Process for the production of a continuous, discontinuous fiber-reinforced composite pipe from phosphogypsum

Abstract

The present application relates to the technical field of chemical modification and manufacturing of artificial fibers, in particular to a process for preparing phosphogypsum continuous and discontinuous fiber reinforced composite pipe; the process comprises the following steps: synthesis of multifunctional modifier, preparation of modified spinning solution, wet spinning, thermal crosslinking and drawing setting, and composite pipe forming; the process combines fluorine-containing monomer, acrylic acid and epoxy-containing monomer to synthesize multifunctional modifier, which is blended with polyvinyl alcohol and covalently crosslinked during heat setting; the core of the process is to introduce fluorine-containing low surface energy chain segment to build a hydrophobic shielding layer to block the penetration of acidic medium, and to form stable chemical coordination bond between the surface carboxyl group and calcium ions in the phosphogypsum matrix to realize active bonding at the interface; the present application overcomes the defects of easy degradation and interface debonding and peeling of fibers caused by simple physical blending, and realizes significant improvement in acid resistance, corrosion resistance, mechanical strength and wet water stability of the composite pipe.

Description

Technical Field

[0001] This invention relates to the field of chemical modification and manufacturing technology of man-made fibers, specifically to a process for continuous and discontinuous fiber-reinforced composite material tubes made of phosphogypsum. Background Technology

[0002] When phosphogypsum is used as a matrix material to manufacture pipes, it suffers from drawbacks such as poor water resistance, weak acidity, and the presence of harmful impurities. Traditional reinforcing fibers are prone to acidic hydrolysis or chemical degradation in phosphogypsum slurry. Furthermore, the chemical inertness of the interface between traditional fibers and phosphogypsum results in only physical and mechanical bonding after curing, which can easily lead to fiber pull-out under humid, hot, or stressed conditions, causing the pipe to break. Existing technologies mostly focus on washing and removing impurities from phosphogypsum powder or physical coating, which not only easily generates secondary wastewater but also cannot effectively solve the problem of interfacial debonding between fibers and the phosphogypsum matrix under humid and hot conditions. Therefore, there is an urgent need to develop a new reinforcing fiber manufacturing technology specifically for phosphogypsum matrix that combines acid resistance, corrosion protection, and active interfacial chemical bonding capabilities. Summary of the Invention

[0003] The purpose of this invention is to provide a process for continuous and discontinuous fiber-reinforced composite pipes made of phosphogypsum, aiming to solve the problems in the prior art where traditional reinforcing fibers are prone to hydrolysis or chemical degradation in acidic phosphogypsum, and the interfacial chemical inertness results in only physical and mechanical bonding, which easily leads to interfacial debonding and fiber pull-out under humid and hot stress, causing brittle fracture of the pipe. Specifically, the technical solution of this invention is as follows: A process for producing continuous and discontinuous fiber-reinforced composite pipes made of phosphogypsum specifically includes the following steps: S1. Synthesis of multifunctional modifier: N,N-dimethylformamide solvent was added to a reactor, followed by the sequential addition of perfluoroalkyl ethyl acrylate, acrylic acid, glycidyl methacrylate, and azobisisobutyronitrile; after purging with nitrogen to remove oxygen, the temperature was raised to 70-80℃ and stirred at a constant temperature; after the reaction was completed, the mixture was concentrated by vacuum distillation, and the pH of the system was adjusted to 7.0-7.5 with triethylamine to obtain an aqueous multifunctional modifier dispersion; S2. Preparation of modified spinning solution: Polyvinyl alcohol is dissolved in deionized water to prepare polyvinyl alcohol spinning solution; the aqueous multifunctional modifier dispersion is added dropwise to the polyvinyl alcohol spinning solution, mixed evenly and allowed to stand to remove bubbles, to obtain modified spinning solution. S3. Wet spinning: The modified spinning solution is extruded through a spinneret into a coagulation bath containing sodium sulfate aqueous solution and coagulated into nascent fibers. S4. Thermal crosslinking and stretching: The nascent fibers are washed with water and then subjected to wet heat stretching, followed by dry heat stretching and heat setting. After cooling, they are wound up to obtain continuous fibers, or cut to obtain discontinuous fibers. S5. Composite pipe forming: The continuous fibers are wound and composited with phosphogypsum slurry, or the discontinuous fibers are added to phosphogypsum slurry for dispersion and mixing, and then cured and formed to obtain a phosphogypsum fiber reinforced composite material pipe; the phosphogypsum slurry is at least prepared by mixing phosphogypsum powder with water, and water-reducing agent and / or retarder are added.

[0004] The beneficial effects of this invention are as follows: This process introduces a multifunctional modifier synthesized from perfluoroalkyl ethyl acrylate, acrylic acid and glycidyl methacrylate into the polyvinyl alcohol spinning solution, and covalently crosslinks the modifier with the polyvinyl alcohol matrix during the heat setting stage; This method utilizes the introduced fluorinated segments to construct a hydrophobic shielding layer, which effectively blocks the penetration of acidic media and water, and overcomes the defects of traditional reinforcing fibers that are prone to acidic hydrolysis or chemical degradation in phosphogypsum matrix; Meanwhile, by utilizing the surface carboxyl groups on the modifier to form stable chemical coordination bonds with calcium ions in phosphogypsum, the traditional physical-mechanical bonding is transformed into active chemical bonding at the interface. This innovation effectively solves the problem of interface debonding and fiber pull-out that is prone to occur in composite pipes under humid or stressed environments, avoids brittle fracture of the pipes, and significantly improves the acid and corrosion resistance, comprehensive mechanical strength, and long-term water resistance stability of phosphogypsum fiber reinforced composite pipes. Detailed Implementation

[0005] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example

[0006] This embodiment provides a process for continuous and discontinuous fiber-reinforced composite material pipes made of phosphogypsum, which specifically includes the following steps; S1, Synthesis of Multifunctional Modifiers 100 parts by mass of N,N-dimethylformamide were added to a three-necked reactor equipped with a condenser, a mechanical stirrer, and a nitrogen inlet. Then, 15 parts by mass of perfluoroalkyl ethyl acrylate, 20 parts by mass of acrylic acid, 10 parts by mass of glycidyl methacrylate, and 0.5 parts by mass of azobisisobutyronitrile were added sequentially. Nitrogen gas was purged for 30 minutes to remove dissolved oxygen from the system. The reaction system was then heated to 75°C and stirred for 8 hours. After the reaction was complete, some of the solvent was removed by vacuum distillation. The pH of the system was then adjusted to 7.0 to 7.5 with triethylamine to obtain a water-based multifunctional modifier dispersion with a solid content of 30%. S2, Preparation of Modified Spinning Solution Polyvinyl alcohol with a degree of polymerization of 1700 and a degree of alcoholysis of 99% was selected and dissolved in deionized water to prepare a polyvinyl alcohol spinning solution with a mass fraction of 15%. The aqueous multifunctional modifier dispersion obtained in step S1 was slowly added dropwise to the polyvinyl alcohol spinning solution at 90°C at a ratio of 3% of the dry weight of the modifier to the dry weight of the polyvinyl alcohol, and mixed evenly under high-speed stirring. The resulting system was allowed to stand for degassing under a vacuum of -0.08 MPa for 12 hours to obtain the modified spinning solution. S3, wet spinning forming The modified spinning solution obtained in step S2 is pumped to a spinneret with a spinneret orifice diameter of 0.08 mm. The spinning solution is extruded into a coagulation bath, which is a 20% sodium sulfate aqueous solution with a bath temperature controlled at 45°C. The fine stream of the solution undergoes solvent and non-solvent dual diffusion in the coagulation bath, which triggers phase separation and forms nascent fibers. S4, Thermo-induced cross-linking and stretching After washing away residual sodium sulfate on the surface of the nascent fibers obtained in step S3, they are subjected to 3 times wet heat stretching at 90°C. The fibers after wet heat stretching are then placed in the dry heat stretching and heat setting zone and set at 220°C. The total stretching ratio is controlled at 12 times and the setting time is 15 seconds. After setting, the fibers are cooled and wound up to obtain continuous fibers; or they can be cut to obtain discontinuous fibers with a length of 6 to 12 mm. S5, Composite Pipe Forming The continuous fibers obtained in step S4 are used for winding reinforcement, or the discontinuous fibers are added to the phosphogypsum slurry for dispersion and mixing, with a fiber addition amount of 1.5 wt%. The phosphogypsum slurry is prepared by mixing phosphogypsum powder and water at a water-to-slurry ratio of 0.4:1, adding 0.5% polycarboxylate superplasticizer and 0.1% citric acid retarder by weight of phosphogypsum, and stirring evenly. After even mixing, the pipe is formed and cured. Specifically, the pipe is prepared by centrifugal molding process, and then the formed pipe is cured in a standard curing chamber at a temperature of 25°C and a relative humidity of over 95% for 24 hours, and then demolded and cured under natural conditions for 7 days to obtain the phosphogypsum fiber reinforced composite material pipe. Example

[0007] This embodiment provides a process for continuous and discontinuous fiber-reinforced composite material pipes made of phosphogypsum, which specifically includes the following steps; S1, Synthesis of Multifunctional Modifiers 100 parts by weight of N,N-dimethylformamide were added to a reactor, followed by 10 parts by weight of perfluoroalkyl ethyl acrylate, 15 parts by weight of acrylic acid, 5 parts by weight of glycidyl methacrylate, and 0.2 parts by weight of azobisisobutyronitrile. After purging with nitrogen for 20 minutes, the temperature was raised to 70°C and the reaction was stirred for 6 hours. After the reaction was completed, some of the solvent was removed by vacuum distillation, and the pH of the system was adjusted to 7.0 to 7.5 with triethylamine to obtain a water-based multifunctional modifier dispersion with a solid content of 25%. This dispersion is used to provide hydrophobic and anchoring modification functions for subsequent fibers. S2, Preparation of Modified Spinning Solution Polyvinyl alcohol with a degree of polymerization of 1600 and a degree of alcoholysis of 98% was selected to prepare a polyvinyl alcohol spinning solution with a mass fraction of 10%. The aqueous multifunctional modifier dispersion obtained in step S1 was added dropwise to the polyvinyl alcohol spinning solution at 85°C at a ratio of 1% of the dry weight of the modifier to the dry weight of the polyvinyl alcohol. After stirring evenly, the solution was allowed to stand at -0.06MPa for 10 hours to remove bubbles, and the modified spinning solution was obtained. S3, wet spinning forming The modified spinning solution was extruded through a spinneret with a pore size of 0.06 mm into a sodium sulfate coagulation bath with a mass fraction of 15%, and the bath temperature was controlled at 40℃ to obtain nascent fibers. S4, Thermo-induced cross-linking and stretching After being washed with water, the nascent fibers are subjected to 2 times wet heat stretching at 85°C, followed by dry heat stretching and heat setting at 210°C, with a total stretching ratio of 10 times and a setting time of 10 seconds. After cooling, they are wound up to obtain continuous fibers, or cut to obtain discontinuous fibers with a length of 6 to 12 mm. S5, Composite Pipe Forming The obtained fibers were compounded with phosphogypsum slurry at an addition rate of 1.0 wt%. The phosphogypsum slurry was prepared by mixing phosphogypsum powder and water at a water-to-slurry ratio of 0.45:1, and adding polynaphthalene sulfonate water-reducing agent at a dry weight of 0.4% of the phosphogypsum. The mixture was then molded and cured, specifically by casting molding. After curing at 30°C and 90% relative humidity for 12 hours, the mixture was demolded and allowed to cure naturally for 7 days to obtain the composite material tube. Example

[0008] This embodiment provides a process for continuous and discontinuous fiber-reinforced composite material pipes made of phosphogypsum, which specifically includes the following steps; S1, Synthesis of Multifunctional Modifiers 100 parts by weight of N,N-dimethylformamide were added to a reactor, followed by 20 parts by weight of perfluoroalkyl ethyl acrylate, 25 parts by weight of acrylic acid, 15 parts by weight of glycidyl methacrylate, and 1.0 part by weight of azobisisobutyronitrile. After purging with nitrogen for 40 minutes, the temperature was raised to 80°C and the reaction was stirred for 10 hours. After the reaction was completed, the system was distilled under reduced pressure, and the pH of the system was adjusted to 7.0 to 7.5 with triethylamine to obtain a water-based multifunctional modifier dispersion with a solid content of 35%. This dispersion is used to provide hydrophobic and anchoring modification functions for subsequent fibers. S2, Preparation of Modified Spinning Solution Polyvinyl alcohol with a degree of polymerization of 1800 and a degree of alcoholysis of 99% was selected to prepare a polyvinyl alcohol spinning solution with a mass fraction of 20%. The aqueous multifunctional modifier dispersion obtained in step S1 was added dropwise to the polyvinyl alcohol spinning solution at 95°C at a ratio of 5% of the dry weight of the modifier to the dry weight of the polyvinyl alcohol. After mixing evenly, the solution was allowed to stand at -0.10 MPa for 14 hours to remove bubbles, and the modified spinning solution was obtained. S3, wet spinning forming The modified spinning solution was extruded through a spinneret with an aperture of 0.10 mm into a sodium sulfate coagulation bath with a mass fraction of 25%. The bath temperature was controlled at 50°C, and the nascent fibers were obtained by coagulation. S4, Thermo-induced cross-linking and stretching After being washed with water, the nascent fibers are subjected to 4 times wet heat stretching at 95°C, followed by dry heat stretching and heat setting at 230°C, with a total stretching ratio of 14 times and a setting time of 20 seconds. After cooling, they are wound up to obtain continuous fibers or cut to obtain discontinuous fibers with a length of 6 to 12 mm. S5, Composite Pipe Forming The obtained fibers were compounded with phosphogypsum slurry at an addition rate of 2.0 wt%. The phosphogypsum slurry was prepared by mixing phosphogypsum powder and water at a water-to-slurry ratio of 0.35:1, and adding 0.6% polycarboxylate superplasticizer and 0.2% citric acid retarder by the dry weight of the phosphogypsum. The mixture was then molded and cured, specifically by extrusion molding. After curing at 20°C and 98% relative humidity for 48 hours, the mixture was demolded and naturally cured for 14 days to obtain the composite material tube. Example

[0009] This embodiment provides a process for continuous and discontinuous fiber-reinforced composite material pipes made of phosphogypsum, which specifically includes the following steps; S1, Synthesis of Multifunctional Modifiers 100 parts by weight of N,N-dimethylformamide were added to a reactor, followed by 12 parts by weight of perfluoroalkyl ethyl acrylate, 18 parts by weight of acrylic acid, 8 parts by weight of glycidyl methacrylate, and 0.3 parts by weight of azobisisobutyronitrile. After purging with nitrogen for 25 minutes, the temperature was raised to 73°C and the reaction was stirred for 7 hours. After the reaction was completed, the mixture was distilled under reduced pressure, and the pH was adjusted to 7.0 to 7.5 with triethylamine to obtain a water-based multifunctional modifier dispersion with a solid content of 28%. This dispersion is used to provide hydrophobic and anchoring modification functions for subsequent fibers. S2, Preparation of Modified Spinning Solution Polyvinyl alcohol with a degree of polymerization of 1650 and a degree of alcoholysis of 98.5% was selected to prepare a polyvinyl alcohol spinning solution with a mass fraction of 12%. The aqueous multifunctional modifier dispersion obtained in step S1 was added dropwise to the polyvinyl alcohol spinning solution at 88℃ according to the ratio of the dry weight of the modifier to the dry weight of the polyvinyl alcohol of 2%. After mixing evenly, the solution was allowed to stand at -0.07MPa for 11 hours to remove bubbles, and the modified spinning solution was obtained. S3, wet spinning forming The modified spinning solution was extruded through a spinneret with an aperture of 0.07 mm into a sodium sulfate coagulation bath with a mass fraction of 18%, and the bath temperature was controlled at 43℃ to obtain nascent fibers. S4, Thermo-induced cross-linking and stretching After being washed with water, the nascent fibers are subjected to 2.5 times wet heat stretching at 88°C, followed by dry heat stretching and heat setting at 215°C, with a total stretching ratio of 11 times and a setting time of 12 seconds. After cooling, they are wound up to obtain continuous fibers or cut to obtain discontinuous fibers with a length of 6 to 12 mm. S5, Composite Pipe Forming The obtained fibers were compounded with phosphogypsum slurry at an addition rate of 1.2 wt%. The phosphogypsum slurry was prepared by mixing phosphogypsum powder and water at a water-to-slurry ratio of 0.4:1, and adding 0.45% polycarboxylate superplasticizer and 0.15% citric acid retarder by the dry weight of the phosphogypsum. The mixture was then molded and cured, specifically by centrifugal molding. After curing at 25°C and 95% relative humidity for 24 hours, the mixture was demolded and naturally cured for 7 days to obtain the composite material tube.

[0010] Comparative Example 1: The difference between this comparative example and Example 1 is that the aqueous multifunctional modifier dispersion obtained in step S1 is not added in step S2, while the remaining operation steps and process parameters are exactly the same as in Example 1; the resulting fiber is essentially an unmodified polyvinyl alcohol fiber reinforced system.

[0011] Comparative Example 2: The difference between this comparative example and Example 1 is that in step S1, 15 parts by mass of perfluoroalkyl ethyl acrylate is replaced with 15 parts by mass of methyl methacrylate, while the remaining operation steps and process parameters are exactly the same as in Example 1; this comparative example retains the polymerization reaction and fiber formation process, but does not have fluorinated hydrophobic segments.

[0012] Comparative Example 3: The difference between this comparative example and Example 1 is that glycidyl methacrylate is not added in step S1, and an equal mass of acrylic acid is used to make up the total amount of monomers. The remaining operation steps and process parameters are exactly the same as in Example 1. This comparative example retains carboxyl groups and hydrophobic segments, but does not have epoxy anchoring groups.

[0013] Comparative Example 4: The difference between this comparative example and Example 1 is that the dry heat stretching and heat setting temperature in step S4 is changed from 220°C to 190°C, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0014] Comparative Example 5: The difference between this comparative example and Example 1 is that the fiber addition amount in step S5 is changed from 1.5wt% to 0.5wt%, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0015] Comparative Example 6: The difference between this comparative example and Example 1 is that the fiber addition amount in step S5 is changed from 1.5wt% to 3.0wt%, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0016] Performance Testing and Datasheets The performance testing methods are as follows; Acid resistance test: The fiber was immersed in a simulated phosphogypsum acidic extract at pH 2, which contained soluble phosphate and fluoride ions. After immersion for 90 days, the fiber was removed, washed, and dried. The tensile strength was determined by the conventional single fiber stretching method, and the tensile strength retention rate was calculated. Pipe mechanical property testing: Pipe ring stiffness was determined by constant-rate compression according to the industry-standard thermoplastic pipe ring stiffness testing specification; pipe tensile strength was determined by constant-rate loading using a pipe-specific mechanical testing machine; water resistance stability was characterized by the retention rate of pipe tensile strength after immersion in room temperature water for 90 days; performance test data are shown in the table below: Table 1. Test Results of Composite Material Pipe and Fiber Properties

[0017] Test Result Mechanism Analysis As shown in Table 1, comparing the test results of Example 1 and Comparative Example 1, after omitting the multifunctional modifier, the tensile strength retention rate of the fiber after 90 days of acid immersion decreased from 96.5% to 42.3%, and the ring stiffness of the pipe decreased from 43.8%. It dropped to 25.8 The tensile strength of the pipe decreased from 17.9 MPa to 11.4 MPa, and the strength retention rate after 90 days of immersion in water decreased from 91.6% to 61.8%. The underlying mechanism is that the surface of unmodified polyvinyl alcohol (PVA) fibers lacks fluorinated hydrophobic segments, making it easier for acidic aqueous phases and phosphorus and fluorine impurities to penetrate into the fiber interior. The PVA segments are also more prone to structural damage under acidic conditions. At the same time, the fiber surface lacks sufficient carboxyl coordination sites, making it difficult to form a stable chemical bond with calcium ions in the phosphogypsum matrix. The interface is still mainly mechanically interlocked, and pull-out is easily caused under external force and humid heat. Therefore, the acid resistance, interfacial bonding strength, and water resistance stability are all significantly reduced. As shown in Table 1, comparing the test results of Example 1 and Comparative Example 2, after replacing perfluoroalkyl ethyl acrylate with methyl methacrylate, the tensile strength retention rate of the fiber after 90 days of acid immersion decreased from 96.5% to 63.7%, and the ring stiffness and tensile strength of the pipe also decreased to 31.2%. The underlying mechanism is that, although Comparative Example 2 still contains carboxyl and epoxy groups, the polymer side chains no longer have low surface energy fluorine-containing structures, making it difficult to form a hydrophobic shielding layer on the fiber surface. Acidic media and moisture are more likely to contact and enter the fiber surface, resulting in a decrease in the stability of the fiber body in acidic systems. Although there is a certain chemical bond at the interface, the fiber body's corrosion resistance is insufficient, so the overall performance is still lower than that of Example 1. As shown in Table 1, comparing the test results of Example 1 and Comparative Example 3, omitting glycidyl methacrylate resulted in a decrease in the retention rate of tensile strength of the fiber after 90 days of acid immersion from 96.5% to 70.8%, and a decrease in the ring stiffness of the pipe from 43.8%. It dropped to 33.6 The strength retention rate of the pipe after 90 days of immersion in water decreased to 76.4%. The underlying mechanism is that without epoxy anchoring groups, it is difficult for the modifier and polyvinyl alcohol molecular chains to form sufficient covalent crosslinks during the heat setting stage. Some modified components exist only in a physical blending state, which makes them more likely to migrate or be lost in subsequent acidic or aqueous environments. This weakens the surface stability enrichment of fluorine-containing segments and the long-term retention of carboxyl sites, reduces the interfacial chemical bonding density, and simultaneously weakens acid and water resistance. As shown in Table 1, comparing the test results of Example 1 and Comparative Example 4, after reducing the dry hot drawing and heat setting temperature from 220℃ to 190℃, the tensile strength retention rate of the fiber after 90 days of acid immersion decreased to 78.6%, and the ring stiffness of the pipe decreased to 35.1%. The tensile strength of the pipe decreased to 14.4 MPa. The underlying mechanism is that the ring-opening etherification reaction between the epoxy group and the hydroxyl group of polyvinyl alcohol is insufficient at 190°C, the anchoring efficiency of the modifier decreases, and the internal orientation and surface enrichment structure of the fiber are not sufficient. The low crosslinking density will reduce the stability of the modified layer, thereby affecting the barrier effect of acidic media and the interfacial chemical bonding effect. Therefore, the overall performance is lower than that of Example 1. As shown in Table 1, comparing the test results of Example 1 and Comparative Example 5, reducing the fiber addition from 1.5 wt% to 0.5 wt% did not significantly change the acid leaching retention rate of the fiber itself, but the pipe ring stiffness increased from 43.8 wt%. It dropped to 31.5 The tensile strength of the pipe decreased from 17.9 MPa to 13.0 MPa. The underlying mechanism is that this change did not change the structural stability of a single fiber, but the number of reinforcing phases in the pipe per unit volume was significantly reduced. The fiber's role in hindering crack propagation and stress transfer was weakened, and the resulting reinforcing network was discontinuous. Therefore, the load-bearing capacity of the pipe layer decreased. As shown in Table 1, comparing the test results of Example 1 and Comparative Example 6, it can be seen that after increasing the fiber addition from 1.5 wt% to 3.0 wt%, the pipe ring stiffness and tensile strength decreased to 36.2 wt%. At 14.9 MPa, the strength retention rate decreased to 83.7% after 90 days of immersion in water. The underlying mechanism is that when the fiber content is too high, the slurry dispersion becomes more difficult, and the fibers are more likely to agglomerate, resulting in localized slurry deficiency and pores. This affects the continuous growth of phosphogypsum crystals and increases interfacial stress concentration. Although individual fibers still have high acid resistance, the overall uniformity of the composite material decreases, resulting in lower mechanical properties and water resistance than in Example 1. As can be seen from the comparison of the test results of Example 1 with Examples 2, 3 and 4 in Table 1, when adjusting the parameters of each step within the scope of the present invention, composite pipes with acid resistance and reinforcement effect can be obtained, but Example 1 has higher overall performance. The reason is that in Example 2, the amount of modifier added, the draw ratio, and the setting strength were too low, resulting in insufficient functional group density and fiber orientation. In Example 3, the amount of monomer added and fiber added was too high. Although the number of chemical functional sites increased, the excessively high proportion of modifier and reinforcing phase would affect the spinning stability, fiber dispersion, and composite uniformity. In Example 4, the parameters were at an intermediate level, which could balance fiber formation and reinforcement effect, but the interfacial chemical bonding density and surface hydrophobic shielding degree were still lower than those in Example 1. Therefore, the parameter combination used in Example 1 showed a better balance in this group of experiments.

[0018] The above are preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art can make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A process for continuous and discontinuous fiber-reinforced composite pipes made of phosphogypsum, characterized in that, Specifically, the following steps are included: S1. Synthesis of multifunctional modifier: N,N-dimethylformamide solvent was added to a reactor, followed by the sequential addition of perfluoroalkyl ethyl acrylate, acrylic acid, glycidyl methacrylate, and azobisisobutyronitrile; after purging with nitrogen to remove oxygen, the mixture was heated to 70-80℃ and stirred to react; after the reaction was completed, the mixture was concentrated by vacuum distillation, and the pH of the system was adjusted to 7.0-7.5 with triethylamine to obtain an aqueous multifunctional modifier dispersion; S2. Preparation of modified spinning solution: Polyvinyl alcohol is dissolved in deionized water to prepare polyvinyl alcohol spinning solution; the aqueous multifunctional modifier dispersion is added dropwise to the polyvinyl alcohol spinning solution, mixed evenly and allowed to stand to remove bubbles, to obtain modified spinning solution. S3. Wet spinning: The modified spinning solution is extruded through a spinneret into a coagulation bath containing sodium sulfate aqueous solution and coagulated into nascent fibers. S4. Thermal crosslinking and stretching: The nascent fibers are washed with water and then subjected to wet heat stretching, followed by dry heat stretching and heat setting. After cooling, they are wound up to obtain continuous fibers, or cut to obtain discontinuous fibers. S5. Composite pipe forming: The continuous fibers are wound and composited with phosphogypsum slurry, or the discontinuous fibers are added to phosphogypsum slurry for dispersion and mixing, and then cured and formed to obtain a phosphogypsum fiber reinforced composite material pipe; the phosphogypsum slurry is at least prepared by mixing phosphogypsum powder with water, and water-reducing agent and / or retarder are added.

2. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1, characterized in that, In step S1, 100 parts by weight of N,N-dimethylformamide solvent are added, followed by 10-20 parts by weight of perfluoroalkyl ethyl acrylate, 15-25 parts by weight of acrylic acid, 5-15 parts by weight of glycidyl methacrylate, and 0.1-1.0 parts by weight of azobisisobutyronitrile. The mixture is heated to 70-80℃ and stirred for 6-10 hours to obtain a dispersion with a solid content of 25%-35%. The polyvinyl alcohol spinning solution in step S2 has a mass fraction of 10%-20%. The modifier is added dropwise at 85-95℃ at a ratio of 1%-5% of the dry weight of polyvinyl alcohol. The degassing vacuum is -0.10 to -0.06 MPa, and the mixture is allowed to stand for degassing for 10-14 hours. In step S3, the spinneret orifice diameter is 0.06-0.10 mm, the coagulation bath mass fraction is 15%-25%, and the temperature is 40-50℃; in step S4, wet heat stretching is performed at 85-95℃ for 2-4 times, and dry heat stretching and heat setting are performed at 210-230℃, with a total stretching ratio of 10-14 times and a setting time of 10-20 seconds; in step S5, the fiber addition amount is 1.0-2.0 wt%.

3. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1 or 2, characterized in that: In step S2, the degree of polymerization of polyvinyl alcohol is 1600-1800 and the degree of alcoholysis is 98%-99%.

4. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 2, characterized in that: In step S1, the amount of perfluoroalkyl ethyl acrylate added is 15 parts by mass, the amount of acrylic acid added is 20 parts by mass, the amount of glycidyl methacrylate added is 10 parts by mass, and the amount of azobisisobutyronitrile added is 0.5 parts by mass.

5. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1 or 2, characterized in that: In step S1, nitrogen is passed through for 30 minutes to remove oxygen, and the temperature is raised to 75°C and stirred for 8 hours to obtain a water-based multifunctional modifier dispersion with a solid content of 30%.

6. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1 or 2, characterized in that: In step S2, the mass fraction of the polyvinyl alcohol spinning solution is 15%, the dropping temperature of the water-based multifunctional modifier dispersion is 90°C, and the dry weight of the modifier accounts for 3% of the dry weight of the polyvinyl alcohol.

7. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1 or 2, characterized in that: In step S2, the vacuum degree for static degassing is -0.08 MPa, and the static degassing time is 12 hours.

8. The process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to claim 1 or 2, characterized in that: In step S3, the spinneret has an aperture of 0.08 mm, the coagulation bath is a 20% sodium sulfate aqueous solution, and the temperature is controlled at 45°C.

9. A process for producing continuous and discontinuous fiber-reinforced composite pipes of phosphogypsum according to any one of claims 1-8, characterized in that: The amount of fiber added in step S5 is 1.5 wt%.

10. A continuous and discontinuous fiber-reinforced composite material pipe made of phosphogypsum, characterized in that: The composite material tube is prepared by the process described in any one of claims 1-9.

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