Phosphogypsum modified polypropylene filling rope and preparation process thereof

Abstract

The invention discloses a phosphogypsum modified polypropylene filling rope and a preparation process thereof, and belongs to the technical field of high polymer materials. The preparation process comprises the following steps: firstly, carrying out deep pretreatment on phosphogypsum through water washing, lime milk neutralization and flotation screening to effectively remove soluble impurities, insoluble impurities and radioactive substances so as to obtain high-purity calcium sulfate dihydrate powder; then stearic acid and composite modified nano boron nitride are adopted to perform surface modification on the powder, so that the interfacial compatibility of the powder and a polypropylene matrix is remarkably enhanced; mixing the modified ardealite powder with polypropylene, a lubricant and an auxiliary agent, and carrying out melt blending through an extruder with precise temperature control; and finally, performing cooling, slitting, stretching, net opening and strand combining treatment to obtain a final product. According to the process, high-value resource utilization of the industrial waste residue ardealite is achieved, the obtained filling rope has the advantages of being excellent in mechanical property, low in radioactivity and remarkable in cost, and the comprehensive performance of the filling rope is superior to that of a traditional calcium carbonate filling system.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a phosphogypsum-modified polypropylene filled rope and its preparation process. Background Technology

[0002] As a crucial component in cable and optical cable manufacturing, filler rope's performance directly impacts the overall quality and lifespan of the cables. Traditional filler ropes are primarily made of materials such as polypropylene and polyethylene, with their mechanical properties and environmental resistance improved through physical foaming or composite modification. However, with the increasing demand for lightweight, environmentally friendly, and high-performance cables, existing filler ropes are gradually showing certain limitations in terms of material selection, manufacturing processes, and overall performance.

[0003] Patent CN103177805B discloses a PP filler rope and its manufacturing method. The filler rope is made of PP fiber filaments torn into a mesh, and its components include 1%-50% calcium carbonate and 50%-99% polypropylene. This patent, through a scientifically designed formula, uses PP rope instead of other filler materials, resulting in good electrical insulation, thermal stability, and flexibility. Furthermore, it does not rot when used in cables for extended periods, increasing environmental friendliness and flexibility. However, the main drawback of this technical solution is that the mechanical properties of the filler rope still have room for improvement, and it does not address how to further optimize the overall performance of the material through modification.

[0004] Patent CN104167257B discloses a tensile filler rope for optical cables, which is prepared using physical foaming technology. Its main components include low-density polyethylene, high-density polyethylene, and micron-sized ultrafine calcium carbonate. This filler rope, acting as an inner layer, can tightly bond with the outer plastic film sheath, thereby increasing the tensile and lateral compressive strength of the filler rope. While this technology offers advantages in improving the mechanical properties of the filler rope, its preparation process requires the use of various additives, which may negatively impact the final material properties.

[0005] In summary, existing filler rope technologies still have room for improvement in terms of material modification, overall performance optimization, and environmental friendliness. To address these issues, there is an urgent need to develop a novel filler rope and its manufacturing process to meet the modern cable industry's demand for high-performance, low-cost, and environmentally friendly filler materials. Summary of the Invention

[0006] One of the objectives of this invention is to provide a preparation process for phosphogypsum-modified polypropylene filled rope, thereby addressing the shortcomings of existing filled ropes in terms of mechanical properties, environmental friendliness, and cost control.

[0007] The second objective of this invention is to provide a phosphogypsum-modified polypropylene filled rope, which is prepared by the above-mentioned phosphogypsum-modified polypropylene filled rope preparation process.

[0008] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a process for preparing a phosphogypsum-modified polypropylene-filled rope includes the following steps: S10: Pre-treat phosphogypsum to remove soluble impurities, insoluble impurities, and radioactive substances to obtain pure calcium sulfate dihydrate powder. S20: Surface modification of calcium sulfate dihydrate powder with stearic acid and composite modified nano boron nitride was carried out to make it have good compatibility with polypropylene matrix, resulting in surface-modified phosphogypsum powder. S30: Surface-modified phosphogypsum powder is mixed with polypropylene, lubricant, additive 1 and additive 2 in a certain proportion and then melt-blended through an extruder feeding system; S40: The melt-blended material is sequentially cooled, slit, stretched, opened, and stranded to form the final phosphogypsum-modified polypropylene filled rope.

[0009] Furthermore, in step S10, the pretreatment of the phosphogypsum includes the following steps: S11: Mix the raw phosphogypsum with clean water or circulating water in a mixing tank at a mass ratio of 1:(3-5) and stir for 10-20 minutes. Then, separate the solid and liquid components by vacuum filtration, centrifuge or belt filter. S12: Add lime milk to the phosphogypsum slurry after solid-liquid separation, control the pH value between 6.5 and 7.5, and age for 1-3 hours to convert the residual soluble phosphorus and soluble fluorine into insoluble substances; S13: The phosphogypsum slurry neutralized with lime is subjected to flotation and screening. During flotation, the mass ratio of collector to frother is 1:(2-3). During screening, a vibrating screen is used to control the particle size at 800-1250 mesh.

[0010] Furthermore, in step S11, the temperature of the clean water or circulating water is controlled between 20-30°C, and the stirring speed is 50-80 revolutions per minute to ensure that the soluble impurities in the phosphogypsum are fully dissolved.

[0011] Furthermore, in step S12, the concentration of the lime slurry is 5%-10%, and the amount added is 1%-3% of the mass of the phosphogypsum slurry.

[0012] Furthermore, in step S13, the collector includes fatty acid collectors, the frother includes pine oil frothers, and the bubble adsorption time during the flotation process is 5-10 minutes.

[0013] Furthermore, in step S20, the surface modification includes the following steps: S21: Dry the pretreated phosphogypsum powder at 100℃ to 110℃ until the moisture content is less than 0.5%; S22: Add the dried phosphogypsum powder to a high-speed mixer and preheat to 100-110℃; S23: Add stearic acid and composite modified nano boron nitride. The amount of stearic acid is 0.5%-1.5% of the mass of phosphogypsum powder, and the amount of composite modified nano boron nitride is 1%-3% of the mass of phosphogypsum powder. S24: Stir in a high-speed mixer for 5-7 minutes to allow stearic acid and composite modified nano boron nitride to fully react synergistically before discharging and cooling.

[0014] Furthermore, the composite modified nano boron nitride includes the following steps: S231: Hydroxylation treatment: Take the original boron nanoparticles, add hydrogen peroxide solution to react, and obtain hydroxylated boron nanoparticles after centrifugation, washing and drying; S232: Silane modification: Hydroxylated nano-boron nitride was dispersed in anhydrous ethanol, silane coupling agent KH-570 was added, the pH value was adjusted and the reaction was refluxed, and the silane-modified boron nitride was obtained by filtration and drying. S233: Polypropylene graft modification: Silane-modified boron nitride is mixed with maleic anhydride-grafted polypropylene (MAH-g-PP), extruded through a twin-screw extruder, granulated, and then pulverized with liquid nitrogen to obtain composite modified nano boron nitride.

[0015] Furthermore, in step S231, the original boron nitride nanoparticles have a particle size of 50-100 nm; the hydrogen peroxide solution has a mass fraction of 10%-15%; the liquid-to-solid ratio is 10 mL: 1 g; the reaction temperature is 80-90 °C; the reaction time is 4-6 hours; after centrifugation, the mixture is washed with deionized water until neutral; and the drying conditions are 120 °C for 4 hours.

[0016] Furthermore, in step S232, the hydroxylated boron nitride nanoparticles are ultrasonically dispersed in anhydrous ethanol for 30 minutes to form a suspension with a mass fraction of 5%; the amount of silane coupling agent KH-570 added is 3%-5% of the mass of the hydroxylated boron nitride nanoparticles; the pH value is adjusted to 4.5-5.5; the reaction temperature is 70-80℃; the reflux reaction time is 3 hours; and the drying conditions after filtration are 110℃ for 3 hours.

[0017] Furthermore, in step S233, the mass ratio of silane-modified boron nitride to maleic anhydride-grafted polypropylene (MAH-g-PP) is 1:2; the grafting rate of MAH-g-PP is 1.2%-1.8%; the extrusion temperature is 170-185℃; the screw speed is 300-350rpm; after extrusion, the material is pelletized and pulverized with liquid nitrogen to a particle size of 2000-3000 mesh.

[0018] Furthermore, in step S30, the mass ratio of the phosphogypsum powder, polypropylene, lubricant, additive 1, additive 2 and composite modified nano boron nitride is (75-80):(15-19):2:1:1:(1-3), the lubricant is paraffin wax, the additive 1 is polyethylene wax, and the additive 2 is at least one of antioxidants B215 and B225.

[0019] Furthermore, in step S30, the heating zone temperature of the extruder feeding system is set sequentially to 210℃, 215℃, 210℃, 200℃, 195℃, 190℃, 180℃, 175℃, 175℃, and 175℃, the screen changer melt pump temperature is set to 200℃ and 195℃, and the extrusion die temperature is set to 185℃, 180℃, and 185℃.

[0020] Furthermore, in step S40, the water temperature of the cooling water tank is controlled between 20°C and 25°C, the baking plate temperature is set sequentially to 133°C, 142°C, 132°C, 126°C, and 120°C, and the stretching speed is 80-140 meters per minute.

[0021] Secondly, a phosphogypsum-modified polypropylene filled rope is prepared by the above-mentioned phosphogypsum-modified polypropylene filled rope preparation process.

[0022] The beneficial effects of this invention are: (1) This invention solves the problems of impurities, weak interfacial bonding, and process compatibility of phosphogypsum as an industrial waste during resource utilization by systematically pretreating and surface modifying it. This treatment method enables phosphogypsum to effectively replace traditional calcium carbonate fillers, while giving the filler rope higher comprehensive performance. The phosphogypsum-modified polypropylene filler rope uses phosphogypsum as filler and combines systematic pretreatment and surface modification technology to solve the problems of impurities, weak interfacial bonding, and process compatibility of phosphogypsum during resource utilization, thus exhibiting high mechanical properties, environmental friendliness, and economic efficiency.

[0023] (2) The present invention first performs deep pretreatment on phosphogypsum, and thoroughly removes soluble impurities, insoluble impurities and radioactive substances through steps such as water washing, neutralization and flotation sieving to obtain high-purity calcium sulfate dihydrate powder, thereby eliminating the adverse effects of impurities on product stability from the source (S10); then, surface modification technology is adopted to form a stable interface layer on the surface of phosphogypsum using organic modifiers, which greatly enhances its compatibility with polypropylene matrix and effectively overcomes the problem of decreased mechanical properties caused by weak interfacial bonding of traditional fillers (S20); in the melt blending stage, by precisely controlling the material ratio and extrusion process parameters, the uniform mixing and stable flow of phosphogypsum powder with polypropylene, lubricant, additives and composite modified nano boron nitride are ensured, and the process adaptability is optimized (S30); finally, after cooling, slitting, stretching, opening and stranding molding processes, a dense and mechanically balanced filler rope is formed (S40).

[0024] (3) This invention innovatively introduces composite modified nano boron nitride as a synergistic modifier to form a synergistic effect with stearic acid: stearic acid mainly improves the basic compatibility between phosphogypsum and polypropylene, while composite modified nano boron nitride strengthens the interfacial bonding force through molecular chain entanglement and chemical bonding. At the same time, by utilizing the layered structure and high thermal conductivity of boron nitride, the filler rope can maintain its mechanical properties while adding excellent thermal conductivity and heat dissipation performance and anti-aging performance. This solves the problem of performance degradation caused by heat accumulation in traditional filler ropes during cable operation, and achieves a multi-dimensional improvement of "mechanical enhancement + environmental protection + thermal conductivity and anti-aging", with effects far exceeding those of a single modification system. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0026] In some embodiments, a process for preparing a phosphogypsum-modified polypropylene-filled rope includes the following steps: S10: Pre-treat phosphogypsum to remove soluble impurities, insoluble impurities, and radioactive substances to obtain pure calcium sulfate dihydrate powder. Phosphogypsum is a byproduct of the phosphate fertilizer industry and typically contains soluble phosphorus, fluorine, organic matter, and trace amounts of radioactive elements. These impurities can degrade the mechanical properties, thermal stability, and safety of polypropylene. Pretreatment involves purifying the phosphogypsum using physicochemical methods to obtain calcium sulfate dihydrate (CaSO4·2H2O) powder, which serves as an inert filler to ensure good interfacial bonding when subsequently compounded with polypropylene, preventing degradation or toxicity caused by impurities.

[0027] S20: Surface modification of calcium sulfate dihydrate powder with stearic acid and composite modified nano boron nitride was carried out to make it have good compatibility with polypropylene matrix, resulting in surface-modified phosphogypsum powder. Calcium sulfate dihydrate has a hydrophilic surface, while polypropylene is a nonpolar hydrophobic polymer. Direct mixing can lead to poor interfacial compatibility, causing filler agglomeration, stress concentration, and decreased mechanical properties. Surface modification introduces hydrophobic groups to cover the surface of phosphogypsum, reducing its surface energy and improving its wettability and adhesion to polypropylene, thereby enhancing the dispersibility and interfacial strength of the composite material.

[0028] S30: Surface-modified phosphogypsum powder is mixed with polypropylene, lubricant, additive 1 and additive 2 in a certain proportion and then melt-blended through an extruder feeding system; Melt blending is a crucial step in polymer compounding, using the high shear and thermal history of the extruder to ensure uniform dispersion of the components. Lubricants reduce melt viscosity and prevent processing degradation; additives 1 and 2 further enhance thermal stability and interfacial bonding. The extruder provides continuous mixing, ensuring a homogeneous phase and laying the foundation for subsequent molding.

[0029] S40: The melt-blended material is sequentially cooled, slit, stretched, opened, and stranded to form the final phosphogypsum-modified polypropylene filled rope.

[0030] Cooling solidifies the melt and controls crystallinity; slitting cuts the strip material into the required size; stretching induces molecular chain orientation, improving tensile strength and rigidity; opening the mesh forms a network structure to increase flexibility and surface area; and stranding twists multiple strands of filament into a rope, enhancing mechanical strength and durability. These post-processing steps optimize the mechanical properties and applicability of the filler rope.

[0031] In some embodiments, the pretreatment of the phosphogypsum in step S10 includes the following steps: S11: Mix the raw phosphogypsum with clean water or circulating water in a mixing tank at a mass ratio of 1:(3-5) and stir for 10-20 minutes. Then, separate the solid and liquid components by vacuum filtration, centrifuge or belt filter. High water-to-water ratio (1:3-1:5) stirring ensures complete dissolution of soluble impurities; stirring speed and time optimize the mass transfer process and avoid particle breakage due to over-stirring. Solid-liquid separation removes dissolved impurities and reduces the load on subsequent processing.

[0032] S12: Add lime milk to the phosphogypsum slurry after solid-liquid separation, control the pH value between 6.5 and 7.5, and age for 1-3 hours to convert the residual soluble phosphorus and soluble fluorine into insoluble substances; Lime milk (Ca(OH)2) neutralizes acidic impurities, resulting in a near-neutral pH of 6.5-7.5. Soluble phosphorus (H3PO4) is converted to insoluble calcium phosphate (Ca3(PO4)2), and soluble fluoride (such as HF) is converted to insoluble calcium fluoride (CaF2). The aging time allows for complete precipitation, which is then removed via subsequent solid-liquid separation, preventing impurities from causing polymer degradation or product embrittlement during processing.

[0033] S13: The phosphogypsum slurry neutralized with lime is subjected to flotation and screening. During flotation, the mass ratio of collector to frother is 1:(2-3). During screening, a vibrating screen is used to control the particle size at 800-1250 mesh.

[0034] Flotation utilizes bubble adsorption to remove light organic matter and residual impurities; the collector makes impurities hydrophobic and allows them to adhere to bubbles, while the foaming agent stabilizes the foam layer; a mass ratio of 1:2 to 1:3 balances collection efficiency and foam stability. Sieving controls particle size to ensure the fineness of the filler, affecting the smoothness and mechanical properties of the composite material—fine particles provide a larger surface area, enhancing the interfacial bonding with polypropylene.

[0035] In some embodiments, in step S11, the temperature of the clean water or circulating water is controlled between 20-30°C, and the stirring speed is 50-80 revolutions per minute to ensure that the soluble impurities in the phosphogypsum are fully dissolved.

[0036] A temperature of 20-30℃ is used to avoid high temperatures causing impurities to redissolve or low temperatures reducing the dissolution rate; a stirring speed of 50-80 rpm provides moderate shear force to promote dissolution without causing excessive particle wear or increased energy consumption.

[0037] In some embodiments, in step S12, the concentration of the lime slurry is 5%-10%, and the amount added is 1%-3% of the mass of the phosphogypsum slurry.

[0038] A lime slurry concentration of 5%-10% ensures a controllable neutralization reaction and avoids localized over-alkaliness; the amount added is 1%-3%, precisely calculated based on the impurity content. Excessive lime will introduce CaO impurities, affecting the purity of phosphogypsum and subsequent modification.

[0039] In some embodiments, in step S13, the collector includes a fatty acid collector, the frother includes a pine oil frother, and the bubble adsorption time during the flotation process is 5-10 minutes.

[0040] Fatty acid collectors selectively adsorb onto the surface of impurities, making them hydrophobic; pine oil generates small, stable bubbles; an adsorption time of 5-10 minutes ensures that the impurities are fully in contact with the bubbles and float to the surface. Too short a time results in incomplete removal, while too long a time reduces efficiency.

[0041] In some embodiments, step S20, the surface modification includes the following steps: S21: Dry the pretreated phosphogypsum powder at 100℃-110℃ until the moisture content is below 0.5%; Drying removes moisture to prevent water vaporization during melt blending, which could cause bubbles or hydrolytic degradation; moisture content below 0.5% ensures effective adhesion of the surface modifier and avoids competitive adsorption of water molecules.

[0042] S22: Add the dried phosphogypsum powder to a high-speed mixer and preheat to 100℃-110℃; Preheating activates the surface of phosphogypsum, enhancing its reactivity and making it easier for surface modifiers to cover the particle surface through physical adsorption or chemical bonding.

[0043] S23: Add stearic acid and composite modified nano boron nitride. The amount of stearic acid is 0.5%-1.5% of the mass of phosphogypsum powder, and the amount of composite modified nano boron nitride is 1%-3% of the mass of phosphogypsum powder. Stearic acid (C 17 H 35 COOH has a low melting point (67-72℃) and is easily melted in the system. Its carboxyl groups react with calcium ions on the surface of phosphogypsum to form a calcium stearate coating layer, and the alkyl chain is compatible with polypropylene; excess will cause free stearic acid to precipitate.

[0044] S24: Stir in a high-speed mixer for 5 to 7 minutes to allow stearic acid and composite modified nano boron nitride to fully react synergistically before discharging and cooling.

[0045] Stirring for 5-7 minutes ensures that stearic acid diffuses and reacts fully to form a complete coating layer; cooling prevents thermal oxidative degradation and stabilizes the modification effect.

[0046] In some embodiments, the composite modified boron nitride nanoparticles include the following steps: S231: Hydroxylation treatment: Take the original boron nanoparticles, add hydrogen peroxide solution to react, and obtain hydroxylated boron nanoparticles after centrifugation, washing and drying; The original BN surface is inert and lacks active groups that can react with organic matter. The fundamental purpose of this step is to introduce hydroxyl groups (-OH) onto the surface of BN particles through oxidation, providing "anchor sites" for subsequent silanization reactions.

[0047] S232: Silane modification: Hydroxylated nano-boron nitride was dispersed in anhydrous ethanol, silane coupling agent KH-570 was added, the pH value was adjusted and the reaction was refluxed, and the silane-modified boron nitride was obtained by filtration and drying. The silane coupling agent KH-570 has a hydrolyzable methoxy group at one end, which can undergo a condensation reaction with the -OH group on the surface of BN; the other end is a methacryloyloxy group containing a carbon-carbon double bond, which can serve as an active site for subsequent grafting with polymers.

[0048] S233: Polypropylene graft modification: Silane-modified boron nitride is mixed with maleic anhydride-grafted polypropylene (MAH-g-PP), extruded through a twin-screw extruder, granulated, and then pulverized with liquid nitrogen to obtain composite modified nano boron nitride.

[0049] Through melt blending, the carbon-carbon double bonds at the end of silane-modified BN react with the maleic anhydride groups on maleic anhydride-grafted polypropylene (MAH-g-PP), chemically grafting PP molecular chains onto the BN surface, thereby achieving the transition from inorganic BN to organic PP.

[0050] In some embodiments, in step S231, the original boron nitride nanoparticles have a diameter of 50-100 nm; the hydrogen peroxide solution has a mass fraction of 10%-15%; the liquid-solid ratio is 10 mL: 1 g; the reaction temperature is 80-90 °C; the reaction time is 4-6 hours; after centrifugation, the mixture is washed with deionized water until neutral; and the drying conditions are 120 °C for 4 hours.

[0051] Hydrogen peroxide, as a relatively mild oxidant, can effectively attack the edges and defect sites of boron (BN) to form B-OH bonds, while avoiding severe damage to the BN crystal structure. A suitable concentration (10%-15%) and temperature (80-90℃) ensure that hydrogen peroxide has sufficient oxidizing power to guarantee the hydroxylation reaction proceeds effectively within a reasonable time (4-6 hours). A liquid-to-solid ratio (10:1) ensures sufficient reaction space and mass transfer efficiency for BN particles, preventing agglomeration due to excessive concentration.

[0052] In some embodiments, in step S232, hydroxylated boron nitride nanoparticles are ultrasonically dispersed in anhydrous ethanol for 30 minutes to form a suspension with a mass fraction of 5%; the amount of silane coupling agent KH-570 added is 3%-5% of the mass of hydroxylated boron nitride nanoparticles; the pH value is adjusted to 4.5-5.5; the reaction temperature is 70-80℃; the reflux reaction time is 3 hours; and the drying conditions after filtration are 110℃ for 3 hours.

[0053] Anhydrous ethanol and ultrasonic dispersion ensure that the hydroxylated BN is fully deagglomerated before the reaction, forming a uniform suspension that allows silane molecules to uniformly contact all BN particles. pH (4.5-5.5): This is the optimal acid catalytic condition for silane hydrolysis and condensation reactions. An acidic environment promotes the hydrolysis of the methoxy group (-OCH3) of KH-570 to silanol (-SiOH) and accelerates its condensation and dehydration reaction with the -OH group on the BN surface, forming a strong Si-OB covalent bond.

[0054] In some embodiments, in step S233, the mass ratio of silane-modified boron nitride to maleic anhydride-grafted polypropylene (MAH-g-PP) is 1:2; the grafting rate of MAH-g-PP is 1.2%-1.8%; the extrusion temperature is 170-185℃; the screw speed is 300-350rpm; after extrusion, the material is pelletized and pulverized with liquid nitrogen to a particle size of 2000-3000 mesh.

[0055] The mass ratio of MAH-g-PP is 1:2. This ratio ensures an excess of MAH-g-PP, which guarantees sufficient coating and grafting of BN particles while also acting as a compatibilizer in the final composite material. MAH-g-PP grafting rate (1.2%-1.8%): This grafting rate provides sufficient reactive functional groups without compromising the properties of the PP matrix due to excessive polar groups.

[0056] In some embodiments, in step S30, the mass ratio of the phosphogypsum powder, polypropylene, lubricant, additive 1, additive 2 and composite modified nano boron nitride is (75-80):(15-19):2:1:1:(1-3), the lubricant is paraffin wax, the additive 1 is polyethylene wax, and the additive 2 is at least one of antioxidants B215 and B225; The heating zone temperatures of the extruder feeding system are set sequentially to 210℃, 215℃, 210℃, 200℃, 195℃, 190℃, 180℃, 175℃, 175℃, and 175℃; the screen changer melt pump temperatures are set to 200℃ and 195℃; and the extrusion die temperatures are set to 185℃, 180℃, and 185℃.

[0057] A mass ratio of 77:19:2:1:1 indicates a high-filling system, significantly reducing costs, but requiring a lubricant to reduce melt viscosity and wear. Additives 1 and 2 prevent degradation and enhance the interface. The composite modified nano-BN is prepared through a three-stage modification process of "hydroxylation-silane coupling-polypropylene grafting." The MAH-g-PP segments grafted onto its surface can form molecular chain entanglements with the polypropylene matrix. Simultaneously, the unsaturated double bonds of the silane coupling agent can synergistically interact with the carboxyl groups of stearic acid, constructing a multi-element interface layer of "stearic acid-silane-BN-polypropylene" on the surface of the phosphogypsum powder. The temperature is gradually decreased from 210℃ to 175℃ to ensure that the polypropylene (melting point approximately 165℃) is fully melted and uniformly mixed, while avoiding high-temperature degradation (polypropylene degradation temperature > 250℃); the later temperature reduction prevents premature melt crystallization. The screen changer and melt pump are kept at 200-195℃ to maintain melt fluidity; the die head temperature is kept at 185-180-185℃ to control the extrusion shape and surface quality.

[0058] In some embodiments, in step S40, the water temperature of the cooling water tank is controlled between 20°C and 25°C, the baking plate temperature is set sequentially to 133°C, 142°C, 132°C, 126°C, and 120°C, and the stretching speed is 80-140 meters per minute.

[0059] Cooling water temperature of 20-25℃ is used to control slow crystallization and avoid rapid cooling that could lead to internal stress or brittleness. A temperature gradient in the baking plate (133℃ to 120℃) is used for heat setting; the high-temperature section (142℃) is close to the melting point of polypropylene, promoting molecular chain relaxation and orientation; gradual cooling stabilizes the crystal structure and improves dimensional stability. A stretching speed of 80-140 m / min balances production efficiency with the degree of molecular chain orientation—too slow a speed results in low efficiency, while too fast a speed leads to insufficient orientation, affecting strength.

[0060] In some embodiments, a phosphogypsum-modified polypropylene filled rope is prepared by the above-described phosphogypsum-modified polypropylene filled rope preparation process.

[0061] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0062] Example 1

[0063] This embodiment provides a phosphogypsum-modified polypropylene filled rope, which is prepared through the following steps: S10: Mix 100kg of raw phosphogypsum with 400kg of water in a mixing tank for 15 minutes at a speed of 60 revolutions per minute, and then separate the solid and liquid by vacuum filtration. S11: Add the solid-liquid separated phosphogypsum slurry to lime milk with a concentration of 8%, control the pH value to 7, and age for 2 hours; S12: The phosphogypsum slurry neutralized with lime is floated with fatty acid collectors and pine oil frothers added at a mass ratio of 1:2.5, and the flotation time is 8 minutes. S13: The phosphogypsum slurry after flotation is screened, and the particle size is controlled to be 1000 mesh using a vibrating screen.

[0064] S20: Dry the pretreated phosphogypsum powder at 105℃ until the moisture content is 0.3%; S21: Add the dried phosphogypsum powder to a high-speed mixer and preheat it to 105°C; S22: Add stearic acid (1% of the mass of phosphogypsum) and composite modified nano boron nitride (2% of the mass of phosphogypsum); S23: Stir in a high-speed mixer for 6 minutes to allow the stearic acid to react fully before discharging and cooling.

[0065] S30: Surface-modified phosphogypsum powder is mixed with polypropylene, paraffin wax, polyethylene wax, antioxidant B215, and composite modified nano boron nitride in a mass ratio of 77:18:2:1:1:2, and then melt-blended through an extruder feeding system. The heating zone temperatures of the extruder feeding system are set sequentially to 210℃, 215℃, 210℃, 200℃, 195℃, 190℃, 180℃, 175℃, 175℃, and 175℃. The screen changer melt pump temperatures are set to 200℃ and 195℃, and the extrusion die temperatures are set to 185℃, 180℃, and 185℃.

[0066] S40: The melt-blended material is sequentially cooled, slit, stretched, screen-opening, and stranding. The water temperature in the cooling water tank is controlled at 22℃, and the drying plate temperature is sequentially set to 133℃, 142℃, 132℃, 126℃, and 120℃. The stretching speed is 100 meters per minute, the screen-opening angle of the screen-opening machine is 35°, the screen-opening speed is 100 meters per minute, and the stranding machine speed is 120 meters per minute.

[0067] Example 2

[0068] Compared with Example 1, the difference in this embodiment is that the aging time in step S12 is shortened to 0.5 hours, while the other parameters remain unchanged. The specific implementation steps are as follows: The phosphogypsum slurry after solid-liquid separation is added to lime milk with a concentration of 8%, the pH value is controlled at 7, and the aging time is 0.5 hours. The remaining raw materials and preparation process are the same as in Example 1.

[0069] Example 3

[0070] The difference between this embodiment and Example 1 is that in step S23, stearic acid is replaced with an equal amount of silane coupling agent KH-550. Specifically, the steps are as follows: add silane coupling agent KH-550, the amount of which is 1% of the mass of the phosphogypsum powder; The remaining raw materials and preparation process are the same as in Example 1.

[0071] Example 4

[0072] Compared with Example 1, the difference in this embodiment is that the proportion of phosphogypsum in step S30 is increased to 80%, the proportion of polypropylene is adjusted to 16% accordingly, and the remaining proportions are slightly adjusted to 2:1:1:3. The specific implementation steps are as follows: the surface-modified phosphogypsum powder is mixed with polypropylene, paraffin wax, polyethylene wax, antioxidant B215 and composite modified nano boron nitride in a mass ratio of 80:16:2:1:1:3; the temperature gradient of the extruder is increased by 5°C at the beginning (215°C→220°C→215°C→205°C→200°C→195°C→185°C→180°C→180°C→180°C). The remaining raw materials and preparation process are the same as in Example 1.

[0073] Example 5

[0074] The difference between this embodiment and Embodiment 1 is that the baking plate temperature in step S40 is changed to an isothermal 130℃, and the temperature gradient is eliminated. Specifically, the baking plate temperature is uniformly set to 130℃. The remaining raw materials and preparation process are the same as in Example 1.

[0075] Example 6

[0076] The difference between this embodiment and Example 1 is that the amount of stearic acid used in step S23 is increased to 2.0%. Specifically, the amount of stearic acid used is 2.0% of the mass of the phosphogypsum powder. The remaining raw materials and preparation process are the same as in Example 1.

[0077] Example 7

[0078] Compared with Example 1, the difference in this embodiment is that the amount of composite modified nano boron nitride is reduced, and the mass ratio of the mixture in S30 is 77:19.5:2:1:1:1; The remaining raw materials and preparation process are the same as in Example 1.

[0079] Comparative Example 1

[0080] Compared with Example 1, this comparative example omits all pretreatment steps (S10). Specifically, the surface modification is performed directly using the original phosphogypsum, omitting steps S11-S13. The remaining raw materials and preparation process are the same as in Example 1.

[0081] Comparative Example 2

[0082] Compared with Example 1, this comparative example differs in that only the S11 water washing step is performed, omitting lime neutralization and flotation. The specific implementation steps are as follows: the original phosphogypsum is mixed with water at a mass ratio of 1:4, stirred at 25°C for 15 minutes, and then the solid and liquid are separated; steps S12 and S13 are omitted. The remaining raw materials and preparation process are the same as in Example 1.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that 77% calcium carbonate is used instead of phosphogypsum. The specific implementation steps are: 77% calcium carbonate is used instead of phosphogypsum as a filler; steps S10 and S20 are omitted. The remaining raw materials and preparation process are the same as in Example 1.

[0085] Comparative Example 4

[0086] The difference between this comparative example and Example 1 is that the surface modification step S20 is omitted. Specifically, the pretreated phosphogypsum powder is directly used for mixing, omitting steps S21-S24. The remaining raw materials and preparation process are the same as in Example 1.

[0087] Comparative Example 5

[0088] The difference between this comparative example and Example 1 is that the amount of stearic acid (S23) is reduced to 0.3%. The specific implementation steps are as follows: the amount of stearic acid is 0.3% of the mass of phosphogypsum powder, and the remaining raw materials and preparation process are the same as in Example 1.

[0089] Comparative Example 6

[0090] The difference between this comparative example and Example 1 is that the proportion of phosphogypsum filler is increased to 85%. The specific implementation steps are as follows: the mass ratio of phosphogypsum powder, polypropylene, lubricant, additive 1, additive 2 and composite modified nano boron nitride is adjusted to 85:11:2:1:1:2; The remaining raw materials and preparation process are the same as in Example 1.

[0091] Comparative Example 7

[0092] The difference between this comparative example and Example 1 is that the "composite modified nano boron nitride" is replaced with an equal amount of unmodified nano boron nitride (particle size 50-100nm, without hydroxylation, silane modification and PP grafting). The remaining raw materials and preparation process are the same as in Example 1.

[0093] Comparative Example 8

[0094] The difference between this comparative example and Example 1 is that the amount of composite modified nano boron nitride is 5% (phosphogypsum mass ratio), and the mixing ratio is adjusted to 77:15:2:1:1:5; The remaining raw materials and preparation process are the same as in Example 1.

[0095] Comparative Example 9

[0096] The difference between this comparative example and Example 1 is that the composite modified nano boron nitride is omitted, and only stearic acid (1% by mass of phosphogypsum) modification is retained, and the mixing ratio is adjusted to 79:18:2:1:1. The remaining raw materials and preparation process are the same as in Example 1.

[0097] Performance testing

[0098] Performance tests were conducted on the embodiments and comparative examples according to the following national standards: 1. Tensile properties: GB / T 1040.2-2022 "Determination of tensile properties of plastics" 2. Oxygen Index: GB / T 2406.2-2009 "Oxygen Index of Plastics" (Flammability) 3. Whiteness: GB / T 5950-2008 "Methods for Measurement of Whiteness of Building Materials and Non-metallic Mineral Products" 4. Radioactivity: GB 6566-2010 "Limits of Radionuclides in Building Materials" 5. Accelerated aging test conditions: 120℃ thermo-oxidative aging for 1000 hours, according to GB / T 7141-2008 "Plastics Thermal Aging Test Method"; The results are shown in Table 1: Table 1

[0099] As shown in Table 1, the test data of Comparative Example 1 shows that its internal radiation index (IRa=1.35) and external radiation index (Ir=1.82) far exceed the national standard limits (IRa≤1.0, Ir≤1.3), indicating a significant deterioration in whiteness and mechanical properties. This proves that the untreated phosphogypsum contains excessive radioactive substances and impurities, failing to meet basic usage requirements. Although the performance of Comparative Example 2 is improved compared to Comparative Example 1, its radioactivity index (IRa=0.92, Ir=1.25) is still close to or exceeds the safety limits, and its mechanical properties are still unsatisfactory, indicating that simple water washing is insufficient to thoroughly purify the phosphogypsum. After adopting a complete "water washing-neutralization-flotation" pretreatment process in Example 1, the radioactivity index (IRa=0.18, Ir=0.25) is far below the national safety standards, indicating a significant improvement in whiteness and mechanical properties. This proves that the multi-stage pretreatment system of the present invention can effectively remove radioactive substances and various impurities from phosphogypsum.

[0100] The tensile strength of Comparative Example 4 was lower than that of Example 1, demonstrating that the interfacial bonding between the unmodified phosphogypsum and the polypropylene matrix was poor, severely affecting the mechanical properties of the material. Although the tensile strength of Comparative Example 5 was better than that of Comparative Example 4, it was still significantly lower than that of Example 1, indicating that insufficient modifier dosage would lead to incomplete interfacial coating, further verifying the technical rationality of the stearic acid dosage range in this invention.

[0101] Comparative Example 6 exhibited the worst mechanical properties, demonstrating that excessively high filler ratios can compromise the structural integrity of the material. Example 4 further optimized Example 1, achieving the optimal balance between tensile strength and cost, indicating that under the process conditions set by this invention, an 80% filler ratio is the preferred technology for achieving both high performance and low cost.

[0102] Although Comparative Example 3 has a slight advantage in terms of cost and radioactivity, its tensile strength is lower than that of Examples 1 and 4, demonstrating that through the systematic processing of the present invention, phosphogypsum can surpass traditional calcium carbonate fillers in mechanical properties, realizing high-value-added utilization of industrial waste.

[0103] The performance indicators of Examples 2 and 5 all showed varying degrees of decline, demonstrating that the aging time and heat treatment gradient in this invention have a significant impact on ensuring product quality. Example 6 failed to bring further performance improvement and instead increased costs, further verifying the technical rationality of the stearic acid dosage range in this invention.

[0104] Example 1 showed a 22.8% increase in tensile strength and a 17.6% increase in tensile strength retention after accelerated aging compared to Comparative Example 9, demonstrating that the composite modified BN and stearic acid synergistically achieve a dual effect of "mechanical enhancement + anti-aging optimization." Comparative Example 7 showed a 28.4% decrease in tensile strength and a 14.2% decrease in aging retention compared to Example 1, highlighting that the three-level modification of "hydroxylation-silane coupling-PP grafting" is the core of BN's compatibility with the system. Unmodified BN is prone to agglomeration and cannot form an effective reinforcement and anti-aging barrier. Example 7 showed limited performance improvement, and Comparative Example 8 suffered from stress concentration and performance degradation due to stacking, while Example 1 showed the best overall performance. Example 1 showed a 22.4% increase in tensile strength and a 9.2% increase in aging retention compared to Comparative Example 3, achieving both high-value utilization of phosphogypsum and comprehensively surpassing the traditional system in mechanical properties and anti-aging properties, solving the problem of mechanical attenuation during long-term use of traditional filled ropes.

[0105] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A preparation process for phosphogypsum-modified polypropylene filled rope, characterized in that, Includes the following steps: S10: Pre-treat phosphogypsum to remove soluble impurities, insoluble impurities, and radioactive substances to obtain pure calcium sulfate dihydrate powder. S20: Surface modification of calcium sulfate dihydrate powder with stearic acid and composite modified nano boron nitride was carried out to make it have good compatibility with polypropylene matrix, resulting in surface-modified phosphogypsum powder. S30: Surface-modified phosphogypsum powder is mixed with polypropylene, lubricant, additive 1 and additive 2 in a certain proportion and then melt-blended through an extruder feeding system; S40: The melt-blended material is sequentially cooled, slit, stretched, opened, and stranded to form the final phosphogypsum-modified polypropylene filled rope.

2. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 1, characterized in that, In step S10, the pretreatment of phosphogypsum includes the following steps: S11: Mix the raw phosphogypsum with clean water or circulating water in a mixing tank at a mass ratio of 1:(3-5) and stir for 10-20 minutes. Then, separate the solid and liquid components by vacuum filtration, centrifuge or belt filter. S12: Add lime milk to the phosphogypsum slurry after solid-liquid separation, control the pH value between 6.5 and 7.5, and age for 1-3 hours to convert the residual soluble phosphorus and soluble fluorine into insoluble substances; S13: The phosphogypsum slurry neutralized with lime is subjected to flotation and screening. During flotation, the mass ratio of collector to frother is 1:(2-3). During screening, a vibrating screen is used to control the particle size at 800-1250 mesh.

3. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 2, characterized in that, In step S11, the temperature of the clean water or circulating water is controlled between 20-30°C, and the stirring speed is 50-80 revolutions per minute to ensure that the soluble impurities in the phosphogypsum are fully dissolved. In step S12, the concentration of the lime slurry is 5%-10%, and the amount added is 1%-3% of the mass of the phosphogypsum slurry; In step S13, the collector includes fatty acid collectors, the frother includes pine oil frothers, and the bubble adsorption time during the flotation process is 5-10 minutes.

4. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 1, characterized in that, In step S20, the surface modification includes the following steps: S21: Dry the pretreated phosphogypsum powder at 100-110℃ until the moisture content is below 0.5%; S22: Add the dried phosphogypsum powder to a high-speed mixer and preheat to 100-110℃; S23: Add stearic acid and composite modified nano boron nitride. The amount of stearic acid is 0.5%-1.5% of the mass of phosphogypsum powder, and the amount of composite modified nano boron nitride is 1%-3% of the mass of phosphogypsum powder. S24: Stir in a high-speed mixer for 5-7 minutes to allow stearic acid and composite modified nano boron nitride to fully react synergistically before discharging and cooling.

5. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 4, characterized in that, The composite modified nano boron nitride includes the following steps: S231: Hydroxylation treatment: Take the original boron nanoparticles, add hydrogen peroxide solution to react, and obtain hydroxylated boron nanoparticles after centrifugation, washing and drying; S232: Silane modification: Hydroxylated nano-boron nitride was dispersed in anhydrous ethanol, silane coupling agent KH-570 was added, the pH value was adjusted and the reaction was refluxed, and the silane-modified boron nitride was obtained by filtration and drying. S233: Polypropylene graft modification: Silane-modified boron nitride is mixed with maleic anhydride-grafted polypropylene, extruded through a twin-screw extruder, granulated, and then pulverized with liquid nitrogen to obtain composite modified nano boron nitride.

6. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 5, characterized in that, In step S231, the original boron nitride nanoparticles have a diameter of 50-100 nm; the hydrogen peroxide solution has a mass fraction of 10%-15%; the liquid-to-solid ratio is 10 mL: 1 g; the reaction temperature is 80-90 °C; the reaction time is 4-6 hours; after centrifugation, the mixture is washed with deionized water until neutral; and the drying conditions are 120 °C for 4 hours. In step S232, hydroxylated boron nitride nanoparticles are ultrasonically dispersed in anhydrous ethanol for 30 minutes to form a suspension with a mass fraction of 5%; the amount of silane coupling agent KH-570 added is 3%-5% of the mass of hydroxylated boron nitride nanoparticles; the pH value is adjusted to 4.5-5.5; the reaction temperature is 70-80℃; the reflux reaction time is 3 hours; and the drying conditions after filtration are 110℃ for 3 hours. In step S233, the mass ratio of silane-modified boron nitride to maleic anhydride-grafted polypropylene is 1:2; the grafting rate of maleic anhydride-grafted polypropylene is 1.2%-1.8%; the extrusion temperature is 170-185℃; the screw speed is 300-350rpm; after extrusion, the material is pelletized and pulverized with liquid nitrogen to a particle size of 2000-3000 mesh.

7. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 1, characterized in that, In step S30, the mass ratio of the phosphogypsum powder, polypropylene, lubricant, additive 1, additive 2 and composite modified nano boron nitride is (75-80):(15-19):2:1:1:(1-3), the lubricant is paraffin wax, the additive 1 is polyethylene wax, and the additive 2 is at least one of antioxidants B215 and B225.

8. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 1, characterized in that, In step S30, the heating zone temperature of the extruder feeding system is set sequentially to 210℃, 215℃, 210℃, 200℃, 195℃, 190℃, 180℃, 175℃, 175℃, and 175℃, the screen changer melt pump temperature is set to 200℃ and 195℃, and the extrusion die temperature is set to 185℃, 180℃, and 185℃.

9. The preparation process of a phosphogypsum-modified polypropylene filled rope according to claim 1, characterized in that, In step S40, the water temperature of the cooling water tank is controlled between 20°C and 25°C, the baking plate temperature is set sequentially to 133°C, 142°C, 132°C, 126°C, and 120°C, and the stretching speed is 80-140 meters per minute.

10. A phosphogypsum-modified polypropylene-filled rope, characterized in that, It is prepared by the preparation process of phosphogypsum modified polypropylene filled rope according to any one of claims 1-9.

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