Mesophase pitch and polyacrylonitrile blend as well as preparation method and application thereof

Abstract

The invention discloses a mesophase pitch and polyacrylonitrile blend as well as a preparation method and application thereof, and belongs to the technical field of carbon fiber preparation. The preparation method comprises the following steps: carrying out high-temperature treatment on coal-based pitch, and then sequentially carrying out solvent extraction, solvent removal and hydrogenation catalysis to obtain mesophase pitch; and heating the mesophase pitch to 200-230 DEG C in an inert atmosphere, then adding the polyacrylonitrile microspheres, and carrying out melt blending to obtain the mesophase pitch and polyacrylonitrile blend. According to the preparation method, a stable single-phase system of the mesophase pitch and the polyacrylonitrile microspheres can be obtained, a uniform blend is formed, the comprehensive performance of the pitch-based fibers and the pitch-based carbon fibers further prepared from the blend is remarkably improved, the tensile strength of the pitch-based carbon fibers is 4500 MPa or above, the elongation at break is 1.2% or above, and the tensile strength of the pitch-based carbon fibers is larger than or equal to 4500 MPa. The defects that traditional pitch-based carbon fibers are low in strength and prone to brittle failure are effectively overcome.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber preparation technology, and in particular to a blend of mesophase pitch and polyacrylonitrile, its preparation method and application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Pitch-based carbon fiber has potential applications in high-performance materials due to its advantages such as high modulus, high thermal conductivity, high temperature resistance, abundant raw materials, low price, and high carbon yield. However, it has significant technical limitations: its tensile strength is generally only 1~3 GPa, significantly lower than that of polyacrylonitrile (PAN) carbon fiber; its fracture strain is only 0.2~0.5%, far lower than the 1.5~2.0% of PAN-based carbon fiber (high-strength type can reach over 2.5%), resulting in low strain tolerance and limiting its application in load-bearing structures. Furthermore, the composition of pitch-based raw materials is complex and highly variable, with poor fiber-forming properties. The narrow processing windows for precursor preparation, spinning, and heat treatment lead to low yield, poor stability, and significant challenges in process control.

[0004] While PAN-based carbon fibers possess high tensile strength and fracture strain, their blending with pitch-based materials presents inherent challenges: unmodified PAN molecules are highly polar, exhibiting poor compatibility with pitch and a tendency for micro-phase separation; traditional mesophase pitch has a high softening point (typically exceeding 240°C), resulting in poor temperature matching with PAN processing, and macro-phase separation easily occurs during blending at PAN's melting temperature, leading to unstable rheological properties; increasing the melting temperature to the pitch's softening point causes PAN decomposition, making uniform mixing and stable spinning difficult. Furthermore, the weak interfacial bonding between pitch and PAN further limits the synergistic improvement of the blend's mechanical properties. These issues constrain the development and application of high-performance pitch-based carbon fibers. Summary of the Invention

[0005] In view of this, the present invention provides a mesophase pitch and polyacrylonitrile blend, its preparation method and application. The present invention can obtain a mesophase pitch and polyacrylonitrile blend with a single-phase system, and the pitch-based fibers and pitch-based carbon fibers prepared by using it have excellent mechanical properties.

[0006] In a first aspect, the present invention provides a method for preparing a blend of mesophase pitch and polyacrylonitrile, comprising the following steps: Coal-based pitch is subjected to high-temperature treatment, followed by solvent extraction, solvent removal, and hydrogenation catalysis to prepare mesophase pitch. Mesophase pitch is heated to 200-230°C under an inert atmosphere, and then polyacrylonitrile microspheres are added and melt-blended to obtain a blend of mesophase pitch and polyacrylonitrile. The polyacrylonitrile microspheres have an average particle size of 10-50 μm and a molecular weight of 200,000-300,000; the mass ratio of mesophase pitch to polyacrylonitrile microspheres is (1-1.5):1.

[0007] Preferably, the high-temperature treatment is performed at a temperature of 320~420℃ for 1~5 hours; the high-temperature treatment is carried out under an inert atmosphere. The solvent used in the solvent extraction is selected from one or more of toluene, cyclohexane, n-hexane, or xylene; The hydrogenation catalysis reaction temperature is 300~450℃, and the reaction time is 1~5h; The softening point of the mesophase asphalt is 200~230℃; the melt blending time is 1~2h.

[0008] Preferably, the method for preparing the polyacrylonitrile microspheres is as follows: preparing an aqueous phase composition containing methyltrimethoxy modified silica; preparing an oil phase composition containing acrylonitrile, comonomer, molecular weight regulator and initiator; then mixing and homogenizing the aqueous phase composition and the oil phase composition; then carrying out a polymerization reaction; washing and drying the polymerization product to obtain polyacrylonitrile microspheres.

[0009] Furthermore, in the aqueous phase composition, the mass fraction of methyltrimethoxy modified silica is 1~5wt%, and the methyltrimethoxy modified silica is obtained by reacting methyltrimethoxysilane and silica under the catalysis of triethylamine; the volume ratio of the aqueous phase composition to the oil phase composition is 1:(0.2~0.4).

[0010] Furthermore, in the oil phase composition, the comonomer is selected from one or more of styrene, acrylic acid, or acrylamide; the mass ratio of acrylonitrile to comonomer is 1:(0.08~0.2); The molecular weight regulator is selected from one or more of n-dodecyl mercaptan, thioacetic acid, 2-mercaptoethanol, or n-octyl mercaptan; the mass ratio of acrylonitrile to the molecular weight regulator is 1: (0.0005~0.001); The initiator is one or more of dicumyl peroxide, benzoyl peroxide, or azobisisobutyronitrile; the mass ratio of acrylonitrile to initiator is 1:(0.005~0.01).

[0011] Furthermore, the mixing and homogenization rotation speed is 6000~12000 rpm; the polymerization reaction temperature is 70~90℃, and the polymerization reaction time is 5~12h.

[0012] Secondly, the present invention provides a blend of mesophase pitch and polyacrylonitrile prepared by the above preparation method.

[0013] Thirdly, the present invention provides the application of the above-mentioned mesophase pitch and polyacrylonitrile blend in the preparation of pitch-based fibers and / or pitch-based carbon fibers.

[0014] Fourthly, the present invention provides a bitumen-based fiber, which is obtained by heating and melting the above-mentioned mesophase bitumen and polyacrylonitrile blend, spinning and stretching it, and then cooling and curing it.

[0015] Fifthly, the present invention provides a pitch-based carbon fiber, which is obtained by pre-oxidation and carbonization treatment of the above-mentioned pitch-based fibers.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention prepares mesophase pitch by high-temperature treatment, solvent extraction, and hydrogenation catalysis of coal-based pitch, and then melt-blends it with polyacrylonitrile microspheres of specific particle size and molecular weight in a certain proportion, thereby achieving uniform dispersion and optimized interfacial bonding of the two precursors. The mesophase pitch transition state obtained after solvent extraction softens to 200~230℃ after hydrogenation catalysis, which matches the softening point of the modified polyacrylonitrile microspheres, forming a stable single-phase system. This significantly improves melt processability, reduces the difficulty of process control, and solves the problem of low yield caused by large fluctuations in raw material composition and poor fiber-forming properties in traditional pitch-based carbon fibers.

[0017] (2) The modified polyacrylonitrile microspheres of the present invention have reduced molecular polarity and improved compatibility with asphalt by introducing methyltrimethoxy modified silica and modifying with comonomers. The micron-sized particles are evenly dispersed in the asphalt melt, reducing the risk of separation between micro and macro phases and improving the rheological properties of the system. At the same time, the larger specific surface area enhances the interfacial bonding force with asphalt. In conjunction with the low viscosity characteristics of the mesophase asphalt, the blend is stably spun during melt spinning. The resulting asphalt-based fiber has a uniform structure, laying the foundation for the high performance of carbon fibers in the future.

[0018] (3) The comprehensive performance of the pitch-based carbon fiber prepared by the above-mentioned mesophase pitch and polyacrylonitrile blend is significantly improved. The tensile strength is above 4500MPa and the elongation at break is above 1.2%. At the same time, it maintains a high modulus of above 300GPa and a thermal conductivity of above 55W / (m·K). It effectively solves the defects of traditional pitch-based carbon fiber, such as low strength and easy brittle fracture, and expands its application potential in the field of high-performance load-bearing structures. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] This invention provides a method for preparing a blend of mesophase pitch and polyacrylonitrile, comprising the following steps: Coal-based pitch is subjected to high-temperature treatment, followed by solvent extraction, solvent removal, and hydrogenation catalysis to prepare mesophase pitch. Mesophase pitch is heated to 200-230°C under an inert atmosphere, and then polyacrylonitrile microspheres are added and melt-blended to obtain a blend of mesophase pitch and polyacrylonitrile. The polyacrylonitrile microspheres have an average particle size of 10-50 μm and a molecular weight of 200,000-300,000; the mass ratio of mesophase pitch to polyacrylonitrile microspheres is (1-1.5):1.

[0021] The above-mentioned technical solution of the present invention optimizes the thermodynamic compatibility and processing adaptability of the two fiber precursors by pretreatment of coal-based pitch and synergistic design of polyacrylonitrile microspheres.

[0022] First, coal-based pitch is treated at high temperature to promote molecular rearrangement and mesophase transformation. Solvent extraction yields medium-molecular-weight, non-crystallized mesophase pitch. Then, hydrogenation catalysis is used to adjust the molecular structure, introduce hydrogen atoms, break some aromatic rings or shorten side chains, and reduce intermolecular forces, lowering the softening point to 200-230℃. This yields equiaxed mesophase pitch with low viscosity and high fluidity. Its isotropic structure avoids the problem of excessive melt elasticity in traditional oriented mesophase pitch, providing a foundation for subsequent melt blending.

[0023] During the melt blending stage, the mass ratio of mesophase pitch to polyacrylonitrile microspheres is controlled at (1~1.5):1, and the average particle size of the microspheres is limited to 10~50μm and the molecular weight to 200,000~300,000. This parameter design is based on the matching between the interfacial energy of the two phases and the rheological behavior of the melt: the micron-sized particle size ensures that the microspheres are uniformly dispersed in the pitch melt under high shear, avoiding stress concentration caused by agglomeration; the specific molecular weight range allows the polyacrylonitrile microspheres to exhibit appropriate melt viscosity at 200~230℃, forming a blend system with similar viscosity to the mesophase pitch, satisfying the "shear-thinning" characteristic and achieving a single-phase molten state. If the molecular weight is too high, it will lead to increased brittleness of the microspheres, resulting in a decrease in the elongation at break of the subsequently prepared fibers and carbon fibers; if the molecular weight is too low, it will lead to decreased thermal stability of the microspheres, which is not conducive to melt blending with the mesophase pitch. It should be noted that the molecular weight of the polyacrylonitrile microspheres mentioned in this invention refers to the weight-average molecular weight (M). wAn inert atmosphere protects the asphalt from premature oxidative crosslinking and polyacrylonitrile cyclization reactions at high temperatures, ensuring the stability and repeatability of the blending process.

[0024] The technical solution of this invention directly solves the core contradictions of "mismatch between raw material softening point and processing window" and "uneven dispersion of multiphase system" in the preparation of traditional pitch-based carbon fibers through the synergy of raw material pretreatment and blending processes. The low softening point of equiaxed mesophase pitch and the melting characteristics of polyacrylonitrile microspheres work synergistically to broaden the temperature operating range of melt spinning and reduce viscosity fluctuations during the spinning process, thereby reducing fiber defects. At the same time, the uniform blending of the two precursors causes the molecular chains to shrink synergistically during subsequent pre-oxidation and carbonization processes, inhibiting crack formation and laying the microstructural foundation for improving the mechanical properties of carbon fibers.

[0025] This invention uses coal-based pitch as raw material, also known as coal tar pitch. It is a byproduct of coal tar produced during the dry distillation of coal for coking or coal gasification. The residue is left after distillation to remove liquid fractions such as light oil, medium oil, heavy oil, and anthracene oil. It appears as a black block, semi-solid, or viscous liquid with a glossy appearance and a special odor. It can be melted when heated and belongs to a type of artificial pitch.

[0026] In this invention, the high-temperature treatment temperature is 320~420℃, more preferably 350~400℃; specifically, it can be 320℃, 350℃, 380℃, 400℃, 420℃, etc.; the high-temperature treatment time is 1~5h, more preferably 2~4h. The heating rate before reaching the high-temperature treatment temperature is 10~15℃ / min. This invention uses high-temperature treatment to induce intramolecular dehydrogenation condensation of polycyclic aromatic hydrocarbons in coal-based pitch, forming planar aromatic macromolecules through C-C bonds, thus increasing the molecular weight. The high-temperature treatment of this invention is carried out under an inert atmosphere; this invention does not impose special limitations on the inert atmosphere, for example, it can be nitrogen, argon, or other rare gases, or a mixture of these gases. The inert atmosphere can isolate oxygen, inhibit the oxidative dehydrogenation reaction of active hydrogen atoms (-CH3, -CH2- side chains) in pitch, and reduce the generation of oxygen-containing functional groups (such as -COOH, -C=O).

[0027] In this invention, the solvent used for solvent extraction is selected from one or more of toluene, cyclohexane, n-hexane, or xylene; medium molecular weight, non-crystalline mesophase pitch is extracted by solvent extraction. This invention does not impose special limitations on the method of solvent removal, such as drying, vacuum distillation, etc., as long as the solvent removal effect is achieved.

[0028] The hydrogenation catalysis reaction temperature described in this invention is 300~450℃, and the reaction time is 1~5h. This invention does not impose special limitations on the specific hydrogenation catalysis process. Preferably, the hydrogen pressure is controlled at 3~5MPa, and the hydrogenation catalyst can be selected from Ni-Mo / Al2O3, Co-Mo / Al2O3, Ru / C, etc., without special limitations. The hydrogenation catalysis process lowers the softening point of the mesophase pitch to 200~230℃.

[0029] In this invention, the preparation method of the polyacrylonitrile microspheres is as follows: an aqueous phase composition containing methyltrimethoxy modified silica is prepared; an oil phase composition containing acrylonitrile, comonomer, molecular weight regulator and initiator is prepared; then the aqueous phase composition and the oil phase composition are mixed and homogenized, and then a polymerization reaction is carried out; the polymerization product is washed and dried to obtain polyacrylonitrile microspheres.

[0030] The above-mentioned preparation method of the present invention prepares polyacrylonitrile microspheres through aqueous suspension polymerization. The oil phase monomer (dispersed phase) is homogeneously sheared and dispersed into micron-sized droplets. Methyltrimethoxy modified silica (dispersion stabilizer) in the aqueous phase is adsorbed on the surface of the droplets to form a physical barrier to prevent droplet aggregation. Subsequently, the oil phase initiator decomposes to initiate polymerization, and the droplets solidify into independent microspheres. Finally, monodisperse particles are obtained after washing and drying.

[0031] In this invention, the aqueous phase composition consists of water and methyltrimethoxy-modified silica, with a mass fraction of 1-5 wt%. The methyltrimethoxy-modified silica is obtained by reacting methyltrimethoxysilane (MTMS) and silica under the catalysis of triethylamine. Unmodified silica (hydrophilic) is difficult to stabilize oil-phase droplets. After modification with methyltrimethoxysilane, its surface is grafted with hydrophobic methyl groups (-CH3) and reactive methoxy groups (-OCH3), forming an amphiphilic interfacial layer. This layer can adsorb at the oil-water interface, preventing droplet collision and coalescence through interparticle physical repulsion; simultaneously, it reduces the oil-water interfacial tension, making the droplets easier to disperse into smaller droplets during homogeneous shearing.

[0032] This invention does not impose any special restrictions on the preparation method of methyltrimethoxy modified silica. The preferred method is to disperse hydrophilic silica nanospheres in a solvent to obtain a silica suspension; add a mixture of methyltrimethoxysilane (silane coupling agent) and triethylamine (catalyst) to the silica suspension, then heat under reflux, separate the solid and liquid, wash the solid material and dry it to obtain the silica.

[0033] In this invention, the volume ratio of the aqueous phase composition to the oil phase composition is 1:(0.2~0.4), with the aqueous phase serving as the continuous phase to provide sufficient dispersion space for the oil phase droplets.

[0034] In the oil phase composition of the present invention, the comonomer is selected from one or more of styrene, acrylic acid, or acrylamide. The introduction of the comonomer can reduce the polarity of polyacrylonitrile molecules and the melting temperature of polyacrylonitrile, thereby enabling the preparation of blended melts. At the same time, the comonomer can reduce the activation energy of the oxidative cyclization reaction of polyacrylonitrile molecules, making the fiber oxidative cyclization process stable and uniform, improving the heat resistance and structural uniformity of the pre-oxidized fiber, and ultimately promoting the improvement of carbon fiber performance. The mass ratio of acrylonitrile to comonomer is 1: (0.08~0.2).

[0035] In this invention, the molecular weight regulator is selected from one or more of n-dodecylthiol, thioacetic acid, 2-mercaptoethanol, or n-octylthiol; the mass ratio of acrylonitrile to the molecular weight regulator is 1:(0.0005~0.001). The molecular weight of the polyacrylonitrile microspheres is adjusted to a suitable range (molecular weight of 200,000 to 300,000) by the molecular weight regulator.

[0036] In this invention, the initiator is one or more selected from dicumyl peroxide, benzoyl peroxide, or azobisisobutyronitrile; the mass ratio of acrylonitrile to initiator is 1:(0.005~0.01). The above-mentioned initiator is an oil-soluble initiator, which initiates the polymerization reaction of the monomers. It is understood that the initiator is not limited to the initiators provided in this invention, and those skilled in the art can select one according to actual needs.

[0037] In this invention, the mixing and homogenization rotation speed is 6000~12000 rpm, more preferably 8000~12000 rpm; by adjusting the rotation speed, the size of the oil phase droplets can be controlled, thereby controlling the particle size of the formed polyacrylonitrile microspheres.

[0038] The polymerization reaction temperature described in this invention is 70~90℃, and the polymerization reaction time is 5~12h, more preferably 6~10h, to ensure that the monomer is basically completely converted.

[0039] Preferably, in this invention, the melt blending is carried out in a twin-screw extruder mixer at a temperature of 200-230°C for 1-2 hours. After the melt blending is extruded, it is cooled and solidified at a rate of 1-5°C / min to obtain a mesophase asphalt-polyacrylonitrile blend.

[0040] The present invention also provides a blend of mesophase pitch and polyacrylonitrile prepared by the above preparation method.

[0041] The present invention also provides the application of the above-mentioned mesophase pitch and polyacrylonitrile blend in the preparation of pitch-based fibers and / or pitch-based carbon fibers.

[0042] The present invention also provides an asphalt-based fiber, which is obtained by heating and melting the above-mentioned mesophase asphalt and polyacrylonitrile blend, spinning and stretching it, and cooling and curing it.

[0043] This invention does not impose any special restrictions on the specific process of heating and melting, spinning and stretching, and cooling and solidifying to prepare asphalt-based fibers; any method commonly used in the field can be used.

[0044] The present invention also provides a pitch-based carbon fiber, which is obtained by pre-oxidation and carbonization treatment of the above-mentioned pitch-based fiber.

[0045] The present invention does not impose any special restrictions on the specific steps of the pre-oxidation and carbonization treatment; commonly used pre-oxidation and carbonization treatment methods in the art can be used.

[0046] The pitch-based carbon fiber prepared by this invention has a Young's modulus of 300 GPa or more, a tensile strength of 4500 MPa or more, and an elongation at break of 1.2% or more.

[0047] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used. The molecular weights mentioned in the following embodiments are weight-average molecular weights.

[0048] In the following examples, the preparation method of methyltrimethoxy modified silica is as follows: 3g of hydrophilic silica nanospheres with an average particle size of 20nm were dispersed in 80mL of toluene to obtain a silica suspension; a mixture of 9mmol of methyltrimethoxysilane (silane coupling agent) and 9mmol of triethylamine (catalyst) was added to the above silica suspension, and then refluxed at 120℃ for 4h. The solid matter was then separated by centrifugation, washed with toluene, and dried to obtain amphiphilic silica as a suspending agent, namely methyltrimethoxy modified silica, with a contact angle of 90°. Multiple preparations were performed to meet the required amounts in the examples.

[0049] Example 1 This embodiment provides a method for preparing mesophase pitch and polyacrylonitrile blends, pitch-based fibers, and pitch-based carbon fibers.

[0050] (1) Preparation of polyacrylonitrile microspheres: An oil phase composition was prepared by mixing 20g of acrylonitrile, 0.12g of dicumyl peroxide (initiator), 1.6g of styrene (comonomer), and 0.01g of n-dodecyl mercaptan (molecular weight regulator). An aqueous phase composition was prepared by ultrasonically dispersing 4g of methyltrimethoxy modified silica in 100mL of deionized water. The oil and aqueous phase compositions were then mixed and homogenized at 8000rpm to obtain a suspension. The suspension was then heated to 70℃ and stirred at 80rpm for 9 hours to obtain a polyacrylonitrile suspension. After filtration, washing with water, and drying, polyacrylonitrile microspheres were obtained, with a molecular weight of 300,000 and an average particle size of approximately 42μm.

[0051] (2) Preparation of mesophase pitch: Coal-based pitch was placed under a nitrogen atmosphere and heated to 350℃ for 4 hours, then cooled to room temperature. The heated product was then extracted with toluene, and the extract was subjected to rotary evaporation at 50℃ to remove the toluene, yielding a mesophase pitch transition state. This transition state was then subjected to hydrogenation catalysis at a hydrogen pressure of 3 MPa, a reaction temperature of 320℃, and a catalyst of Ni-Mo / Al₂O₃ for 2 hours, yielding mesophase pitch. The obtained mesophase pitch was equiaxed and had a softening point of 225℃.

[0052] (3) Preparation of mesophase pitch and polyacrylonitrile blend: The mesophase pitch from step (2) was heated to 225°C in a nitrogen atmosphere in a twin-screw extruder to obtain mesophase pitch melt. Then, polyacrylonitrile microspheres from step (1) were added, and the mass ratio of mesophase pitch to polyacrylonitrile microspheres was controlled to be 1:1. The mixture was melt-mixed at 225°C and 600 rpm for 1 h, and then uniformly extruded. The mixture was then cooled and solidified in a nitrogen atmosphere at a cooling rate of 2°C / min to obtain the mesophase pitch and polyacrylonitrile blend.

[0053] (4) Preparation of pitch-based fibers: The mesophase asphalt obtained in step (3) is heated to 225°C to melt the polyacrylonitrile blend, and then the asphalt-based fiber is obtained by spinning, stretching, and rapid cooling and solidification.

[0054] (5) Preparation of pitch-based carbon fiber: The pitch-based fibers in step (4) are pre-oxidized and carbonized to obtain pitch-based carbon fibers.

[0055] Example 2 This embodiment provides a method for preparing mesophase pitch and polyacrylonitrile blends, pitch-based fibers, and pitch-based carbon fibers.

[0056] (1) Preparation of polyacrylonitrile microspheres: An oil phase composition was prepared by mixing 20g of acrylonitrile, 0.16g of azobisisobutyronitrile (initiator), 2g of acrylic acid (comonomer), and 0.016g of thioacetic acid (molecular weight regulator). An aqueous phase composition was prepared by ultrasonically dispersing 3g of methyltrimethoxy-modified silica in 100mL of deionized water. The oil and aqueous phase compositions were then mixed and homogenized at 10,000 rpm to obtain a suspension. The suspension was then heated to 80℃ and stirred at 80 rpm for 7 hours to obtain a polyacrylonitrile suspension. After filtration, washing with water, and drying, polyacrylonitrile microspheres were obtained, with a molecular weight of 260,000 and an average particle size of 26μm.

[0057] (2) Preparation of mesophase pitch: Coal-based pitch was placed under a nitrogen atmosphere and heated to 380℃ for 3 hours, then cooled to room temperature. The heated product was then extracted with cyclohexane, and the extract was subjected to rotary evaporation at 55℃ to remove cyclohexane, yielding an intermediate pitch transition state. This intermediate pitch was then subjected to hydrogenation catalysis at a hydrogen pressure of 4 MPa, a reaction temperature of 380℃, and a catalyst of Co-Mo / Al₂O₃ for 2 hours, yielding an equiaxed mesophase pitch with a softening point of 210℃.

[0058] (3) Preparation of mesophase pitch and polyacrylonitrile blend: The mesophase pitch from step (2) was heated to 210°C in a nitrogen atmosphere in a twin-screw extruder to obtain mesophase pitch melt. Then, polyacrylonitrile microspheres from step (1) were added, and the mass ratio of mesophase pitch to polyacrylonitrile microspheres was controlled to be 1.2:1. The mixture was melt-mixed at 210°C and 400 rpm for 1.5 h, and then uniformly extruded. The mixture was then cooled and solidified in a nitrogen atmosphere at a cooling rate of 3°C / min to obtain the mesophase pitch and polyacrylonitrile blend.

[0059] (4) Preparation of pitch-based fibers: The mesophase asphalt obtained in step (3) is heated to 210°C to melt with polyacrylonitrile, and then asphalt-based fibers are obtained by spinning, stretching, and rapid cooling and solidification.

[0060] (5) Preparation of pitch-based carbon fiber: The pitch-based fibers in step (4) are pre-oxidized and carbonized to obtain pitch-based carbon fibers.

[0061] Example 3 This embodiment provides a method for preparing mesophase pitch and polyacrylonitrile blends, pitch-based fibers, and pitch-based carbon fibers.

[0062] (1) Preparation of polyacrylonitrile microspheres: An oil phase composition was prepared by mixing 20g of acrylonitrile, 0.2g of azobisisobutyronitrile (initiator), 4g of acrylamide (comonomer), and 0.02g of thioacetic acid (molecular weight regulator). An aqueous phase composition was prepared by ultrasonically dispersing 2g of methyltrimethoxy-modified silica in 100mL of deionized water. The oil and aqueous phase compositions were then mixed and homogenized at 12000rpm to obtain a suspension. The suspension was then heated to 90℃ and stirred at 80rpm for 6 hours to obtain a polyacrylonitrile suspension. After filtration, washing with water, and drying, polyacrylonitrile microspheres were obtained, with a molecular weight of 200,000 and an average particle size of 15μm.

[0063] (2) Preparation of mesophase pitch: Coal-based pitch was placed under a nitrogen atmosphere and heated to 400℃ for 2 hours, then cooled to room temperature. The heated product was then extracted with xylene, and the extract was subjected to rotary evaporation at 60℃ to remove xylene, yielding an intermediate pitch transition state. This intermediate pitch transition state was then subjected to hydrogenation catalytic treatment at a hydrogen pressure of 5 MPa, a reaction temperature of 450℃, a Ru / C catalyst, and a reaction time of 2 hours, yielding an equiaxed mesophase pitch with a softening point of 203℃.

[0064] (3) Preparation of mesophase pitch and polyacrylonitrile blend: The mesophase pitch from step (2) was heated to 203°C in a nitrogen atmosphere in a twin-screw extruder to obtain mesophase pitch melt. Then, polyacrylonitrile microspheres from step (1) were added, and the mass ratio of mesophase pitch to polyacrylonitrile microspheres was controlled to be 1.5:1. The mixture was melt-mixed at 203°C and 300 rpm for 2 hours, and then uniformly extruded. The mixture was then cooled and solidified in a nitrogen atmosphere at a cooling rate of 4°C / min to obtain the mesophase pitch and polyacrylonitrile blend.

[0065] (4) Preparation of pitch-based fibers: The mesophase asphalt obtained in step (3) is heated to 203°C to melt the polyacrylonitrile blend, and then the asphalt-based fiber is obtained by spinning, stretching, and rapid cooling and solidification.

[0066] (5) Preparation of pitch-based carbon fiber: The pitch-based fibers in step (4) are pre-oxidized and carbonized to obtain pitch-based carbon fibers.

[0067] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not contain polyacrylonitrile microspheres.

[0068] Coal-based pitch was placed in a nitrogen atmosphere and heated to 350℃ for 4 hours, then cooled to room temperature. The heated product was then extracted with toluene, and the extract was subjected to rotary evaporation at 50℃ to remove the toluene, yielding a mesophase pitch transition state. This transition state was then subjected to hydrogenation catalytic treatment at a hydrogen pressure of 3 MPa, a reaction temperature of 320℃, and a catalyst of Ni-Mo / Al₂O₃ for 2 hours, yielding the mesophase pitch. The mesophase pitch was heated to 225℃ and then shaped by spinneret drawing and rapid cooling to solidify, producing pitch-based fibers. These fibers were then pre-oxidized and carbonized to obtain pitch-based carbon fibers.

[0069] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example does not contain mesophase pitch.

[0070] The polyacrylonitrile microspheres from Example 1 were heated to 225°C, and polyacrylonitrile-based fibers were obtained by spinning, stretching, and rapid cooling and curing. Then, the polyacrylonitrile-based fibers were subjected to pre-oxidation and carbonization treatments to obtain polyacrylonitrile-based carbon fibers.

[0071] Comparative Example 3 The difference between this comparative example and Example 1 is that commercially available polyacrylonitrile resin is used instead of polyacrylonitrile microspheres in this comparative example, while the other conditions and preparation methods are the same as in Example 1.

[0072] Comparative Example 4 The difference between this comparative example and Example 1 is that no hydrogenation catalysis is performed in step (2) of this comparative example, while the other conditions and preparation methods are the same as those in Example 1.

[0073] Comparative Example 5 The difference between this comparative example and Example 1 is that in step (1) of this comparative example, the rotation speed of the homogenization process is 3000 rpm, and the average particle size of the resulting polyacrylonitrile microspheres is 100 μm.

[0074] Test case The properties of the fibers and carbon fibers obtained in Examples 1-3 and Comparative Examples 1-5 were measured, and the test results are summarized in Table 1.

[0075] Table 1. Performance test results of fibers and carbon fibers obtained in Examples 1-3 and Comparative Examples 1-5

[0076] Examples 1-3 of this invention introduce polyacrylonitrile microspheres to prepare a blend of mesophase pitch and polyacrylonitrile, which is then subjected to low-temperature melt spinning, pre-oxidation treatment, and carbonization treatment to obtain carbon fibers. Comparative Example 1, on the other hand, involves equiaxed mesophase pitch spinning, pre-oxidation treatment, and carbonization treatment to obtain carbon fibers. As can be seen from Table 1, due to the presence of polyacrylonitrile, the tensile strength of the pitch-based fibers prepared in Examples 1-3 of this invention, as well as the tensile strength and elongation at break of the pitch-based carbon fibers, are significantly improved compared to Comparative Example 1, while maintaining a high modulus.

[0077] Compared with Comparative Example 2, Examples 1-3 of the present invention introduced mesophase pitch during the preparation process. The Young's modulus of the pitch-based fibers and pitch-based carbon fibers in Examples 1-3 was significantly improved, while the strength remained at a high level. This indicates that the introduction of mesophase pitch allows the final carbon fibers to combine the advantages of both polyacrylonitrile-based carbon fibers and pitch-based carbon fibers, namely, high strength and high modulus properties.

[0078] Examples 1-3 of this invention introduce polyacrylonitrile microspheres, which differ from the introduction of general polyacrylonitrile resin in Comparative Example 3. This design is based on the matching between the interfacial energy of the two phases and the rheological behavior of the melt. Under the same process parameters, the tensile strength of the prepared pitch-based carbon fiber is significantly improved, while the Young's modulus remains at a high level.

[0079] Compared with Comparative Example 4, Examples 1-3 of the present invention introduce mesophase pitch after hydrogenation catalysis to optimize the thermodynamic compatibility and processing adaptability of the two fiber precursors. Under the same process parameters, although the Young's modulus of the fiber is slightly reduced due to the weakening of molecular orientation after hydrogenation catalysis, the tensile strength of pitch-based fiber and pitch-based carbon fiber is significantly improved.

[0080] The polyacrylonitrile microspheres introduced in Comparative Example 5 are around 100 μm in size. Their interfacial energy with the intermediate pitch phases has a poorer match with the melt rheological behavior. Compared with Example 1, the properties such as Young's modulus and tensile strength of pitch-based fibers and pitch-based carbon fibers are affected to some extent.

[0081] In summary, this invention achieves uniform dispersion and optimized interfacial bonding of the two precursors by preparing mesophase pitch through high-temperature treatment, solvent extraction, and hydrogenation catalysis of coal-based pitch, followed by melt blending with polyacrylonitrile microspheres of specific particle size and molecular weight. The prepared pitch-based carbon fiber exhibits significantly improved overall performance, with a tensile strength exceeding 4500 MPa and an elongation at break exceeding 1.2%, while maintaining a high modulus exceeding 300 GPa and a thermal conductivity exceeding 55 W / (m·K). This effectively addresses the shortcomings of traditional pitch-based carbon fibers, such as low strength and brittleness, expanding their application potential in high-performance load-bearing structures.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a blend of mesophase pitch and polyacrylonitrile, characterized in that, Includes the following steps: Coal-based pitch is subjected to high-temperature treatment, followed by solvent extraction, solvent removal, and hydrogenation catalysis to prepare mesophase pitch. Mesophase pitch is heated to 200-230°C under an inert atmosphere, and then polyacrylonitrile microspheres are added and melt-blended to obtain a blend of mesophase pitch and polyacrylonitrile. The polyacrylonitrile microspheres have an average particle size of 10-50 μm and a molecular weight of 200,000-300,000; the mass ratio of mesophase pitch to polyacrylonitrile microspheres is (1-1.5):

1.

2. The preparation method according to claim 1, characterized in that, The high-temperature treatment is performed at a temperature of 320~420℃ for 1~5 hours; the high-temperature treatment is carried out under an inert atmosphere. The solvent used in the solvent extraction is selected from one or more of toluene, cyclohexane, n-hexane, or xylene; The hydrogenation catalysis reaction temperature is 300~450℃, and the reaction time is 1~5h; The softening point of the mesophase asphalt is 200~230℃; the melt blending time is 1~2h.

3. The preparation method according to claim 1, characterized in that, The preparation method of the polyacrylonitrile microspheres is as follows: an aqueous phase composition containing methyltrimethoxy modified silica is prepared; an oil phase composition containing acrylonitrile, comonomer, molecular weight regulator and initiator is prepared; the aqueous phase composition and the oil phase composition are then mixed and homogenized, and then a polymerization reaction is carried out. The polymerization product is washed and dried to obtain polyacrylonitrile microspheres.

4. The preparation method according to claim 3, characterized in that, In the aqueous phase composition, the mass fraction of methyltrimethoxy modified silica is 1~5wt%, and the methyltrimethoxy modified silica is obtained by reacting methyltrimethoxysilane and silica under the catalysis of triethylamine; the volume ratio of the aqueous phase composition to the oil phase composition is 1:(0.2~0.4).

5. The preparation method according to claim 3, characterized in that, In the oil phase composition, the comonomer is selected from one or more of styrene, acrylic acid, or acrylamide; the mass ratio of acrylonitrile to comonomer is 1:(0.08~0.2). The molecular weight regulator is selected from one or more of n-dodecyl mercaptan, thioacetic acid, 2-mercaptoethanol, or n-octyl mercaptan; the mass ratio of acrylonitrile to the molecular weight regulator is 1: (0.0005~0.001); The initiator is one or more of dicumyl peroxide, benzoyl peroxide, or azobisisobutyronitrile; the mass ratio of acrylonitrile to initiator is 1:(0.005~0.01).

6. The preparation method according to claim 3, characterized in that, The mixing and homogenization rotation speed is 6000~12000 rpm; the polymerization reaction temperature is 70~90℃, and the polymerization reaction time is 5~12h.

7. The mesophase pitch and polyacrylonitrile blend prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the mesophase pitch and polyacrylonitrile blend as described in claim 7 in the preparation of pitch-based fibers and / or pitch-based carbon fibers.

9. A pitch-based fiber, characterized in that, It is prepared by heating and melting the mesophase pitch and polyacrylonitrile blend as described in claim 7, spinning and stretching it into shape, and then cooling and curing it.

10. A pitch-based carbon fiber, characterized in that, It is prepared by pre-oxidation and carbonization treatment of the pitch-based fiber as described in claim 9.

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