WO2022174502A1 - 一种各向异性纤维素基水凝胶制备方法 - Google Patents

一种各向异性纤维素基水凝胶制备方法 Download PDF

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WO2022174502A1
WO2022174502A1 PCT/CN2021/085390 CN2021085390W WO2022174502A1 WO 2022174502 A1 WO2022174502 A1 WO 2022174502A1 CN 2021085390 W CN2021085390 W CN 2021085390W WO 2022174502 A1 WO2022174502 A1 WO 2022174502A1
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cellulose
dopamine
nanosheets
hydrogel
reaction
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French (fr)
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曾宪海
闫贵花
林鹿
孙勇
唐兴
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厦门大学
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Priority to US18/236,549 priority Critical patent/US11987674B2/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
    • C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
    • C08J3/075—Macromolecular gels
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
    • C08B15/05—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur
    • C08B15/06—Derivatives containing elements other than carbon, hydrogen, oxygen, halogens or sulfur containing nitrogen, e.g. carbamates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
    • C08F251/02—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof on to cellulose or derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2351/00—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers
    • C08J2351/02—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers grafted on to polysaccharides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2265—Oxides; Hydroxides of metals of iron
    • C08K2003/2275—Ferroso-ferric oxide (Fe3O4)
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/01—Magnetic additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/011—Nanostructured additives

Definitions

  • the invention belongs to the field of natural polymer materials, in particular to a preparation method of anisotropic cellulose-based hydrogel.
  • Water-rich hydrogel soft structures are similar to biological systems and have wide applications in biomaterials, wearable devices, chemical engineering, and other fields. It is worth noting that the biological tissue of an organism presents a highly ordered composite structure, and thus can withstand large external forces.
  • hydrogels with high anisotropy have received widespread attention in the application of soft materials.
  • most of the synthesized hydrogels exhibit isotropic structures due to disordered cross-linking of monomers. Therefore, it is of great significance to obtain anisotropic hydrogels with good mechanical properties.
  • Fe 3 O 4 nanoparticles loaded on the polymer surface has caused the problem of reduced conductivity (S. Garcia-Jimeno, J. Estelrich, Colloid. Surface. A. 2013, 420, 74-81.).
  • the existing carriers are mostly nanoparticles or nanowires, and the anisotropic structural strength of the formed hydrogel still needs to be improved.
  • the Fe3O4 nanoparticles are easy to aggregate, the nanoparticles are larger, and the nanoparticles are easy to fall off the carrier
  • Oxidation of cellulose by sodium periodate is a traditional method of modifying cellulose.
  • the morphology of cellulose derivatives obtained by different oxidation degrees and different ways of dissolving in water has great changes.
  • the dialdehyde-based cellulose obtained after cellulose is completely oxidized and dissolved in water exhibits a two-dimensional sheet-like morphology with a size ranging from several hundred nanometers to several micrometers, which has become the exploration of Fe3O4 nanoparticle carriers . Target.
  • the purpose of the present invention is to overcome the defects of the prior art.
  • the inventors adopt a cellulose modification method to make cellulose a structure rich in phenolic hydroxyl groups on the surface, and thus attract Fe 3 O 4 nanoparticles to deposit on its surface to form magnetic fibers
  • the Fe 3 O 4 nanoparticles were fixed on the surface of the cellulose-based nanosheets, which effectively prevented the aggregation of the nanoparticles.
  • the design of the cellulose-based nanosheet of the present invention makes the covalent bond formed by the gel polymerization more firm, and realizes the anisotropy, high strength, conductivity, viscosity and viscosity of the hydrogel. The multiple advantages of attachment.
  • the invention provides a preparation method of anisotropic cellulose-based hydrogel, comprising the following steps:
  • dialdehyde cellulose obtained by oxidizing cellulose with sodium periodate
  • the magnetic cellulose-dopamine nanosheets are formed into hydrogels by a simple polymerization method.
  • step (1) cellulose and sodium periodate are fully mixed in a water system, stirred in the dark, and then washed with deionized water and dialyzed to obtain dialdehyde cellulose; the obtained dialdehyde cellulose is heated Dissolved in water to obtain an aqueous solution of dialdehyde cellulose;
  • the dialdehyde cellulose obtained in the step (1) is fully mixed with NH 3 ⁇ H 2 O and methanol; in the reactor, the reaction is heated under pressure with a catalyst and H 2 to obtain the ammoniation The cellulose derivative; wherein the catalyst is selected from iron, cobalt, nickel-based catalyst, Ru/C, Pd/C catalyst. More preferably, the H 2 pressure in the heating reaction is >2.0MPa (preferably 2-3MPa), the reaction temperature is 100-150°C (preferably 120°C), and the reaction time is >2h (preferably 3-5h).
  • the cellulose-dopamine nanosheets obtained in step (3) are dispersed in a mixed solution of water and methanol, and after stirring, a mixture containing FeCl 2 ⁇ 4H 2 O and FeCl 3 ⁇ 6H 2 O is added Then, NH 3 ⁇ H 2 O was added and heated for reaction ; the magnetic cellulose-dopamine nanosheets were obtained by centrifugation and washing; more preferably, the cellulose-dopamine nanosheets were dispersed with water and methanol
  • step (5) acryl monomer, N,N-methylenebisacrylamide, tetramethylethylenediamine, an initiator and the magnetic cellulose-dopamine nanometer obtained in step (4) are combined After the mixed solution is stirred, it is poured into the mold, and after the polymerization is completed, the cellulose-based hydrogel is obtained.
  • the propylene-based monomer is acrylamide or acrylic acid; the initiator is ammonium persulfate or potassium persulfate; the standing temperature is 60-70° C., and the standing time is 1-3 h.
  • the beneficial effects of the present invention are: the cellulose used in the present invention is cheap and easy to obtain, is a wide range of renewable biomass energy sources in nature, and greatly reduces the cost of raw materials; the surface of the cellulose-based nanosheets prepared by the present invention has more Compared with the common nanoparticle and nanowire carrier, the design of the present invention makes the covalent bond formed by gel polymerization stronger. Finally, the hydrogel obtained by the present invention has multiple advantages of anisotropy, high strength, conductivity and adhesion, and has extremely high development potential.
  • FIG. 2 TEM image of the cellulose-based magnetic nanosheets obtained in Example 1. The figure on the right shows that Fe 3 O 4 magnetic nanoparticles are supported on the sheet-like carrier.
  • Figure 3 PFeDAC magnetic nanosheets prepared in Example 1 have good stability in water (left) and magnetic properties (right)
  • Figure 4 Schematic diagram of the formation principle of the hydrogel.
  • FIG. 5 is a graph of the adhesion/stretching results of the hydrogel prepared in Example 1. Among them, the content of PFeDAC magnetic hybrid in each hydrogel is 8wt%.
  • Fig. 6 Compression experiments of the prepared hydrogels. Among them, the content of PFeDAC magnetic hybrid in each hydrogel is 8wt%.
  • the hydrogels prepared in Figure 7 have good adhesion properties to various substrates. Among them, iron sheet (56kPa), glass (48kPa), stainless steel (53kPa), rubber (31kPa), wood (13kPa), PTFE (39kPa), plastic (17kPa), paper (11kPa), skin (63kPa) ).
  • the content of PFeDAC magnetic hybrid in each hydrogel is 8 wt%.
  • FIG. 8 Tensile stress-strain curves of the hydrogel prepared in Example 1 under three different directions of force.
  • the three hydrogels include: (*) represents the hydrogel prepared without the force of the magnetic field, which is isotropic and the force in all directions is the same; (//) represents the force parallel to the force in the direction of the magnetic field; ( ⁇ ) means that the force is perpendicular to the direction of the magnetic field.
  • the content of PFeDAC magnetic hybrid in each hydrogel is 8 wt%.
  • Fig. 9 Compressive stress-strain curves of hydrogels under three different directions of force.
  • the three hydrogels include: (*) represents the hydrogel prepared without the force of the magnetic field, which is isotropic and the force in all directions is the same; (//) represents the force parallel to the force in the direction of the magnetic field; ( ⁇ ) means that the force is perpendicular to the direction of the magnetic field.
  • the content of PFeDAC magnetic hybrid in each hydrogel is 8 wt%.
  • Fig. 10 Tensile stress-strain curve of the hydrogel prepared in Example 1 in a loading-unloading cycle. Among them, the force is parallel to the direction of the magnetic field, and the content of the PFeDAC magnetic hybrid in the hydrogel is 8 wt%.
  • step (2) The dialdehyde cellulose (10 g) obtained in step (1) was centrifuged to remove moisture, and then thoroughly mixed with NH 3 ⁇ H 2 O (6 mL) and methanol (30 mL). A 100 mL reaction kettle was used to react at 100 °C for 2 h under Ru/C catalyst (0.1 g) and 2 MPa H 2 pressure to obtain an ammoniated cellulose derivative.
  • step (4) Coating acrylamide (2.6 g), N,N-methylenebisacrylamide (0.026 g), tetramethylethylenediamine (15 ⁇ L), ammonium persulfate (0.03) and the result of step (4) with Cellulose-based nanosheets of magnetic Fe 3 O 4 nanoparticles (0.052 g), the mixture was stirred and poured into a mold; then the mold was placed at 60° C. for 3 hours to polymerize, and a cellulose-based hydrogel was obtained.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.22 MPa, which is 1.7 times that of the randomly oriented hydrogel; the electrical conductivity is 41 S m -1 ; the adhesion to the skin can reach 63 kPa.
  • more conventional methods are used (refer to K.Liu, L.Han, P.Tang, K.Yang, D.Gan, X.Wang, K.Wang, F.Ren, L.Fan, Y. . Xu, Z. Lu, X. Lu, Nano Lett. 2019, 19, 8343-83.
  • Figure 4 shows a schematic diagram of the formation principle of the hydrogel.
  • the magnetic nanosheets are in a disordered state; when the power is turned on, the magnetic nanosheets are arranged along the direction of the magnetic field under the action of the magnetic field, forming an ordered anisotropic structure.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction time in step (2) is 3h.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, the difference is that the amount of dopamine added in step (3) is 0.03 g, and the reaction pH is 8.2.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction after adding 0.1 mL of 28% NH 3 ⁇ H 2 O in step (4) is 80° C., 5 h.
  • step (5) The operation of step (5) is carried out with reference to the corresponding steps in the first embodiment, the difference is that the amount of the magnetic hybrid added in step (5) is 0.026g. Under these conditions, the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.19MPa, which is 1.5 times that of the randomly oriented hydrogel; the electrical conductivity is 37S m -1 ; the adhesion to the skin can reach 54kPa.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the H 2 pressure in the reaction in step (2) is 3MPa.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, the difference is that the amount of dopamine added in step (3) is 0.03 g, and the reaction pH is 8.5.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, except that the reaction after adding 0.1 mL of 28% NH 3 ⁇ H 2 O in step (4) is 90° C., 1 h.
  • step (5) The operation of step (5) is carried out with reference to the corresponding steps in the first embodiment, the difference is that the amount of the magnetic hybrid added in step (5) is 0.1 g. Under these conditions, the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.3 MPa, which is 2.3 times that of the randomly oriented hydrogel; the electrical conductivity is 45 S m-1; and the adhesion to the skin can reach 66 kPa.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction temperature in step (2) is 110°C.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction pH in step (3) is 9.0.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction after adding 0.1 mL of 28% NH 3 ⁇ H 2 O in step (4) is 80° C., 3 h.
  • step (5) The operation of step (5) is performed with reference to the corresponding steps in the first embodiment.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.20 MPa, which is 1.5 times that of the randomly oriented hydrogel;
  • the electrical conductivity is 39 S m-1; and the adhesion to the skin can reach 58 kPa.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction temperature in step (2) is 140°C.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, except that the amount of dopamine added in step (3) is 0.03 g, and the reaction pH is 8.0.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that in step (4), 20 mL of mixed solution of 3 mg FeCl 2 ⁇ 4H 2 O and 8 mg FeCl 3 ⁇ 6H 2 O is added, and in N 2 under the protection of stirring for 3 h; the reaction after adding 0.1 mL of 28% NH 3 ⁇ H 2 O was 90° C. for 3 h.
  • step (5) The operation of step (5) is performed with reference to the corresponding steps in the first embodiment.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.15 MPa, which is 1.2 times that of the randomly oriented hydrogel;
  • the electrical conductivity is 35 S m-1; and the adhesion to the skin can reach 57 kPa.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the amount of Pd/C catalyst in the reaction in step (2) is 0.2 g.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction pH in step (3) is 8.2.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that in step (4), 20 mL of mixed solution of 3 mg FeCl 2 ⁇ 4H 2 O and 3 mg FeCl 3 ⁇ 6H 2 O is added, and in N 2 under the protection of stirring for 3 h; the reaction after adding 0.1 mL of 28% NH 3 ⁇ H 2 O was 80° C. for 5 h.
  • step (5) The operation of step (5) is performed with reference to the corresponding steps in the first embodiment.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.14 MPa, which is 1.1 times that of the randomly oriented hydrogel;
  • the electrical conductivity is 31 S m-1; and the adhesion to the skin can reach 47 kPa.
  • step (2) The operation of step (2) is performed with reference to the corresponding steps in the first embodiment.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, the difference is that the reaction pH in step (3) is 9.0.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that in step (4), 20 mL of mixed solution of 3 mg FeCl 2 ⁇ 4H 2 O and 5 mg FeCl 3 ⁇ 6H 2 O is added, and in N 2 under the protection of stirring for 3h.
  • step (5) The operation of step (5) is performed with reference to the corresponding steps in the first embodiment.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.24 MPa, which is 1.9 times that of the randomly oriented hydrogel;
  • the electrical conductivity is 48 S m-1; and the adhesion to the skin can reach 67 kPa.
  • step (2) The operation of step (2) is carried out with reference to the corresponding steps in Example 1, the difference is that the amount of Pd/C catalyst in the reaction in step (2) is 0.2 g.
  • step (3) The operation of step (3) is carried out with reference to the corresponding steps in Example 1, except that the amount of dopamine added in step (3) is 0.03 g, and the reaction pH is 8.0.
  • step (4) The operation of step (4) is carried out with reference to the corresponding steps in Example 1, the difference is that in step (4), 20 mL of mixed solution of 3 mg FeCl 2 ⁇ 4H 2 O and 3 mg FeCl 3 ⁇ 6H 2 O is added, and in N 2 under the protection of stirring for 1h.
  • step (5) The operation of step (5) is performed with reference to the corresponding steps in the first embodiment.
  • the longitudinal tensile strength of the obtained oriented hydrogel is ⁇ 0.11 MPa, which is 0.9 times that of the randomly oriented hydrogel;
  • the electrical conductivity is 28 S m-1; and the adhesion to the skin can reach 41 kPa.
  • Example 1 Take Example 1 as an example to conduct relevant performance experiments. They are described as follows:
  • FIG. 1 shows the XRD pictures of the samples at various stages of this example.
  • the XRD pattern analysis shows that the sharp peaks at 30.2°C, 35.5°C, 43.2°C, 57.1°C and 62.8°C are characteristic of the crystal structure of Fe 3 O 4 NPs, indicating that Fe 3 O is formed on the surface of the PFeDAC sheet.
  • the crystalline structure of 4 NPs, and the peaks appearing around 20 °C are consistent with DAC characteristics, confirming that PDA and DAC play important roles in the formation of magnetic flakes.
  • DAC dialdehyde cellulose obtained by oxidizing cellulose with sodium periodate
  • DAC-PDA the composite of DAC grafted and modified by PDA
  • PFeDAC mediated by dopamine (PDA) and dialdehyde cellulose (DAC) of magnetic cellulose-based two-dimensional nanosheets
  • DAC-Fe 3 O 4 only DAC-mediated magnetic hybrid
  • PAD-Fe 3 O 4 only PDA-mediated magnetic hybrid
  • Figure 2 shows the TEM image of the cellulose-based magnetic nanosheets obtained in Example 1. It can be seen from the figure on the right that Fe 3 O 4 magnetic nanoparticles are loaded on the sheet-like carrier.
  • Figure 3 shows a picture of the existing morphology of the PFeDAC magnetic nanosheets prepared in Example 1 in water. It is that the magnetic PFeDCA nanosheets prepared in Example 1 still do not have obvious sedimentation after standing in water for 3 hours, indicating that they have good stability (see the left picture); when the magnet is close, the magnetic nanoparticles have obvious sedimentation. The phenomenon of being attracted indicates that it has good magnetic properties (see the picture on the right).
  • Adhesion/stretching experiments were carried out on the hydrogel prepared in Example 1 according to the conventional method.
  • the prepared hydrogel can adhere to the skin and has a large tensile property (as shown in Figure 5). extension results).
  • the content of PFeDAC magnetic hybrid in the used hydrogel is 8wt%)
  • Adhesion performance experiments were carried out on the hydrogel prepared in Example 1 according to the conventional method. As shown in Figure 7, the prepared hydrogels have good adhesion properties to various substrates. Among them, iron sheet (56kPa), glass (48kPa), stainless steel (53kPa), rubber (31kPa), wood (13kPa), PTFE (39kPa), plastic (17kPa), paper (11kPa), skin (63kPa) ). The content of PFeDAC magnetic hybrid in each hydrogel used is 8 wt%.
  • the tensile properties of the hydrogel prepared in Example 1 were tested by conventional methods. As shown in Fig. 8, the tensile stress-strain curves of the hydrogel under three different directions of force.
  • the three hydrogels include: (*) represents the hydrogel prepared without the force of the magnetic field, which is isotropic and the force in all directions is the same; (//) represents the force parallel to the force in the direction of the magnetic field; ( ⁇ ) means that the force is perpendicular to the direction of the magnetic field.
  • the content of PFeDAC magnetic hybrid in each hydrogel used is 8wt%.
  • Example 1 Tensile strain experiments were performed on the hydrogel prepared in Example 1 according to conventional methods. The results are shown in Figure 9, the compressive stress-strain curves of the hydrogel under three different directions of force.
  • the three hydrogels include: (*) represents the hydrogel prepared without the force of the magnetic field, which is isotropic and the force in all directions is the same; (//) represents the force parallel to the force in the direction of the magnetic field; ( ⁇ ) means that the force is perpendicular to the direction of the magnetic field.
  • the content of PFeDAC magnetic hybrid in each hydrogel used is 8 wt%.
  • the loading-unloading experiments were carried out on the hydrogel prepared in Example 1 according to the conventional method.
  • the results are shown in Fig. 10, the tensile stress-strain curve of the hydrogel during one loading-unloading cycle.
  • the force is parallel to the direction of the magnetic field, and the content of the PFeDAC magnetic hybrid in the hydrogel is 8 wt%.
  • a constant force of 700% deformation was applied to the PFeDAC hydrogel, no obvious hysteresis was observed on the cyclic loading-unloading curves of the 8 wt% PFeDAC hydrogel.

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Abstract

一种各向异性纤维素基水凝胶制备方法，包括下述步骤：将经高碘酸钠氧化后得到的双醛纤维素进行氨化；然后利用氨化的纤维素与多巴胺进行Schiff反应得到纤维素-多巴胺纳米片；再利用沉积法将Fe 3O 4纳米颗粒沉积在纤维素-多巴胺纳米片表面得到磁性的纤维素-多巴胺纳米片；进而利用简单聚合法将沉积有纳米颗粒的纤维素形成水凝胶。利用生物质中广泛存在的纤维素为原料，成本低廉；整个实验过程反应条件温和，且污染少，得到的纤维素基水凝胶具有典型的各向异性和磁性，拓宽了纤维素的应用途径，具有极高的潜在价值。

Description

一种各向异性纤维素基水凝胶制备方法 技术领域
本发明属于天然高分子材料领域，具体涉及一种各向异性纤维素基水凝胶制备方法。
背景技术
富含水的水凝胶软结构类似于生物系统，在生物材料、可穿戴器件、化学工程等领域有广泛的应用。值得注意的是，生物体的生物组织呈现出层次高度有序的复合结构，也因此能够承受较大的外力。受到生物体的启发，具有高度各向异性的水凝胶在软材料的应用中受到了普遍的关注。然而，与之形成鲜明对比的是，大多数合成的水凝胶由于单体的无序交联而呈现各向同性的结构。因此，获得具有良好机械性能的各向异性水凝胶具有重要的意义。
目前，通过定向冻干、自组装、磁场等外力介入的方法，可以从纳米到宏观精准调控使材料具有各向异性。其中，利用磁场制备各向异性的水凝胶是最简单、高效的方法。Gupta等指出，虽然Fe 3O 4纳米粒子可以提供可调谐的电磁场来获得预期的各向异性(A.K.Gupta,M.Gupta,Biomaterials 2005,26,3995-4021.)，但由于Fe 3O 4纳米粒子易在前驱体溶液中形成自聚集，所以对Fe 3O 4纳米粒子的尺寸有较高的要求。其次，Fe 3O 4纳米粒子负载于聚合物表面已造成导电性降低的问题(S.Garcia-Jimeno,J.Estelrich,Colloid.Surface.A.2013,420,74-81.)。而且目前存在的载体多为纳米颗粒或纳米线，对所形成的水凝胶的各向异性结构强度仍有待提高。鉴于以上铁磁流体制备过程所面临的挑战(Fe 3O 4纳米粒子易聚集、纳米颗粒较大、纳米颗粒在载体上易脱落)，需要寻求改进的载体以承载纳米粒子从而形成稳定的铁磁流体，以实现功能材料的优异性能。高碘酸钠氧化纤维素是一个传统的改性纤维素的方法，不同的氧化程度以及不同的溶解于水的方式得到的纤维素衍生物的形貌有很大的变化。其中，当纤维素完全氧化并溶解于水后得到的双醛基纤维素呈现二维片状的形貌，尺寸在几百纳米至几微米之间，这成为Fe 3O 4纳米粒子载体的探索目标。但为了防止铁磁流体在强大磁场下产生聚集，从而导致大多数铁磁流体绝缘，以至于很难利用传统的铁磁就能产生各向 异性导电性的水凝胶。
因此，有必要开发一种在聚合物基体和纳米组分之间具有良好界面的导电铁磁流体，以实现较高的各向异性。
发明内容
本发明的目的在于克服现有技术缺陷，本发明人采用纤维素改性方法，使纤维素成为表面富含酚羟基的结构，并以此吸引Fe 3O 4纳米粒子沉积在其表面形成磁性纤维素基纳米片，将Fe 3O 4纳米粒子固定在纤维素基纳米片表面有效的防止了纳米粒子的聚集。相较于普通的纳米颗粒与纳米线载体，本发明纤维素基纳米片的设计使凝胶聚合形成的共价键更牢固，实现了水凝胶的各向异性、高强度、导电性、粘附性的多重优势。
本发明提供一种各向异性纤维素基水凝胶的制备方法，包括如下步骤：
(1)将高碘酸钠氧化纤维素后得到的双醛纤维素；
(2)对双醛纤维素进行氨化得到氨化的纤维素衍生物；
(3)氨化的纤维素衍生物与多巴胺进行Schiff反应得到纤维素-多巴胺纳米片；
(4)利用沉积法将Fe 3O 4纳米颗粒沉积在纤维素-多巴胺纳米片表面得到磁性的纤维素-多巴胺纳米片；
(5)利用简单聚合法将磁性的纤维素-多巴胺纳米片形成水凝胶。
优选地，步骤(1)中，将纤维素、高碘酸钠在水体系中充分混合，避光搅拌，然后经去离子水洗涤、透析得到双醛纤维素；将所得的双醛纤维素加热溶解于水得到双醛纤维素水溶液；
优选地，步骤(2)中，取步骤(1)所得的双醛纤维素与NH 3·H 2O、甲醇充分混合；在反应釜中，在催化剂、H 2加压下加热反应得到氨化的纤维素衍生物；其中所述的催化剂选自铁、钴、镍基催化剂、Ru/C、Pd/C催化剂。更优选地，所述加热反应中H 2压力为>2.0MPa(优选为2-3MPa)，反应温度为100-150℃(优选为120℃)，反应时间>2h(优选为3-5h)。
优选地，步骤(3)中，将步骤(2)所得的氨化的纤维素衍生物加入到甲醇和水的混合液(优选地，甲醇/水＝1:4(v/v)的混合液)中搅拌，然后加入多巴 胺反应；用调节pH至碱性(优选为调节pH至8.0-9.0)，进一步反应后经离心、干燥得到纤维素-多巴胺纳米片。
优选地，步骤(4)中，将步骤(3)所得的纤维素-多巴胺纳米片分散到水和甲醇混合液中，搅拌后加入含有FeCl 2·4H 2O和FeCl 3·6H 2O的混合液，在N 2保护下搅拌；然后加入NH 3·H 2O并加热反应；经离心、洗涤得到磁性的纤维素-多巴胺纳米片；更优选，其中纤维素-多巴胺纳米片分散与水和甲醇混合液用量的重量比体积比为1mg：2-4ml，水/甲醇＝1-3/1(v/v)，FeCl 2·4H 2O和FeCl 3·6H 2O的混合液中两者的比例3：5-12；加入的NH 3·H 2O为28％的NH 3·H 2O；所述的加热反应温度为80-100℃，反应时间为1-5h。
在更具体的实施方式中，步骤(4)的操作是，将10mg步骤(3)所得的纤维素基纳米片分散到30mL水/甲醇＝2/1(v/v)中，搅拌30min。然后将含有3mg FeCl 2·4H 2O和8mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌1h；然后加入0.1mL 28％的NH 3·H 2O并加热反应。然后经反复离心、洗涤得涂覆有磁性Fe 3O 4纳米粒子的纤维素基纳米片。
优选地，步骤(5)中，将丙烯基单体、N,N-亚甲基双丙烯酰胺、四甲基乙二胺、引发剂及步骤(4)所得到的磁性的纤维素-多巴胺纳米片，混合液搅拌后倒入模具，待聚合完成后，即得纤维素基水凝胶。更优选地，所述的丙烯基单体为丙烯酰胺或丙烯酸；引发剂为过硫酸铵或过硫酸钾；静置温度为60-70℃，静置时间为1-3h。
本发明的有益效果是：本发明所使用的纤维素廉价易得，是自然界存在广泛的可再生生物质能源，大大降低了原料的成本；本发明所制备的纤维素基纳米片表面具有较多的高活性基团，相较于普通的纳米颗粒与纳米线载体，本发明的设计使得凝胶聚合形成的共价键更牢固。最终本发明得到的水凝胶具有各向异性、高强度、导电性、粘附性的多重优势，具有极高的开发潜力。
附图说明
图1实施例一中各阶段样品的XRD图片。
图2实施例一所得纤维素基磁性纳米片的TEM图。右图可看出片状载体上负载有Fe 3O 4磁性纳米颗粒。
图3实施例一所制备的PFeDAC磁性纳米片在水中具有良好的稳定性(左)及磁性(右)
图4水凝胶形成原理示意图。
图5实施例一所制备水凝胶的粘附/拉伸结果图。其中，各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
图6所制备水凝胶的压缩实验。其中，各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
图7所制备的水凝胶对各基材具有良好的粘附性能。其中，铁片(56kPa)、玻璃(48kPa)、不锈钢(53kPa)、橡胶(31kPa)、木材(13kPa)、聚四氟乙烯(39kPa)、塑料(17kPa)、纸片(11kPa)、皮肤(63kPa)。各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
图8三种不同方向作用力下，实施例一所制备的水凝胶的拉伸应力应变曲线。其中，三种水凝胶包括：(*)表示无磁场作用力下制备的水凝胶，其具有各向同性，各方向作用力相同；(//)表示作用力与磁场方向作用力平行；(⊥)表示作用力与磁场方向垂直。各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
图9三种不同方向作用力下，水凝胶的压缩应力应变曲线。其中，三种水凝胶包括：(*)表示无磁场作用力下制备的水凝胶，其具有各向同性，各方向作用力相同；(//)表示作用力与磁场方向作用力平行；(⊥)表示作用力与磁场方向垂直。各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。(实施例一结果图，按常规方法进行拉伸应变实验)
图10一个装载-卸载周期内，实施例一所制备的水凝胶的拉伸应力应变曲线。其中，作用力与磁场方向平行，水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
图11实施例一中的不同浓度PFeDAC所制备水凝胶的电导率(平行磁场方向)。
具体实施方式
以下通过具体实施例来详细说明本发明的技术方案，但本发明的保护范围不 限于此。
实施例1
本实施例按下述方法进行。
(1)将100mL浓度为0.55wt％的木浆纤维素悬浮液、0.6g NaIO4、2mL异丙醇于锥形瓶中混合，于500rpm的搅拌速度下65℃避光反应12h，然后经离心、去离子水洗涤和冷冻干燥得到二醛纤维素；将二醛纤维素加入含有100mL去离子水的圆底烧瓶中，于300rpm的搅拌速度下100℃反应2h，离心、浓缩后得到透明二醛纤维素水溶液，测定其浓度为3.3g/10g。
(2)取步骤(1)所得的双醛纤维素(10g)离心去除水分，然后与NH 3·H 2O(6mL)、甲醇(30mL)充分混合。采用100mL反应釜在Ru/C催化剂(0.1g)、2MPa的H 2压力下，100℃反应2h，得到氨化的纤维素衍生物。
(3)将步骤(2)所得的氨化的纤维素衍生物(5mL)加入到甲醇/水＝1:4(v/v)的混合液中搅拌1h，然后加入多巴胺(0.02g)室温下反应2h；然后用NaOH调节pH至8.2进一步反应后经8000rpm离心5min、-50℃下干燥48h得到纤维素基纳米片。
(4)将10mg步骤(3)所得的纤维素基纳米片分散到30mL水/甲醇＝2/1中，搅拌30min。然后将含有3mg FeCl 2·4H 2O和8mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌1h；然后加入0.1mL 28％的NH 3·H 2O在80℃下反应3h。然后经反复离心、洗涤得涂覆有磁性Fe 3O 4纳米粒子的纤维素基纳米片。
(5)将丙烯酰胺(2.6g)、N,N-亚甲基双丙烯酰胺(0.026g)、四甲基乙二胺(15μL)、过硫酸铵(0.03及步骤(4)所得涂覆有磁性Fe 3O 4纳米粒子的纤维素基纳米片(0.052g)，混合液搅拌后倒入模具；然后将模具放在60℃下静置3h使其聚合，即得纤维素基水凝胶。
在此条件下所得定向水凝胶的纵向抗拉强度为～0.22MPa，是随机方向水凝胶的1.7倍；导电率为41S m -1；对皮肤的黏附力可达63kPa。对于材料性能的测试均采用比较常规的方法(参照K.Liu,L.Han,P.Tang,K.Yang,D.Gan,X.Wang,K.Wang,F.Ren,L.Fan,Y.Xu,Z.Lu,X.Lu,Nano Lett.2019,19,8343-83。
其中，图4示出了水凝胶形成原理示意图。当电源未接通时，磁性纳米片处于无序状态；电源接通时，磁性纳米片在磁场作用下沿磁场方向排列，形成有序 的各向异性结构。
实施例2
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应的时间3h。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中加入的多巴胺量为0.03g，反应pH为8.2。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中加入0.1mL 28％的NH 3·H 2O后的反应为80℃、5h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行，不同的是步骤(5)中添加磁性杂化物的量为0.026g。在此条件下所得定向水凝胶的纵向抗拉强度为～0.19MPa，是随机方向水凝胶的1.5倍；导电率为37S m -1；对皮肤的黏附力可达54kPa。
实施例3
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应中H 2压力为3MPa。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中加入的多巴胺量为0.03g，反应pH为8.5。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中加入0.1mL 28％的NH 3·H 2O后的反应为90℃、1h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行，不同的是步骤(5)中添加磁性杂化物的量为0.1g。在此条件下所得定向水凝胶的纵向抗拉强度为～0.3MPa，是随机方向水凝胶的2.3倍；导电率为45S m-1；对皮肤的黏附力可达66kPa。
实施例4
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应温度为110℃。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中反应pH为9.0。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中加入0.1mL 28％的NH 3·H 2O后的反应为80℃、3h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行。在此条件下所得定向水凝胶的纵向抗拉强度为～0.20MPa，是随机方向水凝胶的1.5倍；导电率为39S m-1；对皮肤的黏附力可达58kPa。
实施例5
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应温度为140℃。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中加入的多巴胺量为0.03g、反应pH为8.0。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中3mg FeCl 2·4H 2O和8mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌3h；加入0.1mL 28％的NH 3·H 2O后的反应为90℃、3h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行。在此条件下所得定向水凝胶的纵向抗拉强度为～0.15MPa，是随机方向水凝胶的1.2倍；导电率为35S m-1；对皮肤的黏附力可达57kPa。
实施例6
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应中Pd/C催化剂用量为0.2g。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中反应pH为8.2。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中3mg FeCl 2·4H 2O和3mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌3h；加入0.1mL 28％的NH 3·H 2O后的反应为80℃、5h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行。在此条件下所得定向水凝胶的纵向抗拉强度为～0.14MPa，是随机方向水凝胶的1.1倍；导电率为31S m-1；对皮肤的黏附力可达47kPa。
实施例7
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中反应pH为9.0。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中3mg FeCl 2·4H 2O和5mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌3h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行。在此条件下所得定向水凝胶的纵向抗拉强度为～0.24MPa，是随机方向水凝胶的1.9倍；导电率为48S m-1；对皮肤的黏附力可达67kPa。
实施例8
本实施例按下述方法进行。
(1)按照实施例步骤(1)得到透明二醛纤维素水溶液。
(2)步骤(2)的操作参照实施例一中的相应步骤进行，不同的是步骤(2)中反应中Pd/C催化剂用量为0.2g。
(3)步骤(3)的操作参照实施例一中的相应步骤进行，不同的是步骤(3)中加入的多巴胺量为0.03g、反应pH为8.0。
(4)步骤(4)的操作参照实施例一中的相应步骤进行，不同的是步骤(4)中3mg FeCl 2·4H 2O和3mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌1h。
(5)步骤(5)的操作参照实施例一中的相应步骤进行。在此条件下所得定向水凝胶的纵向抗拉强度为～0.11MPa，是随机方向水凝胶的0.9倍；导电率为28S m-1；对皮肤的黏附力可达41kPa。
性能测试实施例
以实施例一为例进行相关性能实验。分别说明如下：
图1显示本实施例各阶段样品的XRD图片。由XRD图谱分析得知，在30.2℃、35.5℃、43.2℃、57.1℃、62.8℃处出现的尖锐的峰具有Fe 3O 4NPs的晶体结构的特征，表明在PFeDAC片表面形成了Fe 3O 4NPs的结晶结构，而在20℃左右出现的峰与DAC特征相一致，证实了PDA和DAC在磁性薄片的形成发挥了重要作用。其中DAC：高碘酸钠氧化纤维素后得到的双醛纤维素；DAC-PDA：DAC经PDA接枝改性后的复合物；PFeDAC：多巴胺(PDA)和双醛纤维素(DAC)介导的磁性纤维素基二维纳米片；DAC-Fe 3O 4：仅DAC介导的磁性杂化物；PAD-Fe 3O 4：仅PDA介导的磁性杂化物)。
图2显示了实施例一所得纤维素基磁性纳米片的TEM图。其从右图可看出片状载体上负载有Fe 3O 4磁性纳米颗粒。
图3显示了实施例一所制备的PFeDAC磁性纳米片在水中的存在形态图片。其是将实施例一所制备的磁性PFeDCA纳米片在水中静置3h后仍没有出现明显的沉降，说明其具有良好的稳定性(见左图)；当磁铁靠近时，磁性纳米颗粒有明显的被吸引现象，说明其具有良好的磁性(见右图)。
按常规方法对实施例一所制备水凝胶进行粘附/拉伸实验，所制备的水凝胶能够粘附在皮肤，并具有较大的拉伸性能(如图5所示粘附/拉伸结果图)。其中，所使用水凝胶中的PFeDAC磁性杂化体的含量为8wt％)
按常规方法对实施例一所制备水凝胶进行压缩实验。对所制备的水凝胶施加一定的压力，水凝胶产生明显的变形，当释放压力时，水凝胶快速恢复其原来的形态，说明水凝胶具有良好的抗压缩性能(结果见图6)。其中，所使用水凝胶中的PFeDAC磁性杂化体的含量为8wt％。
按常规方法对实施例一所制备水凝胶进行粘附性能实验。如图7所示，所制备的水凝胶对各基材具有良好的粘附性能。其中，铁片(56kPa)、玻璃(48kPa)、不锈钢(53kPa)、橡胶(31kPa)、木材(13kPa)、聚四氟乙烯(39kPa)、塑料(17kPa)、纸片(11kPa)、皮肤(63kPa)。其中使用的各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
按常规方法对实施例一所制备的水凝胶进行拉伸性能实验。如图8所示，三种不同方向作用力下，所述水凝胶的拉伸应力应变曲线。其中，三种水凝胶包括：(*)表示无磁场作用力下制备的水凝胶，其具有各向同性，各方向作用力相同；(//)表示作用力与磁场方向作用力平行；(⊥)表示作用力与磁场方向垂直。其中，所使用的各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
按常规方法对实施例一所制备的水凝胶进行拉伸应变实验。结果如图9所示，三种不同方向作用力下，水凝胶的压缩应力应变曲线。其中，三种水凝胶包括：(*)表示无磁场作用力下制备的水凝胶，其具有各向同性，各方向作用力相同；(//)表示作用力与磁场方向作用力平行；(⊥)表示作用力与磁场方向垂直。其中使用的各个水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。
按常规方法对实施例一所制备的水凝胶进行装载-卸载实验。结果如图10所示，在一个装载-卸载周期内，水凝胶的拉伸应力应变曲线。其中，作用力与磁场方向平行，水凝胶中的PFeDAC磁性杂化体的含量均为8wt％。从图中可以看出，当对PFeDAC水凝胶施加700％变形的恒力时，在8wt％PFeDAC水凝胶的循环加载-卸载曲线上没有观察到明显的迟滞现象。
按常规方法对实施例一所制备的水凝胶进行电导率实验。结果图11不同浓度PFeDAC所制备水凝胶的电导率(平行磁场方向)。结果表明，对于8wt％PFeDAC未施加磁场作用力水凝胶(＊)，作用力平行于8wt％PFeDAC水凝胶(//)，作用力垂直于8wt％PFeDAC水凝胶(⊥)三种状态，水凝胶的电导率均随着PFeDAC含量的增加而增大。随着PFeDAC浓度的进一步增加，水凝胶的电导率趋于平稳甚至略有下降。

Claims (9)

  1. 一种各向异性纤维素基水凝胶的制备方法，其特征在于：包括如下步骤：
    (1)将高碘酸钠氧化纤维素后得到的双醛纤维素；
    (2)对双醛纤维素进行氨化得到氨化的纤维素衍生物；
    (3)氨化的纤维素衍生物与多巴胺进行Schiff反应得到纤维素-多巴胺纳米片；
    (4)利用沉积法将Fe 3O 4纳米颗粒沉积在纤维素-多巴胺纳米片表面得到磁性的纤维素-多巴胺纳米片；
    (5)利用聚合法将磁性的纤维素-多巴胺纳米片形成水凝胶。
  2. 如权利要求1所述的制备方法，其特征在于：
    步骤(1)中，将纤维素、高碘酸钠在水体系中充分混合，避光搅拌，然后经去离子水洗涤、透析得到双醛纤维素；将所得的双醛纤维素加热溶解于水得到双醛纤维素水溶液。
  3. 如权利要求1所述的制备方法，其特征在于：
    步骤(2)中，取步骤(1)所得的双醛纤维素与NH 3·H 2O、甲醇充分混合；在反应釜中，在催化剂、H 2加压下加热反应得到氨化的纤维素衍生物；其中所述的催化剂选自铁、钴、镍基催化剂、Ru/C、Pd/C催化剂。
  4. 如权利要求3所述的制备方法，其特征在于：所述反应中H 2压力为>2.0MPa(优选为2-3MPa)，反应温度为100-150℃(优选为120℃)，反应时间>2h(优选为3h)。
  5. 如权利要求1所述的制备方法，其特征在于：
    步骤(3)中，将步骤(2)所得的氨化的纤维素衍生物加入到甲醇和水的混合液(优选地，甲醇/水＝1:4(v/v)的混合液)中搅拌，然后加入多巴胺反应；用调节pH至碱性(优选为调节pH至8.0-9.0)，进一步反应后经离心、干燥得到纤维素-多巴胺纳米片。
  6. 如权利要求1所述的制备方法，其特征在于：
    步骤(4)中，将步骤(3)所得的纤维素-多巴胺纳米片分散到水和甲醇混合液中，搅拌后加入含有FeCl 2·4H 2O和FeCl 3·6H 2O的混合液，在N 2保护下搅拌；然后加入NH 3·H 2O并加热反应；经离心、洗涤得到磁性的纤维素-多巴胺纳米片；更优选，其中纤维素-多巴胺纳米片分散与水和甲醇混合液用量的重量比体积比为1mg：2-4ml，水/甲醇＝1-3/1(v/v)，FeCl 2·4H 2O和FeCl 3·6H 2O的混合液中 两者的比例3：5-12；加入的NH 3·H 2O为28％的NH 3·H 2O；所述的加热反应温度为80-100℃，反应时间为1-5h。
  7. 如权利要求6所述的制备方法，其特征在于：步骤(4)的操作是，将10mg步骤(3)所得的纤维素基纳米片分散到30mL水/甲醇＝2/1(v/v)中，搅拌30min。然后将含有3mg FeCl 2·4H 2O和8mg FeCl 3·6H 2O的20mL混合液加入，在N 2保护下搅拌1h；然后加入0.1mL 28％的NH 3·H 2O并加热反应。然后经反复离心、洗涤得涂覆有磁性Fe 3O 4纳米粒子的纤维素基纳米片。
  8. 如权利要求1所述的制备方法，其特征在于：步骤(5)中，将丙烯基单体、N,N-亚甲基双丙烯酰胺、四甲基乙二胺、引发剂及步骤(4)所得到的磁性的纤维素-多巴胺纳米片，混合液搅拌后倒入模具，待聚合完成后，即得纤维素基水凝胶。
  9. 如权利要求8所述的制备方法，其特征在于：所述的丙烯基单体为丙烯酰胺或丙烯酸；引发剂为过硫酸铵或过硫酸钾；静置温度为60-70℃，静置时间为1-3h。
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