites.The preparation method comprises the steps that 1, 4-butanediol and trimethylolpropane triglycidyl ether serve as raw materials and are subjected to a heating reaction under the action of a catalyst, and a hydroxyl branched polymer is obtained; the polymer is blended with epoxy resin and a curing agent to prepare a mixed solution, the mixed solution is subjected to defoaming treatment to obtain an epoxy resin blend, the epoxy resin blend is cast in a pretreated mold to be cured, and the hydroxyl branched polymer modified epoxy resin composite material is obtained. The epoxy resin is modified through the hydroxyl branched polymer, so that the tensile strength, bending strength and impact toughness of the modified epoxy resin composite material at low temperature are remarkably improved compared with those of pure epoxy resin, and the problem of high brittleness of traditional epoxy resin after curing is solved.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, its preparation method, and its application. Background Technology

[0002] Epoxy resin, as a widely used polymer material, has advantages such as high mechanical strength, low curing shrinkage, good chemical stability, excellent electrical insulation properties, and good thermal stability. It is widely used in aerospace resin-based composite materials, electronic and electrical packaging, automobiles, and other fields with stringent requirements for the comprehensive performance of resin matrix materials.

[0003] However, epoxy resins form a highly dense three-dimensional cross-linked network structure during the curing process, resulting in inherent brittleness, limited impact resistance and fracture toughness. Especially at low temperatures, the mobility of molecular chain segments is further restricted, making the material more prone to brittle fracture. This significantly reduces its reliability and safety under low-temperature conditions, limiting the further application of epoxy resins in low-temperature environments. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, its preparation method, and its application. By incorporating hydroxyl-branched polymers into epoxy resin, this invention significantly improves the tensile strength, flexural strength, and impact toughness of the modified epoxy resin composite material at low temperatures, overcoming the problem of high brittleness after curing of traditional epoxy resins.

[0005] One objective of this invention is to provide a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material. The hydroxyl-branched polymer is prepared by mixing 1,4-butanediol, trimethylolpropane triglycidyl ether, and tetrabutylammonium bromide under an inert atmosphere and heating to react. Using epoxy resin as a matrix, the hydroxyl-branched polymer and a curing agent are added to the epoxy resin matrix, followed by solution blending and curing to obtain the low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material. The mass ratio of 1,4-butanediol, trimethylolpropane triglycidyl ether and tetrabutylammonium bromide is (21~23):(150~153):(12~14); The amount of the hydroxyl-branched polymer added is 5-25% of the mass of the epoxy resin, preferably 5%, 10%, 15%, 20%, or 25%. The curing agent is added at a rate of 75% to 85% of the epoxy resin mass.

[0006] This invention involves mixing 1,4-butanediol with trimethylolpropane triglycidyl ether, adding tetrabutylammonium bromide, and heating to react and obtain a hydroxyl-branched polymer. This polymer is then mixed with epoxy resin, a curing agent is added, and the mixture is defoamed and cured by casting to obtain a hydroxyl-branched polymer-modified epoxy resin composite material. Because the hydroxyl-branched polymer contains a large number of hydroxyl groups, it achieves good compatibility with epoxy resin when blended, ensuring uniform dispersion within the epoxy resin and avoiding phase separation or other adverse effects. Furthermore, the highly branched structure and abundant epoxy groups of the hydroxyl-branched polymer effectively improve the strength and toughness of the epoxy resin.

[0007] Furthermore, the heating reaction temperature is 120℃~150℃, and the reaction time is 3h~5h.

[0008] Furthermore, the curing agent is methylhexahydrophthalic anhydride.

[0009] Furthermore, the curing temperature is 130℃~150℃, and the curing time is 20h~35h.

[0010] A second objective of this invention is to provide a method for preparing the above-mentioned low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, comprising the following steps: Under an inert atmosphere, 1,4-butanediol and trimethylolpropane triglycidyl ether were mixed evenly, and then tetrabutylammonium bromide was added. After heating, the reaction was carried out to obtain a hydroxyl-branched polymer. Using epoxy resin as a matrix, 5% to 25% of the hydroxyl-branched polymer and curing agent by mass of epoxy resin are added to the epoxy resin matrix and mixed evenly to obtain a mixed solution. The mixed solution is defoamed to obtain an epoxy resin blend. The epoxy resin blend is cast into a pretreated mold and cured to obtain a hydroxyl-branched polymer modified epoxy resin composite material.

[0011] Furthermore, the specific method for defoaming treatment is as follows: the mixed solution is vacuumed at 40~60℃ for 5min~10min, and after vacuuming, it is taken out and placed in a forced-air drying oven at 50℃~60℃. After the bubbles in the mixed solution disappear, it is taken out and stirred for another 5min~10min. Then it is placed in a forced-air drying oven at 50℃~60℃ for 10min~20min to dry.

[0012] Furthermore, the pretreatment method for the mold is as follows: first, rinse the mold with deionized water 2 to 4 times, then clean it with anhydrous ethanol 3 to 5 times, and finally, when the epoxy resin is curing, place the mold in a drying oven for preheating. The preheating temperature is the curing temperature of the epoxy resin.

[0013] A third objective of this invention is to provide the application of the above-mentioned hydroxyl-branched polymer-modified epoxy resin composite material in aerospace resin-based composite materials.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, hydroxyl-branched polymers are prepared by mixing and heating 1,4-butanediol, trimethylolpropane triglycidyl ether, and tetrabutylammonium bromide under an inert environment. The hydroxyl-branched polymer and a curing agent are then added to an epoxy resin matrix, and the hydroxyl-branched polymer-modified epoxy resin composite material is obtained by solution blending and curing. This invention uses epoxy resin as a matrix and modifies it by introducing 5%–25% (by mass) of hydroxyl-branched polymer and 75%–85% (by mass) of curing agent. While ensuring the integrity of the epoxy resin crosslinking network structure, this proportion of hydroxyl-branched polymer constructs a uniformly dispersed microphase structure in the system, significantly improving the fracture toughness of the epoxy resin composite material. Simultaneously, by adjusting the amount of curing agent added, the crosslinking density of the epoxy resin is changed, providing reliable mechanical strength support for the material. The toughening effect of hydroxyl-branched polymers and the strength-supporting effect of curing agents form a synergistic effect of "toughness enhancement - strength support". This synergistic effect effectively solves the technical problem that epoxy resins are prone to insufficient strength or increased brittleness when the crosslinking density is controlled by curing agents alone, especially at low temperatures of -80℃, and it is difficult to balance strength and toughness. This enables the modified epoxy resin composite material to have good mechanical strength and toughness at the same time in the low temperature environment of -80℃, and ultimately achieves a synergistic improvement in the strength and fracture toughness of epoxy resin composite materials.

[0015] (2) The mechanical properties of the hydroxyl-branched polymer modified epoxy resin composite material prepared by the present invention are greatly improved compared with the unmodified epoxy resin material. Moreover, the preparation process of the present invention is simple and suitable for large-scale production, which is of great significance to the application prospects of epoxy resin composite materials. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation route of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention.

[0017] Figure 2 The Fourier transform infrared spectrum of the hydroxyl-branched polymer prepared in Example 1 of the present invention is shown; wherein, a represents 1,4-butanediol, b represents trimethylolpropane triglycidyl ether, and c represents the hydroxyl-branched polymer.

[0018] Figure 3The images shown are scanning electron microscope images of the impact fracture surfaces of the hydroxyl-branched polymer-modified epoxy resin composite material in Example 1 of the present invention under different fracture temperature conditions. Here, a represents the fracture surface morphology under room temperature conditions, and b represents the fracture surface morphology under low temperature conditions.

[0019] Figure 4 This is a bar chart showing the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. Specifically, a and b represent the tensile strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively; c and d represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively; e and f represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively; g and h represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively; i and j represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively; and k and l represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively.

[0020] Figure 5 This is a bar chart showing the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. Specifically, a and b represent the flexural strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively; c and d represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively; e and f represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively; g and h represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively; i and j represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively; and k and l represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively.

[0021] Figure 6This is a bar chart showing the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. a and b represent the impact strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively. c and d represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively. e and f represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively. g and h represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively. i and j represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively. k and l represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively. Detailed Implementation

[0022] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0023] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0024] The three-dimensional cross-linked network structure formed after curing of unmodified epoxy resin in the background art of this invention results in high brittleness, leading to a decrease in the mechanical properties of epoxy resin and thus limiting its application. Based on the above technical problems, this invention provides a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, its preparation method, and its application.

[0025] The technical solution of the present invention will be described in detail below.

[0026] This invention provides a method for preparing a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, referring to... Figure 1 It includes the following steps: Step S1: Preparation of hydroxyl-branched polymer: 1,4-Butanediol and trimethylolpropane triglycidyl ether were mixed and stirred until the system was homogeneous. Tetrabutylammonium bromide was added, and the mixture was heated to react and obtain a hydroxyl-branched polymer. Step S2: Preparation of hydroxyl-branched polymer-modified epoxy resin composite material: Epoxy resin E51 was mixed with the obtained hydroxy-branched polymer and stirred evenly. A curing agent was added to prepare a mixed solution. The mixed solution was defoamed to obtain an epoxy resin blend. The epoxy resin blend was cast into a pretreated mold and cured to obtain a hydroxy-branched polymer modified epoxy resin composite material. The curing agent is methyl hexahydrophthalic anhydride, and the amount added is 75-85% of the mass of epoxy resin E51. The amount of the hydroxyl-branched polymer added is 5-25% of the mass of epoxy resin E51, preferably 5%, 10%, 15%, 20%, or 25%.

[0027] In the above technical solution, 1,4-butanediol and trimethylolpropane triglycidyl ether are mixed, and tetrabutylammonium bromide is added and heated to react to obtain a hydroxyl-branched polymer; then the polymer is mixed with epoxy resin, a curing agent is added, and the mixture is defoamed and cast to cure, thus obtaining a hydroxyl-branched polymer modified epoxy resin composite material. Since the hydroxyl-branched polymer contains a large number of hydroxyl groups in its structure, it can achieve good compatibility with epoxy resin when blended, ensuring that it is uniformly dispersed in the epoxy resin and avoiding phase separation or other adverse effects. Moreover, the hydroxyl-branched polymer has a highly branched structure and a large number of epoxy groups, which can effectively improve the mechanical properties and toughness of epoxy resin.

[0028] Regarding the addition amounts of the curing agent and hydroxyl-branched polymer, the curing agent in the system of this invention is used to react with epoxy groups to construct a three-dimensional cross-linked network, and its addition amount directly affects the cross-linking density and network structure of the system. When the amount of curing agent added is less than 75% of the mass of epoxy resin E51, the epoxy group reaction is incomplete, the cross-linking density is insufficient, and the resulting material has low mechanical strength and heat resistance, as well as poor performance stability. When the amount of curing agent added is more than 85% of the mass of epoxy resin E51, the cross-linking density of the system is too high, the network structure is too dense, the mobility of molecular chain segments is restricted, the brittleness of the material increases significantly, which is not conducive to energy dissipation under impact loads, thus leading to a decrease in toughness. The hydroxyl-branched polymer, as a modifying component of this invention, plays a role in improving the fracture behavior of epoxy resin by introducing a flexible branched structure and microphase interface. When its addition amount is less than 5% of the mass of epoxy resin E51, the content of hydroxyl branched polymer is insufficient, making it difficult to form an effective energy-dissipating structure in the system. This results in limited inhibition of crack propagation and an insignificant toughening effect. When its addition amount is more than 25% of the mass of epoxy resin E51, the proportion of flexible segments in the system is too high, leading to a decrease in the overall crosslinking density. This may also cause coarsening of the microphase structure, thereby weakening the stress transmission capacity and reducing the tensile, bending, and other load-bearing properties of the material.

[0029] When the amount of 1,4-butanediol is too low, there are insufficient linear segments in the system, resulting in excessively high branching density. This leads to a low molecular weight and overly dense structure in the resulting hydroxyl-branched polymer, which has poor compatibility with epoxy resin and makes it difficult to form an effective energy-dissipating microphase structure, thus weakening the toughening effect. When the amount of 1,4-butanediol is too high, the proportion of linear segments is too high, the degree of branching decreases, and the resulting product tends to be a linear oligomer, making it difficult to exert the inhibitory effect of the branched structure on crack propagation. When the amount of trimethylolpropane triglycidyl ether is too low, there are insufficient branching points, making it difficult to form a stable branched structure, and the hydroxyl density is too low. The following conditions are considered unfavorable for the formation of effective interfacial interactions with the epoxy network: When the amount of trimethylolpropane triglycidyl ether is too high, there are too many branching points, making the system prone to gelation or the formation of insoluble structures, resulting in poor product solubility and dispersibility, affecting subsequent processing and material performance stability; when the amount of tetrabutylammonium bromide is too low, the catalysis is insufficient, the reaction is difficult to proceed completely, leading to unstable product structure and a wide molecular weight distribution; when the amount of tetrabutylammonium bromide is too low or too high, the reaction rate is too fast, easily triggering local overreactions or side reactions, resulting in uneven product structure, which is not conducive to obtaining stable hydroxyl-branched polymers. Therefore, in order to prepare high-performance hydroxyl-branched polymers, this invention selects a mass ratio of 1,4-butanediol, trimethylolpropane triglycidyl ether, and tetrabutylammonium bromide of (21~23):(150~153):(12~14).

[0030] To prepare high-performance hydroxyl-branched polymer-modified epoxy resin composites, the heating reaction in step S1 is carried out at a temperature of 120℃~150℃ for 3h~5h. When the reaction temperature is below 120℃ or the reaction time is below 3h, the reaction is insufficient, the epoxy group conversion rate is low, resulting in insufficient molecular weight and branching degree of the obtained hydroxyl-branched polymer, and low hydroxyl density, which is detrimental to its compatibility and toughening effect in the subsequent epoxy resin system. When the reaction temperature is above 150℃ or the reaction time is above 5h, the reaction rate is too fast or the reaction duration is too long, which can easily lead to local overreaction, excessive branching point reaction, or even gelation or crosslinking, resulting in decreased product solubility and processability, a wider molecular weight distribution, and affecting the performance stability of the epoxy resin.

[0031] In order to prepare high-performance hydroxyl-branched polymer-modified epoxy resin composite materials, the reaction environment in step S1 is an argon atmosphere, and the reactor is a three-necked flask, which is connected to an argon inlet, a condenser reflux device, and a feed inlet, respectively.

[0032] To prepare high-performance hydroxyl-branched polymer-modified epoxy resin composites, the defoaming treatment method in step S2 involves vacuuming the mixed solution at 40℃~60℃ for 5min~10min, then removing it and placing it in a 50℃~60℃ forced-air drying oven. Once the bubbles disappear, remove the solution, stir for another 5min~10min, and then dry it again in the 50℃~60℃ forced-air drying oven for 10min~20min. This defoaming process can minimize the overall process time while ensuring complete elimination of bubbles during curing, thus improving production efficiency, reducing energy consumption and production costs, and is suitable for industrial-scale production.

[0033] To prepare high-performance hydroxyl-branched polymer-modified epoxy resin composites, the curing temperature in step S2 is 130℃~150℃, and the curing time is 20h~35h. When the curing temperature is below 130℃, the reaction rate between the epoxy groups and the acid anhydride decreases significantly, making it difficult for the system to form a complete cross-linked network. This results in insufficient cross-linking density, low mechanical strength and heat resistance, and a large number of residual reactive groups, leading to unstable performance. When the curing temperature is above 150℃, the reaction rate is too fast, and the system gels rapidly. This is not conducive to the formation of a uniform and stable microphase structure of the hydroxyl-branched polymer in the system. At the same time, it is easy to introduce large internal stress, and even trigger thermal degradation or side reactions, thereby increasing the brittleness, warping, or cracking of the material.

[0034] Similarly, when the curing time is too short (less than 20 hours), the curing reaction is incomplete, and when the curing time is too long (more than 35 hours), it is easy to cause thermal aging and coarsening of the microphase structure, both of which are not conducive to obtaining epoxy resin composite materials with excellent comprehensive performance.

[0035] To prepare high-performance hydroxyl-branched polymer-modified epoxy resin composites, the pretreatment method for the mold described in step S2 is as follows: first, the mold is rinsed with deionized water 2-4 times, then cleaned with anhydrous ethanol 3-5 times. Finally, during epoxy resin curing, the mold is placed in a drying oven for preheating at the same temperature as the resin's curing temperature. Preheating the mold ensures a relatively uniform temperature in the resin system during casting and the initial curing stage, preventing excessive differences in curing rates between the surface and interior layers. This effectively reduces internal stress and molding defects, and promotes the formation of a uniform and stable microphase structure of the hydroxyl-branched polymer within the system, further improving the mechanical properties of the composite material.

[0036] The technical content of the present invention will be specifically described below through specific embodiments.

[0037] Example 1 A method for preparing a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material includes the following steps: S1. Preparation of hydroxylated branched polymers 22.5 g of 1,4-butanediol and 151 g of trimethylolpropane triglycidyl ether were added to a 500 ml three-necked flask. A magnetic stirrer was placed in the flask for magnetic stirring. Once the solution was homogeneous, the flask was transferred to an oil bath. The three-necked flask was connected to an argon inlet, a reflux condenser, and a feed inlet. Under an argon atmosphere, 13.88 g of tetrabutylammonium bromide was added to the reaction system, and the heating device was turned on. The temperature was raised to 130 °C and the reaction was carried out for 4 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a pale yellow liquid hydroxyl-branched polymer, which was then used for the preparation and performance characterization of modified epoxy resin composites.

[0038] Step S2: Preparation of hydroxyl-branched polymer-modified epoxy resin composite material First, rinse the mold with deionized water 3 times, then clean it with anhydrous ethanol 4 times. Finally, when the epoxy resin is curing, put the mold into a drying oven for preheating. The preheating temperature is 140℃, which is the curing temperature of the epoxy resin, to obtain the pretreated mold. Weigh 50g of epoxy resin E51 into a beaker, then add 2.5g of hydroxyl-branched polymer. After thorough mechanical stirring, add 41g of curing agent methyl hexahydrophthalic anhydride to obtain a hydroxyl-branched polymer-epoxy resin mixed solution. Stir the mixed solution continuously at 25℃ for 15min. To eliminate the influence of bubbles, vacuum the mixed solution at 60℃ for 8min. After vacuuming, remove it and place it in a 60℃ forced-air drying oven. After the bubbles disappear, remove it and stir for another 10min. Then place it in a 60℃ forced-air drying oven for 15min to obtain an epoxy resin blend colloid. Place the epoxy resin blend colloid in a pretreated mold and place the mold in a 140℃ drying oven for 24h to cure, obtaining a hydroxyl-branched polymer modified epoxy resin composite material.

[0039] Example 2 In this embodiment, the amount of hydroxyl-branched polymer added is 10% of the mass of epoxy resin E51, and the amount of curing agent methyl hexahydrophthalic anhydride added is 80.04% of the mass of epoxy resin. The other preparation methods and parameters are the same as in Example 1.

[0040] Example 3 In this embodiment, the amount of hydroxyl-branched polymer added is 15% of the mass of epoxy resin E51, and the amount of curing agent methyl hexahydrophthalic anhydride added is 80.06% of the mass of epoxy resin. The steps and parameters of other preparation methods are the same as in Example 1.

[0041] Example 4 In this embodiment, the hydroxyl-branched polymer accounts for 20% of the mass of epoxy resin E51, and the curing agent methyl hexahydrophthalic anhydride accounts for 80.08% of the mass of epoxy resin. The other preparation methods and parameters are the same as in Example 1.

[0042] Example 5 In this embodiment, the amount of hydroxyl-branched polymer added is 25% of the mass of epoxy resin E51, and the amount of curing agent methyl hexahydrophthalic anhydride added is 80.1% of the mass of epoxy resin. The steps and parameters of other preparation methods are the same as in Example 1.

[0043] Comparative Example 1 The epoxy resin preparation process in this comparative example is the same as in Example 1, except that no hydroxyl-branched polymer polar modification was added.

[0044] The structure and properties of the hydroxyl-branched polymer and the hydroxyl-branched polymer-modified epoxy resin composite prepared in the above embodiments were tested and analyzed, and the test and analysis results are as follows.

[0045] Figure 2 The Fourier transform infrared spectrum of the hydroxyl-branched polymer obtained in Example 1 of this invention is shown below. a represents 1,4-butanediol, b represents trimethylolpropane triglycidyl ether, and c represents the hydroxyl-branched polymer. Figure 2 As shown, a is at 3300cm -1 The intensity of the hydroxyl absorption peak near point c decreases, while that at point b is at 910 cm⁻¹. -1 The weakening of the peak intensity of the nearby epoxy groups indicates the consumption of the hydroxyl group in a and the epoxy group in b; c at 1295 cm⁻¹ -1 The peak at that point corresponds to the in-plane bending vibration of the secondary aliphatic hydroxyl group, which is formed by the opening of the epoxy group during the proton transfer reaction. This demonstrates the successful preparation of the hydroxyl-branched polymer.

[0046] Figure 3 These are scanning electron microscope images of the impact fracture surfaces of the hydroxyl-branched polymer-modified epoxy resin composite material in Example 1 of this invention under different fracture temperature conditions, where a represents the fracture surface morphology at room temperature and b represents the fracture surface morphology at low temperature. Figure 3As shown, no obvious phase separation was observed on the fracture surfaces at both room temperature and low temperature, indicating that the hydroxyl-branched polymer is uniformly dispersed and has good compatibility in the epoxy resin matrix. At the same time, the dimple size and surface roughness of the low temperature fracture surface are significantly higher than those of the room temperature fracture surface, indicating that the material underwent more complete plastic deformation and energy dissipation under low temperature impact conditions, thus absorbing more impact energy before fracture. This is consistent with the result that the impact toughness value measured under low temperature conditions is higher than that under room temperature conditions, further proving the significant toughening effect of the hydroxyl-branched polymer on epoxy resin.

[0047] Figure 4 This is a bar chart showing the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. Specifically, a and b represent the tensile strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively; c and d represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively; e and f represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively; g and h represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively; i and j represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively; k and l represent the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively. Figure 4As shown, regardless of room temperature or low temperature conditions, the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material exhibits a trend of first increasing and then decreasing with increasing hydroxyl-branched polymer content. Specifically, when the hydroxyl-branched polymer content is 15% of the epoxy resin mass, the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material reaches its maximum value under both room temperature and low temperature conditions. The highest tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material at room temperature reaches 85.47. The highest tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material reached 72.82 MPa at low temperature, which is 80.89% higher than the room temperature tensile strength and 29.73% higher than the room temperature tensile strength of the pure epoxy resin system. It can also be seen that, under the same hydroxyl-branched polymer addition, the tensile strength of the hydroxyl-branched polymer-modified epoxy resin composite material at low temperature (-80℃) is slightly lower than that at room temperature, but the trend remains consistent. This is because when the hydroxyl-branched polymer addition is low, it is insufficient to significantly change the crosslinking structure of the epoxy resin, resulting in limited improvement in mechanical properties. When the addition is moderate, the hydroxyl groups in the hydroxyl-branched polymer molecules can partially participate in the curing reaction and form a uniformly dispersed flexible branched structure in the system, improving the stress transfer capacity of the system while maintaining a high crosslinking density, thus significantly improving the tensile strength of the epoxy resin. However, when the addition is further increased, the proportion of flexible segments in the system becomes too high, the crosslinking density decreases, leading to a decrease in the rigidity of the epoxy resin and a corresponding decrease in tensile strength.

[0048] Figure 5 This is a bar chart showing the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. Specifically, a and b represent the flexural strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively; c and d represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively; e and f represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively; g and h represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively; i and j represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively; k and l represent the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively. Figure 5As shown, regardless of whether it is at room temperature or low temperature (-80℃), the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material shows a trend of first increasing and then decreasing with the increase of the amount of hydroxyl-branched polymer added. Among them, when the amount of hydroxyl-branched polymer added is 15%, the flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material reaches the maximum value under both room temperature and low temperature conditions. The highest flexural strength of the hydroxyl-branched polymer-modified epoxy resin composite material reaches 113.65 MPa at room temperature and 73.75 MPa at low temperature. This is an increase of 135.06% in room temperature flexural strength and 115.83% in low temperature flexural strength compared with the pure epoxy resin system.

[0049] Figure 6 This is a bar chart showing the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material of the present invention under different temperature conditions. Dark gray bars represent test results at room temperature, and light gray bars represent test results at low temperature. a and b represent the impact strength of the pure epoxy resin system obtained in Comparative Example 1 at room temperature and low temperature, respectively. c and d represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 1 at room temperature and low temperature, respectively. e and f represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 2 at room temperature and low temperature, respectively. g and h represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 3 at room temperature and low temperature, respectively. i and j represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 4 at room temperature and low temperature, respectively. k and l represent the impact strength of the hydroxyl-branched polymer-modified epoxy resin composite material prepared in Example 5 at room temperature and low temperature, respectively. Figure 6 As shown, the low-temperature impact strength of epoxy resin composites modified with hydroxyl-branched polymers is significantly higher than that at room temperature. With the addition of hydroxyl-branched polymers at 15% of the epoxy resin mass, the impact strength at room temperature is increased by 63.61% compared to the pure epoxy resin system, and the impact strength at low temperature is increased by 351.58%. Under the same hydroxyl-branched polymer addition, the impact strength of the epoxy resin composites modified with hydroxyl-branched polymers at low temperature (-80℃) is higher than that at room temperature. This is because impact testing is a high-strain-rate dynamic fracture process. At low temperatures, the relaxation ability of molecular chain segments is limited, and the crack propagation rate is suppressed. Simultaneously, the microphase interface and branched structure introduced by the hydroxyl-branched polymers can effectively induce crack deflection and bifurcation, thereby increasing energy dissipation before fracture, resulting in improved impact strength.

[0050] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0051] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material, characterized in that, 1,4-Butanediol, trimethylolpropane triglycidyl ether, and tetrabutylammonium bromide were mixed and heated under an inert atmosphere to prepare a hydroxyl-branched polymer. Using epoxy resin as a matrix, 5% to 25% of the hydroxyl-branched polymer and 75% to 85% of the curing agent were added to the epoxy resin matrix. After solution blending and curing, a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material was obtained. The mass ratio of 1,4-butanediol, trimethylolpropane triglycidyl ether, and tetrabutylammonium bromide was (21 to 23):(150 to 153):(12 to 14).

2. The low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material according to claim 1, characterized in that, The heating reaction is carried out at a temperature of 120℃ to 150℃ for 3 hours to 5 hours.

3. The low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material according to claim 1, characterized in that, The curing agent is methylhexahydrophthalic anhydride.

4. The low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material according to claim 1, characterized in that, The curing temperature is 130℃~150℃, and the curing time is 20h~35h.

5. A method for preparing a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Under an inert atmosphere, 1,4-butanediol and trimethylolpropane triglycidyl ether were mixed evenly, and then tetrabutylammonium bromide was added. After heating, the reaction was carried out to obtain a hydroxyl-branched polymer. Using epoxy resin as a matrix, 5% to 25% of the hydroxyl-branched polymer and curing agent by mass of epoxy resin are added to the epoxy resin matrix and mixed evenly to obtain a mixed solution. The mixed solution is defoamed to obtain an epoxy resin blend. The epoxy resin blend is cast into a pretreated mold and cured to obtain a hydroxyl-branched polymer modified epoxy resin composite material.

6. The method for preparing a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material according to claim 5, characterized in that, The specific method for defoaming treatment is as follows: Vacuum the mixed solution at 40℃~60℃ for 5min~10min. After vacuuming, take it out and put it into a drying oven at 50℃~60℃. Take it out after the bubbles in the mixed solution disappear, stir it for 5min~10min, and then dry it at 50℃~60℃ for 10min~20min.

7. The method for preparing a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material according to claim 5, characterized in that, The pretreatment method for the mold is as follows: first, rinse the mold with deionized water 2 to 4 times, then clean it with anhydrous ethanol 3 to 5 times, and finally preheat the mold when the epoxy resin is curing. The preheating temperature is the curing temperature of the epoxy resin.

8. The application of a low-temperature toughened hydroxyl-branched polymer-modified epoxy resin composite material as described in any one of claims 1 to 4 in aerospace resin-based composite materials.

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