A method for preparing a bio-based dimeric amine type polyamide and a flexible sensor thereof

Abstract

The application discloses a kind of bio-based dimer amine type polyamides and the preparation method of flexible sensor thereof, the preparation of the polyamide includes: under inert gas protection, bio-based dimer amine is added with binary acid according to mole ratio in reaction container, precondensation is carried out by controlling reaction temperature and stirring rate, and pre-polymer is generated;Melt condensation is carried out under vacuum condition, and high molecular weight bio-based dimer amine type polyamide is obtained.The polyamide is physically blended with conductive filler, and flexible sensor can be prepared.The application accurately controls molecular weight by regulating degree of polymerization, and the sensing performance is optimized by combining blending process, and the obtained sensor has excellent flexibility and high sensitivity;Its preparation process does not need complex equipment, and process is safe and simple, and raw material is derived from renewable vegetable oil, meets green chemistry concept;The polyamide product is endowed with outstanding resilience due to long branched chain dimer amine structure, and has significant application potential in the field of wearable health monitoring, human-computer interaction and other flexible sensing.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and flexible sensor technology, specifically to a method for preparing a bio-based dimeric amine polyamide and its flexible sensor. Background Technology

[0002] Currently, flexible sensors, when facing high-dynamic applications, urgently need to simultaneously achieve high sensitivity, high flexibility, and clinical-grade biocompatibility, which constitutes a significant technical bottleneck. Existing sensing element substrates mainly rely on silicon-based materials or petroleum-based polymers. While these possess basic electrical properties, they have significant shortcomings in mechanical properties, biocompatibility, and processing technology. Although bio-based alternatives have emerged in recent years and improved sustainability, their inherent flexibility remains insufficient to meet the demands of high-dynamic sensing environments. Furthermore, current sensor fabrication processes are relatively outdated, not only further deteriorating the matrix flexibility due to the introduction of conductive fillers but also limiting sensor sensitivity due to the constraints of conductive filler content.

[0003] Existing technology CN117700981A discloses a conductive polymer-based thin film for resistive stress-strain sensing, comprising a polymer matrix, a carbon-based conductive additive, and a conductive polymer. The polymer matrix is ​​selected from one or more combinations of polydimethylsiloxane, polyethylene terephthalate, polyimide, and polyurethane. These materials are all petroleum-based, which not only leads to environmental unsustainability and biocompatibility risks, but also have high molecular chain rigidity and high mechanical strength, making them unsuitable for high-deformation scenarios.

[0004] The prior art CN117866241A discloses a bio-based self-healing polymer material, its preparation method, and its application as an electronic sensor. It uses epoxidized soybean oil acrylate as a matrix, compounded with the ionic liquid 1-octyl-3-methylimidazolium tetrafluoroborate, and introduces disulfide bonds into its structure by adding lipoic acid. The dynamic reversibility of the disulfide bonds endows this material with repairability, and a self-healing electronic sensor is prepared. However, its technical solution has limitations. This matrix has defects in mechanical properties, poor ductility, and is prone to stress relaxation under cyclic deformation. It is also prone to ester bond hydrolysis in humid environments, leading to a decrease in conductivity. Furthermore, epoxidized soybean oil acrylate relies on ultraviolet curing process, making it difficult to prepare ultrathin films.

[0005] To address the aforementioned issues, this invention provides a method for fabricating a bio-based dimelamine polyamide and its flexible sensor. This method utilizes dimelamine polyamide, a novel bio-based matrix material, and through block copolymerization molecular structure design, it is expected to overcome the limitations of existing materials, combining excellent resilience and biocompatibility. To this end, a simplified sensor fabrication process has also been developed, aiming to simultaneously achieve the material's high sensitivity and high mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing bio-based dimelamine polyamide and its flexible sensor, so as to solve the problems of traditional polyamide materials relying on petroleum-based raw materials, complex preparation process, high equipment requirements, and insufficient environmental friendliness.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A bio-based diamine polyamide, wherein the bio-based diamine polyamide is formed by the condensation polymerization of a bio-based diamine and a diacid, has the following structural formula:

[0009] ;

[0010] Among them, R1 is selected from C 12 ~C 44 A straight-chain or branched alkylene group; R2 is selected from C-type compounds containing branched or olefinic bonds. 24 ~C 44 Carbon chain; n is an integer from 20 to 200.

[0011] Preferably, the dicarboxylic acid is selected from C derived from vegetable oils. 11 ~C 44 Saturated or unsaturated dicarboxylic acids, wherein the dicarboxylic acid includes, but is not limited to, one or more of undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, docosanoic acid, soybean oil dimer acid, cottonseed oil dimer acid, sunflower seed oil dimer acid, corn germ oil dimer acid, tall oil dimer acid, hydrogenated dimer acid, and erucic acid dimer acid.

[0012] Preferably, the bio-based dimelamine is a dimelamine derived from at least one natural oil selected from castor oil, erucic acid, or oleic acid, with the general structural formula H2N-R2-NH2, wherein R2 is a C-type carbon containing a double or single bond. 24 ~C 44 Aliphatic long chains, or molecules containing at least one six-membered ring, including benzene rings, piperidine rings, or naphthalene rings.

[0013] More preferably, the bio-based diamine includes, but is not limited to, one or more of Priamine 1071, Priamine 1074, or Versamine 551; the structural formula of Versamine 551 is... It contains 100% bio-based ingredients and is manufactured by BASF.

[0014] Preferably, the solvent includes, but is not limited to, one or a combination of chloroform and tetrahydrofuran.

[0015] Preferably, the number-average molecular weight of the bio-based diamine polyamide is 1 × 10⁻⁶. 4 ~7×10 4 g / mol;

[0016] The glass transition temperature of the bio-based diamine polyamide is -30~30℃;

[0017] The tensile strength of the bio-based diamine polyamide is 5~50 MPa.

[0018] This application also claims a method for preparing the above-mentioned bio-based dimeric amine polyamide, comprising the following steps:

[0019] S1. Prepolymerization: Under inert gas protection, bio-based diamine and diacid are mixed in an equal molar ratio and stirred in a reactor at 160~230℃ for 1~4 hours to obtain the prepolymer.

[0020] S2. Polycondensation: Under vacuum conditions, the prepolymer obtained in step S1 is subjected to polycondensation reaction at a temperature of 220~260℃ for 3~5h to obtain the bio-based diamine polyamide.

[0021] Preferably, in step S2, the reaction vacuum degree of the vacuum condition is 70~250 Pa, more preferably 100~200 Pa.

[0022] Preferably, in step S1, the reaction is carried out in a reactor at 180~220°C for 1.5~2 hours with stirring to obtain a prepolymer.

[0023] Preferably, in step S2, the prepolymer obtained in step S1 is subjected to polycondensation reaction at a temperature of 230~240℃ for 3.5~4h to obtain the bio-based diamine polyamide.

[0024] Preferably, in step S1, the step of introducing nitrogen gas under inert gas protection refers to replacing the air three times while maintaining a constant nitrogen gas flow rate.

[0025] This application also claims a bio-based dimelamine-type polyamide-based flexible sensor, said bio-based dimelamine-type polyamide-based flexible sensor comprising the above-mentioned bio-based dimelamine-type polyamide.

[0026] This application also claims a method for preparing the above-mentioned bio-based dimelamine polyamide flexible sensor, wherein the bio-based dimelamine polyamide is mixed with a lightweight conductive filler to form a composite material to obtain the bio-based dimelamine polyamide flexible sensor; the conductive filler includes multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphene, and the proportion of the conductive filler is 1wt% to 5wt%.

[0027] Preferably, the method for mixing the bio-based dimelamine polyamide with the lightweight conductive filler to form the composite material is solution mixing, wherein the solvent for solution mixing is selected from any one or a combination of dichloromethane, chloroform, tetrahydrofuran, and acetone.

[0028] This application also claims the application of the above-mentioned bio-based dimelamine-type polyamide-based flexible sensor in detecting changes in temperature, humidity, resistance, force, or chemical gas concentration.

[0029] The fabrication method of the bio-based dimelamine-type polyamide-based flexible sensor described above utilizes the hydrophobic-hydrophobic interaction between the conductive filler and the polymer elastomer to achieve initial good compatibility between the two. Subsequently, the system leverages the fact that the surface energy of the conductive filler is much higher than that of the elastomer, combined with the natural law that the system tends towards the lowest free energy, to successfully drive the conductive filler to migrate towards the gas-liquid interface for mass transfer. To achieve final structural control, this method further relies on the rapid evaporation mechanism of the solvent: on the one hand, rapid evaporation effectively suppresses Marangoni convection that may be caused by temperature or concentration gradients (which usually drives the solute to migrate inward); on the other hand, solvent evaporation causes a sharp decrease in the mobility of the polymer surface chain segments, thereby forming significant shrinkage stress in the surface layer; under this stress environment, the conductive filler (such as CNT) tends to migrate to the position of least stress and is firmly "locked" in the material surface area. The final effect of this series of synergistic effects is to significantly increase the concentration of conductive filler in the surface area while maintaining a low content inside; this unique structure overcomes the contradictions of traditional technologies and simultaneously achieves high sensitivity and excellent flexibility of the sensor.

[0030] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0031] 1. The bio-based diamine polyamide prepared by this invention can synergistically optimize the molecular weight, thermal properties and mechanical properties of polyamide by flexibly selecting bio-based dicarboxylic acid monomers with different chain lengths and bio-based diamine monomers with specific flexible structures, combined with precise control of the degree of polymerization. In particular, this technology can achieve synergistic optimization of high molecular weight and excellent flexibility, overcome the traditional polyamide material's problem of balancing flexibility and strength, and is suitable for high-performance flexible electronic devices.

[0032] 2. This invention employs melt polycondensation, which has significant advantages over traditional solution polymerization: Solvent-free process: avoids the use of organic solvents, reducing the environmental burden and costs associated with solvent recovery and treatment; High reaction efficiency: high reactant concentration, fast reaction rate, short polymerization time, and high production efficiency; Energy saving and consumption reduction: the product can be directly transported to subsequent processing in a molten state, simplifying operations and reducing energy consumption, which aligns with the trend of green chemistry development.

[0033] 3. The bio-based diamine polyamide flexible sensor prepared in this invention has high sensitivity: after being combined with lightweight conductive fillers, it can accurately detect signals such as strain, temperature, and humidity; it has excellent flexibility and adaptability to human joints: the low glass transition temperature gives the material high flexibility, which can fit closely to human joints and is suitable for wearable devices; it has high signal stability: even under multiple high strain cycles, it can still maintain a stable resistance response, ensuring long-term reliable use. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be made based on these drawings without creative effort.

[0035] Figure 1 This is the Fourier transform infrared (FTIR) curve of the diamine-type polyamide in Example 1 of this invention;

[0036] Figure 2 This is a differential scanning calorimetry (DSC) curve of the diamine-type polyamide in Example 1 of the present invention; wherein, the left figure is a two-stage heating curve showing a melting point of 91.16 ℃; the right figure is a one-stage cooling curve, which does not show a clear crystallization temperature;

[0037] Figure 3 This is an engineering stress-strain curve of the diamine-type polyamide in Example 1 of the present invention;

[0038] Figure 4 This is the dynamic mechanical-thermal analysis (DMA) curve of the diamine-type polyamide in Example 1 of this invention;

[0039] Figure 5 This is the XRD curve of the diamine-type polyamide in Example 1 of the present invention;

[0040] Figure 6 These are conductivity curves of the dimeric amine-type polyamide-based flexible sensors in Examples 1 to 5 and Comparative Example 1 of the present invention. Detailed Implementation

[0041] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0042] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0043] Example 1

[0044] See appendix Figure 1 ~Appendix Figure 6 This embodiment provides a method for preparing a bio-based dimericamine polyamide, comprising the following steps:

[0045] S1. Prepolymerization: Under a nitrogen atmosphere, 0.07 mol of 1,12-dodecanoic acid and 0.07 mol of Priamine 1071 were added to a three-necked flask connected to a mechanical stirrer, a nitrogen inlet, and a condenser. The flask was placed in an oil bath and the temperature was gradually increased to 180°C under a nitrogen atmosphere to start the reaction. The reaction was stirred at 180°C for 1 hour and then at 210°C for 1 hour to obtain the prepolymer.

[0046] S2, Polycondensation: The prepolymer obtained in step S1 is switched to a vacuum environment to continue the reaction; the reaction is carried out at a reduced vacuum of 150 Pa and a temperature of 220 °C for 1.5 h, and finally the temperature is raised to 240 °C for 3 h. After discharge, the product is dried at 50 °C under vacuum for 12 h to obtain the bio-based diamine polyamide product.

[0047] like Figures 1-5 As shown, the bio-based diamine polyamide product prepared in this embodiment has a number-average molecular weight of 3 × 10⁻⁶, as determined by gel permeation chromatography. 4 The sample has the following properties: g / mol, glass transition temperature 17.81℃, melting point 91.16℃, tensile strength 22.5MPa, tensile modulus 91.8MPa, elongation at break 838%, and electrical conductivity 7.98×10⁻⁶. -14 S / cm, and its biocompatibility was verified by ISO10993-5 cytotoxicity test;

[0048] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 20mg of multi-walled carbon nanotubes (mass fraction of 1wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0049] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 21.9 MPa, the tensile modulus is 87.9 MPa, the elongation at break is 740%, and the volumetric conductivity is 1.13 × 10⁻⁶. -13 S / cm, surface conductivity 2.38×10 -9 S / cm.

[0050] Example 2

[0051] This embodiment provides a method for preparing a bio-based diamine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0052] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 40mg of multi-walled carbon nanotubes (mass fraction of 2wt%) are dispersed in 15ml of chloroform, sonicated for 0.5h, and then magnetically stirred for 0.5h. This sonication-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0053] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 22.8 MPa, the tensile modulus is 89.4 MPa, the elongation at break is 700%, and the volumetric conductivity is 5.57 × 10⁻⁶. -12 S / cm, surface conductivity 7.89×10 -7 S / cm.

[0054] Example 3

[0055] This embodiment provides a method for preparing a bio-based diamine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0056] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 60mg of multi-walled carbon nanotubes (mass fraction of 3wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0057] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 23.7 MPa, the tensile modulus is 90.7 MPa, the elongation at break is 650%, and the volumetric conductivity is 3.03 × 10⁻⁶. -9 S / cm, surface conductivity 1.37×10 -5 S / cm.

[0058] Example 4

[0059] This embodiment provides a method for preparing a bio-based diamine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0060] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 80mg of multi-walled carbon nanotubes (mass fraction of 4wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0061] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 24.8 MPa, the tensile modulus is 91.5 MPa, the elongation at break is 645%, and the volumetric conductivity is 2 × 10⁻⁶. -7 S / cm, surface conductivity 9.09×10 - 4 S / cm.

[0062] Example 5

[0063] This embodiment provides a method for preparing a bio-based diamine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0064] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 100mg of multi-walled carbon nanotubes (mass fraction of 5wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0065] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 25.2 MPa, the tensile modulus is 92.3 MPa, the elongation at break is 637%, and the volumetric conductivity is 8 × 10⁻⁶. -7 S / cm, surface conductivity 1×10 -3 S / cm.

[0066] Example 6

[0067] S1. Prepolymerization: Under a nitrogen atmosphere, 0.07 mol of 1,12-dodecanoic acid and 0.07 mol of Priamine 1074 were added to a three-necked flask connected to a mechanical stirrer, a nitrogen inlet, and a condenser. The flask was placed in an oil bath and the temperature was gradually increased to 180°C under a nitrogen atmosphere to start the reaction. The reaction was stirred at 180°C for 1 hour and then at 210°C for 1 hour to obtain the prepolymer.

[0068] S2, Polycondensation: The prepolymer obtained in step S1 is switched to a vacuum environment to continue the reaction; the reaction is carried out at a reduced vacuum of 150 Pa and a temperature of 220 °C for 1.5 h, and finally the temperature is raised to 240 °C for 3 h. After discharge, the product is dried at 50 °C under vacuum for 12 h to obtain the bio-based diamine polyamide product.

[0069] The bio-based diamine polyamide product prepared in this embodiment had a number-average molecular weight of 3.2 × 10⁻⁶, as determined by gel permeation chromatography. 4 The sample has the following properties: g / mol, glass transition temperature of 15.35℃, melting point of 89.70℃, tensile strength of 21.8 MPa, tensile modulus of 90.5 MPa, elongation at break of 855%, and electrical conductivity of 8.01 × 10⁻⁶ g / mol. -14 The S / cm value was measured, and its biocompatibility was verified by ISO 10993-5 cytotoxicity testing.

[0070] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 100mg of multi-walled carbon nanotubes (mass fraction of 5wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0071] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 26.8 MPa, the tensile modulus is 95.1 MPa, the elongation at break is 627%, and the volumetric conductivity is 7.4 × 10⁻⁶. -7 S / cm, surface conductivity 2.5×10 -3 S / cm.

[0072] Example 7

[0073] S1. Prepolymerization: Under a nitrogen atmosphere, 0.07 mol of 1,14-tetradecanoic acid and 0.07 mol of Priamine 1071 were added to a three-necked flask connected to a mechanical stirrer, a nitrogen inlet, and a condenser. The flask was placed in an oil bath and the temperature was gradually increased to 180°C under a nitrogen atmosphere to start the reaction. The reaction was stirred at 180°C for 1 hour and then at 210°C for 1 hour to obtain the prepolymer.

[0074] S2, Polycondensation: The prepolymer obtained in step S1 is switched to a vacuum environment to continue the reaction; the reaction is carried out at a reduced vacuum of 150 Pa and a temperature of 220 °C for 1.5 h, and finally the temperature is raised to 240 °C for 3 h. After discharge, the product is dried at 50 °C under vacuum for 12 h to obtain the bio-based diamine polyamide product.

[0075] The bio-based diamine polyamide product prepared in this embodiment had a number-average molecular weight of 2.8 × 10⁻⁶, as determined by gel permeation chromatography. 4 The sample has the following properties: g / mol, glass transition temperature of 12.45℃, melting point of 86.20℃, tensile strength of 18.6MPa, tensile modulus of 85.3MPa, elongation at break of 920%, and electrical conductivity of 8.25×10⁻⁶. -14 The S / cm value was measured, and its biocompatibility was verified by ISO 10993-5 cytotoxicity testing.

[0076] This embodiment also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this embodiment. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 100mg of multi-walled carbon nanotubes (mass fraction of 5wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the bio-based dimelamine-type polyamide-based flexible sensor for subsequent performance testing.

[0077] The tensile strength of the bio-based dimelamine-type polyamide-based flexible sensor in this embodiment is 21.3 MPa, the tensile modulus is 90.8 MPa, the elongation at break is 690%, and the volumetric conductivity is 7.4 × 10⁻⁶. -7 S / cm, surface conductivity 3.1×10 - 3 S / cm.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing a bio-based dimeric amine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0080] This comparative example also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this comparative example. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 200mg of multi-walled carbon nanotubes (mass fraction of 10wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the sensor, which is ready for subsequent performance testing.

[0081] The tensile strength of the sensor spline in this comparative example is 29.2 MPa, the tensile modulus is 98.2 MPa, the elongation at break is 340%, and the volumetric conductivity is 2.39 × 10⁻⁶. -1 S / cm, surface conductivity 2.89×10 -2 S / cm.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a bio-based dimeric amine polyamide, which is the same as the preparation method in Example 1 above, and will not be described in detail here.

[0084] This comparative example also provides a bio-based dimelamine-type polyamide-based flexible sensor, including the bio-based dimelamine-type polyamide prepared in this comparative example. The preparation method of the bio-based dimelamine-type polyamide-based flexible sensor includes the following steps: 2g of the obtained bio-based dimelamine-type polyamide is placed in 15ml of chloroform and magnetically stirred until completely dissolved. Separately, 400mg of multi-walled carbon nanotubes (mass fraction of 20wt%) are dispersed in 15ml of chloroform, and after ultrasonic treatment for 0.5h, magnetic stirring is performed for 0.5h. This ultrasonic-stirring cycle is repeated three times. Subsequently, the carbon nanotube dispersion is mixed with the polymer solution, and magnetic stirring is continued for 2h. After mixing, the solution is transferred to a petri dish and allowed to stand in the dark for 24h to evaporate most of the solvent. Finally, the sample is placed in a vacuum oven and dried at 40℃ for 6h to obtain the sensor, which is ready for subsequent performance testing.

[0085] The tensile strength of the sensor spline in this comparative example is 35.7 MPa, the tensile modulus is 105.8 MPa, the elongation at break is 260%, the volume conductivity is 5.89 S / cm, and the surface conductivity is 7.17 S / cm.

[0086] The product information of Priamine1071 and Priamine1074 mentioned in the above embodiments is shown in Table 1.

[0087] Table 1

[0088]

[0089] As shown in Example 1, the bio-based diamine polyamide possesses both high flexibility and moderate strength, and its dynamic deformation capability fully meets the requirements of flexible sensor matrix materials for high-dynamic application scenarios. Examples 1, 6, and 7 collectively demonstrate that the preparation method of this invention has good adaptability to diacids with different carbon chain lengths and different types of diamines. By adjusting the monomer combination, the performance of the final polyamide product can be effectively controlled. Examples 5-7 demonstrate that the key electrical properties of different types of diamine polyamide-based flexible sensors under the same conductive filler content fluctuate slightly around a high-performance baseline, illustrating the universality of the technical solution of this invention. Furthermore, the comparative data of Examples 1-5 and Comparative Examples 1-2 show that under low CNT content (e.g., below the percolation threshold), there is a significant difference between the surface conductivity and volume conductivity of the material, with a difference of up to 10. -3 ~10 -4 The difference between the two decreases sharply and almost disappears when the CNT content is excessive. This phenomenon indicates that excessive addition of CNTs leads to the uniform distribution of conductive fillers in the matrix, and the original surface enrichment mechanism fails. At this time, the shrinkage stress formed by the polymer due to solvent evaporation is insufficient to lock the CNTs on the material surface, and the gradient distribution structure between the surface and the internal conductive network cannot be maintained. It is worth noting that Examples 4-5, with a CNT content of 80-100 mg, are in the optimal range, and their surface conductivity increases to 10. -4 ~10 -5 With an elongation on the order of S / cm and a mechanical property retention rate exceeding 80%, the composite material combines high conductivity with excellent flexibility, perfectly overcoming the bottleneck problem of the difficulty in coordinating conductivity and flexibility in traditional flexible sensors. This is sufficient to meet the needs of most flexible sensing applications. In contrast, the drawback of Comparative Example 1 is that the elongation drops to 340%, which is lower than the requirements of flexible sensors for adapting to high strain, thus limiting its practical application scenarios.

[0090] The product testing and characterization methods used in Examples 1 to 5 and Comparative Examples 1 to 2 are as follows:

[0091] Fourier transform infrared spectroscopy analysis method: Functional group analysis of the sample was performed using an INVENIOS Fourier transform infrared spectrometer in the range of 4000 to 500 cm⁻¹. -1 The test was conducted within the spectral range, with a cumulative 32 scans.

[0092] X-ray diffraction testing method: The test was conducted using a SmartlabSE diffractometer with a Cu target radiation source. The diffraction pattern was acquired within the 2θ range of 5° to 50°, and the scanning rate was 2°·min. -1 .

[0093] Molecular weight determination method: An Agilent 1260 Infinity II system (USA) equipped with two PLgel MIXED-C columns (5 μm particle size, 300 × 7.5 mm) connected in tandem configuration was used; HPLC-grade chloroform was used as the mobile phase and maintained at 30 °C by column oven; chromatographic separation was performed under isocratic elution conditions at a flow rate of 1.0 mL·min⁻¹; a calibration curve was established using narrow-distribution polystyrene standards: the standards were dissolved in chloroform (concentration 2 mg·mL⁻¹) and the calibration was completed by three repeated injections.

[0094] Dynamic thermomechanical analysis test method: The test was conducted in tensile mode using a DMA242E dynamic thermomechanical analyzer; the test temperature range was -100℃ to 100℃, and the heating rate was 5℃·min. -1 The frequency is set to 1Hz.

[0095] Methods for testing melting temperature and crystallization temperature: The thermal properties of polyamide were studied using a TAQ20 differential scanning calorimeter (USA); under nitrogen atmosphere, 6-10 mg of sample was heated at 10 °C / min. -1 The sample was heated to 120°C at a rate of [missing value] and held at that temperature for 5 min; then, the sample was heated at 10°C / min. -1 Cool to -50°C at a rate of [missing information]; record the exothermic crystallization curve and read the corresponding crystallization temperature (T [missing information]). c Finally, the sample was heated to 120℃ at a rate of 10℃ / min, the melting curve was recorded, and the corresponding melting point (T) was read. m ).

[0096] Mechanical property testing method: The tensile properties of the material were tested using an Instron 3367 universal testing machine; the copolymer was hot-pressed into a 1 mm thick film, cut into dumbbell-shaped strips, and the samples were placed at room temperature for a period of time before tensile testing was performed at a speed of 50 mm / min. At least five tests were performed on each content sample.

[0097] Electrical performance testing method: The material to be tested is processed into a standard dumbbell-shaped sample, with both ends covered with conductive silver paste and copper wire electrodes embedded to ensure that the contact resistance between the electrode and the material interface is <0.1Ω; the dynamic resistance response of the sample during cyclic tensile testing is monitored using an RK2830 resistance meter, and axial strain is applied simultaneously using a universal testing machine.

[0098] In summary, the bio-based diamine polyamide prepared by this invention, through the flexible selection of bio-based diacid monomers with different chain lengths and bio-based diamine monomers with specific flexible structures, combined with precise control of the degree of polymerization, can synergistically optimize the molecular weight, thermal properties, and mechanical properties of the polyamide. In particular, this technology can achieve synergistic optimization of high molecular weight and excellent flexibility, overcoming the traditional polyamide material's challenge of balancing flexibility and strength, making it suitable for high-performance flexible electronic devices. This invention employs melt polycondensation, which has significant advantages over traditional solution polymerization: solvent-free process: avoids the use of organic solvents, reducing the environmental burden and cost of solvent recovery and treatment; high reactivity... Efficiency: High reactant concentration, fast reaction rate, short polymerization time, and high production efficiency; Energy saving and consumption reduction: The product can be directly transported to subsequent processing in a molten state, simplifying operation and reducing energy consumption, which is in line with the trend of green chemistry development; The bio-based diamine polyamide flexible sensor prepared by this invention has high sensitivity: After being combined with lightweight conductive fillers, it can accurately detect signals such as strain, temperature, and humidity; Excellent flexibility and adaptability to human joints: The low glass transition temperature gives the material high flexibility, which can fit closely to human joints and is suitable for wearable devices; High signal stability: Even under multiple high strain cycles, it can still maintain a stable resistance response, ensuring long-term reliable use.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A bio-based dimelamine-type polyamide-based flexible sensor, characterized in that, The flexible sensor includes a bio-based dimelamine polyamide, wherein the conductive filler accounts for 1 wt% to 5 wt% of the total mass. The bio-based dimelamine polyamide is formed by the condensation polymerization of a bio-based dimelamine with a diacid, and its structural formula is shown below: ； Among them, R1 is selected from C 12 ~C 44 A straight-chain or branched alkylene group; R2 is selected from C-type compounds containing branched or olefinic bonds. 24 ~C 44 Carbon chain; n is an integer from 20 to 200; The dicarboxylic acid is selected from at least one of the following derived from vegetable oils: tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, icosanoic acid, and docosanoic acid. The bio-based diamine is Priamine1071 or Priamine1074; The bio-based dimelamine-type polyamide is prepared by mixing the bio-based dimelamine-type polyamide with a lightweight conductive filler to obtain the bio-based dimelamine-type polyamide-based flexible sensor; the conductive filler includes multi-walled carbon nanotubes and single-walled carbon nanotubes, and the proportion of the conductive filler is 1wt%~5wt%. The method for mixing the bio-based diamine polyamide with the lightweight conductive filler to form the composite material is solution mixing, wherein the solvent for solution mixing is selected from any one or a combination of dichloromethane, chloroform, tetrahydrofuran, and acetone.

2. The bio-based dimelamine-type polyamide-based flexible sensor according to claim 1, characterized in that, The number-average molecular weight of the bio-based diamine polyamide is 1×10⁻⁶. 4 ~7×10 4 g / mol; The glass transition temperature of the bio-based diamine polyamide is -30~30℃; The tensile strength of the bio-based diamine polyamide is 5~50 MPa.

3. A method for preparing the bio-based dimelamine polyamide in the bio-based dimelamine polyamide-based flexible sensor according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Prepolymerization: Under inert gas protection, bio-based diamine and diacid are mixed in an equal molar ratio and stirred in a reactor at 160~230℃ for 1~4 hours to obtain the prepolymer. S2. Polycondensation: Under vacuum conditions, the prepolymer obtained in step S1 is subjected to polycondensation reaction at a temperature of 220~260℃ for 3~5h to obtain the bio-based diamine polyamide.

4. The application of a bio-based dimelamine-type polyamide-based flexible sensor as described in any one of claims 1 to 2 in detecting changes in temperature, humidity, resistance, force, or chemical gas concentration.

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