Ultraviolet-resistant modification method of PBO fiber

Abstract

The invention belongs to the field of high-performance materials, and provides an ultraviolet-resistant modification method of PBO (poly (p-phenylenebenzobisoxazole)) fibers, which comprises the following steps: adding chlorine-containing and hydroxyl-containing terephthalic acid in a PBO polymerization process to replace a part of original terephthalic acid, and reacting with 4, 6-diamino resorcinol hydrochloride to generate a PBO polymer containing-Cl and-OH on a main chain; polymerization is carried out in a reaction kettle and a double-screw extruder in sequence, and a polymer is further spun into fibers through the procedures of spinneret orifice ejection forming, post-spinning drafting, washing, drying and the like. A side group-OH is introduced into PBO, so that a larger conjugated system can be generated in a molecular structure, and intramolecular and intermolecular hydrogen bonds can be formed more easily; the introduction of a side group-Cl can increase the intermolecular polarity, and the C-Cl bond is easier to absorb ultraviolet light to break, so that the oxazole ring of the PBO molecular chain is protected from being damaged by ultraviolet light, and the modification is carried out in the fiber synthesis stage, so that the damage degree to the fiber is small, and the modification effect is stable.

Description

Technical Field

[0001] The present invention relates to the field of preparation of high-performance fiber materials, and particularly to a method for ultraviolet-resistant modification of PBO fibers. Background Art

[0002] PBO (poly(p-phenylene benzobisoxazole)) fiber is a high-performance fiber with polyaryl heterocycles, which has the characteristics of high strength, high modulus, high temperature resistance, and high flame retardancy, and is widely used in key military fields such as armor protection, aerospace structures, and stealth. However, it is reported that the mechanical properties of PBO fibers will decrease sharply in a humid or ultraviolet-irradiated environment, that is, the ultraviolet stability of PBO fibers is poor. Therefore, the safety of PBO downstream application products is directly related to the photostability of PBO. Existing research institutions and scientific research institutes have been constantly looking for the most suitable method to improve the ultraviolet aging resistance of PBO.

[0003] Most of the literature reports modify the ultraviolet resistance of PBO fibers by means of inorganic nanoparticle coatings, and inorganic nanoparticle absorbers such as TiO2, ZnO / POSS, SiO2, graphene oxide, and carbon nanotubes are coated on the fiber surface. This method has a short cycle and simple operation, and is a hot spot in the research on fiber anti-ultraviolet aging. The classical sol-gel method will not damage the fiber itself and can effectively delay the ultraviolet aging of PBO fibers, but it has the problem of poor interfacial adhesion; interfacial modification can make up for this defect of the sol-gel method to a certain extent, but chemical etching will damage the original fiber structure and good properties; plasma modification is very expensive, the process conditions are difficult to control, and it will promote the aging behavior, resulting in a loss of the mechanical properties of the fiber.

[0004] In addition to using the inorganic nanoparticle coating method to improve the ultraviolet aging resistance of fibers, the solvent blending method has also been studied more in recent years. Organic ultraviolet absorbers, stabilizers, and substances such as polydopamine and OB-1 are added to PBO, and there are also many studies on improving the ultraviolet aging resistance of fibers by fluorescence emission on the fiber surface. The anti-ultraviolet substances added by this method will not have an obvious impact on the performance of PBO fibers themselves, but the added ultraviolet-resistant substances cannot stably exist in the PBO polymer. As the application time of the polymer material increases, the ultraviolet-resistant substances will continue to be lost, and the anti-ultraviolet performance will also decrease sharply.

[0005] Some research has also been carried out on introducing polar groups such as hydroxyl groups during the synthesis stage of fibers by in-situ copolymerization method, and introducing substances such as 2,6-naphthalenedicarboxylic acid group or rutin during the process of fiber polymerization into macromolecular chains. Compared with the above several methods, the research on modification by in-situ copolymerization method is relatively less. In-situ copolymerization is carried out for modification during the synthesis stage of fibers. Compared with the coating method and the blending method, the effect is stable, and the damage degree to the fibers is smaller. However, the experimental period is long, the repeatability is low, and a large number of repeated experimental operations are required. Nevertheless, there is still a quite large research and development space. This method has not received extensive attention, but the achieved ultraviolet resistance effect is stronger than that of the surface coating and blending methods. Therefore, whether a more suitable in-situ copolymerization method can be developed to improve the ultraviolet resistance performance of PBO fibers has become the primary problem to be solved by the inventors. Summary of the Invention

[0006] In view of the many deficiencies existing in the prior art, the present invention provides a method for ultraviolet resistance modification of poly(p-phenylene benzobisoxazole) (PBO) fibers. During the PBO polymerization process, terephthalic acid containing chlorine (-Cl) and hydroxyl (-OH) is added to replace a part of the original terephthalic acid to react with 4,6-diaminoresorcinol dihydrochloride, generating a PBO polymer containing -Cl and -OH on the main chain. The polymerization is carried out in a reaction kettle and a twin-screw extruder successively. The polymer is further extruded through a spinneret hole to form a shape, followed by post-spinning drawing, water washing, drying and other processes to spin into fibers. Introducing the side group -OH into PBO will produce a larger conjugated system in the molecular structure and is more likely to form intramolecular and intermolecular hydrogen bonds. Introducing the side group -Cl into PBO can increase the intermolecular polarity, and at the same time, the C-Cl bond is more likely to absorb ultraviolet light and break, thereby protecting the oxazole ring of the PBO molecular chain from being damaged by ultraviolet light. The modification of PBO fibers by in-situ copolymerization method is carried out during the fiber synthesis stage, with less damage to the fibers and stable modification effect.

[0007] The main concept of the present invention is as follows: PBO fibers can be applied in many fields such as armor protection, automotive parts, rail transit, aerospace, optical fiber cables, high-temperature resistant materials, etc. From the application scenarios of downstream products, the safety of the application products is directly related to the light stability of PBO. However, PBO fibers show a sharp decrease in mechanical properties under ultraviolet light irradiation. After 5 years of use, the strength of the bulletproof vest made of PBO decreases significantly. Toyobo reported that the strength retention rate is only about 50% after 100 hours of ultraviolet light irradiation. When PBO fibers are irradiated by ultraviolet rays, not only the surface structure of the fibers is damaged, but also the molecular chain orientation degree and molecular weight decrease, and even the main chain will undergo bond-breaking ring-opening reaction, resulting in a sharp decrease in fiber strength.

[0008] In a composite material, although the fibers are placed inside the resin, due to the uncertain thickness of the resin and the certain light transmittance of the resin, the fibers cannot be completely in an environment without ultraviolet rays. In some specific application scenarios, such as ropes, the probability of the fibers being exposed externally is very high. Therefore, to promote the application of PBO fibers, the problem of improving their ultraviolet resistance must be solved first.

[0009] During the PBO polymerization process, terephthalic acid containing chlorine (-Cl) and hydroxyl (-OH) is added to replace a part of the original terephthalic acid. In this way, a PBO copolymer containing -Cl and -OH on the main chain can be formed. Introducing the side group -OH into PBO will form a p-π conjugation with the π electrons on the vinyl bond in the benzene ring, and the π electrons of the carbonyl group will form a π-π conjugation with the π electrons on the benzene ring, connecting to produce a larger conjugated system; the introduction of -OH is more likely to form intramolecular and intermolecular hydrogen bonds compared to terephthalic acid. Introducing the side group -Cl into PBO can increase the polarity of the molecule, strongly attract the electron cloud on the oxazole ring, and effectively passivate the oxazole ring; in addition, the C-Cl bond is more likely to absorb ultraviolet light and break to protect the oxazole ring of PBO. At the same time, introducing the above side groups can synergistically improve the ultraviolet resistance of PBO fibers. In addition, the interaction force between the strong polar group and the resin molecule is stronger, which can significantly improve the interfacial composite performance of the fiber.

[0010] The terephthalic acid containing chlorine (-Cl) used is 2,5-dichloroterephthalic acid (TACl), a white powder crystal with the chemical formula C8H4Cl2O4, and its structural formula is Formula A, Formula A; The terephthalic acid containing hydroxyl (-OH) is 2,5-dihydroxyterephthalic acid (DHTA), a light yellow powder with the chemical formula C8H6O6, and its structural formula is Formula B, Formula B.

[0011] In addition, the terephthalic acid containing chlorine (-Cl) can also be selected from 2-chloroterephthalic acid, tetrachloroterephthalic acid, 2,6-dichlorobenzene-1,4-dicarboxylic acid; the terephthalic acid containing hydroxyl (-OH) can also be selected from 2-hydroxyterephthalic acid, 2,3-dihydroxy-1,4-benzenedicarboxylic acid, 2,6-dihydroxyisophthalic acid.

[0012] The specific technical solution of the present invention is: A method for ultraviolet resistance modification of PBO fibers, the specific steps are as follows: First, polyphosphoric acid (PPA) is added to the reaction kettle as the solvent and catalyst of the reaction system, and then stannous chloride dihydrate (SnCl2·2H2O) is added as an antioxidant. Subsequently, the reaction monomers 4,6-diaminoresorcinol dihydrochloride (DARHB), terephthalic acid (TPA), 2,5-dichloroterephthalic acid (TACl), and 2,5-dihydroxyterephthalic acid (DHTA) are added in sequence. Finally, phosphorus pentoxide (P2O5) is added as a water absorbent. After the feeding is completed, the reaction is started under a nitrogen atmosphere with gradient temperature increase. The prepolymer with a lower molecular weight is obtained by prepolymerization in the reaction kettle. The prepolymer is further strongly sheared by a twin-screw extruder to complete the post-polymerization to obtain the spinning dope, and the modified PBO fiber can be obtained by the dry-jet wet spinning method of the spinning dope.

[0013] Among them, the total molar ratio of 4,6-diaminoresorcinol dihydrochloride to the mixed dibasic acids composed of terephthalic acid, 2,5-dichloroterephthalic acid, and 2,5-dihydroxyterephthalic acid is 1:1; in the mixed dibasic acids, TACl accounts for 1%-20% in terms of molar percentage, DHTA accounts for 1%-20%, and (TACl + DHTA) accounts for 2%-40% of the mixed dibasic acids; preferably, TACl accounts for 5%-10%, DHTA accounts for 5%-10%, and (TACl + DHTA) accounts for 10%-20% of the mixed dibasic acids.

[0014] The above-mentioned gradient temperature increase reaction is preferably as follows: After the feeding is completed, the temperature of the reaction kettle is first controlled at 65°C and stirred for 3 h. By cooling the material, the system is inhibited from dehydrochlorinating and expanding. Then, the temperature is raised to 80°C and stirred for 4 h, and then raised to 95°C and stirred for 3 h. After that, the reaction kettle is evacuated to remove the remaining small amount of HCl, and then the temperature is raised to 110°C and stirred for 3 h. Finally, the temperature is raised to 120°C and stirred for 2 h, and the prepolymer with a lower molecular weight can be obtained.

[0015] After the prepolymerization reaction is completed, the prepolymer enters the twin-screw extruder for post-polymerization. The temperatures of each stage of the twin-screw extruder also show a gradient temperature increase trend, and the temperature range is controlled at 140°C to 200°C. The specific temperature values are arranged according to the screw stages. The inventor gives the following examples: Taking a twin-screw extruder with a total of 24 zones divided into upper and lower stages as an example, the screw speeds of the upper and lower stage machines are both 10 / 10 (r / min). The temperature settings of the twelve zones of the upper stage screw are 140, 150, 160, 170, 180, 180, 180, 180, 180, 180, 180, 180°C in sequence, and the temperature settings of the twelve zones of the lower stage screw are 170, 180, 170, 175, 175, 180, 180, 190, 180, 190, 200, 200°C in sequence.

[0016] The material stays in the extruder for 90 - 120 min to complete the final polymerization.

[0017] The modified copolymerization reaction equation is as follows: ; Finally, the PBO copolymer in the spinning dope is obtained. Through experimental detection, the above copolymer is a random copolymer, and its molecular structure includes three types: Formula I, Formula II, and Formula III: Formula I; Formula II; Formula III; In Formulas I, II, and III, a, b, and c are all positive integers.

[0018] The ultraviolet aging of PBO is mainly manifested as the absorption of ultraviolet light energy by the molecular chain, resulting in the breaking of the oxazole ring and ring opening, and further bond breaking leading to molecular chain degradation. Therefore, introducing side groups into PBO aims to reduce the occurrence of bond breaking and ring opening reactions. When -OH is introduced into the molecular chain, it will form a p-π conjugate with the π electrons on the vinyl bond in the benzene ring, and the π electrons of the adjacent carbonyl group and the π electrons on the benzene ring will form a π-π conjugate, connecting to generate a larger conjugate system, making the oxazole ring more stable; the introduction of -OH is more likely to form intramolecular and intermolecular hydrogen bonds compared to terephthalic acid, making the electron cloud distribution on the oxazole ring more uniform and stable. Introducing -Cl can increase the molecular polarity, strongly attract the electron cloud on the adjacent oxazole ring, and effectively passivate the oxazole ring; in addition, the C-Cl bond is more likely to absorb ultraviolet light and break, thereby protecting the oxazole ring of PBO. Therefore, introducing the above side groups simultaneously can synergistically improve the ultraviolet resistance of PBO fibers. In addition, the interaction force between the strongly polar group and the resin molecule is stronger, which can significantly improve the interfacial composite performance of the fiber.

[0019] After obtaining the above modified PBO copolymer, it can be made into fibers using it as the spinning dope. The specific steps are as follows: The spinning dope enters the front spinning system for dry-jet wet spinning liquid crystal spinning. The temperature of the front spinning pipeline and the spinning box is set at 180 - 220 °C. The spinning dope is quantitatively transported to the spinning component (composed of a base, a filter screen, a distribution plate, and a spinneret plate) by a spinning pump, and is extruded into filaments through the spinneret holes. The filament bundle enters the duct, and high-temperature (65 - 75 °C) annular blowing is set in the duct. The filament bundle is formed by contacting with water in the coagulation bath, and the fiber bundle enters the back spinning system. After the back spinning water washing and drying processes, the modified fiber sample is finally wound up.

[0020] The method for ultraviolet resistance modification of PBO fiber provided by the present invention has a simple process. Based on the PBO fiber spinning process, except for the increase in the feeding step and a slight extension of the reaction time, there are basically no other new processes, thus saving manpower and material resources. In addition, the PBO fiber modified by this method has mechanical properties close to those of PBO fiber, and its ultraviolet aging resistance performance is significantly improved. This modification method greatly expands the application scope of PBO fiber. Description of the Drawings

[0021] Figure 1 Schematic diagram of the infrared spectrum test results of the products obtained in Example 1 and the comparative example; Figure 2 Fiber samples obtained in Example 1 and Example 2 of the present application, where (a) is the fiber sample of 5% DH - 10% TACl - PBO in Example 1, and (b) is the fiber sample of 10% DH - 5% TACl - PBO in Example 2. Detailed Description of the Invention

[0022] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with examples. The present invention described here is only used to explain the present invention and is not used to limit the present invention. Except for special instructions, other conventional techniques in the art are adopted.

[0023] In the following examples, the intrinsic viscosity of the copolymer sample was measured as follows: The copolymer was dissolved in methanesulfonic acid, and an Ubbelohde viscometer was used in a constant temperature water bath to measure the intrinsic viscosity of the polymer according to the five - point method; for the structural characterization test of the copolymer sample, an ATR attenuated total reflection infrared test was performed using a Magna 750 Fourier transform infrared spectrometer from Nicolet Corporation, USA.

[0024] The mechanical properties of the fiber samples obtained from the experiments were tested using an electronic single - fiber strength tester (model YG005N) for all fiber samples, with a clamping length of 20 mm, a tensile rate of 10 mm / min, and a pre - tension of 0 cN / dtex. The PBO fiber and modified PBO fiber specimens obtained by the dry - jet wet - spinning method were combed and fixed on the sample rack, placed in an ultraviolet accelerated aging test chamber for ultraviolet light accelerated aging test. The distance between the fixed light source and the fiber was 50 cm, the ultraviolet light wavelength was set at 340 nm, the power was 6×40 W, and the irradiation intensity was 0.51 W / m 2 , the blackboard temperature was 63 °C, and the test chamber temperature was 38 °C.

[0025] Preparation of 5% DH - 10% TACl - PBO Fiber in Example 1 First, 32.234 kg of PPA and 49 g of SnCl2·2H2O were added to the reaction kettle, and then 6.105 kg of DARHB (purity 99.59%), 4.030 kg of TPA, 283 g of DHTA, and 671 g of TACl were added in sequence. Finally, 10.365 kg of P2O5 was added, and the gradient temperature-rising reaction was started in a nitrogen atmosphere. The temperature of the reaction kettle was first controlled at 65 °C and stirred for 3 h, then raised to 80 °C and stirred for 4 h, and then raised to 95 °C and stirred for 3 h. At the end of this stage, the reaction kettle was evacuated to remove the remaining small amount of HCl, then raised to 110 °C and stirred for 3 h, and finally raised to 120 °C and stirred for 2 h.

[0026] After the prepolymerization reaction ended, nitrogen was replenished to positive pressure in the reaction kettle, and the material entered the twin-screw extruder. Post-polymerization was carried out, and the temperatures of each stage of the twin-screw extruder showed a gradient temperature-rising trend, and the temperature range was controlled at 140 °C to 200 °C. An experimental twin-screw extruder with a total of 24 zones in the upper and lower two stages was used. The screw speeds of the upper and lower stage machines were both 10 / 10 (r / min). The temperature settings of the twelve zones of the upper-stage screw were 140, 150, 160, 170, 180, 180, 180, 180, 180, 180, 180, 180 °C in sequence, and the temperature settings of the twelve zones of the lower-stage screw were 170, 180, 170, 175, 175, 180, 180, 190, 180, 190, 200, 200 °C in sequence. The material stayed in the extruder for 90 min to complete the final polymerization, and a modified copolymer with an intrinsic viscosity of 20 - 30 dL / g was obtained.

[0027] The copolymer solution (spinning dope) that completed the final polymerization entered the pre-spinning system for dry-jet wet spinning of liquid crystal fibers. The temperature of the pre-spinning pipeline and the spinning box was set at 180 - 220 °C. The spinning dope was quantitatively transported to the spinning component (composed of a base, a filter screen, a distribution plate, and a spinneret plate) by a spinning pump, and was ejected from the spinneret holes to form filaments. The filament bundle entered the duct, and high-temperature (65 - 75 °C) annular blowing was set in the duct. The filament bundle was formed by contacting water in the coagulation bath, and the fiber bundle entered the post-spinning system. After processes such as post-spinning water washing and drying, the modified fiber sample was finally wound up (see Figure 2 Figure (a)).

[0028] For the above spinning process, reference can be made to the description in the applicant's prior application CN112941657B, "A Method for Spinning and Forming Poly(p-phenylene benzobisoxazole) Fibers", and the inventor will not elaborate further.

[0029] The structure and performance analysis of the product in this example are as follows: The intrinsic viscosity of the polymerization product was measured. The intrinsic viscosity of 5% DH-10% TACl-PBO was 24.9 dL / g. Compared with the intrinsic viscosity of pure PBO, which is 24.6 dL / g, it can be seen that the change in the intrinsic viscosity of PBO after adding a certain amount of DHTA and TACl is not significant, that is, the influence on the polymerization reaction activity is relatively small.

[0030] The results of the infrared spectrum test are shown in Figure 1 , where the stretching vibration absorption peak of C-C on the benzene ring is at 1616.6 cm -1 -1492.8 cm -1 ; the stretching vibration absorption peak of C-C on the benzene ring is at 1411.1 cm -1 , 1115.3 cm -1 , 1056.6 cm -1 ; the stretching vibration absorption peak of C-C on the benzene ring is at 1051.4 cm -1 , 1007.0 cm -1 ; the absorption peak of =C-O-C- is at 1051.4 cm -1 . The difference is that for DH-TACl-PBO, a bending vibration peak of the C-Cl bond on the benzene ring appears at 1386.0 cm -1 ; there is an obvious broad absorption peak at 3382 cm

[0031] . This peak corresponds to the hydrogen bond absorption peak formed by the hydroxyl group on the benzene ring and the N element on the adjacent oxazole ring in the DHTA-PBO copolymer. Due to the association effect of the hydrogen bond, the absorption peak becomes broader. These indicate that the hydroxyl group and the chlorine group have been introduced into the polymer macromolecular chain.

[0032] Example 2 Preparation of 10% DH-5% TACl-PBO fiber First, 32.234 kg of PPA and 49 g of SnCl2·2H2O were added to the reaction kettle, and then 6.105 kg of DARHB (purity 99.59%), 4.030 kg of TPA, 566 g of DHTA, and 336 g of TACl were added in sequence. Finally, 10.365 kg of P2O5 was added, and the gradient temperature-rising reaction was started in a nitrogen atmosphere. The temperature of the reaction kettle was first controlled at 65 °C and stirred for 3 h, then raised to 80 °C and stirred for 4 h, and then raised to 95 °C and stirred for 3 h. At the end of this stage, the reaction kettle was evacuated to remove the remaining small amount of HCl, then raised to 110 °C and stirred for 3 h, and finally raised to 120 °C and stirred for 2 h.

[0033] After the prepolymerization reaction ended, nitrogen was replenished to positive pressure in the reaction kettle, and the material entered the twin-screw extruder for post-polymerization. The temperatures of each stage of the twin-screw extruder showed a gradient temperature-rising trend, and the temperature range was controlled at 140 °C to 200 °C. An experimental twin-screw extruder with a total of 24 zones in the upper and lower two stages was used. The screw speeds of the upper and lower stage machines were both 10 / 10 (r / min). The temperatures of the twelve zones of the upper stage screw were set as 140, 150, 160, 170, 180, 180, 180, 180, 180, 180, 180, 180 °C in sequence, and the temperatures of the twelve zones of the lower stage screw were set as 170, 180, 170, 175, 175, 180, 180, 190, 180, 190, 200, 200 °C in sequence. The material stayed in the extruder for 90 min to complete the final polymerization, and a modified copolymer with an intrinsic viscosity of 20 - 30 dL / g was obtained.

[0034] The copolymer solution (spinning dope) that completed the final polymerization entered the front spinning system for dry-jet wet spinning of liquid crystal fibers. The temperature of the front spinning pipeline and the spinning box was set at 180 - 220 °C. The spinning dope was quantitatively transported to the spinning assembly (composed of a base, a filter screen, a distribution plate, and a spinneret) by a spinning pump, and was extruded into filaments through the spinneret holes. The filament bundle entered the tunnel, and high-temperature (65 - 75 °C) annular blowing was set in the tunnel. The filament bundle was formed by contacting with water in the coagulation bath, and the fiber bundle entered the back spinning system. After processes such as back spinning, washing, and drying, the modified fiber sample was finally wound up (see Figure 2 (b)).

[0035] The structure and properties of the product in this example were analyzed as follows: The intrinsic viscosity of the polymerization product was tested. The intrinsic viscosity of 10% DH - 5% TACl - PBO was 25.1 dL / g. Comparing with the intrinsic viscosity of pure PBO, which was 24.6 dL / g, it can be seen that the intrinsic viscosity of PBO after adding a certain amount of DHTA and TACl not only did not decrease, but increased significantly. The main reason is that the addition of this type of monomer has little influence on the polymerization reaction activity, and the molecular weight of this type of monomer is larger than that of terephthalic acid.

[0036] The single-fiber strength test shows that the initial 10% DH-5% TACl-PBO fiber has a single-filament tensile strength of 3.73 GPa, which is 9.2% lower than the single-filament tensile strength of 4.11 GPa of pure PBO fiber but less than 10%. This is mainly because the introduction of polar side groups affects the regularity of the PBO molecular chain, resulting in a certain degree of reduction in the molecular chain orientation. The 10% DH-5% TACl-PBO fiber is irradiated by ultraviolet aging test for 100 hours, and the tensile strength retention rate is 86.3%. After irradiation for 400 hours, the tensile strength retention rate is 71.8%, showing a significant improvement in the ultraviolet aging resistance compared to pure PBO fiber.

[0037] Example 3 Preparation of 2% DH-20% TACl-PBO Fiber The specific scheme is the same as that of Example 1, except that the composition of the mixed diacids is: 3.698 kg TPA, 113 g DHTA, and 1344 g TACl.

[0038] Example 4 Preparation of 20% DH-2% TACl-PBO Fiber The specific scheme is the same as that of Example 1, except that the composition of the mixed diacids is: 3.698 kg TPA, 1132 g DHTA, and 134 g TACl.

[0039] Example 5 Preparation of 5% DH-5% TACl-PBO Fiber The specific scheme is the same as that of Example 1, except that the composition of the mixed diacids is: 4.267 kg TPA, 283 g DHTA, and 336 g TACl.

[0040] Example 6 Preparation of 10% DH-10% TACl-PBO Fiber The specific scheme is the same as that of Example 1, except that the composition of the mixed diacids is: 3.793 kg TPA, 566 g DHTA, and 672 g TACl.

[0041] Comparative Example 1 Preparation of PBO Polymer by Terephthalic Acid Method and Preparation of Fiber First, 32.234 kg PPA and 48.8 g SnCl2·2H2O are added to the reaction kettle, then 6.105 kg DARHB (purity 99.59%), 4.741 kg TPA are added in turn, and finally 10.365 kg P2O5 is added. The reaction starts with gradient temperature increase in a nitrogen atmosphere. The reaction kettle is first controlled at 65°C and stirred for 3 h, then heated to 80°C and stirred for 3 h, then heated to 95°C and stirred for 2 h. At the end of this stage, the reaction kettle is evacuated to remove the remaining small amount of HCl, then heated to 110°C and stirred for 2 h, and finally heated to 120°C and stirred for 2 h.

[0042] After the prepolymerization reaction is completed, nitrogen is filled into the reaction kettle until it reaches positive pressure, and the material enters the twin-screw extruder for post-polymerization. The temperatures of each stage of the twin-screw extruder show a gradient heating trend, and the temperature range is controlled at 140°C to 200°C. An experimental twin-screw extruder with a total of 24 zones in the upper and lower two stages is used. The screw speeds of the upper and lower stage machines are both 10 / 10 (r / min). The temperatures of the twelve zones of the upper stage screw are set as 140, 150, 160, 170, 180, 180, 180, 180, 180, 180, 180, 180°C in sequence, and the temperatures of the twelve zones of the lower stage screw are set as 170, 180, 170, 175, 175, 180, 180, 190, 180, 190, 200, 200°C in sequence. The material stays in the extruder for 90 minutes to complete the final polymerization.

[0043] The copolymer solution (spinning dope) that has completed the final polymerization enters the pre-spinning system for dry-jet wet spinning of liquid crystal fibers. The temperature of the pre-spinning pipeline and the spinning box is set at 180 - 220°C. The spinning dope is quantitatively transported to the spinning pack (composed of a base, a filter screen, a distribution plate, and a spinneret plate) by a spinning pump, and is extruded into filaments through the spinneret holes. The filament bundle enters the duct, and high-temperature (65 - 75°C) annular blowing is set in the duct. The filament bundle is formed into fibers when it meets water in the coagulation bath, and the fiber bundle enters the post-spinning system. After processes such as post-spinning washing and drying, the modified fiber sample is finally wound up.

[0044] The structure and properties of the product of this comparative example are analyzed as follows: The intrinsic viscosity of the polymerization product is tested, and the intrinsic viscosity of PBO is 24.6 dL / g.

[0045] The test result of the infrared spectrum is shown in Figure 1 , where the stretching vibration absorption peak of C-C on the benzene ring is at 1616.6 cm -1 -1492.8 cm -1 ; the skeletal vibration of C-C on the benzene ring is at 1411.1 cm -1 , 1115.3 cm -1 , 1056.6 cm -1 ; the absorption peak of =C-O-C- is at 1051.4 cm -1 , 1007.0 cm -1 .

[0046] The single fiber strength test shows that the tensile strength of a single filament of the initial PBO fiber is 4.811 GPa. After the PBO fiber is irradiated by the ultraviolet aging test for 100 hours, the tensile strength retention rate is only 53.3%. After being irradiated for 400 hours, the tensile strength retention rate is 21.4%. It can be seen that the PBO fiber has poor ultraviolet aging resistance, which greatly limits its application range.

[0047] It can be seen that the ultraviolet resistance of the modified PBO fiber of the present invention is significantly improved, that is, the retention rate of the fiber tensile strength after ultraviolet irradiation is greatly improved. Among many application products of PBO, the improvement of ultraviolet resistance means the improvement of the performance stability of the application products, and at the same time, the service life of the products can be correspondingly extended. This not only improves the use safety of the application products, but also saves the economic expenses caused by frequent product replacement.

[0048] For those of ordinary skill in the art, the specific embodiments only exemplarily describe the present invention. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for ultraviolet resistance modification of PBO fiber, characterized in that, The specific steps are as follows: First, add polyphosphoric acid into the reaction kettle as the solvent and catalyst of the reaction system, then add stannous chloride dihydrate as the antioxidant, and then sequentially add the reaction monomers 4,6-diaminoresorcinol dihydrochloride, terephthalic acid, 2,5-dichloroterephthalic acid, and 2,5-dihydroxyterephthalic acid. Finally, add phosphorus pentoxide as the water absorbent; after the feeding is completed, start the gradient temperature-raising reaction in a nitrogen atmosphere, and carry out prepolymerization in the reaction kettle to obtain a prepolymer with a lower molecular weight; the prepolymer is further strongly sheared by a twin-screw extruder to complete the post-polymerization to obtain a spinning dope, and the modified PBO fiber can be obtained by dry-jet wet spinning of the spinning dope.

2. The method for ultraviolet resistance modification of PBO fiber according to claim 1, wherein, The total molar ratio of 4,6-diaminoresorcinol dihydrochloride to the mixed dibasic acids composed of terephthalic acid, 2,5-dichloroterephthalic acid, and 2,5-dihydroxyterephthalic acid is 1:

1.

3. The ultraviolet resistance modification method of the PBO fiber according to claim 2, wherein In the mixed dibasic acids, 2,5-dichloroterephthalic acid accounts for 1%-20% in terms of molar percentage, 2,5-dihydroxyterephthalic acid accounts for 1%-20% in terms of molar percentage, and the mixture of the two accounts for 2%-40% of the mixed dibasic acids.

4. The method for ultraviolet resistance modification of PBO fiber according to claim 2 or 3, characterized in that In the mixed dibasic acids, 2,5-dichloroterephthalic acid accounts for 5%-10% in terms of molar percentage, 2,5-dihydroxyterephthalic acid accounts for 5%-10% in terms of molar percentage, and the mixture of the two accounts for 10%-20% of the mixed dibasic acids.

5. The ultraviolet resistance modification method of the PBO fiber according to claim 1, characterized in that, The gradient temperature-raising reaction is selected as follows: After the feeding is completed, the temperature of the reaction kettle is first controlled at 65°C and stirred for 3 h. The system is cooled to suppress the evolution of HCl and reduce swelling, then the temperature is raised to 80°C and stirred for 4 h, and then the temperature is raised to 95°C and stirred for 3 h; then the reaction kettle is evacuated to remove the remaining small amount of HCl, and then the temperature is raised to 110°C and stirred for 3 h, and finally the temperature is raised to 120°C and stirred for 2 h to obtain the prepolymer.

6. The ultraviolet resistance modification method of the PBO fiber according to claim 5, characterized in that After the prepolymerization reaction is completed, the prepolymer enters the twin-screw extruder for post-polymerization. The temperatures of each stage of the twin-screw extruder also show a gradient temperature-raising trend, and the temperature range is controlled at 140°C to 200°C, and the material completes the final polymerization in the extruder.

7. The method for ultraviolet resistance modification of PBO fiber according to claim 1, wherein The obtained modified PBO copolymer has three molecular structures, namely Formula I, Formula II, and Formula III: Formula I; Formula II; Formula III; In Formulas I, II, and III, a, b, and c are all positive integers.

8. The method for ultraviolet resistance modification of PBO fiber according to claim 1, characterized in that, The spinning dope enters the front spinning system for dry-jet wet spinning. The temperature of the front spinning pipeline and the spinning box is set at 180-220°C. The spinning dope is quantitatively transported to the spinning component by a spinning pump and ejected from the spinneret holes to form filaments. The filament bundle enters the duct, and high-temperature (65-75°C) annular blowing is set in the duct. The filament bundle is formed by contacting with water in the coagulation bath. The fiber bundle enters the back spinning system, undergoes back spinning water washing and drying processes, and finally is wound up to obtain the modified fiber sample.

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