A high-strength PBO micro-nano composite paper and preparation method thereof

Abstract

The present invention discloses a high-strength PBO micro-nano composite paper and a preparation method thereof. The PBO-based composite paper comprises PBO nanofibers (PBONF) and PBO chopped fibers; the PBO nanofibers form a three-dimensional network structure, and the PBO chopped fibers are located in the three-dimensional network structure. The present invention inhibits the protonation of PBO molecules in the MSA / TFA system by pre-adding inorganic salts to the acidic sol, thereby hindering the formation of PBO nanofibers, and prepares a PBO chopped fiber dispersion to successfully introduce the PBO chopped fibers into the acidic system. The tensile strength of the PBO-based composite paper prepared by the method of the present invention is increased by 62.8 to 81.9 times; compared with the PBONF paper, the tensile strength of the PBO-based composite paper prepared by the method of the present invention is increased by 0.3 to 0.6 times.

Description

Technical Field

[0001] The invention relates to the technical field of high-strength paper-based composite materials, in particular to a high-strength PBO-based composite paper and a preparation method thereof, and in particular to a high-strength PBO micro-nano composite paper and a preparation method thereof. Background Art

[0002] Poly(p-benzobisoxazole) (PBO) paper is a new type of high-performance paper-based composite material made from PBO chopped fibers and pulp using traditional wet papermaking technology. PBO paper has super high heat resistance, flame retardancy, chemical resistance and electrical insulation properties, and has great application potential in rail transportation, aerospace, national defense and military industries. However, due to its inert chemical nature, PBO chopped fibers are only loosely stacked together by weak physical forces, so the PBO paper produced has a weak bearing capacity. In addition, due to the lack of a melting point, PBO pulp cannot play the role of bonding chopped fibers, thereby limiting the efficient transfer of stress inside the paper. The above problems lead to extremely poor mechanical properties of PBO paper, which seriously hinders its practical application.

[0003] In order to improve the surface activity of PBO chopped fibers, researchers have developed a series of surface modification techniques such as acid etching, chemical grafting, plasma treatment, and high-energy radiation. The modified PBO chopped fibers usually have good dispersibility in water, and the interaction between fibers can also be improved, so as to obtain paper with good uniformity and strength. However, most of the modification conditions are relatively harsh, which can easily damage the bulk strength of the fiber, and the type and distribution of active groups are not easy to accurately control. Since then, the dipping method has gradually developed into the main method for strengthening PBO paper. However, the thermal stability of general resins (such as epoxy resin, phenolic resin, etc.) is poor, which seriously limits the application of PBO paper prepared by the dipping method in extreme environments such as high temperature. In addition, the different chemical structures lead to poor interfacial compatibility between fibers and resins, thereby reducing the reinforcement efficiency of this strategy. In summary, previous studies have mainly focused on the surface and interface modification of micrometer-scale PBO fibers and their composites. Research on nanoscale PBO fibers is still extremely rare.

[0004] In 2016, Hao et al. first prepared micron-sized PBO fibers into nanofibers by sol-gel method in a mixed acid of methanesulfonic acid (MSA) and trifluoroacetic acid (TFA). Subsequently, PBO nanofibers (PBONF) as a new type of nanobuilding unit have been widely used in the design and manufacture of various functional composite materials. Recently, Wang et al. prepared a type of pearl-like material with graphene and boron nitride as fillers and a three-dimensional interconnected PBO nanofiber network as a matrix. This type of material exhibits ultra-high ductility and toughness as well as excellent thermal conductivity. Qian et al. developed an ultra-light, ultra-elastic, fire-resistant and heat-insulating PBO aerogel based on a chemically cross-linked PBO nanofiber network. PBO nanofibers are homologous to their microfibers and have similar physical and chemical properties, but their surface activity is significantly improved. Therefore, PBO nanofibers can be used as a matrix to improve the interaction between PBO microfibers, while highly oriented and highly crystalline PBO chopped fibers can be used as a skeleton to improve the load-bearing capacity of the random three-dimensional network of PBO nanofibers. However, since PBO chopped fibers will quickly peel off into PBO nanofibers or dissolve in MSA / TFA mixed acid, the two cannot coexist in the system in a controllable manner, so there are currently no research reports on PBO micro-nano composite structure paper. Summary of the invention

[0005] In order to improve the problem of extremely poor mechanical properties of existing PBO paper, the present invention provides a novel high-strength PBO base paper with a micro-nano composite structure and a preparation method of the PBO base paper. The high-strength PBO paper provided by the present invention has the advantages of high strength, etc., and provides a new preparation method for PBO base paper in the field of high-strength paper-based composite materials.

[0006] To achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] The invention provides a PBO-based composite paper, which comprises PBO nanofibers (PBONF) and PBO chopped fibers; the PBO nanofibers form a three-dimensional network structure, and the PBO chopped fibers are located in the three-dimensional network structure.

[0008] According to an embodiment of the present invention, in the PBO-based composite paper, the mass ratio of the PBO nanofiber to the PBO chopped fiber is 1:0.0005-1000, and exemplified by 1:0.0005, 1:0.001, 1:0.005, 1:0.01, 1:0.05, 1:0.1, 1:0.25, 1:0.5, 1:1, 1:5, 1:10, 1:50, 1:100, 1:200, 1:500, and 1:1000.

[0009] According to an embodiment of the present invention, the diameter of the PBO nanofiber is 10-100 nm, preferably 15-50 nm, more preferably 15-25 nm, and exemplified by 10 nm, 15 nm, 25 nm, 50 nm, and 100 nm.

[0010] According to an embodiment of the present invention, the diameter of the PBO chopped fibers is 5 to 30 μm, preferably 13 to 25 μm, and exemplarily 5 μm, 10 μm, 12.8 μm, 19.6 μm, 20.1 μm, 25 μm, 26.6 μm, and 30 μm; the length of the PBO chopped fibers is 1 to 10 mm, preferably 3 to 6 mm, and exemplarily 1 mm, 3 mm, 5 mm, 6 mm, 8 mm, and 10 mm.

[0011] The present invention also provides a method for preparing the above-mentioned PBO-based composite paper, comprising mixing a PBO nanofiber dispersion and a PBO chopped fiber dispersion to obtain a dispersion, stirring, standing to obtain a gel, then performing solvent exchange until the pH value of the gel is neutral, and then drying and hot pressing to obtain the PBO-based composite paper.

[0012] According to an embodiment of the present invention, in the dispersion, the mass ratio of PBO nanofibers to PBO chopped fibers is 1:0.0005-1000, and exemplified by 1:0.0005, 1:0.001, 1:0.005, 1:0.01, 1:0.05, 1:0.1, 1:0.25, 1:0.5, 1:1, 1:5, 1:10, 1:50, 1:100, 1:200, 1:500, and 1:1000.

[0013] According to an embodiment of the present invention, the preparation of the PBO nanofiber dispersion comprises mixing methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1 to 10, stirring, and then adding PBO fibers, wherein the content of the PBO fibers is 0.1 to 5.0 wt %, and the mixed solution is continuously stirred until the PBO fibers are completely dissolved.

[0014] According to an embodiment of the present invention, the preparation of the PBO chopped fiber dispersion comprises mixing methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1 to 10, stirring, then adding an inorganic salt, continuously stirring the mixed solution, and then adding PBO chopped fibers, wherein the content of the PBO chopped fibers is 0.1 to 3.0 wt%, and stirring until the PBO chopped fibers are uniformly dispersed in the solution.

[0015] Preferably, the mass ratio of the total mass of methanesulfonic acid and trifluoroacetic acid to the inorganic salt is 1:0.05-1, exemplified by 1:0.05, 1:0.0625, 1:0.08, 1:0.1, 1:0.2, 1:0.5, 1:1.

[0016] Preferably, the inorganic salt is a soluble salt, including but not limited to lithium chloride, lithium sulfate, magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium carbonate, magnesium acetate, magnesium nitrate, potassium sulfate, potassium acetate, potassium chloride, potassium carbonate, potassium nitrate, sodium phosphate, sodium carbonate, sodium sulfate, sodium nitrate, sodium acetate, ammonium nitrate, ammonium chloride, aluminum chloride, aluminum sulfate and aluminum nitrate, or a mixture of any proportion of more than one of them.

[0017] The inorganic salt is added to avoid the dissolution of the PBO chopped fibers and to promote the gelation of the PBO nanofiber dispersion in the subsequent step.

[0018] In the present invention, the PBO chopped fibers are obtained by shearing PBO fibers. The present invention has no particular limitation on the length of the PBO fibers, and the length of the PBO fibers has no significant effect on the performance of the PBO-based composite paper. Those skilled in the art can select PBO fibers of any length as needed.

[0019] Preferably, the diameter of the PBO fiber is 5 to 30 μm, preferably 13 to 25 μm, and exemplarily is 5 μm, 10 μm, 12.8 μm, 19.6 μm, 20.1 μm, 25 μm, 26.6 μm, and 30 μm.

[0020] Preferably, the diameter of the PBO chopped fibers is 5 to 30 μm, preferably 13 to 25 μm, and exemplarily 5 μm, 10 μm, 12.8 μm, 19.6 μm, 20.1 μm, 25 μm, 26.6 μm, and 30 μm; the length of the PBO chopped fibers is 1-10 mm, preferably 3 to 6 mm, and exemplarily 1 mm, 3 mm, 5 mm, 6 mm, 8 mm, and 10 mm.

[0021] The present invention has no particular limitation on the stirring temperature and time. For example, the stirring temperature may be 15 to 80° C., and the stirring time may be 0.5 to 5 hours.

[0022] According to an embodiment of the present invention, the standing is standing at 15-40°C for 2-5 hours, and then standing at 5--40°C for 5-8 hours. In the standing process described in the present invention, the mixed solution is gelled under the action of inorganic salts to form a gel with a regular external shape.

[0023] According to an embodiment of the present invention, the solvent used in the solvent exchange is water or alcohol. The trifluoroacetic acid, methanesulfonic acid and inorganic salt in the gel diffuse into the water or alcohol solvent, and the water or alcohol solvent diffuses into the gel to perform solvent exchange with deionized water or alcohol solvent.

[0024] According to an embodiment of the present invention, the drying and hot pressing time is 0.5h to 2h, exemplified by 0.5h, 1h, and 2h.

[0025] According to an embodiment of the present invention, the temperature of the drying hot pressing is 30-200°C, exemplified by 30°C, 50°C, 80°C, 100°C, 120°C, 150°C, and 200°C.

[0026] According to an embodiment of the present invention, the pressure of the drying hot pressing is 0 to 20 MPa, exemplified by 1 MPa, 2 MPa, 5 MPa, 8 MPa, 10 MPa, 15 MPa, and 20 MPa.

[0027] According to an embodiment of the present invention, the method for preparing the PBO-based composite paper comprises the following steps:

[0028] (1) Preparation of PBO nanofiber dispersion

[0029] Methanesulfonic acid and trifluoroacetic acid are mixed in a mass ratio of 1:0.1-10, stirred at 15-40° C., and then PBO fiber is added, wherein the content of PBO fiber is 0.1-5.0wt%, and the mixed solution is continuously stirred at 10-80° C. until the PBO fiber is completely dissolved;

[0030] (2) Preparation of PBO chopped fiber dispersion

[0031] Mix methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1-10, stir at 15-40° C., then add inorganic salt, wherein the mass ratio of the total mass of methanesulfonic acid and trifluoroacetic acid to the inorganic salt is 1:0.05-1; stir the mixed solution at 15-40° C. for 0.5-1 h, then add PBO chopped fibers, wherein the content of PBO chopped fibers is 0.1-3.0 wt%, and stir for 0.5-2 h until the PBO chopped fibers are uniformly dispersed in the solution;

[0032] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0033] The PBO nanofiber solution in step (1) is mixed with the PBO chopped fiber solution in step (2); the mixed solution is stirred at 15 to 40° C. for 0.5 to 5 hours; the mixed dispersion is then allowed to stand at 15 to 40° C. for 2 to 5 hours, and then allowed to stand at 5 to -40° C. for 5 to 8 hours to convert into a gel;

[0034] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0035] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) are placed in deionized water or an alcohol solvent for solvent exchange until the pH value of the gel is neutral;

[0036] (5) Preparation of PBO-based composite paper

[0037] The PBO / PBONF hydrogel obtained in step (4) is dried and hot-pressed to obtain a high-strength PBO base paper with a micro-nano composite structure.

[0038] The present invention also provides the application of the PBO-based composite paper in the fields of rail transportation, aerospace, national defense and military industry.

[0039] Beneficial effects of the present invention:

[0040] (1) In the present invention, inorganic salts are added to the acidic sol in advance to inhibit the protonation of PBO molecules in the MSA / TFA system, thereby hindering the formation of PBO nanofibers, and a PBO chopped fiber dispersion is prepared to successfully introduce the PBO chopped fibers into the acidic system.

[0041] (2) The present invention adopts a micro-nano composite structure, wherein: PBO nanofibers can be used as a matrix to improve the interaction between PBO micro-nano composite paper fibers, and highly oriented, high-crystallinity PBO chopped fibers can be used as a skeleton to improve the load-bearing capacity of the PBO nanofiber random three-dimensional network. The PBO nanofibers and PBO chopped fibers can achieve a homogeneous reinforcement effect, thereby improving the tensile strength of the PBO-based composite paper.

[0042] (3) Compared with conventional PBO paper, the tensile strength of the PBO-based composite paper prepared by the method of the present invention is increased by 62.8 to 81.9 times; compared with PBONF paper, the tensile strength of the PBO-based composite paper prepared by the method of the present invention is increased by 0.3 to 0.6 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a physical picture of the PBO / PBONF hydrogel prepared in Example 1 of the present invention;

[0044] Figure 2 This is a physical picture of the PBO / PBONF composite paper prepared in Example 1 of the present invention;

[0045] Figure 3 This is a SEM image of the freeze-dried PBO / PBONF hydrogel in Example 1 of the present invention;

[0046] Figure 4 Mechanical properties of PBO chopped fiber composite paper with different contents. DETAILED DESCRIPTION

[0047] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0048] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0049] Example 1

[0050] A method for preparing a PBO-based composite paper comprises the following steps:

[0051] (1) Preparation of PBO nanofiber dispersion

[0052] 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred evenly at 25° C. Then 0.4 g of PBO fiber (diameter 26.6 μm) was added, and the mixture was continuously stirred at 25° C. until the PBO fiber was completely dissolved.

[0053] (2) Preparation of PBO chopped fiber dispersion

[0054] Weigh 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid, mix them, stir evenly at 25°C, then add 2.7 g of sodium sulfate, and continue stirring the mixture at 25°C for 0.5 h. Then add 0.4 g of PBO chopped fibers (diameter 26.6 μm, length 6 mm), and after stirring for 1 h, the PBO chopped fibers are evenly dispersed in the solution.

[0055] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0056] 40 g of the PBO nanofiber dispersion prepared in step (1) was mixed with 40 g of the PBO chopped fiber dispersion prepared in step (2), and stirred at 25° C. for 2 h. The dispersion was then poured into a flat-bottomed plastic dish, allowed to stand at 25° C. for 2 h, and then allowed to stand at -10° C. for 8 h to convert into a gel.

[0057] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0058] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) were placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffused into the water, and the water diffused into the gel. After soaking for 5 hours, the water was changed and the cycle was repeated 3 times to obtain a PBO / PBONF hydrogel (such as Figure 1 shown).

[0059] (5) Preparation of PBO-based composite paper

[0060] The PBO / PBONF hydrogel obtained in step (4) was dried and hot-pressed at 120° C. and 10 MPa for 1 h to obtain a novel high-strength PBO base paper having a micro-nano composite structure (such as Figure 2 shown).

[0061] like Figure 3 The figure shows a SEM image of the hydrogel obtained in step (4) of this embodiment after freeze drying. It can be seen from the figure that the PBO chopped fibers are embedded in the three-dimensional network of the PBO nanofibers, and the two achieve a homogeneous reinforcement effect, thereby improving the tensile strength of the PBO-based composite paper.

[0062] like Figure 4 As shown, compared with PBO paper, the tensile strength of the PBO-based composite paper prepared in this embodiment is increased by 81.9 times; compared with PBONF paper, the tensile strength of the PBO-based composite paper is increased by 0.6 times.

[0063] Example 2

[0064] A method for preparing a PBO-based composite paper comprises the following steps:

[0065] (1) Preparation of PBO nanofiber dispersion

[0066] 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred evenly at 25° C. Then 0.8 g of PBO fiber (diameter 19.6 μm) was added, and the mixture was continuously stirred at 60° C. until the PBO fiber was completely dissolved.

[0067] (2) Preparation of PBO chopped fiber dispersion

[0068] Weigh 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid, mix them, stir evenly at 25°C, then add 3.0 g of sodium carbonate salt, and continue stirring the mixture at 25°C for 0.5 h. Then add 0.2 g of PBO chopped fibers (diameter 19.6 μm, length 3 mm), stir for 0.5 h, and the PBO chopped fibers are evenly dispersed in the solution.

[0069] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0070] 40 g of the PBO nanofiber dispersion prepared in step (1) was mixed with 20 g of the PBO chopped fiber dispersion prepared in step (2), and stirred at 25° C. for 2 h. The dispersion was then poured into a flat-bottomed plastic dish, allowed to stand at 25° C. for 3 h, and then allowed to stand at -10° C. for 7 h to convert into a gel.

[0071] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0072] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) are placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffuse into the water, and the water diffuses into the gel. After soaking for 4 hours, the water is changed and the cycle is repeated 4 times to obtain a PBO / PBONF hydrogel.

[0073] (5) Preparation of PBO-based composite paper

[0074] The PBO / PBONF hydrogel obtained in step (4) was dried and hot-pressed at 30° C. and 11 MPa for 2 h to obtain a novel high-strength PBO base paper having a micro-nano composite structure.

[0075] like Figure 4 As shown, the tensile strength of PBO-based composite paper is increased by 79.7 times compared with PBO paper; and the tensile strength of PBO-based composite paper is increased by 0.6 times compared with PBONF paper.

[0076] Example 3

[0077] A method for preparing a PBO-based composite paper comprises the following steps:

[0078] (1) Preparation of PBO nanofiber dispersion

[0079] 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred evenly at 25° C. Then 0.2 g of PBO fiber (with a diameter of 30 μm) was added, and the mixed solution was continuously stirred at 25° C. until the PBO fiber was completely dissolved.

[0080] (2) Preparation of PBO chopped fiber dispersion

[0081] Weigh 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid, mix them, stir evenly at 25°C, then add 2.0 g of sodium phosphate, continue stirring the mixture at 25°C for 0.5 h, then add 0.8 g of PBO chopped fibers (30 μm in diameter, 5 mm in length), stir for 1.5 h, and the PBO chopped fibers are evenly dispersed in the solution.

[0082] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0083] 20 g of the PBO nanofiber dispersion prepared in step (1) was mixed with 30 g of the PBO chopped fiber dispersion prepared in step (2), and stirred at 25° C. for 3 h. The dispersion was then poured into a flat-bottomed plastic dish, allowed to stand at 25° C. for 2 h, and then allowed to stand at -10° C. for 8 h to convert into a gel.

[0084] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0085] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) are placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffuse into the water, and the water diffuses into the gel. After soaking for 4 hours, the water is changed and the cycle is repeated 5 times to obtain a PBO / PBONF hydrogel.

[0086] (5) Preparation of PBO-based composite paper

[0087] The PBO / PBONF hydrogel obtained in step (4) was dried and hot-pressed at 150° C. and 8 MPa for 1.5 h to obtain a novel high-strength PBO base paper having a micro-nano composite structure.

[0088] like Figure 4 As shown, the tensile strength of PBO-based composite paper is increased by 74.9 times compared with PBO paper; and the tensile strength of PBO-based composite paper is increased by 0.5 times compared with PBONF paper.

[0089] Example 4

[0090] A method for preparing a PBO-based composite paper comprises the following steps:

[0091] (1) Preparation of PBO nanofiber dispersion

[0092] 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred evenly at 25° C. Then 0.1 g of PBO fiber (diameter 20.1 μm) was added, and the mixture was continuously stirred at 25° C. until the PBO fiber was completely dissolved.

[0093] (2) Preparation of PBO chopped fiber dispersion

[0094] Weigh 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid, mix them, stir evenly at 25°C, then add 2.0 g of sodium sulfate, and continue stirring the mixture at 25°C for 0.5 h. Then add 0.8 g of PBO chopped fibers (diameter 20.1 μm, length 8 mm), stir for 1.5 h, and the PBO chopped fibers are evenly dispersed in the solution.

[0095] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0096] 40 g of the PBO nanofiber dispersion prepared in step (1) was mixed with 10 g of the PBO chopped fiber dispersion prepared in step (2), and stirred at 25° C. for 2 h. The dispersion was then poured into a flat-bottomed plastic dish, allowed to stand at 25° C. for 2 h, and then allowed to stand at -10° C. for 8 h to convert into a gel.

[0097] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0098] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) are placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffuse into the water, and the water diffuses into the gel. After soaking for 5 hours, the water is changed and the cycle is repeated 5 times to obtain a PBO / PBONF hydrogel.

[0099] (5) Preparation of PBO-based composite paper

[0100] The PBO / PBONF hydrogel obtained in step (4) is dried and hot-pressed at 200° C. and 0 MPa for 1 h to obtain a novel high-strength PBO base paper with a micro-nano composite structure.

[0101] like Figure 4 As shown, the tensile strength of PBO-based composite paper is increased by 74.5 times compared with PBO paper; and the tensile strength of PBO-based composite paper is increased by 0.5 times compared with PBONF paper.

[0102] Example 5

[0103] A method for preparing a PBO-based composite paper comprises the following steps:

[0104] (1) Preparation of PBO nanofiber dispersion

[0105] 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred evenly at 25° C. Then 0.4 g of PBO fiber (diameter 20.1 μm) was added, and the mixture was continuously stirred at 25° C. until the PBO fiber was completely dissolved.

[0106] (2) Preparation of PBO chopped fiber dispersion

[0107] Weigh 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid, mix them, stir evenly at 25°C, then add 2.7 g of sodium sulfate, and continue stirring the mixture at 25°C for 0.5 h. Then add 0.1 g of PBO chopped fibers (diameter 12.8 μm, length 10 mm), stir for 1 h, and the PBO chopped fibers are evenly dispersed in the solution.

[0108] (3) Preparation of PBO chopped fibers and PBO nanofiber gel

[0109] 40 g of the PBO nanofiber dispersion prepared in step (1) was mixed with 40 g of the PBO chopped fiber dispersion prepared in step (2), and stirred at 25° C. for 2 h. The dispersion was then poured into a flat-bottomed plastic dish, allowed to stand at 25° C. for 1 h, and then allowed to stand at -10° C. for 8 h to convert into a gel.

[0110] (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogels

[0111] The PBO nanofibers and PBO chopped fiber gel obtained in step (3) are placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffuse into the water, and the water diffuses into the gel. After soaking for 4 hours, the water is changed and the cycle is repeated 4 times to obtain a PBO / PBONF hydrogel.

[0112] (5) Preparation of PBO-based composite paper

[0113] The PBO / PBONF hydrogel obtained in step (4) is dried and hot-pressed at 150° C. and 10 MPa for 1 h to obtain a novel high-strength PBO base paper having a micro-nano composite structure.

[0114] like Figure 4 As shown, the tensile strength of PBO-based composite paper is increased by 80.7 times compared with PBO paper; and the tensile strength of PBO-based composite paper is increased by 0.6 times compared with PBONF paper.

[0115] Comparative Example 1

[0116] The preparation of PBO paper includes the following steps:

[0117] (1) Preparation of PBO pulp: 40 g of PBO chopped fibers (diameter 26.6 μm, length 6 mm) and 20 L of water were stirred in a stirrer for 1.5 h to prepare PBO pulp.

[0118] (2) Preparation of PBO fiber and pulp dispersion: 0.69 g of PBO chopped fibers (diameter 26.6 μm, length 6 mm) and 1.04 g of the PBO pulp obtained in step (1) were dispersed in a 0.1% by mass concentration hydroxyethyl cellulose aqueous solution to prepare a pulp dispersion.

[0119] (3) Preparation of PBO paper: The pulp dispersion prepared in step (2) is filtered through a round sheeting machine, and the rough paper is repeatedly washed with deionized water to remove hydroxyethyl cellulose, and then dried to obtain PBO paper.

[0120] like Figure 4 As shown, the tensile strength of the PBO paper prepared in this comparative example is 4.3 MPa.

[0121] Comparative Example 2

[0122] The preparation of PBONF paper includes the following steps:

[0123] (1) Preparation of PBO nanodispersion: 20 g of methanesulfonic acid and 20 g of trifluoroacetic acid were weighed and mixed, and stirred at 25° C. Then, 0.4 g of PBO fiber (diameter 26.6 μm) was added, and the mixture was stirred continuously at 25° C. until the PBO fiber was completely dissolved.

[0124] (2) Preparation of PBONF gel: Weigh 2.7 g of sodium sulfate and add it to step (1). Control the temperature at 65°C and stir for 1 hour until the sodium sulfate is completely dissolved. Pour it into a flat-bottomed plastic dish and let it stand at 25°C for 2 hours. Then let it stand at -10°C for 8 hours to convert it into gel.

[0125] (3) Preparation of PBONF hydrogel: The gel obtained in step (2) was placed in deionized water, and the trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel diffused into the water, and the water diffused into the gel. After soaking for 5 hours, the water was changed and the cycle was repeated 3 times to obtain PBONF hydrogel.

[0126] (4) Preparation of PBONF paper: The PBONF hydrogel obtained in step (3) was dried and hot-pressed at 120° C. and 10 MPa for 1 h to obtain PBONF paper.

[0127] like Figure 4 As shown, the tensile strength of the PBONF paper prepared in this comparative example is 207.3 MPa.

[0128] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a PBO-based composite paper, It is characterized in that The method comprises mixing a PBO nanofiber dispersion liquid with a PBO chopped fiber dispersion liquid to obtain a dispersion liquid, stirring, standing to obtain a gel, then performing solvent exchange until the pH value of the gel is neutral, and then drying and hot pressing to obtain the PBO-based composite paper; The preparation of the PBO nanofiber dispersion comprises mixing methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1 to 10, stirring, then adding PBO fibers, wherein the content of the PBO fibers is 0.1 to 5.0 wt %, and continuously stirring the mixture until the PBO fibers are dissolved; The preparation of the PBO chopped fiber dispersion comprises mixing methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1 to 10, stirring, then adding an inorganic salt, continuously stirring the mixture, then adding PBO chopped fibers, wherein the content of the PBO chopped fibers is 0.1 to 3.0 wt %, stirring until the PBO chopped fibers are uniformly dispersed in the solution; The mass ratio of the total mass of methanesulfonic acid and trifluoroacetic acid to the mass of the inorganic salt is 1:0.05-1; The inorganic salt is a soluble salt, including one or a mixture of any proportion of lithium chloride, lithium sulfate, magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium carbonate, magnesium acetate, magnesium nitrate, potassium sulfate, potassium acetate, potassium chloride, potassium carbonate, potassium nitrate, sodium phosphate, sodium carbonate, sodium sulfate, sodium nitrate, sodium acetate, ammonium nitrate, ammonium chloride, aluminum chloride, aluminum sulfate and aluminum nitrate; The PBO-based composite paper comprises PBO nanofibers (PBONF) and PBO chopped fibers; the PBO nanofibers form a three-dimensional network structure, and the PBO chopped fibers are located in the three-dimensional network structure.

2. The method for preparing the PBO-based composite paper according to claim 1, It is characterized in that In the PBO-based composite paper, the mass ratio of the PBO nanofibers to the PBO chopped fibers is 1:0.0005-1000.

3. The method for preparing the PBO-based composite paper according to claim 1, It is characterized in that The diameter of the PBO nanofiber is 10 to 100 nm; And / or, the diameter of the PBO chopped fibers is 5-30 μm, and the length of the PBO chopped fibers is 1-10 mm.

4. The method for preparing the PBO-based composite paper according to claim 3, It is characterized in that The diameter of the PBO nanofiber is 15-50 nm; The diameter of the PBO chopped fibers is 13-25 μm; the length of the PBO chopped fibers is 3-6 mm.

5. The method for preparing the PBO-based composite paper according to claim 4, It is characterized in that The diameter of the PBO nanofiber is 15-25 nm.

6. The preparation method according to claim 1, It is characterized in that In the dispersion, the mass ratio of the PBO nanofibers to the PBO chopped fibers is 1:0.0005-1000.

7. The preparation method according to any one of claims 1 to 6, It is characterized in that The solvent used in the solvent exchange is water or alcohol.

8. The preparation method according to any one of claims 1 to 6, It is characterized in that The drying and hot pressing time is 0.5h to 2h; the drying and hot pressing temperature is 30 to 200°C; and the drying and hot pressing pressure is 0 to 20MPa.

9. The preparation method according to any one of claims 1 to 6, It is characterized in that The following steps are involved: (1) Preparation of PBO nanofiber dispersion Methanesulfonic acid and trifluoroacetic acid are mixed in a mass ratio of 1:0.1-10, stirred at 15-40° C., and then PBO fiber is added, wherein the content of PBO fiber is 0.1-5.0wt%, and the mixed solution is continuously stirred at 10-80° C. until the PBO fiber is dissolved; (2) Preparation of PBO chopped fiber dispersion Mix methanesulfonic acid and trifluoroacetic acid in a mass ratio of 1:0.1-10, stir at 15-40° C., then add inorganic salt, wherein the mass ratio of the total mass of methanesulfonic acid and trifluoroacetic acid to the inorganic salt is 1:0.05-1; stir the mixed solution at 15-40° C. for 0.5-1 h, then add PBO chopped fibers, wherein the content of PBO chopped fibers is 0.1-3.0wt%, and stir for 0.5-2 h until the PBO chopped fibers are uniformly dispersed in the solution; (3) Preparation of PBO chopped fibers and PBO nanofiber gel Mixing the PBO nanofiber solution in step (1) with the PBO chopped fiber solution in step (2); The mixed solution is stirred at 15-40°C for 0.5-5h; The mixed dispersion is then placed at 15-40°C for 2-5 hours, and then placed at 5--40°C for 5-8 hours to convert into a gel; (4) Preparation of PBO chopped fibers and PBO nanofiber hydrogel The PBO nanofiber and PBO chopped fiber gel obtained in step (3) is placed in deionized water or an alcohol solvent for solvent exchange until the pH value of the gel is neutral; (5) Preparation of PBO-based composite paper The PBO / PBONF hydrogel obtained in step (4) is dried and hot-pressed to obtain a high-strength PBO base paper having a micro-nano composite structure.

10. Application of the PBO-based composite paper prepared by the preparation method according to any one of claims 1 to 9 in the fields of rail transportation, aerospace, national defense and military industry.

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