High-throughput Janus structure ternary composite fiber membrane and preparation method and application thereof

Abstract

The invention discloses a high-flux Janus structure ternary composite fiber membrane and a preparation method and application thereof, the composite membrane has three layers of asymmetric structures, and a hydrophobic support layer is a polypropylene spunbond non-woven fabric; the hydrophilic functional layer is a cellulose nanofiber and titanium dioxide nanowire composite fiber membrane; the whole structure is formed by compounding a hydrophobic supporting layer and a hydrophilic functional layer through a laminating process. The preparation method comprises the following steps: preparing cellulose nanofibers with high length-diameter ratio; development of a cellulose nanofiber and TiO2 nanowire composite fiber membrane; preparing a polypropylene spun-bonded non-woven fabric; and laminating and forming the Janus composite fiber membrane. The invention provides the Janus structure ternary composite fiber membrane which integrates high flux, high separation efficiency, excellent pollution resistance, good mechanochemical stability, low cost and easy large-scale production, and the preparation method and application thereof.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and new materials technology, and in particular to a high-flux Janus structure ternary composite fiber membrane, its preparation method, and its application. Background Technology

[0002] Oil-water emulsions are widely found in industrial wastewater from industries such as machining, catering, and oil extraction, and their efficient separation is a major challenge in the field of water treatment.

[0003] Traditional separation techniques such as gravity separation and centrifugation are difficult to handle highly stable emulsified oil droplets. Composite fiber membranes, with their high specific surface area, tunable pore structure, and surface wettability, have become a cutting-edge technology for the efficient separation of emulsified oil and water.

[0004] However, current separation membrane materials on the market generally suffer from the following technical bottlenecks: Low separation flux and poor antifouling properties: Most existing separation membranes are prepared using oleophilic polymers via phase separation methods, resulting in generally low porosity and poor surface resistance to oil adhesion. During the separation process, the membrane is easily fouled and clogged by oil droplets, leading to a sharp decline in separation flux and severely limiting its continuous operation capability.

[0005] The preparation process is complex and industrialization is difficult: As mentioned in the reference document, the preparation of existing high-performance membranes (such as Janus membranes and smart response membranes) often involves multiple complex processes such as chemical modification, plasma etching, phase separation and spraying, which are costly and difficult to achieve large-scale production and application.

[0006] Insufficient mechanical and chemical stability: Many membrane materials experience irreversible reductions in separation flux and efficiency under acid and alkali corrosion or water flow impact, resulting in a short service life.

[0007] Difficult to handle complex operating conditions: When under high external pressure or when handling high-viscosity oils, the oil phase can easily penetrate into the membrane pores, causing membrane fouling and separation failure.

[0008] To address the aforementioned problems, researchers have developed various superwetting membrane materials, mainly categorized as follows: Superhydrophobic-superoleophilic membranes are mainly used for water-in-oil emulsion separation; superhydrophilic-underwater superoleophobic membranes are mainly used for oil-in-water emulsion separation, such as PVA gel membranes, modified PVDF membranes, or PK membranes modified with alginate hydrogels prepared by hydrothermal methods; smart-responsive membranes change wettability through external stimuli such as light, electricity, pH, temperature, and CO2; Janus membranes have asymmetric wettability and can achieve unidirectional permeation. Their preparation methods are diverse, such as single-sided deposition of a hydrophilic layer, double-sided asymmetric modification, and single-sided photodegradation treatment.

[0009] Despite some progress made in the above studies, none of them have been able to systematically and cost-effectively solve the four core challenges of high throughput, strong resistance to fouling, high stability, and easy industrialization at the same time.

[0010] Therefore, in order to solve the defects of existing separation membranes such as low flux, easy fouling, poor stability, complex preparation process and high cost, it is an urgent technical problem to be solved by those skilled in the art to provide a Janus structure ternary composite fiber membrane that integrates high flux, high separation efficiency, excellent antifouling, good mechanochemical stability, low cost and easy large-scale production, as well as its preparation method and application. Summary of the Invention

[0011] In view of this, the present invention provides a high-flux Janus structure ternary composite fiber membrane, its preparation method and application.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A high-flux Janus-structured ternary composite fiber membrane is disclosed. This composite membrane has two asymmetric layers: a hydrophobic support layer, a hydrophilic functional layer, and an integral structure. Hydrophobic support layer: made of polypropylene (PP) spunbond nonwoven fabric, providing mechanical strength and overall hydrophobicity; Hydrophilic functional layer: It is a composite fiber membrane of cellulose nanofibers and titanium dioxide TiO2 nanowires, which is the core functional layer for achieving oil-water separation; Overall structure: The hydrophobic support layer and the hydrophilic functional layer are laminated together to form an overall structure with Janus asymmetric wettability, that is, one side is oleophobic and hydrophilic, and the other side is hydrophobic and oleophilic.

[0013] A method for preparing a high-flux Janus structure ternary composite fiber membrane specifically includes the following steps: Step 1: Low-cost, mass production of high aspect ratio cellulose nanofibers Pretreatment: Alkali pretreatment is performed on the wood pulp fibers; This operation partially disrupts the hydrogen bond structure of cellulose, reducing the energy consumption of subsequent mechanical defiberization.

[0014] Flexible ball milling: A special flexible ball milling technology is used to de-fibrillate the pretreated wood pulp fibers; Post-processing: The ball-milled slurry is dispersed and coupled. The above operations ensure uniform dispersion of the fibers in water and enhance compatibility with subsequent inorganic nanomaterials.

[0015] Step 2: Development of composite fiber membranes of cellulose nanofibers and TiO2 nanowires Composite dispersion: The cellulose nanofibers prepared in step one are mixed with TiO2 nanowires in a certain proportion and then subjected to ultrasonic treatment to form a uniform suspension; Through the above operations, TiO2 nanowires not only enhance the hydrophilicity of the membrane, but their photoactivity also degrades surfactants in oil-water emulsions under light irradiation, achieving demulsification and in-situ anti-fouling.

[0016] Film formation and drying: The composite suspension is formed into a film by vacuum filtration or coating, followed by drying; The above operations are used to construct a porous membrane structure with high porosity, which facilitates the rapid passage of water molecules.

[0017] Step 3: Preparation of polypropylene spunbond nonwoven fabric Raw material ratio: Organic calcium carbonate toughening functional masterbatch and hydrophobic masterbatch are added to polypropylene raw material; The above operations are used to improve the mechanical and hydrophobic properties of nonwoven fabrics.

[0018] Spunbond process: By optimizing the melt temperature, extrusion speed, and cooling stretching parameters, PP spunbond nonwoven fabrics with specific thickness, pore size, and surface roughness are prepared. Step 4: Lamination of Janus Composite Fiber Membrane The PP spunbond nonwoven fabric prepared in step three is laminated with the cellulose / TiO2 composite membrane prepared in step two. By precisely controlling the lamination temperature, pressure and time, the interface between the two is firmly bonded to form a Janus membrane with a "hydrophobic layer / hydrophilic layer" structure, while keeping the pore structure of the membrane intact.

[0019] Preferably, the key technical parameters in the flexible ball mill include: Medium to fiber mass ratio: ranging from 20:1 to 50:1; The above operations can balance the fiberization effect with structural integrity and avoid excessive damage.

[0020] Ball milling medium size: Use flexible medium with a diameter of 0.4-0.6mm; The above operations achieve efficient fiber stripping while maintaining the fiber aspect ratio.

[0021] Ball grinding time: Controlled between 60-90 minutes.

[0022] The above operations are used to obtain the best nanofiberization effect.

[0023] Preferably, the mass ratio of the medium to the fiber is 40:1.

[0024] Preferably, the drying process during film formation and drying is a combination of centrifugal dehydration and freeze drying.

[0025] Application of a high-flux Janus structure ternary composite fiber membrane in the treatment of oily wastewater, especially in the separation of oil-in-water emulsions.

[0026] The present invention achieves the following technical effects compared to the prior art: Novelty and inventiveness: Structural Innovation: For the first time, a ternary composite Janus structure of "polypropylene spunbond nonwoven fabric (hydrophobic layer) / cellulose nanofibers (hydrophilic network) / TiO2 nanowires (functional enhancement)" was proposed and realized. This structural design ingeniously combines low-cost industrial substrate (PP), natural polymer (cellulose), and functional inorganic nanomaterials (TiO2 nanowires) to achieve a synergistic effect of "1+1+1>3".

[0027] Process Innovation: A novel "flexible ball milling" technique is employed to prepare high-performance cellulose nanofibers. By precisely controlling process parameters, the challenge of balancing nanoscale formation with high fiber aspect ratio, a problem inherent in traditional ball milling, is solved, enabling low-cost, large-scale production. This stands in stark contrast to complex chemical grafting or plasma treatments, demonstrating significant advancements and substantial improvements.

[0028] Functional innovation: Introducing the photocatalytic activity of TiO2 nanowires into the Janus membrane structure not only enhances flux by utilizing their superhydrophilicity, but also achieves "in-situ self-cleaning" by degrading surfactants, fundamentally solving the membrane fouling problem, which is not available in existing Janus membranes.

[0029] Practicality: Superior performance: The composite membrane prepared by this invention has an oil emulsion removal rate of ≥95%, a significantly improved water flux, and a daily water treatment capacity of over 180t. The underwater oil contact angle is ≥135°, exhibiting high flux, high efficiency, and superoleophobic properties.

[0030] High stability: The PP substrate provides excellent mechanical strength and chemical resistance, and the composite layer structure of cellulose and TiO2 is stable and can operate under complex working conditions for a long time.

[0031] Costs are controllable and easy to industrialize: The raw materials used (PP, wood pulp, TiO2) are inexpensive and readily available, and the core preparation processes (flexible ball milling, spunbonding, lamination) are all mature industrial technologies that are easy to scale up for production. This overcomes the drawbacks of laboratory technologies being difficult to industrialize and has extremely high market promotion value.

[0032] Environmentally friendly: Made with renewable natural cellulose, conforming to the concepts of green environmental protection and sustainable development. Attached Figure Description

[0033] Figure 1This is a schematic diagram illustrating the process principle of preparing cellulose nanofibers using flexible ball milling as described in this invention. Figure 2 This is a scanning electron microscope (SEM) image showing the effect of different media-to-wood pulp mass ratios on the morphology of nano-wood pulp cellulose fibers according to the present invention. Among them, (a) 10:1; (b) 20:1; (c) 40:1; (d) 100:1; Figure 3 This is an X-ray diffraction (XRD) analysis diagram showing the effect of different media-to-wood pulp mass ratios on the crystallinity of nano-wood pulp cellulose fibers according to the present invention. Figure 4 This is a scanning electron microscope (SEM) image showing the effect of different ball milling times on the morphology of nano-wood pulp cellulose fibers in this invention. Among them, (a) ball milling time 30 min; (b) ball milling time 60 min; (c) ball milling time 90 min; Figure 5 This is a scanning electron microscope (SEM) image showing the effect of different flexible media sizes on the morphology of nano-wood pulp cellulose fibers in this invention. Among them, (a) media size 0.3 mm; (b) media size 0.4-0.6 mm; (c) media size 0.8-1.0 mm. Figure 6 This is a schematic diagram of the measurement method for analyzing the size of nanocellulose using Image-J Pro Plus software, as described in this invention. Among them, red circles indicate granular products; blue arrows indicate large-size fibers; and yellow arrows indicate nanofibers. The product preparation process is evaluated based on the Fm value. Figure 7 This is a process flow diagram of the preparation method of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention discloses a high-flux Janus structure ternary composite fiber membrane, which has a bilayer asymmetric structure consisting of a hydrophobic support layer, a hydrophilic functional layer, and an integral structure; wherein, Hydrophobic support layer: made of polypropylene (PP) spunbond nonwoven fabric, providing mechanical strength and overall hydrophobicity; Hydrophilic functional layer: It is a composite fiber membrane of cellulose nanofibers and titanium dioxide TiO2 nanowires, which is the core functional layer for achieving oil-water separation; Overall structure: The hydrophobic support layer and the hydrophilic functional layer are laminated together to form an overall structure with Janus asymmetric wettability, that is, one side is oleophobic and hydrophilic, and the other side is hydrophobic and oleophilic.

[0036] This invention also discloses a method for preparing a high-flux Janus structure ternary composite fiber membrane, specifically including the following steps: Step 1: Low-cost, mass production of high aspect ratio cellulose nanofibers Pretreatment: Alkali pretreatment is performed on the wood pulp fibers; Flexible ball milling: A special flexible ball milling technology is used to de-fibrillate the pretreated wood pulp fibers; Post-processing: The ball-milled slurry is dispersed and coupled. Step 2: Development of composite fiber membranes of cellulose nanofibers and TiO2 nanowires Composite dispersion: The cellulose nanofibers prepared in step one are mixed with TiO2 nanowires in a certain proportion and then subjected to ultrasonic treatment to form a uniform suspension; Film formation and drying: The composite suspension is formed into a film by vacuum filtration or coating, followed by drying; Step 3: Preparation of polypropylene spunbond nonwoven fabric Raw material ratio: Organic calcium carbonate toughening functional masterbatch and hydrophobic masterbatch are added to polypropylene raw material; Spunbond process: By optimizing the melt temperature, extrusion speed, and cooling stretching parameters, PP spunbond nonwoven fabrics with specific thickness, pore size, and surface roughness are prepared. Step 4: Lamination of Janus Composite Fiber Membrane The PP spunbond nonwoven fabric prepared in step three is laminated with the cellulose / TiO2 composite membrane prepared in step two. By precisely controlling the lamination temperature, pressure and time, the interface between the two is firmly bonded to form a Janus membrane with a "hydrophobic layer / hydrophilic layer" structure, while keeping the pore structure of the membrane intact.

[0037] Key technical parameters in flexible ball milling include: Medium to fiber mass ratio: ranging from 20:1 to 50:1; Ball milling medium size: Use flexible medium with a diameter of 0.4-0.6mm; Ball grinding time: Controlled between 60-90 minutes.

[0038] The mass ratio of medium to fiber is 40:1.

[0039] The drying process during film formation and drying combines centrifugal dehydration with freeze drying.

[0040] This invention also discloses the application of a high-flux Janus structure ternary composite fiber membrane in the treatment of oily wastewater, particularly in the separation of oil-in-water emulsions.

[0041] Example 1: Step 1: Preparation of cellulose nanofibers Take 100g of oven-dried wood pulp fiber, immerse it in a 5wt% NaOH solution, pretreat it at 60°C for 2 hours, and wash it until neutral.

[0042] The pretreated fibers and flexible zirconia ball milling media (0.5 mm in diameter) were added to the milling jar at a mass ratio of 1:40 (fiber:media).

[0043] Ball mill at 300 rpm for 75 minutes.

[0044] The ball-milled slurry was removed, and 0.5 wt% sodium polyacrylate was added as a dispersant. The mixture was then stirred at high speed to disperse the slurry, resulting in a uniform cellulose nanofiber suspension. Coupling treatment was performed using 3-aminopropyltriethoxysilane (KH550) at a dosage of 0.3-0.8 wt% of the fiber mass. The reaction was carried out at 60°C for 2 hours, followed by filtration under a vacuum of 0.1 MPa for 30 minutes. Step 2: Preparation of cellulose / TiO2 composite membrane 1 g of P25 powder was dispersed in 100 mL of NaOH solution (10 mol / L), and the mixture was hydrothermally reacted at 180°C for 24 hours. After centrifugation and washing until neutral, TiO2 nanowires were obtained. The above cellulose nanofiber suspension was mixed with TiO2 nanowires (P25 grown into linear form by hydrothermal method) at a mass ratio of 9:1.

[0045] The cells were processed for 30 minutes using an ultrasonic cell disruptor at 200W power to form a uniform composite dispersion.

[0046] The composite dispersion was formed on a microfiltration membrane by vacuum filtration, then centrifuged at 4000 rpm for 5 minutes to dehydrate, and then placed in a freeze dryer at -50°C for 24 hours to obtain a cellulose / TiO2 composite fiber membrane.

[0047] Step 3: Preparation of PP spunbond nonwoven fabric Polypropylene chips were mixed evenly with 3 wt% organic calcium carbonate toughening masterbatch and 1 wt% hydrophobic masterbatch.

[0048] On a spunbond nonwoven fabric production line, with a melt temperature of 230°C, a metering pump flow rate of 50 kg / h, and a drawing speed of 3500 m / min, a fabric with a basis weight of 40 g / m³ was produced. 2 PP spunbond nonwoven fabric.

[0049] Step 4: Lamination and bonding of Janus membranes PP spunbond nonwoven fabric and cellulose / TiO2 composite film are stacked and placed in a hot press.

[0050] Hot-press composite at 130°C and 0.5 MPa for 3 minutes.

[0051] After cooling to room temperature, the high-flux Janus structure ternary composite fiber membrane of the present invention is obtained.

[0052] Performance testing: The prepared composite membrane was used to separate an oil-in-water emulsion (diesel) containing 0.1 wt% Span-80. At a pressure of 0.1 MPa, the water flux was measured to be 2500 L·m⁻¹. -2 ·h -1 The oil removal rate reached as high as 98.7%. After 10 cycles of separation and washing, the flux retention rate was still above 90%, demonstrating excellent antifouling properties and cycle stability. Table 1 compares the performance of the composite membrane of this invention (Example 1) with that of pure PP spunbond nonwoven fabric and pure cellulose nanofiber membrane.

[0053] Table 1. Composite membrane performance

[0054] This invention is achieved through the specific embodiments described above. Its core lies in the unique ternary structure design and innovative low-cost preparation process, successfully solving the key pain points in the prior art and possessing extremely high industrial applicability. The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A high-flux Janus structure ternary composite fiber membrane, characterized in that, The composite membrane has a three-layer asymmetric structure: a hydrophobic support layer, a hydrophilic functional layer, and an overall structure; among which, Hydrophobic support layer: made of polypropylene (PP) spunbond nonwoven fabric, providing mechanical strength and overall hydrophobicity; Hydrophilic functional layer: It is a composite fiber membrane of cellulose nanofibers and titanium dioxide TiO2 nanowires, which is the core functional layer for achieving oil-water separation; Overall structure: The hydrophobic support layer and the hydrophilic functional layer are laminated together to form an overall structure with Janus asymmetric wettability, that is, one side is oleophobic and hydrophilic, and the other side is hydrophobic and oleophilic.

2. A method for preparing a high-flux Janus-structured ternary composite fiber membrane, characterized in that, Specifically, the following steps are included: Step 1: Low-cost, mass production of high aspect ratio cellulose nanofibers Pretreatment: Alkali pretreatment is performed on the wood pulp fibers; Flexible ball milling: A special flexible ball milling technology is used to de-fibrillate the pretreated wood pulp fibers; Post-processing: The ball-milled slurry is dispersed and coupled. Step 2: Development of composite fiber membranes of cellulose nanofibers and TiO2 nanowires Composite dispersion: The cellulose nanofibers prepared in step one are mixed with TiO2 nanowires in a certain proportion and then subjected to ultrasonic treatment to form a uniform suspension; Film formation and drying: The composite suspension is formed into a film by vacuum filtration or coating, followed by drying; Step 3: Preparation of polypropylene spunbond nonwoven fabric Raw material ratio: Organic calcium carbonate toughening functional masterbatch and hydrophobic masterbatch are added to polypropylene raw material; Spunbond process: By optimizing the melt temperature, extrusion speed, and cooling stretching parameters, PP spunbond nonwoven fabrics with specific thickness, pore size, and surface roughness are prepared. Step 4: Lamination of Janus Composite Fiber Membrane The PP spunbond nonwoven fabric prepared in step three is laminated with the cellulose / TiO2 composite membrane prepared in step two. By precisely controlling the lamination temperature, pressure and time, the interface of the two is firmly bonded to form a Janus membrane with a "hydrophobic layer / hydrophilic layer" structure, while keeping the pore structure of the membrane intact.

3. The method for preparing a high-flux Janus structure ternary composite fiber membrane according to claim 2, characterized in that, The key technical parameters of the flexible ball mill include: Medium to fiber mass ratio: ranging from 20:1 to 50:1; Ball milling medium size: Use flexible medium with a diameter of 0.4-0.6mm; Ball grinding time: Controlled between 60-90 minutes.

4. The method for preparing a high-flux Janus structure ternary composite fiber membrane according to claim 3, characterized in that, The mass ratio of the medium to the fiber is 40:

1.

5. The method for preparing a high-flux Janus structure ternary composite fiber membrane according to claim 2, characterized in that, The drying process during film formation and drying involves a combination of centrifugal dehydration and freeze drying.

6. The application of the high-flux Janus structure ternary composite fiber membrane according to claim 1 in the treatment of oily wastewater, especially in the separation of oil-in-water emulsions.

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