A Method and System for Surface Treatment of PBO Fibers

Abstract

The present invention discloses a method and system for surface treatment of PBO fibers, which relates to the technical field of preparation of resin matrix composites. Dilute phosphoric acid solution generated after cleaning PBO fibers during the production of PBO fibers is used. After concentration, phosphoric acid solution with a concentration of 30-80% is used to pretreat PBO fibers, and then the PBO fibers are further soaked in an epichlorohydrin solution with a concentration of 1-5 wt%, thus obtaining modified PBO fibers. With a matching production system, on the one hand, it can consume part of the by-product - phosphoric acid produced by the company, and at the same time, it can be used for the modification of PBO fibers, increase the interlaminar shear strength of PBO fibers, and expand the application range of PBO fibers.

Description

Technical Field

[0001] The present invention relates to the technical field of resin matrix composite material preparation, and particularly relates to a method and a system for surface treatment of PBO fibers. Background Art

[0002] Poly(p-phenylene benzobisoxazole) (PBO) fiber is a high molecular polymer fiber with good mechanical properties, chemical corrosion resistance and flame retardancy. It can be used alone for weaving clothing fabrics or as a fiber / fabric reinforced composite material. It is used in advanced material fields such as aviation, aerospace and national defense. Because there are insufficient active groups in the molecular structure of PBO fiber, and affected by the liquid crystal spinning technology, the molecular orientation degree is relatively high, the structural regularity is high, and the fiber surface is smooth. This results in excellent properties of PBO fiber, but also makes it difficult for PBO fiber to be compounded with other resins, and the performance advantages of PBO fiber cannot be fully exerted, restricting the further use of PBO fiber.

[0003] In the prior art, such as the literature "Influence of Hydrolysis / Grafting Treatment on the Mechanical Properties of F-12 Fiber / Epoxy Composites" published in the journal "Engineering Plastics Application" on January 15, 2000, discloses that "a dilute potassium hydroxide solution is used to perform surface treatment on F-12 fiber, introducing -COOK ion pairs onto the surface of F-12 fiber, and then initiating the grafting of different graft monomers, and analyzing the influence of different graft monomers and grafting time on the tensile strength of F-12 fiber and the interlaminar shear strength of its epoxy composite material. The research shows that introducing -COOK ion pairs onto the surface of F-12 fiber under mild conditions and initiating the grafting of epichlorohydrin can improve the interlaminar shear strength of F-12 fiber / epoxy composite material." Teacher Huang Yudong of Harbin Engineering University soaked PBO fiber in a mixed solution of epoxy resin and epichlorohydrin and then irradiated it with γ-rays to initiate a reaction, effectively grafting and polymerizing epoxy resin on the fiber, and the interlaminar shear strength (IFSS) increased by 114%.

[0004] It can be seen that through the above-mentioned fiber surface treatment method, the surface properties of the fiber can be improved, and thus the application range of the fiber can be expanded. However, for the technology of modifying the surface properties of PBO fiber by the aforementioned radiation grafting, although it can improve the binding ability between the fiber and the resin and enhance the interlaminar shear strength, the ray radiation will not only damage the fiber properties but also may affect the health of the test production personnel.

[0005] For another example, the patent application with the publication number "CN102277726A" and the name "A Method for Anti-ultraviolet Aging of Poly(p-phenylene benzobisoxazole) Fibers", which was published on December 14, 2011, discloses that after soaking PBO fibers with a TiO2-ZnO composite hydrosol treated with a coupling agent, a uniform anti-ultraviolet aging gel coating with a thickness of 0.02 - 0.05 mm is coated on the surface of the PBO fibers, effectively improving the anti-ultraviolet performance of the PBO fibers. By using this surface coating modification technology, the fibers can be protected from damage, but the effect on improving the interlaminar shear strength between the fibers and the resin is not ideal.

[0006] In addition, during the production process of PBO fibers in our company, a large amount of surplus phosphoric acid is generated. Approximately more than 400 tons of phosphoric acid need to be further processed every year. Currently, the phosphoric acid liquid of our company is mainly centrally processed by related companies, which not only wastes resources but also increases the production cost of the company, making the production cost of such materials remain high, thus restricting the application of this material. Summary of the Invention

[0007] The purpose of the present invention is to provide a new method for surface treatment of PBO fibers. On the one hand, it can consume part of the by-product - phosphoric acid produced by our company, and at the same time, it can be used for the modification of PBO fibers, increasing the interlaminar shear strength of PBO fibers and expanding the application range of PBO fibers.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for surface treatment of PBO fibers uses the dilute phosphoric acid solution generated after washing PBO fibers during the production process of PBO fibers. After concentration, a phosphoric acid solution with a concentration of 30 - 80% is used to pretreat the PBO fibers, and then the PBO fibers are further soaked with an epichlorohydrin solution with a concentration of 1 - 5 wt%, thus obtaining modified PBO fibers.

[0010] More specifically, the method for surface treatment of PBO fibers includes the following steps:

[0011] A. Pretreatment of PBO fibers

[0012] Take the concentrated phosphoric acid solution, and immerse the PBO fibers in the phosphoric acid solution at a ratio of PBO fiber mass: phosphoric acid solution volume of 1:5 - 1:10. Stir at 70 - 100 °C for 5 - 60 min, and then wash the PBO fibers with clear water to obtain PBO fiber A.

[0013] B. Surface treatment of PBO fibers

[0014] Prepare an epichlorohydrin solution with a concentration of 1-5 wt%, stir it evenly, add an alkaline reagent, adjust the pH value of the solution to 9-11, and then immerse PBO fiber A in the epichlorohydrin solution according to the ratio of the mass of PBO fiber A to the volume of the solution of 1:5-1:10. React at 60-80 °C for 2-4 h, then wash the fiber with water until the washing liquid is neutral, and dry it to obtain the modified PBO fiber.

[0015] Further, in step B, the alkaline reagent is sodium hydroxide or potassium hydroxide.

[0016] Further, in step A, use a 45%-75% phosphoric acid solution, stir for 30-50 min, and wash the fiber;

[0017] In step B, use a 2-4 wt% epichlorohydrin solution to further treat the fiber pretreated in step A, add an alkaline reagent to adjust the pH value of the solution to 10, and then immerse PBO fiber A in the epichlorohydrin solution according to the ratio of the mass of PBO fiber A to the volume of the solution of 1:10. React at 60-80 °C for 2-4 h, then wash the fiber with water until the washing liquid is neutral. The interlaminar shear strength of the PBO composite material formed by the obtained modified PBO fiber, epoxy resin, cyanate ester, and polyurethane is not less than 30 MPa.

[0018] In the present invention, a PBO fiber surface treatment system is also proposed, which can match the foregoing treatment process, ensure the continuous and stable operation of the production line, and minimize the floor area of the equipment as much as possible. It includes a pickling tank, a cleaning device I, a treatment liquid washing tank, and a cleaning device II. The pickling tank is connected to a concentrated acid collection tank, and the concentrated acid collection tank is connected to a waste acid collection tank through an acid liquid concentration subsystem. The waste acid collection tank is used to collect the waste dilute acid solution generated during the production of PBO fiber;

[0019] The acid liquid concentration subsystem is used to concentrate the waste dilute acid solution generated during the production of PBO fiber collected, and then send the concentrated concentrated acid solution to the concentrated acid collection tank.

[0020] The cleaning device I and the cleaning device II are connected to a clear water pipeline. The treatment liquid washing tank is connected to an epichlorohydrin treatment liquid pipeline and an alkali liquid supplement pipeline. A pH sensor is also provided in the treatment liquid washing tank.

[0021] Further, the acid liquid concentration subsystem includes a primary heat exchanger and a secondary vacuum distillation device connected in sequence. The concentrated liquid outlet of the secondary vacuum distillation device is connected to the concentrated acid collection tank.

[0022] Further, a jacket for passing a heat transfer medium is provided outside the secondary vacuum distillation device, or a coil for passing a heat transfer medium is provided inside the secondary vacuum distillation device, or a coil for passing a heat transfer medium is provided on the outer wall of the secondary vacuum distillation device.

[0023] Further, the medium outlet of the primary heat exchanger is connected to the medium inlet of the secondary vacuum distillation device after passing through a filter.

[0024] Further, the gas-phase outlet at the top of the secondary vacuum distillation device is connected to a condenser and then to a condensate collector.

[0025] Further, a stirring mechanism is provided on the pickling tank.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] First, in the present invention, by using this method to treat PBO fibers, the treated PBO fibers maintain the excellent tensile strength performance of the original PBO fibers, and significantly improve the physical properties such as interlaminar shear strength, tensile strength, and flexural strength of the fibers, making them more suitable for preparing various forms of composite materials and broadening the uses of PBO fibers.

[0028] Second, in the present invention, the surplus phosphoric acid generated during the production of PBO fibers by the company is used to modify PBO fibers, which can solve the problems of a large amount of phosphoric acid storage and post-treatment in the company, reduce the phosphoric acid treatment cost, reduce the environmental protection pressure, and obtain new products and generate new revenues. Furthermore, the production cost of PBO fibers can be reduced. Calculated based on the scale of 100 tons / year of PBO fiber production by the company, about 400 or more tons of phosphoric acid will be generated. Calculated at 5000 yuan / ton for treating phosphoric acid, it will cost about more than 2 million yuan per year to treat waste phosphoric acid. Therefore, the more this part of phosphoric acid is consumed, the more the production cost of PBO fibers can be reduced.

[0029] Third, in the present invention, by using this method to treat PBO fibers, technologies such as radiation are not used, and equipment related to radiation is not involved. The equipment cost is relatively low, and the production is safer.

[0030] 4. In the present invention, a system matching the surface treatment method of PBO fiber is also proposed, which recycles the waste phosphoric acid liquid in the production of PBO fiber into a waste acid liquid collection tank, and after the waste phosphoric acid is concentrated by the acid liquid concentration subsystem, it is used in the modification treatment of PBO fiber, thereby realizing the recycling of waste phosphoric acid liquid, solving the treatment problem of waste phosphoric acid liquid, reducing the production cost of PBO fiber, and obtaining another modified PBO fiber, thereby broadening the application field of PBO fiber. At the same time, this system can be connected with the original PBO fiber production line to form a continuous modified PBO fiber production system, shortening the production time, reducing the occupied area of the equipment, and facilitating the quality of the product.

[0031] 5. The present invention further proposes an implementation structure suitable for industrial production and with relatively low production cost. The acid liquid concentration subsystem includes a primary heat exchanger and a secondary vacuum distillation device connected in sequence. The concentrated liquid outlet of the secondary vacuum distillation device is connected to a concentrated acid collection tank, that is, the dilute phosphoric acid solution is heated by the primary heat exchanger and then further vacuum distilled by the secondary vacuum distillation device to evaporate the water in the dilute phosphoric acid solution to obtain concentrated phosphoric acid. In order to further achieve efficient use of energy, the medium outlet of the primary heat exchanger is connected to the medium inlet of the secondary vacuum distillation device after the filter. The heat-conducting medium after use in the primary heat exchanger can be continuously used in the secondary vacuum distillation device to achieve multiple utilization of the heat-conducting medium, high heat exchange efficiency, and reduce the loss of heat energy. At the same time, in this scheme, three implementable structures are proposed, and equipment with suitable structures can be selected according to factors such as different use environments.

[0032] 6. In the present invention, the top gas phase outlet of the secondary vacuum distillation device is connected to a condenser and then connected to a condensed water collector for collecting separated water to reduce emissions. At the same time, the recovered water carries heat and can be reused, reducing energy waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural schematic diagram of the PBO fiber surface treatment system in the present invention.

[0034] Figure 2 It is a structural schematic diagram of another implementation method of a PBO fiber surface treatment system.

[0035] Figure 3 It is a structural schematic diagram of an implementation method of an acid concentration subsystem of a PBO fiber surface treatment system.

[0036] Figure 4 It is a structural schematic diagram of another embodiment of the acid concentration subsystem.

[0037] Among them, 1. Pickling tank; 2. Cleaning device I; 3. Processing liquid washing tank; 4. Cleaning device II; 5. Concentrated acid collection tank; 6. Acid liquid concentration subsystem; 7. Spent acid collection tank; 8. Fresh water pipeline; 9. Epichlorohydrin treatment liquid pipeline; 10. Alkali liquid supplement pipeline; 11. pH sensor; 12. Primary heat exchanger; 13. Secondary vacuum distillation device; 14. Jacket; 15. Coiled pipe; 16. Filter; 17. Condenser; 18. Condensate collector; 19. Stirring mechanism; 20. Reactor; 21. Spinning device; 22. Washing device; 23. Drying device; 12.1. Medium outlet I; 13.1. Concentrate outlet; 13.2. Medium inlet I; 13.3. Gas phase outlet. Detailed implementation mode

[0038] The following further illustrates a PBO fiber surface treatment method provided by the present invention through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Those skilled in the art make some non-essential improvements and adjustments to the present invention according to the above invention content and carry out specific implementations, which still fall within the protection scope of the present invention.

[0039] Example 1

[0040] Taking a PBO fiber surface treatment method of our company as an example, this example further illustrates the present solution.

[0041] This PBO fiber surface treatment method adopts the PBO fiber surface treatment as shown in Figure 1 , specifically including a pickling tank 1, a cleaning device I 2, a processing liquid washing tank 3 and a cleaning device II 4. The pickling tank 1 is connected to a concentrated acid collection tank 5, and the concentrated acid collection tank 5 is connected to a spent acid collection tank 7 through an acid liquid concentration subsystem 6. The spent acid collection tank 7 is used to collect the waste dilute acid solution generated during the production of PBO fibers.

[0042] The PBO fiber production system is as follows: In reactor 20, in a polyphosphoric acid solution system, terephthalic acid reacts with 4,6-diaminoresorcinol hydrochloride, experiencing the transformation from a homogeneous polymer to a liquid crystal polymer. Then, through spinning device 21, PBO fiber can be produced using liquid crystal spinning technology. The spun PBO fiber is washed by washing device 22 to remove excess phosphoric acid on the fiber. A large amount of dilute phosphoric acid waste liquid generated during this process is transported through a pipeline to waste acid collection tank 7 for temporary storage. The phosphoric acid concentration in the dilute phosphoric acid waste liquid in waste acid collection tank 7 is about 5%, which is relatively low and cannot be directly recycled. The traditional treatment method is generally to send it to a specialized treatment plant for centralized treatment. In this solution, the collected dilute phosphoric acid waste liquid is concentrated by acid liquid concentration subsystem 6 and then transported through a pipeline to concentrated acid collection tank 5 for temporary storage. The phosphoric acid concentration in the treated phosphoric acid solution can reach 30 - 80%, which can meet the concentration requirements of phosphoric acid for the modification treatment of PBO fiber.

[0043] The cleaning device I2 and the cleaning device II4 are connected to a fresh water pipeline 8. The treatment liquid washing tank 3 is connected to an epichlorohydrin treatment liquid pipeline 9 and an alkali liquid supplementary pipeline 10. The consumed epichlorohydrin is supplemented through the epichlorohydrin treatment liquid pipeline 9. A pH sensor 11 is also provided in the treatment liquid washing tank 3. The pH sensor 11 is used to monitor the pH value of the solution in the treatment liquid washing tank 3 and supplement the alkali in a timely manner to ensure that the pH value in the treatment liquid washing tank 3 is stable at 9 - 11.

[0044] Specifically, it includes the following steps:

[0045] A. Pretreatment of PBO fiber

[0046] Take the dilute phosphoric acid solution generated after washing PBO fiber during the production of PBO fiber, and the phosphoric acid solution with a concentration of 30 - 80% after concentration treatment. Immerse the PBO fiber in the phosphoric acid solution at a ratio of PBO fiber mass: phosphoric acid solution volume of 1:5 - 1:10, stir for 5 - 60 min at 70 - 100 °C, and then wash the PBO fiber with clean water until the washing mixed solution is neutral to obtain PBO fiber A.

[0047] B. Surface treatment of PBO fiber

[0048] Prepare an epichlorohydrin solution with a concentration of 1 - 5 wt%, stir it evenly, add sodium hydroxide, adjust the pH value of the solution to 9 - 11, and then immerse PBO fiber A in the epichlorohydrin solution at a ratio of PBO fiber A mass: solution volume of 1:5 - 1:10, react at 60 - 80 °C for 2 - 4 h, then wash the fiber with water until the washing liquid is neutral, and dry it to obtain the modified PBO fiber.

[0049] In step B of the present invention, a strong base is used to adjust the pH value of the mixed solution, preferably sodium hydroxide or potassium hydroxide. In this embodiment, considering not to introduce new ions, sodium hydroxide is used to adjust the pH value of the mixed solution in this step.

[0050] Using the above preparation method, adjust each condition according to the control parameters of Group 1 to 15 in Table 1 below to obtain different modified PBO fibers.

[0051] Comparative Example 1

[0052] In this comparative example, the PBO fibers are not pretreated with concentrated phosphoric acid, and directly modified with an alkaline solution of epichlorohydrin concentrated solution. The relevant process parameters and control conditions refer to Table 1 to obtain the modified PBO fibers.

[0053] Comparative Example 2

[0054] In this comparative example, the PBO fibers are only pretreated with concentrated phosphoric acid, and not treated with an alkaline solution of epichlorohydrin concentrated solution. The relevant process parameters and control conditions refer to Table 1 to obtain the modified PBO fibers.

[0055] Comparative Example 3

[0056] In this comparative example, the PBO fibers are pretreated with a relatively high-concentration phosphoric acid solution with a concentration of 85%, the treatment temperature is controlled at 100 °C, and stirred for 90 min, and then washed to neutral; then a 5 wt% epichlorohydrin solution is used, and the reaction is carried out in an alkaline environment with a pH value of 12, and the reaction is carried out at 85 °C for 5 h. The remaining control conditions refer to Table 1, and then washed and dried to obtain the modified PBO fibers.

[0057] Table 1

[0058]

[0059] Then, the unmodified PBO fibers and the surface-treated modified PBO fibers of Group 1 to 15 and Comparative Examples 1 to 3 above are tested to obtain the performance parameters of each group as shown in Table 2.

[0060] In the present invention, the interlaminar shear strength of the fiber is tested according to GB / T 30969-2014.

[0061] In the present invention, the tensile strength test is carried out according to GB / T 1447-2005.

[0062] In the present invention, the flexural strength test is carried out according to GB / T 1449-2005, and the equipment used is an electronic universal testing machine.

[0063] The modified PBO fiber of the present invention can be made into composites with epoxy resin, cyanate ester, polyurethane, etc. Compared with the composites formed directly by using the original PBO fiber and the resin, the performance parameters such as the interlaminar shear strength, tensile strength, and flexural strength of the composites can be significantly improved.

[0064] In this embodiment, the tensile strength of the PBO fiber before modification, and the performance parameters such as the interlaminar shear strength, tensile strength, and flexural strength of the composite formed by using the PBO fiber before modification and epoxy resin are shown in Table 2. The mass ratio of the raw materials of the PBO fiber to the epoxy resin is 1:1.

[0065] In addition, the corresponding composites are prepared by using the modified PBO fibers and epoxy resin obtained by each group. The mass ratio of the raw materials of the modified PBO fiber to the epoxy resin in each group is also 1:1. The performance parameters of the modified PBO fibers and the modified PBO fiber composites are shown in Table 3.

[0066] Table 2: Performance parameters of PBO fiber before modification

[0067]

[0068] Table 3: Performance parameters of PBO fibers and composites after modification in each group

[0069]

[0070] It can be seen from Groups 1-15 and Comparative Examples 1-3 in Tables 1-3 that when the PBO fiber is pretreated with a phosphoric acid solution with a concentration of 30-80%, and then the pretreated PBO fiber is treated with an epichlorohydrin solution with a concentration of 1-5 wt%, the tensile strength of the obtained modified PBO fiber is significantly enhanced. Compared with the PBO fiber composite prepared by using the PBO fiber before modification, the interlaminar shear strength, tensile strength, and flexural strength of the composite are all significantly improved. The PBO fiber composite with such excellent performance parameters can be applied to a wider technical field, broadening the application range of the PBO fiber.

[0071] PBO fiber is a high-performance fiber with good acid and alkali resistance. The pretreatment liquid - phosphoric acid used in this scheme is a medium-strong acid, which causes less damage to the fiber. This is also the purpose of selecting phosphoric acid as the treatment agent, to minimize the damage to the fiber as much as possible. It can be seen from Comparative Example 3 that when using a phosphoric acid solution with too high a concentration, the tensile strength of the obtained modified PBO fiber becomes smaller, indicating that there is a certain damage to the PBO.

[0072] In the prior art, the plasma modification grafting method is often used to treat and modify PBO fibers to obtain modified PBO fibers. However, for the composite material obtained with the modified PBO fibers, the interlaminar shear strength is at most 75% higher than that of the composite material obtained with the unmodified fibers.

[0073] In this solution, the phosphoric acid concentration, epichlorohydrin concentration, and pH value during surface treatment all have a great influence on the modification of PBO fibers. Pretreating PBO fibers with phosphoric acid at a certain concentration causes the molecular chains on the surface layer of the PBO fibers to open, increasing the content of surface active groups. When the concentration is too low (below 30%), phosphoric acid cannot effectively micro-etch the PBO fibers and cannot achieve the purpose of improving the performance of PBO composites. Moreover, when the concentration is relatively low, to achieve the same modification effect on PBO fibers means that longer reaction times and higher reaction temperatures are required, which is not conducive to industrialized and batch production. When the concentration is too high (exceeding 80%), it means higher requirements for the treatment of the original collected waste dilute phosphoric acid solution and the need to introduce more expensive equipment for treatment, resulting in too high an investment. And when the phosphoric acid is too high (exceeding 80%), it will cause too much damage to the performance of PBO fibers and is not conducive to the improvement of the performance of subsequent PBO composites.

[0074] In addition, the reaction between PBO fibers and epichlorohydrin must occur under certain concentration conditions and at a certain pH (alkaline condition). When the concentration of the epichlorohydrin solution is too low, epichlorohydrin cannot effectively react; when the concentration of the epichlorohydrin solution is too high, epichlorohydrin undergoes self-crosslinking reaction, and the reagent utilization rate is too low. Similarly, when the pH is too low, epichlorohydrin cannot react, and when the pH is too high, epichlorohydrin mainly undergoes self-crosslinking and cannot achieve the purpose of modifying PBO.

[0075] As can be seen from Table 1-3, in step A, use a phosphoric acid solution of 45% - 75%, stir for 30 - 50 min, and wash the fibers;

[0076] In step B, further treat the fibers pretreated in step A with an epichlorohydrin solution of 2 - 4 wt%, add an alkaline reagent to adjust the pH value of the solution to 10, then immerse PBO fiber A into the epichlorohydrin solution at a ratio of PBO fiber A mass : solution volume of 1:10, react at 60 - 80 °C for 2 - 4 h, and then wash the fibers with water until the washing liquid is neutral to obtain the modified PBO fibers. The tensile strength of the obtained modified PBO fibers is slightly lower than that of the original PBO fibers, but the difference is not significant. It can be inferred that the modified PBO fibers do not damage the PBO fibers themselves. The interlaminar shear strength of the PBO composite materials formed by the modified PBO fibers obtained under the preferred conditions and epoxy resin, cyanate ester, and polyurethane is not less than 30 MPa.

[0077] In this embodiment, it can be seen that after the fiber is pretreated with a 60% concentration phosphoric acid solution at 80 °C for 30 minutes, and then treated with 4 wt% epichlorohydrin at a pH value of about 10 for 3 h to obtain PBO fiber, the epoxy resin composite formed by the PBO fiber has good interlaminar shear strength, tensile strength and flexural strength.

[0078] Example 2

[0079] Compared with Example 1, the difference in this embodiment is that in the system for surface treatment of PBO fiber, the acid solution concentration subsystem 6 includes a primary heat exchanger 12 and a secondary vacuum distillation device 13 connected in sequence, refer to Figure 2 , and the concentrated liquid outlet 13.1 of the secondary vacuum distillation device 13 is connected to the concentrated acid collection tank 5. This acid solution concentration subsystem 6 is suitable for industrial production and has relatively low production cost.

[0080] Example 3

[0081] This embodiment is a further optimization of Example 2. The difference is that a jacket 14 for passing a heat transfer medium is provided outside the secondary vacuum distillation device 13.

[0082] Preferably, the medium outlet of the primary heat exchanger 12 is connected to the medium inlet of the secondary vacuum distillation device 13 after passing through a filter 16. Refer to 2-3. The primary heat exchanger 12 uses steam to heat the dilute phosphoric acid collected in the waste acid collection tank 7. The used steam is discharged from the medium outlet I12.1 of the primary heat exchanger 12, and then enters the jacket 14 from the medium inlet I13.2 of the secondary vacuum distillation device 13 after being filtered by the filter 16 to heat the secondary vacuum distillation device 13, achieving the purpose of efficiently utilizing the heat energy of the heat transfer medium. Adopting this embodiment can save 20% of the energy consumption.

[0083] Preferably, the top gas phase outlet 13.3 of the secondary vacuum distillation device 13 is connected to a condenser 17 and then to a condensate collector 18, reducing the external emission of water vapor. This part of the condensate has a certain amount of heat and can be further recycled.

[0084] Preferably, a stirring mechanism 19 is provided on the pickling tank 1, which can shorten the treatment time.

[0085] Example 4

[0086] Compared with Example 3, the difference in this embodiment is that, refer to Figure 4 , a coil 15 for passing a heat transfer medium is provided on the outer wall of the secondary vacuum distillation device 13.

[0087] Of course, the coiled pipe 15 for conducting heat medium can also be arranged inside the secondary vacuum distillation device 13 according to actual requirements. Compared with the solution of designing the coiled pipe 15 on the outer wall of the secondary vacuum distillation device 13, although this can reduce heat dissipation, in this solution, it is mainly used to process dilute acid, and dilute acid has certain corrosiveness to equipment. When the coiled pipe 15 is arranged inside the secondary vacuum distillation device 13, the requirements for the materials of the equipment and the treatment of pipelines are higher.

[0088] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification or equivalent change made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for surface treatment of PBO fiber, characterized in that, It includes the following steps: A. Pretreatment of PBO fiber Using the dilute phosphoric acid solution generated after cleaning PBO fiber during the production of PBO fiber, concentrating it into a phosphoric acid solution with a concentration of 45 - 75%, and immersing the PBO fiber into the phosphoric acid solution according to the ratio of PBO fiber mass: phosphoric acid solution volume of 1:5 - 1:

10. Stir at 70 - 100 °C for 30 - 50 min, and then wash the PBO fiber with clear water to obtain PBO fiber a; B. Surface treatment of PBO fiber Prepare an epichlorohydrin solution with a concentration of 2 - 4 wt%. After stirring evenly, add an alkaline reagent to adjust the pH value of the solution to 10. Then immerse PBO fiber a into the epichlorohydrin solution according to the ratio of PBO fiber a mass: solution volume of 1:

10. React at 60 - 80 °C for 2 - 4 h, and then wash the fiber with water until the washing liquid is neutral, and dry it to obtain the modified PBO fiber. The interlaminar shear strength of the PBO composite material formed by the modified PBO fiber, epoxy resin, cyanate ester, and polyurethane is not less than 30 MPa.

2. The surface treatment method of PBO fiber according to claim 1, characterized in that: In step B, the alkaline reagent is sodium hydroxide or potassium hydroxide.

3. A system applicable to the PBO fiber surface treatment method as described in claim 1, characterized in that: It includes a pickling tank (1), a cleaning device I (2), a treatment liquid washing tank (3), and a cleaning device II (4). The pickling tank (1) is connected to a concentrated acid collection tank (5). The concentrated acid collection tank (5) is connected to a waste acid collection tank (7) through an acid liquid concentration subsystem (6). The waste acid collection tank (7) is used to collect the waste dilute acid solution generated during the production of PBO fiber; The acid liquid concentration subsystem (6) is used to concentrate the waste dilute acid solution generated during the production of PBO fiber collected, and then send the concentrated concentrated acid solution to the concentrated acid collection tank (5), The cleaning device I (2) and the cleaning device II (4) are connected to a clear water pipeline (8). The treatment liquid washing tank (3) is connected to an epichlorohydrin treatment liquid pipeline (9) and an alkali liquid supplement pipeline (10). A pH sensor (11) is also provided in the treatment liquid washing tank (3).

4. The system according to claim 3, wherein: The acid liquid concentration subsystem (6) includes a primary heat exchanger (12) and a secondary vacuum distillation device (13) connected in sequence. The concentrated liquid outlet (13.1) of the secondary vacuum distillation device (13) is connected to the concentrated acid collection tank (5).

5. The system according to claim 4, wherein: A jacket (14) for passing a heat transfer medium is provided outside the secondary vacuum distillation device (13), or a coil (15) for passing a heat transfer medium is provided inside the secondary vacuum distillation device (13), or a coil (15) for passing a heat transfer medium is provided on the outer wall of the secondary vacuum distillation device (13).

6. The system according to claim 4, wherein: The medium outlet of the primary heat exchanger (12) is connected to the medium inlet of the secondary vacuum distillation device (13) after passing through a filter (16).

7. The system according to claim 4, wherein: The top gas phase outlet (13.3) of the secondary vacuum distillation device (13) is connected to a condenser (17) and then to a condensate collector (18).

8. The system according to claim 3, wherein: A stirring mechanism (19) is provided on the pickling tank (1).

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