Cellulose nanofiber / graphene oxide composite film with layer-by-layer nanostructure, method of preparation and use thereof

Abstract

The application discloses a cellulose nanofiber / graphene oxide composite film with layer-by-layer nanostructure, a preparation method and application thereof. The method adds graphene oxide into a spinning coagulation liquid, uses a cellulose solution as a spinning solution, and continuously and gradually introduces the graphene oxide into a cellulose nanofiber non-woven fabric through wet electrospinning to form a uniform LBL nanostructure. The preparation method is simple, easy to operate, green and efficient, the prepared cellulose nanofiber / graphene oxide composite film has excellent flexibility of the nanofiber and excellent mechanical properties of the two-dimensional material, and has efficient flame-retardant-fireproof sensing performance, and can be used as a fireproof material or a flame response sensor and applied to fireproof packaging materials or fire alarm devices.

Description

Technical Field

[0001] This invention belongs to the field of polymer nanocomposite technology, and relates to a cellulose nanofiber / graphene oxide (CNF / GO) composite film with a layer-by-layer nanostructure, its preparation method and its application. Background Technology

[0002] Renewable biopolymer-based materials such as wood, recycled paper, and cork are widely used in construction, furniture, and decoration due to their lightweight, mechanical strength, texture, and thermal and electrical insulation properties. However, fire safety is a major limitation when using these materials in structural applications due to their undesirable high flammability and moisture sensitivity. With the advent of nanocellulose extracted from wood and other sources, nanoengineering of renewable materials has the potential to produce more effective flame-retardant properties. Previous studies have shown that using nanoscale one-dimensional and two-dimensional materials, such as carbon nanotubes, sepiolite nanorods, kaolin nanotubes, silicate nanolayers, and exfoliated clay, can form a protective layer during combustion, reducing fire spread by converting the carbon / silicon source into a protective layer. Importantly, combining fire sensing methods during the pre-combustion process to monitor abnormal temperatures in the early stages of a fire can prevent its spread in time. This early detection and warning of fire hazards can increase rescue opportunities and shorten the time to extinguish fires. Meanwhile, biosensing materials, with their advantages of low cost, ease of processing, and environmental friendliness, have become a research hotspot in the field of flame retardants.

[0003] However, a challenge facing biopolymer-based structural materials is their poor fire resistance and sensitivity to moisture. Various strategies have been used to improve the moisture sensitivity of cellulose-based materials, such as crosslinking, chemical modification, and hydrophobicity. Two-dimensional nanomaterials such as layered double hydroxides and graphene compounds can provide organic polymer-based nanocomposites with good flame retardancy and excellent mechanical properties. Among them, graphene oxide (GO) has become a research hotspot for cellulose-based nanostructures due to its excellent flame retardancy, fast flame alarm response, and good designability. Pure graphene oxide strips have very stable flame resistance, even when they are well exfoliated and have a high surface area. Li et al.'s bio-nanocomposite fire alarm device based on cellulose paper, GO, and Mxene showed a flame response within 2 seconds. The preparation method is a simple blending, but it requires a large amount of raw materials to achieve good sensing function and cannot prepare ultra-thin films, thus limiting its application potential (Chemical Engineering Journal 431(2022)134108). Cao et al. demonstrated good flame retardancy and rapid response to fire energy by using an interconnected network of GO nanosheets / phosphocellulose nanofibers / tannic acid via the thermally induced reduction of GO (Chemical Engineering Journal 439(2022)134516). This method also employs a blending process, requiring the introduction of tannic acid in addition to cellulose and GO, which presents significant drawbacks in terms of raw material requirements, preparation costs, and the ability to produce thin films. Furthermore, the simple blending process makes GO prone to aggregation during the composite process, greatly reducing its reinforcing / functional efficiency as a nanofiller in graphene oxide-based nanocomposites. Summary of the Invention

[0004] The present invention aims to provide a cellulose nanofiber / graphene oxide (CNF / GO) composite film with a layer-by-layer nanostructure, its preparation method, and its applications. The present invention employs a continuous layer-by-layer (LBL) strategy, using wet electrospinning to fabricate a thin, layered biofilm from a suspension of one-dimensional cellulose nanofibers (CNF) and two-dimensional graphene oxide. The introduction of GO imparts excellent interfacial chemical compatibility to the nanobiofilm, significantly enhancing its mechanical strength and flexibility. Simultaneously, through nanoengineering methods, the electrostatic force between the positively charged cellulose jet and the negatively charged graphene oxide nanosheets is utilized to achieve a stable LBL nanostructure in the biofilm. The flame retardancy of the carbonized layer after GO combustion and the physical shielding effect of the reduced graphene nanosheets effectively promote the flame retardancy and fire-sensing properties of the biofilm.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A method for preparing a cellulose nanofiber / graphene oxide composite film with a layer-by-layer nanostructure includes the following steps:

[0007] (1) Preparation of cellulose solution: The activated cellulose is heated and dissolved in lithium chloride / N,N-dimethylacetamide (LiCl / DMAc) solution to prepare a 1-2 wt.% cellulose solution;

[0008] (2) Electrospinning: Wet electrospinning technology is used, with cellulose solution as spinning solution and 0.05-0.5 wt.% graphene oxide suspension as coagulation bath. The rotating collector is immersed in the coagulation bath and electrospinning is performed to incorporate graphene oxide nanosheets into cellulose nanofiber nonwoven fabric. After spinning, the fabric is dried to obtain a cellulose nanofiber / graphene oxide composite film with a layered nanostructure.

[0009] Preferably, in step (1), the activated cellulose is prepared by conventional methods, specifically by mechanically crushing cotton cellulose long fibers into short fibers, and then heating to 80°C to fully dry and activate them.

[0010] Preferably, in step (1), the concentration of LiCl in the LiCl / DMAc solution is 8 wt.%.

[0011] Preferably, in step (1), the concentration of the cellulose solution is 1.5 wt.%.

[0012] Preferably, in step (2), the concentration of the graphene oxide suspension is 0.2 wt.%.

[0013] Preferably, in step (2), the electrospinning conditions are: spinning voltage of 10-20V, receiving distance of 10-15cm, and spinning solution flow rate of 0.01-0.05mL / min.

[0014] Preferably, the method further includes step (3), in which the cellulose nanofiber / graphene oxide composite film is immersed in a crosslinking agent solution to perform chemical crosslinking, thereby obtaining a moisture-resistant cellulose nanofiber / graphene oxide composite film.

[0015] Preferably, the crosslinking agent is a conventionally used chemical crosslinking agent, such as sodium citrate or glutaraldehyde. Through chemical crosslinking, the carboxyl and hydroxyl groups in the composite film are further reduced, thereby enhancing the water resistance and moisture resistance of the composite film.

[0016] Furthermore, the present invention provides the application of the above-mentioned cellulose nanofiber / graphene oxide composite film as a fire-retardant material or a flame response sensor.

[0017] More specifically, the present invention provides the application of the above-mentioned cellulose nanofiber / graphene oxide composite film as a flame response sensor in a fire alarm device.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The formula is simple, and the basic components of the composite material are only biopolymer cellulose and GO. The raw materials are widely available and easy to obtain.

[0020] (2) The wet electrospinning method is used to prepare the film. Compared with the traditional LBL film preparation method, it has the characteristics of convenient and continuous preparation, high preparation efficiency, and large-scale production capability.

[0021] (3) Compared with the blending method for preparing composite films, the method of the present invention can prevent the aggregation of composite nanounits, give full play to their functionality, and can prepare ultrathin films, thus broadening the application potential.

[0022] (4) After the composite film prepared by the present invention is treated with open flame, GO can be quickly converted into rGO, thereby forming a dense protective carbon layer, which cannot be burned and has excellent flame retardant effect. The thickness of the composite film is as low as tens of micrometers, and it still has excellent moisture resistance, flame retardant performance, mechanical properties and rapid fire response under ultra-thin size. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the CNF / GO composite film with a layer-by-layer nanostructure.

[0024] Figure 2 SEM images of the CNF / GO composite film (left) and cross-sectional morphology (scale bar is 10 micrometers).

[0025] Figure 3 This is a flowchart illustrating the preparation process of CNF / GO composite films.

[0026] Figure 4 A simplified diagram of the chemical changes during the heat treatment of CNF / GO composite thin films.

[0027] Figure 5 This diagram illustrates how CNF / GO composite film is used as a circuit switch in a fire alarm circuit. The heat-treated film undergoes a chemical change, which connects the circuit and enables the fire alarm to function. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] (1) Cotton cellulose long fibers were broken into short fibers by mechanical pulverization, and then heated to 80℃ for more than half an hour to fully dry and activate them, thus obtaining activated cellulose. DMAc was heated to 105℃ to remove residual moisture, and then 8g of dry LiCl was added to 92g of DMAc heated to 80℃. The mixture was magnetically stirred until completely dissolved, and then cooled to room temperature to obtain an 8wt.% LiCl / DMAc solution. 1.5g of activated cellulose was added to 98.5g of LiCl / DMAc solution and stirred at room temperature until completely dissolved to obtain a cellulose solution.

[0031] (2) 3.0 g of graphite flakes and 18.0 g of KMnO4 were added to concentrated H2SO4 / H3PO4 (360:40 mL), generating a slight exothermic reaction at 35-40 °C. The reaction was heated to 50 °C and stirred for 12 h. After cooling to room temperature, 3 mL of 30% H2O2 was added and poured onto 400 mL of ice. The mixture was washed successively with 200 mL of water and 200 mL of 30% hydrochloric acid, followed by centrifugation at 10000 rpm, with repeated washing with water for 10 min per cycle, until the pH of the supernatant was greater than 1. Finally, the product was dialyzed for at least 2 weeks to thoroughly remove ions and impurities, yielding a graphene oxide suspension.

[0032] (3) Samples were prepared using a computer-controlled automated electrospinning apparatus. A 5 mL plastic syringe containing a 0.8 mm stainless steel needle was used. The needle was connected to a high-voltage power supply to generate a positive voltage up to 20 kV. A micropump controlled the flow rate of the cellulose solution at 0.03 mL / min. A 6 cm diameter steel rotating collector, wrapped in aluminum foil, was placed 10 cm from the nozzle tip. The rotating collector was grounded to aid fiber collection. The tangential velocity of the collector was set to 50 m / min. The rotating collector was partially immersed in a 0.2 wt.% graphene oxide suspension coagulation bath. During spinning, the solvent rapidly evaporated and solidified on the nanofiber nonwoven fabric on the collector, while simultaneously introducing graphene oxide nanosheets layer by layer into the nonwoven fabric. Finally, the nonwoven fabric was dried under ventilated conditions to obtain a CNF / GO composite film with a layer-by-layer nanostructure.

[0033] Figure 2 The image shows the SEM surface morphology (left) and cross-sectional morphology (scale bar is 10 micrometers) of the CNF / GO composite film prepared in this embodiment. It can be seen that the thickness of the film is about 30 micrometers.

[0034] The CNF / GO film prepared in this embodiment has a carbon residue rate of 37.3%, and it cannot be ignited even after 10 seconds of continuous flame treatment. In MCC testing, the observed THR (total heat release rate per unit mass of initial sample combustion) was 0.8 kJ / g, PHRR (maximum heat release rate of flame) was 20.73 W / g, HRC (heat capacity) was 21 J / g·K, TPHRR (temperature of maximum heat release rate) was 231.2 °C, and LOI (limiting oxygen index) was 36.3.

[0035] Using pure CNF film as a comparison for flame treatment, the CNF / GO film prepared in this embodiment and the pure CNF film were cut to dimensions of 3cm in length and 1cm in width. The CNF film ignited immediately and burned out rapidly within 2 seconds, while the prepared CNF / GO film could not be ignited when subjected to open flame treatment, exhibiting excellent fire resistance and flame retardant properties. Compared with the pure CNF film, the CNF / GO film with GO incorporation showed significantly enhanced mechanical properties, with a tensile strength of 84.6MPa and an elastic modulus of 6.2GPa.

[0036] Figure 4 This is a simplified diagram of the chemical changes during the heat treatment of CNF / GO composite films. When treated with an open flame, GO rapidly transforms into rGO, forming a dense protective char layer, thus preventing combustion and exhibiting excellent flame-retardant properties.

[0037] Example 2

[0038] The CNF / GO film prepared in the examples was immersed in sodium citrate solution and chemically crosslinked to obtain a moisture-resistant CNF / GO film.

[0039] After chemical crosslinking with sodium citrate, the number of carboxyl and hydroxyl groups in CNF / GO film was significantly reduced, enhancing the water resistance of CNF / GO film. Its water contact angle increased from a very small angle of less than 30 degrees to an obtuse angle (greater than 90 degrees), and its moisture resistance was greatly enhanced.

[0040] Comparative Example 1

[0041] This comparative example is basically the same as Example 1, except that the GO concentration is 0.03 wt.%. Under these conditions, the composite film can be ignited quickly and has poor flame retardant effect.

[0042] Comparative Example 2

[0043] This comparative example is basically the same as Example 1, except that the coagulation bath is water and no GO is added, resulting in a cellulose nanofiber membrane that can be ignited instantly and does not have a flame-retardant effect.

Claims

1. A method for preparing a cellulose nanofiber / graphene oxide composite film having a layer-by-layer nanostructure, characterized by, The method comprises the following steps: (1) preparing a cellulose solution: heating and dissolving activated cellulose in a LiCl / DMAc solution to prepare a 1-2 wt.% cellulose solution; (2) electrospinning: using a wet electrospinning technology, using the cellulose solution as a spinning solution and using a 0.05-0.5 wt.% graphene oxide suspension as a coagulation bath, partially immersing a rotating collector in the coagulation bath, electrospinning, incorporating graphene oxide nanosheets into cellulose nanofiber non-woven fabric, drying after spinning to obtain a cellulose nanofiber / graphene oxide composite film with a layer-by-layer nanostructure.

2. The production method according to claim 1, characterized by, In step (1), the activated cellulose is prepared by: crushing cotton cellulose long fibers into short fibers by a mechanical crushing method, and then heating to 80°C for sufficient drying and activation.

3. The production method according to claim 1, characterized by, In the LiCl / DMAc solution in step (1), the concentration of LiCl is 8 wt.%.

4. The production method according to claim 1, characterized by, In step (1), the concentration of the cellulose solution is 1.5 wt.%; and in step (2), the concentration of the graphene oxide suspension is 0.2 wt.%.

5. The production method according to claim 1, characterized by, In step (2), the electrospinning conditions are: a spinning voltage of 10-20 V, a receiving distance of 10-15 cm, and a spinning solution flow rate of 0.01-0.05 mL / min.

6. The method of claim 1, wherein, The method further comprises step (3): immersing the cellulose nanofiber / graphene oxide composite film in a crosslinking agent solution for chemical crosslinking to obtain a moisture-resistant cellulose nanofiber / graphene oxide composite film.

7. The production method according to claim 6, wherein The crosslinking agent is sodium citrate or glutaraldehyde.

8. A cellulose nanofiber / graphene oxide composite film prepared by the method according to any one of claims 1-7.

9. Use of the cellulose nanofiber / graphene oxide composite film according to claim 8 as a fireproof material or a flame-responsive sensor.

10. Use according to claim 9, characterized in that, The cellulose nanofiber / graphene oxide composite film is used as a flame-responsive sensor in a fire alarm device.

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