CN113881108A

CN113881108A - Pineapple leaf fiber-reinforced flexible electromagnetic shielding film and preparation method thereof

Info

Publication number: CN113881108A
Application number: CN202111167626.8A
Authority: CN
Inventors: 陈港; 钱杨杨; 刘义军; 王淳玉
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2021-10-07
Filing date: 2021-10-07
Publication date: 2022-01-04
Anticipated expiration: 2041-10-07
Also published as: CN113881108B

Abstract

The invention provides an ultrathin, light, flexible, high-strength and high-conductivity pineapple leaf fiber-reinforced electromagnetic shielding film and a preparation method thereof. The invention extracts the micro-and nano-fiber of the high-length-diameter ratio one-dimensional pineapple leaf and the high-conductivity two-dimensional transition metal carbide Ti from the whole pineapple leaf₃C₂T_xMXene combines to form a mechanical interlocking structure to promote Ti₃C₂T_xThe flexibility and the mechanical strength of the base film, and the excellent conductivity and the electromagnetic shielding performance of the composite film are endowed, a new process is provided for the application and the development of the biomass-based wearable electromagnetic shielding film, and the green and environment-friendly development, the resource utilization and the high value of agricultural byproducts are realizedThe chemical utilization provides a new approach.

Description

Pineapple leaf fiber-reinforced flexible electromagnetic shielding film and preparation method thereof

Technical Field

The invention belongs to the field of cellulose-based flexible electromagnetic shielding materials, and particularly relates to an ultrathin, light, flexible, high-strength and high-conductivity pineapple leaf fiber-reinforced electromagnetic shielding film and a preparation method thereof.

Background

Pineapple, second only to banana and mango, is planted in 82 countries worldwide, with an area of over 100 hectares, and in 2028 world pineapple yield will reach 3100 million tons, which is just an indispensable part of farmer income. However, during the process of harvesting and producing pineapples, a large amount of byproducts such as peels, leaves and crowns are generated, the weight of the byproducts accounts for 30-35% of the weight of the whole fresh pineapples, namely about 7640 ten thousand tons of pineapple byproducts can be generated every year in the world, the utilization of pineapple leaf fibers which are byproducts currently on the market is limited in most mature and low-end industrial fields such as yarns, clothes, automobile cushion ornaments or food packaging and the like to improve the added value of wastes, but the gain is not high, most farmers still tend to discard, bury or compost the byproducts, even burn the byproducts in the open air, and the decomposition of organic components in the byproducts causes CO_X、NO_XSulfur dioxide, polycyclic aromatic hydrocarbons, dioxins and the like, pollute the environment and cause health problems. In addition, as the fourth great pineapple producing country which is only inferior to costa rica, philippines and brazil in China, the yield of the pineapples is more than 200 million tons every year, and the annual pineapple leaf fiber yield is estimated to be 10 million tons, so that the finding of a high-added-value and sustainable method for solving the problem of pineapple waste promotes the income increase of farmers and the improvement of environmental problems to become very important.

With the arrival of the big data era, the rapid development of the internet of things technology and the wireless communication technology brings great convenience to the life of people, and simultaneously, the problem of electromagnetic radiation pollution which cannot be ignored is generated, and with the rapid increase of the number of new generation highly integrated, high-power and high-frequency electronic devices led in the 5G era, the problems of electromagnetic interference and radiation caused by electromagnetic waves are increasingly prominent. In addition, with the rapid development of wearable and portable electronic devices in recent years, high dielectric electromagnetic shielding materials capable of satisfying ultra-thin, light, flexible, and high mechanical properties simultaneously have become a research focus beyond conventional conductive materials. The traditional conductive materials are mainly metals and related products thereof, such as silver, iron, copper, nickel and the like, although the electromagnetic shielding efficiency is high, the conductive materials have the defects of high density, poor flexibility, difficult degradation and the like, and secondary pollution is easily caused by using a large amount of the metals as raw materials of the electromagnetic shielding materials due to strong reflection of electromagnetic waves. Therefore, the urgent need to search for new raw materials and develop multifunctional electromagnetic shielding materials becomes an important issue to inhibit electromagnetic interference and radiation, reduce electronic waste, ensure long-term normal operation of electronic equipment and protect human beings from radiation damage.

Transition metal carbide and nitride MXene materials with two-dimensional layered structures have been widely reported to be very different in a plurality of application fields, have the advantages of excellent metal conductivity, large specific surface area, hydrophilicity, low density and the like, and are widely applied to conductive fillers. Two-dimensional Ti₃C₂T_xMXene about electromagnetic interference shielding research is reported by teaching task group Yury Gogotsi of Delisel university in 2016 in the Science journal (Science, 353, 1137-. Natural renewable polymer resources, cellulose and its derived materials play a vital role in national production and life. The micro-nano cellulose has many ideal characteristics, including flexibility, light weight, easy processing, low density, high biodegradability, high thermal expansibility, high mechanical strength and the like, and is an ideal reinforcing material. The plant biomass-MXene composite electromagnetic shielding material reported at present is mainly divided into a two-dimensional or three-dimensional structure, such as a two-dimensional electromagnetic shielding film prepared by Cao waves and the like (ACS Nano, 2018, 4583-Electromagnetic shielding efficiency is only 25 dB, and in addition, the high thickness is not beneficial to the development of ultrathin and flexible wearable materials. Also like Zhan et al (j. mater. chem. C, 2019, 9820) also use bleached board as raw material for making nanocellulose, chemical pulping is known to have adverse effects on the environment. Chemical fibers such as aramid fibers are relatively expensive compared to abundant natural plant fibers. Therefore, the invention provides that the pineapple fiber is extracted from the whole leaves of the agricultural waste pineapple by a pure mechanical method, which not only has the advantages of high efficiency, environmental protection and low cost, but also is obtained by controlling the technological conditions of pulping, chemical pretreatment and micro-nano treatment, and the obtained one-dimensional pineapple leaf micro-fiber, nano-fiber and two-dimensional Ti with high length-diameter ratio₃C₂T_xThe MXene composite can construct a high-performance electromagnetic shielding material, can meet the commercial requirements of high-end wearable electronic devices, effectively solves the problem of poor mechanical performance of MXene, provides a new idea for resource utilization of pineapple waste, provides a new approach for increasing income of farmers, and is more favorable for relieving the problem of environmental pollution.

Disclosure of Invention

The invention aims to provide a pineapple leaf fiber-reinforced flexible electromagnetic shielding film and a preparation method thereof, and the pineapple leaf micro-nano cellulose/Ti provided by the invention₃C₂T_xThe composite conductive film has the characteristics of ultra-thin property, light weight, high strength and high conductivity, is beneficial to solving the environmental problems caused by the use of bleaching agents, electromagnetic radiation pollution and the like in chemical pulping, and provides a new way for resource utilization of agricultural wastes and the like.

In order to achieve the above purpose, the present invention is realized by the following means:

the invention provides a pineapple leaf fiber reinforced flexible electromagnetic shielding film, which comprises one-dimensional pineapple leaf fibers with high length-diameter ratio and two-dimensional transition metal, wherein the pineapple leaf fibers comprise one or more of micron-sized fibers and nano-sized fibers.

Preferably, the micron-sized pineapple leaf fibers have the length of 100-300 mu m and the diameter of 200-400 nm; the nanometer pineapple leaf fiber has length of 0.6-7 μm and diameter of 1-20 nm.

Preferably, the two-dimensional transition metal is selected from MAX Ti₃AlC₂Powder of said MAX Ti₃AlC₂The powder size is 200-400 meshes.

The second aspect of the invention provides a preparation method of a pineapple leaf fiber-reinforced flexible electromagnetic shielding film, which comprises the following steps:

(1) preparing a micro-nano cellulose dispersion by taking agricultural wastes as raw materials and carrying out high-concentration defibering, pulp screening, low-concentration pulping, chemical pretreatment, ultrasonic treatment or high-pressure homogenization;

(2) adopting weak acid selective treatment and mechanical treatment to treat MAX Ti₃C₂T_xEtching and stripping the powder to obtain single-layer Ti₃C₂T_xMXene nanosheets;

(3) suspension of micro-or nano-cellulose fibres and single layer of Ti₃C₂T_xAfter the nano sheets are mixed, the cellulose-based flexible electromagnetic shielding film with ultrathin, high strength and high conductivity is prepared by vacuum-assisted filtration-induced self-assembly and hot-pressing drying.

Preferably, the agricultural waste of step (1) is chopped pineapple leaf strips with the length of 5 cm; the concentration of the high-concentration defibering slurry is 15-25%; the pulp screening refers to screening pineapple leaf fibers separated from leaves and flesh by using pulp screening machines such as a flat plate slit sieve with the slit width of 0.1-0.5 mm or a round hole sieve with the mesh size of 5-12 mm;

most preferably, the low-consistency beating in the step (1) is performed by a wary beater in 3-grade gradient beating, wherein the beating load of the 1 st grade is 0-1 kg and is 60-90 min; the grade 2 beating load is 1.5-3 kg, 30-60 min; the 3 rd level beating load is 3.5-5 kg, 10-20 min; the optimal beating degree is controlled to be 30-65 DEG SR;

preferably, the chemical pretreatment refers to any one or more of a TEMPO oxidation process or a carboxymethylation pretreatment process.

Most preferably, the ultrasonic treatment in step (1) is selected from an ultrasonic cell crusher with power of 650W, and the ultrasonic time is 30-120 min. The high-pressure homogenization adopts a Noozle micro-jet homogenizer, and the homogenization pressure is between 15000 and 25000 Psi.

Preferably, the weak acid in step (2) is weak hydrogen fluoride aqueous solution prepared from lithium fluoride and hydrochloric acid solution; the concentration of the hydrochloric acid solution in the system is preferably 6-9 mol/L.

Preferably, the MAX Ti of step (2)₃AlC₂The powder size is preferably 200-400 meshes; the mechanical etching time is preferably 24-48 h.

Preferably, the stripping mode in the step (2) is ultrasonic, manual shaking, oscillation or magnetic stirring; the stripping time is 10-30 min; the single layer of Ti₃C₂T_xThe lateral size of the nano-sheet is between 500-2000 nm, and the thickness is less than 3 nm.

Preferably, the nanocellulose suspension of step (3) and the single layer of Ti₃C₂T_xThe concentration of the nano-sheets is preferably 1-10 mg/mL; the single layer of Ti₃C₂T_xThe mixing ratio of the nano-sheet to the pineapple leaf nano-cellulose suspension is 0-4.

Most preferably, the hot-pressing drying condition of the step (3) is controlled to be 0.75-1 MPa for 20-40 min, and the temperature is 90-110 ℃.

The pineapple leaf fiber-reinforced flexible electromagnetic shielding film prepared by the steps is characterized in that: the pineapple leaf fiber has a length of 0.6-300 μm and a diameter of 1-400 nm; the Ti₃C₂T_xThe gram weight of the/pineapple leaf cellulose composite conductive film is about 50 g/m²The thickness is 26-28 μm, the tensile strength is 131-215 MPa, the elongation at break is 5.35-20%, and the toughness is 4.1-29.6 MJ/m³The conductivity is 3-5000S/m, the electromagnetic shielding efficiency (EMI SE) is 21.3-44.4 dB, and the specific electromagnetic shielding efficiency (SSE/t) is 3835-8655 dB cm²g^-1Meeting the requirement of commercial electromagnetic shielding material (EMI SE)>20 dB).

The scanning electron microscope picture of the micron-sized fiber with high length-diameter ratio prepared by the process of the invention is shown in figure 1, and the atomic force microscope picture of the nanometer-sized fiber is shown in figure 2; the relationship between the mechanical tensile strength and the elongation at break of the obtained pineapple leaf fiber-reinforced flexible electromagnetic shielding film is shown in fig. 3, and the influence of the fiber proportion on the toughness of the composite film is shown in fig. 4.

Compared with the prior art, the invention has the following beneficial effects:

(1) the conventional MXene-based polymer composite electromagnetic shielding film is enhanced by mainly adopting bleached softwood, hardwood or aramid fibers, but the application directly adopts waste agricultural resource pineapple leaves as raw materials, and has the advantages of high efficiency, greenness, environmental protection and low cost by extracting fibers through physical processes such as high-concentration defibering, pulp screening and the like, so that a new way is provided for resource utilization of wastes; on the other hand, the micro-nano cellulose fiber and the nano cellulose fiber with high length-diameter ratio can be obtained through 3-grade gradient low-concentration pulping, chemical pretreatment, ultrasonic treatment or high-pressure homogenization of the process, and the high-length-diameter ratio fiber plays an important role in the strength of the composite membrane.

(2) The pineapple leaf fiber is subjected to 3-level gradient mechanical pulping treatment by using a Wally pulping machine, the high pulping degree of 30-65 DEG SR is kept, devillicate fibrillation of the fiber is facilitated, a large number of hydroxyl groups are exposed on the surface of the fiber, the mechanical strength of the film is further improved by increasing the bonding force among the fibers and between the fiber and MXene, and stress dispersion is transferred.

(3) The electromagnetic shielding film is maintained to be thinner by adopting a hot pressing method and controlling proper conditions; meanwhile, the drying rate of the film is further accelerated; in addition, compared with common room temperature drying or vacuum drying, the hot pressing is more favorable for promoting the nanofiber and the two-dimensional sheet layer in the composite film to form a compact brick-pulp structure, so that the mechanical strength of the material is improved.

(4) The pure MXene film (Zeying Zhan, J. Mater. chem. C, 2019, 7, 9820) reported in the literature at present has the tensile strength of about 12.8 MPa, the breaking strain of 0.7 percent and the toughness of 0.1 MJ/m³By adopting the process, the mechanical strength of the composite electromagnetic shielding film is obviously improved only when 20% of the addition amount of the pineapple leaf micro and nano fibers is added, wherein the tensile strength is improved by 927%, the breaking strain is improved by 664%, the toughness is improved by 4000%, and the poor mechanical performance of the MXene material is obviously improved.

Drawings

FIG. 1 is a scanning electron microscope image of a high aspect ratio micron-sized fiber

FIG. 2 is an atomic force microscope image of a nanofiber with a high aspect ratio

FIG. 3 is a graph showing the relationship between the mechanical tensile strength and the elongation at break of the composite film obtained by mixing different MXene/pineapple leaf fibers.

FIG. 4 is a diagram showing the relationship between the ratio of MXene/pineapple leaf fibers and the toughness of the composite film.

Detailed Description

In order to make the objects, technical solutions and effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Without being particularly specified, the tensile strength test of the composite film in the context of the present invention adopts the national standard test GB/T1040-.

Example 1

A pure pineapple leaf nanofiber film and a preparation method thereof are disclosed, wherein the preparation method comprises the following steps:

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 15%, screening pineapple leaf fibers separated from leaf pulp by using a flat plate slotted screen with the slot width of 0.35 mm, and conducting 3-grade gradient low-concentration pulping according to the concentration of 4% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 40-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 100 g of ethanol and is soaked for 30 min, 1.1 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added to dissolve the sodium chloroacetate according to the mass ratio of 1:1, then 0.4 g of sodium hydroxide corresponding to 1 g of oven dry fiber is weighed, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 4 wt%, and the temperature is increased to 79 ℃ for refluxing for 1 h. Washing with distilled water to obtain carboxymethylated modified fiber, homogenizing the slurry with high pressure micro jet homogenizer for 2 times (pressure 15000 PSi) to obtain 1.5% mass concentration nanometer cellulose dispersion with nanometer fiber length of 1.5-7 μm and diameter of 5-19 nm;

(2) the 1.5% strength nanocellulose dispersion was diluted to 1mg/mL and then 50 g/m²Preparing a wet nano cellulose membrane by vacuum filtration, and drying the wet membrane at the temperature of 105 ℃ and under the pressure of 0.9 MPa for 30 min to obtain a pure nano cellulose membrane;

the pure pineapple leaf nanofiber membrane is obtained through the steps, the thickness of the membrane is 28 microns, the tensile strength is 215 MPa, the elongation at break is about 20%, and the toughness is 29.6 MJ/m³。

Example 2

A pineapple leaf fiber reinforced flexible electromagnetic shielding film and a preparation method thereof are disclosed, wherein the preparation method comprises the following steps:

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 20%, screening pineapple leaf fibers separated from leaf pulp by using a flat plate slotted screen with the slot width of 0.15 mm, and conducting 3-grade gradient low-concentration pulping according to the concentration of 8% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 55-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 200 g of ethanol and soaked for 15 min, then 0.9 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added to dissolve the sodium chloroacetate according to the mass ratio of 1:1, then sodium hydroxide is weighed according to the amount of 0.3 g of sodium hydroxide corresponding to 1 g of oven dry fiber, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 6 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fibers, and carrying out ultrasonic treatment on the fibers for 60 min to obtain a micron cellulose dispersion with the mass concentration of 1%, wherein the length of the micron fibers is 180-300 mu m, and the diameter is 200-400 nm;

(2) 1 g LiF powder was added to 9M HCl and stirred for 30 min, after which 1 g of 200 mesh MAX Ti₃AlC₂Adding the powder into the system for etching for 48 h, adding a large amount of distilled water after the reaction is finished, washing, centrifuging and drying to obtain pH>6 of multi-layer Ti₃C₂T_xDispersing the powder into distilled water, and ultrasonic treating for 15 min to obtain single-layer Ti₃C₂T_xNanosheets;

(3) mixing a 1% cellulose suspension and 10 mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 8:2, carrying out vacuum filtration, and drying at 90 ℃ for 40 min under 0.9 MPa to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber-reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 27 mu m, the tensile strength is 203.93 MPa, the elongation at break is 17.47%, and the toughness is 23.51 MJ/m³The conductivity was 3S/m, the electromagnetic shielding efficiency (EMI SE) was 21.3 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 3835 dB cm²g^-1。

Example 3

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 25%, screening pineapple leaf fibers separated from leaf pulp by using a flat plate slotted screen with the slot width of 0.5 mm, and conducting 3-grade gradient low-concentration pulping according to the concentration of 4% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 65-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 200 g of ethanol and soaked for 15 min, 1.1 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added according to the mass ratio of 1:1 to dissolve the sodium chloroacetate, 0.4 g of sodium hydroxide corresponding to 1 g of oven dry fiber is weighed, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 6 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fiber, homogenizing the slurry with high pressure microfluidizer for 3 times (pressure 15000 PSi) to obtain 1% mass concentration nanocellulose dispersoid, wherein the length of the nanofiber is 0.6-4.8 μm, and the diameter is 1-5 nm;

(2) 1 g LiF powder is added into 9M HCl and stirred for 30 min, and 1 g MAX T with 400 meshes is addedi₃AlC₂Adding the powder into the system for etching for 48 h, adding a large amount of distilled water after the reaction is finished, washing, centrifuging and drying to obtain pH>6 of multi-layer Ti₃C₂T_xDispersing the powder into distilled water, and stirring for 30 min to obtain single-layer Ti₃C₂T_xNanosheets;

(3) 0.5% of nano-cellulose suspension and 5mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 7:3, carrying out vacuum filtration, and drying at 90 ℃ and 1 MPa for 30 min to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 27 mu m, the tensile strength is 187.73 MPa, the elongation at break is 16.32%, and the toughness is 20.88 MJ/m³The conductivity was 46S/m, the electromagnetic shielding efficiency (EMI SE) was 28.9 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 4648 dB cm²g^-1。

Example 4

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 25%, then screening pineapple leaf fibers separated from leaves and flesh by using a circular hole sieve with the sieve pore size of 10mm, and then conducting 3-grade gradient low-concentration pulping according to the concentration of 4% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 60-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 200 g of ethanol and soaked for 15 min, then 0.98 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added according to the mass ratio of 1:1 to dissolve the sodium chloroacetate, then 0.38 g of sodium hydroxide corresponding to 1 g of oven dry fiber is weighed, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 2 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fibers, and carrying out ultrasonic treatment on the fibers for 90 min to obtain a micron cellulose dispersion with the mass concentration of 1%, wherein the length of the fibers is 150-;

(2) 1 g LiF powder was added to 6M HCl and stirred for 10 min, and 1 g 325 mesh MAX Ti₃AlC₂Adding the powder into the system for etching for 24 h, adding a large amount of distilled water after the reaction is finished, washing, centrifuging and drying to obtain pH>6 of multi-layer Ti₃C₂T_xDispersing the powder into distilled water, and manually shaking for 15 min to obtain single-layer Ti₃C₂T_xNanosheets;

(3) 0.3% cellulose suspension and 3mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 5:5, carrying out vacuum filtration, and drying at 1 MPa and 105 ℃ for 20 min to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 26 mu m, the tensile strength is 156.51 MPa, the elongation at break is 17.42%, and the toughness is 19.97 MJ/m³The conductivity was 125S/m, the electromagnetic shielding efficiency (EMI SE) was 36.6 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 6672 dB cm²g^-1。

Example 5

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 25%, then screening pineapple leaf fibers separated from leaves and flesh by using a circular hole sieve with the sieve pore size of 10mm, and then conducting 3-grade gradient low-concentration pulping according to the concentration of 6% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 55-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven-dried fiber is dispersed in 200 g of ethanol and soaked for 30 min, 1 g of sodium chloroacetate corresponding to 1 g of oven-dried fiber is weighed in a beaker, an equal amount of water soluble sodium chloroacetate is added according to the mass ratio of 1:1, then 0.4 g of sodium hydroxide corresponding to 1 g of oven-dried fiber is weighed, a certain amount of ethanol is added for dissolution, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 2 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fibers, and carrying out ultrasonic treatment on the fibers for 120 min to obtain a micron cellulose dispersion with the mass concentration of 1%, wherein the length of the fibers is 100-;

(2) 1 g LiF powder is added into 6M HCl and stirred for 30 min, and 1 g MAX Ti with 400 meshes is added₃AlC₂Adding the powder into the system for etching for 36 h, adding a large amount of distilled water after the reaction is finished, washing, centrifuging and drying to obtain pH>6 of multi-layer Ti₃C₂T_xDispersing the powder into distilled water, and shaking for 15 min to obtain single-layer Ti₃C₂T_xNanosheets;

(3) 0.2% cellulose suspension and 2mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 3:7, carrying out vacuum filtration, and drying at the temperature of 110 ℃ for 20 min under the pressure of 0.9 MPa to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber-reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 27 mu m, the tensile strength is 133.7 MPa, the elongation at break is 13.09%, and the toughness is 12.46 MJ/m³The conductivity was 833S/m, the electromagnetic shielding efficiency (EMI SE) was 39.5 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 7542 dB cm²g^-1。

Example 6

(1) the method comprises the steps of taking chopped pineapple leaf blocks with the length of 5cm as raw materials, conducting high-concentration defibering according to the concentration of 25%, then screening pineapple leaf fibers separated from leaves and flesh by using a circular hole sieve with the sieve pore size of 10mm, and then conducting 3-grade gradient low-concentration pulping according to the concentration of 2% by using a Wahler beater so that the pulping degree of the pineapple leaf fibers is 50-degree SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven-dried fiber is dispersed in 200 g of ethanol and soaked for 10 min, 1 g of sodium chloroacetate corresponding to 1 g of oven-dried fiber is weighed in a beaker, an equal amount of water soluble sodium chloroacetate is added according to the mass ratio of 1:1, then 0.4 g of sodium hydroxide corresponding to 1 g of oven-dried fiber is weighed, a certain amount of ethanol is added for dissolution, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 4 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fiber, homogenizing the slurry with high pressure micro jet homogenizer for 3 times (pressure 25000 PSi) to obtain 1.5% mass concentration nanometer cellulose dispersion with fiber length of 0.6-2.6 μm and diameter of 1-5 nm;

(2) 1 g LiF powder is added into 9M HCl and stirred for 30 min, and 1 g MAX Ti with 400 meshes is added₃AlC₂Adding the powder into the system for etching for 48 h, adding a large amount of distilled water after the reaction is finished, washing, centrifuging and drying to obtain pH>6 of multi-layer Ti₃C₂T_xPulverizing, and dispersing the multi-layer powder in distilled water for ultrasonic treatment for 10 min to obtain single-layer Ti₃C₂T_xNanosheets;

(3) 0.5% of nano-cellulose suspension and 5mg/mL of two-dimensional Ti₃C₂T_xMixing the nano materials according to the ratio of 2:8, carrying out vacuum filtration, and drying at the temperature of 110 ℃ for 30 min under the pressure of 0.75 MPa to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber-reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 27 mu m, the tensile strength is 131.41 MPa, the elongation at break is 5.35%, and the toughness is 4.1 MJ/m³The conductivity was 5000S/m, the electromagnetic shielding efficiency (EMI SE) was 44.4 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 8655 dB cm²g^-1。

Comparative example 1

(1) cutting pineapple leaf blocks with the length of 5cm as raw materials, performing high-concentration defibering according to the concentration of 25%, then screening pineapple leaf fibers separated from leaf pulp by using a circular hole screen with the size of a screen hole of 10mm, and performing 3-level gradient low-concentration pulping according to the concentration of 4% by using a Wahler pulping machine, wherein the 1 st-level pulping load is 0 kg and is 90 min; the beating load of the 2 nd level is 2 kg, 30 min; the beating load of the 3 rd level is 4 kg, and the beating degree of the pineapple leaf fibers is 60 degrees SR within 15 min. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 200 g of ethanol and soaked for 15 min, then 0.98 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added according to the mass ratio of 1:1 to dissolve the sodium chloroacetate, then 0.38 g of sodium hydroxide corresponding to 1 g of oven dry fiber is weighed, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 2 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fibers, and carrying out ultrasonic treatment on the fibers for 90 min to obtain a micron cellulose dispersion with the mass concentration of 1%, wherein the length of the fibers is 150-;

(3) 0.3% cellulose suspension and 3mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 5:5, carrying out vacuum filtration, and carrying out squeezing and drying at normal room temperature to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber-reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 28 microns, the tensile strength is 141.11 MPa, the elongation at break is 7.73%, and the toughness is 7.39 MJ/m³The conductivity was 99S/m, the electromagnetic shielding efficiency (EMI SE) was 32.8 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 6136 dB cm²g^-1。

Comparative example 2

(1) cutting pineapple leaf blocks with the length of 5cm as raw materials, performing high-concentration defibering according to the concentration of 25%, then screening pineapple leaf fibers separated from leaf pulp by using a circular hole sieve with the sieve pore size of 10mm, and performing 1-level low-concentration pulping according to the concentration of 4% by using a Buhler beater, wherein the pulping load is 3 kg and the pulping time is 50 min; the beating degree of the pineapple leaf fiber is 23 DEG SR. The obtained fiber is subjected to carboxymethylation pretreatment, 10 g of oven dry fiber is dispersed in 200 g of ethanol and soaked for 15 min, then 0.98 g of sodium chloroacetate corresponding to 1 g of oven dry fiber is weighed in a beaker, an equal amount of water is added according to the mass ratio of 1:1 to dissolve the sodium chloroacetate, then 0.38 g of sodium hydroxide corresponding to 1 g of oven dry fiber is weighed, a certain amount of ethanol is added to dissolve, the solutions are mixed and added into a three-neck flask, the concentration of the system is adjusted to be 2 wt%, and the temperature is increased to 50-70 ℃ for reflux for 1 h. Washing with distilled water to obtain carboxymethylated modified fiber, and treating the fiber with ultrasonic wave for 120 min to obtain 1% mass concentration micron cellulose dispersion, wherein the fiber length is 300-;

(3) 0.3% cellulose suspension and 3mg/mL of two-dimensional Ti₃C₂T_xMixing the nano sheets according to the ratio of 5:5, carrying out vacuum filtration, and drying at the temperature of 90 ℃ for 20 min under the pressure of 0.75 MPa to obtain the cellulose-based flexible composite electromagnetic shielding film;

the pineapple leaf fiber-reinforced flexible electromagnetic shielding film is obtained through the steps, the film thickness is 28 microns, the tensile strength is 104.59 MPa, the elongation at break is 4.92%, and the toughness is 2.72 MJ/m³The conductivity was 109S/m, the electromagnetic shielding efficiency (EMI SE) was 34.1 dB, and the specific electromagnetic shielding efficiency (SSE/t) was 6321 dB cm²g^-1。

Comparative example 3

The diameter of Bing Zhou et al (ACS appl. mater. Interfaces 2020, 12, 4895-4905) is adopted4-10 nm, 1-3 μm long cotton nanofiber and 400 mesh MAX Ti₃AlC₂Obtaining Ti with average thickness of 1.2 nm and transverse size of several microns as raw material₃C₂T_xThe nano-sheet is used for preparing the CNF/MXene composite film by a blending method, when the dosage of MXene and cotton nano-fiber reaches 1:1, the thickness of the film is about 35 mu m, the maximum tensile strength is 92.1 MPa, the elongation at break is 2.2%, and the toughness is about 1 MJ/m³The electric conductivity is 2S/m, and the electromagnetic shielding efficiency is 22.6 dB.

Comparative example 4

Wen-Tao Cao et al (ACS Nano 2018, 12, 4583-³The electric conductivity is 9.69S/m, the electromagnetic shielding efficiency is 25 dB, and the specific electromagnetic shielding efficiency (SSE/t) is remarkably lower than 1326 dB cm²g^-1。

Comparative example 5

Zeying Zhan et al (J. mater. chem. C, 2019, 7, 9820) prepared bleached paperboard nanocellulose by TEMPO oxidation and 1200W ultrasonic treatment, then blended with MXene in a ratio of 1:1 and vacuum filtered to prepare the mussel-like structure composite electromagnetic shielding film, when the thickness of the composite film reaches 38 μm, the tensile strength is only about 141.9 MPa, the elongation at break is 2.1%, and the toughness is 1.7 MJ/m³The electrical conductivity is 2837S/m, the electromagnetic shielding efficiency is 39.6 dB, and the specific electromagnetic shielding efficiency (SSE/t) is 4750 dB cm²g^-1。

Comparative example 6

Fan Xie et al (Nanoscale, 2019, 11, 23382) use aramid nano-fiber with length of 548.4 + -44.6, diameter of 44.3 + -2.7 nm and length-diameter ratio of about 12.4 as raw material to enhance mechanical property of MXene, when the composite film is compounded according to the proportion of 1:1, the film is made upThe thickness is 20 μm, but the tensile strength is only 84 MPa, the elongation at break is 3.96%, the conductivity is 696S/m, the electromagnetic shielding efficiency is only 24 dB, and the specific electromagnetic shielding efficiency (SSE/t) is 9363 dB cm²g^-1。

Comparative example 7

Huawei Wei et al (Ceramics International, 2020, 46, 6199-²g^-1Far below commercial electromagnetic shielding materials (EMI SE)>20 dB), and moreover, the related industry stipulates that the shielding effect is extremely poor whenever the electromagnetic shielding efficiency is lower than 10 dB.

TABLE 1 fiber parameters and electromagnetic shielding film Performance parameters obtained by the respective Processes

The statistical results in the table show that the pineapple leaf fiber/MXene composite electromagnetic shielding film prepared by the process has high mechanical strength, good flexibility, high conductivity and high electromagnetic shielding efficiency. As can be seen from examples 1-6, the whole leaves of pineapple are processed by the process of the invention: high-concentration defibering, pulp screening, 3-grade gradient low-concentration pulping, chemical pretreatment, ultrasonic treatment or high-pressure homogenization can obtain high-length-diameter ratio micro-nano fibers with the length of 0.6-300 mu m and the diameter of 1-400 nm; after being mixed with single-layer MXene nano-sheets, the cellulose-based flexible electromagnetic shielding film with ultrathin thickness, high strength and high conductivity can be prepared by hot-pressing and drying.

As can be seen from the example 4 and the comparative examples 1 and 2, under the condition that the proportion of the micro-nano fibers to MXene is the same, the fibers with high beating degree and high length-diameter ratio can be obtained in the comparative example 1 by adopting 3-grade gradient beating and ultrasonic treatment, but the film is not dried by hot pressing, and the obtained film has larger strain difference and lower toughness than the film dried by hot pressing; comparative example 2 only adopts 1-grade beating, the obtained fiber has low beating degree, longer fiber and larger diameter, and the strength of the composite film is obviously reduced even if the composite film is dried by hot pressing. Therefore, it can be shown from example 4 and comparative examples 1 and 2 that the preparation of the composite film can be achieved by using 3-grade gradient beating, ultrasonic wave or high-pressure homogenizing, hot-pressing drying.

Example 6 and comparative example 3 demonstrate that under the condition of similar fiber sizes, 20% of pineapple leaf fiber can be adopted to obtain the electromagnetic shielding film with higher strength, and the fact that beating of the whole pineapple leaves through 3-level gradient is favorable for devillicating and brooming, is favorable for improving the strength of the film, and in addition, the advantage of the pineapple leaf fiber as a reinforcing material is also reflected.

Example 4 and comparative example 4 show that, although the pineapple leaf fiber or garlic skin fiber can obtain similar mechanical properties, the electromagnetic shielding film prepared by the process of the invention has the advantages of thin thickness and high electromagnetic shielding efficiency, is beneficial to saving raw materials, and can be more suitable for the requirements of light weight, ultra-thin property and flexibility of modern wearable electronic materials. And the comparative example 4 adopts bleaches such as sodium chlorite and the like to obtain bleached fibers, which is easy to have adverse effects on the environment, the process of the invention adopts high-concentration defibering, mechanical pulping treatment, ultrasonic wave or high-pressure homogenizing treatment and simple etherification treatment to obtain micro-nano fibers with high length-diameter ratio, and the process is more green and environment-friendly.

Example 4 and comparative example 5 show that although the tensile strength of the bleached paperboard nano-cellulose/MXene composite membrane is similar to that of the pineapple leaf nano-cellulose/MXene composite membrane, the strain and toughness advantages of the fiber and the composite membrane prepared by the 3-stage beating process are obvious, and the importance of fibrillation of the fiber through beating and devillicating is demonstrated.

Embodiment 4 and comparative examples 6 and 7 show that the high aspect ratio of the fiber has a great influence on the strength of the composite membrane, on one hand, the micro-nano fiber with high aspect ratio can be prepared by our process, on the other hand, the pineapple leaf which is agricultural waste is used as raw material, so that the method has natural and abundant advantages, and by high added value design, the problem of pollution of agricultural waste to the environment can be reduced, and economic benefits can be generated. In addition, the chemical aramid fiber is relatively expensive compared with the abundant natural plant fiber pineapple leaves.

The above detailed description section specifically describes the analysis method according to the present invention. It should be noted that the above description is only for the purpose of helping those skilled in the art better understand the method and idea of the present invention, and not for the limitation of the related contents. The present invention may be appropriately adjusted or modified by those skilled in the art without departing from the principle of the present invention, and the adjustment and modification also fall within the scope of the present invention.

Claims

1. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof are characterized by comprising the following preparation steps:

(2) adopting weak acid selective treatment and mechanical treatment to treat MAX Ti₃AlC₂Etching and stripping the powder to obtain single-layer Ti₃C₂T_xMXene nanosheets;

2. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (1): the agricultural waste is chopped pineapple leaf block strips with the length of 5 cm.

3. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (1): the pulp screening refers to screening pineapple leaf fibers separated from the leaves and the flesh by adopting a pulp screening machine such as a flat plate slotted screen or a circular hole screen; the low-consistency beating refers to adopting a 3-level gradient beating method, wherein the 1 st-level beating load is 0-1 kg, and the time is 60-90 min; the grade 2 beating load is 1.5-3 kg, 30-60 min; the 3 rd level beating load is 3.5-5 kg, 10-20 min; controlling the beating degree to be 20-70 DEG SR; the chemical pretreatment refers to any one or more of a TEMPO oxidation method or a carboxymethylation pretreatment method.

4. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (1): the cellulose dispersion is water dispersion liquid consisting of micro-nano cellulose fibers with high length-diameter ratio.

5. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (2): the weak acid selective treatment refers to selective etching of MAX Ti by using weak hydrogen fluoride aqueous solution prepared from lithium fluoride and hydrochloric acid solution₃AlC₂Atomic layer of Al of phase.

6. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (2): the mechanical treatment is ultrasonic, manual shaking, oscillation or magnetic stirring.

7. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (3): the micro-nano cellulose suspension and the single layer of Ti₃C₂T_xThe concentration of the nano-sheets is preferably 1-10 mg/mL; the single layer of Ti₃C₂T_xThe mixing ratio of the nano-sheet to the pineapple leaf cellulose suspension is 0-9.

8. The pineapple leaf fiber-reinforced flexible electromagnetic shielding film and the preparation method thereof according to claim 1, wherein the step (3): the hot-pressing drying condition is controlled to be 0.75-1.5 MPa for 20-60 min, and the temperature is 80-120 ℃.

9. A pineapple leaf fiber-reinforced flexible electromagnetic shielding film obtained by the production method as set forth in any one of claims 1 to 8, wherein: the pineapple leaf fiber has a length of 0.6-300 μm and a diameter of 1-400 nm; the Ti₃C₂T_xThe gram weight of the/pineapple leaf cellulose composite conductive film is about 50 g/m²The thickness is 26-28 μm, the tensile strength is 131-215 MPa, the elongation at break is 5.35-20%, and the toughness is 4.1-29.6 MJ/m³The conductivity is 3-5000S/m, the electromagnetic shielding efficiency (EMI SE) is 21.3-44.4 dB, and the specific electromagnetic shielding efficiency (SSE/t) is 3835-8655 dB cm²g^-1Meeting the requirement of commercial electromagnetic shielding material (EMI SE)>20 dB).