Functional cross-linked network structure polyurethane composite material based on waste PET depolymerization monomer and preparation method of functional cross-linked network structure polyurethane composite material

Abstract

The invention discloses a polyurethane composite material with a functional cross-linked network structure based on a waste PET (Polyethylene Terephthalate) depolymerization monomer and a preparation method of the polyurethane composite material. The preparation method comprises the following steps: by utilizing a polyhydroxy structure of a functional filler, reacting a coupling agent isocyanate propyl triethoxy silane with a waste PET depolymerization monomer bis (2-hydroxyethyl) terephthalate to prepare a functional polyurethane cross-linking agent; according to the invention, organic-inorganic hybridization can be fully realized, and due to relatively small particle size distribution and excellent dispersion stability, the filler can be uniformly dispersed in a polyurethane matrix, so that the interfacial compatibility of the filler and polyurethane is improved, the interfacial interaction is enhanced, and the filler can directly participate in the synthetic reaction of polyurethane through an in-situ polymerization method; and a cross-linked network structure is formed in the polyurethane, so that the polyurethane is endowed with good mechanical properties, electric conduction, heat conduction, electromagnetic shielding effect and the like.

Description

Technical Field:

[0001] The present invention relates to the technical field of polyurethane composites, and particularly relates to a functional crosslinked network structure polyurethane composite based on depolymerized monomers of waste PET and a preparation method thereof. Background Art:

[0002] Polyethylene terephthalate (PET) materials are lightweight, easy to process, and dimensionally stable, and are widely used in packaging bottles. With the development of society and economy, the consumption of PET packaging bottles is increasing. If they are discarded casually after use, it will not only waste resources but also cause environmental pollution. In recent years, the depolymerized monomer bis(2-hydroxyethyl) terephthalate of waste PET has been gradually applied in polyurethane materials. How to prepare high-performance and multifunctional polyurethane composites using the depolymerized monomers of waste PET is one of the current focuses of attention.

[0003] Polyurethane is a polymer resin containing urethane groups, with good wear resistance, toughness, low-temperature flexibility, corrosion resistance, and processability, and is widely used in fields such as construction, the automotive industry, artificial leather, and adhesives. However, traditional polyurethanes can only be used in low-end products due to their single performance and cannot meet specific functional requirements (such as conductivity, heat conduction, and electromagnetic shielding, etc.). With the progress of technology, new requirements have gradually been put forward for the properties of polyurethanes.

[0004] Chinese Patent Application Publication No. CN116217878A discloses a functionalized carbon nanotube / polyurethane composite and a preparation method thereof. Although this preparation method improves the compatibility between the filler and the polyurethane matrix and enhances the mechanical and damping properties of the composite. However, this method cannot form an effective functional crosslinked network structure of the filler in the polyurethane matrix. Therefore, it is impossible to endow polyurethane with good conductivity, heat conduction, electromagnetic shielding, and other properties. Therefore, if high-performance and multifunctional polyurethane composites are manufactured using functionalized modified fillers or new preparation technologies, not only good mechanical properties can be endowed to polyurethane, but also conductivity, heat conduction, and electromagnetic shielding functions can be endowed, which will expand the application of polyurethane in the field of intelligent products. Summary of the Invention:

[0005] The purpose of the present invention is to provide a functional crosslinked network structure polyurethane composite based on depolymerized monomers of waste PET and a preparation method thereof, which solves the problems that polyurethanes prepared by the prior art do not have good conductivity, heat conduction, and electromagnetic shielding functions, the problem that functional fillers are prone to agglomeration in polyurethane in the prior art, and the problem that waste PET is not highly valorized.

[0006] The present invention is realized through the following technical solutions:

[0007] A polyurethane composite material with a functional cross-linked network structure based on waste PET depolymerization monomers is prepared from the following raw materials in parts by weight:

[0008]

[0009] The functional filler is one or more of MXene, graphene oxide (GO), hydroxylated carbon nanotubes (CNT), and hydroxylated boron nitride (BN); the catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, and stannous octoate.

[0010] The polyol is one or more of polytetrahydrofuran, polyethylene glycol, polypropylene glycol, polyether alkyl ether, poly(1,4-butylene adipate), poly(1,6-hexanediol adipate), polyethylene adipate glycol, polypropylene adipate glycol, and poly(1,6-hexanediol carbonate) diol; the number-average molecular weight of the polyol is 1000 - 2000.

[0011] The diisocyanate is one or more of hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and toluene diisocyanate.

[0012] The chain extender is one or more of bis(2-hydroxyethyl) terephthalate, 1,4-butanediol, ethylene glycol, propylene glycol, neopentyl glycol, ethanolamine, diethanolamine, and triethanolamine.

[0013] The organic solvent is one or more of N,N-dimethylformamide, N-methylpyrrolidone, acetone, and butanone.

[0014] The diluent is one or more of butanone, acetone, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0015] The specific preparation method of the waste PET depolymerization monomer bis(2-hydroxyethyl) terephthalate includes the following steps: Under a protective atmosphere, waste PET and ethylene glycol are in a mass ratio of 1:(2 - 4), and react at 180 - 200 °C for 3 - 5 h under the action of a catalyst, and bis(2-hydroxyethyl) terephthalate (BHET) is obtained through filtration, rotary evaporation, cooling crystallization, centrifugal washing, and drying; the catalyst is one or more of zinc acetate, copper acetate, nickel acetate, and manganese acetate; the dosage of the catalyst is 1 - 3% of the mass of waste PET.

[0016] The preparation method of the polyurethane composite material with a functional cross-linked network structure based on waste PET depolymerization monomers includes the following steps:

[0017] 1) Under a protective atmosphere, dissolve bis(2-hydroxyethyl) terephthalate, the depolymerization monomer of waste PET, in a mixture of an organic solvent and the coupling agent isocyanatopropyltriethoxysilane, and react at 60 - 80 °C for 1 - 3 h under the action of a catalyst to obtain bis(2-hydroxyethyl) terephthalate modified with isocyanatopropyltriethoxysilane;

[0018] 2) Add a dispersion of a functional filler with active hydroxyl groups to step 1), and react at 50 - 70 °C for 2 - 4 h under the action of a catalyst to obtain a crude product of a functionalized polyurethane crosslinking agent with the functional filler loaded with bis(2-hydroxyethyl) terephthalate;

[0019] 3) Centrifuge and wash the crude product of the functionalized polyurethane crosslinking agent and dry it under vacuum to obtain a purified functionalized polyurethane crosslinking agent;

[0020] 4) Mix a polyol with a diisocyanate and a chain extender, add a catalyst, and react at 60 - 80 °C to obtain a polyurethane prepolymer; the mixing means stirring at 60 - 80 °C for 20 - 40 min, and the reaction time is 1 - 3 h;

[0021] 5) Mix the polyurethane prepolymer obtained in step 4) with the functionalized polyurethane crosslinking agent obtained in step 3), stir and react at 50 - 70 °C for 1 - 3 h, and add a diluent for dilution during the reaction to obtain a polyurethane emulsion;

[0022] 6) Dry the polyurethane emulsion to form a film to obtain a polyurethane composite material with a functional crosslinked network structure based on the depolymerization monomer of waste PET.

[0023] Preferably, in step 1), the molar ratio of bis(2-hydroxyethyl) terephthalate to isocyanatopropyltriethoxysilane is 1:1; the organic solvent is one or more of N,N-dimethylformamide, N-methylpyrrolidone, acetone, and methyl ethyl ketone.

[0024] Preferably, in step 1), the weight ratio of the organic solvent to bis(2-hydroxyethyl) terephthalate (BHET) is (5 - 15):(0.5 - 1.5), the catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, and stannous octoate; the dosage of the catalyst is 1 - 5% of the mass of the depolymerization monomer bis(2-hydroxyethyl) terephthalate.

[0025] Preferably, in step 2), the functional filler with active hydroxyl groups is one or more of MXene, graphene oxide (GO), hydroxylated carbon nanotubes, and hydroxylated boron nitride.

[0026] Preferably, the weight ratio of the organic solvent to the functional filler in step 2) is (5 - 15):(0.1 - 0.3), and the solvent used for the dispersion liquid in step 2) is one or more of N-methylpyrrolidone, N,N-dimethylformamide, acetone, and methyl ethyl ketone; the catalyst in step 2) is one or more of dibutyltin dilaurate, dibutyltin diacetate, and stannous octoate; the dosage of the catalyst is 1 - 5% of the mass of the functional filler.

[0027] Preferably, the rotation speed of the stirring in step 4) is 50 - 150 rpm;

[0028] Preferably, the rotation speed of the stirring in step 5) is 100 - 200 rpm.

[0029] The functional filler of the present invention is one or more of MXene, graphene oxide (GO), hydroxylated carbon nanotubes (CNT), and hydroxylated boron nitride (BN). These functional fillers have properties such as electrical conductivity, thermal conductivity, and electromagnetic shielding effect. The present invention utilizes the polyhydroxy structure of the functional filler to react with the depolymerization monomer of waste PET, bis(2-hydroxyethyl) terephthalate (BHET), through the coupling agent isocyanatopropyltriethoxysilane to form a functionalized crosslinking agent with BHET grafted on the surface of the functional filler. Because BHET has a rigid benzene ring structure and excellent mechanical properties; therefore, the functionalized polyurethane crosslinking agent prepared by the present invention has versatility, not only has excellent mechanical properties, but also has properties such as electrical conductivity, thermal conductivity, and electromagnetic shielding effect. The functionalized polyurethane crosslinking agent of the present invention can directly participate in the synthesis reaction of polyurethane by in-situ polymerization and form a crosslinked network structure in the polyurethane, thereby endowing the polyurethane with good electrical conductivity, thermal conductivity, and electromagnetic shielding effect. Therefore, the present invention also protects the application of the functional crosslinked network structure polyurethane composite material based on the depolymerization monomer of waste PET, used in the fields of thermal conductive materials, electromagnetic shielding materials, sensors, and medical materials.

[0030] Moreover, the functionalized polyurethane crosslinking agent obtained by the present invention having BHET grafted on the surface has a complete structure, a small particle size distribution, and excellent dispersion stability, can be uniformly dispersed in the polyurethane matrix, improves the interfacial compatibility between the filler and the polyurethane, and enhances the interfacial interaction.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. The functionalized polyurethane crosslinking agent used in the present invention is prepared by loading the depolymerization monomer BHET of waste PET on the functional filler. By utilizing the polyhydroxy structure of the functional filler to react with the depolymerization monomer of waste PET, bis(2-hydroxyethyl) terephthalate (BHET), through the coupling agent isocyanatopropyltriethoxysilane, organic-inorganic hybridization can be fully realized.

[0033] 2. The functionalized polyurethane crosslinking agent used in the present invention participates in the synthesis of polyurethane through in-situ polymerization, playing an incomparable role in enhancing the functionality of polyurethane. The functionalized polyurethane crosslinking agent used in the present invention can not only construct a functional crosslinking network structure in polyurethane, but also promote the uniform dispersion of functional fillers in the polyurethane matrix. In addition, the functionalized polyurethane crosslinking agent endows polyurethane with excellent electrical conductivity, thermal conductivity, electromagnetic shielding performance, etc. The polyurethane obtained in the present invention not only has excellent mechanical properties, but also has properties such as electrical and thermal conductivity and electromagnetic shielding effect, and can be used in the fields of thermal conductive materials, electromagnetic shielding materials, sensors, and medical materials.

[0034] 3. The preparation of the polyurethane composite material with a functional crosslinking network structure based on waste PET depolymerization monomers in the present invention is convenient, efficient, and has good film-forming properties.

[0035] In summary, the present invention uses the polyhydroxy structure of functional fillers to react with the waste PET depolymerization monomer bis(2-hydroxyethyl) terephthalate (BHET) through the coupling agent isocyanatopropyltriethoxysilane to prepare a functionalized polyurethane crosslinking agent. It can not only fully achieve organic-inorganic hybridization, but also, due to its small particle size distribution and excellent dispersion stability, can be uniformly dispersed in the polyurethane matrix, improving the interfacial compatibility between the filler and polyurethane, enhancing the interfacial interaction, and can directly participate in the synthesis reaction of polyurethane through in-situ polymerization and form a crosslinking network structure in polyurethane, thereby endowing polyurethane with good mechanical properties and properties such as electrical and thermal conductivity and electromagnetic shielding effect. Description of the Drawings:

[0036] Figure 1 SEM images of the polyurethane composite materials prepared in Examples 1-3 and Comparative Examples 1-2; among them, a-b are Comparative Examples 1-2 respectively, and c-e are Examples 1-3 respectively;

[0037] Figure 2 Gel content diagrams of the polyurethane composite materials prepared in Examples 1-3 and Comparative Examples 1-2;

[0038] Figure 3 Conductivity diagrams of the polyurethane composite materials prepared in Examples 1-3 and Comparative Examples 1-2;

[0039] Figure 4 Thermal conductivity diagrams of the polyurethane composite materials prepared in Examples 1-3 and Comparative Examples 1-2;

[0040] Figure 5 Electromagnetic interference shielding effectiveness diagrams in the X-band of the polyurethane composite materials prepared in Examples 1-3 and Comparative Examples 1-2. Detailed Embodiments:

[0041] The following is a further description of the present invention, rather than a limitation thereof.

[0042] Example 1:

[0043] (1) Waste PET flakes and ethylene glycol were mixed at a mass ratio of 1:3 and 2 wt% of the catalyst zinc acetate (2% of the mass of waste PET) and added to a reaction vessel. The mixture was stirred and reacted at 190 °C for 4 h. The product was filtered, rotary evaporated, cooled and crystallized, centrifugally washed, and vacuum dried to obtain the depolymerized monomer bis(2-hydroxyethyl) terephthalate (BHET).

[0044] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane being 1:1, 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) was dissolved in 10 parts by weight of N,N-dimethylformamide and added to a reactor. Then, 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate were added. The mixture was stirred at 70 °C at a speed of 150 rpm for 2 h. Then, 10 mL of a 10 mg / mL N,N-dimethylformamide dispersion of MXene (0.1 part by weight) was added to the reactor, and 0.003 part by weight of the catalyst dibutyltin dilaurate was further added. The reaction was carried out at 60 °C for 3 h. The obtained product was centrifugally washed and vacuum dried to obtain the purified functionalized polyurethane crosslinker MXene-s-BHET.

[0045] (3) In a reactor, 6 parts by weight of poly(butylene adipate), 4 parts by weight of hexamethylene diisocyanate, and 1 part by weight of the chain extender bis(2-hydroxyethyl) terephthalate were added. First, the mixture was stirred at 70 °C at a speed of 100 rpm for 30 min, and then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(butylene adipate)) was added. The reaction was carried out with stirring at 70 °C for 2 h to obtain a polyurethane prepolymer for standby.

[0046] (4) The functionalized polyurethane crosslinker MXene-s-BHET (0.1 part by weight) obtained in step (2) was added to the polyurethane prepolymer in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of MXene-s-BHET and the polyurethane prepolymer) was 1 wt%. The mixture was stirred at 60 °C at a speed of 150 rpm for 2 h, and 4 parts by weight of methyl ethyl ketone was added for dilution during the reaction to obtain a functionalized polyurethane emulsion.

[0047] (5) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and smooth surface. It was dried in an oven at 70 °C for 10 h, and then the film was peeled off to obtain the functionalized polyurethane film PU / MXene-s-BHET 1.

[0048] Example 2

[0049] (1) Waste PET bottle chips and ethylene glycol were mixed at a mass ratio of 1:3 and 2 wt% of the catalyst zinc acetate (2% of the mass of waste PET) and added to a reaction vessel. The mixture was stirred and reacted at 190 °C for 4 h. The product was filtered, rotary evaporated, cooled and crystallized, centrifugally washed, and vacuum dried to obtain the depolymerized monomer bis(2-hydroxyethyl) terephthalate (BHET).

[0050] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane of 1:1, 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) was dissolved in 10 parts by weight of N,N-dimethylformamide and added to a reactor. Then, 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate were added. The mixture was stirred at 70 °C at a speed of 150 rpm for 2 h. Then, 20 mL of a 10 mg / mL N,N-dimethylformamide dispersion of MXene (0.2 part by weight) was added to the reactor, and 0.006 part by weight of the catalyst dibutyltin dilaurate was added. The reaction was carried out at 60 °C for 3 h. The obtained product was centrifugally washed and vacuum dried to obtain the purified functionalized polyurethane crosslinker MXene-s-BHET.

[0051] (3) In a reactor, 6 parts by weight of poly(1,4-butylene adipate), 4 parts by weight of hexamethylene diisocyanate, and 1 part by weight of the chain extender bis(2-hydroxyethyl) terephthalate were added. First, the mixture was stirred at 70 °C at a speed of 100 rpm for 30 min, and then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)) was added. The reaction was carried out by stirring at 70 °C for 2 h to obtain a polyurethane prepolymer for standby.

[0052] (4) 0.2 part by weight of the functionalized polyurethane crosslinker MXene-s-BHET was added to the polyurethane prepolymer obtained in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of MXene-s-BHET and the polyurethane prepolymer) was 2 wt%. The mixture was stirred at 60 °C at a speed of 150 rpm for 2 h, and 4 parts by weight of methyl ethyl ketone was added for dilution during the reaction to obtain a functionalized polyurethane emulsion.

[0053] (5) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface. It was dried in an oven at 70 °C for 10 h, and then the film was peeled off to obtain the functionalized polyurethane film PU / MXene-s-BHET 2.

[0054] Example 3

[0055] (1) Waste PET bottle chips and ethylene glycol were mixed in a mass ratio of 1:3 and 2 wt% of the catalyst zinc acetate (2% of the mass of waste PET) and added to a reaction vessel. The mixture was stirred and reacted at 190 °C for 4 h. The product was filtered, rotary evaporated, cooled and crystallized, centrifugally washed, and vacuum dried to obtain the depolymerized monomer bis(2-hydroxyethyl) terephthalate (BHET).

[0056] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane of 1:1, 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) was dissolved in 10 parts by weight of N,N-dimethylformamide and added to a reactor. Then, 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate were added, and the mixture was stirred at 70 °C at a speed of 150 rpm for 2 h. Then, 30 mL of a 10 mg / mL N,N-dimethylformamide dispersion of MXene (0.3 part by weight) was added to the reactor, and 0.009 part by weight of the catalyst dibutyltin dilaurate was added. The reaction was carried out at 60 °C for 3 h, and the resulting product was centrifugally washed and vacuum dried to obtain the purified functionalized polyurethane crosslinker MXene-s-BHET.

[0057] (3) In a reactor, 6 parts by weight of poly(butylene adipate), 4 parts by weight of hexamethylene diisocyanate, and 1 part by weight of the chain extender bis(2-hydroxyethyl) terephthalate were added. First, the mixture was stirred at 70 °C at a speed of 100 rpm for 30 min, and then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(butylene adipate)) was added, and the reaction was stirred at 70 °C for 2 h to prepare a polyurethane prepolymer for standby.

[0058] (4) 0.3 part by weight of the functionalized polyurethane crosslinker MXene-s-BHET was added to the polyurethane prepolymer in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of MXene-s-BHET and the polyurethane prepolymer) was 3 wt%. The mixture was stirred at 60 °C at a speed of 150 rpm for 2 h, and 4 parts by weight of methyl ethyl ketone was added for dilution during the reaction to prepare a functionalized polyurethane emulsion.

[0059] (5) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface. It was dried in an oven at 70 °C for 10 h, and then the film was peeled off to obtain the functionalized polyurethane film PU / MXene-s-BHET 3.

[0060] Comparative Example 1

[0061] (1) In a reactor, 6 parts by weight of poly(1,4-butylene adipate), 4 parts by weight of hexamethylene diisocyanate, and 1 part by weight of the chain extender bis(2-hydroxyethyl) terephthalate were added. First, it was stirred at 70 °C at a speed of 100 rpm for 30 min, and then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)) was added, and the reaction was stirred at 70 °C for 2 h to obtain a polyurethane emulsion for standby.

[0062] (2) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface. It was dried in an oven at 70 °C for 10 h, and then the film was peeled off to obtain the polyurethane film PU as a reference sample.

[0063] Comparative Example 2

[0064] (1) In a reactor, 6 parts by weight of poly(1,4-butylene adipate), 4 parts by weight of hexamethylene diisocyanate, and 1 part by weight of the chain extender bis(2-hydroxyethyl) terephthalate were added. First, it was stirred at 70 °C at a speed of 100 rpm for 30 min, and then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)) was added, and the reaction was stirred at 70 °C for 2 h to obtain a polyurethane emulsion for standby.

[0065] (2) 20 mL of a 10 mg / mL N,N-dimethylformamide dispersion of MXene (0.2 part by weight) was added to the polyurethane emulsion in step (1), and it was stirred at 60 °C at a speed of 150 rpm for 2 h. During the reaction, 4 parts by weight of methyl ethyl ketone was added for dilution to obtain a functionalized polyurethane emulsion.

[0066] (3) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface. It was dried in an oven at 70 °C for 10 h, and then the film was peeled off to obtain the functionalized polyurethane film PU / MXene as a reference sample.

[0067] The scanning electron micrographs of the functionalized polyurethane composites of Examples 1-3 and Comparative Examples 1-2 are as Figure 1 shown. From Figure 1It can be seen that, obviously, the cross-section of the polyurethane in Comparative Example 1 without the addition of MXene / MXene-s-BHET is relatively smooth and flat. However, as Figure 1 shown in b, obvious agglomeration phenomena occurred in the PU / MXene matrix of Comparative Example 2. This is due to the van der Waals force and hydrogen bond aggregation between unmodified MXenes, resulting in the agglomeration of MXene in the PU matrix, and thus the interfacial interaction and adhesion between it and the PU matrix are poor. On the contrary, in Examples 1-3, MXene-s-BHET participated in the synthesis of polyurethane as a functional cross-linking agent, enabling MXene to present a single-layer or few-layer uniform dispersion state in the PU matrix, and constructing an effective interpenetrating network structure, enhancing the interfacial interaction with the polyurethane matrix, so that the inherent rigidity, conductivity and thermal conductivity of MXene are fully demonstrated in polyurethane. In addition, with the increase in the content of MXene-s-BHET, the cross-linking network density in the PU matrix increases. When the dosage of MXene-s-BHET reaches 3 wt% (the mass percentage of the dosage of MXene-s-BHET in the raw materials composed of MXene-s-BHET and polyurethane prepolymer), slight agglomeration phenomena occur in the PU / MXene-s-BHET3 composite matrix due to the formation of hydrogen bonds between excessive MXene sheets. The gel content of the functionalized polyurethane composites in Examples 1-3 and Comparative Examples 1-2 is as Figure 2 shown. It can be Figure 2 seen that when MXene / MXene-s-BHET is not added, the gel content of PU is 0%, indicating that there is no cross-linking structure in PU. However, when the composite contains MXene-s-BHET, the gel content of polyurethane increases significantly, indicating that MXene-s-BHET can participate well in the synthesis of polyurethane as a cross-linking agent to form a cross-linking network structure. In addition, with the increase in the content of MXene-s-BHET, the gel content of the PU / MXene-s-BHET composite shows a gradually increasing trend. However, when the dosage of MXene-s-BHET exceeds 2 wt%, the increasing rate of the gel content of the composite decreases, which is because when the content of MXene-s-BHET is relatively high, it may cause the filler to aggregate in polyurethane, thus unable to construct more cross-linking network structures. The conductivity diagrams of the functionalized polyurethane composites in Examples 1-3 and Comparative Examples 1-2 are as Figure 3 shown. It can be Figure 3It can be seen that, compared with pure PU, the conductivity of the polyurethane composite containing MXene / MXene-s-BHET is significantly improved, which is attributed to the intrinsic conductivity of MXene. Notably, the conductivity of the PU / MXene-s-BHET composite is significantly higher than that of PU / MXene because the MXene modified by organic matter enhances the interfacial compatibility with the polyurethane matrix. At the same time, MXene-s-BHET acts as a functional crosslinking agent and participates in the synthesis of polyurethane, being able to disperse uniformly in the polyurethane matrix and construct a "conductive network" structure, thus endowing the polyurethane with a relatively high conductivity. However, unmodified MXene is prone to agglomeration in the polyurethane matrix and is difficult to form an effective "conductive network" to endow the polyurethane with good conductivity. In addition, with the increase in the dosage of the functional crosslinking agent MXene-s-BHET, the conductivity of the composite gradually increases. When the dosage of MXene-s-BHET reaches 3wt%, certain agglomeration appears in the composite matrix, and more conductive paths cannot be built, resulting in only a slight increase in the conductivity of the composite. The thermal conductivity diagrams of the functionalized polyurethane composites of Examples 1-3 and Comparative Examples 1-2 are as shown in Figure 4 shown. It can be seen from Figure 4 that the thermal conductivities of the polyurethane composites with different contents of MXene-s-BHET and MXene are significantly higher than those of the unfilled PU. Moreover, the thermal conductivity of the PU / MXene-s-BHET composite first gradually increases and then decreases with the increase in the content of MXene-s-BHET. The X-band electromagnetic interference shielding effectiveness diagrams of the functionalized polyurethane composites of Examples 1-3 and Comparative Examples 1-2 are as shown in Figure 5 shown. It can be seen from Figure 5 that, compared with the unfilled PU (0 dB), the incorporation of fillers significantly enhances the EMI shielding effect of the PU composite, and the enhancement effect of the modified MXene (MXene-s-BHET) is the most significant. Under the same content, the EMI SE of PU / MXene-s-BHET 2 is 26.8 dB, which is significantly better than that of PU / MXene (10.1 dB). This is because the crosslinking agent MXene-s-BHET can disperse uniformly in the polyurethane matrix and construct an "interpenetrating network" structure, thus endowing the polyurethane with a better electromagnetic shielding effect.

[0068] Example 4

[0069] (1) The same as step (1) of Example 1.

[0070] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane being 1:1, 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) was dissolved in 10 parts by weight of N,N-dimethylformamide, added to the reactor, then 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate were added, and stirred at 70 °C at a speed of 150 rpm for 2 h; then, 20 mL of an N,N-dimethylformamide dispersion of 10 mg / mL graphene oxide (GO) (0.2 part by weight) was added to the reactor, and 0.006 part by weight of the catalyst dibutyltin dilaurate was added, and reacted at 60 °C for 3 h. The obtained product was centrifuged, washed, and vacuum dried to obtain the purified functionalized polyurethane crosslinker GO-s-BHET.

[0071] (3) In the reactor, 6 parts by weight of polyethylene glycol, 4 parts by weight of dicyclohexylmethane diisocyanate, and 1 part by weight of the chain extender 1,4-butanediol were added. First, stirred at 70 °C at a speed of 100 rpm for 30 min, then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)) was added, and stirred and reacted at 70 °C for 2 h to obtain a polyurethane prepolymer for standby.

[0072] (4) 0.2 part by weight of the functionalized polyurethane crosslinker GO-s-BHET was added to the polyurethane prepolymer in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of GO-s-BHET and the polyurethane prepolymer) was 2%. Stirred at 60 °C at a speed of 150 rpm for 2 h, and 4 parts by weight of methyl ethyl ketone was added for dilution during the reaction to obtain a functionalized polyurethane emulsion.

[0073] (5) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface, dried in an oven at 70 °C for 10 h, and the film was peeled off to obtain the functionalized polyurethane film PU / GO-s-BHET 2.

[0074] Example 5

[0075] (1) The same as step (1) of Example 1.

[0076] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane being 1:1, dissolve 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) in 10 parts by weight of N,N-dimethylformamide, add it to the reactor, then add 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate, and stir at 70 °C at a speed of 150 rpm for 2 h; then, add 20 mL of an N,N-dimethylformamide dispersion of hydroxylated carbon nanotubes (0.2 part by weight) with a concentration of 10 mg / mL to the reactor, and then add 0.006 part by weight of the catalyst dibutyltin dilaurate, react at 60 °C for 3 h, and subject the obtained product to centrifugal washing and vacuum drying to obtain the purified functionalized polyurethane crosslinker CNT-s-BHET.

[0077] (3) In the reactor, add 6 parts by weight of polytetrahydrofuran, 4 parts by weight of isophorone diisocyanate, and 1 part by weight of the chain extender ethylene glycol. First, stir at 70 °C at a speed of 100 rpm for 30 min, then add 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)), and stir and react at 70 °C for 2 h to prepare a polyurethane prepolymer for standby.

[0078] (4) Add 0.2 part by weight of the functionalized polyurethane crosslinker CNT-s-BHET to the polyurethane prepolymer in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of CNT-s-BHET and the polyurethane prepolymer) is 2%, stir at 60 °C at a speed of 150 rpm for 2 h, and add 4 parts by weight of methyl ethyl ketone for dilution during the reaction process to prepare a functionalized polyurethane emulsion.

[0079] (5) Evenly spread the prepared emulsion on a dry and clean mold to form a liquid layer with uniform thickness and a smooth and flat surface, dry it in an oven at 70 °C for 10 h, and remove the film to obtain the functionalized polyurethane film PU / CNT-s-BHET 2.

[0080] Example 6

[0081] (1) The same as step (1) of Example 1.

[0082] (2) According to the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane being 1:1, 1 part by weight of bis(2-hydroxyethyl) terephthalate (BHET) was dissolved in 10 parts by weight of N,N-dimethylformamide, added into the reactor, then 0.97 part by weight of the coupling agent isopropyltriethoxysilane (IPTS) and 0.03 part by weight of the catalyst dibutyltin dilaurate were added, and stirred at 70 °C at a speed of 150 rpm for 2 h; then, 20 mL of a 10 mg / mL N,N-dimethylformamide dispersion of hydroxylated boron nitride (0.2 part by weight) was added into the reactor, and 0.006 part by weight of the catalyst dibutyltin dilaurate was added, and reacted at 60 °C for 3 h. The obtained product was centrifuged, washed, and dried under vacuum to obtain the purified functionalized polyurethane crosslinker BN-s-BHET.

[0083] (3) In the reactor, 6 parts by weight of poly(hexamethylene adipate), 4 parts by weight of toluene diisocyanate, and 1 part by weight of the chain extender propylene glycol were added. First, it was stirred at 70 °C at a speed of 100 rpm for 30 min, then 0.12 part by weight of the catalyst dibutyltin dilaurate (2 wt% of the weight of poly(1,4-butylene adipate)) was added, and stirred and reacted at 70 °C for 2 h to obtain a polyurethane prepolymer for standby.

[0084] (4) 0.2 part by weight of the functionalized polyurethane crosslinker BN-s-BHET was added to the polyurethane prepolymer in step (3). The mass fraction of the functionalized polyurethane crosslinker in the raw materials (the raw materials composed of BN-s-BHET and the polyurethane prepolymer) was 2%. It was stirred at 60 °C at a speed of 150 rpm for 2 h, and 4 parts by weight of methyl ethyl ketone was added for dilution during the reaction to obtain a functionalized polyurethane emulsion.

[0085] (5) The prepared emulsion was evenly spread on a dry and clean mold to form a liquid layer with uniform thickness and smooth surface. It was dried in an oven at 70 °C for 10 h, and the film was peeled off to obtain the functionalized polyurethane film PU / BN-s-BHET 2.

Claims

1. A polyurethane composite material with a functional cross-linked network structure based on depolymerized monomers of waste PET, characterized in that, It is prepared from the following raw materials by weight parts: The functional filler is one or more of MXene, graphene oxide, hydroxylated carbon nanotubes, and hydroxylated boron nitride; the catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, and stannous octoate.

2. The polyurethane composite material according to claim 1, characterized in that, The polyol is one or more of polytetrahydrofuran, polyethylene glycol, polypropylene glycol, polyether alkyl ether, poly(1,4-butanediol adipate), poly(1,6-hexanediol adipate), polyethylene adipate glycol, polypropylene adipate glycol, and poly(1,6-hexanediol carbonate) diol; the number-average molecular weight of the polyol is 1000-2000.

3. The polyurethane composite material according to claim 1, wherein, The diisocyanate is one or more of hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and toluene diisocyanate.

4. The polyurethane composite material according to claim 1, characterized in that, The chain extender is one or more of bis(2-hydroxyethyl) terephthalate, 1,4-butanediol, ethylene glycol, propylene glycol, neopentyl glycol, ethanolamine, diethanolamine, and triethanolamine.

5. The polyurethane composite material according to claim 1, wherein, The organic solvent is one or more of N,N-dimethylformamide, N-methylpyrrolidone, acetone, and methyl ethyl ketone.

6. The polyurethane composite material according to claim 1, characterized in that, The diluent is one or more of methyl ethyl ketone, acetone, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The polyurethane composite material according to claim 1, characterized in that The specific preparation method of the waste PET depolymerization monomer bis(2-hydroxyethyl) terephthalate includes the following steps: under a protective atmosphere, the waste PET and ethylene glycol are in a mass ratio of 1:(2-4), and react at 180-200 °C for 3-5 h under the action of a catalyst, and bis(2-hydroxyethyl) terephthalate is obtained through filtration, rotary evaporation, cooling crystallization, centrifugal washing, and drying; the catalyst is one or more of zinc acetate, copper acetate, nickel acetate, and manganese acetate; the dosage of the catalyst is 1-3% of the mass of the waste PET.

8. The preparation method of the polyurethane composite material with a functional crosslinked network structure based on the depolymerized monomers of waste PET according to claim 1, characterized in that, It includes the following steps: 1) Under a protective atmosphere, the waste PET depolymerization monomer bis(2-hydroxyethyl) terephthalate is dissolved in an organic solvent and mixed with the coupling agent isocyanatopropyltriethoxysilane, and reacts at 60-80 °C for 1-3 h under the action of a catalyst to obtain bis(2-hydroxyethyl) terephthalate modified with isocyanatopropyltriethoxysilane. 2) Add the dispersion liquid of the functional filler with active hydroxyl groups to step 1), and react at 50-70 °C for 2-4 h under the action of a catalyst to obtain a crude product of the functionalized polyurethane crosslinking agent with the functional filler loaded with bis(2-hydroxyethyl) terephthalate. 3) The crude product of the functionalized polyurethane crosslinking agent is centrifugally washed and vacuum dried to obtain a purified functionalized polyurethane crosslinking agent. 4) Mix the polyol with the diisocyanate and the chain extender, add a catalyst, and react at 60-80 °C to obtain a polyurethane prepolymer; the mixing means stirring at 60-80 °C for 20-40 min, and the reaction time is 1-3 h. 5) Mix the polyurethane prepolymer obtained in step 4) with the functionalized polyurethane crosslinking agent obtained in step 3), stir and react at 50-70 °C for 1-3 h, and add a diluent for dilution during the reaction to obtain a polyurethane emulsion. 6) Dry the polyurethane emulsion to form a film to obtain a polyurethane composite material with a functional cross-linked network structure based on the depolymerized monomers of waste PET.

9. The method according to claim 8, characterized in that, In step 1), the molar ratio of bis(2-hydroxyethyl) terephthalate to the coupling agent isopropyltriethoxysilane is 1:1; in step 1), the weight ratio of the organic solvent to bis(2-hydroxyethyl) terephthalate (BHET) is (5-15):(0.5-1.5), and the dosage of the catalyst is 1-5% of the mass of the depolymerized monomer bis(2-hydroxyethyl) terephthalate.

10. The method according to claim 8, characterized in that, In step 2), the weight ratio of the organic solvent to the functional filler is (5-15):(0.1-0.3), the solvent used for the dispersion liquid in step 2) is one or more of N-methylpyrrolidone, N,N-dimethylformamide, acetone, and methyl ethyl ketone; in step 2), the dosage of the catalyst is 1-5% of the mass of the functional filler.

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