A resin glass transition based delamination recycling method for carbon fiber laminates

Abstract

The embodiment of the present application discloses a kind of based on resin glass transition carbon fiber laminated plate delamination recycling method, comprising: carbon fiber laminated plate is heated under preset condition, so that epoxy resin reversibly is changed from glassy state to rubbery state, obtain the carbon fiber laminated plate after heat treatment;The carbon fiber laminated plate after heat treatment is delaminated, so that each carbon fiber layer in the carbon fiber laminated plate after heat treatment is separated, obtain single-layer carbon fiber sheet;Single-layer carbon fiber sheet is naturally cooled to room temperature, and the single-layer carbon fiber sheet after cooling is cut, to obtain multiple size uniform carbon fiber cutting piece;Surface of carbon fiber cutting piece is brushed with adhesive, and then multiple surface adhesive carbon fiber cutting piece is stacked and arranged and hot-pressed into shape, to obtain newly prepared carbon fiber laminated plate.The present application fully retains the length and strength of carbon fiber in CFRP, realizes the green, high-value utilization of carbon fiber and resin, reduces the production cost of carbon fiber, reduces environmental pollution and saves energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon fiber reinforced resin matrix composite recycling, in particular to a carbon fiber laminate delamination recycling method based on resin glass transition. BACKGROUND

[0002] Due to the high strength, light specific gravity, corrosion resistance and good thermal stability of carbon fiber reinforced resin matrix composite (hereinafter referred to as "CFRP"), a large amount of waste CFRP is generated during the preparation and use of CFRP. The waste CFRP cannot be naturally degraded, and the traditional landfill or incineration treatment not only pollutes the environment, but also wastes valuable carbon fiber resources. Carbon fiber production costs are high and energy consumption is large.

[0003] The epoxy resin as the matrix material in CFRP has excellent mechanical properties, heat resistance, corrosion resistance and other characteristics, and the epoxy resin belongs to thermosetting resin. Once cured to form a three-dimensional network structure, it cannot be remelted, reshaped or reprocessed, significantly increasing the difficulty of CFRP recycling technology. The mechanical recycling method recovers CFRP mainly by using cutting, crushing, grinding, screening and other processes to obtain powder or chopped carbon fiber products rich in matrix resin. However, the length and strength of the carbon fiber in the mechanical recycling product are greatly lost, and the recycling product has low utilization value, which seriously limits its industrial application. The main reasons include: (1) CFRP has excellent specific strength and specific modulus, resulting in poor mechanical processing performance of CFRP. Unlike wood and rubber, CFRP, which is hard in texture, cannot be obtained in the form of regular thin slices, fine wires or other customized shapes by mechanical cutting. At present, CFRP can only be obtained in the form of large pieces of coarse crushing by cutting or crushing. These coarse crushing materials have large thickness and irregular size, and a large amount of filler or adhesive is needed to fill the gaps between the coarse crushing products during hot pressing, resulting in a large difference in mechanical properties between the newly prepared CFRP product and the original CFRP; (2) the cured epoxy resin in CFRP, which is in a glassy state (hard and brittle solid), tightly wraps the soft carbon fiber tows, resulting in the breaking of the soft carbon fiber into carbon fiber powder or short fibers with low economic value during mechanical dissociation. SUMMARY

[0004] The present application aims to provide a carbon fiber laminate delamination recycling method based on resin glass transition, which effectively makes up for the shortcomings of traditional mechanical recycling methods that can only recover low-value carbon fiber powder and chopped fibers, fully retains the length and strength of carbon fibers in CFRP, and effectively avoids the environmental pollution caused by the large degradation of epoxy resin in pyrolysis or solvent decomposition methods, realizes green and high-value utilization of resin, reduces carbon fiber production costs, reduces environmental pollution, and saves energy.

[0005] The application provides a resin glass transition-based carbon fiber laminate plate delamination recycling method, which comprises the following steps:

[0006] The waste carbon fiber laminate plate is placed in an oven for heat treatment under preset conditions, so that the epoxy resin in the waste carbon fiber laminate plate undergoes reversible glass transition and changes from a glass state to a rubber state, the waste carbon fiber laminate plate is softened, and a heat-treated carbon fiber laminate plate is obtained, wherein the preset conditions are heating in an air atmosphere between the glass transition temperature and the thermal decomposition temperature of the epoxy resin.

[0007] The heat-treated carbon fiber laminate plate is immediately subjected to delamination treatment after being taken out of the oven, so that each carbon fiber layer in the heat-treated carbon fiber laminate plate is separated from each other, and a single-layer carbon fiber sheet is obtained.

[0008] The single-layer carbon fiber sheet is naturally cooled to room temperature, the epoxy resin returns to a glass state, and the single-layer carbon fiber sheet after cooling is subjected to cutting treatment, and a plurality of carbon fiber cutting sheets with uniform sizes are obtained.

[0009] The surface of the carbon fiber cutting sheet is brushed with an adhesive, a plurality of carbon fiber cutting sheets brushed with the adhesive are arranged in layers and subjected to forming treatment, and a carbon fiber laminate plate with a required shape and thickness is obtained.

[0010] As a further improvement of the application, the preset conditions are heating at 200-350 DEG C in an air atmosphere for 1-15 minutes.

[0011] As a further improvement of the application, the preset conditions are heating at 200-250 DEG C in an air atmosphere for 1-15 minutes, and the shear strength of the epoxy resin is 4.58-7.19% under a normal temperature environment.

[0012] As a further improvement of the application, the preset conditions are heating at 260-350 DEG C in an air atmosphere for 1-15 minutes, and the shear strength of the epoxy resin is 0.35-3.1% under a normal temperature environment.

[0013] As a further improvement of the application, the delamination treatment comprises the following steps:

[0014] The heat-treated carbon fiber laminate plate is subjected to bending treatment by using a bending machine until the relative bending radius of the heat-treated carbon fiber laminate plate reaches 2.5-22, and the bending angle of the heat-treated carbon fiber laminate plate is greater than or equal to 120 degrees, so that each carbon fiber layer in the heat-treated carbon fiber laminate plate is separated from each other.

[0015] As a further improvement of the application, the adhesive is a liquid epoxy resin.

[0016] As a further improvement of the present application, the forming treatment is a hot press forming treatment or a vacuum bag forming treatment.

[0017] As a further improvement of the present application, the hot press forming treatment comprises:

[0018] The pressure heating is performed at a pressure of 0.1-25.0 MPa and a temperature of 25-260°C for 1-180 minutes.

[0019] As a further improvement of the present application, the size of the carbon fiber cutting piece is: length of 50-200 mm, width of 1-30 mm, and thickness of 0.1-1 mm.

[0020] The present application has the advantages of effectively making up for the shortage of traditional mechanical recycling method which can only recycle low-value carbon fiber powder and chopped fibers, fully retaining the length and strength of carbon fibers in CFRP, effectively avoiding the environmental pollution caused by a large amount of degradation of epoxy resin in pyrolysis or solvent decomposition method, realizing green and high-value utilization of resin, reducing the production cost of carbon fibers, reducing environmental pollution, and saving energy. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 The flow chart of the method described in an exemplary embodiment of the present application;

[0023] Figure 2 The state diagram of the carbon fiber laminated plate after heat treatment in the layering process in the method described in an exemplary embodiment of the present application.

[0024] 1, fixed groove; 2, fixed shaft; 3, rotary bending head; 4, carbon fiber laminated plate after heat treatment; 5, carbon fiber piece; 6, epoxy resin. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative positional relationship, movement condition, etc. between components in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directional indications will also change accordingly.

[0027] In addition, in the description of the present application, the terms used are only for illustrative purposes, and are not intended to limit the scope of the present application. The terms "include" and / or "contain" are used to specify the presence of the elements, steps, operations and / or components, but do not exclude the presence or addition of one or more other elements, steps, operations and / or components. The terms "first", "second", etc. can be used to describe various elements, which do not represent the order and do not limit the elements. In addition, in the description of the present application, unless otherwise stated, the meaning of "multiple" is two and more than two. These terms are only used to distinguish one element from another. These and / or other aspects become apparent from the following drawings, and those skilled in the art can more easily understand the description of the embodiments described in the present application. The drawings are used only for illustrative purposes to depict the embodiments described in the present application. Those skilled in the art will easily realize from the following description that alternative embodiments of the structures and methods shown in the present application can be employed without departing from the principles of the present application.

[0028] The method for delaminating and recycling a carbon fiber laminate based on resin glass transition according to the embodiments of the present application comprises:

[0029] The waste carbon fiber laminate is placed in an oven for heat treatment under preset conditions, so that the epoxy resin in the waste carbon fiber laminate undergoes reversible glass transition, changes from glassy state to rubbery state, the waste carbon fiber laminate softens, and a heat-treated carbon fiber laminate is obtained, wherein the preset conditions are heating in air atmosphere between the glass transition temperature and the thermal decomposition temperature of the epoxy resin;

[0030] The heat-treated carbon fiber laminate is immediately delaminated after being taken out of the oven, so that each carbon fiber layer in the heat-treated carbon fiber laminate is separated from each other, and a single-layer carbon fiber sheet is obtained;

[0031] The single-layer carbon fiber sheet is naturally cooled to room temperature, the epoxy resin returns to glassy state, and the single-layer carbon fiber sheet after cooling is cut to obtain a plurality of carbon fiber cutting sheets with uniform size;

[0032] The surface of the carbon fiber cutting sheet is brushed with an adhesive, a plurality of carbon fiber cutting sheets brushed with the adhesive are arranged in layers and formed to obtain a carbon fiber laminate with a required shape and thickness.

[0033] As Figure 1 shown, according to the pre-set size of the waste carbon fiber laminated plate screening, the waste carbon fiber laminated plate greater than the pre-set size is pre-cut, and the waste carbon fiber laminated plate less than or equal to the pre-set size is obtained,

[0034] Step one: the waste carbon fiber laminated plate less than or equal to the pre-set size is directly placed in a high-temperature oven and heated in an air atmosphere between the glass transition temperature and the thermal decomposition temperature of the epoxy resin, the reversible glass transition phenomenon of the epoxy resin in the carbon fiber laminated plate occurs, so that the epoxy resin in the carbon fiber laminated plate is converted from brittle and hard glass state to soft rubber state, and the carbon fiber laminated plate also softens; wherein the pre-set size can be set according to the size of the high-temperature oven and the bending machine and the feeding requirement.

[0035] Step two: the heat-treated carbon fiber laminated plate is taken out from the oven and quickly put into a bending machine, the carbon fiber laminated plate in the softening state (the heat-treated carbon fiber laminated plate) is processed by bending, rolling or pressing, and a single-layer carbon fiber sheet is obtained.

[0036] Step three: the single-layer carbon fiber sheet is naturally cooled to room temperature, the soft rubber state of the epoxy resin attached to the single-layer carbon fiber sheet is restored to the brittle and hard glass state, and the shear strength of the restored glass state epoxy resin is 79.21-96.00% of the original epoxy resin; the cooled single-layer carbon fiber sheet is cut to obtain a plurality of carbon fiber cutting sheets.

[0037] Step four: the surface of the carbon fiber cutting sheet is brushed with an adhesive, and the adhesive is a liquid epoxy resin; a plurality of carbon fiber cutting sheets coated with the adhesive are laid and stacked, and then the stacked carbon fiber cutting sheets are pressed into new carbon fiber laminated plates with different shapes and thicknesses by molding, and the bending strength of the new carbon fiber laminated plates can reach about 50-84% of the original carbon fiber laminated plates, so the recycling of the waste carbon fiber laminated plates is completed.

[0038] An optional embodiment, the pre-set condition is heating at 200-350℃ in air atmosphere for 1-15 minutes.

[0039] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 200-350 DEG C in an air atmosphere for 1-15 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved; moreover, the treatment temperature is lower than the resin degradation temperature, the resin degradation rate is only 0.7%-5.8%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, meanwhile, the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, and the green and high-value utilization of the resin is realized.

[0040] The shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 200-350 DEG C is 0.35%-7.19% of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, the length and strength of the carbon fiber are reserved, meanwhile, the carbon fiber laminated plate also softens, the bending strength of the carbon fiber laminated plate (the carbon fiber laminated plate after heat treatment) after softening is 0.01%-7.18% of the carbon fiber laminated plate at normal temperature, so that the carbon fiber laminated plate is more easily bent during the delamination process, and the energy is saved.

[0041] Preferably, the preset condition is heating at 200-250 DEG C in an air atmosphere for 1-15 minutes.

[0042] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 200-250 DEG C in an air atmosphere for 1-15 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved; the shear strength of the epoxy resin in the carbon fiber laminated plate under the heating condition of 200-250 DEG C is 4.58%-7.19% of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, and the length and strength of the carbon fiber are reserved.

[0043] Preferably, the preset condition is heating at 260-350 DEG C in an air atmosphere for 1-15 minutes.

[0044] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 260-350 DEG C in an air atmosphere for 1-15 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, the process energy consumption is saved; the shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 260-350 DEG C is 0.35%-3.1% of the shear strength of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, and the length and strength of the carbon fiber are reserved.

[0045] Preferably, the preset condition is heating at 350 DEG C in an air atmosphere for 5 minutes.

[0046] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 350 DEG C in an air atmosphere for 5 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, the process energy consumption is saved; and the treatment temperature of the present application is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 5.8%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, at the same time, the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, realizing the green and high-value utilization of the resin.

[0047] The shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 350 DEG C is 0.35% of the shear strength of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, and the length and strength of the carbon fiber are reserved, at the same time, the carbon fiber laminated plate also softens, the bending strength of the carbon fiber laminated plate after softening is 0.01% of the bending strength of the carbon fiber laminated plate at normal temperature, so that the carbon fiber laminated plate is more easily bent during the delamination process, and the energy is saved.

[0048] Preferably, the preset condition is heating at 300 DEG C in an air atmosphere for 8 minutes.

[0049] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 300 DEG C in an air atmosphere for 8 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved; moreover, the treatment temperature of the present application is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 3.4%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, meanwhile, the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, and the green and high-value utilization of the resin is realized.

[0050] The shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 300 DEG C is 2.21% of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible while being delaminated during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, the length and strength of the carbon fiber are reserved, meanwhile, the carbon fiber laminated plate also softens, the bending strength of the softened carbon fiber laminated plate is 0.03% of the carbon fiber laminated plate at normal temperature, so that the carbon fiber laminated plate is more easily bent during the delamination process, and energy is saved.

[0051] Preferably, the preset condition is heating at 275 DEG C in an air atmosphere for 10 minutes.

[0052] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven, heated at 275 DEG C in an air atmosphere for 10 minutes, the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminated plate occurs, so that the epoxy resin in the waste carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved; moreover, the treatment temperature of the present application is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 2.9%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, meanwhile, the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, and the green and high-value utilization of the resin is realized.

[0053] The shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 275 DEG C is 3.01% of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible while being delaminated during the delamination process, the mechanical properties such as shear, compression and tension of the epoxy resin are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, the length and strength of the carbon fiber are reserved, meanwhile, the carbon fiber laminated plate also softens, the bending strength of the softened carbon fiber laminated plate is 0.03% of the carbon fiber laminated plate at normal temperature, so that the carbon fiber laminated plate is more easily bent during the delamination process, and energy is saved.

[0054] Preferably, the preset condition is heating at 260℃ for 15 minutes in air atmosphere.

[0055] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven and heated at 260℃ for 15 minutes in air atmosphere. The reversible glass transition phenomenon occurs in the epoxy resin in the waste carbon fiber laminated plate, so that the epoxy resin in the carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved. Moreover, the treatment temperature of the present application is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 2.3%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, and the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, realizing the green and high-value utilization of the resin.

[0056] The shear strength of the epoxy resin in the waste carbon fiber laminated plate under the heating condition of 260℃ is 3.95% of the shear strength of the epoxy resin at room temperature, so that the carbon fiber sheet can be layered as much as possible while being protected during the delamination process. The mechanical properties of the epoxy resin such as shear, compression and tension are reduced, the mechanical processing performance of the carbon fiber laminated plate is improved, the length and strength of the carbon fiber are reserved, and the carbon fiber laminated plate also softens. The bending strength of the carbon fiber laminated plate that softens is 0.04% of the bending strength of the carbon fiber laminated plate at room temperature, so that the carbon fiber laminated plate is more easily bent during the delamination process, and energy is saved.

[0057] Preferably, the preset condition is heating at 250℃ for 15 minutes in air atmosphere.

[0058] The waste carbon fiber laminated plate less than or equal to the preset size is directly placed in a high-temperature oven and heated at 250℃ for 15 minutes in air atmosphere. The reversible glass transition phenomenon occurs in the epoxy resin in the waste carbon fiber laminated plate, so that the epoxy resin in the carbon fiber laminated plate is converted from the brittle and hard glass state to the soft rubber state, the resin glass transition is quickly realized, and the process energy consumption is saved. Moreover, the treatment temperature of the present application is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 1.9%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, and the waste epoxy resin in the waste carbon fiber laminated plate is transferred to the newly prepared carbon fiber laminated plate together with the carbon fiber, realizing the green and high-value utilization of the resin.

[0059] The shear strength of the epoxy resin in the waste carbon fiber laminate under heating at 250 DEG C is 4.58% of that of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties of the epoxy resin such as shear, compression and tension are reduced, the mechanical processing performance of the carbon fiber laminate is improved, the length and strength of the carbon fiber are reserved, meanwhile, the carbon fiber laminate also softens, the bending strength of the softened carbon fiber laminate is 0.06% of that of the carbon fiber laminate at normal temperature, so that the carbon fiber laminate is more easily bent during the delamination process, and energy is saved.

[0060] Preferably, the preset condition is heating at 200 DEG C for 15 minutes in air atmosphere.

[0061] The waste carbon fiber laminate with a size less than or equal to the preset size is directly placed in a high-temperature oven, heated at 200 DEG C for 15 minutes in air atmosphere, and the reversible glass transition phenomenon of the epoxy resin in the waste carbon fiber laminate occurs, so that the epoxy resin in the carbon fiber laminate is converted from brittle and hard glass state to soft rubber state, the resin glass transition is quickly realized, and energy consumption is saved; moreover, the treatment temperature is lower than the resin degradation temperature, the degradation rate of the epoxy resin is only 0.7%, the environmental pollution problem caused by resin pyrolysis can be effectively avoided, meanwhile, the waste epoxy resin in the waste carbon fiber laminate is transferred to the newly prepared carbon fiber laminate together with the carbon fiber, and green and high-value utilization of the resin is realized.

[0062] The shear strength of the epoxy resin in the waste carbon fiber laminate under heating at 200 DEG C is 7.19% of that of the epoxy resin at normal temperature, so that the carbon fiber sheet can be protected as much as possible during the delamination process, the mechanical properties of the epoxy resin such as shear, compression and tension are reduced, the mechanical processing performance of the carbon fiber laminate is improved, the length and strength of the carbon fiber are reserved, meanwhile, the carbon fiber laminate also softens, the bending strength of the softened carbon fiber laminate is 0.14% of that of the carbon fiber laminate at normal temperature, so that the carbon fiber laminate is more easily bent during the delamination process, and energy is saved.

[0063] In an alternative embodiment, the delamination process comprises:

[0064] The heat-treated carbon fiber laminate is subjected to bending treatment by using a bending machine until the relative bending radius of the heat-treated carbon fiber laminate reaches 2.5-22, and until the bending angle of the heat-treated carbon fiber laminate is greater than or equal to 120 degrees, so that the carbon fiber layers in the heat-treated carbon fiber laminate are separated from each other.

[0065] As Figure 2As shown, in the process of layering, the heat-treated carbon fiber laminate 4 includes carbon fiber sheets 5 and epoxy resin 6, one end of the heat-treated carbon fiber laminate 4 is fixed in the fixed groove 1, the heat-treated carbon fiber laminate is bent along the fixed shaft 2 under the action of the rotary bending head 3, the adjacent carbon fiber layers in the heat-treated carbon fiber laminate 4 will be relatively displaced to generate shear stress on the resin between the carbon fiber layers, as the bending deformation degree of the carbon fiber laminate increases, the shear stress on the resin between the carbon fiber layers also rapidly increases. When the shear stress exceeds the limit that the rubbery epoxy resin can withstand, the epoxy resin between the carbon fiber layers will crack and debond, eventually leading to the separation of each carbon fiber layer in the carbon fiber laminate, and single-layer carbon fiber sheets are obtained which are easy to mechanically cut. When the relative bending radius of the heat-treated carbon fiber laminate reaches 2.5-22 and the bending angle of the heat-treated carbon fiber laminate is ≥120°, the shear stress on the resin between the carbon fiber layers exceeds the limit that the rubbery epoxy resin can withstand, leading to cracking or debonding of the epoxy resin between the carbon fiber layers, and causing the separation of each carbon fiber layer in the carbon fiber laminate. Each carbon fiber layer includes a carbon fiber sheet 5 and an epoxy resin 6.

[0066] Preferably, the heat-treated carbon fiber laminate is taken out of the oven and quickly placed in a bending machine, and the carbon fiber laminate in a softened state (heat-treated carbon fiber laminate) is bent by pressure bending to a bending radius of 5 and a bending angle of 130°, and the carbon fiber layers in the carbon fiber laminate separate from each other to obtain single-layer carbon fiber sheets.

[0067] Preferably, the carbon fiber laminate in a softened state (heat-treated carbon fiber laminate) is bent by pressure bending to a bending radius of 20 and a bending angle of 150°, and the carbon fiber layers in the carbon fiber laminate separate from each other to obtain single-layer carbon fiber sheets.

[0068] Preferably, the carbon fiber laminate in a softened state (heat-treated carbon fiber laminate) is bent by tension bending to a bending radius of 10 and a bending angle of 140°, and the carbon fiber layers in the carbon fiber laminate separate from each other to obtain single-layer carbon fiber sheets.

[0069] Preferably, the carbon fiber laminate in a softened state (heat-treated carbon fiber laminate) is bent by roll bending or tension bending to a bending radius of 5 and a bending angle of 120°, and the carbon fiber layers in the carbon fiber laminate separate from each other to obtain single-layer carbon fiber sheets.

[0070] Preferably, the carbon fiber laminate in a softened state (heat-treated carbon fiber laminate) is bent by roll bending or tension bending to a bending radius of 2.5 and a bending angle of 120°, and the carbon fiber layers in the carbon fiber laminate separate from each other to obtain single-layer carbon fiber sheets.

[0071] Preferably, the bending radius of the carbon fiber laminated plate in the softened state is 22 and the bending angle of the carbon fiber laminated plate is 120°, and the carbon fiber layers in the carbon fiber laminated plate are separated from each other to obtain a single-layer carbon fiber sheet.

[0072] In step three, the single-layer fiber sheet is cut into a carbon fiber cutting sheet with a length of 50mm to 200mm, a width of 1mm to 30mm, and a thickness of 0.1mm to 1mm.

[0073] In step four, the molding treatment method can be a commonly used treatment method on the market, and the application does not make specific limitations on the treatment method. Preferably, the molding treatment is a hot pressing molding treatment or a vacuum bag molding treatment. Optionally, the hot pressing molding treatment includes: pressurizing and heating at a pressure of 0.1 to 25.0Mpa and a temperature of 25 to 260℃ for 1 to 180 minutes.

[0074] Example 1:

[0075] The waste carbon fiber laminated plate smaller than or equal to the preset size is placed in a high-temperature oven, heated at 350℃ in an air atmosphere for 5min, the shear strength of the epoxy resin in the waste carbon fiber laminated plate is 0.35% of the shear strength of the epoxy resin at room temperature, and the bending strength of the softened carbon fiber laminated plate (the carbon fiber laminated plate after heat treatment) is 0.01% of the bending strength of the carbon fiber laminated plate at room temperature. The carbon fiber laminated plate after heat treatment is taken out of the oven and quickly placed in a bending machine. The carbon fiber laminated plate in the softened state (the carbon fiber laminated plate after heat treatment) is bent by a bending radius of 5 and a bending angle of 130°, and the carbon fiber layers in the carbon fiber laminated plate are separated from each other to obtain a single-layer carbon fiber sheet. The single-layer carbon fiber sheet obtained by delamination treatment is naturally cooled to room temperature, and then the single-layer carbon fiber sheet is cut into a carbon fiber cutting sheet with a length of 150mm, a width of 20mm, and a thickness of 0.2mm. The shear strength of the glassy epoxy resin is 45.56% of the shear strength of the original epoxy resin, and the degradation rate of the epoxy resin is 5.8% during the entire heating process. Liquid epoxy resin is brushed on the surface of the carbon fiber cutting sheet, and then the carbon fiber cutting sheet with epoxy resin on the surface is laid and pressed. Then, the carbon fiber cutting sheet is pressed into a carbon fiber laminated plate with different shapes and thicknesses by using a hot pressing molding process or a vacuum bag molding process. The molding pressure is 5.0Mpa, the molding heating temperature is 120℃, and the molding time is 180 minutes. The bending strength of the newly prepared carbon fiber laminated plate can reach about 84% of the original carbon fiber laminated plate.

[0076] Example 2:

[0077] The waste carbon fiber laminate sheet less than or equal to the preset size is placed in a high-temperature oven and heated at 300°C in an air atmosphere for 8 min. The shear strength of the epoxy resin in the waste carbon fiber laminate sheet is 0.2.21% of the shear strength of the epoxy resin at room temperature, and the bending strength of the softened carbon fiber laminate sheet is 0.03% of the bending strength of the carbon fiber laminate sheet at room temperature. The carbon fiber laminate sheet after heat treatment is taken out of the oven and quickly placed in a bending machine. The softened carbon fiber laminate sheet is bent to a radius of 20 by pressure bending, and the bending angle of the carbon fiber laminate sheet is 150°. At this time, the carbon fibers in the carbon fiber laminate sheet are separated from each other, and a single-layer carbon fiber sheet is obtained. The single-layer carbon fiber sheet obtained by delamination is naturally cooled to room temperature. Then, the single-layer carbon fiber sheet is cut into a carbon fiber cutting sheet with a length of 80 mm, a width of 10 mm, and a thickness of 0.1 mm. The shear strength of the carbon fiber cutting sheet is 98.55% of the shear strength of the original epoxy resin. The degradation rate of the epoxy resin during the entire heating process is 3.4%. Liquid epoxy resin is applied to the surface of the carbon fiber cutting sheet. The carbon fiber cutting sheet with epoxy resin on the surface is laid and then pressed into a carbon fiber laminate sheet with different shapes and thicknesses by using a hot-pressing forming process or a vacuum bag forming process. The molding pressure is in the range of 10.0 Mpa, the molding heating temperature is in the range of 160°C, and the molding time is 120 min. The bending strength of the newly prepared carbon fiber laminate sheet can reach about 75% of the original carbon fiber laminate sheet.

[0078] Example 3:

[0079] The waste carbon fiber laminate sheet less than or equal to the preset size is placed in a high-temperature oven and heated at 275°C in an air atmosphere for 10 min. The shear strength of the epoxy resin in the waste carbon fiber laminate sheet is 3.01% of the shear strength of the epoxy resin at room temperature, and the bending strength of the softened carbon fiber laminate sheet is 0.03% of the bending strength of the carbon fiber laminate sheet at room temperature. The carbon fiber laminate sheet after heat treatment is taken out of the oven and quickly placed in a bending machine. The softened carbon fiber laminate sheet is bent to a bending radius of 10 by a bending method. When the bending angle of the carbon fiber laminate sheet is 140°, the carbon fibers in the carbon fiber laminate sheet are separated from each other, and a single-layer carbon fiber sheet is obtained. The single-layer carbon fiber sheet obtained by delamination is naturally cooled to room temperature. Then, the single-layer carbon fiber sheet is cut into a carbon fiber cutting sheet with a length of 100 mm, a width of 20 mm, and a thickness of 0.2 mm. The shear strength of the carbon fiber cutting sheet is 93.75% of the shear strength of the original epoxy resin. The degradation rate of the epoxy resin during the entire heating process is 2.9%. Liquid epoxy resin is applied to the surface of the carbon fiber cutting sheet. The carbon fiber cutting sheet with epoxy resin on the surface is laid and then pressed into a carbon fiber laminate sheet with different shapes and thicknesses by a hot pressing forming process or a vacuum bag forming process. The molding pressure is in the range of 5.0 Mpa, the molding heating temperature is in the range of 120°C, and the molding time is 120 min. The bending strength of the newly prepared carbon fiber laminate sheet can reach about 69% of the original carbon fiber laminate sheet.

[0080] Example 4:

[0081] The waste carbon fiber laminate sheet less than or equal to the preset size is placed in a high-temperature oven and heated at 250°C in an air atmosphere for 15 min. The shear strength of the epoxy resin in the waste carbon fiber laminate sheet is 4.58% of the shear strength of the epoxy resin at room temperature, and the bending strength of the softened carbon fiber laminate sheet is 0.06% of the bending strength of the carbon fiber laminate sheet at room temperature. The carbon fiber laminate sheet after heat treatment is taken out of the oven and quickly placed in a bending machine. The softened carbon fiber laminate sheet is bent by a roller to a bending radius of 5, and the bending angle of the carbon fiber laminate sheet is 120°. The carbon fibers in the carbon fiber laminate sheet are separated from each other, and a single-layer carbon fiber sheet is obtained. The single-layer carbon fiber sheet obtained by delamination is naturally cooled to room temperature. Then, the single-layer carbon fiber sheet is cut into a carbon fiber cutting sheet with a length of 80 mm, a width of 2 mm, and a thickness of 0.3 mm. The shear strength of the carbon fiber cutting sheet is 95.52% of the shear strength of the original epoxy resin. The degradation rate of the epoxy resin during the entire heating process is 1.9%. Liquid epoxy resin is applied to the surface of the carbon fiber cutting sheet. The carbon fiber cutting sheet with epoxy resin on the surface is laid and then pressed into a carbon fiber laminate sheet with different shapes and thicknesses by a hot pressing forming process or a vacuum bag forming process. The molding pressure is in the range of 1 MPa, the molding heating temperature is in the range of 120°C, and the molding time is 180 min. The bending strength of the newly prepared carbon fiber laminate sheet can reach about 65% of the original carbon fiber laminate sheet.

[0082] Example 5:

[0083] The waste carbon fiber laminate plate less than or equal to the preset size is placed in a high-temperature oven, heated at 200 DEG C in an air atmosphere for 15 min, the shear strength of the epoxy resin in the waste carbon fiber laminate plate is 7.19% of the shear strength of the epoxy resin at room temperature, and the bending strength of the softened carbon fiber laminate plate is 0.14% of the bending strength of the carbon fiber laminate plate at room temperature. The carbon fiber laminate plate after heat treatment is taken out from the oven and quickly put into a bending machine, and the softened carbon fiber laminate plate is bent by a bending radius of 5 through a bending mode, and when the bending angle of the carbon fiber laminate plate is 120 DEG, the carbon fibers in the carbon fiber laminate plate are separated from each other, and a single-layer carbon fiber sheet is obtained; the single-layer carbon fiber sheet obtained by the delamination treatment is naturally cooled to room temperature, and then the single-layer carbon fiber sheet is cut into a carbon fiber cutting sheet with a length of 80 mm, a width of 2 mm and a thickness of 0.3 mm; the shear strength of the recovered glassy epoxy resin is 87.61% of the original epoxy resin, and the degradation rate of the epoxy resin is 0.7% during the whole heating process; the surface of the carbon fiber cutting sheet is coated with liquid epoxy resin, and then the carbon fiber cutting sheet coated with the epoxy resin is laid, and then the carbon fiber cutting sheet is pressed into carbon fiber laminate plates with different shapes and thicknesses by using a hot pressing forming process or a vacuum bag forming process; the molding pressure is 1 MPa, the molding heating temperature is 140 DEG C, and the molding time is 180 min; the bending strength of the newly prepared carbon fiber laminate plate can reach about 59% of the original carbon fiber laminate plate.

[0084] Compared with the prior art, the present application has the following advantages:

[0085] 1. The method of the present application can effectively overcome the problems of poor mechanical processing performance of CFRP and great damage to the length and strength of carbon fibers during mechanical recycling, and significantly improve the utilization value of the mechanical recycling products. The cured epoxy resin in the CFRP is in a glassy state (hard and brittle solid), which tightly wraps the soft carbon fiber tows, resulting in the breaking of the soft carbon fibers together with the brittle epoxy resin into carbon fiber powder or short fibers with low economic value during the mechanical dissociation of the CFRP. To solve this problem, the present application is based on the glass transition principle of epoxy resin, and the brittle glassy epoxy resin is converted into a high-elastic state by adjusting the heating temperature, which reduces the shear, compression and tensile mechanical properties of the epoxy resin, and improves the mechanical processing performance of the CFRP. Then, the CFRP is delaminated and recycled by mechanical bending and delamination. The CFRP delamination product is easy to be cut into thin slices, long strips or filaments with uniform length and thickness by mechanical cutting, and the strength of the carbon fibers in the CFRP is less affected during the delamination and cutting process. The CFRP delamination product can be re-prepared into lightweight and high-strength CFRP products after cutting, gluing, laying and hot pressing.

[0086] 2、The application can effectively overcome the problems of high energy consumption, serious pollution and difficult effective utilization of resin in the traditional pyrolysis recycling method. The traditional pyrolysis recycling process needs to degrade epoxy resin under high temperature conditions (500-1200℃, 30-120 minutes), which causes high energy consumption of pyrolysis process, and the resin degradation products have low utilization value, and also contain a large amount of toxic phenolic substances, which need to be properly disposed to avoid environmental pollution. The heat treatment condition of the application is mild (200-350℃, 1-15 minutes) to quickly realize the glass transition of resin, so the process energy consumption is significantly lower than that of the traditional pyrolysis method; and the treatment temperature of the application is lower than the resin degradation temperature, and the resin degradation rate is only 0.7%-5.8%, which can effectively avoid the environmental pollution problem caused by resin pyrolysis, and at the same time, the waste resin and carbon fiber in CFRP are transferred to new CFRP together, realizing the green and high-value utilization of resin.

[0087] In the description provided herein, a large number of specific details are explained. It is understood, however, that embodiments of the application can be practiced without these specific details.

[0088] Well-known methods, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

[0089] In addition, it is to be understood that the same or equivalent elements or features in different embodiments of the application are in many instances designated with reference numerals. Furthermore, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. In particular, as used herein, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context clearly indicates otherwise. For example, "comprising" (or "comprises") is used throughout to mean "including" (or "includes") or "consisting of."

[0090] Those skilled in the art will appreciate that, although the application has been described with reference to example embodiments, various modifications can be made to the embodiments without departing from the scope of the application. For example, the application is not limited to the specific embodiments disclosed herein, but includes all embodiments falling within the scope of the claims.

Claims

1. A resin glass transition based delamination recycling method of carbon fiber laminates, characterized by, The method comprises: placing the waste carbon fiber laminated board in an oven for heat treatment under preset conditions, so that the epoxy resin in the waste carbon fiber laminated board undergoes reversible glass transition, changes from glassy state to rubbery state, the waste carbon fiber laminated board softens, and a heat-treated carbon fiber laminated board is obtained, wherein the preset conditions are heating in air atmosphere between the glass transition temperature and thermal decomposition temperature of the epoxy resin; immediately performing delamination treatment on the heat-treated carbon fiber laminated board taken out of the oven, so that each carbon fiber layer in the heat-treated carbon fiber laminated board is separated from each other, and a single-layer carbon fiber sheet is obtained; naturally cooling the single-layer carbon fiber sheet to room temperature, the epoxy resin returns to glassy state, and the cooled single-layer carbon fiber sheet is cut to obtain a plurality of carbon fiber cut sheets with uniform size; applying adhesive to the surface of the carbon fiber cut sheet, layering and forming a plurality of carbon fiber cut sheets with adhesive applied to obtain a carbon fiber laminated board with required shape and thickness.

2. The method of claim 1, wherein, The preset conditions are heating at 200-350℃ in air atmosphere for 1-15 minutes.

3. The method of claim 1, wherein, The preset conditions are heating at 200-250℃ in air atmosphere for 1-15 minutes, and the shear strength of the epoxy resin at this time is 4.58-7.19% of that in normal temperature environment.

4. The method of claim 1, wherein, The preset conditions are heating at 260-350℃ in air atmosphere for 1-15 minutes, and the shear strength of the epoxy resin at this time is 0.35-3.1% of that in normal temperature environment.

5. The method of claim 1, wherein, The delamination treatment comprises: bending the heat-treated carbon fiber laminated board by a bending machine until the relative bending radius of the heat-treated carbon fiber laminated board reaches 2.5-22, and the bending angle of the heat-treated carbon fiber laminated board is greater than or equal to 120 degrees, so that each carbon fiber layer in the heat-treated carbon fiber laminated board is separated from each other.

6. The method of claim 1, wherein, The adhesive is a liquid epoxy resin.

7. The method of claim 1, wherein, The forming treatment is hot pressing forming treatment or vacuum bag forming treatment.

8. The method of claim 7, wherein, The hot pressing forming treatment comprises: pressurizing and heating at a pressure of 0.1-25.0 Mpa and a temperature of 25-260℃ for 1-180 minutes.

9. The method of claim 1, wherein, The size of the carbon fiber cut sheet is: length 50-200 mm, width 1-30 mm, and thickness 0.1-1 mm.

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