Recyclable epoxy resin / glass fiber composite material containing acetal structure as well as preparation method, recycling method and application of recyclable epoxy resin / glass fiber composite material

Abstract

The invention discloses a recoverable epoxy resin / glass fiber composite material containing an acetal structure. The recoverable epoxy resin / glass fiber composite material comprises epoxy resin, a phenolic curing agent containing the acetal structure, a curing accelerator, a release agent and glass fibers, compared with the prior art, the prepared recoverable epoxy resin / glass fiber composite material has the advantages that the acetal structure in an epoxy network can be easily disconnected and release the glass fibers under the action of a catalyst under the condition of ice-water bath at 0 DEG C, the glass fibers and the epoxy resin are recycled, the whole recycling process is short in time and only needs one hour, and the cost is low. Therefore, the recovery efficiency is greatly improved; and meanwhile, the cost in the recycling process is greatly reduced due to the recycling conditions, and large-scale commercial recycling of the wind turbine blades becomes possible.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and in particular to a recyclable epoxy resin / glass fiber composite material containing an acetal structure, a preparation method thereof, a recycling method thereof, and an application thereof. Background Art

[0002] Epoxy resin, a typical thermosetting material, has important applications in adhesives, coatings, electronic packaging materials, fiber-reinforced composites, and other fields due to its excellent dimensional stability, corrosion resistance, insulation, and mechanical properties. Demand for epoxy resin is particularly increasing in advanced composite materials such as automobiles, aircraft, and wind turbine blades. However, the insoluble and infusible nature of traditional epoxy resins due to their cross-linked structure makes them difficult to effectively recycle. Most methods of disposing of epoxy resins involve filling and incineration, which causes significant environmental pollution and a significant waste of resources. Therefore, the recycling of epoxy resins and their composites is particularly urgent.

[0003] Introducing dynamic covalent bonds into epoxy resins is a viable method for recycling epoxy resin composites. Under specific stimulation conditions, the dynamic covalent bonds break, causing the epoxy resin network to depolymerize, releasing glass fibers. Currently, methods for introducing dynamic covalent bonds into epoxy resins include transesterification, disulfide bonds, and dynamic imine bonds.

[0004] For example, CN114195984B discloses a bisphenol A epoxy curing agent containing a dynamic enamine bond and a degradable epoxy resin. Its infusion product can be used on wind turbine blades. It can be degraded and recycled, but this can only be achieved under heating and stirring, and in an acid solvent.

[0005] CN114891317A discloses a degradable pultruded sheet composite material, which achieves decomposition by combining amine groups with acetoacetate groups in a degradable modified resin (Formula I) to form dynamic enamine bonds. Decomposition requires heating to 80-200°C under alkaline conditions.

[0006] In summary, after dynamic covalent bonds such as ester exchange, disulfide bonds or dynamic imine bonds are introduced into epoxy resins, degradation can only be carried out under relatively harsh conditions such as high temperature and acidic or alkaline conditions. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a recyclable epoxy resin / glass fiber composite material containing an acetal structure and its preparation method, recycling method and application, so as to solve the problem in the prior art that the working conditions for recycling existing epoxy resin composite materials are relatively harsh.

[0008] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution: a recyclable epoxy resin / glass fiber composite material containing an acetal structure, comprising an epoxy resin, a phenolic curing agent containing an acetal structure, a curing accelerator, a release agent and glass fiber.

[0009] Furthermore, the epoxy resin contains at least two epoxy groups; preferably, the epoxy resin is a bisphenol A epoxy resin; further preferably, the bisphenol A epoxy resin is bisphenol A diglycidyl ether and its structural formula is:

[0010]

[0011] Furthermore, the phenolic curing agent is prepared by reacting hydroquinone and dimethoxymethane as raw materials. The molar ratio of hydroquinone to dimethoxymethane is 2:1. The specific synthesis route of the phenolic curing agent is as follows: 80mmol of hydroquinone is dissolved in 100ml of toluene solvent, 4mmol of p-toluenesulfonamide (p-TSA) and 40mmol of dimethoxymethane are added, and the mixture is refluxed at room temperature for 5 hours to obtain the curing agent;

[0012] The reaction route is:

[0013]

[0014] Furthermore, the curing accelerator is an imidazole compound and its addition amount is 0.5wt% of the epoxy resin; preferably, the imidazole compound is one of 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole and 1,2-dimethylimidazole;

[0015] More preferably, the imidazole compound is 1-methylimidazole.

[0016] Furthermore, the release agent is zinc stearate, and its addition amount is 1-2.5wt% of the epoxy resin.

[0017] The second aspect of the present invention adopts the following technical solution: a method for preparing a recyclable epoxy resin / glass fiber composite material containing an acetal structure as described in the first aspect of the present invention, comprising the following steps:

[0018] Weighing epoxy resin, phenolic curing agent, imidazole compound and release agent;

[0019] The phenolic curing agent is dissolved in an ethanol solution, and then the phenolic curing agent, a release agent and an epoxy resin are added and mixed evenly, and then degassed in a vacuum oven at a temperature of 50° C. for 1 hour to obtain a mixed intermediate;

[0020] The mixed intermediate is introduced into glass fiber through a pultrusion process or a vacuum infusion process to prepare a recyclable epoxy resin / glass fiber composite material.

[0021] Furthermore, the pultrusion process is specifically:

[0022] The mixed intermediate is impregnated with glass fiber and pultruded, and then passed through a mold under traction for curing and molding to prepare a recyclable epoxy resin / glass fiber composite material;

[0023] The curing process in the mold is divided into three stages, and the curing temperatures of the three stages are 140°C, 150°C and 160°C respectively.

[0024] The pulling speed of the traction is 0.2-3 m / min.

[0025] Furthermore, the vacuum infusion process is specifically:

[0026] The mixed intermediate was added into a mold covered with glass fiber by vacuum infusion and cured at 110° C. for 2 hours to obtain a recyclable epoxy resin / glass fiber composite material.

[0027] The third aspect of the present invention adopts the following technical solution: a method for recycling a recyclable epoxy resin / glass fiber composite material containing an acetal structure as described in the first aspect of the present invention, wherein the recyclable epoxy resin / glass fiber composite material is immersed in a dichloromethane solution containing trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine in an ice-water bath for 1 hour;

[0028] Preferably, the molar ratio of trimethylsilyl trifluoromethanesulfonate to 2,2'-bipyridine is 1:1, and the total mass concentration of trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine in the dichloromethane solution is 1-10 g / L.

[0029] The fourth aspect of the present invention adopts the following technical solution: an application of using the recyclable epoxy resin / glass fiber composite material containing acetal structure described in the first aspect of the present invention as a raw material for wind turbine blades.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention is that under the action of a curing accelerator, a phenolic curing agent with an acetal structure can quickly undergo a curing reaction with an epoxy resin, and glass fiber is compounded through a pultrusion process or a vacuum infusion process, so that the mechanical properties of the prepared recyclable epoxy resin / glass fiber composite material meet the requirements of wind turbine blade main beams and infused wind turbine blades;

[0032] 2. The recyclable epoxy resin / glass fiber composite material prepared by the present invention can be easily disconnected under the action of a catalyst in an ice-water bath at 0°C, releasing the glass fiber, thereby realizing the recycling of the glass fiber and epoxy resin. The entire recycling process is short, taking only 1 hour, thereby greatly improving the recycling efficiency; at the same time, its recycling conditions also greatly reduce the cost of the recycling process, making large-scale commercial recycling of wind turbine blades possible. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below through specific embodiments:

[0034] The invention provides a recyclable epoxy resin / glass fiber composite material containing an acetal structure, which comprises an epoxy resin, a phenolic curing agent containing an acetal structure, a curing accelerator, a release agent and glass fiber.

[0035] Furthermore, the epoxy resin contains at least two epoxy groups; preferably, the epoxy resin is a bisphenol A epoxy resin; further preferably, the bisphenol A epoxy resin is bisphenol A diglycidyl ether and its structural formula is:

[0036]

[0037] Furthermore, the phenolic curing agent is prepared by reacting hydroquinone and dimethoxymethane as raw materials. The molar ratio of hydroquinone to dimethoxymethane is 2:1. The specific synthesis route of the phenolic curing agent is as follows: 80mmol of hydroquinone is dissolved in 100ml of toluene solvent, 4mmol of p-toluenesulfonamide (p-TSA) and 40mmol of dimethoxymethane are added, and the mixture is refluxed at room temperature for 5 hours to obtain the curing agent;

[0038] The reaction route is:

[0039]

[0040] Furthermore, the curing accelerator is an imidazole compound and its addition amount is 0.5wt% of the epoxy resin; preferably, the imidazole compound is one of 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole and 1,2-dimethylimidazole; further preferably, the imidazole compound is 1-methylimidazole.

[0041] Furthermore, the release agent is zinc stearate, and its addition amount is 1-2.5wt% of the epoxy resin.

[0042] The present invention also provides a method for preparing a recyclable epoxy resin / glass fiber composite material containing an acetal structure, comprising the following steps:

[0043] Weighing epoxy resin, phenolic curing agent, imidazole compound and release agent;

[0044] The phenolic curing agent is dissolved in an ethanol solution, and then the phenolic curing agent, a release agent and an epoxy resin are added and mixed evenly, and then degassed in a vacuum oven at a temperature of 50° C. for 1 hour to obtain a mixed intermediate;

[0045] The mixed intermediate is introduced into glass fiber through a pultrusion process or a vacuum infusion process to prepare a recyclable epoxy resin / glass fiber composite material.

[0046] Furthermore, the pultrusion process is specifically:

[0047] The mixed intermediate is impregnated with glass fiber and pultruded, and then passed through a mold under traction for curing and molding to prepare a recyclable epoxy resin / glass fiber composite material;

[0048] The curing process in the mold is divided into three stages, and the curing temperatures of the three stages are 140°C, 150°C and 160°C respectively.

[0049] The pulling speed of the traction is 0.2-3 m / min.

[0050] Furthermore, the vacuum infusion process is specifically:

[0051] The mixed intermediate was added into a mold covered with glass fiber by vacuum infusion and cured at 110° C. for 2 hours to obtain a recyclable epoxy resin / glass fiber composite material.

[0052] The present invention also provides a method for recovering a recyclable epoxy resin / glass fiber composite material containing an acetal structure, comprising soaking the recyclable epoxy resin / glass fiber composite material in a recovery liquid under ice-water bath conditions for 1 hour; the recovery liquid is a dichloromethane solution containing trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine;

[0053] Preferably, the molar ratio of trimethylsilyl trifluoromethanesulfonate to 2,2'-bipyridine is 1:1, and the total mass concentration of trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine in the dichloromethane solution is 1-10 g / L.

[0054] The present invention also proposes an application, in which the recyclable epoxy resin / glass fiber composite material containing an acetal structure is used as a raw material for wind turbine blades.

[0055] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0056] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial-grade raw materials or raw materials of conventional purity used in the field of epoxy resin wind turbine blade preparation.

[0057] Specific raw materials:

[0058] Bisphenol A diglycidyl ether E51 (Daosheng Tianhe Co., Ltd.), trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine (Shanghai Mairui Reagent Co., Ltd.), 1-methylimidazole (Aladdin Reagent Co., Ltd.), p-toluenesulfonamide (McLean Reagent Co., Ltd.), dimethoxymethane (Aladdin Reagent Co., Ltd.), dichloromethane (Aladdin Reagent Co., Ltd.), glass fiber and its wind power yarn unidirectional cloth (Chongqing International Composite Materials Co., Ltd., brand: TMIII 468GS).

[0059] Test method:

[0060] 1.Tensile strength and bending properties:

[0061] According to GB / T 2567-2008

[0062] 2. Fiber content:

[0063] It is calculated by placing the composite material into a muffle furnace for calcination.

[0064] Example 1:

[0065] 5 kg of the phenolic curing agent of the present invention was dissolved in 10 L of ethanol solvent, and then 5 kg of epoxy resin, 50 g of 1-methylimidazole, and 200 g of zinc stearate were added. The mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0066] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 50cm / min, and the mold cross-sectional size is 150*5mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0067] The prepared epoxy resin / glass fiber composite material was immersed in the recovery solution of the present invention with a concentration of 1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0068] Example 2:

[0069] 5 kg of the phenolic curing agent of the present invention was dissolved in 10 L of ethanol solvent, and then 5 kg of epoxy resin, 50 g of 2-methylimidazole, and 250 g of zinc acetylacetonate were added. The mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0070] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 100 cm / min, and the mold cross-sectional size is 150*5 mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0071] The prepared epoxy resin / glass fiber composite material was immersed in the recovery solution of the present invention with a concentration of 1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0072] Example 3:

[0073] 5 kg of the phenolic curing agent of the present invention was dissolved in 10 L of ethanol solvent, and then 5 kg of epoxy resin, 50 g of 2-ethyl-4-methylimidazole, and 100 g of zinc stearate were added. The mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0074] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 100 cm / min, and the mold cross-sectional size is 150*5 mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0075] The prepared epoxy resin / glass fiber composite material was immersed in the recovery solution of the present invention with a concentration of 1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0076] Example 4:

[0077] 1 kg of the phenolic curing agent of the present invention was dissolved in 1 L of ethanol solvent, and then 1 kg of epoxy resin, 10 g of 2-methylimidazole, and 40 g of zinc stearate were added. After stirring evenly, the mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0078] The above resin was injected into a mold on which multiple layers of glass fiber were laid using a vacuum infusion method, and cured at 120°C for 2 hours to obtain an epoxy resin / glass fiber composite material by vacuum infusion.

[0079] The prepared epoxy resin / glass fiber composite material was immersed in the recycling solution of the present application having a concentration of 1 g / L for 1 hour under ice water bath conditions, and the separation of the glass fiber from the epoxy resin was observed.

[0080] Example 5:

[0081] 1 kg of the phenolic curing agent of the present application was dissolved in 1 L of an ethanol solvent, and then 1 kg of an epoxy resin, 10 g of 2-ethyl-4-methylimidazole, and 20 g of zinc stearate were added. After stirring, degassing was performed in a vacuum oven at 50°C for 1 hour, and the ethanol was volatilized.

[0082] The above resin was injected into a mold on which multiple layers of glass fiber were laid using a vacuum infusion method, and cured at 120°C for 2 hours to obtain an epoxy resin / glass fiber composite material by vacuum infusion.

[0083] The prepared epoxy resin / glass fiber composite material was immersed in the recycling solution of the present application having a concentration of 1 g / L for 1 hour under ice water bath conditions, and the separation of the glass fiber from the epoxy resin was observed.

[0084] Example 6:

[0085] 1 kg of the phenolic curing agent of the present application was dissolved in 1 L of an ethanol solvent, and then 1 kg of an epoxy resin, 10 g of 2-ethyl-4-methylimidazole, and 20 g of zinc stearate were added. After stirring, degassing was performed in a vacuum oven at 50°C for 1 hour, and the ethanol was volatilized.

[0086] The above resin was injected into a mold on which multiple layers of glass fiber were laid using a vacuum infusion method, and cured at 120°C for 2 hours to obtain an epoxy resin / glass fiber composite material by vacuum infusion.

[0087] The prepared epoxy resin / glass fiber composite material was immersed in the recycling solution of the present application having a concentration of 10 g / L for 1 hour under ice water bath conditions, and the separation of the glass fiber from the epoxy resin was observed.

[0088] Comparative Example 1:

[0089] 5 kg of hydroquinone was dissolved in 10 L of an ethanol solvent, and then 5 kg of an epoxy resin, 50 g of 1-methylimidazole, and 200 g of zinc stearate were added. Degassing was performed in a vacuum oven at 50°C for 1 hour, and the ethanol was volatilized.

[0090] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 50cm / min, and the mold cross-sectional size is 150*5mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0091] The prepared epoxy resin / glass fiber composite material was immersed in the recovery solution of the present invention with a concentration of 1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0092] Comparative Example 2:

[0093] 1 kg of hydroquinone was dissolved in 1 L of ethanol solvent, and then 1 kg of epoxy resin, 10 g of 2-methylimidazole, and 50 g of zinc stearate were added. After stirring evenly, the mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0094] The resin was injected into a mold covered with multiple layers of glass fiber by vacuum infusion and cured at 120° C. for 2 hours to obtain a vacuum infused epoxy resin / glass fiber composite material.

[0095] The prepared epoxy resin / glass fiber composite material was immersed in the recovery solution of the present invention with a concentration of 1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0096] Comparative Example 3:

[0097] 1 kg of the phenolic curing agent of the present invention was dissolved in 1 L of ethanol solvent, and then 1 kg of epoxy resin, 10 g of 2-methylimidazole, and 50 g of zinc stearate were added. After stirring evenly, the mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0098] The resin was injected into a mold covered with multiple layers of glass fiber by vacuum infusion and cured at 120° C. for 2 hours to obtain a vacuum infused epoxy resin / glass fiber composite material.

[0099] The prepared epoxy resin / glass fiber composite material was immersed in a recovery solution prepared by the present invention and diluted to a concentration of 0.1 g / L in an ice-water bath for 1 hour, and the separation of the glass fiber and the epoxy resin was observed.

[0100] Comparative Example 4:

[0101] Dissolve 5 kg of a curing agent containing diphenyl disulfide (such as 4,4'-diphenyl disulfide) in 10 L of ethanol solvent, then add 5 kg of epoxy resin, 50 g of 1-methylimidazole, and 200 g of zinc stearate. Degas the mixture in a vacuum oven at 50°C for 1 hour to evaporate the ethanol.

[0102] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 50cm / min, and the mold cross-sectional size is 150*5mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0103] The prepared epoxy resin / glass fiber composite was immersed in a 0.1 g / L 2-mercaptoethanol solution in an ice-water bath for 24 hours, and the separation of the glass fiber and epoxy resin was observed. The recovered solution was then heated to 110°C and refluxed, and the separation of the glass fiber and epoxy resin was observed.

[0104] Comparative Example 5:

[0105] Dissolve 1 kg of a curing agent containing -C=N- (e.g., a phenolic cyanate ester) in 1 L of ethanol solvent, then add 1 kg of epoxy resin, 10 g of 2-methylimidazole, and 40 g of zinc stearate. Stir well and degas in a vacuum oven at 50°C for 1 hour to evaporate the ethanol.

[0106] The resin was injected into a mold covered with multiple layers of glass fiber by vacuum infusion and cured at 120° C. for 2 hours to obtain a vacuum infused epoxy resin / glass fiber composite material.

[0107] The prepared epoxy resin / glass fiber composite was immersed in a 1 mol / L ethylenediamine / DMF solution in an ice-water bath for one hour, and the separation of the glass fiber and epoxy resin was observed. The recovered solution was then heated to 160°C and refluxed, and the separation of the glass fiber and epoxy resin was observed.

[0108] Comparative Example 6:

[0109] 5 kg of the phenolic curing agent of the present invention was dissolved in 10 L of ethanol solvent, and then 5 kg of epoxy resin, 50 g of 1-methylimidazole, 200 g of zinc stearate, and 100 g of zinc acetylacetonate (ester exchange catalyst) were added. The mixture was degassed in a vacuum oven at 50° C. for 1 hour to evaporate the ethanol.

[0110] The neatly arranged fiber raw materials are evenly impregnated with the above-mentioned resin glue. During the impregnation process, it is ensured that the fibers can be completely impregnated with the resin glue. Under the action of traction, the pre-impregnated fiber raw materials pass through the preforming device and the high-temperature mold, and are formed by high-temperature curing to obtain a composite material plate. The curing temperature is divided into three zones, namely 140°C, 150°C, and 160°C. The pultrusion rate is 50cm / min, and the mold cross-sectional size is 150*5mm to obtain a pultruded epoxy resin / glass fiber composite material.

[0111] The prepared epoxy resin / glass fiber composite was immersed in a 1g / L zinc acetylacetonate / ethylene glycol recovery solution in an ice-water bath for 12 hours, and the separation of the glass fiber and epoxy resin was observed. The recovery solution was then heated to 160°C and refluxed, and the separation of the glass fiber and epoxy resin was observed.

[0112] Table 1: Mechanical properties of epoxy resin / glass fiber composite materials

[0113]

[0114] Table 2: Mechanical properties of epoxy resin / glass fiber composite materials

[0115]

[0116] Table 3: Mechanical properties of virgin glass fiber and recycled glass fiber fabrics

[0117]

[0118]

[0119] Comparison of the results of Examples 1-6 and Comparative Examples 1-6 in Tables 1, 2, and 3 demonstrates that the introduction of an acetal structure into the curing agent does not degrade the mechanical properties of the composite material. Instead, it readily dissolves into the recovery solution prepared by the present invention at low temperatures, enabling recycling of the composite material. In contrast, composite materials prepared using three types of dynamic covalent bonds—disulfide bonds, Schiff base bonds, and transesterification—cannot be recycled at low temperatures and can only be recycled at high temperatures. Furthermore, the mechanical properties of the composite materials deteriorate to varying degrees.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A recyclable epoxy resin / glass fiber composite material containing an acetal structure, characterized in that: The invention comprises epoxy resin, phenolic curing agent containing acetal structure, curing accelerator, release agent and glass fiber.

2. The recyclable epoxy resin / glass fiber composite material containing an acetal structure according to claim 1, characterized in that: The epoxy resin contains at least two epoxy groups; Preferably, the epoxy resin is bisphenol A epoxy resin; More preferably, the bisphenol A epoxy resin is bisphenol A diglycidyl ether and its structural formula is:

3. The recyclable epoxy resin / glass fiber composite material containing an acetal structure according to claim 1, characterized in that: The phenolic curing agent is prepared by reacting hydroquinone and dimethoxymethane as raw materials.

4. The recyclable epoxy resin / glass fiber composite material containing an acetal structure according to claim 1, characterized in that: The curing accelerator is an imidazole compound; Preferably, the imidazole compound is one of 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole and 1,2-dimethylimidazole; More preferably, the imidazole compound is 1-methylimidazole.

5. The recyclable epoxy resin / glass fiber composite material containing acetal structure according to claim 1, characterized in that: The release agent is zinc stearate.

6. A method for preparing a recyclable epoxy resin / glass fiber composite material containing an acetal structure as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Weighing epoxy resin, phenolic curing agent, imidazole compound and release agent; The phenolic curing agent is dissolved in an ethanol solution, and then the phenolic curing agent, a release agent and an epoxy resin are added and mixed evenly, and then degassed in a vacuum oven at a temperature of 50° C. for 1 hour to obtain a mixed intermediate; The mixed intermediate is introduced into glass fiber through a pultrusion process or a vacuum infusion process to prepare a recyclable epoxy resin / glass fiber composite material.

7. The method for preparing a recyclable epoxy resin / glass fiber composite material containing an acetal structure according to claim 6, characterized in that: The pultrusion process is specifically: The mixed intermediate is impregnated with glass fiber and pultruded, and then passed through a mold under traction for curing and molding to prepare a recyclable epoxy resin / glass fiber composite material; The curing process in the mold is divided into three stages, and the curing temperatures of the three stages are 140°C, 150°C and 160°C respectively. The pulling speed of the traction is 0.2-3 m / min.

8. The method for preparing a recyclable epoxy resin / glass fiber composite material containing an acetal structure according to claim 6, characterized in that: The vacuum infusion process is specifically: The mixed intermediate was added into a mold covered with glass fiber by vacuum infusion and cured at 110° C. for 2 hours to obtain a recyclable epoxy resin / glass fiber composite material.

9. A method for recycling a recyclable epoxy resin / glass fiber composite material containing an acetal structure according to any one of claims 1 to 5, characterized in that: The recyclable epoxy resin / glass fiber composite material was immersed in a dichloromethane solution containing trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine in an ice-water bath for 1 hour; Preferably, the molar ratio of trimethylsilyl trifluoromethanesulfonate to 2,2'-bipyridine is 1:1, and the total mass concentration of trimethylsilyl trifluoromethanesulfonate and 2,2'-bipyridine in the dichloromethane solution is 1-10 g / L.

10. An application, characterized in that: The recyclable epoxy resin / glass fiber composite material containing an acetal structure according to any one of claims 1 to 5 is used as the raw material for wind turbine blades.

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