Synergistic catalytic degradation recovery method of amine cured epoxy resin and composite material thereof

Abstract

The invention discloses a synergistic catalytic degradation and recovery method of amine-cured epoxy resin and a composite material thereof, and belongs to the technical field of degradation and recovery of epoxy resin. The method comprises the following steps: mixing waste epoxy resin or a waste epoxy resin composite material with an oxidative degradation solution according to a mass ratio of 1: (1-10), and carrying out heating reflux reaction for 1-24 hours under the protection of nitrogen at 50-120 DEG C; and filtering, washing, carrying out rotary evaporation and drying on the mixture after the reaction is finished to remove redundant catalyst and solvent, thereby respectively obtaining a liquid-phase product 1 and a solid-phase product 2. Swelling is promoted through the solvent, so that the catalyst and the oxidant can enter an epoxy resin cross-linked network; lewis acid and an oxidizing agent are utilized to synergistically catalyze and degrade waste epoxy resin, the Lewis acid can capture electrons from N to generate amine free radical cations, so that a C-N bond is weakened due to the captured electrons, meanwhile, central atom boron in the Lewis acid can perform coordination, activation energy of hydrolysis reaction is reduced, and hydrolysis is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of degradation and recycling of epoxy resins, and particularly relates to a method for co-catalytic degradation and recycling of amine-cured epoxy resins and their composites. By co-catalyzing with Lewis acid and an active oxidant, the C-N bond in the epoxy resin is broken, thereby destroying the epoxy resin structure and achieving degradation and recycling. Background Art

[0002] Thermosetting polymers play an important role in the plastics industry due to their excellent mechanical and thermal properties, accounting for 15-20% of plastics. As a typical thermosetting material, epoxy resins are widely used in aerospace, wind turbine blades, adhesives, and electronics. With the expiration of the service life of epoxy resins, a large amount of waste epoxy resins will be generated. Now, many technologies for recycling epoxy resins have been developed, such as mechanical recycling, pyrolysis, and chemical recycling. Among them, chemical recycling has become the most efficient treatment method due to its high product utilization rate and high economic value.

[0003] For the degradation of amine-cured epoxy resins, the main problem focuses on the C-N bond formed by the reaction of amine groups and epoxy groups at their crosslinking points. At present, some patents have successfully degraded epoxy resins by decomposing the C-N bond. For example, CN114456439B discloses a method for degrading amine-cured epoxy resin composites, which degrades epoxy resins through a nitrate, glacial acetic acid, and water system, and uses metal ions to act on N to successfully break the C-N bond; however, a strong oxidant such as nitric acid will be formed in its system, which is not friendly to the recovery of fibers in the composite material, and its strong oxidizing property will damage the fiber structure and reduce the strength of fiber reuse. Another example is that CN114479176B discloses a method for degrading amine-cured epoxy resins and their composites by DES. By forming a deep eutectic solvent (DES) with an organic acid and choline chloride, the C-N bond in the epoxy resin is successfully broken, but the reaction temperature needs to be 160-240°C, the reaction conditions are demanding, the energy consumption is large, and too high a temperature will also cause damage to other components such as fibers. Another example is that CN112662008A discloses a method for microwave degradation of epoxy resins, which uses an organic acid and a solvent system, and the reaction conditions are mild; however, the solvent consumption is large during the reaction process, and the solvent system is highly toxic. Therefore, for amine-cured epoxy resins and their composites, a green and environmentally friendly recovery method with mild reaction conditions and beneficial to recycling is desired. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for the synergistic catalytic degradation and recycling of amine-cured epoxy resins and their composites. This method can efficiently degrade and recycle epoxy resins and their composites under mild reaction conditions. The oxidant can oxidize amine radical cations to imine intermediates, and the synergistic catalysis of Lewis acid can reduce the hydrolysis activation energy, making the C-N bond of epoxy resins more easily broken, achieving low-energy consumption and environmentally friendly degradation. The obtained degradation products can be reused again, having great industrial value.

[0005] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] A method for the synergistic catalytic degradation and recycling of amine-cured epoxy resins and their composites, the method comprising the following steps:

[0007] Step 1: Mix waste epoxy resin or waste epoxy resin composite with an oxidative degradation solution at a mass ratio of 1:1 - 10, and heat and reflux the reaction under nitrogen protection at 50 - 120 °C for 1 - 24 h;

[0008] Step 2: After the reaction is completed, filter, wash with water, rotary evaporate, and dry the mixture to remove the excess catalyst and solvent, respectively obtaining a liquid-phase product 1 and a solid-phase product 2.

[0009] Further, in Step 1, the waste epoxy resin is an epoxy resin cured by an amine curing agent, including one or more amine curing agents among aliphatic amines, cycloaliphatic amines, and aromatic amines.

[0010] Further, in Step 1, the waste epoxy resin composite is prepared from an epoxy resin, a curing agent, a reinforcing body, and auxiliary materials; the epoxy resin is an epoxy resin cured by an amine curing agent, including one or more amine curing agents among aliphatic amines, cycloaliphatic amines, and aromatic amines; the reinforcing body includes at least one of carbon fiber, glass fiber, natural fiber, chemical fiber, fabric made of fiber material, nano-carbon material, boron nitride nano-material, metal nano-particle, metal oxide nano-particle, and organic nano-particle; the auxiliary materials include at least one of accelerator, diluent, plasticizer, toughening agent, thickening agent, coupling agent, defoaming agent, leveling agent, ultraviolet absorber, antioxidant, brightening agent, fluorescent reagent, pigment, and filler.

[0011] Further, in Step 1, the oxidative degradation solution is composed of an oxidant, a catalyst, and a solvent; the mass proportion of the oxidant in the oxidative degradation solution is 1 - 50%, the mass proportion of the catalyst in the oxidative degradation solution is 1 - 10%, and the mass proportion of the solvent in the oxidative degradation solution is 40 - 98%.

[0012] Further, in Step 1, the oxidant includes at least one of m-chloroperbenzoic acid, di-tert-butyl peroxide, sodium persulfate, tert-butyl hydroperoxide, perchlorate, peroxy acid, acetic anhydride, TEMPO; the catalyst is a Lewis acid, including BF 3 , BCl 3 , BBr 3 , B(C 2 H 5 ) 3 , B(C 4 H 9 ) 3 , B(C 6 H 5 ) 3 , B(C 6 F 5 ) 3 , B(C 6 Cl 5 ) 3 , B(3,5-(CF 3 ) 2 C 6 H 3 ) 3 ; and the solvent includes at least one of toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, tetrahydrofuran, chloroform, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide.

[0013] Further, in Step 2, the main component of the liquid-phase product 1 is a product containing a carboxyl functional group, and it can be reacted with epichlorohydrin to make epoxy resin again.

[0014] Further, in Step 2, the main component of the solid-phase product 2 is a product containing amino and carboxyl functional groups, and it can be used to make adhesives, polyurethanes and other materials again.

[0015] The beneficial effects of the present invention compared with the prior art are as follows: the present invention promotes swelling through a solvent, which is beneficial for the catalyst and the oxidant to enter the epoxy resin cross-linking network; when the waste epoxy resin is degraded by the synergistic catalysis of Lewis acid and oxidant, the Lewis acid can take electrons from N to generate amine free radical cations, thereby weakening the CN bond due to the taken electrons, and at the same time, the central atom boron in the Lewis acid can coordinate to reduce the activation energy of the hydrolysis reaction and promote hydrolysis; and then the oxidant is used for further oxidation, and the oxidant can further oxidize the amine free radical cations into imine intermediates to promote the further progress of the oxidation reaction, thereby the oxidant and the Lewis acid synergistically catalyze and destroy the cross-linking network of the epoxy resin to achieve the purpose of degradation and recycling. In addition, the degradation products obtained by degrading the waste epoxy resin by oxidation can be reused in the synthesis of epoxy resin, the synthesis of materials such as polyurethane, etc., and have great industrial economic value. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below in conjunction with the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0017] Embodiment 1:

[0018] (1) tert-butyl hydroperoxide, BCl 3 Mix it with dichloromethane in a mass ratio of 40:10:50 to form the oxidative degradation liquid to be used.

[0019] (2) Waste epoxy resin and oxidative degradation liquid were mixed in a mass ratio of 1:3 and placed in a reaction flask. The mixture was condensed and refluxed under nitrogen protection and heated to 60° C. for reaction for 6 h.

[0020] (3) After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove excess catalyst and solvent, thereby obtaining a liquid product 1 and a solid product 2, respectively.

[0021] (4) The degradation products are synthesized into new epoxy resins, and the epoxy resins obtained by degradation and reuse can have a tensile strength of up to 58 MPa and an elongation at break of up to 3.5%.

[0022] Embodiment 2:

[0023] (1) TEMPO, BBr 3 Mix with acetonitrile in a mass ratio of 30:10:60 to form the oxidative degradation solution to be used.

[0024] (2) Waste epoxy resin and oxidative degradation liquid were mixed in a reaction flask at a mass ratio of 1:1. The mixture was condensed and refluxed under nitrogen protection, and heated to 80°C for 6 hours.

[0025] (3) After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove the excess catalyst and solvent, obtaining liquid product 1 and solid product 2 respectively, and the degradation is completed.

[0026] (4) The degraded product is synthesized into a new epoxy resin. The tensile strength of the epoxy resin prepared by reusing the degradation can reach 62 MPa, and the elongation at break can reach 3.8%.

[0027] Example 3:

[0028] (1) Mix meta-chloroperbenzoic acid and B(3,5-(CF 3 ) 2 C 6 H 3 ) 3 with tetrahydrofuran in a mass ratio of 40:1:59 to form a ready-to-use oxidative degradation solution.

[0029] (2) Mix waste epoxy resin and the oxidative degradation solution in a mass ratio of 1:1 and place them in a reaction flask. Under nitrogen protection, carry out condensation reflux and heat to 50 °C for reaction for 8 h.

[0030] (3) After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove the excess catalyst and solvent, obtaining liquid product 1 and solid product 2 respectively, and the degradation is completed.

[0031] (4) The degraded product is synthesized into a new epoxy resin. The tensile strength of the epoxy resin prepared by reusing the degradation can reach 63 MPa, and the elongation at break can reach 3.8%.

[0032] Example 4:

[0033] (1) Mix sodium persulfate and B(C 6 F 5 ) 3 with N,N-dimethylformamide in a mass ratio of 50:10:40 to form a ready-to-use oxidative degradation solution.

[0034] (2) Mix waste epoxy resin and the oxidative degradation solution in a mass ratio of 1:5 and place them in a reaction flask. Under nitrogen protection, carry out condensation reflux and heat to 100 °C for reaction for 8 h.

[0035] (3) After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove the excess catalyst and solvent, obtaining liquid product 1 and solid product 2 respectively, and the degradation is completed.

[0036] (4) The degraded product is synthesized into a new epoxy resin. The tensile strength of the epoxy resin prepared by reusing the degradation can reach 68 MPa, and the elongation at break can reach 4.2%.

[0037] Example 5:

[0038] (1) Mix sodium perchlorate, B(C 4 H 9 ) 3 with N-methylpyrrolidone in a mass ratio of 20:10:70 to form a ready-to-use oxidative degradation solution.

[0039] (2) Mix waste epoxy resin with the oxidative degradation solution in a mass ratio of 1:10 and place it in a reaction flask. Under nitrogen protection, carry out condensation reflux and heat to 80 °C for reaction for 8 h.

[0040] (3) After the reaction is completed, filter, wash with water, rotary evaporate, and dry the mixture to remove the excess catalyst and solvent, and obtain liquid-phase product 1 and solid-phase product 2 respectively, and the degradation is completed.

[0041] (4) Synthesize the degraded product into a new epoxy resin. The tensile strength of the epoxy resin prepared by recycling the degradation can reach 64 MPa, and the elongation at break can reach 4.0%.

[0042] Example 6:

[0043] (1) Mix TEMPO, B(C 2 H 5 ) 3 with acetonitrile in a mass ratio of 30:10:60 to form a ready-to-use oxidative degradation solution.

[0044] (2) Mix waste epoxy resin carbon fiber reinforced composite material with the oxidative degradation solution in a mass ratio of 1:3 and place it in a reaction flask. Under nitrogen protection, carry out condensation reflux and heat to 80 °C for reaction for 18 h.

[0045] (3) After the reaction is completed, filter, wash with water, rotary evaporate, and dry the mixture to remove the excess catalyst and solvent, and obtain carbon fibers, liquid-phase product 1 and solid-phase product 2 respectively.

[0046] (4) Take out the carbon fibers, soak and clean them with dichloromethane. Measure the tensile strength of its single filaments, and the strength retention rate is 93%, indicating that the fibers after degradation still maintain good strength.

[0047] Example 7:

[0048] (1) Mix tert-butyl hydroperoxide, B(C 6 F 5 ) 3 with acetonitrile in a mass ratio of 40:10:50 to form a ready-to-use oxidative degradation solution.

[0049] (2) Mix waste epoxy resin glass fiber reinforced composite material with the oxidative degradation solution in a mass ratio of 1:3 and place it in a reaction flask. Under nitrogen protection, carry out condensation reflux and heat to 60 °C for reaction for 18 h.

[0050] (3) After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove the excess catalyst and solvent, obtaining glass fiber, liquid-phase product 1, and solid-phase product 2 respectively.

[0051] (4) The glass fiber is taken out and soaked and cleaned with dichloromethane. The tensile strength of its single filament is measured, and the strength retention rate is 95%, indicating that the degraded fiber still maintains good strength.

[0052] Comparative example: Referring to Patent CN114479176B, methane sulfonic acid and choline chloride are used to degrade amine-cured epoxy resin.

[0053]

Claims

1. A method for the coordinated catalytic degradation and recovery of amine-cured epoxy resins and composite materials thereof, characterized in that: The method comprises the following steps: Step 1: Mix the waste epoxy resin or waste epoxy resin composite material with the oxidative degradation liquid in a mass ratio of 1:1-10, and heat under reflux at 50-120°C under nitrogen protection for 1-24 hours; Step 2: After the reaction is completed, the mixture is filtered, washed with water, rotary evaporated, and dried to remove excess catalyst and solvent, thereby obtaining a liquid product 1 and a solid product 2, respectively.

2. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1, characterized in that: In step 1, the waste epoxy resin is an epoxy resin cured by an amine curing agent, including one or more amine curing agents selected from aliphatic amines, alicyclic amines, and aromatic amines.

3. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1, characterized in that: In step one, the waste epoxy resin composite material is prepared from epoxy resin, curing agent, reinforcement, and auxiliary materials; the epoxy resin is an epoxy resin cured by an amine curing agent, including one or more amine curing agents of aliphatic amines, alicyclic amines, and aromatic amines; the reinforcement includes at least one of carbon fiber, glass fiber, natural fiber, chemical fiber, and fabric made of fiber material, nano-carbon material, boron nitride nano-material, metal nano-particles, metal oxide nano-particles, and organic nano-particles; the auxiliary materials include at least one of accelerators, diluents, plasticizers, toughening agents, thickeners, coupling agents, defoamers, leveling agents, ultraviolet absorbers, antioxidants, brighteners, fluorescent agents, pigments, and fillers.

4. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1, characterized in that: In step 1, the oxidative degradation liquid consists of an oxidant, a catalyst and a solvent; the mass proportion of the oxidant in the oxidative degradation liquid is 1-50%, the mass proportion of the catalyst in the oxidative degradation liquid is 1-10%, and the mass proportion of the solvent in the oxidative degradation liquid is 40-98%.

5. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1 or 4, characterized in that: In step one, the oxidant includes at least one of m-chloroperbenzoic acid, di-tert-butyl peroxide, sodium persulfate, tert-butyl hydroperoxide, perchlorate, peracid, acetic anhydride, and TEMPO; the catalyst is a Lewis acid, including at least one of BF3, BCl3, BBr3, B(C2H5)3, B(C4H9)3, B(C6H5)3, B(C6F5)3, B(C6Cl5)3, and B(3,5-(CF3)2C6H3)3; the solvent includes at least one of toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, tetrahydrofuran, chloroform, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

6. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1, characterized in that: In step 2, the main component of the liquid phase product 1 is a product containing a carboxyl functional group, which can be used to react with epichlorohydrin to prepare epoxy resin again.

7. The method for synergistic catalytic degradation and recovery of an amine-cured epoxy resin and a composite material thereof according to claim 1, characterized in that: In step 2, the main component of the solid phase product 2 is a product containing amino and carboxyl functional groups, which can be used to make adhesives or polyurethane materials again.

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