阅读说明：本技术 一种高性能电磁屏蔽复合纸基材料及其制备方法与应用 (High-performance electromagnetic shielding composite paper-based material and preparation method and application thereof ) 是由 李金鹏 王斌 陈克复 曾劲松 程峥 段承良 于 2020-12-11 设计创作，主要内容包括：本发明公开了一种高性能电磁屏蔽复合纸基材料及其制备方法与应用。所述的制备方法包括：以芳纶沉析纤维和芳纶短切纤维为基本原料,通过对芳纶纤维表面进行自聚合改性,增加芳纶纤维的粗糙度和表面活性；对纤维素纳米纤丝进行表面改性作为增强剂使用,赋予更多的化学官能团,实现芳纶纤维和纤维素纳米纤维的优势互补；在湿法抄造芳纶纸过程中掺入高长径比的银纳米线,经过湿热压成型制备出高性能电磁屏蔽复合纸基材料。所述高性能电磁屏蔽复合纸基材料生产过程简便,不仅具有优异机械性能和电磁屏蔽性能,且有效降低了芳纶纸的生产成本,便于工业化生产,可以广泛应用到5G电信基材、电磁屏蔽材料、防护材料、内饰材料和电子产品基材等众多领域。(The invention discloses a high-performance electromagnetic shielding composite paper base material and a preparation method and application thereof. The preparation method comprises the following steps: aramid fibrid and aramid chopped fiber are used as basic raw materials, and the surface of the aramid fiber is subjected to self-polymerization modification to increase the roughness and the surface activity of the aramid fiber; the surface modification is carried out on the cellulose nano-fibrils to be used as a reinforcing agent, more chemical functional groups are endowed, and the advantage complementation of the aramid fibers and the cellulose nano-fibers is realized; the silver nanowires with high length-diameter ratio are doped in the wet-process aramid paper making process, and the high-performance electromagnetic shielding composite paper base material is prepared through wet hot-pressing molding. The high-performance electromagnetic shielding composite paper base material is simple and convenient in production process, has excellent mechanical performance and electromagnetic shielding performance, effectively reduces the production cost of the aramid paper, is convenient for industrial production, and can be widely applied to various fields such as 5G telecommunication base materials, electromagnetic shielding materials, protective materials, interior materials and electronic product base materials.)

1. A preparation method of a high-performance electromagnetic shielding composite paper-based material is characterized by comprising the following steps:

(1) surface modification of aramid fiber: taking aramid precipitated fiber and aramid chopped fiber as basic raw materials, mixing the aramid precipitated fiber and the aramid chopped fiber, adding the mixed aramid precipitated fiber and aramid chopped fiber into an alkaline solution, and adding an amino modifier for reaction to prepare aminated aramid fiber;

(2) surface modification of cellulose nanofibrils: adding an oxidant to perform surface hydroformylation modification on the cellulose nanofibrils to obtain hydroformylation cellulose nanofibrils;

(3) and (3) wet papermaking: fully and uniformly mixing the aminated aramid fiber prepared in the step (1) and the aldehyde cellulose nano-fibril prepared in the step (2), and carrying out Schiff base crosslinking reaction; and after the reaction is finished, adding silver nanowires, diluting the suspension obtained by the reaction to a certain concentration, performing wet papermaking to obtain an aramid wet paper sheet, and performing direct wet thermal forming to finally prepare the high-performance electromagnetic shielding composite paper base material.

2. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: the type of the aramid fiber in the step (1) is at least one of wholly aromatic polyamide fiber or heterocyclic aromatic polyamide fiber; wherein the mass ratio of the aramid chopped fiber to the aramid fibrid is (1-10) to (1-10).

3. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: in the step (1), the amino modifier is at least one of dopamine, lysine and L-3, 4-dihydroxyphenylalanine.

4. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: the alkaline solution in the step (1) is a tris (hydroxymethyl) aminomethane-hydrochloric acid buffer solution, and the pH is adjusted to 7.5-11; the reaction temperature is 20-80 ℃, and the treatment time is 0.1-48 h.

5. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: the cellulose nanofibrils in the step (2) have a length of more than 1 μm, a diameter of less than 100nm and an aspect ratio of more than 500.

6. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: the mass ratio of the cellulose nanofibrils to the oxidant in the aldehyde modification in the step (2) is 1 (0.1-10); the reaction temperature is 0-80 ℃ and the reaction time is 0.1-24 h.

7. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: in the Schiff base crosslinking reaction in the step (3), the mass ratio of the aminated aramid fiber to the aldehyde cellulose nano-fibril is (0.1-100): 1, and the reaction pH is 3-6; the reaction temperature is 20-80 ℃ and the reaction time is 0.1-24 h.

8. The method for preparing the high-performance electromagnetic shielding composite paper-based material according to claim 1, wherein: the length-diameter ratio of the silver nanowires in the step (3) is more than 1000, and the mass ratio of the silver nanowires to the aminated aramid fibers is 0.01-100%;

the wet papermaking concentration in the step (3) is 0.01-1%; the temperature of the wet-heat forming is 100-280 ℃, the pressure is 0.01-20.0Mpa, and the time is 0.01-60 min.

9. A high performance electro-magnetic shielding composite paper based material made by the method of any one of claims 1 to 8.

10. The use of the high performance electromagnetically shielding composite paper-based material as claimed in claim 9 in the fields of 5G telecommunication materials, electromagnetic shielding materials, protective materials, interior materials and electronic product substrates.

Technical Field

The invention belongs to the cross field of paper industry and high polymer materials, and particularly relates to a high-performance electromagnetic shielding composite paper base material and a preparation method and application thereof.

Background

The electromagnetic wave is easy to cause the injury of human body because of the change of the frequency. The small magnet is generally used, so that the human body is not injured. However, when the electromagnetic radiation exceeds a certain intensity (i.e. the safety and health standard limit), negative effects are generated on the human body, which causes symptoms such as headache, insomnia, memory deterioration, blood pressure increase or decrease, and limitation abnormality of the heart, and the phenomenon is called electromagnetic pollution. Electromagnetic pollution and atmospheric pollution, water pollution and noise pollution are recognized as four major hazards. If the device is operated under the environment of ultra-intense electromagnetic radiation for a long time, the device can cause partial abortion, cataract and even carcinogenesis seriously. Electromagnetic energy causes immeasurable damage to human bodies and electronic equipment, so that the electromagnetic wave damage is urgently prevented.

The aramid paper material is prepared by mixing aramid fibrid and chopped fiber according to a certain proportion, wet-making into base paper, and then carrying out heat treatment on the base paper by a high-temperature high-pressure calendaring technology. However, due to the higher crystallinity and the steric hindrance of the benzene ring of the aramid fiber, the surface of the fiber is smooth, and the number of active functional groups is small, so that the interface compatibility between the aramid fiber and a matrix material is poor, and the aramid fiber is difficult to play a role of a high-performance reinforcement. At present, chemical treatment methods are generally adopted to increase active functional groups on the surface of aramid fibers, or reactive compatibilizers are added to enhance the interfacial compatibility of composite materials. However, the general modification method greatly damages the structure of the fiber or uses a toxic solvent, and the operation is complicated, and polydopamine becomes a newly developed surface modifier due to its excellent adhesion. In the previous surface modification of aramid fibers, active functional groups are constructed to achieve the purpose of enhancing the bonding strength between fibers, which is a common method, such as the three invention examples of application numbers 201710599787.1202010055750.4 and 201210245728.1, and dopamine is polymerized under alkaline conditions to form polydopamine, so that the surface of the aramid fibers is subjected to amination modification. However, the conventional patents disclose only a single modification method and are not generally applicable. Therefore, improving the fiber bonding strength in aramid paper by a suitable method is the key to obtaining high performance aramid composites.

Cellulose nanofibrils as a novel green nano material have a nano effect and continue excellent physical and chemical properties of cellulose, and are increasingly attracted by people in recent years. The cellulose nanofibrils are from plants, animals and microorganisms, the size of the cellulose is reduced to be below 100nm through a physical, chemical, biological or combined treatment process, single linear nano-level fibers are provided with excellent mechanical properties, huge specific surface area, high crystallinity, good hydrophilicity, high transparency, low density, good biodegradability and biocompatibility and stable chemical properties, the research on the preparation and high-value utilization of the cellulose nanofibril functional material becomes the focus of attention of scholars at home and abroad, and the application of the cellulose nanofibril functional material relates to the fields of reinforcing materials, electronic industry, light industrial food, biological medicine and the like.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention mainly aims to provide a high-performance electromagnetic shielding composite paper base material;

the invention also aims to provide a preparation method of the high-performance electromagnetic shielding composite paper-based material;

still another object of the present invention is to provide the application of the above high-performance electromagnetic shielding composite paper base material.

The purpose of the invention is realized by the following technical scheme:

(1) surface modification of aramid fiber: taking aramid precipitated fiber and aramid chopped fiber as basic raw materials, mixing the aramid precipitated fiber and the aramid chopped fiber, adding the mixed aramid precipitated fiber and aramid chopped fiber into an alkaline solution, and adding an amino modifier for reaction to prepare the aminated aramid fiber. The purpose is to introduce amino on the surface of aramid fiber and increase the roughness and surface activity of the aramid fiber.

(2) Surface modification of cellulose nanofibrils: and adding an oxidant to carry out surface hydroformylation modification on the cellulose nanofibrils, and increasing the cross-linking effect and the hydrogen bond connection effect among fibers to obtain the hydroformylation cellulose nanofibrils.

(3) And (3) wet papermaking: fully and uniformly mixing the aminated aramid fiber prepared in the step (1), the aldehyde cellulose nano-fibril prepared in the step (2) and the silver nanowire under a specific condition, and carrying out Schiff base reaction on amino and aldehyde groups in the raw materials to fully crosslink; adding silver nanowires after the reaction is finished, and providing a conductive network by the silver nanowires; and then diluting the suspension obtained by the reaction to a certain concentration, carrying out wet papermaking to obtain an aramid wet paper sheet, and carrying out wet thermal forming to finally prepare the high-performance electromagnetic shielding composite paper base material.

Preferably, the type of the aramid fiber in the step (1) may be at least one of wholly aromatic polyamide fiber or heterocyclic aromatic polyamide fiber.

Preferably, the mass ratio of the aramid chopped fibers to the aramid fibrids in the step (1) is (1-10) to (1-10); preferably 5: 5.

Preferably, the amino modifier in the step (1) is at least one of dopamine, lysine, L-3, 4-dihydroxyphenylalanine and the like; l-3, 4-dihydroxyphenylalanine is preferred. Wherein the amino modifier is added in excess.

Preferably, the buffer solution selected from the alkaline solution in the step (1) is tris-hydroxymethyl aminomethane-hydrochloric acid buffer solution, and the pH is adjusted to 7.5-11; the reaction temperature is 20-80 ℃, and the treatment time is 0.1-48 h; preferably, the pH is 8.5, the temperature is 40 ℃ and the treatment time is 10 h. Preferably, the mass (g) of the aramid fiber in the step (1): the volume (ml) of the alkaline solution was 1: 50.

Preferably, the cellulose nanofibrils of step (2) are nano-scale derived products of cellulose having an aspect ratio of more than 500.

Preferably, the mass ratio of the cellulose nanofibrils to the oxidant in the aldehyde modification in the step (2) is 1 (0.1-10), the temperature of the aldehyde modification is 0-80 ℃, and the time is 0.1-24 hours; preferably, the mass ratio of the cellulose nanofibrils to the oxidant in the aldehyde modification is 1:1.5, the temperature is 50 ℃, and the time is 3 hours.

Preferably, in the Schiff base reaction in the step (3), the mass ratio of the aminated aramid fiber to the aldehyde cellulose nanofibrils is (0.1-100): 1, the reaction pH is 3-6, the temperature is 20-80 ℃, and the time is 0.1-24 h; preferably, the mass ratio of the aminated aramid fiber to the aldehyde cellulose nano-fibril is 5:1, the reaction pH is 4.5, the temperature is 50 ℃, and the time is 4 hours.

Preferably, the length-diameter ratio of the silver nanowires in the step (3) is preferably greater than 1000, and the mass ratio of the silver nanowires to the aminated aramid fibers is 0.01-100%.

Preferably, the wet papermaking concentration in the step (3) is 0.01-10%, the thermoforming temperature is 100-280 ℃, and the pressure is 0.01-20.0 MPa; preferably, the wet papermaking concentration is 0.1%, the thermoforming temperature is 250 ℃, and the pressure is 5 Mpa.

The high-performance electromagnetic shielding composite paper base material can be applied to various fields such as 5G telecommunication materials, electromagnetic shielding materials, protective materials, interior materials, electronic product base materials and the like.

The preparation process of the high-performance electromagnetic shielding composite paper base material is shown in figure 1.

Compared with the prior art, the invention has the following advantages and effects:

according to the high-performance electromagnetic shielding composite paper base material, the aramid fiber is subjected to surface modification, oxidation and self-polymerization are carried out under an alkaline condition to form a high polymer surface with strong viscosity, amino with high reaction activity is introduced into the surface of the aramid fiber, the surface is rough, the chemical activity is endowed, and the high polymer surface is used as an aramid fiber and aldehyde modified cellulose nanofiber cross-linked bridge to realize advantage complementation. The cellulose nano-fibril is a new nano-material and is widely applied to reinforced composite materials, and after active aldehyde groups are constructed on the surface of the cellulose nano-fibril by performing aldehyde modification on the cellulose nano-fibril, amino groups on the surface of aramid fiber and the aldehyde groups of the cellulose nano-fibril can perform Schiff base cross-linking reaction through simple Schiff base reaction, so that hydrogen bond network connection is enhanced, and the interface combination between fiber raw materials in the aramid paper can be effectively improved.

The silver nanowires have been widely applied to the preparation of electromagnetic shielding materials due to the intentional conductive effect, and mostly only use the conductivity of the silver nanowires, neglecting the integrity of the microstructure and the conductive network of the silver nanowires in the aramid fiber composite paper base. Based on the excellent conductivity of the silver nanowires, the silver nanowires are subjected to high-temperature thermal fusion treatment to construct a stable 3D interconnection conductive network in the aramid paper base, so that the high-performance electromagnetic shielding composite paper base material is obtained while the interface performance and the mechanical property of the aramid composite paper base are improved, the production cost of the existing aramid composite paper base material can be reduced, and the high-performance electromagnetic shielding composite paper base material has huge market prospect and economic value.

In conclusion, the stable structure of the Schiff base is formed between the aminated modified aramid fiber and the aldehyde modified cellulose nanofibrils, so that the interface crosslinking and combination effects of the fibers in the composite paper base are improved, the high-strength aramid paper base is prepared, and the manufacturing cost can be saved; the silver nanowires are introduced mainly for expanding the functional application of the aramid fiber in accordance with the paper base. In addition, the influence of thermal fusion on the implementation effect of the silver nanowire conductive network is further optimized through experiments in the embodiment, and the technical implementation effect data shows that the effect is completely superior to the effect of the prior art, so that the method has outstanding progress and innovation.

Drawings

Fig. 1 is a schematic diagram of a preparation process of a high-performance electromagnetic shielding composite paper-based material.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

The starting materials in the preparation method of the invention can be obtained from the market or prepared according to the prior art method, and the aramid fiber used in the embodiment of the invention is meta-aramid fiber, but is not limited in this way. The preparation method of the silver nanowire is obtained by referring to a preparation method of the silver nanowire with high length-diameter ratio (application number 2019113519033), and the preparation of the cellulose nanofibril refers to the prior reports: bin mixing; li jin Peng; chenkefu (application No.: 2017113380549), but is not limited to this method. The tensile strength index and electromagnetic shielding detection refer to GB/T12914-2008 and GB/T35575-2017.

Example 1

A high-performance electromagnetic shielding composite paper base material is prepared by the following steps:

(1) surface modification of aramid fiber: uniformly mixing aramid fibrid and aramid chopped fiber (purchased from a certain fiber material science and technology company limited in China) according to a mass ratio of 9:1, and then adding a trihydroxymethyl aminomethane-hydrochloric acid buffer solution (Tris-HCl buffer solution) with the pH value of 8.5, wherein the mass ratio of the aramid fiber (namely the total mass of the aramid fibrid and the aramid chopped fiber) to the Tris-HCl buffer solution (g) is as follows: adding dopamine as an amino modifier with the volume (ml) of 1:50, wherein the final concentration is 0.01 g/L; and (3) carrying out the modification reaction at the temperature of 20 ℃, protecting with nitrogen at the flow rate of 30ml/min, carrying out suction filtration for 48 hours, and collecting the modified aminated aramid fiber (aminated aramid fiber) for later use.

(2) Surface modification of cellulose nanofibrils: adopting cellulose nano-fibrils with the length-diameter ratio of 500-700, wherein the mass ratio of the cellulose nano-fibrils to the oxidant in the hydroformylation modification is 1:0.1, mixing the cellulose nano-fibrils with the oxidant, adding the mixture into water to ensure that the mass concentration of the cellulose nano-fibrils in the mixed reaction solution is 1%, the hydroformylation modification temperature is 0 ℃, and the time is 24 hours, and finally centrifugally collecting the modified hydroformylation cellulose nano-fibrils (hydroformylation cellulose nano-fibrils) for later use.

(3) And (3) wet papermaking: mixing the aminated aramid fiber and the aldehyde cellulose nano-fibril fiber raw materials obtained in the two steps according to the mass ratio of 100:1, and adding water to prepare a mixed solution (the fiber raw materials are used as the raw materials) with the mass concentration of 0.1 percentGross amount), adjusting the pH value to 3, fully mixing and dispersing under the specific condition of nitrogen protection to ensure that amino groups and aldehyde groups in the raw materials are subjected to Schiff base reaction and fully cross-linking, wherein the reaction temperature is 20 ℃, and the reaction time is 12 h; after the reaction is finished, silver nanowires with the length-diameter ratio of 1000 are added into the obtained suspension, the addition amount of the silver nanowires is 0.01 percent of that of the aminated aramid fiber, the concentration of the fibers (the mass sum of the aramid chopped fibers, the fibrids and the cellulose nano fibrils) in the suspension is adjusted to be 1 percent, the mixture is stirred and mixed uniformly, and the quantitative weight of 60g/m is obtained through wet papermaking²The paper of (1); and (2) squeezing and dehydrating the wet paper web at 25 ℃ under the pressure of 0.2MPa for 5min, and then directly carrying out thermal forming (namely, carrying out wet papermaking to obtain an aramid wet paper web, and then carrying out drying forming), wherein the temperature is 100 ℃, the pressure is 20MPa, and the time is 4h, so as to finally prepare the high-performance electromagnetic shielding composite paper base material.

The prepared high-performance electromagnetic shielding composite paper base material is subjected to performance test, and the tensile strength index and the electrical breakdown strength are respectively 20.4 N.m/g and 4.3 dB.

Example 2

A high-performance electromagnetic shielding composite paper base material is prepared by the following steps:

(1) surface modification of aramid fiber: uniformly mixing aramid fibrid and aramid chopped fiber (purchased from a certain fiber material science and technology company limited in China) according to the mass ratio of 3:7, and then adding a trihydroxymethyl aminomethane-hydrochloric acid buffer solution (Tris-HCl buffer solution) with the pH value of 8.5, wherein the mass ratio of the aramid fiber (namely the total mass of the aramid fibrid and the aramid chopped fiber) to the Tris-HCl buffer solution (g) is as follows: volume (ml) 1: 50; adding dopamine serving as an amino modifier, wherein the final concentration of the dopamine is 0.01 g/L; and (3) carrying out the modification reaction at the temperature of 50 ℃, protecting with nitrogen at the flow rate of 30ml/min, carrying out suction filtration for 8 hours, and collecting the modified aminated aramid fiber (aminated aramid fiber) for later use.

(2) Surface modification of cellulose nanofibrils: adopting cellulose nano-fibrils with the length-diameter ratio of 1000, wherein the mass ratio of the cellulose nano-fibrils to an oxidant in the aldehyde modification is 1:0.1, mixing the cellulose nano-fibrils with the oxidant, adding the mixture into water to ensure that the mass concentration of the cellulose nano-fibrils in the mixed reaction solution is 1%, the aldehyde modification temperature is 80 ℃, the aldehyde modification time is 0.1h, and finally centrifugally collecting the modified aldehyde cellulose nano-fibrils (aldehyde cellulose nano-fibrils) for later use.

(3) And (3) wet papermaking: mixing the aminated aramid fiber and the aldehyde cellulose nanofibril fiber raw materials obtained in the two steps according to the mass ratio of 100:1, adding water to prepare a mixed solution (based on the total amount of the fiber raw materials) with the mass concentration of 0.1%, adjusting the pH value of the mixed solution to 6, and fully mixing and dispersing under the specific condition of nitrogen protection to ensure that amino groups and aldehyde groups in the raw materials are subjected to Schiff base reaction and fully cross-linking, wherein the reaction temperature is 80 ℃ and the reaction time is 0.1 h; after the reaction is finished, silver nanowires with the length-diameter ratio of 1500 are added into the obtained suspension, the addition amount of the silver nanowires is 10 percent of that of the aminated aramid fiber, the concentration of the fibers (the mass sum of the aramid chopped fibers, the fibrids and the cellulose nano fibrils) in the suspension is adjusted to be 0.1 percent, the mixture is stirred and mixed uniformly, and the quantitative weight of 60g/m is obtained through wet papermaking²The paper of (1); squeezing and dehydrating the wet paper web at 25 ℃ under the pressure of 0.2MPa for 5min, and then directly carrying out thermal forming (namely, wet papermaking to obtain aramid wet paper web, drying and forming), wherein the temperature is 280 ℃, the pressure is 5MPa, and the time is 10min, thus finally preparing the high-performance electromagnetic shielding composite paper base material.

The tensile strength index and the electric breakdown strength of the prepared high-performance electromagnetic shielding composite paper base material are respectively 36.6 N.m/g and 35.5dB through performance tests.

Example 3

A high-performance electromagnetic shielding composite paper base material is prepared by the following steps:

(1) surface modification of aramid fiber: uniformly mixing aramid fibrid and aramid chopped fiber (purchased from a certain fiber material science and technology company limited in China) according to the mass ratio of 6:4, and then adding a trihydroxymethyl aminomethane-hydrochloric acid buffer solution (Tris-HCl buffer solution) with the pH value of 8.5, wherein the mass ratio of the aramid fiber (namely the total mass of the aramid fibrid and the aramid chopped fiber) to the Tris-HCl buffer solution (g) is as follows: volume (ml) 1: 50; adding L-3, 4-dihydroxyphenylalanine as amino modifier with final concentration of 0.01 g/L; and (3) carrying out the modification reaction at the temperature of 50 ℃, protecting with nitrogen at the flow rate of 30ml/min, carrying out suction filtration for 12 hours, and collecting the modified aminated aramid fiber (aminated aramid fiber) for later use.

(2) Surface modification of cellulose nanofibrils: adopting cellulose nano-fibrils with the length-diameter ratio of 1500, wherein the mass ratio of the cellulose nano-fibrils to an oxidant in the hydroformylation modification is 1:10, mixing the cellulose nano-fibrils with the oxidant, adding the mixture into water to ensure that the mass concentration of the cellulose nano-fibrils in the mixed reaction solution is 1%, performing hydroformylation modification at the temperature of 60 ℃ for 4h, and finally centrifugally collecting the modified hydroformylation cellulose nano-fibrils (hydroformylation cellulose nano-fibrils) for later use.

(3) And (3) wet papermaking: mixing the aminated aramid fiber and the aldehyde cellulose nanofibril fiber raw materials obtained in the two steps according to the mass ratio of 50:1, adding water to prepare a mixed solution (based on the total amount of the fiber raw materials) with the mass concentration of 0.1%, adjusting the pH value of the mixed solution to 6, and fully mixing and dispersing under the specific condition of nitrogen protection to ensure that amino groups and aldehyde groups in the raw materials are subjected to Schiff base reaction and fully cross-linking, wherein the reaction temperature is 60 ℃ and the reaction time is 18 hours; after the reaction is finished, silver nanowires with the length-diameter ratio of 1000 are added into the obtained suspension, the addition amount of the silver nanowires is 30% of that of the aminated aramid fiber, the concentration of the fibers (the mass sum of the aramid chopped fibers, the fibrids and the cellulose nanofibrils) in the suspension is adjusted to be 0.5%, the mixture is stirred and mixed uniformly, and the quantitative rate of 60g/m is obtained through wet papermaking²The paper of (1); and (2) squeezing and dehydrating the wet paper web at 25 ℃ under the pressure of 0.2MPa for 5min, and then directly carrying out thermal forming (namely, carrying out wet papermaking to obtain an aramid wet paper web, and then carrying out drying forming) at the temperature of 200 ℃, the pressure of 0.5MPa and the time of 30min to finally prepare the high-performance electromagnetic shielding composite paper base material.

The tensile strength index and the electric breakdown strength of the prepared high-performance electromagnetic shielding composite paper base material are respectively 44.1 N.m/g and 72.6dB through performance tests.

Example 4

A high-performance electromagnetic shielding composite paper base material is prepared by the following steps:

(1) surface modification of aramid fiber: uniformly mixing aramid fibrid and aramid chopped fiber (purchased from a certain fiber material science and technology company limited in China) according to the mass ratio of 5:5, and then adding a trihydroxymethyl aminomethane-hydrochloric acid buffer solution (Tris-HCl buffer solution) with the pH value of 8.5, wherein the mass ratio of the aramid fiber (namely the total mass of the aramid fibrid and the aramid chopped fiber) to the Tris-HCl buffer solution (g) is as follows: volume (ml) 1: 50; adding L-3, 4-dihydroxyphenylalanine as amino modifier with final concentration of 0.01 g/L; and (3) carrying out the modification reaction at the temperature of 50 ℃, protecting with nitrogen at the flow rate of 30ml/min, carrying out suction filtration for 3 hours, and collecting the modified aminated aramid fiber (aminated aramid fiber) for later use.

(2) Surface modification of cellulose nanofibrils: adopting cellulose nano-fibrils with the length-diameter ratio of 1500, wherein the mass ratio of the cellulose nano-fibrils to an oxidant in the hydroformylation modification is 1:2, mixing the cellulose nano-fibrils with the oxidant, adding the mixture into water to ensure that the mass concentration of the cellulose nano-fibrils in the mixed reaction solution is 1%, performing hydroformylation modification at the temperature of 60 ℃ for 2h, and finally centrifugally collecting the modified hydroformylation cellulose nano-fibrils (hydroformylation cellulose nano-fibrils) for later use.

(3) And (3) wet papermaking: mixing the aminated aramid fiber and the aldehyde cellulose nanofibril fiber raw materials obtained in the two steps according to the mass ratio of 4:1, adding water to prepare a mixed solution (based on the total amount of the fiber raw materials) with the mass concentration of 0.1%, adjusting the pH value of the mixed solution to 4.5, and fully mixing and dispersing under the specific condition of nitrogen protection to ensure that amino groups and aldehyde groups in the raw materials are subjected to Schiff base reaction and fully cross-linking, wherein the reaction temperature is 60 ℃ and the reaction time is 10 hours; after the reaction is finished, silver nanowires with the length-diameter ratio of 1500 are added into the obtained suspension, the addition amount of the silver nanowires is 50% of that of the aminated aramid fiber, the concentration of the fibers (the mass sum of the aramid chopped fibers, the fibrids and the cellulose nanofibrils) in the suspension is adjusted to be 0.3%, the mixture is stirred and mixed uniformly, and the quantitative rate of 60g/m is obtained through wet papermaking²The paper of (1); squeezing wet paper web at 25 deg.C under 0.2MPa for 5min, and directly thermoforming (wet-forming)And (3) manufacturing the aramid wet paper sheet, drying and forming), wherein the temperature is 220 ℃, the pressure is 7Mpa, and the time is 3min, and finally preparing the high-performance electromagnetic shielding composite paper base material.

The tensile strength index and the electric breakdown strength of the prepared high-performance electromagnetic shielding composite paper base material are respectively 62.9 N.m/g and 113.7dB through performance tests.

Comparative example 1

A high-performance electromagnetic shielding composite paper base material is prepared by the following steps:

(1) surface modification of aramid fiber: uniformly mixing aramid fibrid and aramid chopped fiber (purchased from a certain fiber material science and technology company limited in China) according to the mass ratio of 5:5, and then adding a trihydroxymethyl aminomethane-hydrochloric acid buffer solution (Tris-HCl buffer solution) with the pH value of 8.5, wherein the mass ratio of the aramid fiber (namely the total mass of the aramid fibrid and the aramid chopped fiber) to the Tris-HCl buffer solution (g) is as follows: volume (ml) 1: 50; adding L-3, 4-dihydroxyphenylalanine as amino modifier with final concentration of 0.01 g/L; and (3) carrying out the modification reaction at the temperature of 50 ℃, protecting with nitrogen at the flow rate of 30ml/min, carrying out suction filtration for 3 hours, and collecting the modified aminated aramid fiber (aminated aramid fiber) for later use.

(2) Surface modification of cellulose nanofibrils: adopting cellulose nano-fibrils with the length-diameter ratio of 1500, wherein the mass ratio of the cellulose nano-fibrils to an oxidant in the hydroformylation modification is 1:2, mixing the cellulose nano-fibrils with the oxidant, adding the mixture into water to ensure that the mass concentration of the cellulose nano-fibrils in the mixed reaction solution is 1%, performing hydroformylation modification at the temperature of 60 ℃ for 2h, and finally centrifugally collecting the modified hydroformylation cellulose nano-fibrils (hydroformylation cellulose nano-fibrils) for later use.

(3) And (3) wet papermaking: mixing the aminated aramid fiber and the aldehyde cellulose nanofibril fiber raw materials obtained in the two steps according to the mass ratio of 4:1, then adding water to prepare a mixed solution (based on the total amount of the fiber raw materials) with the mass concentration of 0.1%, adjusting the pH value of the mixed solution to 4.5, fully mixing and dispersing under the specific condition of nitrogen protection to enable amino groups and aldehyde groups in the raw materials to have Schiff base reaction so as to fully crosslink,the reaction temperature is 60 ℃, and the reaction time is 10 hours; after the reaction is finished, silver nanowires with the length-diameter ratio of 500 are added into the obtained suspension, the addition amount of the silver nanowires is 50% of that of the aminated aramid fiber, the concentration of the fibers (the mass sum of the aramid chopped fibers, the fibrids and the cellulose nanofibrils) in the suspension is adjusted to be 0.3%, the mixture is stirred and mixed uniformly, and the quantitative rate of 60g/m is obtained through wet papermaking²The paper of (1); squeezing and dehydrating the wet paper web at 25 ℃ under the pressure of 0.2MPa for 5min, and then directly carrying out thermal forming (namely, wet papermaking to obtain aramid wet paper web, drying and forming), wherein the temperature is 220 ℃, the pressure is 7MPa, and the time is 3min, thus finally preparing the high-performance electromagnetic shielding composite paper base material.

The tensile strength index and the electric breakdown strength of the prepared high-performance electromagnetic shielding composite paper base material are respectively 49.6 N.m/g and 76.1dB when the performance test is carried out.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.