Polyurethane plastic track composite material containing dpu waste and preparation method thereof

Abstract

The present application relates to solid waste recycling technical field, specifically to a kind of polyurethane plastic track composite material containing DPU waste and its preparation method, comprising the following steps: step (1) pretreatment waste particle preparation: batching, mixing, carbonization, microwave treatment obtain pretreatment waste particle;Step (2) modified waste particle preparation: pretreatment waste particle surface modification, grafting, obtain modified waste particle;Step (3) composite material preparation: modified waste particle batching, extrusion, granulation, obtain polyurethane plastic track composite material.The present application improves the performance defects of DPU waste by the combination of components and process, and realizes its efficient application in high-performance plastic track composite material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of solid waste recycling, and particularly relates to a polyurethane plastic track composite material containing DPU waste and a preparation method thereof. BACKGROUND

[0002] With the enhancement of environmental protection consciousness and the growth of resource recycling demand, the recycling of waste polymer materials has become a research hotspot. In particular, the application of DPU waste in polyurethane plastic track composites is limited by problems such as poor activation performance, easy cracking, aging and peeling. Therefore, how to effectively activate DPU waste and apply it to high-performance plastic track composites has become a technical problem to be solved.

[0003] Publication No. CN110055858A discloses an environmentally friendly mixed plastic track and a preparation method thereof. The patent provides a modular environmentally friendly mixed plastic track prepared from shoe material waste as the main raw material. The shoe material waste is used instead of EPDM rubber particles as the elastic filler in the mixed track, which can not only meet the requirements of the elastic performance of the plastic track, but also can make part of the shoe material waste into a useful resource, reduce waste and the adverse effects on the environment during disposal. In addition, the assembly is convenient, and the influence of thermal expansion on the elasticity of the plastic track can be effectively reduced. However, it is found in experiments that the surface of the DPU waste particles is inert, and it is difficult to form effective chemical bonding with the polyurethane matrix. Experiments show that when the recycled DPU particles (particle size 0.1-1 mm) are directly mixed, the addition amount > 15% can cause the elongation at break of the composite material to decrease from 320% to 150%, and the tensile strength to decrease by 50%. And the traditional process directly mixes inorganic fillers (such as calcium carbonate and talc), but physical mixing is difficult to activate the surface active groups of the waste. Research shows that the interfacial shear strength between untreated DPU particles and the matrix is less than 30% of that of the virgin material. The composite material containing DPU waste is weakened due to the weak interface, and the microcracks expand into macrocracks under dynamic load. The residual amine catalyst (such as triethylene diamine) in the DPU waste can catalyze the hydrolysis of the matrix and accelerate the embrittlement of the material. The traditional plastic track is broken under ultraviolet radiation, which leads to powdering, and the DPU waste is further reduced in UV resistance due to the damage to the molecular chain during the recycling process. The composite material containing waste is more easily oxidized due to the promotion of the residual catalyst.

[0004] CN110819060B discloses a method for improving the viscosity of waste ABS plastic. The patent adds hydroxyl-terminated polybutadiene (HTPB) and antioxidant to the waste ABS plastic, increases the molecular weight and avoids the quality decline caused by the decrease of molecular weight, providing a new direction for the recycling of waste plastics. However, this technical solution is mainly aimed at the modification of ABS plastic, and is not suitable for the activation of DPU waste and its application in polyurethane plastic track. The chemical structure of DPU waste is significantly different from that of ABS, and direct application of this method may not effectively solve the performance defects of DPU waste in plastic track composites, such as easy cracking and peeling.

[0005] The above problems show that the existing high molecular material recycling technology still has deficiencies in the activation treatment of DPU waste and its application in polyurethane plastic track composites. SUMMARY

[0006] To achieve the above purpose, the present application provides a polyurethane plastic track composite containing DPU waste and a preparation method thereof, which aims to improve the performance defects of DPU waste through a specific activation treatment process and realize its efficient application in high-performance plastic track composites, thereby meeting the needs of environmental protection and resource recycling.

[0007] The present application adopts the following technical solutions:

[0008] A polyurethane plastic track composite containing DPU waste is prepared by the following steps:

[0009] by weight,

[0010] Step (1) Preparation of pretreated waste particles: 100 parts by mass of DPU waste particles crushed to a particle size of 0.1-1 mm are mixed with 5-50 parts by mass of silica aerogel powder and then subjected to surface carbonization treatment at a temperature of 150-350℃ for 10-120 minutes, followed by microwave treatment at a power of 300-1500W for 1-30 minutes. After dispersion, pretreated waste particles are obtained;

[0011] Step (2) Preparation of modified waste particles: the pretreated waste particles are subjected to surface modification treatment, and then grafted with polyurethane monomers in the presence of a catalyst at a temperature of 40-90℃ for 0.5-5 hours to obtain modified waste particles;

[0012] Step (3) Preparation of composite material: 100 parts by mass of modified waste particles are mixed with 20-200 parts by mass of plastic polyurethane base material, extruded and granulated to obtain a polyurethane plastic track composite material.

[0013] Preferably, the process for preparing the pre-treated waste material particles comprises the following steps:

[0014] Step (1-1) mixing: 100 parts of DPU waste material particles with a particle size of 0.1-1 mm are put into a conical mixer, stirring at a low speed of 50 rpm; 5-50 parts of silica aerogel powder with a particle size of 1-100 μm are added in three portions, with an interval of 2 minutes each time, in order to reduce adhesion and improve wear resistance; the speed is increased to 300 rpm, and after mixing for 15 minutes, the wall is scraped to avoid dead angles, and then mixed for another 5 minutes, with a filler coverage of more than 90%;

[0015] Step (1-2) surface carbonization treatment: the mixture is moved into a carbonization device, high-purity nitrogen gas (nitrogen content 99.99%) is introduced into the carbonization device to make the oxygen volume concentration <0.5%; the temperature is raised at a rate of 10°C / min to prevent deformation of the particles due to thermal shock; in the holding stage, due to the difference in thermal conductivity caused by the difference in particle size, the carbonization temperature and holding time are determined according to the particle size; for particles with a particle size of 0.1-0.3 mm, the carbonization temperature is set to 150-200°C, and the holding time is 10-30 minutes; for particles with a particle size of 0.3-0.6 mm, the carbonization temperature is set to 200-300°C, and the holding time is 30-90 minutes; for particles with a particle size of 0.6-1.0 mm, the carbonization temperature is set to 300-350°C, and the holding time is 90-120 minutes; a micro-carbon layer is formed on the surface by dehydrogenation; using high-temperature treatment for small particles will cause the particles to fuse and agglomerate, and using low-temperature treatment for large particles will result in a low thickness of the carbon layer, and incomplete subsequent reaction;

[0016] Step (1-3) microwave treatment: the particles after surface carbonization are laid flat in a quartz boat with a thickness of ≤3 cm, and excessive thickness will result in uneven microwave penetration; a rotating tray (5-10 rpm) is set in the microwave cavity to ensure uniform heating; the microwave parameters are set according to the particle size; for particles with a particle size of 0.1-0.3 mm, the treatment is carried out at a power of 300-600 W for 5-15 minutes; for particles with a particle size of 0.3-0.6 mm, the treatment is carried out at a power of 600-1200 W for 10-25 minutes; for particles with a particle size of 0.6-1.0 mm, the treatment is carried out at a power of 1200-1500 W for 15-30 minutes; to promote pore development and dispersion; after the microwave is stopped, nitrogen gas is introduced for rapid cooling (to prevent oxidation), and the temperature is cooled to <60°C before being transferred to a sealed container;

[0017] Preferably, the process for preparing the modified waste material particles is as follows: the surface modifier in step (2) is at least one of a silane coupling agent, a titanate coupling agent, or plasma treatment, and the specific methods of the three modification treatments are as follows:

[0018] (1.a) Silane coupling agent treatment: dilute silane coupling agent (KH-550 / KH-570) with ethanol-water (volume ratio 9:1) solution to a concentration of 2-5wt%; put the pretreated particles into a vortex disperser, stir at a low speed of 200rpm, spray the coupling agent solution at an atomization pressure of 0.2MPa, warm up to 70-80℃, increase the speed to 1500rpm, and react for 20min.

[0019] (1.b) Titanate coupling agent treatment: suitable for silica aerogel powder filler system; mix titanate (NDZ-201) with anhydrous toluene at a volume ratio of 1:10, add the pretreated particles, stir at 60℃ for 30min; add deionized water with a mass fraction of 0.5% of the titanate, warm up to 90℃, and react for 10min to form Ti-O-Si bonds;

[0020] (1.c) Plasma treatment: use an atmospheric argon plasma jet instrument, set the power to 800W, the argon flow rate to 15L / min, the treatment distance to 50mm, and the treatment time to 3min; plasma treatment introduces -COOH / -OH groups on the surface of the particles.

[0021] In step (2), the specific process of the grafting reaction includes the following steps:

[0022] Step (2-1) reaction system construction: put 100 parts of DPU modified particles into a reaction kettle, preheat to 40℃, add 1-20 parts of polyurethane monomer, and drop the catalyst (dissolved in five times the mass of acetone) with a mass fraction of 0.1%-5% of the polyurethane monomer through a metering pump, and carry out the grafting reaction in the presence of the catalyst;

[0023] Preferably, the polyurethane monomer is a mixture of isocyanate compounds and polyol compounds, wherein the isocyanate compounds include at least one of toluene diisocyanate TDI, diphenylmethane diisocyanate MDI, and isophorone diisocyanate IPDI, and the polyol compounds are polyether polyol or polyester polyol;

[0024] Preferably, the catalyst is an organic tin or amine catalyst;

[0025] Step (2-2) reaction with temperature and time controlled in stages: stage 1 low temperature anchoring, heating to 50±1℃, stirring speed 200-300rpm, reaction 0.5h, making -NCO react with particle surface active group preferentially, slight increase in system viscosity; stage 2 moderate temperature chain extension, heating to 70±1℃, stirring speed 400rpm, reaction 1.5h, making polyol react with residual -NCO to lengthen grafting chain, particle surface wrapped with gel layer; stage 3 high temperature curing, heating to 90±1℃, stirring speed 100rpm, reaction 1h, promoting unreacted -NCO to form biuret crosslinking, particle color changing from brownish yellow to dark brown;

[0026] Step (2-3) reaction termination and post-treatment: adding terminating agent, adding 1.2 times of molar number of catalyst of benzoyl chloride dropwise at 70℃, stirring for 20min; devolatilization and desolventization, treating at 80℃, -0.08MPa for 1h, removing 90% of solvent, increasing temperature to 100℃, treating at -0.095MPa for 2h, making residual monomer <100ppm; product separation: centrifugal filtration through 300 mesh screen, washing after filtration, placing product in fluidized bed at 80℃ for 30min after washing, obtaining modified waste material particles.

[0027] Preferably, the process for preparing the composite material is as follows:

[0028] Step (3-1) internal mixing: preheating internal mixing cavity to 150℃, putting in 100 parts of plastic polyurethane base (thermoplastic polyurethane TPU base), melting and plasticizing for 2min, then putting in modified waste material particles and auxiliary agents; then increasing stirring speed in steps, first stirring at 30rpm for 1min, gentle mixing to prevent particle breakage, then stirring at 60rpm for 2min, moderate shearing and tearing carbonized layer, finally stirring at 90rpm for 2min, high temperature and high pressure promoting interface entanglement; stopping internal mixing when internal mixer power curve tends to be stable with fluctuation <5%.

[0029] Step (3-2) extrusion molding: transferring internal mixed material to extruder using conveying belt with surface temperature of 160℃, preventing material cooling leading to secondary agglomeration; setting extrusion temperature zones as follows: feeding section 120℃, gentle compression to prevent degradation; melting section 170℃, fully melting TPU; mixing section 190℃, dispersing inorganic fillers; die head 185℃, stable striping to prevent die swelling; after striping, cutting in water at 40℃, obtaining polyurethane plastic track composite material particles with particle size of 1-10mm, controlling material moisture content to be less than 0.1% by dehydrating the prepared particles in centrifuge at 3000rpm for 5min.

[0030] The scheme of the present application realizes DPU waste regeneration through multi-component synergy and process precise adaptation, wherein the silica aerogel powder serves as a key medium throughout the whole process. In the mixing stage, the silica aerogel powder is embedded on the surface of the DPU particles in batches, and the nanoporous structure thereof provides a uniform heat conduction path for the subsequent carbonization process, effectively inhibiting local overheating; in the carbonization process, the gradient temperature control under the inert atmosphere enables the aerogel to synchronously catalyze the selective cracking of the surface layer, thereby assisting in the formation of a homogeneous microporous structure; and in the microwave treatment stage, the high dielectric properties of the aerogel are relied on to enhance the energy absorption efficiency, and the power parameters matched with the particle size are used to deeply activate the carbonized layer.

[0031] The surface modification process fully utilizes the reactivity of the silicon hydroxyl groups on the surface of the aerogel: the silane coupling agent is condensed and grafted with the amino group through ethanol solution spraying, the titanate is hydrolyzed to form a Ti-O-Si bond, and the plasma treatment further introduces active groups at the interface of the aerogel, thereby jointly constructing high-density grafting anchor points. In the three-stage temperature control strategy of the grafting reaction, the isocyanate is preferentially bonded to the active sites of the aerogel to form a rigid anchor layer, the polyol chain extender constructs a flexible coating network on the surface of the particles, and high-temperature crosslinking finally realizes the strengthening of the core-shell structure.

[0032] The compounding process highlights the bridging function of the aerogel: the stepped speed of the internal mixer makes the aerogel become a physical crosslinking point of the TPU molecular chain and the carbonized layer in the high-temperature field at 150℃ - low-speed mixing protects the porous structure, medium-speed shearing promotes the penetration of TPU chain segments into the aerogel pores, and high-speed stirring realizes the penetration and entanglement of molecular chains. The temperature zoning design of the extrusion process enables the aerogel to play a structure guiding role: the feeding section is at 120℃ to protect the thermal stability of the aerogel, and the mixing section is at 190℃ to utilize the high specific surface of the aerogel to induce the ordered dispersion of fillers, thereby finally forming a four-component synergistic reinforced phase of carbonized layer-aerogel-grafted chain-TPU matrix, and realizing the performance optimization of the waste material at a high content.

[0033] The present scheme also proposes a preparation method of the above-mentioned polyurethane plastic track composite material containing DPU waste, comprising the following steps:

[0034] Step (1) Preparation of pretreated waste particle: batching, mixing, carbonization, and microwave treatment to obtain pretreated waste particle;

[0035] Step (2) Preparation of modified waste particle: surface modification of the pretreated waste particle, grafting, to obtain a modified waste particle;

[0036] Step (3) Preparation of composite material: batching of the modified waste particle, extrusion, and granulation to obtain a polyurethane plastic track composite material.

[0037] Compared with the prior art, the present application has the following advantages:

[0038] 1. Silica aerogel powder as a multifunctional medium throughout the whole process, its nanoporous structure is embedded on the surface of DPU particles in the mixing stage, acts as a heat diffusion barrier to prevent local overheating during carbonization, and uses high dielectric properties to enhance energy absorption efficiency during microwave treatment; at the same time, the active silicon hydroxyl on the surface of the aerogel is efficiently bonded with silane / titanate coupling agent, which builds a high-density anchor point for grafting reaction, and finally becomes a physical cross-linking hub in the compounding stage, which realizes the three-level enhancement of waste-matrix interface-carbonized layer-aerogel-grafted chain.

[0039] 2. The whole process accurately matches the material characteristics: temperature control by particle size grading in the carbonization stage, combined with nitrogen quenching to lock the microporous structure, and simultaneously avoiding the risk of oxidative degradation; microwave treatment through dynamic adaptation of particle size-power to deeply activate the surface, and forms a synergistic effect with the dielectric response of aerogel; the three-stage temperature control strategy of grafting reaction realizes the molecular-level ordered assembly of isocyanate anchoring, polyol chain extension, and high-temperature crosslinking; in the compounding process, the stepwise mixing speed and extrusion temperature are partitioned to protect the particle structure first and then gradually shear fusion, so that high-load waste forms a uniformly dispersed reinforcing phase network in the TPU matrix. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0041] General embodiment

[0042] A polyurethane plastic track composite containing DPU waste is prepared by the following steps in parts by weight:

[0043] Step (1) Preparation of pretreated waste particles;

[0044] Step (1-1) Mixing: 100 parts of DPU waste particles with a particle size of 0.1-1 mm are put into a conical mixer and stirred at a low speed of 50 rpm; 5-50 parts of silica aerogel powder with a particle size of 1-100 μm are added in three times, with an interval of 2 minutes each time; the speed is increased to 300 rpm, mixed for 15 minutes, then stopped and scraped, and then mixed for another 5 minutes;

[0045] Step (1-2) surface carbonization treatment: move the mixture into the carbonization device, introduce high-purity nitrogen into the carbonization device to make the oxygen volume concentration <0.5%; the temperature is raised at a rate of 10°C / min; in the holding stage, due to the difference in heat conduction efficiency caused by the difference in particle size, the carbonization temperature and holding time are determined according to the particle size; for particles with a particle size of 0.1-0.3 mm, the carbonization temperature is set to 150-200°C, and the holding time is 10-30 min; for particles with a particle size of 0.3-0.6 mm, the carbonization temperature is set to 200-300°C, and the holding time is 30-90 min; for particles with a particle size of 0.6-1.0 mm, the carbonization temperature is set to 300-350°C, and the holding time is 90-120 min;

[0046] Step (1-3) microwave treatment: the particles after surface carbonization are laid flat in a quartz boat with a thickness of ≤3 cm; a rotating tray (5-10 rpm) is set in the microwave cavity to ensure uniform heating; the microwave parameters are set according to the particle size; particles with a particle size of 0.1-0.3 mm are treated at a power of 300-600 W for 5-15 min, particles with a particle size of 0.3-0.6 mm are treated at a power of 600-1200 W for 10-25 min, and particles with a particle size of 0.6-1.0 mm are treated at a power of 1200-1500 W for 15-30 min; after the microwave is stopped, nitrogen is introduced for rapid cooling, and the temperature is cooled to <60°C before being transferred to a sealed container;

[0047] Step (2) preparation of modified waste particles;

[0048] Step (2-1) surface modification treatment: three different technical solutions can be used for surface modification treatment:

[0049] (1.a) silane coupling agent treatment: dilute the silane coupling agent (KH-550 / KH-570) with an ethanol-water (volume ratio 9:1) solution to a concentration of 2-5 wt%; put the pretreated particles into a vortex disperser, stir at a low speed of 200 rpm, spray the coupling agent solution at an atomizing pressure of 0.2 MPa, heat to 70-80°C, and increase the speed to 1500 rpm for 20 min.

[0050] (1.b) titanate coupling agent treatment: suitable for silica aerogel powder filler system; mix the titanate (NDZ-201) with anhydrous toluene at a volume ratio of 1:10, add the pretreated particles, and stir at 60°C for 30 min; add deionized water with a mass fraction of 0.5% of the titanate, heat to 90°C, and react for 10 min to form Ti-O-Si bonds;

[0051] (1.c) plasma treatment: use an atmospheric argon plasma jet instrument, set the power to 800 W, the argon flow rate to 15 L / min, the treatment distance to 50 mm, and the treatment time to 3 min; plasma treatment introduces -COOH / -OH groups on the surface of the particles;

[0052] Step (2-2) grafting reaction: the grafting reaction process is divided into the following steps:

[0053] (2.a) Reaction system construction: 100 parts of DPU modified particles are put into a reaction kettle, preheated to 40°C, 1-20 parts of polyurethane monomer: a mixture of isocyanate compound (at least one of TDI, MDI, IPDI) and polyol compound (polyether polyol or polyester polyol) are added, a catalyst (organic tin or amine catalyst) with a mass fraction of 0.1%-5% of the polyurethane monomer is added by a metering pump (dissolved in five times the mass of acetone), and the grafting reaction is carried out in the presence of the catalyst;

[0054] (2.b) Reaction by controlling temperature and time in stages: stage 1 low temperature anchoring, heating to 50±1°C, stirring speed 200-300 rpm, reaction 0.5 h, making -NCO and the surface active group of the particles preferably react, and the viscosity of the system slightly rises; stage 2 medium temperature chain extension, heating to 70±1°C, stirring speed 400 rpm, reaction 1.5 h, making the polyol react with the remaining -NCO to lengthen the grafting chain, and the particle surface is wrapped with a gel layer; stage 3 high temperature curing, heating to 90±1°C, stirring speed 100 rpm, reaction 1 h, promoting the formation of biuret crosslinking of unreacted -NCO, and the particle turns from brownish yellow to dark brown;

[0055] (2.c) Reaction termination and post-treatment: adding a terminating agent, adding 1.2 times the molar amount of benzoyl chloride of the catalyst at 70°C, stirring for 20 min; devolatilization and desolventization, treating at 80°C and -0.08 MPa for 1 h to remove 90% of the solvent, increasing the temperature to 100°C and treating at -0.095 MPa for 2 h to make the residual monomer <100 ppm; product separation: centrifugal filtration through a 300-mesh screen, washing after filtration, and then placing the product in a fluidized bed at 80°C for drying for 30 min to obtain modified waste particles.

[0056] Step (3) composite material preparation.

[0057] Step (3-1) internal mixing: preheat the internal mixing cavity to 150°C, put in 100 parts of TPU base material, melt and plasticize for 2 minutes, and then put in modified waste particles and auxiliary agents; then increase the rotation speed in stages, first stir at a rotation speed of 30 rpm for 1 minute to gently mix and prevent particle breakage, then stir at a rotation speed of 60 rpm for 2 minutes to moderately shear and tear the carbonized layer, and finally stir at a rotation speed of 90 rpm for 2 minutes to promote interface entanglement at high temperature and high pressure; stop the internal mixing when the power curve of the internal mixer tends to be stable and the fluctuation is <5%.

[0058] Step (3-2) Extrusion molding: The material is transferred to the extruder with a conveying belt of surface temperature 160℃ to prevent the material from cooling and causing secondary agglomeration; the extrusion temperature settings are as follows: 120℃ for the feeding section to prevent degradation; 170℃ for the melting section to fully melt the TPU; 190℃ for the mixing section to disperse the inorganic filler; 185℃ for the die to stabilize the strip to prevent die swelling; and the strip is cut into particles of 1-10 mm in size in water at 40℃, obtaining polyurethane plastic track composite particles; the particles are dehydrated in a centrifuge at a speed of 3000 rpm for 5 minutes to control the water content of the material to be less than 0.1%.

[0059] Example 1

[0060] A polyurethane plastic track composite containing DPU waste, prepared by the following steps in parts by weight:

[0061] Step (1) Preparation of pretreated waste particle;

[0062] Step (1-1) Mixing: 100 parts of DPU waste particles with a particle size of 0.5 mm are put into a conical mixer and stirred at a low speed of 50 rpm; 20 parts of silica aerogel powder with a particle size of 10 μm are added in three portions, with an interval of 2 minutes each; the speed is increased to 300 rpm, and after mixing for 15 minutes, the wall is scraped, and then mixed for another 5 minutes;

[0063] Step (1-2) Surface carbonization treatment: The mixture is moved to the carbonization device, high-purity nitrogen is introduced into the carbonization device to make the oxygen volume concentration <0.5%; the temperature is raised at a rate of 10℃ / min; in the holding stage, the carbonization temperature is set to 250℃, and the holding time is 60 minutes;

[0064] Step (1-3) Microwave treatment: The surface carbonized particles are laid flat in a quartz boat with a thickness ≤3 cm; a rotating tray (5-10 rpm) is set in the microwave cavity to ensure uniform heating; the treatment is carried out at a power of 800 W for 15 minutes; after the microwave is stopped, nitrogen is introduced for rapid cooling, and the temperature is cooled to <60℃ and transferred to a sealed container;

[0065] Step (2) Preparation of modified waste particles;

[0066] Step (2-1) Surface modification treatment: Silane coupling agent treatment: The silane coupling agent KH-550 is diluted with an ethanol-water (volume ratio 9:1) solution to a concentration of 3wt%; the pretreated particles are put into a vortex disperser, stirred at a low speed of 200 rpm, and the coupling agent solution is sprayed at an atomizing pressure of 0.2 MPa; the temperature is raised to 80℃, the speed is increased to 1500 rpm, and the reaction is carried out for 20 min.

[0067] Step (2-2) Grafting reaction: The grafting reaction process is divided into the following steps;

[0068] (2.a) Reaction system construction: 100 parts of DPU modified particles were put into the reaction kettle, preheated to 40°C, and polyurethane monomers composed of 4 parts of MDI and 5.2 parts of polyether polyol were added. The grafting reaction was carried out in the presence of a catalyst by adding 0.4% of the mass of the polyurethane monomer through a metering pump.

[0069] (2.b) Reaction by controlling temperature and time in stages: stage 1 low temperature anchoring, heating to 50°C, stirring speed 250 rpm, reaction 0.5 h; stage 2 medium temperature chain extension, heating to 70°C, stirring speed 400 rpm, reaction 1.5 h; stage 3 high temperature curing, heating to 90°C, stirring speed 100 rpm, reaction 1 h;

[0070] (2.c) Reaction termination and post-treatment: addition of a terminating agent, 1.2 times the molar amount of the catalyst was added dropwise at 70°C, stirring for 20 min; devolatilization and desolubilization, treatment at 80°C, -0.08 MPa for 1 h, removal of 90% of the solvent, heating to 100°C, -0.095 MPa for 2 h, so that the residual monomer is <100 ppm; product separation: centrifugal filtration through a 300 mesh screen, washing after filtration with petroleum ether, and drying the product at 80°C in a fluidized bed for 30 min after washing to obtain modified waste particles.

[0071] Step (3) composite material preparation.

[0072] Step (3-1) internal mixing: preheat the internal mixing cavity to 150°C, put in 100 parts of TPU base material, melt and plasticize for 2 minutes, then put in 100 parts of modified waste particles; then step up the rotation speed, first stir at 30 rpm for 1 minute, then stir at 60 rpm for 2 minutes, and finally stir at 90 rpm for 2 minutes; stop internal mixing when the power curve of the internal mixer tends to be stable with a fluctuation of <5%.

[0073] Step (3-2) extrusion molding: transfer the internal mixed material to the extruder using a conveyor belt with a surface temperature of 160°C to prevent material cooling leading to secondary agglomeration; the extrusion temperature settings for each temperature zone are as follows: feeding section 120°C, gentle compression to prevent degradation; melting section 170°C, sufficient melting of TPU; mixing section 190°C, dispersion of inorganic fillers; die 185°C, stable strip extrusion to prevent die swelling; after extrusion, cut into particles in water at 40°C to obtain polyurethane plastic track composite material particles with a particle size of 3 mm, and the prepared particles are dehydrated in a centrifugal machine at a rotation speed of 3000 rpm for 5 minutes to control the moisture content of the material to be less than 0.1%.

[0074] Example 2

[0075] A polyurethane plastic track composite material containing DPU waste, prepared by the following steps:

[0076] Step (1) Preparation of pretreated waste particles;

[0077] Step (1-1) Mixing: 100 parts of DPU waste particles with a particle size of 0.1 mm were put into a conical mixer and stirred at a low speed of 50 rpm; 5 parts of silica aerogel powder with a particle size of 1 μm were added in three portions, with an interval of 2 minutes each; the speed was increased to 300 rpm, and after mixing for 15 minutes, the wall was scraped and then mixed for another 5 minutes;

[0078] Step (1-2) Surface carbonization treatment: the mixture was moved to a carbonization device, high-purity nitrogen was introduced into the carbonization device to make the oxygen volume concentration <0.5%; the temperature was raised at a rate of 10°C / min in the heating stage; in the holding stage, the carbonization temperature was set to 180°C, and the holding time was 30 minutes;

[0079] Step (1-3) Microwave treatment: the surface carbonized particles were laid flat in a quartz boat with a thickness ≤3 cm; a rotating tray (5-10 rpm) was set in the microwave cavity to ensure uniform heating; the treatment was carried out at a power of 400 W for 10 minutes; after the microwave was stopped, nitrogen was introduced for rapid cooling, and the temperature was cooled to <60°C and transferred to a sealed container;

[0080] Step (2) Preparation of modified waste particles;

[0081] Step (2-1) Surface modification treatment: plasma treatment: an atmospheric argon plasma jet instrument was used, with a power of 800 W, an argon gas flow rate of 15 L / min, a treatment distance of 50 mm, and a treatment time of 3 min;

[0082] Step (2-2) Grafting reaction: the grafting reaction process is divided into the following steps;

[0083] (2.a) Reaction system construction: 100 parts of DPU modified particles were put into a reaction kettle, preheated to 40°C, and 2 parts of IPDI and 2.4 parts of polyether polyol were added to form a polyurethane monomer; 0.2% of Dabco T-12 was added to the polyurethane monomer by a metering pump, and the grafting reaction was carried out in the presence of a catalyst;

[0084] (2.b) Reaction by controlling temperature and time in stages: stage 1 low temperature anchoring, heating to 50°C, stirring speed 250 rpm, reaction 0.5 h; stage 2 medium temperature chain extension, heating to 70°C, stirring speed 400 rpm, reaction 1.5 h; stage 3 high temperature curing, heating to 90°C, stirring speed 100 rpm, reaction 1 h;

[0085] (2.c) Reaction termination and post-treatment: add a termination agent, drop 1.2 times the molar number of the catalyst of benzoyl chloride at 70°C, stir for 20 min; devolatilization and desolventization, treat at 80°C, -0.08 MPa for 1 h, remove 90% of the solvent, increase the temperature to 100°C, treat at -0.095 MPa for 2 h, so that the residual monomer is <100 ppm; product separation: centrifugal filtration through a 300-mesh screen, wash after filtration with petroleum ether, and then dry the product in a fluidized bed at 80°C for 30 min to obtain modified waste particles.

[0086] Step (3) composite material preparation.

[0087] Step (3-1) internal mixing: preheat the internal mixing chamber to 150°C, add 100 parts of TPU base material, melt and plasticize for 2 min, then add 100 parts of modified waste particles; then increase the rotation speed in stages, first stir at 30 rpm for 1 min, then stir at 60 rpm for 2 min, and finally stir at 90 rpm for 2 min; when the power curve of the internal mixer tends to be stable with a fluctuation of <5%, stop the internal mixing.

[0088] Step (3-2) extrusion molding: use a conveyor belt with a surface temperature of 160°C to transfer the internal mixed material to the extruder to prevent material cooling from causing secondary agglomeration; the extrusion temperature settings for each temperature zone are as follows: 120°C for the feeding section to prevent degradation; 170°C for the melting section to fully melt the TPU; 190°C for the mixing section to disperse the inorganic filler; 185°C for the die to stabilize the strip to prevent die swelling; and after the strip is cut into particles in water at 40°C to obtain polyurethane plastic track composite particles with a particle size of 1 mm. The prepared particles are dehydrated in a centrifuge at a rotation speed of 3000 rpm for 5 min to control the moisture content of the material to be less than 0.1%.

[0089] Example 3

[0090] A polyurethane plastic track composite containing DPU waste, prepared by the following steps in parts by weight:

[0091] Step (1) preparation of pretreated waste particle;

[0092] Step (1-1) mixing: add 100 parts of DPU waste particles with a particle size of 1.0 mm to a conical mixer and stir at a low speed of 50 rpm; add 50 parts of silica aerogel powder with a particle size of 80 μm in 3 portions, with an interval of 2 min between each addition; increase the rotation speed to 300 rpm, mix for 15 min, stop and scrape the wall, and then mix for another 5 min;

[0093] Step (1-2) surface carbonization treatment: move the mixture into the carbonization device, introduce high-purity nitrogen into the carbonization device to make the oxygen volume concentration <0.5%; the temperature is raised at a rate of 10°C / min in the heating stage; in the holding stage, the carbonization temperature is set to 320°C, and the holding time is 120 minutes;

[0094] Step (1-3) microwave treatment: the surface carbonized particles are laid flat in a quartz boat with a thickness ≤3 cm; a rotating tray (5-10 rpm) is set in the microwave cavity to ensure uniform heating; the particles are treated at a power of 1400 W for 25 minutes; after the microwave is stopped, nitrogen is introduced for rapid cooling, and the temperature is cooled to <60°C before being transferred to a sealed container;

[0095] Step (2) preparation of modified waste material particles;

[0096] Step (2-1) surface modification treatment: titanate coupling agent treatment: mix titanate (NDZ-201) with anhydrous toluene at a volume ratio of 1:10, add the pretreated particles, and stir at 60°C for 30 min; add deionized water containing 0.5% of the mass of the titanate, heat to 90°C, and react for 10 min to form Ti-O-Si bonds;

[0097] Step (2-2) grafting reaction: the grafting reaction process is divided into the following steps;

[0098] (2.a) reaction system construction: 100 parts of DPU modified particles are put into a reaction kettle, preheated to 40°C, and 6 parts of TDI and 7.8 parts of polyester polyol are added to form a polyurethane monomer; a DBTDL solution containing 0.8% of the mass of the polyurethane monomer is added through a metering pump, and the grafting reaction is carried out in the presence of the catalyst;

[0099] (2.b) reaction by controlling temperature and time in stages: stage 1 low temperature anchoring, heated to 50°C, stirring speed 250 rpm, reaction 0.5 h; stage 2 medium temperature chain extension, heated to 70°C, stirring speed 400 rpm, reaction 2 h; stage 3 high temperature curing, heated to 90°C, stirring speed 100 rpm, reaction 1 h;

[0100] (2.c) reaction termination and post-treatment: add a terminating agent, add 1.2 times the molar amount of benzoyl chloride to the catalyst at 70°C, stir for 20 min; devolatilization and desolubilization, treat at 80°C and -0.08 MPa for 1 h to remove 90% of the solvent, heat to 100°C and treat at -0.095 MPa for 2 h to make the residual monomer <100 ppm; product separation: centrifugal filtration through a 300-mesh screen, wash with petroleum ether after filtration, and dry the product in a fluidized bed at 80°C for 30 min to obtain modified waste material particles.

[0101] Step (3) composite material preparation.

[0102] Step (3-1) Compounding: Preheat the compounding chamber to 150℃, put in 100 parts of TPU base material, melt and plasticize for 2 minutes, then put in 200 parts of modified waste particles; then step up the rotation speed, first stir at 30 rpm for 1 minute, then stir at 60 rpm for 2 minutes, and finally stir at 90 rpm for 2 minutes; when the power curve of the compounding machine tends to be stable with a fluctuation of <5%, stop compounding.

[0103] Step (3-2) Extrusion molding: Use a conveying belt with a surface temperature of 160℃ to transfer the compounded material to the extruder to prevent the material from cooling and causing secondary agglomeration; set the extrusion temperature zones as follows: 120℃ for the feeding section to prevent degradation; 170℃ for the melting section to fully melt the TPU; 190℃ for the mixing section to disperse the inorganic fillers; 185℃ for the die to stabilize the strip to prevent die swelling; after extruding, cut the strip into particles in water at 40℃ to obtain polyurethane plastic track composite particles with a particle size of 10mm; dry the particles in a centrifugal machine at a rotation speed of 3000rpm for 5 minutes to control the water content of the material to be less than 0.1%.

[0104] Comparative Example 1

[0105] The difference from Example 1 is that no inorganic fillers are added during the pretreatment mixing.

[0106] Comparative Example 2

[0107] The difference from Example 1 is that only air is used instead of high-purity nitrogen during carbonization, with an oxygen volume concentration of about 20%.

[0108] Comparative Example 3

[0109] The difference from Example 1 is that the DPU particle size is 0.2mm, the carbonization temperature is 280℃, and the holding time is 20min.

[0110] Comparative Example 4

[0111] The difference from Example 1 is that the DPU particle size is 0.8mm, the carbonization temperature is 180℃, and the holding time is 100min.

[0112] Comparative Example 5

[0113] The difference from Example 1 is that the DPU waste particle size does not match the microwave frequency, and it is treated at 1400W power for 25 minutes.

[0114] Comparative Example 6

[0115] The difference from Example 1 is that only carbonization is performed on the DPU waste, without subsequent microwave treatment.

[0116] Comparative Example 7

[0117] The difference from Example 1 is that the DPU waste is not carbonized, but directly subjected to microwave treatment.

[0118] Comparative Example 8

[0119] The difference from Example 1 is that step 2 is not subjected to surface modification treatment.

[0120] Comparative Example 9

[0121] The difference from Example 1 is that step 3 is not subjected to internal mixing.

[0122] Comparative Example 10

[0123] The difference from Example 1 is that the particle size of the DPU waste does not match the microwave frequency, and is treated at 400 W for 10 minutes.

[0124] Comparative Example 11

[0125] The difference from Example 1 is that step (1-1) mixing, the added filler is calcium carbonate.

[0126] Performance test:

[0127] Tensile strength: tested according to the method specified in GB / T 10654.

[0128] Elongation at break: tested according to the method specified in GB / T 10654.

[0129] Impact absorption: tested according to the method specified in GB / T 36246.

[0130] TVOC release: tested according to the method specified in GB / T 36246.

[0131] The test results are shown in Table 1.

[0132] Table 1 Performance test results of examples and comparative examples

[0133]

[0134]

[0135] The embodiment realizes performance improvement through multi-dimensional collaborative design: first, the high specific surface area and porous structure of the silica aerogel powder effectively adsorb the residual pollutants in the DPU waste material in the pretreatment stage, reducing the subsequent TVOC release; second, the rich hydroxyl groups on the surface of the aerogel form hydrogen bonds with the silane coupling agent, enhancing the interfacial bonding force between the waste material particles and the modifier, promoting the grafting reaction to generate stable chemical bonds; third, the low thermal conductivity of the aerogel delays the aging of the matrix, and its nano-network structure expands the pore through the "micro-explosion effect" in microwave treatment, releasing more active sites and strengthening the π-π conjugation effect with the polyurethane matrix; finally, the lightweight characteristics of the aerogel and the rigid support balance the toughness and strength of the material, comprehensively improving the tensile strength, elongation at break and impact absorption performance.

[0136] Compared with Example 1, Comparative Example 1 (without filler): lacking the physical support and interface enhancement of aerogel or calcium carbonate, the DPU waste material particles only rely on their own surface modification for combination, the interfacial force is weak, and the mechanical properties and impact absorption are significantly reduced; at the same time, the porous adsorption without filler increases the residual amount of pollutants, and the TVOC increases. Comparative Example 2 (air carbonization): the high oxygen content leads to insufficient oxidation of the carbonized layer, and the sp 2development, weak π-π conjugation with polyurethane matrix; high residual amount of un-pyrolyzed contaminants, TVOC surge; oxidative environment can also damage molecular chains, weaken mechanical properties. Comparative Example 3 (small particle size + high temperature short time carbonization): DPU particles too small (0.2 mm) to form hard shell on the surface at 280°C, preventing exposure of grafting sites; short holding time (20 min) results in thin carbonization layer and few active sites, weak interface bonding, and decreased mechanical properties and impact absorption; small particles have high specific surface area to adsorb contaminants but not fully pyrolyzed, high TVOC. Comparative Example 4 (large particle size + low temperature long time carbonization): DPU particles too large (0.8 mm) to have sufficient heat conduction at 180°C, resulting in uneven internal carbonization (tender on the inside and hard on the outside), few surface active groups, and insufficient grafting reaction; long holding time (100 min) results in a loose carbon layer, decreased adsorption capacity, and high TVOC; large particles are difficult to disperse and tend to agglomerate, reducing material uniformity. Comparative Example 5 (microwave parameters not matched): 1400W high power processing of small particle size (0.2 mm) DPU particles, local microwave energy overload leading to carbon layer pyrolysis / burning, structure damage (cracks / holes), and reduced active sites; long time microwave (25 min) exacerbates damage, weak interface bonding, and decreased mechanical properties and impact absorption; carbon layer damage reduces contaminant adsorption capacity, but incomplete pyrolysis releases more TVOC. Comparative Example 6 (carbonization only without microwave): carbonization layer does not effectively expand due to lack of microwave “micro-explosion effect”, low porosity, few active sites, and limited grafting reaction; dense carbon layer prevents modification agent penetration, weak interface bonding, and low mechanical properties and impact absorption; more contaminants remain in the carbon layer, high TVOC. Comparative Example 7 (no carbonization, direct microwave): original DPU surface inert (many non-polar groups), no chemical bonding with modification agent, grafting reaction only relies on physical adsorption, and weak bonding force; microwave only softens the surface but cannot form graphene-like or active sites, extremely low mechanical properties (tensile strength, elongation at break); original contaminants are not pyrolyzed, highest TVOC. Comparative Example 8 (no surface modification): omitting the coupling agent modification, DPU surface active groups are not chemically bonded with the modification agent, weak grafting reaction; sp 2The π-π conjugation of hybrid carbon and polyurethane is not enhanced, the interfacial bonding force is significantly reduced, the mechanical properties and impact absorption are greatly reduced; the unmodified surface affects the hole expansion of the carbon layer, the adsorption of pollutants is weak, and the TVOC is high. Comparative Example 9 (without internal mixing): the modified particles are simply mixed with TPU without high shear dispersion and interfacial entanglement, and the particles are easy to agglomerate; the interface has no dual action of “physical entanglement + chemical combination”, the mechanical properties and impact absorption are significantly reduced; uneven dispersion leads to local stress concentration, further reducing the performance. Comparative Example 10 (microwave parameters do not match): 400W low power treatment of small particle size (0.2mm) DPU particles, insufficient microwave energy absorption, poor carbon layer hole expansion effect (low porosity), and few active sites; the treatment time is too short (10min), the pollutants are not fully removed, the residual amount is high, and the TVOC is high; insufficient hole expansion makes it difficult for the modifier to penetrate into the carbon layer, the interfacial bonding is weak, and the mechanical properties and impact absorption are low. Comparative Example 11 (filler is calcium carbonate): calcium carbonate is a solid particle, the surface is inert (few hydroxyl groups), and the interfacial bonding with DPU or modifier is weaker than aerogel; no porous structure to adsorb pollutants, weak adsorption capacity, TVOC slightly high; weak interfacial bonding with DPU, easy to rub and agglomerate in internal mixing / microwave, reducing material uniformity, mechanical properties and impact absorption slightly lower than Example 1.

Claims

1. A polyurethane plastic waste containing DPU track composite material, characterized by, By weight parts, the following steps are taken to prepare: By weight parts, Step (1) Preparation of pretreated waste material particles: 100 parts by mass of DPU waste material particles, which are pulverized to a particle size of 0.1-1 mm, are mixed with 5-50 parts by mass of silica aerogel powder, and then subjected to surface carbonization treatment in an inert atmosphere or a vacuum environment with an oxygen volume concentration of less than 0.5% at a treatment temperature of 150-350°C for 10-120 minutes, followed by microwave treatment at a microwave power of 300-1500W for 1-30 minutes. After dispersion, pretreated waste material particles are obtained. During the surface carbonization treatment process, the carbonization temperature of DPU waste material particles with a particle size of 0.1-0.3 mm is set to 150-200°C, and the holding time is 10-30 minutes; the carbonization temperature of DPU waste material particles with a particle size of 0.3-0.6 mm is set to 200-300°C, and the holding time is 30-90 minutes; the carbonization temperature of DPU waste material particles with a particle size of 0.6-1.0 mm is set to 300-350°C, and the holding time is 90-120 minutes. During the microwave treatment process, particles with a particle size of 0.1-0.3 mm are treated at a power of 300-600W for 5-15 minutes, particles with a particle size of 0.3-0.6 mm are treated at a power of 600-1200W for 10-25 minutes, and particles with a particle size of 0.6-1.0 mm are treated at a power of 1200-1500W for 15-30 minutes. Step (2) Preparation of modified waste material particles: the pretreated waste material particles are subjected to surface modification treatment, and then grafted with monomers of polyurethane in the presence of a catalyst at a reaction temperature of 40-90°C for 0.5-5 hours to obtain modified waste material particles. Step (3) Preparation of composite material: 100 parts by mass of modified waste material particles are mixed with 20-200 parts by mass of a plastic polyurethane base material, and then subjected to mixing, extrusion, and granulation to obtain a polyurethane plastic track composite material. The mixing process is as follows: the mixing chamber is preheated to 150°C, 100 parts of TPU base material are added, and then melted and plasticized for 2 minutes, followed by the addition of modified waste material particles and auxiliary agents; then the rotation speed is increased step by step, first stirred at a rotation speed of 30 rpm for 1 minute to gently mix and prevent particle breakage, then stirred at a rotation speed of 60 rpm for 2 minutes to moderately shear and tear the carbonized layer, and finally stirred at a rotation speed of 90 rpm for 2 minutes to promote interface entanglement at high temperature and high pressure; when the power curve of the mixing machine tends to be stable with a fluctuation of less than 5%, the mixing is stopped.

2. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The particle size of the silica aerogel powder in step (1) is 1-100 μm.

3. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The surface modification treatment in step (2) is at least one method selected from the group consisting of silane coupling agent, titanate coupling agent, and plasma treatment.

4. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The monomers of polyurethane in step (2) are a mixture of isocyanate compounds and polyol compounds, wherein the isocyanate compounds include at least one of toluene diisocyanate, diphenylmethane diisocyanate, and isophorone diisocyanate, and the polyol compounds are polyether polyol or polyester polyol.

5. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The amount of polyurethane monomer added in step (2) is 1% to 20% of the mass of the polyurethane waste particles.

6. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The catalyst in step (2) is an organic tin catalyst or an amine catalyst, and the amount used is 0.1% to 5% of the mass of the polyurethane monomer.

7. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The plasticized polyurethane base in step (3) is a thermoplastic polyurethane or a polyurethane prepolymer.

8. The DPU-containing scrap polyurethane plastic track composite material of claim 1, wherein: The temperature of the extrusion in step (3) is 120 to 200°C, and the particle size of the granulation is 1 to 10 mm.

9. A method of preparing a polyurethane plastic track composite material containing DPU waste material as claimed in any one of claims 1 to 8, characterised in that, The method comprises the following steps: Step (1) Preparation of pretreated waste particle: batching, mixing, carbonization, and microwave treatment to obtain pretreated waste particles; Step (2) Preparation of modified waste particles: surface modification and grafting of the pretreated waste particles to obtain modified waste particles; Step (3) Preparation of composite material: batching of the modified waste particles, extrusion, and granulation to obtain a polyurethane plastic track composite material.

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