Flame-retardant polyurethane dielectric elastomer material, preparation method and fireproof dielectric driver

Abstract

The invention relates to a flame-retardant polyurethane dielectric elastomer material, a preparation method and a fireproof dielectric driver. The flame-retardant polyurethane dielectric elastomer material is a segmented copolymer composed of a soft segment and a hard segment, and a reactive flame retardant is introduced into part of the hard segment on a main chain; the soft segment is polyether or polyacrylate containing hydroxyl functional groups, and the molecular weight of the soft segment is 50000-50000. According to the dielectric elastomer material, a flame retardant structure is copolymerized and introduced into a polyurethane hard segment, so that the problem of material hardening caused by introduction of a rigid flame retardant structure is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of polyurethane dielectric elastomers, and in particular to a flame-retardant polyurethane dielectric elastomer material, a preparation method and a fireproof dielectric driver. Background Art

[0002] Soft and elastic dielectric elastomer materials will produce large electro-induced deformation when driven under an electric field, with a driving strain greater than 100%, millisecond-level response, and high energy density, up to 3.4 MJ / m³. The performance is comparable to that of biological muscles, and has broad application prospects in fields with close human-machine interaction, such as flexible actuators and soft robots.

[0003] However, dielectric elastomer materials with high dielectric constants (such as polyacrylates and polyurethanes) have a serious risk of combustion when driving electrical breakdown. This is mainly due to the poor thermal stability of the material itself, which is prone to thermal decomposition at high temperatures and releases flammable gases to intensify combustion; at the same time, the material has poor charring properties and is difficult to cross-link into char when burning, and cannot form a physical barrier to isolate oxygen and heat in time.

[0004] In the field of polymer material science, it is a common strategy to improve the flame retardant properties of polymers by introducing flame retardants. However, such flame retardants usually have a rigid molecular structure, and their addition will inevitably affect the flexibility of the polymer chain segments.

[0005] For functional materials such as dielectric elastomers that have strict requirements on mechanical flexibility and deformation ability, even a slight loss of flexibility may have a significant negative impact on key performance indicators such as its electrodeformability, response speed and energy conversion efficiency. Therefore, how to achieve effective flame retardant treatment without sacrificing the inherent high elasticity and flexibility of dielectric elastomers has become a major challenge facing this field. So far, there is no ideal solution that can effectively solve the flame retardant problem while ensuring the excellent electromechanical response characteristics of dielectric elastomers, which limits the further promotion and use of dielectric elastomers in applications with extremely high safety requirements. In addition, it is unstable to directly compound rigid structures in elastomers. Over time, they will separate and migrate, and the performance will also be unstable. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a flame retardant polyurethane dielectric elastomer material, a preparation method and a fireproof dielectric driver. The dielectric elastomer material is a flame retardant structure introduced into the polyurethane hard segment by copolymerization, which effectively solves the problem of material hardening caused by the introduction of a rigid flame retardant structure.

[0007] In addition, the present invention also endows the polyurethane dielectric elastomer material with excellent gas phase flame retardant properties through phosphorus-nitrogen synergistic flame retardancy, thereby avoiding the problem of material hardening caused by the introduction of a rigid flame retardant structure; at the same time, soft segments such as polyether and polyacrylate with a low glass transition temperature are selected for copolymerization to ensure that the polyurethane dielectric elastomer material can still maintain soft and elastic mechanical properties, meet the driving requirements under high electric fields, reduce the risk of combustion caused by electrical breakdown of the material under high electric fields, and provide fire safety protection for the wide application of dielectric elastomer materials in the fields of flexible actuators and soft robots.

[0008] The scheme of the present application is as follows: a flame-retardant polyurethane dielectric elastomer material, which is a block copolymer composed of a soft segment and a hard segment, and a reactive flame retardant is introduced into part of the hard segment on the main chain; the soft segment is a polyether or polyacrylate containing a hydroxyl functional group, and the molecular weight is 500-50,000.

[0009] Furthermore, the reactive flame retardant is a reactive DOPO derivative flame retardant.

[0010] Further, it has the following structural formula: Wherein, R1 is the structure of the diisocyanate monomer except the terminal isocyanate group; R2 is the structure of the reactive flame retardant except for the terminal hydroxyl group; R3 is the structure of polyisocyanate excluding the terminal isocyanate group; R4 has a molecular weight of 500-50,000 and is a polyether or polyacrylate structure except for the hydroxyl group; n, m, and h are the numbers of the above blocks, respectively.

[0011] Furthermore, the ratio of the hard segment introduced with the reactive flame retardant to all the hard segments is calculated as S=h / (h+m)×100%.

[0012] The preparation method of the flame-retardant polyurethane dielectric elastomer material comprises: capping a reactive flame retardant with a diisocyanate monomer to generate a new hard segment containing a flame retardant, reacting the new hard segment with a diol to synthesize a prepolymer having a hydroxyl end group, and finally cross-linking the prepolymer with a polyisocyanate cross-linking agent to obtain a flame-retardant polyurethane dielectric elastomer material.

[0013] A fireproof dielectric driver comprises the flame-retardant polyurethane dielectric elastomer material and stretchable flexible electrodes coated on the upper and lower surfaces of the material.

[0014] Furthermore, the stretchable flexible electrode is selected from a composite material of carbon nanotubes, carbon paste, hydrogel, carbon powder and polymer.

[0015] The beneficial effects of the present invention are as follows: the dielectric elastomer material is a material in which a flame retardant structure is introduced into the hard segment of polyurethane by copolymerization, which effectively solves the problem of material hardening caused by the introduction of a rigid flame retardant structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the H-NMR spectrum of the reactive flame retardant; Figure 2 This is the NMR carbon spectrum of the reactive flame retardant; Figure 3 is the mass spectrum of reactive flame retardant; Figure 4 The vertical combustion test of the flame retardant polyurethane dielectric elastomer and PU of Example 1; Figure 5 The stress-strain curves of the flame-retardant polyurethane dielectric elastomer and PU of Example 1; Figure 6 The Young's modulus strain curve of the flame retardant polyurethane dielectric elastomer and PU of Example 1; Figure 7 The driving performance test of the flame retardant polyurethane dielectric elastomer of Example 1 under different pre-stretching ratios; Figure 8 It is a structural schematic diagram of the fireproof dielectric driver of Example 1; Fig. 9 The application of the fireproof dielectric actuator of Example 1 in a bionic arm; Fig.10 The application of the fireproof dielectric actuator of Example 1 in a bionic arm; Among them, there are a first stretchable flexible electrode 1, a second stretchable flexible electrode 2, and a flame-retardant polyurethane dielectric elastomer 3. DETAILED DESCRIPTION

[0017] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0018] In this application, the synthesis steps of the reactive flame retardant (DHIP) are as follows: In a 500mL three-necked flask, add (3.64g, 0.02mol) syringaldehyde and (2.18g, 0.02mol) p-aminophenol, then add 150mL of anhydrous ethanol, stir magnetically until completely dissolved, and react at 90℃ for 4h under nitrogen atmosphere. Then (4.32g, 0.02mol) DOPO was dissolved in 100mL of anhydrous ethanol solution and added to the three-necked flask, and reacted at 90℃ for 12h under nitrogen atmosphere. After the reaction, the precipitate was filtered and placed in a vacuum oven at 60℃ for 5 hours to obtain a reactive flame retardant (DHIP) (8.31g, yield of about 85%).

[0019] In certain embodiments, reactive DOPO may also be used.

[0020] When preparing the elastomer in the present invention, the reactive flame retardant is capped with a diisocyanate monomer to generate a new hard segment containing the flame retardant, which is then reacted with a diol to synthesize a prepolymer with a hydroxyl end group, and finally a polyisocyanate crosslinking agent is used to crosslink the prepolymer to obtain a flame retardant polyurethane dielectric elastomer material. Based on this, those skilled in the art can undoubtedly determine that the structure of the product obtained in the present invention is a block copolymer composed of a soft segment and a hard segment, and a reactive flame retardant is introduced into part of the hard segment on the main chain.

[0021] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0022] Example 1 The reactive flame retardant DHIP (0.489 g, 0.001 mol) and isophorone diisocyanate (0.667 g, 0.003 mol) were dissolved in tetrahydrofuran and reacted at 75 ° C for 1 h under a nitrogen atmosphere. Then, polytetrahydrofuran (Mn=2900) (11.6 g, 0.004 mol) and catalyst dibutyltin dilaurate (0.316 g, 0.005 mol) were added and reacted at 75 ° C for 2 h under a nitrogen atmosphere. Then, the cross-linking agent polymethylene polyphenyl polyisocyanate (MDI-400) (0.75 g) was added and stirred for 5 min. The polymer was poured into a tetrafluoroethylene mold and dried in a vacuum oven at 80 ° C for 8 h to obtain a flame retardant polyurethane dielectric elastomer (50% DHIP-PU).

[0023] By changing the addition amount of reactive flame retardant DHIP and increasing the number of hard segments introduced into the flame retardant, flame retardant polyurethane dielectric elastomers of 25% DHIP-PU, 75% DHIP-PU and 100% DHIP-PU were prepared respectively.

[0024] The reaction formula is as follows: ; The prepared flame retardant polyurethane dielectric elastomer has the following structure: ; DHIP H NMR spectrum Figure 1 As shown, the results are as follows: 1 HNMR (400MHz, DMSO-d6): δ=3.58(s,6H),5.1(s,1H),5.64(s,1H),6.44(s,2H),6.57(s,4H),7.20(s,1H),7.31( s,1H),7.43(s,1H),7.50(s,1H),8.16(s,1H),8.20(s,1H),8.24(s,1H),8.49(s,1H).

[0025] DHIP NMR carbon spectrum Figure 2 As shown, the results are as follows: 13C NMR (400MHz, DMSO-d6): δ=56.30,57.99,106.66,115.76,115.97,120.55,121.99,123.06,124.22,124.97,125 .46,125.97,128.69,131.20,133.74,135.37,135.84,140.33,147.97,149.49,149.81.

[0026] DHIP mass spectrum Figure 3 As shown, the results are as follows: .MSIMS: 490.14[M+H] + ,512.12[M+Na] + , 528.09[M+K] + .

[0027] The flame retardant properties of the above-mentioned 25% DHIP-PU, 50% DHIP-PU, 75% DHIP-PU, 100% DHIP-PU flame retardant polyurethane dielectric elastomers and the comparative sample (PU) were tested. Figure 4 Table 1 shows the vertical combustion test of polyurethane without flame retardant and with flame retardant added in different proportions. When the flame retardant added accounts for more than 50% of the polyurethane hard segment, the flame retardant grade of V-0 can be achieved.

[0028] Table 1 Vertical burning test results of VHB, PU and PU-SPAD sample Two burning times Is it lit? Whether it is molten drop Is the absorbent cotton burning? grade PU 1.8 / 0.8 no yes yes V-2 25%DHIP-PU 1.0 / 0.9 no yes yes V-2 50%DHIP-PU 0.8 / 0.9 no yes no V-0 75%DHIP-PU 0.7 / 1.0 no yes no V-0 100% DHIP-PU 0.6 / 0.8 no yes no V-0 The flame retardant polyurethane dielectric elastomers of 25% DHIP-PU, 50% DHIP-PU, 75% DHIP-PU, and 100% DHIP-PU and the comparative samples (PU, flame retardant) were subjected to thermogravimetric analysis, as shown in Table 2. The results show that DHIP can promote the carbonization of polyurethane, and during the pyrolysis process, SAPD will decompose in advance to release phosphorus-containing free radicals to block the chain reaction of combustion and promote carbonization.

[0029] Table 2 Thermogravimetric analysis data of DHIP, PU and DHIP-PU under nitrogen atmosphere sample <![CDATA[T 5% (℃) a ]]> <![CDATA[T max (℃) a ]]> Carbon residue at 800℃ DHIP 217.1±1.2 363.1±2.3 23.81±0.82 PU 301.8±1.1 410.8±1.3 2.40±0.21 25%DHIP-PU 283.6±1.7 398.7±0.9 3.18±0.13 50%DHIP-PU 281.7±1.3 402.9±1.7 4.19±0.21 75%DHIP-PU 275.9±0.9 390.6±2.2 5.27±0.24 100% DHIP-PU 263.8±2.1 389.8±1.6 7.60±0.19 a T 5% is the temperature when the mass decreases by 5%, b T max is the temperature at which the mass loss rate is fastest.

[0030] The above-mentioned flame-retardant polyurethane dielectric elastomers of 25% DHIP-PU, 50% DHIP-PU, 75% DHIP-PU, and 100% DHIP-PU and the control sample (PU) were subjected to cone calorimetry tests, which proved that DHIP can promote charring and reduce the total heat release and heat release rate, while producing inert gases such as CO2 and CO to inhibit combustion.

[0031] Table 3 Cone calorimetry data of PU and DHIP-PU a pHRR represents the peak heat release rate, THR is the total heat release, pCOP represents the peak CO generation, pCO2P represents the peak CO2 generation, and Residue represents the carbon residue after 600 seconds of cone calorimeter test.

[0032] in addition, Figure 5 and Figure 6 As for the mechanical properties of the flame-retardant polyurethane elastomer, as the proportion of the flame retardant increases, its performance is affected to a certain extent, but compared with the ordinary blending mode, it has a significant effect. When the introduction ratio of the hard segment reaches 100%, it can still maintain a relatively low initial elastic modulus of 0.349MPa. When the hard segment accounts for 50%, the flame-retardant polyurethane dielectric elastomer of this application can achieve an initial elastic modulus of 0.18MPa.

[0033] Figure 7 The driving performance of 50% DHIP-PU flame retardant polyurethane dielectric elastomer under different pre-stretching ratios. When the pre-stretching area strain is 500% and the external electric field is 104MV / m, the flame retardant polyurethane dielectric elastomer produces an area driving strain of 109%.

[0034] like Figure 8 A dielectric actuator is made of 50% DHIP-PU flame-retardant polyurethane dielectric elastomer, and the specific structure includes a first stretchable flexible electrode 1 and a second stretchable flexible electrode 2 and a flame-retardant polyurethane dielectric elastomer 3 between the first stretchable flexible electrode 1 and the second stretchable flexible electrode 2. The first stretchable flexible electrode 1 and the second stretchable flexible electrode 2 are selected from a composite material of carbon nanotubes, carbon paste, hydrogel, carbon powder and polymer.

[0035] Fig. 9 and Fig.10 The application of 50% DHIP-PU flame-retardant polyurethane dielectric elastomer in bionic arms. Compared with traditional dielectric elastomer materials, flame-retardant polyurethane dielectric elastomers can avoid catching fire when the material is electrically broken down, and can also load and do work. These flame-retardant polyurethane dielectric elastomer materials are expected to provide safety guarantees for the large-scale application of DE materials.

[0036] The dielectric elastomer material of the present application is a flame retardant structure introduced into the polyurethane hard segment by copolymerization, which effectively solves the problem of material hardening caused by the introduction of a rigid flame retardant structure. Not only does the polyurethane dielectric elastomer material have excellent gas phase flame retardant properties through phosphorus-nitrogen synergistic flame retardancy, but it can also avoid the problem of material hardening caused by the introduction of a rigid flame retardant structure; at the same time, soft segments such as polyether and polyacrylate with low glass transition temperatures are selected for copolymerization to ensure that the polyurethane dielectric elastomer material can still maintain soft and elastic mechanical properties, meet the driving requirements under high electric fields, reduce the risk of combustion caused by electrical breakdown of the material under high electric fields, and provide fire safety guarantees for the wide application of dielectric elastomer materials in the fields of flexible actuators and soft robots.

[0037] Example 2 The reactive flame retardant DHIP (0.489 g, 0.001 mol) and isophorone diisocyanate (1.112 g, 0.005 mol) were dissolved in tetrahydrofuran and reacted at 75 °C for 1 h under a nitrogen atmosphere. Polytetrahydrofuran (Mn=500) (4 g, 0.008 mol) and catalyst dibutyltin dilaurate (0.01264 g, 0.0002 mol) were added and reacted at 75 °C for 2 h under a nitrogen atmosphere. Then, the cross-linking agent polymethylene polyphenyl polyisocyanate (MDI-400) (0.75 g) was added and stirred for 5 min. The polymer was poured into a tetrafluoroethylene mold and dried in a vacuum oven at 80 °C for 8 h to obtain a flame retardant polyurethane dielectric elastomer (25% DHIP-PU).

[0038] After testing, it can achieve an initial elastic modulus of 0.674MPa. When the pre-stretched area strain is 300% and the applied electric field is 116MV / m, the flame-retardant polyurethane dielectric elastomer produces an area-driven strain of 89%. Example 3 The reactive flame retardant DHIP (0.489 g, 0.001 mol) and isophorone diisocyanate (0.4447 g, 0.002 mol) were dissolved in tetrahydrofuran and reacted at 75 ° C for 1 h under a nitrogen atmosphere. Then, polytetrahydrofuran (Mn=50000) (100 g, 0.002 mol) and catalyst dibutyltin dilaurate (0.632 g, 0.01 mol) were added and reacted at 75 ° C for 2 h under a nitrogen atmosphere. Then, the cross-linking agent polymethylene polyphenyl polyisocyanate (MDI-400) (0.75 g) was added and stirred for 5 min. The polymer was poured into a tetrafluoroethylene mold and dried in a vacuum oven at 80 ° C for 8 h to obtain a flame retardant polyurethane dielectric elastomer (100% DHIP-PU).

[0039] After testing, it can achieve an elastic modulus of 0.103MPa. When the pre-stretched area strain is 900% and the applied electric field is 136MV / m, the flame-retardant polyurethane dielectric elastomer produces an area driven strain of 123%. The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A flame retardant polyurethane dielectric elastomer material, characterized in that: It is a block copolymer composed of a soft segment and a hard segment, and a reactive flame retardant is introduced into part of the hard segment on the main chain; the soft segment is a polyether or polyacrylate containing a hydroxyl functional group, and the molecular weight is 500-50,000.

2. The flame-retardant polyurethane dielectric elastomer material according to claim 1, characterized in that: The reactive flame retardant is a reactive DOPO derivative flame retardant.

3. The flame-retardant polyurethane dielectric elastomer material according to claim 1, characterized in that: It has the following structural formula: Wherein, R1 is the structure of the diisocyanate monomer except the terminal isocyanate group; R2 is the structure of the reactive flame retardant except for the terminal hydroxyl group; R3 is the structure of polyisocyanate excluding the terminal isocyanate group; R4 has a molecular weight of 500-50,000 and is a polyether or polyacrylate structure except for the hydroxyl group; n, m, and h are the numbers of the above blocks, respectively.

4. The method for preparing the flame-retardant polyurethane dielectric elastomer material according to claim 1, characterized in that: include: The reactive flame retardant is capped with a diisocyanate monomer to generate a new hard segment containing the flame retardant, which is then reacted with a diol to synthesize a prepolymer with a hydroxyl end group, and finally a polyisocyanate crosslinking agent is used to crosslink the prepolymer to obtain a flame retardant polyurethane dielectric elastomer material.

5. A fireproof dielectric driver, characterized in that It comprises the flame-retardant polyurethane dielectric elastomer material as described in any one of claims 1 to 4 and stretchable flexible electrodes coated on the upper and lower surfaces of the material.

6. The fireproof dielectric driver according to claim 5, characterized in that The stretchable flexible electrode is selected from a composite material of carbon nanotubes, carbon paste, hydrogel, carbon powder and polymer.

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