Preparation method of laminated waterproof electromagnetic shielding film toughened by fruit peel pomace fibers

Abstract

The invention provides the preparation method of the high-strength, flexible and waterproof laminated electromagnetic shielding film compounded by the fruit peel pomace fibers. According to the invention, the fruit peel residue micro-nano cellulose with high length-diameter ratio is used as the flexible supporting layer, the cellulose / MXene mixed upper layer with high conductivity is used as the electromagnetic wave loss layer, and the silicone with low surface energy is used as the waterproof packaging layer, so that the flexibility and waterproofness of the laminated composite film are effectively improved; the invention provides a new process for the development of an antioxidant peel residue cellulose-based electromagnetic shielding film which can stably operate for a long time in a high-humidity outdoor working environment, and provides a new way for high-valued utilization of fruit peel residue wastes rich in lignocellulose.

Description

Technical Field

[0001] The present invention belongs to the field of cellulose-based flexible electromagnetic shielding materials, and particularly relates to a high-strength, flexible, waterproof and antioxidant laminated electromagnetic shielding film composed of fruit peel residue cellulose and a preparation method thereof. Background Art

[0002] Fruit peel residues are the main by-products generated during fruit harvesting and processing, but they are often discarded as leftovers. Common tropical fruits such as durian, mango, coconut, pineapple, and jackfruit all contain a large amount of peel residues. According to research, these residues contain rich lignocellulose, hemicellulose, polyphenolic compounds, pectin, vitamins, and minerals. These substances are considered valuable biological resources with potential applications in the food and chemical industries, and thus have important economic and research values. In the lignocellulose separation industry, wood is the main source. However, compared with wood, fruit peel residues have higher economic value, are easier to obtain, and have higher yields. As a derivative material of lignocellulose, nanocellulose is one of the important research directions in the current biomass field. Nanocellulose has the advantages of biodegradability, high reactivity, renewability, and high strength, and has broad application prospects in many fields such as packaging, biomedicine, and cosmetics. In addition, nanocellulose also has good biocompatibility and can be widely used as a reinforcing filler, effectively binding with various substrates such as starch-based, polysaccharide-based, polyvinyl alcohol, polylactic acid, and montmorillonite. It is an ideal material to replace petroleum-based plastics. Therefore, carrying out research on lignocellulose in fruit peel residues and realizing its reuse are of great significance for the sustainable development of the economy and environmental governance.

[0003] With the rapid development of electronic communication technologies and personal wearable devices, people's quality of life has become more comfortable and superior. However, these advancements have also brought serious electromagnetic interference and radiation problems. High electromagnetic wave pollution not only seriously affects the sensitivity of instruments but also threatens people's health, thus causing people's concerns. Therefore, it is urgent to develop shielding materials with excellent electromagnetic shielding performance for the next generation of flexible wearable electronic products. Recently, two-dimensional transition metal carbonitride MXene materials have attracted great interest from researchers. Due to their ultra-high electrical conductivity (20000 S cm -1 ) and good water compatibility, they show great application potential in the field of electromagnetic interference shielding. For example, in 2016, Shahzad and Gogotsi first reported self-supporting Ti3C2T in the Science journal (Science, 353, 1137-1140). xThe MXene film exhibits an excellent shielding efficiency (SE) of 92 dB even at a thickness of only 45 μm. Nevertheless, due to the weak interaction between adjacent MXene nanosheets, pure MXene films show poor mechanical strength and flexibility. In recent years, related research has shown that plant nanocellulose, based on its own advantages, is expected to improve the mechanical properties of MXene-based shielding films through mechanical interlocking and hydrogen bond interactions. For example, Professor Mingguo Ma of Beijing Forestry University et al. (ACS Nano, 2018, 4583 - 4593) prepared a Ti3C2T x MXene / mulberry husk nanocellulose (MXene / CNF) composite paper. When the content of MXene is 50%, the tensile strength of the composite paper is 135.4 MPa and the SE is 25 dB. Subsequently, other researchers have also used nanocellulose from other biomass sources, such as bleached board nanocellulose (Journal of Materials Chemistry C, 2019, 7, 9820), moso bamboo nanocellulose (Industrial Crops & Products, 2023, 199, 116762), pine nanocellulose (Carbohydrate Polymers, 2021, 274, 118652) or cotton nanocellulose (Journal of Materials Science & Technology, 2022, 129, 127 - 134) as stabilizers, dispersants and reinforcing agents to prepare MXene / CNF composite shielding film materials. The results show that biomass nanocellulose can significantly improve the mechanical strength and toughness of the composite film. Despite the great progress made currently, it is also difficult to balance the mechanical properties and shielding properties of the uniformly mixed MXene / CNF composite film due to the inherent insulating properties of CNF. How to balance the mechanical properties and EMI shielding properties of the MXene / CNF composite film remains a huge challenge. In addition, the polar groups on the surfaces of CNF and MXene make the composite film exhibit excellent hygroscopicity, resulting in the film being easily affected by moisture and even oxidized in a humid environment, which inevitably leads to structural deformation and functional failure. In view of this, the present invention proposes to extract micro-nano cellulose with a high aspect ratio from tropical fruit peel residues, and then obtain a flexible, waterproof and antioxidant laminated electromagnetic shielding film through layer-by-layer suction filtration, hot pressing and drying, and silicone encapsulation. The innovative methods of the laminated structure and silicone encapsulation introduced in the present invention can endow the flexible shielding film with excellent mechanical properties and shielding properties at the same time, and the film also has the advantage of long-term stable operation in a high-humidity outdoor working environment. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fibers and a preparation method thereof. The fruit peel residue micro-nano cellulose / MXene composite film provided by the present invention has the characteristics of flexibility, high strength, and stable electromagnetic shielding efficiency under high humidity conditions. The present invention is beneficial to solving the problems of poor durability and easy oxidation of the MXene / CNF composite film in a high humidity environment, as well as the challenge of difficult balance between the mechanical properties and shielding performance of the uniformly mixed MXene / CNF composite film, and provides an innovative way for the high-value utilization of tropical fruit peel residue.

[0005] To achieve the above object, the present invention is realized by the following means:

[0006] The first aspect of the present invention provides a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fibers, including fruit peel residue micro-nano cellulose with a high aspect ratio and two-dimensional transition metal MXene material. The fruit peel residue micro-nano cellulose is one or more of durian shells, mango peels, coconut shells, pineapple peels, and jackfruit shells.

[0007] Preferably, the precursor of the Ti3C2T x MXene material is selected from MAX Ti3AlC2 powder with a size of 400 mesh.

[0008] The second aspect of the present invention provides a preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fibers, including the following steps:

[0009] (1) Using waste fruit peel residue as raw material, after retting, degumming, cooking, beating, bleaching, biochemical pretreatment, and fibrillation peeling, a micro-nano cellulose dispersion is obtained;

[0010] (2) Selectively etching and peeling MAX Ti3AlC2 powder with a LiF-HCl solution to obtain monolayer Ti3C2T x MXene nanosheets;

[0011] (3) Vacuum filtering micro-nano cellulose and the micro-nano cellulose / MXene mixed solution in sequence, and the wet cake is dried by hot pressing to obtain a flexible, high-strength laminated composite film with a micro-nano cellulose flexible support layer on the lower layer and a cellulose / MXene mixed conductive layer on the upper layer;

[0012] (4) The laminated composite film is encapsulated with silicone to obtain a waterproof and antioxidant laminated electromagnetic shielding film.

[0013] Preferably, in step (1), the degumming is specifically: adjusting the retted peel residue fibers to an appropriate concentration, temperature, and pH, and adding pectinase for degumming.

[0014] Preferably, the suitable concentration for degumming is 0.02 - 0.2%, the suitable temperature is 45 - 55°C, and the suitable pH is 3.0 - 4.0.

[0015] Preferably, in step (1), the cooking specifically is: adding the degummed skin residue fibers into an alkaline solution with a suitable concentration and cooking at a suitable temperature to remove part of the hemicellulose and lignin.

[0016] Preferably, the alkali concentration of the cooking solution is 1 - 8%, the temperature is 80 - 120°C, and the time is 2 - 10 h.

[0017] Preferably, in step (1), the beating specifically is: placing the skin residue fibers obtained by cooking into a Valley beater for beating, and the beating adopts a gradient specific pressure - time control method to control the beating degree to be 30 - 60°SR.

[0018] Preferably, the gradient specific pressure - time is: the first gradient specific pressure load is 0 - 1 kg and the time is 30 - 90 min; the second gradient specific pressure load is 1.5 - 2 kg and the time is 30 - 90 min; the third gradient specific pressure load is 2.5 - 3 kg and the time is 30 - 60 min.

[0019] Preferably, in step (1), the bleaching specifically is: bleaching the beaten skin residue fibers with acidic sodium chlorite.

[0020] Preferably, the concentration of the acidic sodium chlorite is 1 - 5%, the treatment time is 3 - 6 h, and the temperature is 70 - 100°C.

[0021] Preferably, the biochemical pretreatment in step (1) is any one or two or three of TEMPO oxidation method, carboxymethylation method or enzyme method; the dosage of sodium hypochlorite in the TEMPO oxidation method is preferably 3 - 15 mmol / g relative to the absolutely dry fiber amount; the ratio of the dosage of sodium chloroacetate to the absolutely dry fiber amount in the carboxymethylation method is preferably 0.8 - 1.2; the enzyme method uses a single - component endoglucanase, the dosage of the enzyme is preferably 80 - 320 mg / kg, the optimum reaction temperature is 50°C, the pH is 4.8, and the reaction time is preferably 30 - 240 min.

[0022] Preferably, in step (1), the fibrillation peeling specifically is: subjecting the skin residue fibers after biochemical pretreatment to high - speed shearing, ultrasonic crushing treatment or high - pressure homogenization to obtain a micro - nano cellulose dispersion with a length of 1 - 6 μm and a diameter of 5 - 40 nm.

[0023] Preferably, the stirring speed of the high-speed shearing treatment equipment blender is 800 - 1600 rpm / min; the power of the ultrasonic crushing treatment equipment is 650 W; the working pressure of the homogenization treatment is between 10000 - 30000 Psi; the fibrillation stripping time is preferably 30 - 60 min.

[0024] Preferably, in step (2), the size of the MAX Ti3AlC2 powder is 400 mesh; the etching and stripping time is 48 h; the x lateral size of the single-layer Ti3C2T nanosheets is 500 - 3000 nm, and the thickness is less than 3 nm.

[0025] Preferably, in step (3), the grammage of the lower micro-nano cellulose flexible support layer is 50 g / m 2 , the amount of the upper cellulose / MXene mixed conductive layer is 10 - 90% of that of the lower layer, and the optimal ratio of fiber to MXene in the upper layer is 1:4; the temperature of hot pressing and drying is 80 - 100 °C, the pressure of hot pressing and drying is 0.1 - 0.75 MPa, and the time of hot pressing and drying is 15 - 30 min.

[0026] Preferably, in step (4), the silicone is composed of HMDS silicon nanoparticles and PDMS mixed solution; the content of HMDS silicon nanoparticles is 0 - 75%, and the size is 7 nm; the PDMS in the silicone is selected from Dow Corning DC184, and the ratio of component A to B is 10:1; the dispersion solvent of the silicone is hexane, and the concentration is 2%; the silicone encapsulation preferably uses the impregnation-room temperature curing method, the impregnation time is 10 - 30 s, and the curing time is 24 - 48 h.

[0027] The laminated waterproof electromagnetic shielding film toughened by fruit peel residue fiber prepared by the above steps is characterized in that: the length of the micro-nano cellulose is 1 - 6 μm, the diameter is 5 - 40 nm; the thickness of the laminated waterproof electromagnetic shielding film is 30 - 58 μm, the tensile strength is 100 - 270 MPa, the elongation at break is 16 - 20%, and the toughness is 12 - 38 MJ / m 3 , the electromagnetic shielding efficiency is 20 - 65 dB, and the specific electromagnetic shielding efficiency of the conductive layer is 8000 - 41000 dB cm 2 g -1 , the surface waterproof contact angle is 105 - 170°, meeting the requirements of commercial electromagnetic shielding materials (EMI SE > 20 dB) and the needs of long-term durability.

[0028] The present invention has the following beneficial effects compared with the prior art:

[0029] (1) Most of the existing MXene / CNF composite electromagnetic shielding films use expensive wood fibers, bamboo fibers or cotton fibers as reinforcing raw materials. From the perspective of raw material economy, this invention uses tropical fruit peel residues (such as durian, mango, coconut, pineapple and jackfruit, etc.) as raw materials, which not only helps to solve the negative impact of waste on the environment, but also provides an innovative solution for the high-value utilization of residues. On the other hand, fruit peel residues usually contain a high pectin content, making it difficult to separate micro-nano cellulose with a high aspect ratio. Traditional combined steam explosion-high temperature degumming methods or steam flash explosion (Ma Jingxia et al., Characteristics of hemp fibers and progress in their degumming, Silk, 2023, 60(08)) need to consider safety factors (1-4 MPa, 150-250 °C), and the severe operating conditions are prone to cause the degradation of lignocellulose. In this invention, gentle enzymatic degumming combined with a specific pressure-time control method for gradient beating is also beneficial for the removal of pectin and fibrillation of fibers, and then fibrillated separation to obtain micro-nano cellulose with a high aspect ratio, which is conducive to the construction of a high-strength and tough cellulose support layer and the micro-nano cellulose in the upper layer of the laminated film serving as a tough scaffold material between MXene sheets.

[0030] (2) Although significant progress has been made in using CNF for MXene reinforcement to construct a uniform composite shielding film, the mechanical properties of the uniformly mixed MXene / CNF composite film are generally limited (the tensile strength is mostly below 200 MPa). At the same time, due to the inherent insulating properties of CNF, the conductive and EMI shielding properties are also sacrificed. High loading of conductive fillers (>50%) usually can obtain excellent electromagnetic shielding performance, but the price is a significant decrease in mechanical properties and deterioration of flexibility (tensile strength <100 MPa, ACS Nano, 2018, 12, 4583-4593), and the cost increases (increases with the increase in the amount of MXene used). Therefore, this invention proposes a shielding film with a laminated structure designed by sequential vacuum filtration and hot pressing drying, using micro-nano cellulose with a high aspect ratio as a mechanically robust and flexible support layer or framework to support the upper composite conductive layer. The proposed innovative strategy realizes performance optimization, not only endows the MXene / CNF composite film with high mechanical properties, but also effectively solves the problem of poor conductivity and shielding performance of the composite film when the cellulose content is high.

[0031] (3) This invention introduces a silicone encapsulation method, and by regulating the proportions of the components in the silicone, the laminated structure shielding film has the function of waterproofing, effectively solving the problem that the composite film is prone to moisture absorption and even oxidation under humid, acidic and other corrosive conditions, ensuring its high conductivity, long-term stability and reliability in practical applications. Description of the Drawings

[0032] Figure 1 It is a morphology diagram of peel residue micro-nano cellulose.

[0033] Figure 2 It is a schematic structural diagram of a laminated waterproof electromagnetic shielding film.

[0034] Figure 3 It shows the toughness and tensile strength (weight 1 kg) of the laminated waterproof electromagnetic shielding film. Specific implementation manners

[0035] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] In the case of no special description, the tensile strength test of the composite film in the context of the present invention is carried out according to the national standard GB / T 1040-2006.

[0037] Example 1

[0038] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fiber, comprising the following steps:

[0039] (1) Retting mango peel as raw material for 15 days, then placing the peel residue fiber in a pectinase solution with a concentration of 0.1% and degumming at 50 °C and pH = 3.5 for 3 h, and then cooking the degummed fiber with a 5% alkali solution at 80 °C for 2 h to remove part of hemicellulose and lignin. Placing the cooked fiber in a Valley beater and carrying out beating by using the gradient specific pressure-time control method, setting the first gradient specific pressure load to 0 kg and the time to 30 min; the second gradient specific pressure load to 1.5 kg and the time to 30 min; the third gradient specific pressure load to 3 kg and the time to 30 min, and measuring the beating degree of the fiber to be 40 °SR. Bleaching the beaten fiber with a 1.5% acidic sodium chlorite solution at 75 °C for 3 h and then carrying out carboxylation modification by TEMPO oxidation (the amount of sodium hypochlorite is 10 mmol / g relative to the absolute dry fiber amount), and obtaining micro-nano cellulose with a length of 1-4 μm and a diameter of 5-20 nm after the modified fiber is subjected to high-speed shearing treatment at 1600 rpm / min by a cell disruptor for 60 min.

[0040] (2) Placing MAX Ti3AlC2 powder with a size of 400 mesh in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain a single-layer MXene nanosheet with a lateral size of 500-3000 nm and a thickness less than 3 nm.

[0041] (3) The grammage is 50 g / m 2, Micro-nano cellulose with a concentration of 1% is vacuum-filtered, and then the mixed solution of micro-nano cellulose and MXene nanosheets is suction-filtered (the upper layer is 20% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 20 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with 2% pure PDMS silicone and cured at room temperature for 24 h for waterproof modification.

[0042] Through the above steps, the laminated waterproof electromagnetic shielding film obtained has a thickness of 34 μm, a tensile strength of 255 MPa, an elongation at break of 18.5%, and a toughness of 32 MJ / m 3 , the electromagnetic shielding efficiency is 30 dB, and the conductive layer ratio electromagnetic shielding efficiency is 29000 dBcm 2 g -1 , the surface waterproof contact angle is 105°, and the shielding efficiency of the composite film after being used in the outdoor environment for one week is 28.4 dB.

[0043] Example 2

[0044] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fiber, comprising the following steps:

[0045] (1) Use durian shells as raw materials for retting for 25 days, and then place the peel residue fiber in a pectinase solution with a concentration of 0.15% and degum it at 50 °C and pH = 3.5 for 3 h. Then, cook the degummed fiber with a 5% alkali solution at 90 °C for 4 h to remove part of the hemicellulose and lignin. Place the cooked fiber in a Valley beater and use the gradient specific pressure-time control method for beating. Set the first gradient specific pressure load to 0 kg and the time to 60 min; the second gradient specific pressure load to 1.5 kg and the time to 60 min; the third gradient specific pressure load to 3 kg and the time to 60 min, and measure the beating degree of the fiber to be 45° SR. The beaten fiber is bleached with a 3% sodium chlorite solution at 75 °C for 3 h and then carboxylated by the carboxymethylation method (the ratio of the amount of sodium chloroacetate to the amount of absolute dry fiber is 1.08). The modified fiber is homogenized 3 times at a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1-4 μm and a diameter of 5-15 nm.

[0046] (2) Place MAX Ti3AlC2 powder with a mesh size of 400 in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500-3000 nm and a thickness of less than 3 nm.

[0047] (3) The gram weight is 50 g / m 2, Vacuum filter micro-nano cellulose with a concentration of 1%, and then suction filter the mixed solution of micro-nano cellulose and MXene nanosheets (the upper layer is 30% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with a 2% HMDS / PDMS mixed solution (the amount of HMDS accounts for 15%) and cured at room temperature for 48 h for waterproof modification.

[0048] Through the above steps, the laminated waterproof electromagnetic shielding film has a thickness of 38 μm, a tensile strength of 257 MPa, an elongation at break of 19.4%, and a toughness of 34 MJ / m 3 , the electromagnetic shielding efficiency is 35 dB, and the conductivity layer ratio electromagnetic shielding efficiency is 22500 dBcm 2 g -1 , the surface waterproof contact angle is 122°, and the shielding efficiency of the composite film after being used in the outdoor environment for one week is 33.8 dB.

[0049] Example 3

[0050] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel and residue fibers, comprising the following steps:

[0051] (1) Use coconut shell as raw material for retting for 30 days, then place the peel and residue fibers in a pectinase solution with a concentration of 0.2% and degum at 50 °C and pH = 3.5 for 12 h. Then, cook the degummed fibers with an 8% alkali solution at 100 °C for 5 h to remove part of the hemicellulose and lignin. Place the cooked fibers in a Valley beater and beat them using the gradient specific pressure-time control method. Set the first gradient specific pressure load to 0 kg and the time to 90 min; the second gradient specific pressure load to 1.5 kg and the time to 90 min; the third gradient specific pressure load to 3 kg and the time to 60 min. Measure the beating degree of the fibers to be 51°SR. Bleach the beaten fibers with a 5% sodium chlorite solution at 75 °C for 4 h, and then carry out carboxylation modification using the carboxymethylation method (the ratio of the amount of sodium chloroacetate to the amount of absolute dry fiber is 1.2). Homogenize the modified fibers 3 times at a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1 - 5 μm and a diameter of 5 - 30 nm.

[0052] (2) Place MAX Ti3AlC2 powder with a size of 400 mesh in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500 - 3000 nm and a thickness less than 3 nm.

[0053] (3) The grammage is 50 g / m 2, Micro-nano cellulose with a concentration of 1% is vacuum filtered, and then the mixed solution of micro-nano cellulose and MXene nanosheets is suction filtered (the upper layer is 40% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with a 2% HMDS / PDMS mixed solution (the amount of HMDS accounts for 30%) and cured at room temperature for 48 h for waterproof modification.

[0054] Through the above steps, the laminated waterproof electromagnetic shielding film obtained has a thickness of 41 μm, a tensile strength of 232 MPa, an elongation at break of 19.4%, and a toughness of 31.1 MJ / m 3 , the electromagnetic shielding efficiency is 39 dB, and the conductivity layer ratio electromagnetic shielding efficiency is 17500 dBcm 2 g -1 , the surface waterproof contact angle is 137°, and the shielding efficiency of the composite film after being used in the outdoor environment for one week is 38.5 dB.

[0055] Example 4

[0056] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel and residue fiber, comprising the following steps:

[0057] (1) Using coconut shell as raw material, retting is carried out for 30 days, and then the peel and residue fiber is placed in a pectinase solution with a concentration of 0.2% and degummed at 50 °C and pH = 3.5 for 12 h. Then the degummed fiber is cooked with an 8% alkali solution at 100 °C for 5 h to remove part of the hemicellulose and lignin. The cooked fiber is placed in a Valley beater and beaten using the gradient specific pressure-time control method. The first gradient specific pressure load is set to 0 kg and the time is 90 min; the second gradient specific pressure load is 1.5 kg and the time is 90 min; the third gradient specific pressure load is 3 kg and the time is 60 min. The beating degree of the fiber is measured to be 51°SR. The beaten fiber is bleached with a 5% acidic sodium chlorite solution at 75 °C for 4 h and then carboxylated and modified by the carboxymethylation method (the ratio of the amount of sodium chloroacetate to the amount of absolute dry fiber is 1.2). The modified fiber is homogenized 3 times under a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1 - 5 μm and a diameter of 5 - 30 nm.

[0058] (2) MAX Ti3AlC2 powder with a size of 400 mesh is placed in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500 - 3000 nm and a thickness less than 3 nm.

[0059] (3) The basis weight is 50 g / m 2, Vacuum filter micro-nano cellulose with a concentration of 1%, and then suction filter the mixed solution of micro-nano cellulose and MXene nanosheets (the upper layer is 40% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with a 2% HMDS / PDMS mixed solution (the amount of HMDS accounts for 45%) and cured at room temperature for 48 h for waterproof modification.

[0060] Through the above steps, the laminated waterproof electromagnetic shielding film obtained has a thickness of 41 μm, a tensile strength of 232 MPa, an elongation at break of 19.4%, and a toughness of 31.1 MJ / m 3 , The electromagnetic shielding efficiency is 39 dB, and the conductive layer ratio electromagnetic shielding efficiency is 17500 dBcm 2 g -1 , The surface waterproof contact angle is 137°, and the shielding efficiency of the composite film after being used in the outdoor environment for one week is 38.9 dB.

[0061] Example 5

[0062] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fiber, comprising the following steps:

[0063] (1) Use pineapple peel as raw material for retting for 20 days, and then place the peel residue fiber in a pectinase solution with a concentration of 0.1% and degum it at 50 °C and pH = 3.5 for 3 h. Then, cook the degummed fiber with a 3% alkali solution at 80 °C for 3 h to remove part of the hemicellulose and lignin. Place the cooked fiber in a Valley beater and beat it using the gradient specific pressure-time control method. Set the first gradient specific pressure load to 0 kg and the time to 60 min; the second gradient specific pressure load to 1.5 kg and the time to 60 min; the third gradient specific pressure load to 3 kg and the time to 30 min, and measure the beating degree of the fiber to be 49.5 °SR. The beaten fiber is bleached with a 2.6% sodium chlorite solution at 75 °C for 3 h and then reacted with a single-component endoglucanase (dose of 240 mg / kg) at 50 °C and pH = 4.8 for 3 h. The enzyme-treated fiber is homogenized 3 times at a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1-6 μm and a diameter of 5-20 nm.

[0064] (2) Place MAX Ti3AlC2 powder with a mesh size of 400 in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500-3000 nm and a thickness of less than 3 nm.

[0065] (3) The gram weight is 50 g / m 2, vacuum filter micro-nano cellulose with a concentration of 1%, and then suction filter the mixed solution of micro-nano cellulose and MXene nanosheets (the upper layer is 50% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with a 2% HMDS / PDMS mixed solution (the amount of HMDS accounts for 60%) and cured at room temperature for 48 h for waterproof modification.

[0066] Through the above steps, the laminated waterproof electromagnetic shielding film obtained has a thickness of 44.2 μm, a tensile strength of 162 MPa, an elongation at break of 16.7%, and a toughness of 19.1 MJ / m 3 , the electromagnetic shielding efficiency is 45.5 dB, and the conductivity layer ratio electromagnetic shielding efficiency is 15000 dB cm 2 g -1 , the surface waterproof contact angle is 165°, and the shielding efficiency of the composite film is about 45.5 dB after being used in the outdoor environment for one week.

[0067] Example 6

[0068] A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel and residue fiber, comprising the following steps:

[0069] (1) Use jackfruit shell as raw material for retting for 30 days, then place the peel and residue fiber in a pectinase solution with a concentration of 0.15% and degum at 50 °C and pH = 3.5 for 3 h. Then cook the degummed fiber with a 5% alkali solution at 90 °C for 4 h to remove part of the hemicellulose and lignin. Place the cooked fiber in a Valley beater and beat it using the gradient specific pressure-time control method. Set the first gradient specific pressure load to 0 kg and the time to 60 min; the second gradient specific pressure load to 1.5 kg and the time to 60 min; the third gradient specific pressure load to 3 kg and the time to 60 min, and measure the beating degree of the fiber to be 47.2 °SR. The beaten fiber is bleached with a 3% sodium chlorite solution at 75 °C for 3 h and then carboxylated by TEMPO oxidation method (the amount of sodium hypochlorite relative to the absolute dry fiber amount is 10 mmol / g). The modified fiber is homogenized 3 times at a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1 - 4.5 μm and a diameter of 5 - 20 nm.

[0070] (2) Place MAX Ti3AlC2 powder with a mesh size of 400 in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500 - 3000 nm and a thickness less than 3 nm.

[0071] (3) The gram weight is 50 g / m 2, vacuum filter micro-nano cellulose with a concentration of 1%, and then suction filter the mixed solution of micro-nano cellulose and MXene nanosheets (the upper layer is 70% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film. The composite film is encapsulated with a 2% HMDS / PDMS mixed solution (the amount of HMDS accounts for 75%) and cured at room temperature for 48 h for waterproof modification.

[0072] Through the above steps, the laminated waterproof electromagnetic shielding film is obtained with a thickness of 50.2 μm, a tensile strength of 140.4 MPa, an elongation at break of 11.3%, and a toughness of 8.9 MJ / m 3 , the electromagnetic shielding efficiency is 54.7 dB, and the conductivity layer specific electromagnetic shielding efficiency is 10750 dB cm 2 g -1 , the surface waterproof contact angle is 170°, and the shielding efficiency of the composite film is about 54.7 dB after being used in the outdoor environment for one week.

[0073] Comparative Example 1

[0074] A preparation method of a laminated electromagnetic shielding film toughened by fruit peel residue fiber, comprising the following steps:

[0075] (1) Use jackfruit shells as raw materials for retting for 30 days, and then place the peel residue fiber in a pectinase solution with a concentration of 0.15% and degum it at 50 °C and pH = 3.5 for 3 h. Then, cook the degummed fiber with a 5% alkali solution at 90 °C for 4 h to remove part of the hemicellulose and lignin. Place the cooked fiber in a Valley beater and beat it using the gradient specific pressure-time control method. Set the first gradient specific pressure load to 0 kg and the time to 60 min; the second gradient specific pressure load to 1.5 kg and the time to 60 min; the third gradient specific pressure load to 3 kg and the time to 60 min. Measure the beating degree of the fiber to be 47.2 °SR. The beaten fiber is bleached with a 3% sodium chlorite solution at 75 °C for 3 h and then carboxylated by TEMPO oxidation method (the amount of sodium hypochlorite relative to the absolutely dry fiber amount is 10 mmol / g). The modified fiber is homogenized 3 times at a pressure of 15000 Psi to obtain micro-nano cellulose with a length of 1 - 4.5 μm and a diameter of 5 - 20 nm.

[0076] (2) Place MAX Ti3AlC2 powder with a size of 400 mesh in a 9M LiF-HCl solution for selective etching and peeling for 48 h to obtain single-layer MXene nanosheets with a lateral size of 500 - 3000 nm and a thickness of less than 3 nm.

[0077] (3) The gram weight is 50 g / m 2, Vacuum filter micro-nano cellulose with a concentration of 1%, and then suction filter the mixed solution of micro-nano cellulose and MXene nanosheets (the upper layer is 70% of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4). The wet cake is hot-pressed and dried at 0.6 MPa and 90 °C for 30 min to obtain a flexible, high-strength, and highly conductive laminated composite film.

[0078] Through the above steps, the thickness of the laminated electromagnetic shielding film is 50.2 μm, the tensile strength is 140.4 MPa, the elongation at break is 11.3%, and the toughness is 8.9 MJ / m 3 , the electromagnetic shielding efficiency is 54.7 dB, and the specific electromagnetic shielding efficiency of the conductive layer is 10750 dB cm 2 g -1 , the surface contact angle is 78°, and the shielding efficiency of the composite film is about 48.9 dB after being used in the outdoor environment for one week.

[0079] Comparative Example 2

[0080] Prepared by the method in the prior art (Materials Today Nano 2023, 24, 100393) as follows: Use nanocellulose with a diameter of 1.5 - 3 nm and an average length of 2.21 μm as the reinforcing phase for MXene nanosheets with a lateral size of about 1.5 μm. The MXene / PALNF composite electromagnetic shielding film was prepared by the methods of uniform blending and suction filtration. When the dosage of MXene and PALNF reached 1:1, the performance of the composite film reached equilibrium. At this time, the thickness of the film was about 28 μm, its maximum tensile strength was 159.6 MPa, the elongation at break was 6.7%, and the toughness was about 5.8 MJ / m 3 , the electromagnetic shielding efficiency is 33.5 dB, and the specific electromagnetic shielding efficiency is 6541.1 dB cm 2 g -1 , the shielding efficiency of the composite film is about 31.3 dB after being used in the outdoor environment for one week.

[0081] Comparative Example 3

[0082] Prepared by the method in the prior art (ACS Appl. Mater. Interfaces 2020, 12, 4895 - 4905) as follows: The CNF / MXene composite film prepared by uniformly blending nanocellulose separated from cotton (length 1 - 3 μm, diameter 4 - 10 nm) and MXene nanosheets with an average thickness of 1.2 nm and a lateral size of several microns. Similarly, when the dosage of each component reached 1:1, the film thickness was about 35 μm, the tensile strength was 92.1 MPa, the elongation at break was 2.2%, and the toughness was about 1 MJ / m 3 , the electromagnetic shielding efficiency is 22.6 dB.

[0083] Comparative Example 4

[0084] Prepared by the method in the prior art (ACS Nano 2018, 12, 4583 - 4593) as follows: Garlic skin nanocellulose (with a length of a few micrometers and a width of 20 - 50 nm) was used to reinforce MXene nanosheets. When the dosage of each component was uniformly mixed at a ratio of 1:1, the thickness of the composite film was 167 μm, the tensile strength was 135.4 MPa, the elongation at break was 16.7%, the toughness was 14.8 MJ / m 3 , and the electromagnetic shielding efficiency was 25 dB, and the specific electromagnetic shielding efficiency was 1326 dB cm 2 g -1 .

[0085] Comparative Example 5

[0086] Prepared by the method in the prior art (J.Mater.Chem.C, 2019, 7, 9820) as follows: A composite electromagnetic shielding film was prepared by uniformly blending bleached cardboard nanocellulose and MXene nanosheets at a ratio of 1:1. When the thickness of the obtained composite film was 38 μm, the tensile strength was about 141.9 MPa, the elongation at break was 2.1%, the toughness was 1.7 MJ / m 3 , and the electromagnetic shielding efficiency was 39.6 dB, and the specific electromagnetic shielding efficiency (SSE / t) was 4750 dB cm 2 g -1 .

[0087] Verification Example 1

[0088] Samples of Examples 1 - 6 and Comparative Examples 1 - 5 were taken respectively for performance testing, and the test results are shown in Tables 1 and 2 below.

[0089] Table 1 Performance Parameters of the Layered Waterproof Electromagnetic Shielding Films Obtained by Each Process

[0090]

[0091]

[0092] Table 2 Performance Parameters of MXene / CNF Electromagnetic Shielding Films in the Prior Art

[0093]

[0094] As can be seen from the statistical results in Table 1, the laminated electromagnetic shielding film made of fruit peel residue micro-nano cellulose composite prepared by the process of the present invention has low thickness, high strength, good toughness and high electromagnetic shielding efficiency. After silicone encapsulation, the waterproof property of the composite film increases significantly. Even after being placed outdoors for a week, it still maintains good electromagnetic shielding efficiency, indicating that the durability of the composite film has been significantly improved.

[0095] As can be seen from Examples 1-6, when the amount of the upper-layer micro-nano cellulose mixed with MXene nanosheets in the laminated structure gradually increases compared with the lower layer, the thickness of the film gradually increases, and the tensile strength, elongation at break and toughness show a trend of first increasing and then decreasing. When the proportion of the upper-layer raw material relative to the lower layer is 30%, the mechanical properties reach the optimum. Generally speaking, when the amount of the raw material in the upper layer of the composite film is less than 50%, the tensile strength of the composite film is good, all greater than 200 MPa, and the toughness is as high as 30 MJ / m 3 . In addition, the electromagnetic shielding efficiency of the composite film increases with the increase of the thickness, and the specific electromagnetic shielding efficiency shows the opposite trend, but the shielding efficiency of the composite film is greater than 20 dB, meeting the requirements of commercial electromagnetic shielding materials (SE > 20 dB). At the same time, it can be seen that the proportion of HMDS silicon nanoparticles in silicone has a significant impact after the laminated composite film is waterproofed with silicone. As the content of HMDS silicon nanoparticles gradually increases, the waterproof property (contact angle) of the composite film gradually increases, and the enhancement of the waterproof property promotes the significant enhancement of the durability of the composite film in the environment. The trend of the shielding efficiency of the composite film decreasing after being placed outdoors for a week becomes smaller and smaller.

[0096] From Examples 3 and 4, Examples 6 and Comparative Example 1, under the same preparation process of the laminated composite film, when the mechanical properties remain unchanged, the composite film is waterproofed. When the amount of HMDS silicon nanoparticles in silicone is changed or silicone encapsulation is not used, the waterproof property will change greatly, resulting in a large change in the shielding efficiency of the film after being placed outdoors for a week. After waterproof modification, the durability of the composite film is improved. In addition, through Examples 6 and Comparative Example 2 in Tables 1 and 2, it is also proved that the waterproof method developed by the present invention can endow the laminated composite film with stable electromagnetic shielding performance and solve the problem of easy oxidation of the film.

[0097] As can be seen from Examples 1-4 and Comparative Examples 2-5 in Tables 1 and 2, the innovative design of the composite film laminated structure of the present invention has significantly improved mechanical properties compared to the uniformly blended composite film. The tensile strength, elongation at break, and toughness are all significantly better than those of the uniform blend. These cases indicate that the innovative design of the laminated structure can fully utilize the strength and toughness advantages of the micro-nano cellulose support layer or scaffold. In addition, the innovative design of the laminated structure in Examples 1-4 also endows the composite film with excellent electromagnetic shielding performance, solving the problem of the difficulty in balancing the strength and shielding performance of the uniformly blended composite film. At the same time, the innovative method of encapsulating with low surface energy silicone improves the waterproof performance of the composite film, facilitating the long-term stable operation of the film in a high-humidity outdoor working environment. Therefore, the above cases demonstrate that the waterproof design of the laminated structure coupled with the low surface energy silicone layer is essential for the preparation of a composite film with high strength, flexibility, excellent electromagnetic shielding performance, and durability.

[0098] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a laminated waterproof electromagnetic shielding film toughened by fruit peel residue fiber, characterized in that, It includes the following preparation steps: (1) Retting: Using waste fruit peels and residues as raw materials, and then retting. (2) Degumming: Adjusting the retted peel fiber to appropriate concentration, temperature and pH, and adding pectinase for degumming. (3) Cooking: Adding the degummed peel fiber into an alkaline solution with appropriate concentration and cooking at an appropriate temperature to remove part of hemicellulose and lignin. (4) Beating: Placing the cooked peel fiber obtained in step (3) into a Valley beater for beating. The beating adopts a gradient specific pressure-time control method, and the beating degree is controlled at 30 - 60°SR. (5) Bleaching: Bleaching the beaten peel fiber with acidic sodium chlorite with a concentration of 1 - 5% at 70 - 100°C for 3 - 6 h. (6) Biochemical pretreatment: Pretreating the bleached peel fiber by any one or two or three of TEMPO oxidation method, carboxymethylation method or enzymatic method for biochemical pretreatment. (7) Fiberization and peeling: Subjecting the biochemically pretreated peel fiber obtained in step (6) to high-speed shearing, ultrasonic crushing treatment or high-pressure homogenization to obtain a micro / nano cellulose dispersion with a length of 1 - 6 μm and a diameter of 5 - 40 nm. (8) Preparation of MXene nanosheets: Monolayer Ti3C2Tx MXene nanosheets were obtained by selectively etching and exfoliating 400-mesh MAX Ti3AlC2 powder with 9M LiF-HCl solution for 48 hours. x MXene nanosheets; (9) Preparation of laminated composite film: Sequentially passing through vacuum filtration of micro / nano cellulose and a mixed solution of micro / nano cellulose and MXene nanosheets, and then obtaining a flexible and high-strength composite film with a lower layer of micro / nano cellulose flexible support layer and an upper layer of cellulose / MXene mixed conductive layer through hot pressing and drying. (10) Waterproof encapsulation: After encapsulating the laminated composite film prepared in step (9) with silicone, obtaining a waterproof and antioxidant laminated electromagnetic shielding film with a silicone waterproof layer on the surface.

2. The preparation method according to claim 1, characterized in that, In step (1), the fruit peel and residue raw material is one or more of durian shells, mango peels, coconut shells, pineapple peels and jackfruit shells; the retting time is 15 - 30 days.

3. The preparation method according to claim 1, characterized in that, In step (2), the appropriate concentration of pectinase degumming is 0.02 - 0.2%, the temperature is 45 - 55°C, and the pH is 3.0 - 4.

0.

4. The preparation method according to claim 1, characterized in that, In step (3), the alkali concentration of the cooking solution is 1 - 8%, the temperature is 80 - 120°C, and the time is 2 - 10 h.

5. The preparation method according to claim 1, wherein In step (4), the gradient specific pressure-time is as follows: the first gradient specific pressure load is 0 - 1 kg, and the time is 30 - 90 min; the second gradient specific pressure load is 1.5 - 2 kg, and the time is 30 - 90 min; the third gradient specific pressure load is 2.5 - 3 kg, and the time is 30 - 60 min.

6. The preparation method according to claim 1, characterized in that, In step (6), the dosage of sodium hypochlorite in the TEMPO oxidation method is 3 - 15 mmol / g relative to the absolute dry fiber amount; the ratio of the dosage of sodium chloroacetate to the absolute dry fiber amount in the carboxymethylation method is 0.8 - 1.2; the enzymatic method uses a single-component endoglucanase, the dosage of the enzyme is 80 - 320 mg / kg, the reaction temperature is 50°C, the pH is 4.8, and the time is 30 - 240 min.

7. The preparation method according to claim 1, characterized in that, The high-speed shearing processing equipment described in step (7) is a wall breaker, and the stirring speed is 800 - 1600 rpm / min; the power of the ultrasonic crushing processing equipment is 650 W; the working pressure of the homogenization treatment is between 10,000 - 30,000 Psi; the fibrillation stripping time is 30 - 60 min.

8. The preparation method according to claim 1, wherein In step (9), the grammage of the lower micro-nano cellulose flexible support layer in the laminated composite film is 50 g / m 2 , and the amount of the upper cellulose / MXene mixed conductive layer is 10-90% of that of the lower layer, and the ratio of fiber to MXene in the upper layer is 1:4; the temperature of the hot pressing and drying is 80-100 °C, the pressure is 0.1-0.75 MPa, and the time is 15-30 min.

9. The preparation method according to claim 1, wherein The silicone described in step (10) consists of a mixed solution of HMDS silicon nanoparticles and PDMS, where the size of the HMDS silicon nanoparticles is 7 nm and the content is 0 - 75%. The encapsulation is carried out by the impregnation-room temperature curing method, with an impregnation time of 10 - 30 s and a curing time of 24 - 48 h.

10. The laminated waterproof electromagnetic shielding film toughened with fruit peel residue fiber prepared by the preparation method according to any one of claims 1-9, characterized in that: The thickness of the electromagnetic shielding film is 30 - 58 μm, the tensile strength is 100 - 270 MPa, the elongation at break is 16 - 20%, and the toughness is 12 - 38 MJ / m 3 , the electromagnetic shielding efficiency is 20 - 65 dB, and the conductive layer specific electromagnetic shielding efficiency is 8000 - 41000 dB cm 2 g -1 , and the surface waterproof contact angle is 105 - 170°.

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