Flame-retardant polyurethane dielectric elastomer material, preparation method and fireproof dielectric driver
By using a copolymerizable flame retardant in the polyurethane hard segment and a soft segment with a low glass transition temperature, the combustion risk and flexibility issues of dielectric elastomer materials are solved, achieving fire safety and driving performance under high electric fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG FORESTRY UNIVERSITY
- Filing Date
- 2025-03-17
- Publication Date
- 2026-07-21
AI Technical Summary
Existing dielectric elastomer materials are easily combustible under high electric fields and have poor char formation, which affects their promotion in applications with high safety requirements. Furthermore, the introduction of rigid flame retardants will impair the flexibility of the materials.
In the copolymerization of polyurethane rigid segments, reactive flame retardants are introduced, combined with phosphorus and nitrogen synergistic flame retardancy, and soft segment copolymerization with low glass transition temperature is used to ensure that the material has excellent flame retardant properties while maintaining flexibility.
This technology achieves fire safety for dielectric elastomer materials under high electric fields, maintains the material's flexibility and electrodeformation properties, reduces the risk of combustion during electrical breakdown, and provides safety assurance for flexible actuators and soft robots.
Smart Images
Figure CN119978306B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polyurethane dielectric elastomers, specifically to a flame-retardant polyurethane dielectric elastomer material, its preparation method, and a fire-resistant dielectric actuator. Background Technology
[0002] When driven by an electric field, soft and elastic dielectric elastomer materials can produce large electroinduced deformation, with a driving strain greater than 100%, millisecond-level response, and high energy density, up to 3.4 MJ / m³. Their performance is comparable to that of biological muscles, and they have broad application prospects in fields with close human-computer interaction, such as flexible actuators and soft robots.
[0003] However, high dielectric constant dielectric elastomer materials (such as polyacrylates and polyurethanes) pose a serious risk of combustion during driven electrical breakdown. This is mainly due to the poor thermal stability of the materials themselves, which easily undergo thermal decomposition at high temperatures and release flammable gases that intensify combustion; at the same time, the materials have poor char-forming properties, making it difficult to cross-link and form char during combustion, thus failing to form a physical barrier that isolates oxygen and heat in a timely manner.
[0004] In the field of polymer materials science, introducing flame retardants to improve the flame retardant properties of polymers is a common strategy. However, such flame retardants typically have rigid molecular structures, and their addition inevitably affects the flexibility of polymer segments.
[0005] For functional materials like dielectric elastomers, which have stringent requirements for mechanical flexibility and deformability, even a slight loss of flexibility can significantly negatively impact key performance indicators such as electro-deformation properties, response speed, and energy conversion efficiency. Therefore, achieving effective flame retardant treatment without sacrificing the inherent high elasticity and flexibility of dielectric elastomers has become a major challenge in this field. To date, no ideal solution has been found that can effectively address the flame retardancy issue while ensuring the excellent electromechanical response characteristics of dielectric elastomers, limiting their further promotion and use in applications with extremely high safety requirements. Furthermore, directly incorporating rigid structures into elastomers is unstable; over time, phase separation and migration occur, leading to performance instability. Summary of the Invention
[0006] To address the aforementioned problems, this invention provides a flame-retardant polyurethane dielectric elastomer material, its preparation method, and a fire-resistant dielectric actuator. This dielectric elastomer material incorporates a flame-retardant structure through copolymerization in the rigid segments of polyurethane, effectively solving the problem of material hardening caused by the introduction of a rigid flame-retardant structure.
[0007] Furthermore, this invention endows polyurethane dielectric elastomer materials with excellent gas-phase flame retardant properties through phosphorus and nitrogen synergistic flame retardancy, avoiding the problem of material hardening caused by the introduction of rigid flame retardant structures. At the same time, by selecting soft segments such as polyether and polyacrylate with low glass transition temperatures for copolymerization, it ensures that the polyurethane dielectric elastomer material can still maintain its soft and elastic mechanical properties, meet the driving requirements under high electric fields, and reduce the risk of combustion caused by electrical breakdown of the material under high electric fields. This provides fire safety protection for the widespread application of dielectric elastomer materials in the fields of flexible actuators and soft robots.
[0008] The present application provides the following solution: a flame-retardant polyurethane dielectric elastomer material, which is a block copolymer composed of soft segments and hard segments, wherein a reactive flame retardant is introduced into some of the hard segments of the main chain; the soft segments are polyethers or polyacrylates containing hydroxyl functional groups, with a molecular weight of 500-50,000.
[0009] Furthermore, the reactive flame retardant is a reactive DOPO derivative flame retardant.
[0010] Furthermore, it has the following structural formula:
[0011]
[0012] R1 is the structure of the diisocyanate monomer excluding the terminal isocyanate group;
[0013] R2 is a reactive flame retardant with the terminal hydroxyl group removed;
[0014] R3 is the structure of a polyisocyanate excluding the terminal isocyanate group;
[0015] R4 has a molecular weight of 500,000 to 50,000 and is a polyether or polyacrylate structure with hydroxyl groups removed.
[0016] n, m, and h represent the number of segments mentioned above.
[0017] Furthermore, the calculation method for the proportion of hard segments containing reactive flame retardants to all hard segments is S=h / (h+m)×100%.
[0018] The preparation method of the above-mentioned flame-retardant polyurethane dielectric elastomer material includes: end-capping the reactive flame retardant with a diisocyanate monomer to generate a new hard segment containing the flame retardant, then reacting it with a glycol to synthesize a prepolymer with hydroxyl end groups, and finally crosslinking the prepolymer with a polyisocyanate crosslinking agent to obtain the flame-retardant polyurethane dielectric elastomer material.
[0019] A fire-resistant dielectric actuator includes the aforementioned flame-retardant polyurethane dielectric elastomer material and stretchable flexible electrodes coated on the upper and lower surfaces of the material.
[0020] Furthermore, the stretchable flexible electrode is selected from composite materials of carbon nanotubes, carbon paste, hydrogels, carbon powder and polymers.
[0021] The beneficial effects of this invention are as follows: the dielectric elastomer material is a flame retardant structure introduced by copolymerization in the hard segment of polyurethane, which effectively solves the problem of material hardening caused by the introduction of rigid flame retardant structure. Attached Figure Description
[0022] Figure 1 The 1H NMR spectrum of the reactive flame retardant;
[0023] Figure 2 The carbon NMR spectrum of the reactive flame retardant;
[0024] Figure 3 This is the mass spectrum of a reactive flame retardant;
[0025] Figure 4 Vertical burning test of flame-retardant polyurethane dielectric elastomer and PU in Example 1;
[0026] Figure 5 The stress-strain curves of the flame-retardant polyurethane dielectric elastomer and PU in Example 1 are shown.
[0027] Figure 6 The image shows the Young's modulus strain curves of the flame-retardant polyurethane dielectric elastomer and PU in Example 1.
[0028] Figure 7 This is a test of the driving performance of the flame-retardant polyurethane dielectric elastomer of Example 1 under different pre-stretching ratios.
[0029] Figure 8 This is a schematic diagram of the fireproof dielectric driver of Example 1;
[0030] Figure 9 The application of the fire-resistant dielectric actuator of Example 1 in a bionic arm;
[0031] Figure 10 The application of the fire-resistant dielectric actuator of Example 1 in a bionic arm;
[0032] Among them, there is a first stretchable flexible electrode 1, a second stretchable flexible electrode 2, and a flame-retardant polyurethane dielectric elastomer 3. Detailed Implementation
[0033] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.
[0034] In this application, the synthesis steps of the reactive flame retardant (DHIP) are as follows:
[0035] In a 500 mL three-necked flask, (3.64 g, 0.02 mol) eugenaldehyde and (2.18 g, 0.02 mol) p-aminophenol were added, followed by 150 mL of anhydrous ethanol. The mixture was magnetically stirred until completely dissolved, and then reacted at 90 °C for 4 h under a nitrogen atmosphere. Then, (4.32 g, 0.02 mol) DOPO was dissolved in 100 mL of anhydrous ethanol and added to the three-necked flask. The mixture was reacted at 90 °C for 12 h under a nitrogen atmosphere. After the reaction was complete, the precipitate was filtered and dried in a vacuum oven at 60 °C for 5 h to obtain a reactive flame retardant (DHIP) (8.31 g, yield approximately 85%).
[0036] In some embodiments, reactive DOPO may also be used.
[0037] In the preparation of the elastomer in this invention, a reactive flame retardant is end-capped with a diisocyanate monomer to generate a new hard segment containing the flame retardant. This hard segment is then reacted with a glycol to synthesize a prepolymer with hydroxyl-terminated groups. 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 product structure obtained in this invention is a block copolymer composed of soft and hard segments, and that a reactive flame retardant is introduced into some of the hard segments of the main chain.
[0038] The embodiments of the present invention will be further described below with reference to several examples.
[0039] Example 1
[0040] 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 dibutyltin dilaurate catalyst (0.316 g, 0.005 mol) were added and reacted at 75 °C for 2 h under a nitrogen atmosphere. Then, the crosslinking 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 flame-retardant polyurethane dielectric elastomer (50% DHIP-PU).
[0041] By changing the amount of reactive flame retardant DHIP added and increasing the number of hard segments introduced by the flame retardant, flame-retardant polyurethane dielectric elastomers of 25% DHIP-PU, 75% DHIP-PU, and 100% DHIP-PU were prepared respectively.
[0042] Its reaction formula is as follows: 043]
[0043] The prepared flame-retardant polyurethane dielectric elastomer has the following structure:
[0044] ;
[0045] DHIP 1H NMR spectrum as follows Figure 1 As shown, the results are as follows:
[0046] 1 HNMR (400MHz, DMSO-d6):
[0047] 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).
[0048] DHIP carbon NMR spectrum as follows Figure 2 As shown, the results are as follows:
[0049] 13C NMR (400MHz, DMSO-d6):
[0050] 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.
[0051] DHIP mass spectrum as shown Figure 3 As shown, the results are as follows:
[0052] .MSIMS:
[0053] 490.14 [M+H] + 512.12[M+Na] + 528.09 [M+K] + .
[0054] Flame retardant performance tests were conducted on the above-mentioned flame-retardant polyurethane dielectric elastomers with 25% DHIP-PU, 50% DHIP-PU, 75% DHIP-PU, and 100% DHIP-PU, as well as the control sample (PU). Figure 4Table 1 shows the vertical burning tests of polyurethane without flame retardant and with flame retardants of different proportions. When the amount of flame retardant added accounts for more than 50% of the polyurethane hard segment, the flame retardant rating of V-0 can be achieved.
[0055] Table 1. Vertical combustion test results of VHB, PU, and PU-SPAD
[0056] sample Two burning times Is it lit? Whether it melts or drips Does absorbent cotton burn? 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
[0057] Thermogravimetric analysis was performed on the flame-retardant polyurethane dielectric elastomers of 25%DHIP-PU, 50%DHIP-PU, 75%DHIP-PU, and 100%DHIP-PU and the control samples (PU, flame retardant), as shown in Table 2. The results show that DHIP can promote the char formation 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 char formation.
[0058] Table 2. Thermogravimetric analysis data of DHIP, PU, and DHIP-PU under nitrogen atmosphere.
[0059] sample <![CDATA[T 5% (℃) a ]]> <![CDATA[T max (℃) a ]]> Residual carbon 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
[0060] a T 5% The temperature at which the mass decreases by 5%. b T max This is the temperature at which the rate of mass loss is the fastest.
[0061] Cone calorimetry tests were conducted on the flame-retardant polyurethane dielectric elastomers (25%, 50%, 75%, and 100% DHIP-PU) and the control sample (PU). The results showed that DHIP can promote char formation, reduce total heat release and heat release rate, and at the same time generate inert gases such as CO2 and CO to inhibit combustion.
[0062] Table 3. Cone calorimetry data for PU and DHIP-PU
[0063]
[0064] a pHRR represents the peak value of the heat release rate, THR is the total heat release, pCOP represents the peak value of CO generation, pCO2P represents the peak value of CO2 generation, and Residue represents the amount of carbon residue after a 600-second cone calorimeter test.
[0065] in addition, Figure 5 and Figure 6Regarding the mechanical properties of flame-retardant polyurethane elastomers, their performance is somewhat affected as the proportion of flame retardant increases. However, compared to ordinary blending methods, it exhibits significant effects. Even when the hard segment content reaches 100%, it can still maintain a relatively low initial elastic modulus of 0.349 MPa. When the hard segment content is 50%, the flame-retardant polyurethane dielectric elastomer of this application can achieve an initial elastic modulus of 0.18 MPa.
[0066] Figure 7 The driving performance of 50% DHIP-PU flame-retardant polyurethane dielectric elastomer under different pre-stretch ratios was studied. Under an applied electric field with a pre-stretch area strain of 500% and 104MV / m, the flame-retardant polyurethane dielectric elastomer produced an area-driven strain of 109%.
[0067] like Figure 8 A dielectric actuator, manufactured using 50% DHIP-PU flame-retardant polyurethane dielectric elastomer, specifically comprises 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 composite materials of carbon nanotubes, carbon paste, hydrogels, carbon powder, and polymers.
[0068] Figure 9 and Figure 10 For the application of 50% DHIP-PU flame-retardant polyurethane dielectric elastomer in a bionic arm, compared to traditional dielectric elastomer materials, flame-retardant polyurethane dielectric elastomers do not ignite or burn upon electrical breakdown and can still perform work under load. These flame-retardant polyurethane dielectric elastomer materials are expected to provide safety assurance for the large-scale application of DE materials.
[0069] The dielectric elastomer material of this application incorporates a flame retardant structure through copolymerization in the hard segments of polyurethane, effectively solving the problem of material hardening caused by the introduction of rigid flame retardant structures. It not only imparts excellent gas-phase flame retardant properties to the polyurethane dielectric elastomer material through phosphorus-nitrogen synergistic flame retardancy, but also avoids the material hardening problem caused by the introduction of rigid flame retardant structures. Simultaneously, by selecting soft segments such as polyether and polyacrylate with low glass transition temperatures for copolymerization, it ensures that the polyurethane dielectric elastomer material retains its soft and elastic mechanical properties, meeting the actuation requirements under high electric fields and reducing the risk of combustion caused by electrical breakdown under high electric fields. This provides fire safety assurance for the widespread application of dielectric elastomer materials in flexible actuators and soft robots.
[0070] Example 2
[0071] 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. Then, polytetrahydrofuran (Mn=500) (4 g, 0.008 mol) and dibutyltin dilaurate (0.01264 g, 0.0002 mol) were added and reacted at 75 °C for 2 h under a nitrogen atmosphere. Then, the crosslinking 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 flame-retardant polyurethane dielectric elastomer (25% DHIP-PU).
[0072] Testing showed that it can achieve an initial elastic modulus of 0.674 MPa. Under an applied electric field with a pre-stretched area strain of 300% and an applied electric field of 116 MV / m, the flame-retardant polyurethane dielectric elastomer generates 89% area-driven strain.
[0073] Example 3
[0074] 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 dibutyltin dilaurate catalyst (0.632 g, 0.01 mol) were added and reacted at 75 °C for 2 h under a nitrogen atmosphere. Then, the crosslinking 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 flame-retardant polyurethane dielectric elastomer (100% DHIP-PU).
[0075] Tests showed that it can achieve an elastic modulus of 0.103 MPa. Under an applied electric field with a pre-stretched area strain of 900% and an applied electric field of 136 MV / m, the flame-retardant polyurethane dielectric elastomer generates an area-driven strain of 123%.
[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A flame-retardant polyurethane dielectric elastomer material, characterized in that, It is a block copolymer composed of soft and hard segments, and the main chain contains a reactive flame retardant DHIP in some of the hard segments. The reactive flame retardant DHIP has the following structural formula: ； The soft segment is a polyether or polyacrylate containing hydroxyl functional groups, with a molecular weight of 500,000 to 50,000. The flame-retardant polyurethane dielectric elastomer material has the following structural formula: ； R1 is the structure of the diisocyanate monomer excluding the terminal isocyanate group; R2 is a reactive flame retardant with the terminal hydroxyl group removed; R3 is the structure of a polyisocyanate excluding the terminal isocyanate group; R4 has a molecular weight of 500,000 to 50,000 and is a polyether or polyacrylate structure with hydroxyl groups removed. n, m, and h represent the number of segments mentioned above; The flame-retardant polyurethane dielectric elastomer material is prepared by the following method: a reactive flame retardant is end-capped with a diisocyanate monomer to generate a hard segment containing the flame retardant, which is then reacted with a glycol to synthesize a prepolymer with hydroxyl end groups. Finally, a polyisocyanate crosslinking agent is used to crosslink the prepolymer to obtain the flame-retardant polyurethane dielectric elastomer material.
2. The preparation method of the flame-retardant polyurethane dielectric elastomer material as described in claim 1, characterized in that, include: The reactive flame retardant is end-capped with diisocyanate monomer to generate a hard segment containing the flame retardant. This segment is then reacted with glycol to synthesize a prepolymer with hydroxyl end groups. Finally, the prepolymer is cross-linked with a polyisocyanate crosslinking agent to obtain a flame-retardant polyurethane dielectric elastomer material.
3. A fire-resistant dielectric actuator, characterized in that, It includes the flame-retardant polyurethane dielectric elastomer material as described in claim 1 and the stretchable flexible electrodes coated on the upper and lower surfaces of the material.
4. The fire-resistant dielectric actuator according to claim 3, characterized in that, The stretchable flexible electrode is selected from composite materials of carbon nanotubes, carbon paste, hydrogels, carbon powder and polymers.