Recovery method of waste flexible diamond wire saw and regenerated TPU composite material

Abstract

The invention provides a recovery method of a waste flexible diamond wire saw and a regenerated TPU composite material, and relates to the technical field of waste flexible diamond wire saw recovery. The recycling method of the waste flexible diamond wire saw comprises the following steps that 1, the waste flexible diamond wire saw is frozen and crushed under the freezing condition, and TPU fragments, steel wire bundles and diamond particles are separated out; 2, the TPU fragments are subjected to catalytic degradation, steel wire bundles are subjected to acidolysis, and diamond particles are recycled; wherein the TPU fragment catalytic degradation step comprises the step of enabling a mixture comprising dihydric alcohol, a catalyst and TPU fragments to react under the condition that supercritical fluid is introduced, so as to obtain a TPU degradation product. According to the recovery method of the waste flexible diamond wire saw, provided by the invention, the recovery and regeneration cyclic utilization of the waste flexible diamond wire saw are realized; rapid freezing is combined with supercritical fluid degradation, and the bottleneck of interface separation and molecular weight control of a traditional process is broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste flexible diamond wire saw recycling, and particularly relates to a waste flexible diamond wire saw recycling method and a regenerated TPU composite material. BACKGROUND

[0002] As a typical heterogeneous composite material structure, the flexible diamond wire saw is mainly composed of a copper-plated steel wire rope base, a TPU (thermoplastic polyurethane elastomer rubber) coating layer and diamond abrasive particles, and is widely used in high-precision stone, ceramic and semiconductor wafer cutting. After being scrapped, the multi-component interface is tightly combined and the chemical properties are significantly different. The existing recycling process generally has low resource utilization rate, large process destructiveness and performance degradation of regenerated materials, and has the following key technical bottlenecks: 1. Low multi-component resource utilization rate: Carbon footprint problem caused by TPU burning: TPU accounts for 15%-25% of the total mass of the wire saw. The existing process generally adopts direct burning treatment, which not only causes waste of high molecular resources, but also generates about 2.8 tons of CO2 equivalent carbon emissions per ton of TPU burned, which aggravates the greenhouse effect.

[0003] Low diamond recovery rate and serious particle size degradation: The diamond is difficult to be separated by conventional screening or flotation due to the residual TPU (adhesion rate > 15%) on the surface, and the average recovery rate in the industry is less than 50%. And in the conventional crushing process, the diamond particles are easily cracked due to shear stress and impact force, generating particles with a particle size of <0.3mm (industrial application threshold), which is much lower than the lower limit of the industrial diamond application particle size, resulting in degradation of high-value abrasive to low-end filler.

[0004] 2. Physical and chemical defects of separation process: Structural damage of mechanical crushing is significant: When using traditional hammering or shearing type crushing process, the copper-plated steel wire is easily entangled and agglomerated (entanglement rate > 70%) in the crushing process due to its high ductility, which seriously affects the continuous separation efficiency, and additional manual intervention is required to untangle. At the same time, the brittle diamond has a crushing rate of more than 40% when crushed, which leads to serious degradation of its performance.

[0005] Environmental risk of high-temperature pyrolysis: TPU generates hydrogen cyanide (HCN) and other toxic gases (concentration > 200ppm) when pyrolyzed in an oxygen-free environment (400-600℃), which requires a complex tail gas purification system, and the high pyrolysis temperature also causes oxidation of the steel wire base and peeling of the copper plating layer, reducing the value of the steel for subsequent renewable use.

[0006] 3. Performance degradation of regenerated materials: Downcycling of TPU alcoholysis products: Although existing alcoholysis methods (such as ethylene glycol depolymerization) can recover TPU monomers, the depolymerization reaction is random, the product has a wide molecular weight distribution (PDI = 3.0-5.0), and the end groups contain residual catalyst metal ions (such as titanium esters), which further reduce the activity of the system, and the mechanical properties of the regenerated TPU are significantly reduced, with a tensile strength more than 50% lower than that of the original material, which cannot meet the performance requirements of the wire saw coating.

[0007] Diamond surface contamination weakens the interface bonding ability: After mechanical peeling, the diamond surface is left with a carbonized layer of TPU (thickness > 50 nm) that is difficult to completely remove through simple cleaning. The carbon layer significantly weakens the interface bonding strength between the diamond and the matrix polymer (decreased by > 30%), leading to reduced cutting efficiency and increased abrasive particle shedding rate of the subsequent composite material, which is not conducive to the high-performance reuse of the material.

[0008] In summary, the existing recycling process of flexible diamond wire saws is limited by the physical-chemical performance differences and high interface bonding strength between the heterogeneous multi-component materials, making it difficult to achieve efficient, low-damage, and environmentally friendly co-recycling. In particular, in terms of the separation and regeneration of key components such as the TPU thermoplastic coating, superhard diamond abrasive particles, and copper-plated steel wire matrix, existing methods generally have serious resource loss, significant material degradation, and high environmental pollution risk, which restricts the high-value utilization of such solid waste resources. SUMMARY

[0009] In view of the above analysis, the present application aims to provide a recycling method for waste flexible diamond wire saws and a regenerated TPU composite material to solve at least one of the following problems of the prior art: achieving efficient, low-damage, and environmentally friendly co-recycling of waste flexible diamond wire saws, and improving the overall performance of the regenerated TPU composite material.

[0010] The purpose of the present application is mainly achieved through the following technical solutions: In a first aspect, the present application provides a recycling method for waste flexible diamond wire saws, comprising the following steps: Step 1: freezing the waste flexible diamond wire saw, breaking it under frozen conditions, and separating out TPU fragments, steel wire bundles, and diamond particles; Step 2: catalytically degrading the TPU fragments, and acidizing the steel wire bundles and recycling the diamond particles; wherein the step of catalytically degrading the TPU fragments comprises: reacting a mixture comprising dihydric alcohol, a catalyst, and TPU fragments under the condition of passing a supercritical fluid to obtain a TPU degradation product.

[0011] Preferably, in step 1, the freezing temperature is -190°C to -200°C.

[0012] Preferably, in step 1, the freezing time is 10-15 minutes.

[0013] Preferably, in step 1, the average particle size of the broken TPU fragments, steel wire bundles and diamond particles is 2-8 mm.

[0014] Preferably, in the step of catalytic degradation of the TPU fragments, the catalyst comprises at least one of nano-ZnO and carbon nanotube-supported bimetallic catalyst A-B / CNT.

[0015] Preferably, in the carbon nanotube-supported bimetallic catalyst A-B / CNT, metal A comprises at least one of Ti, Zr, La, Nd, Bi and Sn, and metal B comprises at least one of Co, Ni, Bi, Fe, Mn, Cr, Zn, Al and Cu.

[0016] Preferably, the mass ratio of metal A to metal B is (1-3.5):1, and the total loading of metal A and metal B is 5-10 wt% based on the total weight of the catalyst.

[0017] Preferably, the average particle size of the catalyst is 10-30 nm.

[0018] Preferably, in the step of catalytic degradation of the TPU fragments, the amount of the catalyst is 1%-6% of the mass of the TPU fragments.

[0019] Preferably, in the step of catalytic degradation of the TPU fragments, the mass ratio of the TPU fragments to the glycol is 1:(1-2).

[0020] Preferably, the mass ratio of the TPU fragments to the supercritical fluid introduced is (10:1)-(10:1.5).

[0021] Preferably, in the step of catalytic degradation of the TPU fragments, the reaction temperature is 120-150℃.

[0022] Preferably, in the step of catalytic degradation of the TPU fragments, the reaction pressure is 12-18 MPa.

[0023] Preferably, in the step of catalytic degradation of the TPU fragments, the glycol comprises at least one of 1,4-butanediol, ethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, bisphenol A, polycarbonate glycol, 1,2-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, m-xylylene glycol, p-xylylene glycol, m-dihydroxybenzene and p-dihydroxybenzene.

[0024] Preferably, the step of acidolysis of the steel wire bundle comprises: reacting a mixture comprising the steel wire bundle and mixed acid solution, adjusting the pH, separating and recovering the generated iron-containing precipitate, and forming a first solution from the solution after separating the iron-containing precipitate; countercurrently extracting the first solution with a hydrophobic ionic liquid, adding dilute sulfuric acid to the obtained copper ion-rich ionic liquid phase, and recovering the generated copper sulfate crystals.

[0025] Preferably, in the step of acidolysis of the steel wire bundle, the mixed acid solution comprises a citric acid aqueous solution and a hydrogen peroxide aqueous solution, the mass concentration of the citric acid aqueous solution is 30-40%, the mass concentration of the hydrogen peroxide aqueous solution is 25-35%, and the volume ratio of the citric acid aqueous solution to the hydrogen peroxide aqueous solution is (2-4):1.

[0026] Preferably, in the step of acidolysis of the steel wire bundle, the reaction temperature is 45-55℃.

[0027] Preferably, in the step of acidolysis of the steel wire bundle, the hydrophobic ionic liquid is [C4mim][PF6].

[0028] Preferably, in the step of acidolysis of the steel wire bundle, the volume ratio of the hydrophobic ionic liquid to the first solution is (1:3)-(1:5).

[0029] In a second aspect, the present application provides a regenerated TPU composite material, raw materials of which comprise the TPU degradation product, diamond particles, nano-silica, isocyanate and 3-aminopropyltrimethoxysilane.

[0030] Preferably, the mass ratio of the TPU degradation product to the diamond particles is (8-13):1.

[0031] Preferably, the addition amount of the nano-silica is 0.5-3.0% of the total mass of the raw materials.

[0032] Preferably, the addition amount of the isocyanate is 5-15wt% of the total mass of the TPU degradation product and the isocyanate.

[0033] Preferably, the addition amount of the 3-aminopropyltrimethoxysilane is 1-10wt% of the total mass of the TPU degradation product and the 3-aminopropyltrimethoxysilane.

[0034] Preferably, the average particle size of the nano-silica is 20-50nm.

[0035] Preferably, the diamond particles are the diamond particles recovered in the recycling method of the waste flexible diamond wire saw.

[0036] In a third aspect, the present application provides a preparation method of the composite material, which comprises the following steps: generating the regenerated TPU composite material in situ by using a reaction extrusion process for a mixture comprising a TPU degradation product, diamond particles, nano-silica, isocyanate and 3-aminopropyltrimethoxysilane.

[0037] Compared with the prior art, the present application can at least achieve one of the following beneficial effects: A) The application provides a recycling method of waste flexible diamond wire saw, which realizes the recycling and recycling of waste flexible diamond wire saw, realizes the efficient separation of waste flexible diamond wire saw and the green regeneration of each component, significantly improves the resource utilization efficiency of solid waste, and meets the technical guidance of "zero landfill, low carbonization and high value"; Deep cold-supercritical collaborative technology: liquid nitrogen rapid freezing combined with supercritical fluid degradation, breaking through the interface separation and molecular weight control bottleneck of traditional process.

[0038] B) The application provides a recycling method of waste flexible diamond wire saw, which realizes interface decoupling and molecular reconstruction collaborative optimization, uses supercritical fluid and TPU fragments for mixing, and enhances the adsorption activation ability of the catalyst to isocyanate group, promotes the rupture of urethane, and degrades TPU into oligomers.

[0039] C) The application provides a recycling method of waste flexible diamond wire saw, which realizes non-strong corrosion green hydrometallurgy, citric acid system replaces strong corrosive acid, and copper recovery rate is improved without heavy metal pollution.

[0040] D) The application provides a recycling method of waste flexible diamond wire saw, which realizes the high-performance design of regenerated materials, and gives regenerated TPU with heat conduction and mechanical properties by blending diamond / nano SiO2.

[0041] E) The application provides a recycling method of waste flexible diamond wire saw, which has strong process chain closed loop circulation ability: acid, solvent and other additives can be recycled and reused more than 10 times, effectively reducing operation cost and reducing secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The viscosity test curve comparison chart of the TPU degradation product of embodiments 1-6 provided by the application; Figure 2 The Fourier infrared curve comparison chart of the TPU degradation product of embodiment 1 and industrial polyether polyol 4110 provided by the application; Figure 3 The thermal gravimetric curve comparison chart of the regenerated material of embodiment 1 and comparative example 4 provided by the application. DETAILED DESCRIPTION

[0043] The preferred embodiments of the application will be specifically described below in combination with the drawings, wherein the drawings constitute a part of the application and are used to illustrate the principles of the embodiments of the application.

[0044] In a first aspect, the application provides a recycling method of waste flexible diamond wire saw, comprising the following steps: Step 1: treatment of raw materials: freeze the waste flexible diamond wire saw, break under the condition of freezing, separate out TPU fragments, steel wire bundle and diamond particles; Step 2: catalytic degradation of TPU fragments, acidolysis of steel wire bundle and recovery of diamond particles; In the step of catalytic degradation of TPU fragments, the mixture comprising dihydric alcohol, catalyst and TPU fragments is reacted under the condition of passing supercritical fluid, pressurized and heated, so that the TPU fragments are catalytically degraded to obtain TPU degradation product (degradation oligomer); In the step of acidolysis of steel wire bundle, the mixture comprising steel wire bundle and mixed acid solution is reacted, the pH is adjusted, the generated iron-containing precipitate is separated and recovered, and the solution after separation of the iron-containing precipitate forms a first solution; the first solution is countercurrently extracted by using a hydrophobic ionic liquid, dilute sulfuric acid is added to the obtained copper ion-rich ionic liquid phase, and the generated copper-containing crystals are recovered; In the step of recovery of diamond particles, the diamond particles are cleaned by plasma under the condition of power of 200-300 W to remove surface carbides.

[0045] In the specific embodiment of the present application, step 1 performs gradient cryogenic breaking and interface separation, and in step 1, the freezing temperature is -190 to -200℃, and the freezing time is 10-15 minutes; the freezing environment is liquid nitrogen environment. It should be noted that the present application uses rapid freezing, which takes advantage of the difference in embrittlement temperature between TPU and metal (TPU: -50℃, steel: -150℃), so that the interface bonding force decreases by >80%, and good interface separation can be achieved.

[0046] In the specific embodiment of the present application, the particle size of the broken materials (TPU fragments, loose steel wire bundle and diamond particles) is 2-8 mm, and the breaking can be performed by a multi-stage roller crusher in a liquid nitrogen environment, and the TPU fragments, loose steel wire bundle and diamond particles are separated by a vortex sorting machine under the condition of magnetic field strength of 0.5-1.2 T.

[0047] In the specific embodiment of the present application, the breaking pressure of the multi-stage roller crusher in step 1 is 5-8 MPa, and the roller speed is 20-50 rpm.

[0048] In the specific embodiment of the present application, in the step of catalytic degradation of TPU fragments, the average particle size of the catalyst is 10-30 nm, and the type of the catalyst is at least one of ZnO, supported AB bimetallic catalyst A-B / CNT (A and B site metals are supported on carbon nanotube catalyst).

[0049] In the specific embodiment of the present application, in the supported AB-site bimetallic catalyst A-B / CNT, metal A can be at least one of Ti, Zr, La, Nd, Bi, Sn, etc., metal B can be at least one of Co, Ni, Bi, Fe, Mn, Cr, Zn, Al, Cu, etc., the mass ratio of metal A and metal B is (1-3.5):1, for example 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, etc. or a range composed thereof, preferably (3-3.5):1. The total loading of metal A and metal B is 5-10 wt%, for example 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% or a range composed thereof, preferably 8-10 wt%, based on the total weight of the catalyst. It should be noted that the mass ratio of metal A and metal B is (1-3.5):1, and a reasonable range of metal mass ratio can ensure the maximization of bimetallic synergy. When the mass ratio of metal A and metal B is higher or lower than the range defined in the present application, the active of the one with higher mass ratio will cover the other, weakening the synergistic effect and failing to achieve the purpose of efficient catalytic degradation; Excessive amount of one metal may also lead to metal aggregates, reducing the effective active surface area.

[0050] It should be noted that the present application does not limit the preparation method of AB-site bimetallic catalyst A-B / CNT, which can be prepared by conventional methods, such as impregnation reduction method, in-situ synthesis method, etc.

[0051] In the specific embodiment of the present application, in the step of catalytic degradation of TPU fragments, the amount of catalyst is 1%~6% of the mass of TPU fragments, for example 1%, 2%, 3%, 4%, 5%, 6% or a range composed thereof, preferably 5%~6%. It should be noted that when the catalyst is less than the minimum amount, the TPU degradation efficiency is too slow or cannot be completely degraded under the same reaction time; when the amount of catalyst is too high, it will cause waste of resources, and a large amount of residual catalyst will also have an unacceptable impact on the performance of the product.

[0052] In the specific embodiment of the present application, in the step of catalytic degradation of TPU fragments, the mass ratio of TPU fragments to dihydric alcohol is 1:(1-2), for example 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2 or a range composed thereof. It should be noted that when the mass ratio of TPU to dihydric alcohol is higher than the range defined in the present application, i.e. the dihydric alcohol content is insufficient, the urethane bond in TPU cannot be fully broken, resulting in a too high molecular weight of the degradation product; when the mass ratio of TPU to dihydric alcohol is lower than the range defined in the present application, i.e. the dihydric alcohol content is too high, a large amount of dihydric alcohol will be left, and free dihydric alcohol will interfere with the recombination equilibrium of the degradation product, resulting in uneven molecular weight distribution of the regenerated polyol.

[0053] In the detailed description of the present application, the dihydric alcohol is at least one of 1,4-butanediol, ethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, bisphenol A, polycarbonate dihydric alcohol, 1,2-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, m-xylene glycol, p-xylene glycol, m-dihydroxybenzene, p-dihydroxybenzene, and the like.

[0054] In the detailed description of the present application, in the step of catalytic degradation of TPU fragments, the reaction temperature is 120-150℃, for example 120, 130, 140, 150℃ or a range consisting of the foregoing, and the reaction time is 1-3 hours.

[0055] In the detailed description of the present application, in the step of catalytic degradation of TPU fragments, the reaction pressure is 12-18 MPa, for example 12, 13, 14, 15, 16, 17, 18 MPa or a range consisting of the foregoing, and the supercritical fluid can be supercritical carbon dioxide. The supercritical CO2 is injected and pressurized to a pressure of 12-18 MPa to maintain a supercritical state. In the detailed description of the present application, the mass ratio of TPU to the injected supercritical carbon dioxide is (10:1)-(10:1.5). It should be noted that if the mass ratio of TPU to supercritical carbon dioxide is higher than the range defined in the present application, the amount of supercritical CO2 is too large, which reduces the surface contact area of the catalyst and dihydric alcohol with the TPU, thereby reducing the reaction rate. If the mass ratio of TPU to supercritical carbon dioxide is lower than the range defined in the present application, the amount of supercritical CO2 is too small, and the supercritical carbon dioxide is difficult to penetrate the hard segment region of the TPU, thus failing to play an auxiliary catalytic role and failing to achieve the purpose of efficient degradation.

[0056] In the detailed description of the present application, in the step of catalytic degradation of TPU fragments, the TPU degradation product is a degradation oligomer, the TPU degradation product is a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 4000-5000, the product PDI=1.2-1.3, and the hydroxyl value is 240-300 mg KOH / g.

[0057] It should be noted that in the step of catalytic degradation of TPU fragments, the supercritical fluid penetrates into the elastomer crosslinked network under high pressure, preferentially swells the amorphous region and weakens the molecular chain interaction, provides a diffusion channel for the catalyst and dihydric alcohol, promotes the breaking of chemical bonds, and plays a role in accelerating the catalytic rate.

[0058] The recycling method of the waste flexible diamond wire saw provided by the application realizes interface decoupling and molecular reconstruction collaborative optimization, utilizes supercritical CO2 and TPU fragments for mixing, controls the mass ratio of dihydric alcohol and the addition amount of nano zinc oxide or supported bimetallic catalyst, and under certain temperature and time, the adsorption activation capacity of the bimetallic catalyst A-B electronic coupling to isocyanate groups is enhanced, the activity of the catalyst is improved, the breaking of the urethane is promoted, and the TPU is efficiently degraded into an oligomer.

[0059] In the embodiment of the application, the mixed acid solution in the step of acidolysis of the steel wire bundle comprises a citric acid aqueous solution and a hydrogen peroxide aqueous solution, the mass concentration of the citric acid aqueous solution is 30-40%, the mass concentration of the hydrogen peroxide aqueous solution is 25-35%, and the volume ratio of the citric acid aqueous solution to the hydrogen peroxide aqueous solution is (2-4):1.

[0060] In the embodiment of the application, the mass ratio of the mixed acid solution to the steel wire bundle is (4-6):1.

[0061] In the embodiment of the application, the reaction temperature in the step of acidolysis of the steel wire bundle is 45-55℃, and the reaction time is 1-3 hours.

[0062] In the embodiment of the application, in the step of acidolysis of the steel wire bundle, the pH is adjusted to 3-3.5, and the generated iron hydroxide colloid precipitate is separated and recovered.

[0063] In the embodiment of the application, in the step of acidolysis of the steel wire bundle, the hydrophobic ionic liquid is [C4mim][PF6], and the volume ratio of the hydrophobic ionic liquid to the first solution is (1:3)-(1:5), for example, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or the like or a range composed of the foregoing. It should be noted that the volume ratio of the extraction liquid to the aqueous phase is required to be neither too high nor too low. If the ratio of the extraction liquid to the aqueous phase is too high, the efficiency of extraction can be accelerated, but the economy is low; if the ratio is too low, the extraction efficiency cannot reach the expected effect; the range defined in the application can better balance the relationship between economy and efficiency.

[0064] In the embodiment of the application, in the step of acidolysis of the steel wire bundle, the concentration of the dilute sulfuric acid is 1-4 mol / L, and preferably 3 mol / L.

[0065] It should be noted that in the step of acidolysis of the steel wire bundle, the steel wire bundle is immersed in a citric acid-hydrogen peroxide mixed solution, the citric acid solution preferentially dissolves iron to generate divalent iron ions, then the hydrogen peroxide oxidizes the divalent iron ions into trivalent iron ions, the pH value is adjusted to 3.0-3.5, Fe 3+The hydrolysis generates Fe(OH)3colloidal precipitate. Filtration achieves solid-liquid separation, multi-stage countercurrent extraction is carried out by using [C4mim][PF6] ionic liquid, and the copper-rich ionic liquid phase and the copper-lean aqueous phase are separated by gravity separation. Dilute sulfuric acid is added to the copper-rich ionic liquid phase, and high-concentration copper sulfate solution is obtained by back extraction through oscillation. Blue copper sulfate pentahydrate crystals are obtained by evaporation crystallization.

[0066] In the specific embodiment of the present application, the recycling method of the waste flexible diamond wire saw comprises the following steps: Step 1: Treatment of raw materials (gradient cryogenic crushing and interface dissociation): The waste flexible diamond wire saw is immersed in liquid nitrogen (-196℃) for rapid freezing for 10-15 minutes, the interface bonding force is reduced by more than 80% by taking advantage of the difference in embrittlement temperature between TPU and metal (TPU: -50℃, steel: -150℃), and the waste flexible diamond wire saw is crushed to a particle size of 2-8 mm by using a multi-stage roller crusher in a liquid nitrogen environment. TPU chips, loose steel wire bundles and diamond particles are separated by a vortex separator under the condition of a magnetic field strength of 0.5-1.2T.

[0067] Step 2a: Supercritical catalytic degradation of TPU: Binary alcohol and catalyst are mixed to form a dispersion liquid, stirred for 20-30 minutes, and then TPU chips are added. The mass ratio of TPU to binary alcohol is 1: (1-2). Then the TPU and the catalyst and binary alcohol dispersion liquid are added to a high-pressure reaction kettle, supercritical CO2 is injected, and the pressure is increased to 12-18 MPa. The supercritical state of CO2 is maintained, and the reaction is carried out at 120-150℃ for 1-3 hours. TPU is degraded into hydroxyl-terminated oligomers with a number average molecular weight (Mn) of 4000-5000. The product has a PDI of 1.2-1.3 and a hydroxyl value of 240-300 mg KOH / g.

[0068] Step 2b: Green acidolysis of steel wire (composition of steel wire Fe, Cu): The steel wire bundle is immersed in a citric acid-hydrogen peroxide mixed solution, and ultrasonic assistance (40 kHz) is carried out at a temperature of 45-55℃ for 1-3 hours. The pH is adjusted to 3-3.5. Iron ions hydrolyze to generate iron hydroxide colloidal precipitate, and the iron recovery rate reaches 90-95%. Hydrophobic ionic liquid [C4mim][PF6] is used, and the volume ratio of [C4mim][PF6] to the liquid (after the iron hydroxide colloidal precipitate is separated) is 1:3-1:5. Cu is separated by 3-5 stage mixed clarifiers 2+ , dilute sulfuric acid is added, the stirring speed is 150-400 rpm, copper sulfate solution is obtained, and copper sulfate pentahydrate crystals are obtained by evaporation crystallization. The copper recovery rate is 85-92%. The citric acid-hydrogen peroxide mixed acid solution is regenerated by electro-Fenton method and recycled for 10-15 times.

[0069] Step 2c: The diamond particles are cleaned by plasma at a power of 200-300 W to remove surface carbide, with a purity of 90-98% and a recovery rate of 86-94%. It should be noted that the plasma cleaning gas can be a mixture of argon (Ar) and hydrogen (H2), and the plasma energy is set at 200-300 W, which effectively removes the residual carbonized contamination layer on the surface of the diamond and restores the surface activity of the abrasive particles.

[0070] In a second aspect, the present application provides a recycled TPU composite material, the raw materials of which include the TPU degradation product, recycled diamond particles, nano-silica, isocyanate and 3-aminopropyltrimethoxysilane.

[0071] In the specific embodiment of the present application, the mass ratio of the TPU degradation product to the diamond particles is (8-13):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, or ranges composed thereof. The addition amount of silica is 0.5-3.0% of the total mass of the raw materials (the sum of the total mass of the TPU degradation product, recycled diamond, silica, isocyanate and 3-aminopropyltrimethoxysilane), such as 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or ranges composed thereof.

[0072] In the specific embodiment of the present application, the particle size of the nano-silica ranges from 20 to 50 nm.

[0073] In the specific embodiment of the present application, the diamond particles can be recycled from the recycled diamond particles in the recycling method of the waste flexible diamond wire saw.

[0074] In the specific embodiment of the present application, the recycled TPU composite material can be reused in the flexible diamond wire saw.

[0075] In the specific embodiment of the present application, the addition amount of isocyanate is 5-15 wt% of the mass of isocyanate and TPU degradation product, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 wt%, or ranges composed thereof, preferably 10 wt%. The type of isocyanate can be at least one of polymethylene polyphenyl diisocyanate (PAPI), diphenylmethane diisocyanate (MDI) and toluene diisocyanate and its isomers (TDI).

[0076] In the specific embodiment of the present application, the addition amount of 3-aminopropyltrimethoxysilane is 1-10 wt% of the total mass of 3-aminopropyltrimethoxysilane and TPU degradation product, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 wt%, or ranges composed thereof, preferably 5 wt%. The model of 3-aminopropyltrimethoxysilane can be KH540.

[0077] The application discloses a kind of full-component recovery method of waste flexible diamond rope saw, by deep cold interface dissociation, supercritical directional degradation and green metallurgical technology, realize the synergistic high-value regeneration of polyurethane elastomer (TPU), diamond and steel wire rope.The synergistic separation and efficient regeneration of diamond particles and steel wire rope three components.After the regenerated TPU is reconstructed with oligomer and synergistically enhanced with inorganic nanoparticles, the obtained TPU / diamond composite material has excellent mechanical properties.The regenerated TPU composite material has mechanical properties and thermal conductivity characteristics.

[0078] In a third aspect, the application provides a method for preparing a regenerated TPU composite material, comprising the steps of: Regenerated TPU composite material preparation: a mixture comprising TPU degradation products, diamond particles, nano-silica, isocyanate, and 3-aminopropyltrimethoxysilane is used to generate the regenerated TPU composite material in situ using a reactive extrusion process.

[0079] In the specific embodiment of the application, in the method for preparing a regenerated TPU composite material, the reactive extrusion process refers to the generation of a polyurethane-siloxane crosslinked network in situ using a twin-screw extruder at a temperature of 190-215°C and a screw speed of 55-80 rpm. Preferably, the TPU degradation products, isocyanate, and KH540 are first added to the twin-screw extruder and stirred for 5 min, and then the prepared diamond particles and nano-silica are added to the twin-screw extruder and stirred for 10 min to obtain a polyurethane-siloxane crosslinked network. The tensile strength of the regenerated material can reach 36 MPa (the tensile strength of the virgin TPU is 34 MPa).

[0080] The application proposes a multi-component synergistic recovery and recycling method for waste flexible diamond rope saw, constructs a four-in-one closed-loop recycling process system of "gradient decoupling-green degradation-selective extraction-functional reconstruction", realizes efficient separation of resource components, minimization of pollution control, and high-performance preparation of functional regenerated materials, and realizes: 1. High-precision separation: diamond recovery rate ≥80%, particle size >0.5mm accounting for ≥95%; 2. Closed-loop polymer regeneration: TPU degradation products have controllable molecular weight (PDI <1.5), and the mechanical properties of the regenerated material are retained by ≥85%; 3. Efficient recovery of metal elements and recycling of solution: iron / copper recovery rate in steel wire ≥85%, and acid solution can be recycled for ≥10 times; 4. Performance of functional regenerated materials meets the standards: tensile strength reaches ≥30 MPa, and thermal conductivity coefficient reaches ≥0.40 W / m·K.

[0081] The following preferred embodiments of the present application are described in detail to illustrate the principles of the present application, and are not intended to limit the scope of the present application.

[0082] In the following examples, the reagents used are commercially available products unless otherwise specified.

[0083] In the following examples, the waste flexible diamond wire saw has a diamond mass content of 18%, a TPU mass content of 15%, and a steel wire mass content of 67%. The copper mass content in the steel wire is 5%, the iron mass content is 94%, and the carbon mass content is 1%.

[0084] The mass of the filtered Fe(OH)3 after drying is Y, and the Fe recovery rate calculation formula is: (Y x 52.56%) ÷ (X x 67% x 94%).

[0085] The mass of the dried copper sulfate pentahydrate crystal is T, and the Cu recovery rate calculation formula is: (T x 25.45%) ÷ (X x 67% x 5%).

[0086] The mass of the recovered diamond after drying is Z, and the diamond recovery rate calculation formula is: Z ÷ (X x 18%).

[0087] In the following examples, the preparation method of the A-B / CNT catalyst used in the step of catalytic degradation of TPU fragments adopts an in-situ synthesis method: A salt and / or B salt are mixed and stirred with CNT dispersion liquid respectively, and a reducing agent is added (for example, after mixing A salt with CNT dispersion liquid, the reducing agent is added, and then B salt and the reducing agent are added), A and / or B elements are reduced onto CNT, and finally A-B / CNT catalyst, A / CNT catalyst or B / CNT catalyst is obtained through drying, ion water washing and drying, with an average particle size of 20 nm.

[0088] The average particle size of the nano-silicon dioxide is 50 nm.

[0089] Example 1: ‌(1) Recovery method of waste flexible diamond wire saw: Step 1: The waste flexible diamond wire saw is immersed in liquid nitrogen (-196℃) and rapidly frozen for 15 minutes, broken to a particle size of 2-3 mm by using a multi-stage roller crusher in a liquid nitrogen environment, and TPU fragments, loose steel wire bundles and diamond particles are separated by a vortex separator under the condition of a magnetic field strength of 1.2 T.

[0090] Step 2a: TPU supercritical catalytic degradation: 1,4-butanediol and catalyst Ti-Fe / CNT (catalyst composition and addition amount see Table 1) are mixed to form a dispersion, stirred for 30 min, then TPU fragments are added, the mass ratio of TPU and 1,4-butanediol is 1:2, then the dispersion of TPU and catalyst and 1,4-butanediol is added to a high-pressure reaction kettle, supercritical CO2 is injected, and the pressure is increased to 12-18 MPa, the supercritical state of carbon dioxide is maintained, and the reaction is carried out at 150°C for 3 hours. TPU is degraded into hydroxyl-terminated oligomer with number average molecular weight (Mn) of 4000, the product PDI = 1.2, and the hydroxyl value is 300 mg KOH / g. Figure 2 The Fourier infrared curve comparison chart of the TPU degradation product of Example 1 provided by the present application and the industrial polyether polyol 4110 can be seen that the curves of the two are almost similar, verifying that the TPU is successfully degraded into polyether polyol after supercritical catalytic degradation.

[0091] Step 2b: The steel wire bundle is immersed in a mixed acid solution of citric acid and hydrogen peroxide (the mixed solution of citric acid and hydrogen peroxide has a compounding ratio of 36% citric acid aqueous solution with a mass concentration and 28% H2O2 aqueous solution with a mass concentration mixed in a volume ratio of 3:1, and the mass ratio of the mixed acid solution to the steel wire is 5:1), and ultrasonic assisted reaction is carried out at a temperature of 55°C and a frequency of 40 kHz for 3 hours, and the pH is adjusted to between 3-3.5, the iron ions are hydrolyzed to generate iron hydroxide colloid precipitate, the iron recovery rate reaches 95%, and the solution after separating the iron hydroxide colloid precipitate forms a first solution. The first solution is extracted by using a hydrophobic ionic liquid [C4mim][PF6], the volume ratio of [C4mim][PF6] to the first solution is 1:3, Cu 2+ is separated by 3-5 stage mixing and clarifying tanks, a copper ion rich ionic liquid phase is obtained, dilute sulfuric acid is added to the copper ion rich ionic liquid phase, the stirring speed is 400 rpm, a copper sulfate solution is obtained, and copper sulfate pentahydrate crystals are obtained by evaporation crystallization, the copper recovery rate is 92%, and the citric acid-hydrogen peroxide mixed acid solution is regenerated by electro-Fenton method and recycled for 15 times.

[0092] Step 2c: The diamond is cleaned by Ar-H2 plasma at a power of 300 W, the surface carbide is removed, the purity reaches 98%, and the recovery rate reaches 94%.

[0093] (2) Preparation method of recycled TPU composite material: the mass ratio of degraded TPU oligomer to recycled diamond is 8:1, the amount of nano-silicon dioxide is 3% (based on the total weight of raw materials), the amount of isocyanate (PAPI) added is 10% of the total mass of isocyanate and TPU degradation product, and the amount of 3-aminopropyl trimethoxysilane (KH540) added is 5% of the total mass of 3-aminopropyl trimethoxysilane and TPU degradation product. First, the TPU degradation product, isocyanate and KH540 are simultaneously added to the twin-screw extruder, stirred for 5 min, then the prepared diamond particles and nano-silicon dioxide are added to the twin-screw extruder, stirred for 10 min, and the polyurethane-siloxane crosslinking network is generated in situ by reaction extrusion process (temperature 200℃, rotation speed 30rpm). The tensile strength of the recycled material reaches 36MPa, and the thermal conductivity coefficient increases to 0.50 W / m·K.

[0094] Example 2: ‌(1) Recycling method of waste flexible diamond wire saw: Step 1: immerse the waste flexible diamond wire saw in liquid nitrogen (-196℃) and freeze rapidly for 14 minutes, break it into particles with a particle size of 3~4 mm by using a multi-stage roller crusher in a liquid nitrogen environment, and separate TPU fragments, loose wire bundles and diamond particles under the condition of a magnetic field strength of 1.1 T by using a vortex separator.‌

[0095] Step 2a: TPU supercritical catalytic degradation: 1,6-hexanediol and catalyst La-Zn / CNT (catalyst composition and addition amount see Table 1) are mixed to form a dispersion liquid, stirred for 30 min, then TPU fragments are added, the mass ratio of TPU to 1,6-hexanediol is 1:1.5, then the dispersion liquid of TPU, catalyst and 1,6-hexanediol is added to a high-pressure reaction kettle, supercritical CO2 is injected, and the pressure is increased to 12-18MPa to maintain the supercritical state of carbon dioxide, and the reaction is carried out at 145℃ for 3 hours. TPU is degraded into hydroxyl-terminated oligomer with number average molecular weight (Mn) of 4250, the product PDI=1.22, and the hydroxyl value is 280mg KOH / g.

[0096] Step 2b: immerse the wire bundle in a mixed acid solution of citric acid-hydrogen peroxide (the mixing ratio of the mixed acid solution is the same as in Example 1), and perform ultrasonic assisted reaction at a temperature of 53℃ and a frequency of 40 kHz for 3 hours, adjust the pH to 3-3.5, and the iron ions are hydrolyzed to form a ferric hydroxide colloid precipitate, the iron recovery rate reaches 94%, and the solution after separating the ferric hydroxide colloid precipitate forms a first solution. The first solution is extracted with hydrophobic ionic liquid [C4mim][PF6], the volume ratio of [C4mim][PF6] to the first solution is 1:3.5, and Cu 2+, and then the copper ion-rich ionic liquid phase was added into dilute sulfuric acid with a stirring speed of 350 rpm to obtain a copper sulfate solution, and copper sulfate pentahydrate crystals were obtained by evaporation crystallization, with a copper recovery rate of 90%, and the citric acid-hydrogen peroxide mixed acid solution was regenerated by the electro-Fenton method and recycled for 14 times.

[0097] Step 2c: The diamond was cleaned by Ar-H2 plasma at a power of 280 W to remove surface carbides, with a purity of 96% and a recovery rate of 93%.

[0098] (2) Preparation method of regenerated TPU composite material: the mass ratio of degraded TPU oligomer to recycled diamond was 9:1, the amount of nano-silicon dioxide was 2.5% (based on the total weight of raw materials), the addition amount of PAPI was 10% of the total mass of PAPI and TPU degradation product, and the addition amount of KH540 was 5% of the total mass of KH540 and TPU degradation product. First, the TPU degradation product, isocyanate and KH540 were simultaneously added into a twin-screw extruder and stirred for 5 min, then the prepared diamond particles and nano-silicon dioxide were added into the twin-screw extruder and stirred for 10 min, and a polyurethane-siloxane crosslinked network was generated in situ by reaction extrusion process (temperature 200℃, rotation speed 30rpm). The tensile strength of the regenerated material reached 35 MPa, and the thermal conductivity coefficient increased to 0.48 W / m·K.

[0099] Example 3: ‌(1) Recovery method of waste flexible diamond wire saw: Step 1: The waste flexible diamond wire saw was rapidly frozen in liquid nitrogen (-196℃) for 13 minutes, and then broken into particles with a particle size of 4-5 mm by using a multi-stage roller crusher in a liquid nitrogen environment. The TPU fragments, loose steel wire bundles and diamond particles were separated by a vortex separator under the condition of a magnetic field intensity of 1.0 T.

[0100] Step 2a: Supercritical catalytic degradation of TPU: 1,2-pentanediol and catalyst Bi-Mn / CNT (catalyst composition and addition amount see Table 1) were mixed to form a dispersion liquid, stirred for 30 min, then TPU fragments were added, and the mass ratio of TPU to 1,2-pentanediol was 1:1. The TPU and catalyst and 1,2-pentanediol dispersion liquid were added into a high-pressure reaction kettle, supercritical CO2 was injected, and the pressure was increased to 12-18 MPa to maintain the supercritical state of carbon dioxide. The reaction was carried out at 140℃ for 2.5 hours. The TPU was degraded into a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 4400, the product PDI=1.24, and the hydroxyl value was 270 mg KOH / g.

[0101] Step 2b: Steel wire bundle is immersed in a citric acid-hydrogen peroxide mixed solution (the mixing ratio of the mixed acid is the same as in Example 1), and ultrasonic-assisted reaction is carried out at a temperature of 51°C and a frequency of 44 kHz for 2.5 hours, with the pH adjusted to between 3 and 3.5. Iron ions are hydrolyzed to generate iron hydroxide colloid precipitate, and the iron recovery rate reaches 93%. After separating the iron hydroxide colloid precipitate, the solution forms a first solution. The first solution is extracted with a hydrophobic ionic liquid [C4mim][PF6], and the volume ratio of [C4mim][PF6] to the solution is 1:4. Cu is separated by 3-5 stage mixing and clarifying tanks 2+ , to obtain a copper-rich ionic liquid phase. Dilute sulfuric acid is added to the copper-rich ionic liquid phase at a stirring speed of 300 rpm to obtain a copper sulfate solution. Evaporation and crystallization obtain copper sulfate pentahydrate crystals, and the copper recovery rate is 89%. The citric acid-hydrogen peroxide mixed acid solution is regenerated by electro-Fenton method and recycled for 13 times.

[0102] Step 2c: The diamond is cleaned by Ar-H2 plasma at a power of 260 W to remove surface carbides, with a purity of 95% and a recovery rate of 92%.

[0103] (2) Preparation method of regenerated TPU composite material: the mass ratio of degraded TPU oligomer to recovered diamond is 10:1, the amount of nano-silicon dioxide is 2.0% (based on the total weight of raw materials), the addition amount of PAPI is 10% of the total mass of PAPI and TPU degradation product, and the addition amount of KH540 is 5% of the total mass of KH540 and TPU degradation product. First, the TPU degradation product, isocyanate, and KH540 are simultaneously added to a twin-screw extruder, stirred for 5 min, and then the prepared diamond particles and nano-silicon dioxide are added to the twin-screw extruder, stirred for 10 min. The polyurethane-siloxane crosslinked network is generated in situ by reaction extrusion process (temperature 200°C, rotation speed 30 rpm). The tensile strength of the regenerated material reaches 34 MPa, and the thermal conductivity coefficient increases to 0.46 W / m·K.

[0104] Example 4: ‌(1) Method for recycling waste flexible diamond wire saw: Step 1: The waste flexible diamond wire saw is immersed in liquid nitrogen (-196°C) and rapidly frozen for 12 minutes. A multi-stage roller crusher in a liquid nitrogen environment is used to break it to a particle size of 5-6 mm. TPU fragments, loose steel wire bundles, and diamond particles are separated by a vortex separator under the condition of a magnetic field strength of 0.8 T.

[0105] Step 2a: TPU supercritical catalytic degradation: 1,2-propanediol and catalyst Sn-Cu / CNT (catalyst composition and addition amount see Table 1) were mixed to form a dispersion, stirred for 30 min, then TPU fragments were added, the mass ratio of TPU and 1,2-propanediol was 1:2, then the dispersion of TPU and catalyst and 1,2-propanediol was added to a high-pressure reaction kettle, supercritical CO2 was injected, and the pressure was increased to 12-18 MPa to maintain the supercritical state of carbon dioxide, and the reaction was carried out at 135℃ for 2 hours. TPU was degraded into hydroxyl-terminated oligomer with number average molecular weight (Mn) of 4600, the product PDI=1.26, and the hydroxyl value was 260 mg KOH / g.

[0106] Step 2b: The steel wire bundle was immersed in a citric acid-hydrogen peroxide mixed solution (the mixing ratio of the mixed acid solution was the same as in Example 1), and ultrasonic assisted reaction was carried out at a temperature of 49℃ and a frequency of 40 kHz for 2 hours, and the pH was adjusted between 3-3.5. Iron ions hydrolyzed to form iron hydroxide colloid precipitate, and the iron recovery rate reached 92%. After separating the iron hydroxide colloid precipitate, the solution formed a first solution. The first solution was extracted with hydrophobic ionic liquid [C4mim][PF6], and the volume ratio of [C4mim][PF6] to liquid was 1:4.5. Cu 2+ was separated by 3-5 stage mixing and clarifying tanks to obtain a copper ion-rich ionic liquid phase. Dilute sulfuric acid was added to the copper ion-rich ionic liquid phase, and the stirring speed was 250 rpm to obtain a copper sulfate solution. Evaporation and crystallization obtained copper sulfate pentahydrate crystals, and the copper recovery rate was 87%. The citric acid-hydrogen peroxide mixed acid solution was regenerated by electro-Fenton method and recycled for 12 times.

[0107] Step 2c: The diamond was cleaned by Ar-H2 plasma at a power of 240 W to remove surface carbides, and the purity reached 94% and the recovery rate reached 90%.

[0108] (2) Preparation method of regenerated TPU composite material: the mass ratio of degraded TPU oligomer and recycled diamond was 11:1, the addition amount of nano-silicon dioxide was 1.5% (based on the total weight of raw materials), the addition amount of PAPI was 10% of the total mass of PAPI and TPU degradation product, and the addition amount of KH540 was 5% of the total mass of KH540 and TPU degradation product. First, the TPU degradation product, isocyanate and KH540 were added into the twin-screw extruder at the same time, stirred for 5 min, then the prepared diamond particles and nano-silicon dioxide were added into the twin-screw extruder, stirred for 10 min, and the polyurethane-siloxane crosslinking network was generated in situ by reaction extrusion process (temperature 200℃, rotation speed 30 rpm). The tensile strength of the regenerated material reached 33 MPa, and the thermal conductivity coefficient increased to 0.44 W / m·K.

[0109] Example 5: (1) A method for recycling waste flexible diamond wire saws: Step 1: The waste flexible diamond wire saw is immersed in liquid nitrogen (-196°C) and rapidly frozen for 11 minutes. A multi-stage roller crusher is used to break the wire saw into particles with a particle size of 6-7 mm. A vortex separator is used to separate TPU fragments, loose steel wire bundles, and diamond particles under the condition of a magnetic field strength of 0.6 T.

[0110] Step 2a: Supercritical catalytic degradation of TPU: Ethylene glycol and catalyst Nd-Co / CNT (catalyst composition and addition amount see Table 1) are mixed to form a dispersion liquid, stirred for 30 min, then TPU fragments are added, the mass ratio of TPU to ethylene glycol is 1:1.5, then the dispersion liquid of TPU and catalyst and ethylene glycol is added to a high-pressure reaction kettle, supercritical CO2 is injected, and the pressure is increased to 12-18 MPa to maintain the supercritical state of carbon dioxide, and the reaction is carried out at 130°C for 1.5 hours. TPU is degraded into a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 4850, the product has a PDI of 1.28 and a hydroxyl value of 250 mg KOH / g.

[0111] Step 2b: The steel wire bundle is immersed in a citric acid-hydrogen peroxide mixed solution (the mixing ratio of the acid solution is the same as in Example 1), and ultrasonic assisted reaction is carried out at a temperature of 47°C and a frequency of 40 kHz for 1.5 hours. The pH is adjusted to between 3-3.5, iron ions are hydrolyzed to form iron hydroxide colloid precipitate, the iron recovery rate reaches 91%, and the solution after separating the iron hydroxide colloid precipitate forms a first solution. The first solution is extracted with hydrophobic ionic liquid [C4mim][PF6], the volume ratio of [C4mim][PF6] to liquid is 1:5, and Cu 2+ is separated by 3-5 stage mixing and clarification tank, a copper ion-rich ionic liquid phase is obtained, dilute sulfuric acid is added to the copper ion-rich ionic liquid phase, the stirring speed is 200 rpm, a copper sulfate solution is obtained, and copper sulfate pentahydrate crystals are obtained by evaporation and crystallization. The copper recovery rate is 86%, and the citric acid-hydrogen peroxide mixed acid solution is regenerated by electro-Fenton method and recycled for 11 times.

[0112] Step 2c: The diamond is cleaned by Ar-H2 plasma at a power of 220 W to remove surface carbides, the purity reaches 92%, and the recovery rate reaches 88%.

[0113] (2) Preparation method of recycled TPU composite: the mass ratio of degraded TPU oligomer to recycled diamond is 12:1, the addition amount of nano-silicon dioxide is 1.0% (based on the total weight of raw materials), the addition amount of PAPI is 10% of the total mass of PAPI and TPU degradation product, and the addition amount of KH540 is 5% of the total mass of KH540 and TPU degradation product. First, the TPU degradation product, isocyanate and KH540 are simultaneously added into a double screw extruder, stirred for 5 min, then the prepared diamond particles and nano-silicon dioxide are added into the double screw extruder, stirred for 10 min, and a polyurethane-siloxane crosslinking network is generated in situ by reaction extrusion process (temperature 200℃, rotation speed 30rpm). The tensile strength of the recycled material reaches 32MPa, and the thermal conductivity increases to 0.42 W / m·K.

[0114] Example 6: ‌(1) Recycling method of waste flexible diamond wire saw: Step 1: immerse the waste flexible diamond wire saw in liquid nitrogen (-196℃) and freeze rapidly for 10 minutes, then crush to a particle size of 7-8 mm using a multi-stage roller crusher in a liquid nitrogen environment, and separate the TPU fragments, loose wire bundles and diamond particles under the condition of a magnetic field strength of 0.5 T through a vortex separator.

[0115] ‌Step 2a: Supercritical catalytic degradation of TPU: mix m-xylylenediol and catalyst La-Ni / CNT (catalyst composition and addition amount see Table 1) to form a dispersion, stir for 30 min, then add TPU fragments, the mass ratio of TPU to m-xylylenediol is 1:1, then add the dispersion of TPU, catalyst and m-xylylenediol into a high-pressure reaction kettle, inject supercritical CO2, and pressurize to 12-18 MPa to maintain the supercritical state of carbon dioxide, react at 120℃ for 1 hour, TPU is degraded into hydroxyl-terminated oligomer with number average molecular weight (Mn) of 5000, the product PDI=1.3, hydroxyl value 240 mg KOH / g.

[0116] Step 2b: immerse the wire bundle in a citric acid-hydrogen peroxide mixed solution (the mixing ratio of the mixed acid solution is the same as in Example 1), and under the condition of a temperature of 45℃ and a frequency of 40 kHz, ultrasonic-assisted reaction for 1 hour, the iron recovery rate reaches 90%. Use hydrophobic ionic liquid [C4mim][PF6], the volume ratio of [C4mim][PF6] to liquid is 1:5, separate Cu 2+ by 3-5 stage mixing and clarification tank, the stirring speed is 150 rpm, the copper recovery rate is 85%, and the acid solution is regenerated by electro-Fenton method and recycled for 10 times.

[0117] Step 2c: The diamond is cleaned by Ar-H2 plasma at a power of 200 W to remove surface carbide, with a purity of 90% and a recovery rate of 86%.

[0118] (2) Preparation method of the recycled TPU composite material: the mass ratio of the degraded TPU oligomer to the recycled diamond is 13:1, the amount of nano-silica is 0.5% (based on the total weight of the raw materials), the amount of PAPI added is 10% of the total mass of PAPI and the degraded TPU product, and the amount of KH540 added is 5% of the total mass of KH540 and the degraded TPU product. First, the degraded TPU product, isocyanate, and KH540 are simultaneously added to a twin-screw extruder, stirred for 5 min, and then the prepared diamond particles and nano-silica are added to the twin-screw extruder, stirred for 10 min. The polyurethane-siloxane crosslinking network is generated in situ by reaction extrusion process (temperature 200℃, rotation speed 30rpm). The tensile strength of the recycled material reaches 30 MPa, and the thermal conductivity coefficient increases to 0.40 W / m·K.

[0119] Example 7 This example is basically the same as Example 1, except that the waste flexible diamond wire saw is immersed in liquid nitrogen (-196℃) for rapid freezing for 5 minutes. Due to the short freezing time, part of the components of the waste flexible diamond wire saw cannot be reduced to the brittle temperature, resulting in low component separation effect, and the recovery rates of Fe, Cu, and diamond are 75%, 60%, and 80%, respectively.

[0120] Example 8 This example is basically the same as Example 1, except that in Step 2a, the type of catalyst is nano-zinc oxide (average particle size 20 nm), and the degraded TPU is a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 4580. The product has a PDI of 1.25 and a hydroxyl value of 230 mg KOH / g.

[0121] Example 9 This example is basically the same as Example 1, except that in the preparation method of the recycled TPU composite material, the mass ratio of the degraded TPU oligomer to the recycled diamond is 20:1. The tensile strength of the recycled material is 20 MPa, and the thermal conductivity coefficient is 0.30 W / m·K.

[0122] Example 10 This example is basically the same as Example 1, except that in Step 2a, the catalyst is Ti / CNT, and the loading amount of Ti and the addition amount of the catalyst are the same as in Example 1. The degraded TPU is a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 5000. The product has a PDI of 1.3 and a hydroxyl value of 240 mg KOH / g.

[0123] Example 11 This example is substantially the same as Example 1, except that in step 2a, the catalyst is Fe / CNT, and the loading of Fe and the amount of catalyst added are the same as in Example 1. The TPU is degraded into hydroxyl-terminated oligomers with a number average molecular weight (Mn) of 6500, and the product has a PDI of 1.45 and a hydroxyl value of 150 mg KOH / g.

[0124] Example 12 This example is substantially the same as Example 1, except that in step 2a, the catalyst is Ti-Ni / CNT. The TPU is degraded into hydroxyl-terminated oligomers with a number average molecular weight (Mn) of 4150, and the product has a PDI of 1.21 and a hydroxyl value of 290 mg KOH / g.

[0125] Example 13 This example is substantially the same as Example 1, except that in the preparation of the recycled TPU composite material, the amount of nano-silica added is 1.5% (based on the total weight of the raw materials).

[0126] Comparative Example 1 (1) Recovery method of waste flexible diamond wire saw: The waste flexible diamond wire saw is cut into short sections of 20-40 cm using a hydraulic shearing machine, and a double-shaft shredder is used to perform primary crushing at a speed of 35 rpm, with the discharge particle size controlled to be 5-8 cm, so as to separate the TPU matrix from the steel wire bundle. A hammer crusher is used to crush the TPU into 1-3 mm fragments at a speed of 1500 rpm, and the diamond remains at an original particle size of 0.2-0.5 mm due to its high hardness. A three-layer vibrating screen is configured, with a 20-mesh vibrating screen on the upper layer to intercept TPU blocks that have not been completely crushed, a 60-mesh screen to separate the main TPU product in the middle layer, and a 100-mesh screen to collect diamond powder at the bottom layer. An air flow separator is used to purify the undersize material at a wind speed of 10-12 m / s, with light TPU fragments being carried by the air flow to the top collector, and heavy diamond particles settling to the bottom bin, so as to finally separate the TPU fragments, loose steel wire bundle, and diamond particles.

[0127] The experimental method and conditions for the supercritical catalytic degradation of TPU, green acidolysis of steel wire, and recovery of diamond are the same as in Example 1.

[0128] (2) Preparation method of recycled TPU composite material: The experimental method and conditions for the preparation of recycled TPU / diamond composite material are the same as in Example 1.

[0129] Comparative Example 2 (1) Recovery method of waste flexible diamond wire saw: The experimental method and condition are basically the same as those of Example 1, except that in step 2a, the catalyst is an alkaline earth catalyst (nano-magnesium oxide, average particle size 20 nm), and the TPU is degraded into a hydroxyl-terminated oligomer with a number average molecular weight (Mn) of 6000, the product has a PDI of 1.5 and a hydroxyl value of 200 mg KOH / g.

[0130] The steel wire green acidolysis and diamond recovery are the same as the experimental method and condition of Example 1.

[0131] (2) Preparation method of recycled TPU composite material: the preparation of recycled TPU / diamond composite material is the same as the experimental method and condition of Example 1.

[0132] Comparative Example 3 (1) Recovery method of waste flexible diamond wire saw: The treatment of raw materials and supercritical catalytic degradation of TPU are the same as the experimental method and condition of Example 1.

[0133] The difference is that in step 2b, nitric acid and hydrochloric acid are mixed in a volume ratio of 3:1, the steel wire bundle is soaked in the acid solution at a liquid-solid ratio of 5:1, the temperature is controlled at 50-60℃, and the soaking time is 3h. Although the dissolution rate of Fe and Cu can reach 95%, harmful gas NO will be generated during the acidolysis process, which seriously pollutes the environment, and the acid solution is only used once. Under the condition of current density of 150 A / m², the recovery rate of copper plating layer is 75%. Through the shaking table separation method, the diamond is separated from the impurities using tribromomethane with a density of 2.89 g / cm³. Due to too many impurities, the separation effect is limited, and the recovery rate of diamond is only 70%, and the purity is only 80%.

[0134] (2) Preparation method of recycled TPU composite material: the preparation of recycled TPU / diamond composite material is the same as the experimental method and condition of Example 1.

[0135] Comparative Example 4 (1) Recovery method of waste flexible diamond wire saw: The treatment of raw materials, supercritical catalytic degradation of TPU and steel wire green acidolysis and diamond recovery are the same as the experimental method and condition of Example 1.

[0136] (2) The preparation method of recycled TPU composite material is basically the same as that of Example 1, except that no nano-silicon dioxide is added, and the tensile strength of the recycled material is 25 MPa, and the thermal conductivity coefficient is 0.18 W / m·K.

[0137] From Figure 3 It can be seen that the thermal weight loss curve of Comparative Example 4 decreases faster than that of Example 1, indicating that the stability of the recycled material is stronger under the synergistic effect of nano-silicon dioxide.

[0138] Comparative Example 5 (1) The recovery method of waste flexible diamond wire saw: The treatment of raw materials, green acidolysis of steel wire and recovery of diamond were the same as those in Example 1, but no supercritical catalytic degradation of TPU was performed.

[0139] (2) The preparation method of recycled TPU composite material: basically the same as Example 1, the difference is that the degraded TPU oligomer is replaced by polyether polyol 4110, and the tensile strength of the recycled material reaches 37 MPa, and the thermal conductivity coefficient is increased to 0.52 W / m·K.

[0140] Comparative Example 6 This comparative example is basically the same as Example 1, the difference is that in step 2a, no supercritical CO2 is introduced, and the pressure and temperature are the same as Example 1. The TPU is degraded into hydroxyl-terminated oligomer with number average molecular weight (Mn) of 4750, and the product PDI=1.27, hydroxyl value 255 mg KOH / g.

[0141] Table 1 Composition and addition amount of catalyst used in TPU degradation of examples

[0142]

[0143] Note: Total loading = (mass of metal A + mass of metal B) / (mass of carrier + total mass of metal) x 100% (for example, if the total loading is 10wt%, and the ratio of metals is 1:1, then metal A accounts for 5wt%, and metal B accounts for 5wt%), addition amount = mass of catalyst / mass of TPU x 100%.

[0144] Table 2 Performance data of examples and comparative examples

[0145]

[0146] As shown in the above table, the method of gradient cryogenic crushing and interface dissociation, TPU supercritical catalytic degradation, steel wire green acidolysis and diamond recycling and TPU / diamond composite material preparation adopted in examples 1-13 of the present application has better effect. Among them, the traditional raw material treatment method adopted in comparative example 1 has poor separation effect, and the recovery rate and purity of diamond in the subsequent steps are all less than 95%, so that the strength and thermal conductivity of the prepared recycled material are only 28 MPa and 0.35 W / m·K respectively. Comparative example 2 adopts traditional alcoholysis method for degrading TPU, because of poor or incomplete degradation effect, the number average molecular weight of the degraded material reaches 6000, and the hydroxyl value is only 200 mg KOH / g, which leads to the strength and thermal conductivity of the prepared recycled material being only 26 MPa and 0.30 W / m·K respectively. Comparative example 3 adopts the method of dissolving metal with strong acid, recovering Cu by electrolysis and purifying diamond with methyl tribromide, that is, the recovery rate of Fe reaches more than 90%, but harmful gas is generated in the dissolution process, which must be purified, so that the experimental steps are complex and the economic benefit is low. The efficiency of electrolytic recovery of Cu is low, and the recovery rate of Cu is less than 80%, and at the same time, due to too many impurities, the recovery rate and purity of diamond are also less than 80%. Comparative example 4 directly mixes the degraded TPU oligomer with diamond, which is different from example 1 in that it lacks nano silicon dioxide as a fixing agent and a thermal conductor, so that the strength and thermal conductivity of the prepared recycled material are only 25 MPa and 0.18 W / m·K respectively.

[0147] In the experimental process of the present application, the brittle TPU matrix is preferentially broken into millimeter-sized particles by multi-stage roller crusher at-196℃ in liquid nitrogen environment, while the steel wire and diamond remain intact due to their toughness. Subsequently, the TPU fragments, steel wire and diamond particles can be better separated according to the particle size difference by using an eddy current separator. By supercritical catalytic degradation of TPU, the supercritical fluid weakens the hydrogen bond force between TPU molecular chains, reduces the entanglement strength of polymer chains, and the catalyst adsorbs and activates the TPU molecular chain through the surface active site, reduces the activation energy of the fracture reaction, and promotes the thermodynamic unstable fracture of the urethane bond in the TPU molecular chain to generate low molecular weight polyurethane oligomer or monomer.

[0148] In the aspect of metal recovery, the metal is dissolved by a mixed solution of citric acid and hydrogen peroxide under ultrasonic assistance through a multi-mechanism synergistic effect, citric acid as a chelating agent forms a stable water-soluble complex with dissolved metal ions in an acidic environment, reduces the ion concentration to drive the dissolution balance to move forward, hydrogen peroxide oxidizes and decomposes metal oxides by releasing active oxygen free radicals to reduce them into soluble ions and avoid impurities, and the local high-temperature and high-pressure environment generated by ultrasonic cavitation effect accelerates the decomposition of H2O2 and the generation of free radicals, and the mechanical vibration destroys the passivation layer on the metal surface and strengthens mass transfer, thereby significantly improving the dissolution rate and efficiency, and finally realizing the efficient acidolysis of metal under mild conditions through the synergistic effect of oxidation-chelation-physical.

[0149] In the aspect of recycled material construction, the TPU oligomer and nano-SiO2 generate a polyurethane-siloxane crosslinked network through in-situ reaction of isocyanate groups and silicon hydroxyl groups, strengthen the interface bonding between the matrix and diamond fillers, inhibit crack propagation, and improve the tensile strength; meanwhile, as an auxiliary heat-conducting filler, it constructs a three-dimensional heat-conducting network with diamond, reduces the interface thermal resistance, and optimizes the filler distribution through ultrasonic dispersion effect, thereby improving the thermal conductivity, and in the reaction extrusion process, the high specific surface area accelerates the crosslinking reaction, stabilizes the processing performance, and finally realizes the synergistic improvement of mechanical and thermal conductivity properties.

[0150] The product prepared by the application is tested for structure, Figure 1 The viscosity test curve of the TPU degradation product of Example 1-6 shows that the viscosity of the degradation product of the polyol gradually decreases with the increase of the amount of catalyst, and the decreasing rate is fast, which indicates that the addition of the catalyst significantly promotes the degradation rate. Figure 2 The Fourier infrared curve comparison chart of the TPU degradation product of Example 1 and the industrial polyether polyol 4110 provided by the application shows that the curves of the two are almost similar, which verifies that the TPU is successfully degraded into polyether polyol after supercritical catalytic degradation. Figure 3 The thermal gravimetric curve of the recycled material of Example 1 and Comparative Example 4 shows that the decomposition temperature of the recycled material prepared in Example 1 increases and the decomposition rate decreases, which indicates that the thermal stability is better than that of the recycled material prepared in the traditional experimental Comparative Example 4.

[0151] The gradient cryogenic crushing and interface dissociation, TPU supercritical catalytic degradation, steel wire green acidolysis, diamond recovery, and recycled TPU / diamond composite material preparation method adopted by the application are significantly superior to the traditional recovery and preparation methods in terms of metal recovery rate, diamond purity, and performance of recycled materials.

[0152] It should be noted that the foregoing examples have been provided merely for the purposes of illustration and are not intended to limit the application in any way. Descriptions and examples of materials and processes of the application are intended to be illustrative not limiting. Any modifications of the application and other applications of the application will occur to those skilled in the art to which the application pertains and many options for modification of the application will suggest themselves. The application lies in the broadest aspects of the art, and there are many alternatives for carrying out the application. Accordingly, the scope of the application should be determined not with reference to the above description but with reference to the claims that follow.

Claims

1. A method for recycling waste flexible diamond wire saws, characterized in that, Includes the following steps: Step 1: Freeze the waste flexible diamond wire saw, crush it under freezing conditions, and separate TPU fragments, wire bundles and diamond particles. Step 2: Catalytically degrade the TPU fragments and acid-hydrolyze the steel wire bundles and recover the diamond particles; The TPU fragment catalytic degradation step includes: reacting a mixture of diol, catalyst and TPU fragments under supercritical fluid conditions to obtain TPU degradation products.

2. The method according to claim 1, characterized in that, In step 1, the freezing temperature is -190℃ to -200℃. And / or, in step 1, the freezing time is 10-15 minutes. And / or, in step 1, the average particle size of the crushed TPU fragments, wire bundles and diamond particles is 2-8 mm.

3. The method according to claim 1, characterized in that, In the step of catalytic degradation of TPU fragments, the catalyst includes at least one of nano-ZnO and carbon nanotube-supported bimetallic catalyst AB / CNT; Preferably, in the carbon nanotube-supported bimetallic catalyst AB / CNT, metal A includes at least one of Ti, Zr, La, Nd, Bi, and Sn, and metal B includes at least one of Co, Ni, Bi, Fe, Mn, Cr, Zn, Al, and Cu. More preferably, the mass ratio of metal A to metal B is (1-3.5):1, and the total loading of metal A and metal B is 5-10 wt% based on the total weight of the catalyst. More preferably, the average particle size of the catalyst is 10-30 nm.

4. The method according to claim 1, characterized in that, In the step of catalytic degradation of TPU fragments, the amount of catalyst is 1% to 6% of the mass of the TPU fragments; And / or, in the step of catalytic degradation of TPU fragments, the mass ratio of TPU fragments to diols is 1:(1~2). And / or, the mass ratio of TPU fragments to the introduced supercritical fluid is (10:1) to (10:1.5).

5. The method according to claim 1, characterized in that, In the TPU fragment catalytic degradation step, the reaction temperature is 120~150℃. And / or, in the step of catalytic degradation of TPU fragments, the reaction pressure is 12~18 MPa. And / or, in the step of catalytic degradation of TPU fragments, the diol includes at least one of 1,4-butanediol, ethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, bisphenol A, polycarbonate diol, 1,2-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, isophthalic acid, terephthalic acid, resorcinol, and hydroquinone.

6. The method according to claim 1, characterized in that, The steps of acid hydrolysis of steel wire bundle include: reacting a mixture including steel wire bundle and mixed acid solution, adjusting the pH, separating and recovering the generated iron-containing precipitate, and forming a first solution from the solution after separating the iron-containing precipitate; performing countercurrent extraction on the first solution using a hydrophobic ionic liquid, adding dilute sulfuric acid to the obtained copper-rich ionic liquid phase, and recovering the generated copper sulfate crystals.

7. The method according to claim 6, characterized in that, In the acid hydrolysis step of steel wire bundle, the mixed acid solution includes citric acid aqueous solution and hydrogen peroxide aqueous solution. The mass concentration of citric acid aqueous solution is 30-40%, the mass concentration of hydrogen peroxide aqueous solution is 25-35%, and the volume ratio of citric acid aqueous solution to hydrogen peroxide aqueous solution is (2-4):

1. And / or, the mass ratio of the mixed acid solution to the steel wire bundle is (4-6):1; And / or, in the step of acid hydrolysis of steel wire bundle, the reaction temperature is 45~55℃; And / or, in the step of acid hydrolysis of steel wire bundle, the hydrophobic ionic liquid is [C4mim][PF6]; And / or, in the step of acid hydrolysis of steel wire bundle, the volume ratio of hydrophobic ionic liquid to the first solution is (1:3)-(1:5).

8. A recycled TPU composite material, characterized in that, The raw materials include the TPU degradation product, diamond particles, nano-silica, isocyanate and 3-aminopropyltrimethoxysilane as described in any one of claims 1-6.

9. The composite material according to claim 8, characterized in that, The mass ratio of TPU degradation products to diamond particles is (8~13):1; And / or, the amount of nano-silica added is 0.5~3.0% of the total mass of the raw materials; And / or, the amount of isocyanate added is 5-15% of the total mass of TPU degradation products and isocyanate; And / or, the amount of 3-aminopropyltrimethoxysilane added is 1-10 wt% of the total mass of the TPU degradation products and 3-aminopropyltrimethoxysilane; And / or, the average particle size of nano-silica is 20~50nm; And / or, the diamond particles are diamond particles recovered in the recycling method of the waste flexible diamond wire saw.

10. A method for preparing the composite material according to any one of claims 8-9, characterized in that, The process includes the following steps: using a reactive extrusion process to generate the recycled TPU composite material in situ from a mixture comprising TPU degradation products, diamond particles, nano-silica, isocyanate and 3-aminopropyltrimethoxysilane.

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