Coaxial electrospinning radiation phase change cooling fiber membrane and preparation method thereof

Abstract

The invention belongs to the technical field of cooling fiber membranes, and particularly relates to a coaxial electrospinning radiation phase change cooling fiber membrane and a preparation method thereof.The preparation method comprises the steps that a shell layer spinning solution is prepared, specifically, poly (vinylidene fluoride-co-hexafluoropropylene) is added into a mixed solvent of N, N-dimethylformamide and acetone, the mixture is heated and stirred for 6 h at the temperature of 45-60 DEG C, and a uniform solution is obtained; standing the uniform solution at room temperature for 6 hours to eliminate bubbles; preparing a core layer spinning solution, namely adding n-octadecane into trichloromethane, stirring for 30 minutes, and storing at 35 DEG C; spinning by adopting electrostatic spinning equipment and a 22G / 17G coaxial needle head, respectively transferring the shell layer spinning solution and the core layer spinning solution into an injector, connecting corresponding parts of the coaxial needle head, and adjusting electrostatic spinning parameters to carry out electrostatic spinning, so as to obtain a coaxial electrospinning radiation phase change cooling fiber membrane with a wrinkle structure; the weight-average molecular weight Mw of the poly (vinylidene fluoride-co-hexafluoropropylene) is 455000, and the number-average molecular weight Mn of the poly (vinylidene fluoride-co-hexafluoropropylene) is 110000.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cooling fiber membranes, and particularly relates to a coaxial electrospun radiation phase change cooling fiber membrane and a preparation method thereof. BACKGROUND

[0002] With the continuous improvement of the miniaturization of electronic equipment, building energy saving and personal thermal management needs, high-efficiency passive cooling technology has become a key direction to solve the energy consumption problem of traditional cooling solutions. Traditional active cooling methods need to rely on external energy input, which not only has high energy consumption, but also is limited by the use scene; and the radiation cooling technology can realize energy-free cooling by radiating infrared energy to the universe, and has outstanding potential in the field of low-energy cooling. However, single radiation cooling materials lack effective heat buffering capacity in the daytime strong sunlight or environmental temperature fluctuation scene, and it is difficult to maintain stable cooling effect, so combining the radiation cooling function with the phase change heat storage characteristics has become an important research idea to improve the environmental adaptability of the cooling material.

[0003] The current related technology of radiation phase change cooling fiber membrane still has obvious limitations: most schemes adopt a simple blending or unstructured composite method of phase change materials and polymer matrices, which is easy to cause leakage of the phase change materials in long-term use, resulting in attenuation of the cooling performance of the material and insufficient durability; at the same time, the surface microstructure of the fiber membrane is difficult to control, and the solar reflectivity cannot be further enhanced by optimizing the surface morphology, which restricts the improvement of the cooling efficiency. In addition, some preparation processes are complicated and have strict parameter control requirements, which not only increases the production cost, but also makes it difficult to realize large-scale preparation, and cannot meet the dual needs of performance stability and preparation convenience of the cooling material in actual application. SUMMARY

[0004] The purpose of the present application is to provide a coaxial electrospun radiation phase change cooling fiber membrane and a preparation method thereof in view of the above-mentioned technical problems.

[0005] Therefore, the present application provides a preparation method of a coaxial electrospun radiation phase change cooling fiber membrane, which comprises the following steps:

[0006] Step 1: preparation of a shell layer spinning solution

[0007] Poly (vinylidene fluoride-co-hexafluoropropylene) is added to a mixed solvent of N,N-dimethylformamide and acetone, heated and stirred at 45 to 60 DEG C for 6h to obtain a uniform solution, and the uniform solution is left to stand at room temperature for 6h to eliminate bubbles and is ready for use;

[0008] Step 2: preparation of a core layer spinning solution

[0009] Octadecane is added to chloroform, stirred for 30 min, and then stored at 35 DEG C and is ready for use;

[0010] Step three: coaxial electrospinning:

[0011] The shell layer and core layer spinning solutions are transferred into syringes and fixed on the syringe pump by using electrospinning equipment and 22G / 17G coaxial needle. The syringe containing the shell layer spinning solution is connected to the outer needle of the coaxial needle, and the syringe containing the core layer spinning solution is connected to the inner needle of the coaxial needle. The electrospinning parameters are adjusted to obtain coaxial electrospun radiative phase change cooling fiber membranes with wrinkle structures.

[0012] The weight average molecular weight Mw of the poly(vinylidene fluoride-co-hexafluoropropylene) is 455000, and the number average molecular weight Mn is 110000.

[0013] The electrospinning parameters include: temperature 36±2℃, humidity 45-50%, positive voltage 14.5±2kV, negative voltage -3 to -1kV, receiving distance 20cm, shell layer pushing speed 0.2mm / min, and core layer pushing speed 0.01-0.04mm / min.

[0014] Preferably, the mass ratio of N,N-dimethylformamide and acetone is 7:3, 5:5 or 3:7.

[0015] Preferably, the solid content of the obtained shell layer spinning solution is 20%.

[0016] Preferably, the type of the wrinkle structure is realized by adjusting the mass ratio of N,N-dimethylformamide and acetone: when the mass ratio of N,N-dimethylformamide and acetone is 7:3, a honeycomb-shaped wrinkle is formed.

[0017] When the mass ratio of N,N-dimethylformamide and acetone is 5:5 or 3:7, a wrinkle with parallel ridges and valleys is formed.

[0018] Preferably, the height of the wrinkle structure and the surface roughness of the fiber membrane are realized by adjusting the core layer pushing speed: the lower the core layer pushing speed, the flatter the fiber membrane surface and the smaller the wrinkle amplitude.

[0019] The higher the core layer pushing speed, the longer the wrinkle wavelength, the larger the amplitude, and the clearer the wrinkle lines.

[0020] Preferably, the electrospinning parameters are any one of the following combinations:

[0021] Positive voltage 16kV, negative voltage -3kV, core layer pushing speed 0.01mm / min;

[0022] Positive voltage 14.5kV, negative voltage -2kV, core layer pushing speed 0.02mm / min;

[0023] Spinning positive voltage 16.5kV, negative voltage -2kV, core layer advancing speed 0.03mm / min;

[0024] Spinning positive voltage 14.3kV, negative voltage -2kV, core layer advancing speed 0.04mm / min;

[0025] Spinning positive voltage 16kV, negative voltage -1.5kV, core layer advancing speed 0.01mm / min;

[0026] Spinning positive voltage 14kV, negative voltage -1.7kV, core layer advancing speed 0.02mm / min;

[0027] Spinning positive voltage 14kV, negative voltage -1.8kV, core layer advancing speed 0.03mm / min;

[0028] Spinning positive voltage 16.5kV, negative voltage -1.9kV, core layer advancing speed 0.04mm / min;

[0029] Spinning positive voltage 12.5kV, negative voltage -1.6kV, core layer advancing speed 0.01mm / min;

[0030] Spinning positive voltage 13.5kV, negative voltage -1.5kV, core layer advancing speed 0.02mm / min;

[0031] Spinning positive voltage 13.6kV, negative voltage -1.5kV, core layer advancing speed 0.03mm / min;

[0032] Spinning positive voltage 13.5kV, negative voltage -2.5kV, core layer advancing speed 0.04mm / min.

[0033] The coaxial electrospun radiation phase change cooling fiber membrane has micro-nano fiber diameter and pore structure, and maintains high emission characteristics at an atmospheric window, and has an average temperature reduction of about 7.6℃ during outdoor daytime testing, a peak temperature difference of up to 12.4℃, an enthalpy of 122J / g after 50 thermal cycles, and no n-octadecane leakage.

[0034] Preferably, the solar reflectivity of the fiber membrane is improved by multiple diffuse reflection and angle randomization of the corrugated structure, and is higher than that of the fiber membrane with a smooth surface spun without a core layer.

[0035] Preferably, the fiber membrane has a heat preservation effect on the environment at night and has a high temperature buffer phase change platform characteristic.

[0036] The beneficial effects of the present application are:

[0037] The prepared coaxial electrospinning radiation phase change cooling fiber film can not only rely on the micro-nano pores and the surface wrinkle structure to improve the solar reflectivity through multiple diffuse reflection in the strong sunlight scene during the day, but also can form a high-temperature buffer platform by the phase change characteristics of n-octadecane to effectively inhibit the temperature rise, and the actual measured average cooling is 7.6 DEG C, and the peak temperature difference is 12.4 DEG C at most; at night, the heat preservation effect can be played to avoid excessive heat dissipation, and the enthalpy value still remains 122 J / g after 50 times of thermal cycle, and the packaging effect of the coaxial structure solves the problem that the phase change material is easy to leak in the traditional composite film, and the durability of the material is significantly improved.

[0038] With the simple coaxial electrospinning process as the core, the honeycomb or parallel ridge valley wrinkle can be accurately prepared by adjusting the mass ratio of the shell N,N-dimethylformamide and acetone, and the wrinkle height and surface roughness can be flexibly changed by adjusting the core layer propelling speed, so that the microstructure customization can be realized without complex equipment; the whole process is simple and easy to operate, and the parameters are easy to control, which not only reduces the production cost, but also stably produces the fiber film with uniform performance, and can be widely adapted to the heat management of electronic equipment, building energy saving, personal protection and other scene requirements, and effectively makes up for the short board of the traditional cooling material process and single performance. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The physical map and optical micrograph of the radiation-phase change cooling fiber film of examples 1-12.

[0040] Figure 2 The system trajectory snapshot of the molecular dynamics simulation.

[0041] Figure 3 The reflectance spectrum of the fiber film in examples 4, 8, 12 and comparative example 1 measured by using the ultraviolet-visible-near infrared spectrophotometer equipped with an integrating sphere.

[0042] Figure 4 The infrared emission spectrum of the fiber film in examples 4, 8, 12 and comparative example 1 measured by using the Fourier transform infrared spectrometer equipped with a gold integrating sphere.

[0043] Figure 5 The reflectance spectrum of the fiber film in examples 1, 2, 3, 4 measured by using the ultraviolet-visible-near infrared spectrophotometer equipped with an integrating sphere.

[0044] Figure 6 The reflectance spectrum of the fiber film in examples 5, 6, 7, 8 measured by using the ultraviolet-visible-near infrared spectrophotometer equipped with an integrating sphere.

[0045] Figure 7 The reflectance spectrum of the fiber film in examples 9, 10, 11, 12 measured by using the ultraviolet-visible-near infrared spectrophotometer equipped with an integrating sphere.

[0046] Figure 8 Infrared thermal image of cotton fabric, Comparative Example 1 and Example 4 when heated at constant temperature.

[0047] Figure 9 Real-time change graph of the under surface temperature of Example 4, Comparative Example 1 and pure cotton fabric under daytime outdoor environment.

[0048] Figure 10 Real-time change graph of the under surface temperature of Example 4, Comparative Example 1 and pure cotton fabric under nighttime outdoor environment.

[0049] Figure 11 Transmission electron microscope image of Example 4.

[0050] Figure 12 DSC curve of Example 4 at a temperature rising and falling rate of 10℃ / min.

[0051] Figure 13 Appearance photos of Example 1, 2, 3, 4 before and after continuous heating for 30 hours.

[0052] Figure 14 Mass residual rate curve of Example 1, 2, 3, 4 after continuous heating for 30 hours.

[0053] Figure 15 Appearance photos of Example 5, 6, 7, 8 before and after continuous heating for 30 hours.

[0054] Figure 16 Mass residual rate curve of Example 5, 6, 7, 8 after continuous heating for 30 hours.

[0055] Figure 17 Appearance photos of Example 9, 10, 11, 12 before and after continuous heating for 30 hours.

[0056] Figure 18 Mass residual rate curve of Example 9, 10, 11, 12 after continuous heating for 30 hours.

[0057] Figure 19 Infrared thermal image of Example 4 covered on the surface of clothes. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application will be clearly described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art belong to the scope of protection of the present application.

[0059] It should be noted that all the terms indicating direction and position in the present application, such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inner", "outer", "top", "low", "transverse", "longitudinal", "center", etc., are only used to explain the relative position relationship, connection condition, etc. between components in a certain state (as shown in the drawings), and are only for the convenience of describing the present application, and thus cannot be understood as a limitation on the present application. In addition, the description of "first", "second", etc. in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features.

[0060] In the description of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection; it can be directly connected, or indirectly connected through intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0061] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0062] The raw materials used in the present application include: poly (vinylidene fluoride-co-hexafluoropropylene), n-octadecane, N,N-dimethylformamide, acetone, chloroform.

[0063] The poly (vinylidene fluoride-co-hexafluoropropylene) described in the present application has a Mw of 455,000 and a Mn of 110,000.

[0064] A coaxial electrospinning preparation method of a radiation phase change cooling fiber membrane, a shell layer spinning solution preparation method: poly (vinylidene fluoride-co-hexafluoropropylene) is added into a mixed solvent of N, N-dimethylformamide and acetone, heated and stirred at 45 to 60 DEG C for 6 hours to obtain a uniform solution, and the mixed solution obtained in the above step is placed at room temperature for 6 hours to eliminate bubbles and standby; a core layer spinning solution preparation method: n-octadecane is added into chloroform, stirred for 30 minutes, and stored at 35 DEG C for standby; the shell layer and core layer spinning solutions are transferred into syringes respectively and fixed on a syringe pump, the syringe containing the shell layer spinning solution is connected with the outer needle of the coaxial needle, the syringe containing the core layer spinning solution is connected with the inner needle of the coaxial needle, electrostatic spinning equipment and 22G / 17G coaxial needle are used for spinning, electrostatic spinning parameters are adjusted, and electrostatic spinning is carried out to obtain a phase change-radiation cooling fiber membrane.

[0065] Further, the mass ratio of N, N-dimethylformamide and acetone is 7:3, 5:5 or 3:7.

[0066] Further, the solid content of the shell layer spinning solution is 20%.

[0067] Further, the electrospinning specific parameters are as follows: temperature is 36±2 DEG C, humidity is 45 to 50%, positive voltage is 14.5±2kV, negative voltage is -3 to -1kV, receiving distance is 20cm, shell layer advancing speed is 0.2mm / min, and core layer advancing speed is 0.01-0.04mm / min.

[0068] In the application, the core layer TCM and the shell layer mixed solvent have a significant asymmetric evaporation rate, the TCM continuously and rapidly escapes after deposition and produces strong dispersion adsorption / local plasticization on the PVDF-HFP segment, so that the fiber network generates in-plane shrinkage stress accumulation and out-of-plane buckling instability, and macroscopic wrinkles are formed. By adjusting the proportion of the shell layer mixed solvent, a honeycomb-shaped wrinkle with a two-dimensional buckling main network can be formed, or the anisotropy is enhanced to form a parallel ridge valley wrinkle. By changing the core layer flow rate, the wrinkle height and the fiber membrane surface roughness can also be changed. The preparation method is simple and easy to control.

[0069] The application will be further described in combination with specific examples.

[0070] Example 1: Poly (vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, stirred at 55°C for 6h to obtain a shell spinning solution with a solid content of 20%, and left to stand at room temperature for 6h. The mass ratio of N,N-dimethylformamide and acetone was 7:3. N-octadecane was added to chloroform, and after stirring for 30min, a uniformly mixed core spinning solution was obtained, which was stored at 35°C. Using an electrospinning device and a 22G / 17G coaxial needle, the shell and core spinning solutions were transferred to syringes and fixed to a syringe pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2°C, the humidity was 45 to 50%, the positive voltage was 16kV, the negative voltage was -3kV, the receiving distance was 20cm, the shell advancing speed was 0.2mm / min, and the core advancing speed was 0.01mm / min.

[0071] Example 2: The core spinning speed was adjusted to 0.02mm / min, the positive voltage was 14.5kV, and the negative voltage was -2kV to obtain the corresponding radiation-phase change cooling fiber membrane, and the other conditions were consistent with Example 1.

[0072] Example 3: The core spinning speed was adjusted to 0.03mm / min, the positive voltage was 16.5kV, and the negative voltage was -2kV to obtain the corresponding radiation-phase change cooling fiber membrane, and the other conditions were consistent with Example 1.

[0073] Example 4: The core spinning speed was adjusted to 0.04mm / min, the positive voltage was 14.3kV, and the negative voltage was -2kV to obtain the corresponding radiation-phase change cooling fiber membrane, and the other conditions were consistent with Example 1.

[0074] Example 5: Poly (vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, stirred at 55°C for 6h to obtain a shell spinning solution with a solid content of 20%, and left to stand at room temperature for 6h. The mass ratio of N,N-dimethylformamide and acetone was 5:5. N-octadecane was added to chloroform, and after stirring for 30min, a uniformly mixed core spinning solution was obtained, which was stored at 35°C. Using an electrospinning device and a 22G / 17G coaxial needle, the shell and core spinning solutions were transferred to syringes and fixed to a syringe pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2°C, the humidity was 45 to 50%, the positive voltage was 16kV, the negative voltage was -1.5kV, the receiving distance was 20cm, the shell advancing speed was 0.2mm / min, and the core advancing speed was 0.01mm / min.

[0075] Example 6: The core layer spinning speed was adjusted to 0.02 mm / min, the positive voltage was 14 kV, and the negative voltage was -1.7 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 5.

[0076] Example 7: The core layer spinning speed was adjusted to 0.03 mm / min, the positive voltage was 14 kV, and the negative voltage was -1.8 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 5.

[0077] Example 8: The core layer spinning speed was adjusted to 0.04 mm / min, the positive voltage was 16.5 kV, and the negative voltage was -1.9 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 5.

[0078] Example 9: Poly (vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, stirred at 55°C for 6h to obtain a shell layer spinning solution with a solid content of 20%, and then placed at room temperature for 6h. The mass ratio of N,N-dimethylformamide and acetone was 3:7. Stearic acid octadecane was added to chloroform, and after stirring for 30 min, a uniformly mixed core layer spinning solution was obtained, which was stored at 35°C. Using an electrospinning device and a 22G / 17G coaxial needle, the shell and core layer spinning solutions were transferred to syringes and fixed on a syringe pump. The syringe containing the shell layer spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core layer spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2°C, the humidity was 45 to 50%, the positive voltage was 12.5 kV, the negative voltage was -1.6 kV, the receiving distance was 20 cm, the shell layer advancing speed was 0.2 mm / min, and the core layer advancing speed was 0.01 mm / min.

[0079] Example 10: The core layer spinning speed was adjusted to 0.02 mm / min, the positive voltage was 13.5 kV, and the negative voltage was -1.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 9.

[0080] Example 11: The core layer spinning speed was adjusted to 0.03 mm / min, the positive voltage was 13.6 kV, and the negative voltage was -1.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 9.

[0081] Example 12: The core layer spinning speed was adjusted to 0.04 mm / min, the positive voltage was 13.5 kV, and the negative voltage was -2.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane, and other conditions were consistent with Example 9.

[0082] Comparative Example 1: Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and stirred at 55°C for 6 hours to obtain a shell spinning solution with a solid content of 20%, which was then allowed to stand at room temperature for 6 hours. The mass ratio of N,N-dimethylformamide to acetone was 3:7. Electrospinning was performed using an electrospinning device and a 22G / 17G coaxial needle. The shell spinning solution was transferred to a syringe and fixed to an injection pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and an empty syringe was fixed to the injection pump and connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2°C, the humidity to 45-50%, the positive spinning voltage to 12.5kV, the negative voltage to -1.6kV, the receiving distance to 20cm, the shell advance speed to 0.2mm / min, and no spinning solution was injected into the core layer.

[0083] Appendix Figure 1 Examples 1-12 are shown in physical images and optical micrographs. The final pattern of the folds can be altered by changing the ratio of the shell-mixing solvent. During flight, the jet forms initial fibers and deposits on the receiver due to the rapid evaporation of acetone. When the DMF content is high, the shell evaporates slowly, curing is slow, the inter-fiber welds are strong, the network is softer, and stress can be transmitted in all directions, forming a uniform polygonal pattern. Increasing the acetone content leads to faster shell evaporation and curing. The fibers become more independent, and the network becomes more rigid. Rapid evaporation may result in a faster curing rate along the fiber axis, making it easier for stress to be released along the fiber direction, forming parallel ridges and valleys. Changing the spinning speed of the core layer can alter the amplitude of the folds. At low core speeds, the surface is basically flat or has only fine ripples, occasionally with short-wavelength, low-amplitude fine wrinkles; as the core speed increases, the wavelength gradually becomes longer, the amplitude increases, and the fold patterns gradually become clearer. Molecular dynamics simulations were used to demonstrate the interaction energies between DMF, acetone, and chloroform and PVDF-HFP at the shell-core interface. Figure 2 The image shows a snapshot of the system trajectory from molecular dynamics simulations. Table 1 shows the interaction energies. In the shell solvent, acetone has weak interactions with the polymer, leading to rapid solidification, while DMF has strong interactions, which is beneficial for forming a homogeneous solution. The interaction between chloroform and PVDF-HFP is dominated by strong van der Waals forces, indicating that chloroform strongly adsorbs onto PVDF-HFP through dispersion / induction forces, causing chain segment relaxation and localized plasticization. Due to its strong interaction with the polymer, volatilization generates strong localized stress. The faster the core velocity, the greater the amount of core layer per unit time (i.e., the more chloroform), resulting in a larger and more continuous area of ​​plasticized region, stronger synergistic contraction force, and increasingly clear wrinkle patterns.

[0084] Appendix Figure 3 and attached Figure 4Solar reflectance spectra and infrared emissivity spectra of Example 4, 8, 12 and Comparative Example 1. The surface corrugated structure of Example 4, 8, 12 can improve solar reflectance by multiple diffuse reflection and angle randomization of geometric optics, and the fiber diameter and pore of electrospun fiber membrane are micro-nano level, the synergistic design makes the gain greater, while the surface of Comparative Example 1 is smooth, the scattering efficiency is low, and the solar reflectance is low. The corrugated structure does not affect the high emission characteristics of the material in the atmospheric window. Figure 5 Reflectance spectra of Example 1-4, attached Figure 6 Reflectance spectra of Example 5-8, attached Figure 7 Reflectance spectra of Example 9-12, and average reflectance data of Example 1-12 in Table 2, it can be seen that under the condition of the same solvent ratio of the shell layer, the faster the core layer speed, the higher the reflectivity, because the high core layer makes the fiber membrane surface corrugation more obvious.

[0085] A polytetrafluoroethylene plate was placed on a constant temperature heating table at 50°C, and after the surface temperature of the polytetrafluoroethylene plate rose to 45°C, cotton fabric, Comparative Example 1 and Example 4 were placed on it, and an infrared thermal imager was used to take pictures every two seconds to monitor the temperature rise of the sample. Attached Figure 8 Infrared thermal images of cotton fabric, Comparative Example 1 and Example 4 during constant temperature heating. The cotton fabric turned red quickly in 8 seconds, and Comparative Example 1 did not turn red after one minute. Example 4 has a lower surface temperature and a slower temperature rise rate in the early stage of heating due to the presence of phase change material.

[0086] Attached Figure 9 And attached Figure 10 Cooling performance test of Example 4 and Comparative Example 1 in outdoor daytime and nighttime. The test device is: four 12x12x5cm cavities are made on the surface of a 30x30x30cm polystyrene foam box, a thermocouple is placed in the center of the cavity and fixed to test the temperature of the lower surface of the sample, and the sample is tightly covered on the thermocouple. At the same time, leave a cavity and only place the thermocouple probe without covering the sample to test the ambient temperature. The surface of the foam box is wrapped with aluminum foil paper except for the cavity to reduce the heating of the test device by sunlight. The top of the device is covered with an infrared transparent polyethylene film to isolate the thermal convection and conduction of the surrounding environment. During the daytime outdoor test, the phase change platform can be observed at the beginning, and the material temperature remains unchanged, showing high temperature buffering performance. The average daytime cooling is about 7.6°C, and the peak temperature difference reaches 12.4°C; the nighttime relative single radiation cooling sample (Comparative Example 1) shows a heat preservation effect.

[0087] Attached Figure 11 TEM image of Example 4, it can be seen that the shell layer successfully wraps the phase change material in the core layer, and is uniformly distributed in the center without offset. Attached Figure 12For the DSC curve of Example 4, the enthalpy value after 50 cycles has almost no loss (122 J / g), indicating the durability and leakproofness of the prepared coaxial structure. To prove its long-acting property, Examples 1-12 were continuously heated in a blast oven at 50°C for 30 h, and then the mass loss was calculated. The results are shown in Table 1. Figures 13-18 As can be seen from the table, the fiber film has no obvious damage, and there is no trace of phase change material leakage on the surface of the filter paper. The residual mass after heating is more than 98%. Without the solid n-octadecane encapsulated in the core layer, it completely changes to liquid state in <5 s.

[0088] Example 4 was attached to the surface of the clothes, and the clothes were worn in the summer. The infrared thermal imaging showed that the temperature of the clothes was lower than that of the daily clothes, which demonstrated its practical value in the summer outdoors. Figure 19 The infrared thermal imaging showed that the temperature of the clothes was lower than that of the daily clothes, which demonstrated its practical value in the summer outdoors.

[0089] Table 1;

[0090] van der Waals interaction (kJ / mol) Coulomb interaction (kJ / mol) Total interaction energy (kJ / mol) DMF -4.03 -1.58 -5.61 Acetone -1.55 -0.67 -2.22 Chloroform -10.54 -0.08 -10.46

[0091] Table 2;

[0092] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Comparative Example 1 Reflectance % 92.1 93.2 94.3 97.2 90.3 91.7 92.7 95.1 92.3 92.8 94.0 95.6 86.5

[0093] The embodiments of the present application are described above with reference to the drawings, and the embodiments and features in the present application can be combined with each other without conflict, and the present application is not limited to the specific embodiments described above. The specific embodiments described above are only illustrative, rather than limiting, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the scope of the present application and the protection scope of the claims.

Claims

1. A method for preparing a coaxial electrospun radiation phase change cooled fiber membrane, characterized in that: Includes the following steps: Step 1: Preparation of shell spinning solution: Add poly(vinylidene fluoride-co-hexafluoropropylene) to a mixed solvent of N,N-dimethylformamide and acetone, heat and stir at 45 to 60°C for 6 hours to obtain a homogeneous solution, and let the homogeneous solution stand at room temperature for 6 hours to eliminate bubbles and set aside. Step 2: Prepare the core spinning solution: Add n-octadecane to chloroform, stir for 30 minutes, and store at 35°C for later use; Step 3: Coaxial electrospinning: Using electrospinning equipment and 22G / 17G coaxial needles, the shell and core spinning solutions are transferred to syringes and fixed to the injection pump. The syringe containing the shell spinning solution is connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution is connected to the inner needle of the coaxial needle. Electrospinning was performed by adjusting the electrospinning parameters to obtain a coaxial electrospinned radiation phase change cooling fiber membrane with a pleated structure. The poly(vinylidene fluoride-co-hexafluoropropylene) has a weight-average molecular weight Mw of 455,000 and a number-average molecular weight Mn of 110,000. The electrospinning parameters include: temperature of 36±2℃, humidity of 45 to 50%, positive spinning voltage of 14.5±2kV, negative voltage of -3 to -1kV, receiving distance of 20cm, shell spinning solution propulsion speed of 0.2mm / min, and core spinning solution propulsion speed of 0.01-0.04mm / min. The mass ratio of N,N-dimethylformamide to acetone is 7:3, 5:5 or 3:7; The solid content of the resulting shell spinning solution was 20%.

2. The method for preparing a coaxial electrospun radiation phase change cooled fiber membrane according to claim 1, characterized in that: The type of the folded structure is achieved by adjusting the mass ratio of N,N-dimethylformamide and acetone: when the mass ratio of N,N-dimethylformamide to acetone is 7:3, honeycomb-like folds are formed. When the mass ratio of N,N-dimethylformamide to acetone is 5:5 or 3:7, parallel ridge valleys are formed.

3. The method for preparing a coaxial electrospun radiation phase change cooled fiber membrane according to claim 1, characterized in that: The height of the pleated structure and the surface roughness of the fiber membrane are achieved by adjusting the core layer propulsion speed: the lower the core layer propulsion speed, the flatter the fiber membrane surface and the smaller the pleat amplitude. The higher the core layer advance speed, the longer the fold wavelength and the greater the amplitude, and the clearer the fold texture.

4. The method for preparing a coaxial electrospun radiation phase change cooled fiber membrane according to claim 1, characterized in that: The electrospinning parameters are any combination of the following: The spinning positive voltage is 16kV, the negative voltage is -3kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 14.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 16.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 14.3kV, the negative voltage is -2kV, and the core layer advance speed is 0.04mm / min; The spinning positive voltage is 16kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 14kV, the negative voltage is -1.7kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 14kV, the negative voltage is -1.8kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 16.5kV, the negative voltage is -1.9kV, and the core layer advance speed is 0.04mm / min; The spinning positive voltage is 12.5kV, the negative voltage is -1.6kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 13.5kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 13.6kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 13.5kV, the negative voltage is -2.5kV, and the core layer advance speed is 0.04mm / min.

5. A coaxial electrospun radiation phase change cooling fiber membrane, comprising a method for preparing a coaxial electrospun radiation phase change cooling fiber membrane according to any one of claims 1-4, characterized in that: The fiber membrane has micro- and nano-scale fiber diameters and pore structures, and maintains high emission characteristics in the atmospheric window. During outdoor daytime testing, the average temperature drop is about 7.6℃, the peak temperature difference can reach 12.4℃, the enthalpy value is 122J / g after 50 thermal cycles, and there is no n-octadecane leakage.

6. The coaxial electrospun radiation phase change cooling fiber membrane according to claim 5, characterized in that: The solar reflectivity of the fiber membrane is enhanced by multiple diffuse reflections and angle randomization of the pleated structure, and is higher than that of a fiber membrane with a smooth surface spun in a coreless spinning solution.

7. The coaxial electrospun radiation phase change cooling fiber membrane according to claim 5, characterized in that: The fiber membrane has a heat-insulating effect on the environment at night and has a phase change plateau characteristic for high-temperature buffering.

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