CN114561717A

CN114561717A - Hydrophilic block modified polycaprolactone electrostatic spinning fiber and preparation method thereof

Info

Publication number: CN114561717A
Application number: CN202210138316.1A
Authority: CN
Inventors: 李战雄; 何晓祥; 王雪婷
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2022-02-15
Filing date: 2022-02-15
Publication date: 2022-05-31
Also published as: WO2023155361A1

Abstract

The invention discloses a hydrophilic block modified polycaprolactone electrostatic spinning fiber and a preparation method thereof, wherein PCL-bThe WPU solution and the PEO solution are respectively used as a shell solution and a core solution, and the hollow fiber is prepared by coaxial electrospinning and is a hydrophilic block modified polycaprolactone electrospun fiber. PCL-bIn WPU solution, the solvent is CHCl₃And/or DMF at a concentration of 15-30%; in PEO solution, the solvent is water or CHCl₃The concentration is 1.5-5%. The LF-NMR is used for measuring the water distribution and adsorption state of the solid fiber, the non-porous hollow fiber and the porous hollow fiber, the water content ratios of the three fibers are respectively about 14.5%, 27.5% and 31.1%, the modern characterization method is used for verifying that the fiber cavities and the fiber walls are porous and can adsorb the bound water, and the microstructures are favorable for improving the hydrophilic materialThe hydrophilic property of the material.

Description

Hydrophilic block modified polycaprolactone electrostatic spinning fiber and preparation method thereof

Technical Field

The invention belongs to the polymer technology, and particularly relates to hydrophilic block modified polycaprolactone, an electrostatic spinning fiber and a preparation method.

Background

Nuclear Magnetic Resonance (NMR) is a physical phenomenon of the interaction of substances in alternating Magnetic fields and static high-intensity Magnetic fields^，The application technique is based on 6 important parameters: chemical shift delta, dipole indirect interaction J, dipole-dipole direct interaction DD, and longitudinal relaxation time T_lTransverse relaxation time T₂And a diffusion coefficient D. The three parts are mainly used for researching molecular chemical structures, namely, the correlation and the spatial position relation of functional groups and atoms, and belong to the research category of high-field nuclear magnetic resonance (Fourier magnetic resonance), the magnetic field strength is usually more than 11.7T, and the higher the field strength is, the better the parameter resolution is; the latter two are mainly used for reflecting the motion characteristics of molecules, and belong to the technical research field of low-field nuclear magnetic resonance (time-domain magnetic resonance) analysis and test, and the magnetic field intensity is below 1T. Wherein, Low-Field Nuclear Magnetic Resonance (LF-NMR) is used to monitor the hydrogen-containing fluid in the sample, such as oil, water, gas, etc., so as to observe the distribution and change rule of the hydrogen-containing fluid in the sample under the condition of no damage. The method is widely applied in the research fields of textile industry and the like, such as core porosity analysis, oil-gas exploration and energy development; drug efficacy analysis and animal tissue imaging in the field of biomedicine^[13](ii) a The cross-linking density of the rubber and the pore size distribution of the porous medium; detecting the water and oil content, moisture regain and adhesive amount of the fiber; the interaction between the dye and water in the ink, and the like. In the prior art, hydrophilic block modified polycaprolactone hollow fibers are rarely seen, and the research on the hollow fibers by an LF-NMR technology is not seen.

Disclosure of Invention

The invention discloses preparation of hydrophilic block modified polycaprolactone and electrostatic spinning fiber.

A hydrophilic block modified polycaprolactone electrostatic spinning fiber which has a hollow structure and a shell layer of PCL-bWPU with wall thickness of 1-2 μm.

The invention discloses a preparation method of the hydrophilic block modified polycaprolactone electrostatic spinning fiber, which uses PCL-bThe WPU solution and the PEO solution are respectively used as a shell solution and a core solution and are prepared by coaxial electrostatic spinningPreparing hollow fiber which is hydrophilic block modified polycaprolactone electrostatic spinning fiber.

In the present invention, PCL-b-WPU solution in CHCl₃And/or DMF at a concentration of 15-30%, preferably 20-25%. In PEO solution, the solvent is water or CHCl₃The concentration is 1.5-5%, preferably 2-3%.

In the invention, during coaxial electrostatic spinning, the flow rate of the shell solution is 0.5-0.8 mL/h; the flow rate of the core solution is 0.1-0.3 ml/h.

The invention discloses application of the hydrophilic block modified polycaprolactone electrospun fiber in preparation of a hydrophilic material.

In the invention, PCL-b-WPU is hydrophilic block modified polycaprolactone, isophorone diisocyanate and polyethylene glycol are used as raw materials, 2, 2-bis (hydroxymethyl) propionic acid (DMPA) is used as a micromolecule hydrophilic chain extender, and the materials are subjected to addition polymerization under the catalysis of an organic tin catalyst to prepare an isocyanate-terminated prepolymer; then, PCL-OH and the isocyanate-terminated prepolymer are subjected to addition reaction under the action of a catalyst to prepare the aqueous polyurethane hydrophilic block modified polycaprolactone (PCL-b-WPU). Preferably, the polyethylene glycol is polyethylene glycol-400 and the catalyst is dibutyltin dilaurate (DBTDL).

The invention uses PCL-bThe hollow fiber is prepared by coaxial electrostatic spinning with WPU and PEO solution as shell solution and core solution respectively, and the shell solution concentration is 22% (mixed solvent CHCl)₃DMF =4:1, v/v); the concentration of the core solution is 2 percent (the solvent is ultrapure water); the flow rate of the shell solution is 0.6 mL/h; the flow rate of the core solution is 0.2 ml/h; the voltage is 13 kv; receiving distance is 16 cm; the winding speed is 100 mm/s; the temperature is 17.0 +/-0.5 ℃; humidity is 40 +/-5%. The resulting fibers had an average inner diameter of about 16.63 μm and a wall thickness of 1.37. mu.m. Solvent used for core solution was changed to CHCl₃The hollow fiber with porous shell layers is prepared through coaxial electrostatic spinning, and the morphology of the fiber is observed through SEM to present a hole structure. The miscibility of the two materials during spinning also resulted in a smaller fiber lumen with an average fiber inner diameter of 6.11 μm and a wall thickness of 1.56 μm. The water content distribution and adsorption state of the solid fibers, the non-porous hollow fibers and the porous hollow fibers were measured by LF-NMR, and it was found that water was bound in the three fibersThe proportion is respectively 14.5%, 27.5% and 31.1%, and the modern characterization method proves that the fiber cavity and the fiber wall are porous and can absorb bound water, and the microstructures are beneficial to improving the hydrophilic performance of the hydrophilic material.

Drawings

FIG. 1 shows the infrared spectra of the raw material, the final product and the intermediate product, which are shown as a, PCL, b, PCL-OH, c, IPDI, d, WPU-NCO and e, PCL-b-WPU。

FIG. 2 shows PCL-bThe cross-sectional morphology of the WPU hollow fiber is a.2 percent and b.4 percent.

FIG. 3 shows PCL-bThe cross-sectional morphology of the WPU hollow fiber is a, 0.5mL/h, b, 0.8mL/h and c, 2 mL/h.

FIG. 4 shows PCL-containing materials under different core solventsbThe cross-sectional morphology of the WPU hollow fiber comprises a ultrapure water and b chloroform.

FIG. 5 is a scanning electron microscope image of three fibers, i.e., a solid fiber, b non-porous hollow fiber, and c porous hollow fiber.

FIG. 6 is a graph of solid fiber low-field nuclear magnetic detection spectrum (a, 2D) and a graph (b, 3D).

FIG. 7 is a drawing of a non-porous hollow fiber low-field nuclear magnetic detection spectrum, a, 2D, b, 3D.

FIG. 8 is a graph of porous hollow fiber low-field nuclear magnetic detection spectrum, which is shown in a figure, 2D and a graph b, 3D.

Detailed Description

Experimental Material

Injecting: a concave nozzle is adopted, the inner diameter of an inner needle is 0.34mm, the inner diameter of an outer needle is 0.84mm, the wall thickness is 0.1mm, and the inner needle is retracted by 0.5 mm. Experimental reagents and raw materials

And (3) testing by a Scanning Electron Microscope (SEM), putting the hollow fiber membrane with the same orientation into liquid nitrogen, soaking for 30min, cutting the hollow fiber membrane after the sample is completely frozen and crisp, and performing cross-sectional morphology testing. Section diameter, void size, etc. were analyzed using ImageJ software.

Nuclear magnetic resonance particle surface property analyzer (LF-NMR). In order to detect the state and distribution of moisture, a nuclear magnetic resonance particle surface characteristic analyzer was used for the test. Three fibrous membranes, 40 + -1 mg, cut into about 0.2X 0.5mm shreds, were individually placed in 2ml lidded clear sample vials without rubber ring pads and tested. When signals are collected, the testing conditions of all samples are ensured to be completely consistent. Correcting to enable the difference value of the maximum value of the two modes to be less than 1% so as to determine the repeated sampling waiting time; reasonable gains were set based on the results of the strongest and weakest hydrogen proton signals in the experiment. The test temperature was 32. + -. 0.01 ℃. Other test parameters are shown in table 1 below.

Synthesis example

Firstly, Polycaprolactone (PCL) is ammonolyzed and activated by 6-amino-1-hexanol, and hydroxyl (PCL-OH) is grafted to the end of the PCL chain, thereby improving the reactivity. Hydrophilic block copolymer PCL-bThe synthesis of the WPU takes isophorone diisocyanate (IPDI) and polyethylene glycol-400 (PEG-400) as raw materials, 2, 2-bis (hydroxymethyl) propionic acid (DMPA) as a small molecular hydrophilic chain extender, and gradually carries out addition polymerization under the catalysis of dibutyltin dilaurate (DBTDL) as a catalyst to prepare the isocyanate-terminated prepolymer with a certain molecular weight. Then, PCL-OH and the waterborne polyurethane prepolymer continue to carry out addition polymerization under the action of a catalyst to prepare the waterborne polyurethane hydrophilic block modified polycaprolactone (PCL-b-WPU）。

PCL (10.000 g) was dissolved in 200mL of ultra-dry 1, 4-dioxane at room temperature, 10.400g of 6-amino-1-hexanol was added, the air was exhausted under nitrogen protection, the temperature was raised to 37 ℃ and the reaction was carried out for 8 hours. After the reaction is finished, the reaction solution is absorbed into a large amount of deionized water, and a white flocculent solid product is separated out. Washing the obtained crude product in deionized water for 10min, repeating for 2 times, sucking water by using filter paper, and drying in a vacuum oven at 30 ℃ for 24h to obtain the final product PCL-OH.

0.292g (0.73 mmol) of polyethylene glycol-400 (PEG-400) was dissolved in 5.0mL of ultra-dry 1, 4-dioxane, 0.5 μ L (0.075%) of dibutyltin dilaurate (DBTDL) was added, the temperature was raised to 80 ℃, and under nitrogen protection, stirring was carried out for 1h to remove water. Then 0.267g (1.2 mmol, R = 1.2) of isophorone diisocyanate (IPDI) was added and dissolved sufficiently. Meanwhile, 0.036g (0.27 mmol) of dimethylolpropionic acid (DMPA) was weighed out and dissolved in a small amount of ultra-dry 1, 4-dioxane, added to the reaction system after complete dissolution, and reacted for 3h at 80 ℃. And after the reaction is finished, cooling to 50 ℃ to obtain the waterborne polyurethane end isocyanate prepolymer WPU-NCO, and directly using the waterborne polyurethane end isocyanate prepolymer WPU-NCO in the next reaction.

7.560g (22.690 g for theoretical amount when 0.134mmol, R =3, and R = 1) of PCL-OH was dissolved in 30.0mL of ultra-dry 1, 4-dioxane, and thoroughly mixed with the reaction solution obtained in the previous synthesis step. Adding a catalyst DBTDL (6.0 mu L, 0.075%) and reacting for 3h at 50 ℃ in a nitrogen atmosphere. Separating out a product in a large amount of deionized water after the reaction is finished, fully washing, absorbing water, and drying for 24h at the temperature of 30 ℃ to obtain the hydrophilic block copolymer PCL-b-WPU。

FIG. 1 shows PCL, PCL-OH, IPDI, WPU-NCO and PCL-b-infrared spectra of WPU. In the a and b curves, 2940 cm^-1，2864 cm^-1The peak shared by the two is the typical CH (-CH) on the PCL chain₂) Symmetrical telescopic vibration peaks; 1734 cm^-1Strong peak of stretching vibration absorption with ester group C = O^[24]；1293 cm^-1Is a C-C skeleton vibration peak; 1160 cm^-1An antisymmetric vibration peak at O-C (C); 1106 cm^-1Is represented by CH₂-O-CH₂Characteristic stretching vibration peak of (2). b at 3441cm^-1And 1635 cm^-1Unique characteristic peaks are respectively assigned to-OH and C-N stretching vibration peaks, which indicates that-OH active groups are successfully introduced into a PCL chain. Compared with c, the spectrum of d is 3346 cm^-1An N-H stretching vibration absorption peak appears; 2267 cm^-1The absorption peak of-NCO is clearly reduced. According to the literature^[25,26]The absorption of N-H in the infrared spectrum is mainly 3450 cm^-1Non-hydrogen bond shock absorption; 3290-3310 cm^-1The vibration absorption of hydrogen bonds formed between the carbon atoms and the C-O-C ether bond; and 3300-3350 cm^-1Vibration absorption with hydrogen bond formation with C = O. d is 3346 cm^-1A peak appeared at, and 2267 cm^-1The reduced spectral peaks indicate that-NH in the terminal isocyanate group waterborne polyurethane WPU-NCO is-N = C = O and-C = O forms hydrogen bond formation. Spectra c and d are 2957 cm respectively^-1、2922 cm^-1Peak at is-CH₂and-CH₃An absorption peak in which the stretching vibrations are superposed together; spectrum d at 1705 cm^-1Is a carbonyl C = O absorption peak attributed to a hydrogen-bonded polyether carbonyl peak in the carbamate group^[27]；1517 cm^-1、1454 cm^-1Bending vibration at N-H, stretching vibration at C-N and characteristic absorption mixed peak band at-COOH^[26](ii) a 1232. 1109, and 953 cm^-1Is a C-O-C stretching vibration peak; 872 cm^-1Is CH₂CH₂C-H plane rocking vibration peak of O^[28]. The above analysis results confirmed the successful synthesis of the intermediate WPU-NCO. Panel e at 3437cm compared to d^-1、3346 cm^-1And the peak of N-H spectrum appears at the position, and the peak is respectively assigned to non-hydrogen bond vibration absorption and vibration absorption peak forming hydrogen bond with C = O. In addition, research shows that the strength of hydrogen bonding of N-H in the waterborne polyurethane is weakened along with the increase of the soft segment content, so that the spectrogram e is at 3437cm^-1The peak at (a) may also be a shift caused by the introduction of the PCL soft segment in the aqueous polyurethane. Spectrum e at 1725 cm compared to a, b and d^-1the-C = O absorption peak at (B) becomes significantly stronger because of the assignment to the end product PCL-bThe mixed peaks of polyether carbonyl and polyester carbonyl in WPU, i.e. polyether carbonyl peak of hydrogen bonding in the carbamate group in the WPU segment, and polyester carbonyl peak in the PCL soft segment.

Gel Permeation Chromatography (GPC) was used to characterize the molecular weights and molecular weight distributions of the polymer and intermediates before and after modification, and the test results are shown in Table 2. During GPC, the polymer with relatively large molecular weight is excluded from the gel particles at the beginning of elution, resulting in short course and stagnationThe retention time is short; whereas polymers with a lower relative molecular mass will require longer elution times, i.e. longer residence times, due to their ability to diffuse into the interior of the particle. The retention times of PCL, PCL-OH and WPU-NCO in the column were tested at 12.817, 12.886 and 14.778 min, respectively, corresponding to number average molecular weights of 58317, 56735 and 12086, respectively, in accordance with the principle of GPC testing. Notably, modified PCL-bThe WPU has a longer retention time in the column than that of PCL, but the number average molecular weight is larger because the molecular weight distribution of the resulting block copolymer is broader, and the elution time of the component having a smaller molecular weight is longer, which results in a longer average retention time of the copolymer. As can be seen in Table 1, PCL-bWPU has a polydispersity index PDI of 1.790, greater than that of PCL of 1.563, showing a broader molecular weight distribution, consistent with the above analysis. Test of the end product PCL-bThe number average molecular weight of WPU was 80365, further indicating that the WPU chain was successfully incorporated into the PCL chain.

Thermal Gravimetric Analysis (TGA) is adopted to characterize the thermal stability of the polymer before and after the modification of the hydrophilic blockb-thermogravimetric curve of WPU. The initial decomposition temperature of the PCL is measured to be 340 ℃, the final decomposition temperature is 460 ℃, and the carbon residue rate is about 17%; PCL-modified blockbDue to the introduction of the waterborne polyurethane chain segment, the initial decomposition temperature of the WPU is reduced to 260 ℃, the final decomposition temperature is reduced to 360 ℃, and the carbon residue rate is 0%. This is because the urethane group in the aqueous polyurethane segment has a thermal decomposition temperature of about 250 ℃ and, upon thermal decomposition, the chemical bond of the group is first broken to gradually dissociate the entire molecular structure. TGA tests show that the heat resistance of the PCL is reduced by embedding the aqueous polyurethane in the PCL chain segment.

Preparing hollow hydrophilic fiber, wherein the shell layer is PCL-bWPU, polycaprolactone (PCL-b-WPU) solution preparation, solvent trichloromethane (CHCl)₃) AndN, N’-Dimethylformamide (DMF) as a mixed solvent（CHCl₃: DMF =4:1, volume ratio); the core layer is formed by polyethylene oxide (PEO) solutions with different concentrations (g/mL), and the solvents adopt ultrapure water and trichloromethane as single solvents respectively.

The preparation process of the spinning solution comprises the following steps: shell solution (PCL-b-WPU), stirring for 4h, performing ultrasonic treatment for 30min, and standing for 4h for defoaming. The core solution (PEO) was stirred for 12 hours and allowed to stand for 6 hours for defoaming. A homogeneous, foamless and transparent spinning dope is obtained.

During spinning, the prepared solution is sucked into an injector and is respectively conveyed to a core layer solution conveying pipe and a shell layer solution conveying pipe of a spray head through a propelling pump. Adjusting spinning technological parameters: core concentration, core solvent, core flow rate, take-up distance, etc., to receive the jet in a wound manner to produce a hollow fiber.

Example one

Shell solution: 22% PCL-bWPU solution with CHCl₃: 4:1, mixing a solvent; receiving distance is 16 cm; the shell flow rate is 0.6 mL/h; core solution, 2% PEO ultrapure water solution, core flow rate 0.2 mL/h; the winding speed is 100 mm/s; the voltage is 13 kV; the temperature is 16.8 ℃; the humidity was 45%. Thereby spinning the hollow fiber a.

Shell solution: 22% PCL-bWPU solution with CHCl₃: 4 of DMF: 1, mixing a solvent; receiving distance is 16 cm; the shell flow rate is 0.6 mL/h; core solution, 4% PEO ultrapure water solution, core flow rate 0.2 mL/h; the winding speed is 100 mm/s; the voltage is 7.55 kV; the temperature is 17.5 ℃; humidity was 36%. Thereby spinning the hollow fiber b.

As can be seen from the scanning electron microscope in FIG. 2, the cross section of the fiber a is nearly circular, and the cross section of the fiber b is nearly elliptical; and the fiber wall thickness of a is about 0.52 μm, and b is about 1.73 μm, the latter being thicker. The reason is that in the process that the jet flow is drawn by the electric field force, chloroform solvent of the shell layer is volatilized rapidly, a thin skin layer is formed on the surface firstly, then solvent water of the core layer is evaporated to form a hollow structure, and because the concentration of the solution b serving as the core solution is high, the amount of fluid drawn in unit time is more than that of the fluid a, after the solvent in the core solution is volatilized, the amount of PEO attached to the inner part of the shell layer is more, and the fiber wall is thicker; meanwhile, in the drying and forming process, the hollow fiber thin shell layer is subjected to the action of external atmospheric pressure and the gravity of the internal core layer, so that the section of the b is in an approximately oval shape, the diameter of the section of the fiber is increased to 24.42 mu m, and the development trend of ribbon-shaped fibers is realized. In addition, a small amount of nano-filaments exist in b, which affects the continuity of spinning and causes a phenomenon of 'flying filaments'.

Example two

Other spinning process parameters are fixed (shell solution: 24% PCL-bWPU solution with CHCl ₃4 of DMF: 1, mixing a solvent; core solution: 2% PEO ultrapure water solution; the flow rate of a shell layer is 0.6 mL/h; spinning voltage is 7.55 kv; the receiving distance is 20 cm; winding speed 100 mm/s), different hollow fibers a, b and c can be prepared by performing spinning tests with different core solution flow rates. The spinning conditions were as follows:

a: the flow rate of the core solution is 0.5ml/h; the temperature is 10.3 ℃, and the ambient humidity is 45%;

b: the flow rate of the core solution is 0.8ml/h; the temperature is 16.8 ℃; the ambient humidity is 25%;

c: the flow rate of the core solution is 2 ml/h; the temperature is 16.6 ℃, and the ambient humidity is 35%.

As can be seen in FIG. 3, the flow rate of the shell solution is unchanged, when the flow rate of the core solution is 0.5mL/h, the fiber-forming morphology is poor, flat ribbon-shaped fibers and cylindrical fibers coexist, and the peak value of the cross-sectional diameter of the cylindrical fibers is 18.86 μm; when the flow rate is 0.8mL/h, the fiber forming morphology is good, and the diameter peak value is 19.52 mu m; when the flow rate was increased to 2mL/h, it was found that the fibers no longer had a cylindrical shape but completely had a flat ribbon shape, and the wall of the layer was significantly thinned, with a peak in the cross-sectional diameter of the ribbon-shaped fiber of 34.71 μm. As the core flow rate increases, the fiber diameter tends to increase; and when the core flow rate is too high, a flat ribbon is formed.

EXAMPLE III

The core solvent properties are different, and the electrospinning is very different. Fixed spinning process parameters (shell solution: 22% PCL-bWPU solution with CHCl ₃4 of DMF: 1, mixing a solvent; the shell flow rate is 0.6 mL/h; the core flow rate is 0.2 mL/h; the spinning voltage is 13 kV; the receiving distance is 10.5 cm; the winding speed is 100mm/s, and the temperature is 17.0 +/-0.5 ℃; humidity of 40 +/-5%), preparing two groups of spinning solutions by adopting different core solvents for spinning tests, and carrying out other technological parameters:

solution a: the core solution was a 2.0% PEO ultrapure water solution;

solution b: the core solution was a 2.5% PEO in chloroform.

Thereby respectively spinning hollow fibers a and b (fig. 4). In FIG. 4a, when the core solvent is ultrapure water, the fiber has a non-porous hollow structure, a cavity diameter of 16.63 μm and a wall thickness of 1.37 μm, and a good hollow morphology can be obtained; when the core solvent is changed to chloroform, the graph b shows that a large number of tiny holes with different sizes are formed on the surface of the fiber and penetrate through the inner cavity of the fiber, meanwhile, the diameter of the cavity of the fiber is reduced to 6.11 mu m, the wall of the fiber is thickened to 1.56 mu m, so that the cavity is not obvious any more, and the phenomenon is shown that the size of the cavity is reduced, and the wall of the fiber is thickened.

Example four

Selecting three spinning processes to respectively prepare a solid fiber a, a non-porous hollow fiber b and a porous hollow fiber c, wherein the adopted specific process parameters are as follows:

solid fiber: uniaxial electrospinning with a concentration of 20% (PCL-b-WPU/CHCl₃) The flow rate is 0.5mL/h, the voltage is 12kV, and the receiving distance is 20 cm;

non-porous hollow fiber: coaxial electrostatic spinning with shell concentration of 22% (PCL-b-WPU / CHCl₃DMF =4: 1) (ii) a Core concentration 2% (PEO/ultrapure water); the shell flow rate is 0.6 mL/h; the core flow rate is 0.2 mL/h; the voltage is 13 kV; the receiving distance is 16 cm; the winding speed is 100 mm/s; the temperature is 17.0 +/-0.5 ℃; humidity is 40 +/-5%;

porous hollow fibers: coaxial electrostatic spinning with shell concentration of 22% (PCL-b-WPU / CHCl₃DMF =4: 1) (ii) a Core concentration 2.5% (PEO/chloroform); the shell flow rate is 0.6 mL/h; the core flow rate is 0.2 mL/h; the voltage is 7.5 kV; receiving distance is 11 cm; the winding speed is 100 mm/s; the temperature is 17.0 +/-0.5 ℃; humidity is 40 +/-5%.

FIG. 5 is a scanning electron micrograph of three fibers, wherein fiber a is a solid fiber and the surface morphology thereof is measured; b and c, testing the section appearance.

The transverse relaxation times of various water contents in the fiber were measured by using low-field nuclear magnetic resonance technique, as shown in fig. 6, 7 and 8. Each peak in the spectrogram represents different types of water, and the time corresponding to the peak top is the average relaxation time of the water in the state; the peak height is the relaxation signal intensity and reflects the hydrogen proton in the systemMass fraction of (a); the peak area corresponds to the moisture content in this state. In the excited state in the theory of nuclear magnetic resonance¹The process by which the magnetic moment of the H atom decays in the transverse plane is called transverse relaxation, with a corresponding relaxation time constant T₂The process is related to intermolecular, molecular-to-surface interactions within the fluid system. From the low-field NMR chart 6 of the solid fiber a, 3 peaks at different times are observed, and the relaxation time is defined as T in sequence₂₁（0.1～10ms）、T₂₂(10 to 100 ms) and T₂₃(100 to 1000 ms). Table 3 shows the test data of each water peak under different water addition amount, and it is found that as the water addition amount increases, the amounts of the bound water and the free water also increase, but the occupation ratios are similar. The average value of the ratio data of the free water under the condition of four different water adding amounts is about 85.5 percent, the capacity of the solid fiber for adsorbing the bound water can be calculated, and the ratio of the bound water is 14.5 percent.

FIG. 7 is a diagram showing a state where the hollow fibers adsorb moisture. Compared to solid fibers, hollow fibers show a new water peak at 10 ms. Since the hollow lumens also reduce water mobility when adsorbing water, the degree of freedom of bound water inside the lumens is lower than that of deep bound water outside the fibers and relatively free water. T is_2a(0.1-5 ms) is deep bonding water which is bonded by hydrophilic groups attached to the inner wall and the outer wall of the cavity and water through hydrogen bonding, and T in figure 6₂₁Peak ratio, T_2aThe peak shifts to the left and the peak area becomes larger, confirming that the part is more tightly combined with water and has lower degree of freedom; t is_2b(5-50 ms) is water with relatively high degree of freedom attached to the interior of the cavity and attached to the exterior of the deep bonding water, and is a new peak generated due to the existence of a hollow system; t is_2c(50-200 ms) is relatively free water attached to the outside of the fiber; t is a unit of_2d(200-1000 ms) is free water with the highest degree of freedom. Table 4 shows the peak data at different water addition levels of the hollow fiber, T at 40. mu.L and 60. mu.L_2c、T_2dThe water peaks are overlapped and can not be accurately obtainedFree water ratio, but T is found_2cAnd T_2dThe total proportion of (a) is still lower than the free water proportion of the solid fibers, indicating that the hollow fibers can adsorb more water than the solid fibers. The average of the ratio data of free water at 80. mu.L and 100. mu.L was taken to be about 72.5%, and the capacity of the hollow fiber to adsorb bound water was estimated to be 27.5%.

Fig. 8 is a distribution diagram of the moisture state of the porous hollow fiber, and it is observed that when a large number of micropores are formed in the shell layer of the hollow fiber, the peaks of water adsorbed in different adsorption states are mostly overlapped, and no single peak is present. According to the scanning electron microscope image of fig. 5(c), it is found that the porous hollow fibers are filled with pores of different sizes, nanometer-scale, micron-scale, and pores between nanometer-scale and micron-scale, and the pores are communicated with each other due to the existence of hollow cavities. In the figure, T is shown in the spectrum when 80. mu.L and 100. mu.L of water are added_2IThe short relaxation time peak between (0.1-1 ms) corresponds to the water in the nanoscale pores, and belongs to 'in-pore coupling'. The peaks were not observed in the spectra corresponding to 40. mu.L and 60. mu.L of water, and the analysis was not possible because the amount of water was too small and the signal value was too weak. T is_2Ⅱ、T_3Ⅲ、T_2ⅣMultiple continuous overlapping peaks appear between 1-100 ms, which belongs to 'coupling between pores', and reflects that the porous fiber has better communication among pores. T is_2ⅤIs free water in the system. Table 5 shows the peak data of the non-porous hollow fiber under different water addition conditions, and the average value of the ratio data of free water at 60 μ L, 80 μ L and 100 μ L is about 68.9%, so that the capacity of the porous hollow fiber for adsorbing bound water is 31.1%, and the water adsorption capacity is significantly improved, indicating that the fiber wall is porous and can also adsorb bound water, which is beneficial to improving the hydrophilic performance.

Table 6 shows the bound water ratio data of the solid fiber, the hollow fiber (shell layer without pores), and the porous hollow fiber under different water addition amounts, where the bound water amounts are 14.7%, 27.5%, and 31.1%, respectively. This shows that the formation of cavities or micro-porous structures on the fibers is beneficial to adsorbing more bound water, thereby improving the hydrophilic performance.

Claims

1. The hydrophilic block modified polycaprolactone electrostatic spinning fiber is characterized by having a hollow structure and a shell layer of PCL-b-WPU。

2. The hydrophilic block modified polycaprolactone electrospun fiber according to claim 1, wherein the wall thickness is 1-2 μm.

3. The hydrophilic block-modified polycaprolactone electrospun fiber according to claim 1, characterized in that isophorone diisocyanate and polyethylene glycol are used as raw materials, 2, 2-bis (hydroxymethyl) propionic acid is used as a small molecular chain extender, and the isocyanate-terminated prepolymer is prepared by addition polymerization under the catalysis of an organic tin catalyst; then PCL-OH and the isocyanate-terminated prepolymer are subjected to addition reaction under the action of a catalyst to prepare PCL-b-WPU.

4. The hydrophilic block modified polycaprolactone electrospun fiber according to claim 3, wherein the molar ratio of isophorone diisocyanate, polyethylene glycol, 2-bis (hydroxymethyl) propionic acid and PCL-OH is 1.2: 0.7-0.75: 0.25-0.3: 0.13-0.135.

5. The method for preparing the hydrophilic block modified polycaprolactone electrospun fiber as claimed in claim 1, wherein PCL-bThe WPU solution and the PEO solution are respectively used as a shell solution and a core solution, and the hollow fiber is prepared by coaxial electrospinning and is a hydrophilic block modified polycaprolactone electrospun fiber.

6. The method for preparing the hydrophilic block modified polycaprolactone electrospun fiber according to claim 5, wherein PCL-bIn WPU solution, the solvent is CHCl₃And/or DMF at a concentration of 15-30%.

7. The method for preparing the hydrophilic block modified polycaprolactone electrospun fiber according to claim 5, wherein the solvent in the PEO solution is water or CHCl₃The concentration is 1.5-5%.

8. The preparation method of the hydrophilic block modified polycaprolactone electrospun fiber according to claim 5, characterized in that the flow rate of the shell solution is 0.5-0.8 mL/h during coaxial electrospinning; the flow rate of the core solution is 0.1-0.3 ml/h.

9. The application of the hydrophilic block modified polycaprolactone in the preparation of the hollow electrostatic spinning fiber is characterized in that isophorone diisocyanate and polyethylene glycol are used as raw materials, 2, 2-bis (hydroxymethyl) propionic acid is used as a micromolecule chain extender, and the isocyanate-terminated prepolymer is prepared by addition polymerization under the catalysis of an organic tin catalyst; then PCL-OH and the isocyanate-terminated prepolymer are subjected to addition reaction under the action of a catalyst to prepare the hydrophilic block modified polycaprolactone.

10. Use of the hydrophilic block modified polycaprolactone electrospun fiber of claim 1 in the preparation of a hydrophilic material.