Hydrophilic polyurethane nanofiber and method for manufacturing same

Abstract

The present disclosure is to provide a method for producing polyurethane (PU) nanofibers with significantly improved hydrophilicity by producing water-soluble polymer/PU blend nanofiber by coaxial-electrospinning water-soluble polymer and hydrophobic PU, and, subsequently, dissolving and removing the water-soluble polymer from the blend nanofiber in water.

Claims

1. A method for producing a polyurethane nanofiber having hydrophilic and water-absorptive properties from a hydrophobic polyurethane, the method comprising: providing a polyvinyl alcohol (PVA) solution comprising a PVA dissolved in water; providing a hydrophobic polyurethane solution comprising a hydrophobic polyurethane dissolved in organic solvent; injecting the PVA solution and the hydrophobic polyurethane solution into an inner nozzle and an outer nozzle for coaxial-electrospinning, respectively, and, performing coaxial-electrospinning to produce a coaxial-electrospun nanofiber comprising the PVA and the hydrophobic polyurethane; and hydrothermally-treating the coaxial-electrospun nanofiber to remove the PVA therefrom and to produce the polyurethane nanofiber having hydrophilic and water-absorptive properties, wherein the produced polyurethane nanofiber has a lower water contact angle and higher water absorption when compared with the coaxial-electrospun nanofiber prior to hydrothermal treatment.

2. The method of claim 1, wherein the organic solvent includes at least one organic solvent selected from a group consisting of DMF, DMAc, MEK, and THF.

3. The method of claim 1, wherein the hydrothermal treatment is hydrothermal treatment using distilled water at 0 to 100 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of a coaxial-electrospinning process for producing PVA/PU blend nanofiber in accordance with the present disclosure.

(2) FIG. 2 shows scanning electron microscope (SEM) photographs (a) and (b) of PVA nanofiber and PU nanofiber respectively.

(3) FIG. 3 is a SEM image of PVA/PU blend nanofiber.

(4) FIG. 4 shows SEM images (a) and (b) of hydrothermal-treated PU and hydrothermal-treated PVA/PU blend nanofiber respectively.

(5) FIG. 5 shows: (a) indicates a result of infrared (IR) spectroscopic analysis of PU nanofiber before hydrothermal treatment and (b) indicate a result of infrared (IR) spectroscopic analysis of PU nanofiber after hydrothermal treatment; (c) indicate a result of Infrared (IR) spectroscopic analysis of PVA/PU blend nanofiber before hydrothermal treatment, and (d) indicates a result of infrared (IR) spectroscopic analysis of PVA/PU blend nanofiber after hydrothermal treatment.

(6) FIG. 6 shows: (a) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PU nanofiber before hydrothermal treatment; (b) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PU nanofiber after hydrothermal treatment; (c) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PVA/PU blend nanofiber before hydrothermal treatment; (d) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PVA/PU blend nanofiber after hydrothermal treatment.

(7) FIGS. 7a and 7b show an image of a contact angle of PU and PVA/PU blend nanofibers respectively.

(8) FIG. 8 shows contact angle measurement results of PU and PVA/PU blend nanofibers over time.

DETAILED DESCRIPTIONS

(9) Examples of various embodiments are illustrated and described further below. It will be understood that the description herein is not intended to limit the claims to the specific embodiments described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims. The same reference numbers in different figures denote the same or similar elements, and as such perform similar functionality.

(10) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms a and an are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and including when used in this specification, specify the presence of the stated features, integers, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components, and/or portions thereof. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. Expression such as at least one of when preceding a list of elements may modify the entire list of elements and may not modify the individual elements of the list.

(11) Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(12) The PVA/PU blend nanofiber was produced by coaxial-electrospinning a variety of water-soluble polymer solutions including PVA, which is the most representative water-soluble polymer, and PU solutions dissolved in organic solvents. Then, the resulting PVA/PU blend nanofiber is hydrothermally treated to remove the PVA. This allows the applicants to produce PU nanofibers with improved hydrophilicity.

(13) Accordingly, in accordance with the present disclosure, a method for producing a PU nanofiber with improved hydrophilicity, which comprises the following steps:

(14) (a) producing PVA electrospinning solution by dissolving water-soluble polymer containing PVA in distilled water;

(15) (b) dissolving PU in an organic solvent to produce a PU electrospinning solution;

(16) (c) inserting the water-soluble polymer electrospinning solution and the PU electrospinning solution into first and second syringes respectively;

(17) (d) applying a voltage to electrodes connected to the first and second syringes respectively, discharging and coaxial-electrospinning the water-soluble polymer and the PU solution using a dual coaxial-nozzle to form a water-soluble polymer/PU nanofiber;

(18) (e) dissolving and removing the water-soluble polymer component in the water-soluble polymer/PU nanofiber in water; and

(19) (f) vacuum-drying the PU nanofiber with water-soluble polymer removed.

(20) In the step (a), the water-soluble polymer may be a synthetic polymer such as PVA, PVP, PEO, PAA and PSA; cellulose derivatives including CMC; SA, CS and derivatives thereof; polysaccharide-based polymers such as pullulan and starch; protein-based polymers such as gelatin and collagen; or a mixture thereof.

(21) In the step (b), the organic solvent may be a mixed solvent containing one or more organic solvents selected from the group consisting of DMF, DMAc, MEK, and THF.

(22) In the step (d), the applied voltage may be 1 kV to 100 kV, and the ejection speed may be adjusted according to the type of the polymer and the difference in voltage applied to the electrode.

(23) In step (e), removal of the water-soluble polymer by hydrothermal treatment may be performed in distilled water at 0 to 100 C. The present disclosure is not limited to these temperatures. Other temperatures that may remove water-soluble polymers are also available.

(24) In accordance with one embodiment of the present disclosure, coaxial-electrospinning of the water-soluble polymer PVA and polar organic solvent-soluble PU was performed to produce a PVA/PU blend nanofiber. The resulting PVA/PU blend nanofiber was subjected to hydrothermal treatment to remove PVA to produce the PU nanofiber. Changes in the hydrophilicity of these intermediate and final products were determined by measuring the structure, component properties, and contact angle thereof.

(25) As a result of observing SEMs of nanofibers resulting from spinning of PVA and PU solution, and the PVA/PU blend nanofiber, PVA and PU nanofibers were found to have a diameter of several hundred nanometers and uniform thickness in the optimal electrospinning condition. The diameter of PVA/PU blend nanofiber increased. Further, removal of the water-soluble PVA via hydrothermal treatment reduces the contact angle of the resulting PU nanofiber, and, thus, it rapidly absorbs water over time

(26) Hereinafter, the present disclosure is described in more detail in the following examples, which are merely illustrative of the content of the present disclosure and are not intended to limit the technical scope of the present disclosure.

Example 1

(27) PVA Nanofiber Production by Electrospinning

(28) PVA (Mw 88,000, 99+% hydrolyzed, OCI, Korea) was injected into distilled water at 10% (w/v) to form a first solution. The first solution was stirred at 80 degree C. for 4 hours to completely dissolve the PVA to produce a PVA electrospinning solution. The PVA electrospinning solution was subjected to electrospinning at a voltage of 12 kV, a distance of 15 cm, and a discharge rate of 0.2 ml/h to produce a PVA nanofiber.

Example 2

(29) PU Nanofiber Production by Electrospinning

(30) PU (polyester-based thermoplastic polyurethane, Lubrizol, USA) was injected into DMF at 13 wt % to form a second solution. The second solution was stirred at room temperature for 4 hours to completely dissolve the PU to form PU electrospinning solution, which, in turn, was subjected to electrospinning at a voltage of 12 kV, a distance of 15 cm and a discharge rate of 0.3 ml/h to produce PU nanofiber.

Example 3

(31) Hydrothermal-Treated PU Nanofiber Production

(32) The PU nanofiber produced in example 2 was placed in tertiary distilled water at 80 C. and the distilled water was slowly stirred for 24 hours. The distilled water was vacuum-dried at room temperature for 24 hours to produce hydrothermal-treated PU nanofiber.

Example 4

(33) Production of PVA/PU blend nanofiber by coaxial-electrospinning

(34) PVA electrospinning solution was prepared by dissolving PVA (Mw 88,000, 99+% hydrolyzed, OCI, Korea) in distilled water at 10% (w/v). Then, PU (polyester-based thermoplastic polyurethane, Lubrizol, USA) was added to DMF at 13 wt %, and DMF was stirred at room temperature for 4 hours to completely dissolve PU to produce PU electrospinning solution. Then, the two spinning solutions produced above were subjected to coaxial-electrospinning to produce a PVA/PU blend nanofiber (see FIG. 1). In this connection, the coaxial-electrospinning was executed under the conditions of a voltage of 20 kV, a distance of 15 cm, a discharge rate of PVA (core) of 0.2 ml/h and a discharge rate of PU (shell) of 0.3 ml/h.

Example 5

(35) Hydrothermal-Treated PVA/PU Nanofiber Production

(36) The PVA/PU blend nanofiber produced in Example 4 was placed in a third distilled water at 80 C. and the distilled water was slowly stirred for 24 hours. Then, the solution was vacuum-dried at room temperature for 24 hours. This yielded hydrothermal-treated PVA/PU nanofiber.

(37) Morphological Observation

(38) Platinum was coated on the nanofiber produced by the above method. The external morphological structure of the coated nanofibers was observed using SEM. FIGS. 2 (a) and (b) are SEM images of PU nanofibers of PVA nanofibers, respectively. FIG. 3 is a SEM image of a PVA/PU blend nanofiber. The thickness of the PVA/PU blend nanofiber was slightly increased when comparing the SEM photographs of PVA nanofiber and PU nanofiber with the SEM photograph of PVA/PU blend nanofiber.

(39) FIG. 4 shows SEM images (a) and (b) of hydrothermal-treated PU and hydrothermal-treated PVA/PU blend nanofiber respectively. In this connection, the nanofibers were hydrothermal-treated in distilled water at 80 C. for 24 hours and dried in a vacuum for 12 hours. There was no significant change in fiber thickness before and after hydrothermal treatment. Curling is generally exhibited. This is probably due to the removal of residual solvent and PVA component during hydrothermal treatment, and the heat shrinkage of PU by heating.

(40) These results suggest that hydrothermal treatment of PU nanofibers and PVA/PU blend nanofibers may lead to nanostructure changes in the nanofiber, and the degree of the change is considered to be larger in the PVA/PU blend nanofiber due to the fact that the residual solvent and PVA with high molecular weight are simultaneously released therefrom.

(41) IR Spectroscopy Results

(42) IR spectroscopy was performed to analyze the compositions of PU nanofiber and PVA/PU blend nanofiber. FIG. 5 shows: (a) indicates a result of infrared (IR) spectroscopic analysis of PU nanofiber before hydrothermal treatment and (b) indicate a result of infrared (IR) spectroscopic analysis of PU nanofiber after hydrothermal treatment; (c) indicate a result of Infrared (IR) spectroscopic analysis of PVA/PU blend nanofiber before hydrothermal treatment, and (d) indicates a result of infrared (IR) spectroscopic analysis of PVA/PU blend nanofiber after hydrothermal treatment. PU nanofiber showed PU characteristic absorption peaks at 3400 to 3200 cm.sup.1 and at 1800 to 1630 cm.sup.1, and no peak change due to absence or presence of hydrothermal treatment was observed. In the case of PVA/PU blend nanofiber, a strong characteristic absorption peak of OH group was observed at 3650 to 3000 cm.sup.1 together with PU characteristic absorption peak due to the influence of PVA, but this strong characteristic absorption peak disappeared after hydrothermal treatment. This may confirm that PVA was removed and only PU remained via the hydrothermal treatment.

(43) 13.sup.C-Solid NMR Spectroscopy Results

(44) 13.sup.C-solid NMR spectroscopy was performed for the analysis of PU nanofiber and PVA/PU blend nanofiber components. FIG. 6 shows: (a) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PU nanofiber before hydrothermal treatment; (b) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PU nanofiber after hydrothermal treatment; (c) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PVA/PU blend nanofiber before hydrothermal treatment; (d) indicates a result of 13.sup.C-solid nuclear magnetic resonance (13.sup.C-solid NMR) spectroscopic analysis of PVA/PU blend nanofiber after hydrothermal treatment. In FIG. 6, PU characteristic peaks could be found at 24-41 ppm, 65 ppm, 120-136 ppm, 154 ppm before and after hydrothermal treatment of the PU nanofiber. Before the hydrothermal treatment of the PVA/PU blend nanofiber, PVA characteristic peaks could be observed at around 45 ppm and 70 ppm. After hydrothermal treatment of PVA/PU blend nanofiber, PVA characteristic peaks were not observed at around 45 ppm and 70 ppm. This could confirm that PVA was removed and only PU remained.

(45) Contact Angle Measurement Result

(46) In order to evaluate the hydrophilicity of PU nanofiber and PVA/PU nanofiber, the contact angle between water and nano-web surface was measured at temperature 21 C. and humidity 25%20 using a contact angle measurement device.

(47) In the case of a pure PVA nanofiber, upon contact with moisture, the PVA nanofiber dissolves. Therefore, the angel was not measured. FIG. 7(a) shows the contact angle of PU nanofiber before hydrothermal treatment. The initial contact angle was 133.1, and after 5 minutes, the contact angle was 130.4. After hydrothermal-treatment, the initial contact angle of the PU nanofiber was 126, and after 5 minutes, it showed a contact angle of 78.2. FIG. 7(b) shows the contact angle of PVA/PU blend nanofiber before hydrothermal treatment. The initial contact angle was 109.8, and after 5 minutes, it was 19.8. In the PVA/PU blend nanofiber after hydrothermal-treatment, the initial contact angle was 82.0 and the water was fully absorbed into the fiber before 30 seconds passed. Therefore, the contact value was no longer measured.

(48) The hydrothermal treatment of the PU nanofiber is thought to result in a fine pore in the nanofiber due to the removal of the residual solvent and an increase in water absorption due to the capillary phenomenon. In the case of PVA/PU blend nanofiber, the contact angle was greatly reduced due to the presence of water-soluble polymer PVA. As may be seen in FIG. 8, the rapid decrease in contact angle due to the dissolution of PVA as a water-soluble polymer is observed, and the decrease in the contact angle may be observed to slow down after a certain amount of PVA has been dissolved.

(49) In the case of the hydrothermal-treated PVA/PU blend nanofiber, the PVA was removed and only the PU remained, but the initial contact angle was lowest and the absorption rate was the fastest so that the water was completely absorbed before 30 seconds. Thus, the measurement of the contact angle was not performed. This is thought to be due to the greatest increase in water uptake due to increased micro-space generation and associated capillary phenomena due to the removal of PVA and residual solvent via the hydrothermal treatment.

(50) Blending a hydrophilic polymer PU with a water-soluble polymer such as PVA incompatible with the PU via the coaxial-electrospinning is a modification method that may impart hydrophilicity. However, when the nanofiber is used as water treatment, plasma filters or wetting wound dressings, the water-soluble polymer components are dissolved and absorbed into the treatment liquid, blood, and skin, resulting in side effects. In order to prevent this situation, an insolubilization process of water-soluble polymer such as crosslinking or crystallization may additionally required.

(51) According to the present disclosure, water-soluble polymers blended with PU are removed exclusively by dissolving in water, resulting in physical changes within the nanofiber, resulting in a superior hydrophilicity compared to the case in which the water-soluble polymer remains, thereby to bring about an improvement in hydrophilicity.

(52) The foregoing description of the preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.