A method for preparing a glass fiber reinforced epoxy resin composite material

Abstract

The application discloses a preparation method of a glass fiber reinforced epoxy resin composite material, and belongs to the field of functional fiber reinforced resin composite materials. In the method, dimethyl phosphite and diethanolamine are subjected to a condensation reaction to synthesize a phosphorus-containing flame retardant with a low refractive index, which is used for flame-retardant modification of an epoxy resin matrix; by adjusting the ratio between the resin matrix and the flame retardant, the overall refractive index of the resin system can be accurately adjusted to match the refractive index of glass fibers, so that the composite material has excellent flame-retardant performance, good optical transparency and mechanical strength. The ultraviolet-visible transmittance test shows that the prepared composite material can maintain a high light transmittance in the visible light region and has a certain absorption or shielding effect on ultraviolet rays.

Description

Technical Field

[0001] This invention belongs to the field of functional fiber-reinforced resin composites, and specifically relates to a method for preparing glass fiber reinforced epoxy resin composites. Background Technology

[0002] Glass fiber reinforced epoxy resin composites (GFREP) are widely used in construction, transportation, electronics, aerospace, and new energy fields due to their advantages such as light weight, high specific strength, corrosion resistance, fatigue resistance, and ease of processing and molding. With the development of transparent structural materials and functional composite materials, the market demand for transparent composite materials that combine high light transmittance, low haze, and long-term service stability is increasing. For example, transparent building components, skylights, photovoltaic encapsulation materials, electronic display protective panels, and transparent safety structural components all place higher demands on the optical and weather resistance properties of materials.

[0003] Glass fiber itself possesses excellent mechanical properties, natural non-flammability, and high visible light transmittance, theoretically providing the fundamental conditions for preparing transparent composite materials. When the refractive indices of glass fiber and the transparent resin matrix are close, the reflection and scattering of light at the interface between the two phases can be effectively reduced, thereby achieving high light transmittance. Therefore, glass fiber reinforced epoxy resin composites have broad application prospects in the field of transparent functional materials.

[0004] However, most existing glass fiber reinforced epoxy resin composites primarily focus on improving mechanical properties, with relatively insufficient attention paid to optical properties. Due to the refractive index difference between glass fibers and epoxy resin, and factors such as fiber surface condition, interfacial bonding quality, and internal defects in the composite material, light scattering can occur. The resulting composites often suffer from low light transmittance and high haze, making it difficult to meet the requirements of flame-retardant and high-transparency applications. Furthermore, during the composite material preparation process, insufficient fiber wetting, interfacial voids, and the presence of microbubbles further increase light scattering loss, affecting the material's transparency.

[0005] Epoxy resin, as a matrix material for composite materials, possesses excellent adhesion, mechanical properties, and chemical resistance. However, it is essentially an organic polymer compound, with its molecular chains primarily composed of carbon, hydrogen, and oxygen elements. Its limiting oxygen index (LOI) is typically only 19%–22%, making it highly flammable in air and releasing significant amounts of heat and toxic fumes during combustion. This flammability severely limits the widespread application of epoxy resin-based composite materials in fields with stringent fire safety requirements, such as transparent building components, rail transit interiors, and electronic packaging. Furthermore, under prolonged exposure to sunlight and outdoor environments, the epoxy resin matrix is ​​susceptible to ultraviolet radiation, leading to photo-oxidative degradation reactions. This causes molecular chain breakage, cross-linking structure destruction, and surface aging, resulting in problems such as yellowing, decreased light transmittance, increased haze, and deterioration of mechanical properties.

[0006] Although existing technologies typically improve the weather resistance of materials by adding UV absorbers, light stabilizers, or surface coatings, these methods often suffer from defects such as uneven dispersion of additives, migration and precipitation, decreased transparency, or insufficient long-term stability, making it difficult to simultaneously achieve flame retardancy, high transparency, low haze, and excellent UV aging resistance.

[0007] Therefore, how to effectively improve the interfacial compatibility between glass fiber and resin matrix, reduce light scattering, increase light transmittance and reduce haze, and simultaneously impart excellent UV aging resistance to the material while ensuring the mechanical properties of glass fiber reinforced epoxy resin composites, and how to modify the epoxy resin matrix with flame retardancy to improve the fire safety performance of the composite material, has become an urgent technical problem to be solved in this field. Developing a flame-retardant, highly transparent, low-haze, and UV-resistant glass fiber reinforced epoxy resin composite material and its preparation method is of great significance for expanding the application of glass fiber composite materials in transparent buildings, optoelectronic devices, display protection, and high-end functional structural materials. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for preparing glass fiber reinforced epoxy resin composite materials. This invention leverages the structural differences between different resins and the refractive index differences caused by the varying properties of different curing agents, blending them together. Simultaneously, a flame retardant, DNAP, is introduced into the epoxy resin matrix to further impart flame retardant properties and further regulate the refractive index of the resin and its composite material, ultimately yielding a highly transparent, low-haze, UV-resistant composite material.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] The preparation method of the glass fiber reinforced epoxy resin composite material of the present invention includes the following steps:

[0011] Step 1: Blend epoxy resin with ZH181 alicyclic epoxy resin (hydrogenated bisphenol A type epoxy resin) and heat to mix them evenly (80 ℃ oil bath).

[0012] Step 2: Mix the epoxy resin mixture obtained in Step 1 with the curing agent and flame retardant, heat and stir until fully melted and mixed to form a homogeneous system. If necessary, raise the temperature to help the components completely dissolve. Then place it under vacuum to remove the air bubbles trapped inside the resin system until no visible air bubbles overflow. Take it out for later use.

[0013] Step 3: Impregnate the pretreated glass fiber cloth in the mixed resin system obtained in Step 2, ensuring that the resin fully impregnates and fills all the micro gaps between the glass fiber bundles. After full impregnation, remove the glass fiber cloth and flatten it onto the surface of a smooth substrate that has been pre-sprayed with a release agent. Stack the layers according to the required number of layers, place a fixed thickness pad around the perimeter, and cover the top layer with another smooth substrate to form a sandwich pre-cured assembly.

[0014] Step 4: Place the pre-cured assembly mold obtained in Step 3 in a vacuum oven for degassing. After the air bubbles are removed, transfer the device to a flat vulcanizing machine to apply pressure to the sample and heat it for curing. After curing, cool and demold to obtain the glass fiber reinforced epoxy resin composite material.

[0015] In step 1, the epoxy resin is a bisphenol A type epoxy resin, selected from one of the E135 series bisphenol A type epoxy resin, the E51 series bisphenol A type epoxy resin, and the E44 series bisphenol A type epoxy resin.

[0016] Furthermore, the mass ratio of the epoxy resin to the ZH181 alicyclic epoxy resin is in the range of 1-4:1.

[0017] In step 2, the curing agent is one of 4,4′-diaminodiphenylmethane, polyetheramine D230, polyetheramine D2000, and diethylenetriamine. The mass ratio of the epoxy resin mixture to the curing agent is 100:11 to 100:285.

[0018] In step 2, the flame retardant is a pale yellow, low-viscosity liquid flame retardant DNAP prepared in one step using dimethyl phosphite, diethanolamine, and paraformaldehyde as raw materials and methanol as solvent. The mass of DNAP added is 15-25 wt% of the total mass of the epoxy resin mixture and curing agent. The structure of the flame retardant DNAP is shown below:

[0019] .

[0020] Furthermore, the molar ratio of dimethyl phosphite, diethanolamine, and paraformaldehyde was 1:1:1.05, the reaction temperature was 60 °C, the reaction time was 8 h, and the product was obtained by rotary evaporation.

[0021] Furthermore, the molecular formula of DNAP is (HOCH2CH2)2–N-CH2-P(=O)(OCH3)2.

[0022] In step 3, the pretreatment method for the fiberglass cloth is as follows: the fiberglass cloth is soaked in ethanol and acetone for 2 hours each, dried and flattened to remove grease, slurry and dust from the surface of the fiberglass cloth.

[0023] In step 3, the refractive index of the glass fiber cloth is 1.5691.

[0024] In step 3, the thickness of the gasket is between 0.1 and 3.0 mm.

[0025] In step 3, the number of layers of the glass fiber cloth stacked is between 1 and 36.

[0026] The vacuum environment in step 4 needs to provide a certain temperature to ensure that the resin system has a certain viscosity in order to facilitate the degassing process.

[0027] In step 4, the curing time is between 4 and 24 hours, and the curing pressure is 5-15 MPa. The specific temperature and time depend on the type of curing agent. For example, when using 4,4′-diaminodiphenylmethane as the curing agent, the curing procedure is 80℃ / 2 hours, 100℃ / 2 hours, and 120℃ / 2 hours; when using polyetheramine D230 or polyetheramine D2000 as the curing agent, the curing procedure is 3 hours at room temperature and 24 hours at 60℃; when using diethylenetriamine as the curing agent, the curing procedure is 4 hours at room temperature.

[0028] Furthermore, in step 4, the glass fiber content in the composite material is between 50 wt% and 70 wt%, and the composite material thickness is between 0.1 and 3.0 mm. The specific number of glass fiber cloth layers is determined by the composite material thickness, the glass fiber content in the composite material, and the glass fiber areal density. After curing, the test sample is cut using a cutting machine according to national standard testing standards.

[0029] It should be noted that DNAP is an additive flame retardant, which is uniformly dispersed in the epoxy resin matrix through physical doping. The active hydroxyl groups in its molecular structure can form intermolecular hydrogen bonds with the polar groups in the epoxy curing network. This physical cross-linking effect improves the interfacial compatibility between the additive and the matrix, which is beneficial for maintaining the optical uniformity of the system.

[0030] The refractive index of the epoxy resin matrix is ​​one of the key factors determining the optical transparency of glass fiber reinforced composites. Conventional bisphenol A epoxy resin, after curing, exhibits a high electronic polarization density due to the dense benzene ring structure in its crosslinked network, resulting in a refractive index of approximately 1.60, significantly higher than the 1.57–1.58 of glass fibers. Hydrogenated bisphenol A epoxy resin, lacking benzene rings in its structure, has a cured refractive index of around 1.54, but its charring effect is poor.

[0031] This invention utilizes the low-refractive-index flame retardant DNAP (refractive index 1.40-1.44) to optically modulate an epoxy system. The incorporation of DNAP reduces the effective concentration of aromatic structural units in the cured system, weakening the contribution of benzene ring polarization to the refractive index, thus bringing the overall refractive index of the resin matrix closer to the refractive index range of glass fibers. Furthermore, as a low-viscosity component, DNAP improves the rheological properties of the resin system, facilitating its uniform wetting and full penetration into the glass fiber cloth. This improved refractive index matching effectively suppresses light scattering loss at the phase interface, thereby endowing the composite material with flame retardant properties while achieving high transparency and low haze optical performance.

[0032] The beneficial effects of this invention are reflected in:

[0033] 1. The DNAP flame retardant used in this invention can achieve refractive index regulation and flame retardant function by simply incorporating it into the epoxy resin system through physical blending. There is no need to chemically modify the resin matrix or pre-treat the glass fiber. The operation process is simple, the process compatibility is strong, and it is easy to connect with existing composite material molding processes (such as vacuum infusion, compression molding, etc.), making it suitable for industrial mass production.

[0034] 2. The introduction of hydrogenated bisphenol A epoxy resin and DNAP significantly reduces the refractive index of the epoxy resin matrix, enabling the epoxy resin matrix to achieve refractive index matching with the glass fiber. This reduces the refraction and scattering of visible light at the interface of the composite material, making the composite material transparent to visible light.

[0035] 3. This invention effectively reduces the viscosity of the resin system by incorporating DNAP to synergistically regulate the rheological properties of the resin system, thereby improving the wettability and penetration uniformity of the resin on the glass fiber reinforcement. Good impregnation effect can be obtained without the introduction of additional diluents or solvents, which simplifies the process steps and avoids the use of volatile organic solvents, meeting the requirements of green and environmentally friendly preparation.

[0036] 4. The modified glass fiber reinforced epoxy resin matrix composite material can maintain a transmittance of 88%+, a haze as low as 8.3%, and tensile and flexural strengths above 260 MPa. Furthermore, the hydrogenated bisphenol A epoxy resin and flame retardant DNAP reduce the brittleness of the epoxy resin and improve the toughness of the composite material. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the chemical reaction equation and structural formula for the synthesis of DNAP.

[0038] Figure 2 The data are the proton NMR spectra (a) and phosphorus NMR spectra (b) of the raw materials dimethyl phosphite (DHP) and DNAP.

[0039] Figure 3 The data are Fourier transform infrared spectra of the raw materials dimethyl phosphite (DHP) and DNAP.

[0040] Figure 4 The refractive index data of the epoxy resin matrix prepared in Comparative Examples 2, 3, 1, 4 and 5 are shown.

[0041] Figure 5 The ultraviolet-visible transmittance curves (a) and transmittance data at 550 nm of the composite materials prepared in Comparative Examples 1, 3, 1, 4, 2 and 5 are shown in Figure 5 (b).

[0042] Figure 6 The haze data are for the composite materials prepared in Comparative Examples 2, 3, 1, 4 and 5.

[0043] Figure 7 Digital photographs illustrating the haze effects of Comparative Examples 2, 3, 1, 4, and 5.

[0044] Figure 8 The stress-strain curves of the composite materials prepared in Comparative Examples 2, 3, 1, 4, 1 and 5 are shown.

[0045] Figure 9 The graph shows the tensile strength and elongation at break of the composite materials prepared in Comparative Examples 2, 3, 1, 4, 1 and 5.

[0046] Figure 10 The results show the vertical burning rating and limiting oxygen index of the composite materials prepared in Comparative Examples 1, 2, 3, 1, 4, and 5.

[0047] Figure 11The graph shows the heat release rate (a) and total heat release (b) of the composite materials prepared by cone calorimetry in Comparative Examples 1, 2, 3, 1, 4 and 5.

[0048] Figure 12 The graph shows the CO(a) and CO2(b) generation rate test data of the composite materials prepared by the cone calorimeter in Comparative Examples 1, 2, 3, 1, 4 and 5.

[0049] Figure 13 The graph shows the smoke release rate (a) and total smoke release (b) of the composite materials prepared by the cone calorimeter in Comparative Examples 1, 2, 3, 1, 4, and 5.

[0050] Figure 14 Digital photographs and SEM images of the conical calorimetric test carbon slags of the composite materials prepared for Comparative Examples 2(a), 3(b), 1(c), 4(d), and 5(e).

[0051] Figure 15 The conical calorimetric test char Raman spectra of the composite materials prepared for Comparative Examples 2(a), 3(b), 1(c), 4(d), and 5(e) are shown. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0054] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are conventional commercially available raw materials or conventional processing techniques in the art.

[0055] Example 1:

[0056] Step 1: Weigh 40 g of E51 type bisphenol A epoxy resin and 10 g of ZH181 alicyclic epoxy resin, and stir at 80 ℃ until dissolved and mixed evenly.

[0057] Step 2: Weigh 17.57 g DNAP and 12.29 g 4,4′-diaminodiphenylmethane, add them to the epoxy resin solution obtained in Step 1, heat to 95 °C and stir until homogeneous, then place in a vacuum environment to remove air bubbles from the resin system.

[0058] Step 3: Cut the fiberglass plain weave fabric into 60×60 mm sizes, immerse the front and back sides in ethanol and acetone solvents for 2 hours each, remove, flatten and dry, and set aside.

[0059] Step 4: Immerse the glass fiber cloth pretreated in Step 3 into the epoxy resin system obtained in Step 2. Stir the glass fiber cloth appropriately to ensure that the resin fully impregnates and coats the glass fiber. Remove the glass fiber cloth and drain off the excess resin. Lay it flat on a smooth plate that has been pre-sprayed and dried with a release agent. Press out any large air bubbles appropriately. Repeat the stacking process up to 6 layers. Place 4-8 0.5 mm thick pads at the edge of the lower plate and cover it with the upper plate to obtain the pre-cured sample mold.

[0060] Step 5: Place the pre-cured sample mold in an 80℃ vacuum environment, vacuum degas for 3 minutes, repeat twice to ensure all bubbles are removed, transfer it to a flat vulcanizing machine with a pressure of 5 MPa, and cure it according to the temperature increase program of 80℃ for 2 h, 100℃ for 2 h, and 120℃ for 2 h to finally obtain glass fiber reinforced epoxy resin composite material.

[0061] Comparative Example 1:

[0062] Step 1: Weigh 40 g of E51 type bisphenol A epoxy resin and 10 g of ZH181 alicyclic epoxy resin, and stir at 80 ℃ until dissolved and mixed evenly.

[0063] Step 2: Weigh 12.29 g of 4,4′-diaminodiphenylmethane and add it to the epoxy resin solution obtained in Step 1. Heat the solution to 95 °C and stir until homogeneous. Then place the solution in a vacuum environment to remove air bubbles from the resin system.

[0064] Step 3: Pour the resin system into a polytetrafluoroethylene mold that has been pre-sprayed with release agent and dried, then transfer it to an oven and cure it according to the temperature increase program of 80 ℃ for 2 h, 100 ℃ for 2 h, and 120 ℃ for 2 h to obtain epoxy resin board.

[0065] Comparative Example 2:

[0066] Step 1: Weigh 40 g of E51 type bisphenol A epoxy resin and 10 g of ZH181 alicyclic epoxy resin, and stir at 80 ℃ until dissolved and mixed evenly.

[0067] Step 2: Weigh 12.29 g of 4,4′-diaminodiphenylmethane and add it to the epoxy resin solution obtained in Step 1. Heat the solution to 95 °C and stir until homogeneous. Then place the solution in a vacuum environment to remove air bubbles from the resin system.

[0068] Step 3: Cut the fiberglass plain weave fabric into 60×60 mm sizes, immerse the front and back sides in ethanol and acetone solvents for 2 hours each, remove, flatten and dry, and set aside.

[0069] Step 4: Immerse the glass fiber cloth pretreated in Step 3 into the epoxy resin system obtained in Step 2. Stir the glass fiber cloth appropriately to ensure that the resin fully impregnates and coats the glass fiber. Remove the glass fiber cloth and drain off the excess resin. Lay it flat on a smooth plate that has been pre-sprayed and dried with a release agent. Press out any large air bubbles appropriately. Repeat the stacking process up to 6 layers. Place 4-8 0.5 mm thick pads at the edge of the lower plate and cover it with the upper plate to obtain the pre-cured sample mold.

[0070] Step 5: Place the pre-cured sample mold in an 80℃ vacuum environment, vacuum degas for 3 min, repeat twice to ensure all bubbles are removed, transfer to a flat vulcanizing machine with a pressure of 5 MPa, and cure according to the temperature increase program of 80 ℃ for 2 h, 100 ℃ for 2 h, and 120 ℃ for 2 h to finally obtain glass fiber reinforced epoxy resin composite material.

[0071] Comparative Example 3:

[0072] Step 1: Weigh 40 g of E51 type bisphenol A epoxy resin and 10 g of ZH181 alicyclic epoxy resin, and stir at 80 ℃ until dissolved and mixed evenly.

[0073] Step 2: Weigh 15.57 g DNAP and 12.29 g 4,4′-diaminodiphenylmethane, add them to the epoxy resin solution obtained in Step 1, heat to 95 °C and stir until homogeneous, then place in a vacuum environment to remove air bubbles from the resin system.

[0074] Step 3: Cut the fiberglass plain weave fabric into 60×60 mm sizes, immerse the front and back sides in ethanol and acetone solvents for 2 hours each, remove, flatten and dry, and set aside.

[0075] Step 4: Immerse the glass fiber cloth pretreated in Step 3 into the epoxy resin system obtained in Step 2. Stir the glass fiber cloth appropriately to ensure that the resin fully impregnates and coats the glass fiber. Remove the glass fiber cloth and drain off the excess resin. Lay it flat on a smooth plate that has been pre-sprayed and dried with a release agent. Press out any large air bubbles appropriately. Repeat the stacking process up to 6 layers. Place 4-8 0.5 mm thick pads at the edge of the lower plate and cover it with the upper plate to obtain the pre-cured sample mold.

[0076] Step 5: Place the pre-cured sample mold in an 80℃ vacuum environment, vacuum degas for 3 minutes, repeat twice to ensure all bubbles are removed, transfer it to a flat vulcanizing machine with a pressure of 5 MPa, and cure it according to the temperature increase program of 80℃ for 2 h, 100℃ for 2 h, and 120℃ for 2 h to finally obtain glass fiber reinforced epoxy resin composite material.

[0077] Comparative Example 4:

[0078] Step 1: Weigh 40 g of E51 type bisphenol A epoxy resin and 10 g of ZH181 alicyclic epoxy resin, and stir at 80 ℃ until dissolved and mixed evenly.

[0079] Step 2: Weigh 19.67 g DNAP and 12.29 g 4,4′-diaminodiphenylmethane, add them to the epoxy resin solution obtained in Step 1, heat to 95 °C and stir until homogeneous, then place in a vacuum environment to remove air bubbles from the resin system.

[0080] Step 3: Cut the fiberglass plain weave fabric into 60×60 mm sizes, immerse the front and back sides in ethanol and acetone solvents for 2 hours each, remove, flatten and dry, and set aside.

[0081] Step 4: Immerse the glass fiber cloth pretreated in Step 3 into the epoxy resin system obtained in Step 2. Stir the glass fiber cloth appropriately to ensure that the resin fully impregnates and coats the glass fiber. Remove the glass fiber cloth and drain off the excess resin. Lay it flat on a smooth plate that has been pre-sprayed and dried with a release agent. Press out any large air bubbles appropriately. Repeat the stacking process up to 6 layers. Place 4-8 0.5 mm thick pads at the edge of the lower plate and cover it with the upper plate to obtain the pre-cured sample mold.

[0082] Step 5: Place the pre-cured sample mold in an 80℃ vacuum environment, vacuum degas for 3 minutes, repeat twice to ensure all bubbles are removed, transfer it to a flat vulcanizing machine with a pressure of 5 MPa, and cure it according to the temperature increase program of 80℃ for 2 h, 100℃ for 2 h, and 120℃ for 2 h to finally obtain glass fiber reinforced epoxy resin composite material.

[0083] Comparative Example 5:

[0084] Step 1: Weigh 50 g of E51 type bisphenol A epoxy resin and preheat it in an oil bath at 80 ℃.

[0085] Step 2: Add 12.64 g of 4,4′-diaminodiphenylmethane to the epoxy resin solution obtained in Step 1, heat to 95 °C and stir until homogeneous, then place in a vacuum environment to remove air bubbles from the resin system.

[0086] Step 3: Cut the fiberglass plain weave fabric into 60×60 mm sizes, immerse the front and back sides in ethanol and acetone solvents for 2 hours each, remove, flatten and dry, and set aside.

[0087] Step 4: Immerse the glass fiber cloth pretreated in Step 3 into the epoxy resin system obtained in Step 2. Stir the glass fiber cloth appropriately to ensure that the resin fully impregnates and coats the glass fiber. Remove the glass fiber cloth and drain off the excess resin. Lay it flat on a smooth plate that has been pre-sprayed and dried with a release agent. Press out any large air bubbles appropriately. Repeat the stacking process up to 6 layers. Place 4-8 0.5 mm thick pads at the edge of the lower plate and cover it with the upper plate to obtain the pre-cured sample mold.

[0088] Step 5: Place the pre-cured sample mold in an 80℃ vacuum environment, vacuum degas for 3 minutes, repeat twice to ensure all bubbles are removed, transfer it to a flat vulcanizing machine with a pressure of 5 MPa, and cure it according to the temperature increase program of 80℃ for 2 h, 100℃ for 2 h, and 120℃ for 2 h to finally obtain glass fiber reinforced epoxy resin composite material.

[0089] like Figure 1 As shown, DNAP is obtained by reacting diethanolamine, paraformaldehyde, and dimethyl phosphite.

[0090] like Figure 2-3 As shown, the proton, phosphorus, and infrared spectra of nuclear magnetic resonance characterize the successful preparation of the flame retardant DNAP.

[0091] like Figure 4 As shown in the data, the refractive index data of the epoxy resin matrix prepared by Comparative Examples 2, 3, 1, 4 and 5 show that the refractive index of the epoxy resin system gradually decreases with the increase of DNAP addition. The refractive index of Example 1 is closest to the refractive index of the glass fiber used in this study (1.5691). In contrast, the two epoxy resin systems without DNAP have higher refractive indices.

[0092] like Figure 5 As shown, by observing and comparing the visible light transmittance data of the composite materials prepared by Comparative Example 1, Comparative Example 3, Example 1, Comparative Example 4, Comparative Example 2 and Comparative Example 5, it can be seen that in the visible light range, compared with the pure epoxy resin matrix, the transmittance of the glass fiber modified composite material changes only slightly, and the transmittance characteristics are basically unaffected by the glass fiber filling. Moreover, it can maintain a high transmittance level (88%+) at 550nm. The ultraviolet light band test results show that all composite materials can achieve almost complete absorption of UVB and UVC ultraviolet light. However, in the UVA band within the range of 350-380 nm, the transmittance of each sample is lower than that of Comparative Example 1, which confirms that the composite material has excellent ultraviolet absorption and shielding effects.

[0093] like Figure 6 As shown, observing the haze data of the composite materials prepared in Comparative Examples 2, 3, 1, 4, and 5 reveals that the haze of the composite materials first decreases and then increases with the increase of DNAP addition. This result indicates that the formulation used in Example 1 achieves optimal matching between the refractive index of the resin system and the refractive index of the glass fiber. This pattern corroborates the aforementioned refractive index test conclusions; when the amount of DNAP addition is further increased, the refractive index difference between the resin system and the glass fiber increases, which in turn causes the haze of the composite material to increase.

[0094] like Figure 7 As shown, digital photographs of the haze effects of Comparative Examples 2, 3, 1, 4, and 5 are presented. Visually, the clarity of the flower samples at a distance of 5 cm from the composite material exhibits a pattern of initial clarity followed by blurring. This phenomenon further demonstrates that the epoxy resin composite formulation in Example 1 has the best compatibility with the glass fiber, and this conclusion corroborates the aforementioned haze analysis results.

[0095] like Figure 8 and Figure 9 As shown, the stress-strain curves and bar charts of tensile strength and elongation at break of the composite materials of Comparative Example 2, Comparative Example 3, Example 1, Comparative Example 4, Comparative Example 1, and Comparative Example 5 are presented. The test results show that the tensile strength of the glass fiber reinforced composite materials is significantly improved compared to pure epoxy resin, proving that this application can successfully prepare high-strength composite materials. Simultaneously, due to the presence of hydroxyl structures in DNAP, hydrogen bonds can be formed between DNAP and the epoxy resin matrix, further improving the tensile properties of the composite materials; however, excessive introduction of DNAP will reduce the tensile strength of the composite materials.

[0096] like Figure 10 As shown, Figure 10 The vertical flammability rating and limiting oxygen index (LOI) test results of the composite materials prepared by Comparative Examples 1, 2, 3, 1, 4, and 5 are shown. It can be seen that DNAP can effectively improve the vertical flammability rating of the composite materials; when the DNAP addition amount reaches the proportion in Example 1, the vertical flammability rating of the composite material can reach UL-94 V-1. The limiting oxygen index test results further illustrate that the limiting oxygen index (LOI) of the composite material increases with the DNAP content.

[0097] like Figure 11As shown, the curves illustrating the changes in heat release rate and total heat release of the composite materials prepared by Comparative Examples 1, 3, 2, 1, 4, and 5 using cone calorimetry are presented. The test results indicate that the introduction of glass fiber can reduce the peak heat release rate of the epoxy resin to a certain extent; while the introduction of DNAP further reduces the peak heat release rate and total heat release of the composite material to varying degrees. This confirms that the flame retardant plays a catalytic role in char formation during the combustion process of the composite material, and the dense char layer generated during combustion effectively blocks heat transfer as a physical barrier, endowing the material with excellent flame retardant and heat-suppressing properties.

[0098] like Figure 12 As shown, the cone calorimetry curves for CO and CO2 production rates of the composite materials prepared in Comparative Examples 1, 3, 2, 1, 4, and 5 are presented. The test results indicate that the carbon layer generated during the combustion process not only blocks heat conduction but also adsorbs the gaseous products produced during combustion, thus providing a barrier effect.

[0099] like Figure 13 As shown, the cone calorimetry data curves of smoke release rate and total smoke release of the composite materials prepared in Comparative Examples 1, 3, 2, 1, 4, and 5 are presented. The test results show that the smoke release level of the glass fiber reinforced composite material during combustion is significantly lower than that of the pure epoxy resin system; and with the introduction of DNAP, a dense char layer can be formed during combustion, which plays a good physical barrier role, further inhibiting smoke release and reducing the total smoke release, effectively reducing the fire smoke toxicity risk and overall fire hazard of the composite material during combustion.

[0100] like Figure 14 As shown, digital photographs and SEM images of the carbon residue from the cone calorimetry test of the composite materials prepared by Comparative Examples 2, 3, 1, 4, and 5 are displayed. It can be seen that with the increase of the amount of flame retardant DNAP added, the amount of residual carbon residue on the glass fiber surface increases, proving that DNAP can promote the carbonization of epoxy resin.

[0101] like Figure 15 As shown, the cone calorimetry (CFC) results of the composite materials prepared in Comparative Examples 2, 3, 1, 4, and 5 are presented, along with their Raman spectra of the carbon slag. It can be seen that the unmodified epoxy resin system in Comparative Example 2 produces almost no carbon layer after combustion; while the DNAP addition amount in Example 1 has a significant catalytic carbonization effect on the epoxy resin, effectively improving the graphitization degree of the carbon slag. From the electron microscopy images combined with the microscopic morphology results, it can be seen that the carbon layer attached to the glass fiber surface of the composite material gradually becomes denser and more complete with the appropriate doping of DNAP.

[0102] In summary, the composite material prepared according to the method of Example 1 has the optimal amount of DNAP added. The presence of DNAP not only enables the composite material to achieve flame retardancy and fire resistance, but also enables the fiber and resin refractive index to achieve the best match, thus successfully preparing a flame retardant, transparent, low-haze high-strength glass fiber reinforced epoxy resin matrix composite material.

Claims

1. A method for preparing a glass fiber reinforced epoxy resin composite material, characterized in that... Includes the following steps: Step 1: Blend epoxy resin with ZH181 alicyclic epoxy resin and heat to mix them evenly; Step 2: Mix the epoxy resin mixture obtained in Step 1 with the curing agent and flame retardant, heat and stir until fully melted and mixed to form a homogeneous system, then place it under vacuum to remove air bubbles, and take it out for later use; Step 3: Impregnate the pretreated glass fiber cloth in the mixed resin system obtained in Step 2, ensuring that the resin fully impregnates and fills all the micro gaps between the glass fiber bundles. After full impregnation, remove the glass fiber cloth and flatten it onto the surface of a smooth substrate that has been pre-sprayed with a release agent. Stack the layers according to the required number of layers, and cover the top layer with another smooth substrate to form a sandwich pre-cured assembly. Step 4: Place the pre-cured assembly obtained in Step 3 in a vacuum oven for degassing. After the air bubbles are removed, transfer it to a flat vulcanizing machine to apply pressure and heat it for curing. After curing, cool and demold to obtain the glass fiber reinforced epoxy resin composite material. In step 2, the structure of the flame retardant is as follows: 。 2. The preparation method according to claim 1, characterized in that: In step 1, the epoxy resin is a bisphenol A type epoxy resin, selected from one of the E135 series bisphenol A type epoxy resin, the E51 series bisphenol A type epoxy resin, and the E44 series bisphenol A type epoxy resin.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the epoxy resin to the ZH181 alicyclic epoxy resin is in the range of 1-4:

1.

4. The preparation method according to claim 1, characterized in that: In step 2, the curing agent is one of 4,4′-diaminodiphenylmethane, polyetheramine D230, polyetheramine D2000, and diethylenetriamine.

5. The preparation method according to claim 4, characterized in that: The mass ratio of the epoxy resin mixture to the curing agent is 100:11 to 100:

285.

6. The preparation method according to claim 1, characterized in that: The flame retardant is added at a mass of 15-25 wt% of the total mass of the epoxy resin mixture and the curing agent.

7. The preparation method according to claim 1, characterized in that: In step 3, the number of layers of the glass fiber cloth stacked is between 1 and 36.

8. The preparation method according to claim 1, characterized in that: In step 4, the curing time is 4-24 h and the curing pressure is 5-15 MPa.

9. The preparation method according to claim 1, characterized in that: In step 4, the glass fiber content in the composite material is 50 wt%-70 wt%, and the thickness of the composite material is 0.1 ~ 3.0 mm.

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