Preparation method of inorganic ion oligomer reinforced bacterial cellulose nanocomposite film

Abstract

The application provides a preparation method of inorganic ion oligomer reinforced bacterial cellulose nanocomposite film. The method comprises the following steps: (1) extruding a bacterial cellulose wet film to reduce the water content; (2) immersing the bacterial cellulose wet film into a polyvinyl alcohol / inorganic ion oligomer solution to absorb and swell until equilibrium; and (3) stretching and orienting the bacterial cellulose / polyvinyl alcohol / inorganic ion oligomer wet film at a certain rate and drying the film to obtain a bacterial cellulose-based nanocomposite film. In the application, inorganic oligomers are used as crosslinking agents, which are in-situ polymerized in the highly oriented bacterial cellulose nanofiber network, and the organic-inorganic interface is firmly welded together to form an interlocking laminated structure, effectively solving the problems of phase separation and interface defects in organic-inorganic composite materials, and significantly improving the transparency, mechanical strength and toughness of the bacterial cellulose film. The method provides an effective way for manufacturing high-performance bacterial cellulose-based organic-inorganic nanocomposite materials.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and particularly relates to a method for preparing an inorganic ion oligomer-reinforced bacterial cellulose nanocomposite membrane. Background Technology

[0002] Natural cellulose materials (such as wood, paper, and clothing) are among the materials widely used by humankind for thousands of years. They have long been considered inexhaustible, renewable, and sustainable natural polymers for construction, textiles, tools, writing, and reading. Cellulose fibers are composed of glucose units arranged at the molecular scale, and a single cellulose fiber possesses a high strength of 1.6 to 3.0 GPa. With its unique microstructure and abundant hydroxyl groups, cellulose will provide us with more high-performance materials for various high-strength, lightweight applications, such as electronics, construction, and automobiles.

[0003] The manufacture of inorganic materials typically uses ions as precursors, with nucleation and growth occurring through electrostatic interactions. Limited by classical crystalline growth, inorganic materials are usually nano- or micron-sized solid powders rather than continuous monolithic structures. Introducing them into a cellulose matrix often results in uncontrolled aggregation of inorganic particles, phase separation, and heterogeneous structures, as well as insufficient bonding between the inorganic particles and the organic matrix, leading to brittle composites with poor fracture resistance. For example, in the typical paper industry, the addition of inorganic mineral fillers such as calcium carbonate, talc, and kaolin reduces the bonding strength between cellulose fibers, resulting in decreased paper strength.

[0004] However, cellulose fibers are typically extracted from natural plant resources through top-down strategies (mechanical, chemical, or enzymatic treatment) to remove lignin and other components such as hemicellulose. During these processes, the natural microstructure and crystalline structure of cellulose are inevitably disrupted, introducing numerous structural defects into the final cellulose-inorganic composite membrane, resulting in significantly weakened mechanical properties. Unlike cellulose extracted from plants, bacterial cellulose is pure cellulose nanofibers (containing no hemicellulose or lignin) with high crystallinity (70-89%) produced by bacteria or cell-free systems. This highly crystalline structure of the basic protofibrils endows the fibers with exceptional mechanical properties (Young's modulus of 114 GPa). However, bacterial cellulose nanofibers tend to be randomly distributed, and the tensile strength of bacterial cellulose films in the dry state generally does not exceed 200 MPa, and even only a few MPa in the wet state. Their disordered and isotropic internal structure limits their mechanical properties and application range. Effective orientation strategies (e.g., cold stretching, prestress-induced, and electric / magnetic field-assisted orientation) have been used to prepare anisotropic bacterial cellulose composite membranes, whose superior mechanical properties have attracted increasing attention. However, these composite membranes still cannot achieve an ideal continuous structure, and the defects caused by structural imperfections further limit the improvement of their mechanical properties. Therefore, constructing a cellulose-based organic-inorganic nanocomposite membrane material with a continuous structure and ultra-high tensile strength remains a huge challenge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing inorganic ion oligomer-reinforced bacterial cellulose nanocomposite membranes. The nanocomposite membranes prepared by this invention exhibit a hierarchical continuous structure and ultra-high mechanical strength.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] One of the technical solutions of the present invention provides a method for preparing an inorganic ionic oligomer-reinforced bacterial cellulose nanocomposite membrane. The method constructs a bacterial cellulose-based nanocomposite membrane with a high-density cross-linked interface at multiple scales through the polymerization and cross-linking strategy of inorganic ionic oligomers, and includes the following steps:

[0008] (1) Dissolve polyvinyl alcohol in water. Then mix the polyvinyl alcohol aqueous solution with the inorganic ionic oligomer.

[0009] (2) The bacterial cellulose wet film is squeezed under a certain pressure to reduce its water content;

[0010] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0011] (4) Stretch and orient the bacterial cellulose membrane from step (3) and dry it to obtain a bacterial cellulose / polyvinyl alcohol / inorganic ion oligomer nanocomposite membrane.

[0012] Preferably, the molecular weight of the polyvinyl alcohol in step (1) is between 200,000 and 300,000. More preferably, the molecular weight of the polyvinyl alcohol is 170,000.

[0013] Preferably, the concentration of the polyvinyl alcohol solution in step (1) is 0.1 wt.% to 10 wt.%.

[0014] Preferably, the inorganic ionic oligomer in step (1) includes one or more of calcium carbonate oligomer, calcium phosphate oligomer, calcium sulfate oligomer, and copper sulfate oligomer.

[0015] Preferably, the mass ratio of polyvinyl alcohol to inorganic ionic oligomer in step (1) is 1-5:5-20. More preferably, the mass ratio of polyvinyl alcohol to inorganic ionic oligomer is 3-5:5-15.

[0016] Preferably, the pressure in step (2) is 0.01-50 MPa.

[0017] Preferably, the tensile rate in step (4) is 1-200 mm / min, and the tensile strain is 5%-70%. More preferably, the tensile rate is 100 mm / min, and the tensile strain is 40%.

[0018] Preferably, the drying process described in step (4) is carried out while the object is in a stretched state. The drying temperature is room temperature - 80°C.

[0019] The second technical solution of this invention provides an inorganic ion oligomer-reinforced bacterial cellulose nanocomposite membrane, prepared by the above method. This nanocomposite membrane exhibits a visible light transmittance exceeding 85%. Furthermore, the membrane displays excellent mechanical properties. Its tensile strength, Young's modulus, and toughness can reach up to 1.2 GPa, 38 GPa, and 35 MJ / m², respectively. -3 .

[0020] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0021] (1) This invention prepares a transparent, high-strength bacterial cellulose-based nanocomposite membrane without damaging the bacterial cellulose membrane structure. The proposed preparation method has mild process conditions, is simple to operate, and is easy to control, and is expected to achieve large-scale production, with important application prospects and value.

[0022] (2) This invention uses inorganic oligomers as crosslinking agents to uniformly polymerize in situ in a highly oriented bacterial cellulose nanofiber network, firmly welding the organic-inorganic interface together to form an interlocking laminate structure, effectively solving the phase separation and interface defects problems existing in organic-inorganic composite materials, and significantly improving the mechanical strength and toughness of bacterial cellulose membranes.

[0023] (3) This invention overcomes the drawback of poor hydrogen bonding between cellulose molecular chains caused by numerous nanoscale pore defects in bacterial cellulose membranes. The nanocomposite membrane prepared by this invention forms a dense stacked layer, similar to the "brick-mortar-sand" structure of nacre. The dense laminated structure enhances the load-bearing capacity of the unit cells, leading to the deflection of serrated cracks and the propagation of long-range cracks, dissipating a large amount of energy, thereby greatly improving the mechanical properties of the nanocomposite membrane.

[0024] (4) The inorganic amorphous oligomer proposed in this invention matches the optical refractive index of polyvinyl alcohol and bacterial cellulose, and eliminates interface defects to form a continuous structure, thereby giving the material excellent transparency. Attached Figure Description

[0025] Figure 1 A digital photograph of the PCB nanocomposite film prepared in Example 1 of the present invention;

[0026] Figure 2 Scanning electron microscope images (a) of the PCB nanocomposite film prepared in Example 1 of the present invention, (b) longitudinal section and (cd) transverse section;

[0027] Figure 3 Atomic force microscopy images and height distribution curves of (a) BC film and (b) PCB nanocomposite film prepared in Comparative Example 1 and Example 1 of the present invention;

[0028] Figure 4 The stress-strain curves are for the BC, PB, CB and PCB nanocomposite films prepared in Example 1 and Comparative Examples 1-3 of this invention.

[0029] Figure 5 This demonstrates the ultra-high tensile strength of the PCB nanocomposite film prepared in Example 1 of the present invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto. For parameters and processes not specified herein, conventional techniques can be used.

[0031] Example 1

[0032] (1) Prepare 150 mL of a 0.5 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium phosphate oligomer at a mass ratio of 3:7.

[0033] (2) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0034] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0035] (4) The bacterial cellulose membrane from step (3) was stretched and oriented by 30% at a rate of 100 mm / min and dried at 60 °C. The resulting nanocomposite membrane was labeled PCB. Figure 1 and Figure 2 The images are digital photographs and SEM images of the PCB nanocomposite film, respectively.

[0036] like Figure 1 As shown, because inorganic calcium phosphate oligomers can eliminate defects and porosity through a pre-stretching process to shape and fuse between bacterial cellulose nanofiber interfaces, the PCB nanocomposite film exhibits a light transmittance of 89%. (SEM image of the PCB nanocomposite film is shown.) Figure 2 As can be seen, bacterial cellulose nanofibers are bridged by calcium phosphate oligomers and PVA to form sheets, which are densely stacked into a layered structure. The dense layered structure enhances the load-bearing capacity of the unit cells, causing stress to propagate along complex paths at the interfaces of these stacked layers during tensile testing, dissipating a large amount of energy and thus greatly improving strength and toughness.

[0037] Example 2

[0038] (1) Prepare 150 mL of a 1 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium carbonate oligomer at a mass ratio of 4:6.

[0039] (2) The bacterial cellulose wet film was squeezed under a pressure of 10 MPa to reduce its moisture content;

[0040] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0041] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 40% at a rate of 180 mm / min and dried at room temperature.

[0042] Example 3

[0043] (1) Prepare 150 mL of a 3 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium sulfate oligomer at a mass ratio of 5:10.

[0044] (2) The bacterial cellulose wet film was squeezed under a pressure of 30 MPa to reduce its moisture content;

[0045] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0046] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 40% at a rate of 200 mm / min and dried at 50°C.

[0047] Example 4

[0048] (1) Prepare 150 mL of a 5 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with copper sulfate oligomer at a mass ratio of 5:10.

[0049] (2) The bacterial cellulose wet film was squeezed under a pressure of 4 MPa to reduce its moisture content;

[0050] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0051] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 50% at a rate of 200 mm / min and dried at 80°C.

[0052] Example 5

[0053] (1) Prepare 150 mL of polyvinyl alcohol solution with a concentration of 1 wt.%. Then mix the polyvinyl alcohol aqueous solution with copper sulfate oligomer at a mass ratio of 4:15.

[0054] (2) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0055] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0056] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 20% at a rate of 150 mm / min and dried at 60°C.

[0057] Example 6

[0058] (1) Prepare 150 mL of polyvinyl alcohol solution with a concentration of 1 wt.%. Then mix the polyvinyl alcohol aqueous solution with copper sulfate oligomer at a mass ratio of 3:15.

[0059] (2) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0060] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0061] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 10% at a rate of 100 mm / min and dried at 40°C.

[0062] Example 7

[0063] (1) Prepare 150 mL of a 3 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium phosphate oligomer at a mass ratio of 5:15.

[0064] (2) The bacterial cellulose wet film was squeezed under a pressure of 3 MPa to reduce its moisture content;

[0065] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0066] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 20% at a rate of 50 mm / min and dried at 60°C.

[0067] Example 8

[0068] (1) Prepare 150 mL of a 5 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium phosphate oligomer at a mass ratio of 5:15.

[0069] (2) The bacterial cellulose wet film was squeezed under a pressure of 5 MPa to reduce its moisture content;

[0070] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0071] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 30% at a rate of 200 mm / min and dried at 80°C.

[0072] Example 9

[0073] (1) Prepare 150 mL of a 5 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium phosphate oligomer at a mass ratio of 3:7.

[0074] (2) The bacterial cellulose wet film was squeezed under a pressure of 5 MPa to reduce its moisture content;

[0075] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0076] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 40% at a rate of 160 mm / min and dried at 25°C.

[0077] Example 10

[0078] (1) Prepare 150 mL of a 7 wt.% polyvinyl alcohol solution. Then mix the polyvinyl alcohol aqueous solution with calcium phosphate oligomer at a mass ratio of 3:7.

[0079] (2) The bacterial cellulose wet film was squeezed under a pressure of 7 MPa to reduce its moisture content;

[0080] (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomer.

[0081] (4) The bacterial cellulose membrane from step (3) is stretched and oriented by 40% at a rate of 180 mm / min and dried at 25°C.

[0082] Comparative Example 1

[0083] (1) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0084] (2) Immerse the bacterial cellulose wet film from step (1) in deionized water to fully absorb water and swell.

[0085] (3) The bacterial cellulose membrane from step (2) was stretched and oriented by 40% at a rate of 100 mm / min and dried at 60 °C. The resulting composite membrane was labeled BC.

[0086] Figure 3 AFM three-dimensional morphology images and height distribution curves of the BC film and PCB nanocomposite film are shown, respectively. The AFM images show that the surface of the PCB nanocomposite film is very smooth, with a height variation of approximately 6 nm and a surface roughness value (Ra) of 3.3 nm. The smooth surface is attributed to the dense structure resulting from the fusion of calcium phosphate oligomer nanoparticles driven by the transverse compressive stress generated by the positive Poisson effect during wet stretching.

[0087] Comparative Example 2

[0088] (1) Prepare 150 mL of polyvinyl alcohol solution with a concentration of 0.3 wt.%.

[0089] (2) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0090] (3) Immerse the bacterial cellulose wet film from step (2) into the polyvinyl alcohol solution from step (1) to absorb the polyvinyl alcohol solution.

[0091] (4) The bacterial cellulose membrane from step (3) was stretched and oriented by 40% at a rate of 100 mm / min and dried at 60 °C. The resulting composite membrane was labeled PB.

[0092] Comparative Example 3

[0093] (1) Prepare 150 mL of calcium phosphate oligomer suspension with a concentration of 0.3 wt.%.

[0094] (2) The bacterial cellulose wet film was squeezed under a pressure of 1 MPa to reduce its moisture content;

[0095] (3) Immerse the bacterial cellulose wet film from step (2) into the suspension from step (1) to absorb calcium phosphate oligomers.

[0096] (4) The bacterial cellulose membrane from step (3) was stretched and oriented by 40% at a rate of 100 mm / min and dried at 60 °C. The resulting composite membrane was labeled CB.

[0097] To evaluate the reinforcing effectiveness of inorganic ionic oligomers at multi-scale interfaces, the stress-strain curves of nanocomposite films were investigated. Figure 4 Tensile tests showed that binary nanocomposite films such as PB and CB exhibited higher tensile strength than BC films, but the enhancement of mechanical properties was limited due to defects such as porosity and heterogeneous structures. PCB nanocomposite films showed significantly reduced interfacial and grain boundary defects, exhibiting a tensile strength of 1168 MPa, 1.75 times that of BC films. Furthermore, the Young's modulus and toughness of PCB nanocomposite films were significantly enhanced, reaching a maximum of 37.8 GPa and 34.1 MJ / m², respectively. -3 .

[0098] like Figure 5 As shown, the PCB nanocomposite film (10cm long, 1cm wide, 90μm thick, and 80mg in weight) can withstand a weight of 40kg without breaking, which means it can withstand at least 500,000 times its own weight.

[0099] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an inorganic ionic oligomer-reinforced bacterial cellulose nanocomposite film, characterized by, The preparation steps include the following: (1) Dissolve polyvinyl alcohol in water, and then mix the polyvinyl alcohol aqueous solution with the inorganic ionic oligomer evenly; The molecular weight of the polyvinyl alcohol is 20,000 to 300,000. (2) The bacterial cellulose wet film is squeezed under a certain pressure to reduce its water content; the concentration of the polyvinyl alcohol solution is 0.1 wt.%-10 wt.%; the inorganic ionic oligomer includes one or more of calcium carbonate oligomer, calcium phosphate oligomer, calcium sulfate oligomer and copper sulfate oligomer; the mass ratio of polyvinyl alcohol to inorganic ionic oligomer is 1-5:5-20; the pressure is 0.01-50 MPa; (3) Immerse the bacterial cellulose wet film from step (2) into the mixed solution from step (1) to absorb the polyvinyl alcohol / inorganic ionic oligomers; the immersion time of the bacterial cellulose wet film is 12-72h; (4) The bacterial cellulose membrane from step (3) is stretched and oriented, and dried while in a stretched state to obtain a bacterial cellulose / polyvinyl alcohol / inorganic ion oligomer nanocomposite membrane; wherein the nanocomposite membrane forms an interlocked laminate structure in which bacterial cellulose nanofibers, polyvinyl alcohol and polymerized inorganic ion oligomers are bridged and densely stacked; the stretching rate is 1-200 mm / min and the tensile strain is 5%-70%.

2. A high-strength bacterial cellulose / polyvinyl alcohol / inorganic ionic oligomer nanocomposite membrane prepared by the preparation method described in claim 1.

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