A method for preparing polyethylene composites from thermoset epoxy / glass fiber scrap upcycling

Abstract

The application is suitable for the technical field of polymer composite material preparation and solid waste resource utilization, and provides a method for preparing polyethylene composite material by upgrading and recycling thermosetting epoxy / glass fiber waste, wherein a lignin-based reactive surface activation medium prepared by alkali lignin and acrylic monomer is used to perform lossless pre-dissociation on the waste filler, and meanwhile, polymerizable double bonds and ester group functional groups are introduced on the surface of the fiber; carbon-coated fly ash catalyst is prepared by mixing waste fly ash and alkali lignin and calcining in an inert atmosphere, under the action of organic peroxide initiator, grafting copolymerization and interface dynamic exchange reconstruction reaction between the fiber and the matrix are realized in the melting blending process, and a combination layer capable of dynamic repair and rearrangement is formed in situ at the interface; through the synergistic high-value utilization of multiple industrial wastes, the application simultaneously realizes multiple goals of reducing fiber damage, high strength, high toughness, multiple remolding and the like, and forms a circular economy closed loop of waste treatment by waste.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer composite material preparation and solid waste resource utilization, and particularly relates to a method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials. Background Technology

[0002] Composite materials are widely used in aerospace, automotive, construction, and new energy fields due to their superior properties such as high specific strength, high specific stiffness, corrosion resistance, and design flexibility. Among them, thermosetting composite materials with epoxy resin as the matrix and glass fiber as the reinforcement occupy an important position in the field of structural components due to their excellent mechanical properties and chemical stability. However, the three-dimensional cross-linked network structure of the thermosetting resin matrix makes it impossible to reprocess it by heating and melting, which poses a serious challenge to the recycling of such composite material waste. A large amount of waste can only be disposed of by landfill or incineration, resulting in serious resource waste and environmental pollution.

[0003] Existing recycling technologies for thermosetting composite material waste mainly include the following categories: (1) Pyrolysis method: The resin matrix is ​​thermally decomposed under high temperature and oxygen deficiency conditions to recover glass fiber. However, it has high energy consumption, complex process, and high temperature treatment leads to the decomposition of the original sizing agent on the surface of glass fiber and a decrease in the strength of the fiber itself.

[0004] (2) Solvent decomposition: The resin matrix is ​​dissolved using organic solvents or supercritical fluids to recover fibers. Although the fiber properties can be well preserved, the solvent cost is high, the recovery process is complicated, and there are environmental and safety risks caused by the volatilization of organic solvents.

[0005] (3) Chemical depolymerization method: The resin matrix is ​​degraded by acid, alkali or specific chemical reagents. The process conditions are harsh, the chemical consumption is large, the waste liquid treatment cost is high, and it is highly corrosive to equipment.

[0006] (4) Mechanical crushing method: Waste materials are crushed into particles or powder by mechanical means such as shearing and grinding. The process is simple and the cost is low. However, the glass fibers in the filler obtained by mechanical crushing are mostly in the form of resin-encapsulated fiber bundles. In order to achieve the ideal reinforcement effect in the non-polar thermoplastic polyethylene matrix, the fiber bundles must be dissociated into monofilaments and a strong interfacial bond must be established. Conventional treatment methods usually use silane coupling agents to modify the surface of the filler, which can improve the interfacial bond to a certain extent. However, this method relies on high shear processing conditions to achieve fiber bundle dissociation. High shear will seriously damage the fiber length. Summary of the Invention

[0007] This invention provides a method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials, aiming to solve the above-mentioned problems.

[0008] This invention is achieved by a method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials, comprising the following steps: Step 1: Pretreatment and mechanical crushing of thermosetting waste Thermosetting epoxy / glass fiber composite waste is cut into short segments and then subjected to cyclic crushing using a shear crusher to obtain filler containing resin-coated fiber bundles. The weighted average fiber length of the filler is 5.0–8.0 mm, and the glass fiber mass fraction is 75%–85%.

[0009] Step 2: Preparation and pre-dissociation activation treatment of lignin-based reactive surface activation medium (2.1) Alkali lignin and acrylic monomers containing carbon-carbon double bonds are mixed at a mass ratio of 1:2 to 1:8 and stirred for 0.5 to 2 hours under nitrogen purging conditions at 60 to 90°C. Under these conditions, the acrylic monomers serve as both reactants and dispersion media, allowing the lignin macromolecules to fully swell and disperse. By controlling the reaction temperature and time, the lignin undergoes moderate acrylate esterification without excessive cross-linking, resulting in a reactive surface activation medium with good permeability composed of lignin acrylate, unreacted acrylic monomers, and dissolved lignin macromolecules.

[0010] (2.2) Add the filler obtained in step one to the reactive surface-activating medium obtained in step (2.1) and immerse it at 40-70°C for 60-120 minutes. The medium fully penetrates into the polar region of the epoxy interface layer between the fiber bundles, producing swelling and wedging effects, and achieving pre-dissociation of the fiber bundles without high shear force damage. After treatment, filter, wash with alcohol solvent to remove unreacted monomers, and dry to obtain pre-dissociated activated fibers.

[0011] After alcohol washing, the infiltrated lignin macromolecules and lignin acrylates are enriched and anchored on the fiber surface due to their molecular size and the interactions with epoxy resin such as hydrogen bonds and π-π stacking. This anchoring layer introduces polymerizable carbon-carbon double bonds and ester functional groups on the fiber surface, while also introducing rigid aromatic nuclei and ultraviolet absorbing groups from lignin.

[0012] Step 3: Preparation of carbon-coated fly ash catalyst Waste fly ash is ultra-finely ground to an average particle size ≤500nm, then mixed with an alkali lignin aqueous solution at a fly ash to soda ash lignin mass ratio of 1:0.2 to 1:1. After drying, the mixture is heated to 500–700℃ at a rate of 2–10℃ / min under nitrogen or argon protection, held at that temperature for 1–3 hours, and then naturally cooled to obtain a carbon-coated fly ash catalyst. The core function of this catalyst in subsequent melt blending is to catalyze the dynamic exchange and reconstruction reaction of interfacial ester bonds.

[0013] Step 4: Reactive melt blending and dynamic interface reshaping The pre-dissociated activated fibers obtained in step two are mixed with the polyethylene matrix, the carbon-coated fly ash catalyst obtained in step three, and the organic peroxide initiator at a ratio of 20% to 50% of the total mass of the composite material, and the mixture is homogeneous. The amount of the carbon-coated fly ash catalyst is 0.5% to 3% of the total mass of the mixture, and the amount of the organic peroxide initiator is 0.05% to 0.3% of the total mass of the mixture. The mixture is fed into a screw extruder for reactive melt blending at an extrusion temperature of 150 to 230°C and a screw speed of 30 to 60 rpm. The resulting melt blend is then molded or injection molded, cooled, and demolded to obtain the target composite material.

[0014] During melt blending, the pre-dissociated loose fiber bundles effectively dissociate into monofilaments under mild shearing. The organic peroxide initiator decomposes upon heating to generate free radicals, which initiate graft copolymerization between the polyethylene macromolecular free radicals and the acrylate double bonds in the fiber surface active layer, chemically bonding polyethylene segments to the fiber surface. Under high temperature and shearing, the carbon-coated fly ash catalyst, uniformly distributed in the interfacial region, catalyzes the dynamic exchange and reconstruction of ester groups in the fiber surface active layer, forming a dynamically repairable and rearrangeable bonding layer in situ at the interface. This bonding layer can undergo topological rearrangement at high temperatures, endowing the composite material with the ability to be reprocessed multiple times.

[0015] Further, the alkali lignin mentioned in step (2.1) is derived from the acid precipitation product of black liquor from alkali pulping, with a weight-average molecular weight of 2000-10000 Da and a phenolic hydroxyl content of 2-5 mmol / g; the acrylic monomer containing carbon-carbon double bonds is selected from at least one of acrylic acid, methacrylic acid, and hydroxyethyl acrylate; the preferred reaction temperature is 75-85℃, and the reaction time is 60-90 minutes.

[0016] Further, in step (2.2), the mass ratio of the filler to the reactive surface-activating medium is 1:1 to 1:4. The immersion treatment is preferably carried out at 50–60°C for 80–100 minutes; the alcohol solvent is methanol, ethanol, or isopropanol. The drying is performed under vacuum at 50–70°C for 12–24 hours.

[0017] Further, the waste fly ash mentioned in step three contains 3-12 wt% Fe2O3, 1-8 wt% CaO, 0.5-3 wt% TiO2, and 0.3-2 wt% MgO. The ultrafine grinding is performed by planetary ball milling or stirred ball milling, with a grinding time of 2-8 hours; the mass concentration of the alkali lignin aqueous solution is 5%-20%. The heating rate during the calcination process is preferably 5℃ / min, and the holding time is preferably 2 hours; the amorphous porous carbon layer formed by the carbonization of alkali lignin coats the surface of the fly ash particles, forming a core-shell structure with the fly ash particles as the core and the amorphous porous carbon layer as the shell.

[0018] Further, the polyethylene matrix mentioned in step four is low-density polyethylene, linear low-density polyethylene, or high-density polyethylene, or a mixture thereof; the organic peroxide initiator is dicumyl peroxide. The screw extruder is a single-screw extruder or a twin-screw extruder. When a single-screw extruder is used, its length-to-diameter ratio is 10 to 15.

[0019] The present invention also provides a thermosetting waste-filled polyethylene composite material prepared by any of the above methods.

[0020] Compared with the prior art, the embodiments of this application have the following main advantages: The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials provided by this invention uses a lignin-based reactive surface-activated medium to pre-dissociate and loosen the fiber bundles without damage, so that they can be effectively dissociated into monofilaments under subsequent mild melt blending conditions. This reduces fiber damage and breaks the dilemma of traditional mechanical crushing methods that rely on high shear for dissociation, which severely damages the fibers.

[0021] By using carbon-coated fly ash catalysts to promote the dynamic exchange and reconstruction of interfacial ester bonds, a bonding layer that can be dynamically repaired and rearranged is formed in situ at the interface, enabling the composite material to maintain excellent mechanical properties even after multiple cycles of processing.

[0022] The alkali lignin from papermaking black liquor serves as both a raw material for reactive surface activation media and a carbon source for catalysts; fly ash from coal-fired power plants serves as a catalyst matrix; and composite material waste serves as a reinforcing filler, forming a closed-loop circular economy of treating waste with waste.

[0023] The mechanical properties have been comprehensively improved thanks to the triple synergy of reduced fiber damage, effective dissociation, and organic-inorganic hybrid dynamic interface layer. Tensile strength, flexural modulus, and impact toughness are all improved at high filler content. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method for preparing polyethylene composite materials by upgrading and reusing thermosetting epoxy / glass fiber waste, as provided by the present invention.

[0025] Figure 2 This is a bar chart comparing the tensile strength and flexural modulus of various embodiments and comparative examples of the present invention. Detailed Implementation

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0027] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0028] The sources or models of the main raw materials and equipment are as follows: Thermosetting epoxy / glass fiber waste: derived from pultrusion rod waste.

[0029] Alkali lignin: an acid precipitation product derived from black liquor of alkaline pulping, with a weight-average molecular weight of about 5000 Da and a phenolic hydroxyl content of about 3.2 mmol / g; optionally, the alkali lignin is pretreated, the pretreatment including alkali dissolution, filtration, acid precipitation, washing with water to neutral, and drying, to reduce its inorganic salt and sulfur-containing impurity content.

[0030] Waste fly ash: derived from primary fly ash from coal-fired power plants, containing approximately 8 wt% Fe2O3, 4 wt% CaO, 1.5 wt% TiO2, and 0.9 wt% MgO.

[0031] High-density polyethylene (HDPE): melt index 0.9 g / 10min (190℃, 2.16kg), density 0.954 g / cm3.

[0032] Low-density polyethylene (LDPE): melt index 1.9 g / 10min, density 0.924 g / cm3.

[0033] Organic peroxide initiator: dicumyl peroxide (DCP), industrial grade.

[0034] Silane coupling agent: γ-aminopropyltriethoxysilane (KH-550), industrial grade.

[0035] Single screw extruder: screw diameter 60mm, length-to-diameter ratio L / D=15.

[0036] Example 1 (E1): HDPE based, 40 wt% filler (1) Cut the thermosetting waste into short segments with a length not exceeding 15 mm and feed them into a shear crusher for 4 cycles to obtain EP filler with a weighted average fiber length of about 6.3 mm and a glass fiber mass fraction of about 78%.

[0037] (2) Take 50g of alkali lignin and 200g of acrylic acid (mass ratio 1:4) in a reactor, stir and react for 90 minutes at 80℃ and under nitrogen purging. The lignin is fully swollen and dispersed by the dispersion medium of acrylic acid monomer to obtain lignin-based reactive surface activation medium.

[0038] (3) Take 100g of EP filler and immerse it in 200g of the reactive surface activation medium obtained in step (2). Stir at 55°C for 90 minutes. After the treatment is completed, filter it, wash it twice with anhydrous ethanol, and vacuum dry it at 60°C for 20 hours to obtain pre-dissociated activated fiber.

[0039] (4) Take 30g of waste fly ash, wet mill it in a planetary ball mill for 6 hours until the average particle size is about 420nm, dry it and disperse it in 150mL of aqueous solution containing 10g of alkali lignin, stir for 30 minutes and dry it at 100℃; put the dried product in a tube furnace, heat it to 600℃ at 5℃ / min under nitrogen protection and keep it at 600℃ for 2 hours, and cool it naturally to obtain carbon-coated fly ash catalyst.

[0040] (5) Take 40g of pre-dissociated activated fiber, 60g of HDPE, 1.5g of carbon-coated fly ash catalyst and 0.15g of DCP, mix them evenly, and feed them into a single screw extruder. The temperatures of the three zones are 185℃, 210℃ and 225℃ respectively, and the screw speed is 50 rpm. After extrusion granulation, it is molded at 215℃ and 3.5 MPa to obtain the target composite material E1.

[0041] Example 2 (E2): LDPE based, 30 wt% filler In step (5), 60g HDPE was replaced with 70g LDPE, the amount of pre-dissociated activated fiber was adjusted to 30g, the amount of carbon-coated fly ash catalyst was adjusted to 1.2g, the amount of DCP was adjusted to 0.10g, the extrusion temperature was adjusted to 175℃, 200℃, and 215℃, and the remaining steps were the same as in Example 1; the resulting composite material was denoted as E2.

[0042] Example 3 (E3): HDPE based, 50 wt% filler In step (5), the amount of pre-dissociated activated fiber was adjusted to 50g, the amount of HDPE was adjusted to 50g, the amount of carbon-coated fly ash catalyst was adjusted to 2.0g, the amount of DCP was adjusted to 0.20g, the screw speed was adjusted to 45 rpm, and the remaining steps were the same as in Example 1; the resulting composite material was denoted as E3.

[0043] Comparative Example 1 (C1): Pre-dissociation only, no catalyst or initiator The carbon-coated fly ash catalyst and DCP in steps (4) and (5) are omitted, and the rest is the same as in Example 1. The resulting composite material is denoted as C1.

[0044] The results show that although C1 has relatively less fiber damage (average length 1.37 mm), its tensile strength (35.6 MPa), flexural modulus (2.60 GPa), and notched impact strength (7.5 kJ / m2) are much lower than E1 due to the lack of chemical bonding and a dynamic repair and rearrangement bonding layer at the interface. Furthermore, it has no reprocessing capability (the sample cannot be effectively fused when it is cut and remolded, and there are a large number of interface defects inside the molded strip, resulting in extremely low mechanical properties that cannot meet the test requirements). This proves that the purpose of this invention cannot be achieved by pre-dissociation alone.

[0045] Comparative Example 2 (C2): Catalyst and initiator only, no pre-dissociation Replace steps (2) and (3) with: take 100g of untreated EP filler and use it directly in step (5), the rest is the same as in Example 1; the resulting composite material is denoted as C2.

[0046] The results showed that the fibers in C2 were severely broken during processing, with an average length of only 0.85 mm. The mechanical properties were significantly deteriorated, and the fibers were completely unprocessable (they broke apart when the samples were remolded after being cut, and could not be formed into complete test strips). This proved that without a pre-dissociation step to loosen and surface-activate the fiber bundles, the catalyst and initiator could not effectively penetrate to the fiber-matrix interface and play their role. At the same time, the fiber length was also severely damaged, resulting in the fibers having neither initial performance advantages nor reprocessability.

[0047] Comparative Example 3 (C3): Replacing the pre-dissociation and catalytic system of the present invention with a silane coupling agent. Steps (2), (3) and (4) are omitted; 100g of EP filler is taken, and 1.5g of silane coupling agent KH-550 is used for surface treatment. After drying, it is mixed evenly with 60g of HDPE and the composite material is prepared under the same extrusion and molding conditions; the resulting composite material is denoted as C3.

[0048] The results show that, although C3, treated with a commercially available silane coupling agent, exhibits significantly improved tensile strength (48.5 MPa) and flexural modulus (3.65 GPa) compared to C1 and C2, it is still significantly lower than E1. Crucially, while C3 possesses certain initial properties, its strength retention rate after three remodeling cycles is only 62%, far lower than E1's 91%. This demonstrates that conventional coupling agent treatment cannot impart the material with the ability to be reprocessed multiple times. In contrast, this invention, by forming a dynamically repairable and rearrangeable interfacial bonding layer, achieves cyclic processing stability unattainable by conventional methods while maintaining excellent initial mechanical properties.

[0049] Comparative Example 4 (C4): Pre-dissociation + initiator, no catalyst Based on Example 1, step (4) of carbon-coated fly ash catalyst is omitted, and the rest is the same as in Example 1; the resulting composite material is denoted as C4.

[0050] The results show that the initial mechanical properties of C4 (tensile strength 52.0 MPa, flexural modulus 3.85 GPa) are significantly better than those of C1, proving that graft copolymerization effectively improves interfacial bonding. However, its strength retention rate after three remodeling cycles is only 58%, far lower than E1's 91%, demonstrating that without a carbon-coated fly ash catalyst to promote the dynamic exchange and reconstruction reaction at the interface to form a bonding layer, the interfacial layer formed solely by graft copolymerization lacks the ability to be reprocessed multiple times. This directly proves that the carbon-coated fly ash catalyst and the dynamic exchange and reconstruction reaction it promotes at the interface are key to achieving reprocessability.

[0051] Performance testing methods: Tensile properties: tested according to ASTM D3039.

[0052] Bending performance: Three-point bending test according to ASTM D7264.

[0053] Impact performance: Izod notched impact test performed according to ASTM D256.

[0054] Average fiber length: Statistical analysis of optical microscopy images after fiber separation by ashing method.

[0055] Reprocessability: The sample was cut and remolded, and the cycle was repeated 3 times. The tensile strength retention rate after each remolding was tested.

[0056] The performance test results are shown in Table 1 below: As can be seen from the table, Examples E1-E3 all achieved long fiber retention, high strength, high rigidity and high toughness, and have excellent reprocessing capability.

[0057] Comparative Example C1 (pre-dissociation only) retained fiber length but lacked interfacial chemical bonding, resulting in poor mechanical properties and reprocessability. Comparative Example C2 (catalyst and initiator only) suffered severe fiber breakage during processing due to the lack of pre-dissociation. Comparative Example C3 (silane coupling agent treatment) represents a mature fiber surface treatment solution currently used in industry. Although its initial mechanical properties were somewhat improved, its reprocessability was significantly insufficient. Comparative Example C4 (pre-dissociation + initiator, no catalyst) had good initial properties, but due to the lack of a bonding layer formed by interfacial dynamic exchange and reconstruction reaction, its reprocessability was also poor.

[0058] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0059] It should be understood that the disclosed technical solutions in the embodiments provided in this application can be implemented in other ways. For example, the technical solution embodiments described above are merely illustrative. For instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or communication connections shown or discussed may be indirect coupling or communication connections between devices or units through some interfaces, and may be in telecommunications or other forms.

[0060] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs. The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features in the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions are also within the scope of protection of the present invention.

Claims

1. A method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials, characterized in that, Includes the following steps: Step 1: Mechanically crush the waste thermosetting epoxy / glass fiber composite material to obtain filler containing resin-coated fiber bundles; Step 2: Add the filler to the lignin-based reactive surface activation medium and immerse it at 40-70°C for 60-120 minutes; after treatment, filter, wash with alcohol solvent, and dry to obtain pre-dissociated activated fibers; The lignin-based reactive surface-activating medium is prepared by mixing and reacting alkali lignin with acrylic monomers containing carbon-carbon double bonds; Step 3: The pre-dissociated activated fibers are mixed with polyethylene matrix, carbon-coated fly ash catalyst and organic peroxide initiator at a ratio of 20% to 50% of the total mass of the composite material. The mixture is then melt-blended and molded to obtain the target composite material. The carbon-coated fly ash catalyst is prepared by ultra-fine grinding of waste fly ash, mixing it with an alkali lignin aqueous solution, drying it, and then calcining it under an inert atmosphere. Its dosage is 0.5% to 3% of the total mass of the mixture; the dosage of the organic peroxide initiator is 0.05% to 0.3% of the total mass of the mixture.

2. The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials as described in claim 1, characterized in that, The lignin-based reactive surface-activating medium described in step two is prepared by the following method: alkali lignin and acrylic monomers containing carbon-carbon double bonds are mixed at a mass ratio of 1:2 to 1:8, and the mixture is stirred and reacted at 60–90°C under nitrogen purging conditions for 0.5–2 hours.

3. The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials as described in claim 2, characterized in that, The alkali lignin is derived from the acid precipitation product of black liquor from alkaline pulping, with a weight-average molecular weight of 2000-10000 Da and a phenolic hydroxyl content of 2-5 mmol / g; the acrylic monomer containing carbon-carbon double bonds is selected from at least one of acrylic acid, methacrylic acid, and hydroxyethyl acrylate.

4. The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials as described in claim 1, characterized in that, In step two, the mass ratio of the filler to the lignin-based reactive surface-activating medium is 1:1 to 1:4; the washing is performed using methanol, ethanol, or isopropanol; and the drying is performed under vacuum at 50–70°C for 12–24 hours.

5. The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials as described in claim 1, characterized in that, The carbon-coated fly ash catalyst described in step three is prepared by the following method: waste fly ash is ultra-finely ground to an average particle size ≤500nm, then mixed with an alkali lignin aqueous solution at a mass ratio of fly ash to soda alkali lignin of 1:0.2 to 1:

1. After drying, the mixture is heated to 500-700℃ at a rate of 2-10℃ / min under nitrogen or argon protection, held at this temperature for 1-3 hours, and then cooled to obtain the final product.

6. The method for preparing polyethylene composite materials by upgrading and reusing thermosetting epoxy / glass fiber waste as described in claim 5, characterized in that, The waste fly ash contains 3-12 wt% Fe2O3, 1-8 wt% CaO, 0.5-3 wt% TiO2 and 0.3-2 wt% MgO.

7. The method for upgrading and reusing thermosetting epoxy / glass fiber waste to prepare polyethylene composite materials as described in claim 5, characterized in that, The ultrafine grinding is performed by planetary ball milling or stirred ball milling, with a grinding time of 2 to 8 hours; the mass concentration of the alkali lignin aqueous solution is 5% to 20%; the heating rate is 5℃ / min, and the holding and calcining time is 2 hours.

8. The method for preparing polyethylene composite materials by upgrading and reusing thermosetting epoxy / glass fiber waste as described in claim 1, characterized in that, The polyethylene matrix mentioned in step three is at least one of low-density polyethylene, linear low-density polyethylene, and high-density polyethylene; the organic peroxide initiator is dicumyl peroxide; the melt blending is carried out using a screw extruder with an extrusion temperature of 150-230°C and a screw speed of 30-60 rpm.

9. The method for preparing polyethylene composite materials by upgrading and reusing thermosetting epoxy / glass fiber waste as described in claim 1, characterized in that, The filler in step one contains 75% to 85% glass fiber by mass, and the weighted average fiber length is 5.0 to 8.0 mm.

10. A thermosetting waste-filled polyethylene composite material, characterized in that, Prepared by the method according to any one of claims 1 to 9.

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