Method and system for improving interface performance of PBO fiber through continuous high-temperature oxidation modification

Abstract

The invention discloses a method and system for improving the interface performance of PBO fibers through continuous high-temperature oxidation modification, and belongs to the technical field of PBO fiber performance improvement. According to the method, the original PBO fibers are subjected to continuous high-temperature oxidation treatment on the basis of the continuous oxidation treatment device; then, carrying out secondary modification treatment by adopting a sizing agent; and finally, carrying out adaptive post-treatment to obtain a modified PBO fiber product. The PBO fiber interface performance can be greatly improved, the tensile strength reduction amplitude of the PBO fiber is greatly reduced, the tensile strength retention rate of the PBO fiber is larger than or equal to 95%, and meanwhile the tensile modulus of the PBO fiber can be greatly improved.

Description

Technical Field

[0001] This invention relates to a method for enhancing the interfacial properties of modified PBO fibers, specifically a method for enhancing the interfacial properties of modified PBO fibers through continuous high-temperature oxidation treatment, belonging to the field of PBO fiber performance improvement technology. Background Technology

[0002] PBO (poly(p-phenylenebenzobisoxazole)) is produced by solution polycondensation, liquid crystal spinning, washing, and drying of 4,6-diaminoresorcinol hydrochloride and terephthalic acid as monomers, with polyphosphoric acid as solvent. PBO fiber is a new generation of ultra-high-performance fiber following Kevlar fiber, and is currently considered one of the best-performing organic fibers in terms of overall performance. Developed in the 1980s by the United States for the development of aerospace, it is a reinforcing material for composite materials. Among existing chemical fibers, it has the highest tensile properties, with a breaking strength reaching 5.8 GPa and an elastic modulus reaching 280 GPa, exceeding not only steel fibers but also aramid fibers. PBO fiber has a working temperature of 300-350℃, a heat resistance temperature of up to 650℃, a limiting oxygen index of 68, and does not burn or shrink in flames. Its heat resistance and flame retardancy are higher than other organic fibers. Furthermore, PBO fiber exhibits excellent impact resistance, abrasion resistance, and dimensional stability, and is lightweight and flexible. Due to these excellent comprehensive properties, PBO fibers are widely used in high-performance composite materials prepared from them in high-tech fields such as aerospace, aviation, and planetary exploration.

[0003] Modern fiber-reinforced resin-based composites are a new type of polymer material generally composed of organic synthetic resins as the matrix and synthetic fibers as the reinforcement, synthesized through specific processing techniques. Structurally, they are multi-component, multi-phase systems. The continuous resin phase is the most important part of the material, acting as a carrier and binder; the dispersed fiber phase bears external loads; and the interface between the resin and fibers is responsible for stress transfer. The quality of the interface is one of the key factors directly affecting the performance of the composite material. PBO fibers have a rigid molecular structure, and the relevant structural formulas are as follows:

[0004] As can be seen from the structural formula, its surface is very smooth with few active groups, making it difficult to wet and adsorb onto the resin matrix. This results in low interfacial bonding strength between the fiber and the resin in the composite material, severely limiting its application in composite materials. In recent years, numerous studies have focused on surface modification of PBO fibers, mainly including plasma treatment, high-energy ray irradiation treatment, and chemical grafting methods. Although these methods have made some progress in improving the interfacial properties of PBO fibers, they often come at the cost of sacrificing the tensile strength of the fiber itself. For example, after plasma treatment or high-energy ray irradiation treatment, the tensile strength of the PBO fiber itself decreases by 10-20%, and after chemical grafting modification, the tensile strength of the PBO fiber decreases by more than 20%. These factors will hinder the full realization of the comprehensive performance of the composite material.

[0005] Although the prior art CN102808325A discloses "a method for surface modification of PBO fibers", it first pretreats PBO with hydrogen peroxide and enzymes to introduce active groups on its surface, and then condenses it with a coupling agent to introduce different active functional groups on its surface to meet the needs of different thermosetting resins, thereby improving the interfacial bonding performance between the fiber and the resin; CN104194010A discloses "a method and application of atomic oxygen to improve the interfacial performance of PBO fiber-epoxy composite materials", but it mainly solves the problem that the chemical inertness of the surface of existing PBO fibers leads to poor wettability with the matrix resin. Summary of the Invention

[0006] To address the problem that PBO fibers in fiber-reinforced resin matrix composites cannot achieve their optimal performance due to their smooth surface structure, few active groups, and poor adhesion to the resin matrix, thus limiting their application in advanced composite materials; and to solve the technical problem that existing PBO fiber surface modification methods sacrifice the tensile strength of the fiber itself to improve the interfacial properties, a method and system for improving the interfacial properties of PBO fibers through continuous high-temperature oxidation modification is proposed.

[0007] In this technical solution, based on the self-developed continuous oxidation treatment device and the corresponding control conditions, not only can the interfacial properties of PBO fibers be significantly improved, but the decrease in tensile strength of PBO fibers can also be greatly reduced, so that the tensile strength retention rate of PBO fibers is ≥95%, and the tensile modulus of PBO fibers can also be significantly improved.

[0008] To achieve the above technical objectives, the following technical solution is proposed: The primary objective of this technical solution is to provide a method for improving the interfacial properties of PBO fibers through continuous high-temperature oxidation modification, comprising the following steps: S1: Continuous high-temperature oxidation treatment Using a five-roller traction machine I, PBO fiber filaments are continuously fed into a high-temperature oxidation treatment device. A mixed gas with an oxygen content of 25-60% and a temperature of 500-650°C is introduced into the high-temperature oxidation treatment device. The oxidation treatment temperature is stabilized at 500-650°C through a tubular heating furnace, and the oxidation treatment is carried out for 20-150 seconds to obtain oxidized PBO fiber. Then, using a five-roller traction machine II, the treated PBO fiber (oxidized PBO fiber) is continuously fed into a sizing device. The flow rate of the mixed gas is 100–250 L / min; The stretching speed ratio between the five-roller traction machine I and the five-roller traction machine II is 1.0 to 1.5; In this process, the degree of oxidation, tensile strength retention, and tensile modulus of the PBO fibers are controlled by adjusting the oxygen content in the mixed gas, gas flow rate, oxidation temperature, oxidation time (determined by the traction rate of the PBO fibers), traction rate (the stretching rate of the five-roller traction machine II), and the stretching speed ratio between the five-roller traction machine I and the five-roller traction machine II (the stretching rate of the five-roller traction machine I ≤ the stretching rate of the five-roller traction machine II). Specifically, this involves: In the high-temperature oxidation treatment unit, the oxygen content is regulated by a gas mixing tank at the front of the workstation. A higher oxygen content in the mixed gas results in a higher degree of oxidation of the PBO fibers, leading to better interfacial properties in the subsequent PBO fibers. However, excessive oxidation can cause a decrease in the tensile strength of the PBO fibers, thus affecting their subsequent applications. Therefore, the oxygen content is controlled within the range of 25% to 60%, with air (A being its volume percentage) at 50% to 100% and oxygen (B being its volume percentage = 1 - A) at 0% to 50%.

[0009] Similarly, increasing the gas flow rate, oxidation temperature, and oxidation time can enhance the oxidation degree of PBO fibers and improve their interfacial properties. A higher mixed gas flow rate ensures a more complete oxidation reaction, but when the oxidation reaction is already complete, an excessively high gas flow rate will only waste resources. Therefore, the gas flow rate is controlled at 100–250 L / min. On the other hand, excessively high oxidation temperature and excessively long oxidation time will also lead to over-oxidation of PBO fibers, causing a decrease in the tensile strength of PBO fibers. Therefore, the oxidation temperature is limited to 500–650℃, and the oxidation time is limited to 20–150 s. Generally, increasing the tensile modulus of PBO fibers increases with increasing heat treatment temperature (i.e., oxidation temperature) and the stretching speed ratio between the front and rear traction machines. However, excessively high temperatures and excessively large stretching speed ratios can also lead to a decrease in the tensile strength of PBO fibers. Therefore, the stretching speed ratio between the five-roll traction machine I and the five-roll traction machine II is controlled at 1.0 to 1.5. S2: Sizing treatment The oxidized PBO fibers treated in step S1 are fed into the sizing device via a five-roller traction machine II for one-time continuous rolling coating and sizing. Then, the excess sizing material is squeezed out by the pressure rollers to obtain modified PBO fibers with a sizing agent content of 0.5-5.0%. The sizing agent is a mixture comprising 0.5-8.0% aminosiloxane and 0.5-2.0% ethylenepropylsiloxane by mass, and the solvent involved is a mixture of water and ethanol, acetone, ethyl acetate, etc., with the volume percentage of water not exceeding 20%. Aminosiloxanes include one or a mixture of any two or more of γ-aminopropyltriethoxysilane (APTES), γ-aminopropylmethyldimethoxysilane (APMDS), N-methyl-aminopropyltrimethoxysilane (MAPTMS), and bis(γ-triethoxypropylamine); Vinylsiloxanes include vinyltrimethoxysilane (VTMO), vinyltriethoxysilane (VTEO), or mixtures thereof; In this process, by adjusting the depth of the sizing agent's lower edge immersion in the sizing tank, the running tension between the guide roller and the sizing roller, the sizing agent concentration, the sizing agent temperature, the fiber stretching rate, and the pressure of the rear pressure roller, not only is the sizing agent uniformly coated onto the oxidized PBO fiber, but also modified PBO fibers with a sizing agent content of 0.5% to 5.0% are obtained. Specifically, this involves: The sizing agent is a mixture of aminosiloxane (D being its mass percentage in the sizing agent) and vinylsiloxane (E being its mass percentage in the sizing agent), with D ranging from 0.5% to 8.0% and E from 0.5% to 2.0%. Higher siloxane concentrations in the sizing agent result in higher sizing content in the PBO fiber, leading to a thicker SiO2 coating after subsequent drying and curing, and thus improving the interfacial properties of the PBO fiber. However, excessively thick coatings can cause the PBO fiber to harden and become excessively bundled, which is detrimental to subsequent applications such as weaving. Therefore, modified PBO fibers with a sizing agent content controlled to 0.5%–5.0% are obtained. The aminosiloxane has high activity; after hydrolysis, it can form covalent bonds with the hydroxyl and carboxyl groups on the surface of oxidized PBO fibers through dehydration condensation at high temperatures. It is the main component of the sizing agent, with a content of 0.5–8.0%. The vinylsiloxane has lower activity and undergoes an addition grafting reaction with the free radicals in the oxidized PBO fibers. Since there are relatively few free radicals in PBO fibers, the amount used should not be too high, with a content of 0.5–2.0%. After coating with a coating roller and extrusion by a pressure roller, the sizing agent content in the PBO fibers is controlled at 0.5–5.0%. During sizing, the stretching rate of oxidized PBO fibers must be consistent with the stretching rate of PBO fiber precursors in the high-temperature oxidation treatment device. Therefore, the stretching rate of oxidized PBO fibers is 25-100 m / min. Tension is applied between the guide roller and the coating roller to further ensure that the PBO fibers are fully dispersed and uniformly impregnated with the sizing agent. Therefore, the running tension between the guide roller and the coating roller is controlled to be 50-200 cN. During sizing, increasing the depth of the lower edge of the coating roller into the sizing tank can increase the sizing content in the PBO fiber. However, if the lower edge is immersed too deeply, it will lead to increased sizing loss and increased production costs. Therefore, the depth of the coating roller's lower edge immersed in the sizing liquid in the sizing tank is set to 5-20 cm. When sizing, appropriately increasing the temperature of the sizing agent can increase the sizing content in the fiber. However, its solvent is low-boiling-point ethanol, acetone or ethyl acetate, etc. If the temperature is too high, the solvent will evaporate. Therefore, the temperature of the sizing agent is set at 20-60℃. By adjusting the pressure, the pressure roller can remove 90% of the solvent from the PBO fiber and minimize the loss of sizing agent from the PBO fiber. For this purpose, the pressure is set to 0.5 to 5.0 MPa. S3: Post-processing The modified PBO fiber after step S2 is fed into a drying device for high-temperature curing and rapid drying to obtain the modified PBO fiber product. The high-temperature curing temperature is 80–150℃, the curing time is 2.5–10 min, and the tensile rate during curing is 25–100 m / min. During high-temperature curing, a SiO2 nanoscale coating is rapidly formed; simultaneously, a large amount of residual solvent evaporates quickly at high temperatures. Increasing the curing temperature can improve the curing reaction rate, which is beneficial for the formation of the SiO2 coating; however, excessively high temperatures can easily lead to explosive polymerization and excessive condensation of siloxanes, causing PBO fibers to harden and become overly bundled, which is not conducive to subsequent applications such as PBO fiber weaving. Therefore, the curing temperature is set to 80–150℃. The curing time is limited by the tensile rate (25-100 m / min), therefore, the curing time is set to 2.5-10 min; Finally, the PBO fiber final product is wound into a tube using a winding device at a winding rate of 25–100 m / min (preferably 75 m / min). The wound PBO fiber is then put back into the drying oven and dried at 80–160°C for 1–5 hours to completely remove the solvent before performance testing or storage.

[0010] The second objective of this technical solution is to provide: a system for improving the interfacial properties of PBO fibers through continuous high-temperature oxidation modification, comprising a high-temperature oxidation treatment device, a sizing device, an extrusion device, a drying device, and a winding device, wherein... High-temperature oxidation treatment device: includes a gas mixing tank, a heater and a tubular furnace. The bottom of the gas mixing tank is connected to an oxygen inlet pipe and an air inlet pipe. The oxygen inlet pipe is equipped with an oxygen feed flow meter and an oxygen feed control valve. The air inlet pipe is equipped with an air feed flow meter and an air feed control valve. The gas mixing tank is equipped with a stirring mechanism. The outlet of the gas mixing tank is connected to the tubular heater via a mixed gas delivery pipe, and the heater is located on the mixed gas delivery pipe; a mixed gas flow meter is installed on the mixed gas delivery pipe. The tubular heating furnace was originally part of the high-modulus PBO production unit (the tubular heating furnace was only connected to a nitrogen inlet pipe), and could not be connected to oxygen or have its oxygen content controlled. By adding a gas mixing tank, and connecting a nitrogen inlet pipe to the bottom of the gas mixing tank, with a nitrogen feed flow meter and a nitrogen feed control valve installed on the nitrogen inlet pipe, the high-temperature oxidation treatment unit can be used for both continuous high-temperature oxidation modification of PBO fibers and high-modulus treatment of PBO fibers through the control of the mixed gas composition and ratio. The process involves the following steps: After the mixed gas in the gas mixing tank is stirred and thoroughly mixed, it is output through the top gas delivery pipe and preheated to 500-650°C by a heater (to prevent the mixed gas temperature from falling below the temperature inside the tubular heating furnace, which would cause temperature fluctuations and affect the PBO fiber oxidation effect). Then, after being metered by a mixed gas flow meter, it is input into the tubular heating furnace (500-650°C) for continuous high-temperature oxidation treatment of the PBO fibers. With the gas mixing tank connected externally to the tubular heating furnace, not only can various gases such as oxygen, air, and nitrogen be introduced, but the oxygen content in the mixed gas can also be precisely controlled. For example, in the preparation of low-oxygen-content oxidized PBO fibers, this invention uses air instead of nitrogen to adjust the oxygen content in the mixed gas, which can greatly reduce the production cost during oxidation treatment; and, when the oxygen and air inlets are closed and nitrogen is introduced, the PBO fibers can be re-treated at high temperature to continue producing high-modulus PBO fibers. This is a dual-purpose device, greatly improving the utilization rate of the equipment.

[0011] A five-roller traction machine I is installed on one side of the tubular heating furnace, and a PBO fiber feeding device is installed in front of the station of the five-roller traction machine I; a five-roller traction machine II is installed on the other side of the tubular heating furnace. Sizing device: Located at the rear of the station of the five-roller traction machine II, the sizing device includes a material trough and guide rollers and coating rollers installed in the material trough; the guide rollers include a first guide roller and a second guide roller, the coating roller is located between the first guide roller and the second guide roller, and the lower edge of the coating roller is immersed in the sizing liquid in the material trough to a depth of 5 to 20 cm. Extrusion device: Located behind the sizing device, the extrusion device includes a set of pressure rollers; Drying device: located behind the extrusion unit station; Rewinding device: Located behind the workstation of the drying unit; A continuous pathway for the preparation of modified PBO fiber products is formed between the PBO fiber feeding device, the five-roller traction machine I, the high-temperature oxidation treatment device, the five-roller traction machine II, the sizing device, the extrusion device, the drying device, and the winding device.

[0012] The mechanisms involved in this technical solution include: .

[0013] In this technical solution, the chemical reaction formulas (closed-ring reactions) involved include: .

[0014] The positional relationships such as "behind the workstation", "between", "above", "front of the workstation", "one side", and "the other side" involved in this technical solution are defined according to the actual usage conditions and are conventional terms in this technical field, as well as conventional terms used by those skilled in the art in actual use.

[0015] In the description of this technical solution, it should be noted that, unless otherwise explicitly specified and limited, the terms "setting" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0016] The beneficial technical effects of adopting this technical solution are as follows: 1. The oxidation modification of the present invention is a continuous high-temperature oxidation modification method. During the modification process, the high-temperature oxidation reaction of the fiber and the closed-loop reaction under heat treatment, as well as the tensile orientation of the fiber, occur simultaneously. Compared with the previous oxidation modification, the mechanical properties of PBO fiber show a smaller decline trend, the tensile strength retention rate is not less than 95%, and the tensile modulus of the fiber can be increased by 20-50%. 2. The PBO fibers treated with oxidation in this invention produce new hydroxyl, carboxyl, amino, and benzoquinone structures, and remove a small amount of residual moisture, phosphoric acid, and other small molecule impurities. This enhances the fiber's hydrophilicity, reactivity, and surface roughness, and improves the wettability and adhesion of PBO fibers to resins such as epoxy resin and cyanate ester. After oxidation modification, the interfacial shear strength between PBO fibers and resins is increased by 10-25%. 3. In this invention, sizing treatment combined with high-temperature oxidation treatment performs secondary modification of PBO fibers, based on the hydroxyl, carboxyl, amino, and benzoquinone structures on the surface of the PBO fibers after high-temperature oxidation treatment. Specifically, after secondary modification with the sizing agent, the interfacial shear strength between the PBO fibers and the resin is increased by 27-51%. 4. In this invention, the processing system includes a high-temperature oxidation treatment device, a sizing device, an extrusion device, a drying device, and a winding device. The high-temperature oxidation treatment device includes a gas mixing tank and a tubular heating furnace. That is, a gas mixing tank is added to the existing high-modulus PBO production device. This equipment modification cost is low. Furthermore, by controlling the composition of the mixed gas, both continuous high-temperature oxidation modification of PBO fibers and high-modulus treatment of PBO fibers can be achieved. By adjusting the component ratio of the mixed gas, the oxidation rate, and the treatment time, the oxidation degree of PBO fibers can be controlled. Compared with existing atomic oxygen oxidation and chemical reagent oxidation, the operation process is simple, easy to control, and can be carried out continuously, enabling large-scale production. Attached Figure Description

[0017] Figure 1 The flowchart involved in this invention; Figure 2 This is a schematic diagram illustrating the working principle of the present invention; Figure 3 The infrared spectra of PBO fibers before and after treatment in this invention (Detection 1); Figure 4 These are XPS full-spectrum scans of PBO fibers before and after treatment in the present invention (detection 2); In the diagram, 1 represents the PBO fiber dispensing device; 2. Five-roller traction machine I; 3. High-temperature oxidation treatment device; 30. Gas mixing tank; 300. Stirring mechanism; 31. Heater; 32. Tubular furnace; 33. Oxygen inlet pipe; 34. Air inlet pipe; 35. Oxygen feed flow meter; 36. Oxygen feed control valve; 37. Air feed flow meter; 38. Air feed control valve. 4. Five-roller traction machine II; 5. Sizing device; 50. Material trough; 51. First guide roller; 52. Coating roller; 53. Second guide roller; 6. Extrusion device; 60. Pressure roller; 7. Drying device; 8. Winding device; 9. Mixed gas delivery pipe; 10. Mixed gas flow meter. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 This embodiment uses 1000D PBO fiber filament as an example. Figure 1 As shown, a method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification is provided, comprising the following steps: S1 Continuous High-Temperature Oxidation Treatment Using a five-roller traction machine I2, PBO fiber filaments (denoted as PBO-1) are continuously fed into a high-temperature oxidation treatment device 3. A mixed gas with an oxygen content of 36% and a temperature of 580°C is introduced into the high-temperature oxidation treatment device 3 at a gas flow rate of 150 L / min (where oxygen accounts for 20% by volume and air accounts for 80% by volume, forming a mixed gas atmosphere, i.e., the oxidation content in the mixed gas is 36%). The temperature inside the high-temperature oxidation treatment device 3 is controlled at 580°C, and the PBO fiber filaments are oxidized (high-temperature oxidation stretching, stretching rate of 75 m / min) for 40 s using a stretching speed ratio of 1.2 to obtain oxidized PBO fiber (denoted as PBO-2). Then, the treated PBO fibers are continuously fed into the sizing device 5 using a five-roller traction machine II4. S2: Sizing treatment The PBO fibers treated in step S1 are fed into the sizing device 5 by the five-roller traction machine II4 for one-time continuous rolling coating and sizing; then, the excess sizing material is squeezed out by the pressure roller 60 to obtain modified PBO fibers with a sizing agent content of 2%. The sizing agent includes APTES aminosilane coupling agent and VTMO vinylsilane coupling agent, with APTES aminosilane coupling agent accounting for 4.0% by mass and VTMO vinylsilane coupling agent accounting for 1.0% by mass. The solvent is a mixture of ethyl acetate (90% by volume) and water (10% by volume). During sizing, the sizing agent content in the PBO fiber is kept at 2.0%, the operating tension between the guide roller and the coating roller 52 is kept at 90 cN, the sizing agent temperature is kept at 40℃, the stretching rate of the oxidized PBO fiber is kept at 75 m / min, and the pressure of the pressure roller 60 is kept at 2.0 MPa by adjusting the running tension between the guide roller and the coating roller 52, the sizing agent temperature is kept at 40℃, the stretching rate of the oxidized PBO fiber during sizing is kept at 75 m / min, and the pressure of the pressure roller 60 is kept at 2.0 MPa. S3: Post-processing The modified PBO fiber treated in step S2 is fed into the drying device 7 at a traction rate of 75 m / min. It is then subjected to high-temperature curing and rapid drying at 120°C for 2.7 min to form a nano-scale SiO2 coating. At the same time, the residual solvent in the PBO fiber is fully evaporated, thus obtaining the modified PBO fiber product. Finally, the modified PBO fiber product is wound into a cylinder using a winding device 8 at a winding speed of 75 m / min. Then, the wound modified PBO fiber final product is placed in an oven again and dried at 150°C for 2 hours to completely remove the solvent, yielding the modified PBO fiber final product (denoted as PBO-3).

[0020] Example 2 This embodiment provides a system for improving the interfacial properties of PBO fibers through continuous high-temperature oxidation modification, such as... Figure 2 As shown, it includes a high-temperature oxidation treatment device 3, a sizing device 5, an extrusion device 6, a drying device 7, and a winding device 8, wherein, High-temperature oxidation treatment device 3: includes a gas mixing tank 30, a heater 31 and a tubular furnace 32. The bottom of the gas mixing tank 30 is connected to an oxygen inlet pipe 33 and an air inlet pipe 34. The oxygen inlet pipe 33 is equipped with an oxygen feed flow meter 35 and an oxygen feed control valve 36. The air inlet pipe 34 is equipped with an air feed flow meter 37 and an air feed control valve 38. The gas mixing tank 30 is equipped with a stirring mechanism 300. The outlet of the gas mixing tank 30 is connected to the tubular heater 32 through the mixed gas conveying pipe 9, and the heater 31 is installed on the mixed gas conveying pipe 9; the mixed gas conveying pipe 9 is equipped with a mixed gas flow meter 10; The tubular heating furnace 32 is the original high-modulus PBO production device (the tubular heating furnace 32 is only connected to the nitrogen inlet pipe), and cannot be connected to oxygen or have its oxygen content controlled. By adding a gas mixing tank 30, and connecting a nitrogen inlet pipe to the bottom of the gas mixing tank 30, and installing a nitrogen feed flow meter and a nitrogen feed control valve on the nitrogen inlet pipe, the high-temperature oxidation treatment device 3 can be used for both continuous high-temperature oxidation modification of PBO fibers and high-modulus treatment of PBO fibers through the control of the mixed gas composition and ratio. The process involves the following steps: After the mixed gas in the gas mixing tank 30 is stirred and mixed evenly, it is output through the mixed gas delivery pipe 9 at the top, preheated to 500-650℃ by the heater 31 (to prevent the temperature of the mixed gas from falling below the temperature inside the tubular heater 32, which would cause temperature fluctuations in the tubular heater 32 and affect the oxidation effect of PBO fibers), and then metered by the mixed gas flow meter 10 before being input into the tubular heater 32 (500-650℃) for continuous high-temperature oxidation treatment of PBO fibers. With the gas mixing tank 30 connected externally to the tubular heater 32, not only can various gases such as oxygen, air, and nitrogen be introduced, but the oxygen content in the mixed gas can also be precisely controlled. For example, in the preparation of low-oxygen-content oxidized PBO fibers, the present invention uses air instead of nitrogen to adjust the oxygen content in the mixed gas, which can greatly reduce the production cost during oxidation treatment; and when the oxygen inlet pipe 33 and the air inlet pipe 34 are closed and nitrogen is introduced, the PBO fiber can be re-treated at high temperature to continue producing high-modulus PBO fibers. It is a dual-purpose device that greatly improves the utilization rate of the equipment.

[0021] A five-roller traction machine I2 is provided on one side of the tubular heating furnace 32, and a PBO fiber feeding device 1 is provided in front of the station of the five-roller traction machine I2; a five-roller traction machine II4 is provided on the other side of the tubular heating furnace 32. Sizing device 5: Located at the rear of the station of the five-roller traction machine II4, the sizing device 5 includes a material trough 50 and guide rollers and coating rollers 52 located in the material trough 50; the guide rollers include a first guide roller 51 and a second guide roller 53, the coating roller 52 is located between the first guide roller 51 and the second guide roller 53, and the lower edge of the coating roller 52 is immersed in the sizing liquid in the material trough 50 to a depth of 5 to 20 cm; Extrusion device 6: Located behind the work station of the sizing device 5, the extrusion device 6 includes a set of pressure rollers 60; Drying device 7: Located behind the station of extrusion device 6; Rewinding device 8: Located behind the workstation of drying device 7; A continuous pathway for the preparation of modified PBO fiber products is formed between the PBO fiber feeding device 1, the five-roller traction machine I 2, the high-temperature oxidation treatment device 3, the five-roller traction machine II 4, the sizing device 5, the extrusion device 6, the drying device 7, and the winding device 8.

[0022] Test 1 Based on Example 1, infrared spectroscopy was performed on PBO-1 (PBO fiber precursor), PBO-2 (oxidized PBO fiber: only subjected to continuous high-temperature oxidation treatment), and PBO-3 (modified PBO fiber final product: secondary modification involving continuous high-temperature oxidation treatment and sizing treatment), specifically including: Take 0.1g of PBO-1, 0.1g of PBO-2, and 0.1g of PBO-3, insert them into the test cavity, compact them, and then use a Nicolet iS5 infrared spectrometer at 400–4000 cm⁻¹. -1 The scan within the range yielded the results shown in Table 1 below. Figure 3 As shown.

[0023] Table 1 shows the intrinsic characteristic peaks of PBO fibers and the characteristic absorption peaks of modified PBO fibers.

[0024] From Table 1 and Figure 3 It can be seen that: compared to unmodified PBO fiber - virgin PBO fiber (PBO-1), oxidized PBO fiber (PBO-2) and secondary modified PBO fiber (PBO-3) have a lower viscosity at 3381cm. -1 New absorption peaks for amino and hydroxyl groups were added at 1668 cm⁻¹. -1 The discovery of a new C=O absorption peak in the amide bond of the small molecule chain after PBO molecular chain breakage indicates the presence of oxidized modification groups and structures in both PBO-2 and PBO-3. The Si-OC and Si-O-Si absorption peaks in the secondary modified PBO fibers overlap with the intrinsic characteristic absorption peaks of the PBO fibers, making them indistinguishable. Therefore, further XPS scanning energy dispersive spectroscopy is needed to determine the changes in oxygen and silicon content before and after modification, in order to ascertain the differences between PBO-2 and PBO-3.

[0025] Test 2 Based on Example 1, XPS scanning energy dispersive spectroscopy tests were performed on the PBO-1 (PBO fiber precursor), PBO-2 (oxidized PBO fiber: only subjected to continuous high-temperature oxidation treatment), and PBO-3 (modified PBO fiber final product: secondary modification involving continuous high-temperature oxidation treatment and sizing treatment), specifically including: Take 0.01g of PBO-1, 0.01g of PBO-2, and 0.01g of PBO-3, insert them into the test cavity, compact them, and then scan them using a Thermo Scientific ESCALAB Xi+XPS scanner in the range of 200–1200 eV. The results are shown in Table 2 below. Figure 4 As shown.

[0026] Table 2 shows the surface elemental composition and content of PBO fibers before and after treatment.

[0027] From Table 2 and Figure 4It can be seen that the oxygen content of the PBO fiber after oxidation modification (PBO-2) is higher than that of the original PBO fiber; the nitrogen, oxygen and silicon content of the secondary modified PBO fiber (PBO-3) is increased compared with the oxidized PBO fiber, and the O / C and N / C ratios are also improved.

[0028] Comparative Examples 1-18 Based on Example 1, the continuous high-temperature oxidation process of PBO fiber precursors with specifications of 1000D and 250D was optimized by controlling the following factors: the composition and ratio of mixed gas and its flow rate, oxidation temperature, stretching rate of PBO fiber during oxidation, and oxidation treatment time, as shown in Table 3.

[0029] Table 3 shows the oxidation treatment parameters and results of PBO fibers.

[0030] Table 5 shows that the suitable oxidation treatment conditions for 1000D PBO fiber precursor are: when the oxygen content is 52% (i.e., air accounts for 60% and oxygen accounts for 40%), the flow rate is 200 m / min, the stretching rate is 75 m / min, and the oxidation temperature is 580℃, the modified PBO fiber has a tensile modulus of 251 GPa, a strength retention rate of 96.6%, and an interlaminar shear strength of 37.5 MPa, with the interlaminar shear strength increased by 25%. The optimal oxidation conditions for 250D PBO fiber precursor are as follows: when the oxygen content is 36% (i.e., 80% air and 20% oxygen), the flow rate is 120 m / min, the stretching rate is 100 m / min, and the oxidation temperature is 520℃, the modified PBO fiber has a tensile modulus of 250 GPa, a strength retention rate of 96.9%, and an interlaminar shear strength of 37.0 MPa, representing a 23% increase in interlaminar shear strength. Furthermore, it was verified that the process conditions suitable for oxidation treatment of PBO fiber filaments of different specifications are slightly different. When the treatment conditions of PBO fiber filaments are not within the controllable range, the fiber strength retention rate is reduced (far below 95%), or the interlaminar shear strength of the treated fiber is lower than that of the PBO fiber filament, or the improvement is not significant (the improvement rate is less than 3%, and the average interlaminar shear strength of PBO fiber filaments is 30.0 MPa).

[0031] Comparative Examples 19-36 Different specifications of PBO fiber precursors require different sizing processes. Table 4 below compares the sizing processes for 1000D and 250D oxidized modified PBO fibers. Since the sizing device and the high-temperature oxidation treatment device are continuous, meaning their rates are consistent, the stretching rate is 75 m / min for 1000D sizing and 100 m / min for 250D sizing. In the sizing process of oxidized modified PBO fibers, the process conditions for sizing were optimized by controlling the following: the depth of the coating roller's lower edge immersed in the sizing solution in the trough, the running tension between the guide roller and the coating roller, the concentration of the sizing agent, the temperature of the sizing agent, the pressure of the pressure roller, the curing temperature, and the sizing content in the oxidized PBO fibers.

[0032] Table 4. Sizing parameters and results of PBO fibers after oxidation.

[0033] Table 4 shows that the suitable sizing conditions for 1000D oxidized modified PBO fiber are: the depth of the coating roller immersed in the sizing solution in the trough is 14cm, the running tension between the guide roller and the coating roller is 130cN, the sizing agent concentration is 5.0% (of which the concentration of aminosiloxane is 4.0% and the concentration of vinylsiloxane is 1.0%), the sizing agent temperature is 40℃, and the pressure of the pressure roller is 2MPa. After curing at 120℃, the sizing agent content in the modified fiber is 3.0%, and the interlaminar shear strength of the fiber is increased to 45.3MPa, which is 51% higher than that of the original PBO fiber (30.0MPa). The suitable sizing conditions for 250D oxidized modified PBO fiber are as follows: the depth of the sizing solution immersed in the sizing tank at the lower edge of the coating roller is 9cm, the running tension between the guide roller and the coating roller is 90cN, the sizing agent concentration is 3.0% (of which the concentration of aminosiloxane is 2.5% and the concentration of vinylsiloxane is 0.5%), the sizing agent temperature is 50℃, and the pressure of the pressure roller is 1.0MPa. After curing at 120℃, the sizing agent content in the modified fiber is 1.8%, and the interlaminar shear strength of the fiber is increased to 45.1MPa. Furthermore, it was verified that the sizing process conditions adapted to different specifications of oxidized modified PBO fibers are slightly different. When the sizing conditions are not within the controllable range, the secondary modification does not significantly improve the interlaminar shear strength of the fibers.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification, characterized in that, Includes the following steps: S1: Continuous high-temperature oxidation treatment Using a five-roller traction machine I (2), PBO fiber filaments are continuously fed into a high-temperature oxidation treatment device (3). A mixed gas with an oxygen content of 25-60% and a temperature of 500-650°C is introduced into the high-temperature oxidation treatment device (3). The oxidation treatment temperature is stabilized at 500-650°C by a tubular heating furnace (32). The oxidation treatment lasts for 20-150 seconds to obtain oxidized PBO fiber. Then, using a five-roller traction machine II (4), the treated PBO fiber is continuously fed into a sizing device (5). S2: Sizing treatment The PBO fibers treated in step S1 are fed into the sizing device (5) by the five-roller traction machine II (4) for coating and sizing; then, the excess sizing material is squeezed out by the pressure roller (60) to obtain modified PBO fibers with a sizing agent content of 0.5 to 5.0%. S3: Post-processing The modified PBO fiber after step S2 is sent into the drying device (7) for high-temperature curing and rapid drying to obtain the modified PBO fiber product.

2. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 1, characterized in that, In step S1, the flow rate of the mixed gas is 100-250 L / min; The stretching speed ratio between the five-roller traction machine I (2) and the five-roller traction machine II (4) is 1.0 to 1.

5.

3. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 1, characterized in that, In step S2, the sizing agent is a mixture comprising 0.5-8.0% aminosiloxane and 0.5-2.0% ethylenepropylsiloxane by mass, and the volume percentage of water in the sizing agent is not higher than 20%.

4. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 3, characterized in that, In step S2, the aminosiloxane includes one or a mixture of any two or more of γ-aminopropyltriethoxysilane, γ-aminopropylmethyldimethoxysilane, N-methyl-aminopropyltrimethoxysilane and bis(γ-triethoxypropylamine); Vinylsiloxanes include vinyltrimethoxysilane, vinyltriethoxysilane, or mixtures thereof.

5. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 3, characterized in that, In step S2, the running tension between the guide roller and the coating roller (52) inside the sizing device (5) is 50-200 cN; The lower edge of the coating roller (52) is immersed in the slurry in the material tank (50) to a depth of 5-20 cm; The temperature of the sizing agent is 20–60℃; The pressure applied by the pressure roller (60) is 0.5 to 5.0 MPa.

6. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 5, characterized in that, In step S3, the high-temperature curing temperature is 80-150℃, and the curing time is 2.5-10 min.

7. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to any one of claims 1-6, characterized in that, The modified PBO fiber product is wound into a cylinder using a winding device (8); then, it is placed in an oven and dried at 80-160℃ for 1-5 hours to obtain the final modified PBO fiber product.

8. The method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 7, characterized in that, The stretching rate of the PBO fiber precursor, the stretching rate of the oxidized PBO fiber during sizing, the stretching rate of the modified oxidized PBO fiber during curing, and the winding rate of the PBO fiber product are all the same, ranging from 25 to 100 m / min.

9. A system for improving the interfacial properties of PBO fibers through continuous high-temperature oxidation modification, characterized in that, The system used in the method for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification as described in any one of claims 1-8, the system comprising a high-temperature oxidation treatment device (3), a sizing device (5), an extrusion device (6), a drying device (7), and a winding device (8), wherein, The high-temperature oxidation treatment device (3) includes a gas mixing tank (30), a heater (31) and a tubular furnace (32). The bottom of the gas mixing tank (30) is connected to an oxygen inlet pipe (33) and an air inlet pipe (34). An oxygen feed flow meter (35) and an oxygen feed control valve (36) are installed on the oxygen inlet pipe (33), and an air feed flow meter (37) and an air feed control valve (38) are installed on the air inlet pipe (34). A stirring mechanism (300) is installed inside the gas mixing tank (30). The outlet of the gas mixing tank (30) is connected to the tubular heater (32) through the mixed gas conveying pipe (9), and the heater (31) is installed on the mixed gas conveying pipe (9); a mixed gas flow meter (10) is installed on the mixed gas conveying pipe (9). A five-roller traction machine I (2) is provided on one side of the tubular heating furnace (32), and a PBO fiber feeding device (1) is provided in front of the station of the five-roller traction machine I (2); a five-roller traction machine II (4) is provided on the other side of the tubular heating furnace (32). The sizing device (5) is located on the back side of the station of the five-roller traction machine II (4). The sizing device (5) includes a material trough (50) and a guide roller and a coating roller (52) located in the material trough (50). The extrusion device (6) is located behind the work station of the sizing device (5), and the extrusion device (6) includes a set of pressure rollers (60). The drying device (7) is located behind the station of the extrusion device (6); The winding device (8) is located behind the workstation of the drying device (7); A continuous pathway for the preparation of modified PBO fiber products is formed between the PBO fiber feeding device (1), the five-roller traction machine I (2), the high-temperature oxidation treatment device (3), the five-roller traction machine II (4), the sizing device (5), the extrusion device (6), the drying device (7), and the winding device (8).

10. The system for improving the interfacial properties of PBO fibers by continuous high-temperature oxidation modification according to claim 9, characterized in that, The guide rollers include a first guide roller (51) and a second guide roller (53), and the coating roller (52) is located between the first guide roller (51) and the second guide roller (53); the lower edge of the coating roller (52) is immersed in the material tank (50) to a depth of 5-20cm for applying the slurry.

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