Composite paper with adjustable aperture structure and preparation method thereof

Abstract

The invention provides composite paper with an adjustable aperture structure and a preparation method thereof.The preparation method comprises the steps that S1, micron-sized polylactic acid short fibers are soaked in a 0.5%-3.0% surfactant solution and then subjected to low-temperature plasma treatment, and modified polylactic acid fibers are obtained; wherein the surfactant is one or two of lauryl sodium sulfate and anionic polyacrylamide; and S2, mixing, defibering and dispersing the modified polylactic acid fiber, the plant fiber pulp and the nano-scale inorganic filler solution to prepare mixed pulp, performing papermaking by adopting a wet forming technology, and performing squeezing and drying to obtain the composite paper. The wettability of the paper can be changed by controlling the pore structure of the paper, so that the paper can adapt to different types of liquid flowing requirements.

Description

Technical Field

[0001] The invention relates to the field of preparation of special paper, and in particular to a composite paper with adjustable pore size structure prepared by composite of modified polylactic acid fiber and plant fiber, wherein the composite paper can be used as a base material of a paper-based instant detection device. Background Art

[0002] Paper-based instant detection devices have been widely used in medical diagnosis, environmental monitoring, and food safety testing in recent years due to their low cost, simple operation, and portability. However, traditional paper substrates have certain limitations in terms of pore structure, fluid transport performance, and mechanical strength, making it difficult to meet the needs of high-sensitivity detection. Pore structure is one of the important characteristics of the substrate of paper-based instant detection devices, and it plays a key role in the flow rate and uniformity of the liquid. The controllable pore structure can accurately adjust the flow behavior of the liquid in the capillary, improve the transmission speed and stability of the fluid, and thus enhance the accuracy and sensitivity of the detection. Therefore, the preparation of paper substrates with controllable pore structures has become a research focus for improving the performance of paper-based instant detection devices.

[0003] Polylactic acid (PLA) fiber is a biodegradable polyester fiber with good hydrophobicity and mechanical properties. Its raw materials come from renewable resources (such as corn, wheat, etc.) and can be completely degraded into water and carbon dioxide in the natural environment, so it is regarded as an environmentally friendly material. Introducing polylactic acid fiber into the cellulose fiber network can not only enhance the mechanical properties of paper, but also optimize the flow behavior of liquid in paper by adjusting the fiber network structure and surface properties.

[0004] Chinese invention patent CN114481681B discloses a cellulose / PLA fiber composite paper and a preparation method thereof, wherein the polylactic acid fiber is first modified by alkali treatment, and then the modified polylactic acid fiber is composited with cellulose fiber to prepare paper. The disadvantage is that the modification process of the polylactic acid fiber by alkali treatment is relatively drastic and difficult to accurately control, which easily causes irreversible hydrolysis of the polylactic acid fiber in an alkaline environment, significantly reducing the porosity of the composite paper and reducing the capillary pore size, limiting the controllability of its pore structure. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a composite paper with adjustable pore structure and a preparation method thereof, which can change the wettability of the paper by controlling the pore structure of the paper to adapt it to the flow requirements of different types of liquids.

[0006] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing a composite paper with adjustable pore size structure, comprising: S1, micron-sized polylactic acid short fibers are immersed in a 0.5% to 3.0% surfactant solution, and then subjected to low-temperature plasma treatment to obtain modified polylactic acid fibers; wherein the surfactant is one or both of sodium dodecyl sulfate and anionic polyacrylamide; S2, mixing and dispersing the modified polylactic acid fiber, plant fiber pulp and nano-scale inorganic filler solution to prepare a mixed pulp, and papermaking by wet molding technology, and obtaining the composite paper after pressing and drying.

[0007] Preferably, in S1, the length of the polylactic acid staple fibers is 500-800 µm.

[0008] Preferably, in S1, the soaking treatment time is 60 to 90 minutes.

[0009] Preferably, in S1, the low temperature plasma treatment time is 30 to 60 minutes.

[0010] Preferably, in S2, the beating degree of the plant fiber slurry is 35~45°SR.

[0011] Preferably, in S2, the nano inorganic filler is one or a mixture of nano silicon dioxide, nano alumina and amorphous calcium carbonate microspheres.

[0012] Preferably, in S2, the composition of the composite paper is, by mass percentage, 10% to 70% of modified polylactic acid fiber, 20% to 80% of plant fiber, and 5% to 15% of nano-scale inorganic filler.

[0013] In a second aspect, the present invention provides composite paper obtained by the preparation method.

[0014] Preferably, the composite paper has a porosity of 70% to 90% and a pore size of 20 to 35 µm.

[0015] In a third aspect, the present invention provides a paper-based instant detection device using the composite paper as a base material.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention first uses sodium dodecyl sulfate (SDS) and / or anionic polyacrylamide (APAM) to modify the surface of polylactic acid fiber, and then further uses low-temperature plasma to treat the polylactic acid fiber. The surfactant solution is mainly used to improve the wettability and charging properties of polylactic acid fiber. The SDS molecule has a hydrophilic and hydrophobic amphiphilic structure, which can form an ordered adsorption layer on the surface of polylactic acid fiber; and APAM forms a flexible coating with the surface of polylactic acid fiber through polymer chains to regulate the interfacial properties of polylactic acid fiber. Low-temperature plasma treatment can further introduce polar groups such as polar hydroxyl, carboxyl, aldehyde or amide bond on the surface of polylactic acid fiber. Its etching effect can form a nano-scale rough structure on the surface of polylactic acid fiber, increase the specific surface area of ​​polylactic acid fiber, enhance the capillary adsorption effect, and make it easier for water to diffuse along the surface of polylactic acid fiber. Compared with the traditional alkali modification method, the modification strategy of the present invention has the advantages of being mild, controllable and adjustable, avoiding irreversible hydrolysis of polylactic acid fiber under alkaline conditions, thereby maintaining the structural integrity of polylactic acid fiber. Then, by precisely controlling the ratio of modified polylactic acid fiber to plant fiber, precise control of the internal pore size microstructure of the paper is achieved. Compared with traditional paper substrates, the present invention optimizes the pore distribution and capillary performance of the paper while ensuring the good mechanical strength of the polylactic acid fiber composite paper, and improves the flow rate and uniformity of the fluid in the paper substrate. Compared with the substrates of existing commercial paper-based instant detection devices (such as Whatman filter paper, cellulose nitrate membrane, etc.), the polylactic acid fiber composite paper with a controllable pore size structure prepared by the method of the present invention has the advantages of low production cost, a wide variety of liquids that can be transported, and high liquid transport efficiency, which can meet the high requirements of the new generation of paper-based instant detection devices for the porous structure of the base material and fluid regulation. This achievement provides a new direction for the research and development of paper-based functional materials, and helps to promote the industrial application of green, low-cost, and high-performance composite paper. DETAILED DESCRIPTION

[0017] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0018] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0019] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0020] The method for preparing the composite paper with adjustable pore size structure of the present invention comprises: S1, micron-sized polylactic acid short fibers are immersed in a 0.5% to 3.0% surfactant solution, and then subjected to low-temperature plasma treatment to obtain modified polylactic acid fibers; wherein the surfactant is one or both of sodium dodecyl sulfate and anionic polyacrylamide; S2, mixing and dispersing the modified polylactic acid fiber, plant fiber pulp and nano-scale inorganic filler solution to prepare a mixed pulp, and papermaking by wet molding technology, and obtaining the composite paper after pressing and drying.

[0021] In some embodiments of the present invention, the preparation method of the polylactic acid short fibers is: shearing and grinding the polylactic acid fibers with an ultrafine pulverizer, washing and drying to obtain micron-grade polylactic acid short fibers; preferably, the shearing time is 15 to 30 minutes, and the length of the polylactic acid fibers obtained after the treatment is 500 to 800 µm. The polylactic acid fibers are commercial polylactic acid fibers.

[0022] In some embodiments of the present invention, the polylactic acid staple fibers are immersed in a 0.5% to 3.0% surfactant solution for 60 to 90 minutes.

[0023] In some embodiments of the present invention, the polylactic acid fiber is treated with low-temperature plasma for 30 to 60 minutes.

[0024] In some embodiments of the present invention, the method for preparing the plant fiber slurry is: soaking a natural plant fiber pulp board in water to loosen it, and then beating it with a trough-type pulping machine to obtain the plant fiber slurry.

[0025] Among them, the natural plant fiber pulp board is a mixture of one or more of commercial hardwood pulp board, commercial softwood pulp board and commercial waste paper pulp board; the commercial hardwood pulp board is a mixture of one or more of poplar pulp board, eucalyptus pulp board and birch pulp board; the commercial softwood pulp board is a mixture of one or more of redwood pulp board, Masson pine pulp board and deciduous wood pulp board; the commercial waste paper pulp board is office waste paper pulp board.

[0026] Wherein, the beating degree of the plant fiber slurry is 35~45°SR.

[0027] In some embodiments of the present invention, the nano-scale inorganic filler is one or a mixture of nano-silicon dioxide, nano-alumina and amorphous calcium carbonate microspheres. The nano-silicon dioxide has a particle size of 50-100 nm, the nano-alumina has a particle size of 100-150 nm, and the amorphous calcium carbonate microsphere has a particle size of 500-800 nm.

[0028] The present invention can modify the surface of polylactic acid fibers by regulating the type of surface modifier, the treatment time and the amount of polylactic acid fibers added, thereby optimizing the pore structure and flow properties of the composite paper.

[0029] The composite paper obtained by the preparation method of the present invention comprises, based on the total mass of polylactic acid fiber, plant fiber and nano-scale inorganic filler, 10% to 70% by mass of polylactic acid fiber, 20% to 80% by mass of plant fiber and 5% to 15% by mass of nano-scale inorganic filler.

[0030] The composite paper of the present invention has a thickness of 200-300 μm, a porosity of 70%-90%, a pore size of 20-35 μm, can drive liquid to flow spontaneously through capillary effect, and can be used as a base material for paper-based instant detection devices.

[0031] The preparation method selected by the present invention is a wet forming technology, that is, using water as a medium to evenly disperse the papermaking raw materials (including modified polylactic acid fibers), and then forming wet paper sheets through a mesh mold or forming equipment, and then undergoing processes such as dehydration, pressing and drying to obtain composite paper.

[0032] Example 1 (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 0.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:55:5. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0033] Example 2 (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the eucalyptus pulp board in deionized water for 12 hours, and then fully deflate it with a fiber deflaker (running at 10,000 revolutions). Then, the deflaked pulp is pressurized (with a 1 kg weight) in a trough beater at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:50:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0034] Example 3 (1) The polylactic acid fibers were treated with an ultrafine grinder for 20 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 3.0%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fibers, the plasma gas is O2, the equipment power is 100W, the processing time is 40min, and the gas pressure is 100Pa to obtain modified polylactic acid short fibers; (4) Soak the redwood pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-silica weight) in a mass ratio of 40:45:15. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0035] Example 4 (1) treating the polylactic acid fibers with an ultrafine grinder for 30 minutes, cutting the polylactic acid fibers into short fibers with a length of 500 to 800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 3.0%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 90 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 40min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-silica weight) in a mass ratio of 40:45:15. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0036] Example 5 (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing an anionic polyacrylamide solution with a mass concentration of 0.5%, adding polylactic acid staple fibers to the anionic polyacrylamide solution (the mass ratio of polylactic acid staple fibers to the anionic polyacrylamide solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 50min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the Masson pine pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized (with a 1 kg weight) in a trough-type pulper at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-alumina filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-alumina weight) in a mass ratio of 40:45:15. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0037] Example 6 (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing an anionic polyacrylamide solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the anionic polyacrylamide solution (the mass ratio of polylactic acid staple fibers to the anionic polyacrylamide solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 50min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the Masson pine pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized (with a 1 kg weight) in a trough-type pulper at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:55:5. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0038] Example 7 (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing an anionic polyacrylamide solution with a mass concentration of 3.0%, adding polylactic acid staple fibers to the anionic polyacrylamide solution (the mass ratio of polylactic acid staple fibers to the anionic polyacrylamide solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 60min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the office waste paper pulp board in deionized water for 12 hours, and then use a fiber defiberizer to fully defiberize (run at 10,000 revolutions). Then, the defiberized pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-silica weight) in a mass ratio of 40:50:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0039] Example 8 (1) treating the polylactic acid fibers with an ultrafine grinder for 30 minutes, cutting the polylactic acid fibers into short fibers with a length of 500 to 800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing an anionic polyacrylamide solution with a mass concentration of 3.0%, adding polylactic acid staple fibers to the anionic polyacrylamide solution (the mass ratio of polylactic acid staple fibers to the anionic polyacrylamide solution is 1:50), treating at a temperature of 40°C for 90 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 60min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the office waste paper pulp board in deionized water for 12 hours, and then use a fiber defiberizer to fully defiberize (run at 10,000 revolutions). Then, the defiberized pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:50:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0040] Comparative Example 1 The composite paper without surfactant modification treatment is used as a blank sample, and the implementation method is as follows: (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) adding the polylactic acid staple fibers into anhydrous ethanol and treating them at 40°C for 60 min, then washing them with deionized water until neutral, and drying them for later use; (3) using a low-temperature plasma device to perform surface modification on the polylactic acid short fibers dried in step (2), wherein the plasma gas is O2, the equipment power is 100 W, the processing time is 30 min, and the gas pressure is 100 Pa, to obtain modified polylactic acid fibers; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:50:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0041] Comparative Example 2 The composite paper of alkali-modified polylactic acid fiber is used as a comparative sample, and the implementation method thereof is as follows: (1) The polylactic acid fibers were treated with an ultrafine grinder for 15 minutes, and the polylactic acid fibers were cut into short fibers with a length of 500 to 800 μm, and then washed with deionized water and dried to obtain micron-sized polylactic acid short fibers; (2) preparing a NaOH solution with a mass concentration of 0.5%, adding the polylactic acid staple fibers into the NaOH solution (the mass ratio of the polylactic acid staple fibers to the NaOH solution is 1:50), treating at a temperature of 40°C for 60 min, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving amorphous calcium carbonate microsphere filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (measured by absolute dry weight) and filler solution (measured by mass of amorphous calcium carbonate microspheres) in a mass ratio of 40:50:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0042] The composite paper without surfactant modification was used as a blank sample, and the composite paper of alkali-modified polylactic acid fiber was used as a comparative sample. The composite paper modified according to the embodiment of the present invention was compared with the composite paper. The results are shown in Table 1.

[0043] Table 1 Comparison of properties of composite papers prepared in Examples 1 to 8 and Comparative Examples

[0044] As shown in Table 1, compared with the composite paper without surfactant modification, the mechanical strength and liquid flow rate of the composite paper after surfactant modification have been greatly improved, among which the Young's modulus of the paper increased by 39.71%~140.67%, and the liquid flow rate increased by 78.41%~137.75%. At the same time, the surfactant modification treatment also improved the porosity and pore size of the paper, but the increase was small. Compared with the composite paper treated with alkali modification, after surfactant modification, the composite paper maintained a higher porosity and adjustable pore structure, while improving the bonding force between fibers, and improving the mechanical properties and fluid control ability of the composite paper.

[0045] Example 9 (1) treating the polylactic acid fibers with an ultrafine grinder for 15 minutes, cutting the polylactic acid fibers into short fibers with a length of 500-800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (by absolute dry weight) and filler solution (by nano-silica weight) in a mass ratio of 10:80:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0046] Example 10 (1) treating the polylactic acid fibers with an ultrafine grinder for 15 minutes, cutting the polylactic acid fibers into short fibers with a length of 500-800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the Masson pine pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized (with a 1 kg weight) in a trough-type pulper at a pulping concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-silica weight) in a mass ratio of 30:60:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0047] Embodiment 11 (1) treating the polylactic acid fibers with an ultrafine grinder for 30 minutes, cutting the polylactic acid fibers into short fibers with a length of 500-800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the Masson pine pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 45° SR to obtain plant fiber pulp; (5) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-silica weight) in a mass ratio of 50:40:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0048] Example 12 (1) treating the polylactic acid fibers with an ultrafine grinder for 30 minutes, cutting the polylactic acid fibers into short fibers with a length of 500-800 μm, and then washing with deionized water and drying to obtain micron-sized polylactic acid short fibers; (2) preparing a sodium dodecyl sulfate solution with a mass concentration of 1.5%, adding polylactic acid staple fibers to the sodium dodecyl sulfate solution (the mass ratio of polylactic acid staple fibers to the sodium dodecyl sulfate solution is 1:50), treating at a temperature of 40°C for 60 minutes, then washing with deionized water until neutral, and drying to obtain modified polylactic acid staple fibers; (3) Using a low-temperature plasma device to modify the surface of the modified polylactic acid short fiber, the plasma gas is O2, the equipment power is 100W, the processing time is 30min, and the gas pressure is 100Pa to obtain the modified polylactic acid fiber; (4) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber decompressor to fully decompress it (running at 10,000 revolutions). Then, the decompressed pulp is pressurized in a trough-type pulper (with a 1 kg weight) at a pulping concentration of 2% and a beating degree of 45° SR to obtain plant fiber pulp; (5) dissolving the nano-alumina filler in deionized water to prepare a filler solution with a mass concentration of 1%; (6) The mixed slurry is composed of modified polylactic acid fiber, plant fiber slurry (absolute dry weight) and filler solution (nano-alumina weight) in a mass ratio of 70:20:10. The modified polylactic acid fiber, plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and the composite paper is obtained after pressing and drying.

[0049] Comparative Example 3 Pure plant fiber paper without adding polylactic acid fiber is used as a blank sample, and the implementation method is as follows: (1) Soak the poplar pulp board in deionized water for 12 hours, and then use a fiber deflaker to fully deflake it (running at 10,000 revolutions). Then, the deflaked pulp is pressurized in a trough beater (with a 1 kg weight) at a beating concentration of 2% and a beating degree of 35° SR to obtain plant fiber pulp; (2) dissolving the nano-silica filler in deionized water to prepare a filler solution with a mass concentration of 1%; (3) The mixed slurry is composed of plant fiber slurry (measured by absolute dry mass) and filler solution (measured by nano-silica mass) in a mass ratio of 90:10. The obtained plant fiber slurry and filler solution are mixed, fully disintegrated and evenly dispersed to form a mixed slurry. The paper is made by a wet forming process, and pure plant fiber paper is obtained after pressing and drying.

[0050] Pure fiber paper without adding polylactic acid fiber was used as a blank sample, and compared with the composite paper with added modified polylactic acid fiber. The results are shown in Table 2.

[0051] Table 2 Performance comparison of the composite paper prepared in Examples 9-12 and the pure plant fiber paper prepared in Comparative Example 2

[0052] As shown in Table 2, the addition of modified polylactic acid fiber can control the internal pore size distribution and microporous structure of the composite paper, and effectively improve the flow performance of the liquid on the composite paper. After adding polylactic acid fiber, the porosity, pore size and liquid flow rate of the composite paper have been greatly improved, among which the porosity has increased by 30.63%~39.66%, the pore size has increased by 68.16%~113.47%, and the liquid flow rate has increased by 71.43%~152.22%.

Claims

1. A method for preparing composite paper with adjustable pore size structure, characterized in that: include: S1, micron-sized polylactic acid short fibers are immersed in a 0.5% to 3.0% surfactant solution, and then subjected to low-temperature plasma treatment to obtain modified polylactic acid fibers; wherein the surfactant is one or both of sodium dodecyl sulfate and anionic polyacrylamide; S2, mixing and dispersing the modified polylactic acid fiber, plant fiber pulp and nano-scale inorganic filler solution to prepare a mixed pulp, and papermaking by wet molding technology, and obtaining the composite paper after pressing and drying.

2. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S1, the length of the polylactic acid staple fibers is 500-800 µm.

3. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S1, the soaking treatment time is 60~90min.

4. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S1, the low-temperature plasma treatment time is 30 to 60 minutes.

5. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S2, the beating degree of the plant fiber pulp is 35~45°SR.

6. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S2, the nano inorganic filler is one or a mixture of nano silicon dioxide, nano aluminum oxide and amorphous calcium carbonate microspheres.

7. The method for preparing composite paper with adjustable pore size structure according to claim 1, characterized in that: In S2, the composition of the composite paper is, by mass percentage, 10% to 70% of modified polylactic acid fiber, 20% to 80% of plant fiber, and 5% to 15% of nano-scale inorganic filler.

8. Composite paper obtained by the preparation method according to any one of claims 1 to 7.

9. The composite paper according to claim 8, characterized in that: The composite paper has a porosity of 70% to 90% and a pore size of 20 to 35 μm.

10. A paper-based instant detection device, characterized in that: The composite paper according to claim 8 is used as the base material.

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