Method of forming polyacrylonitrile polymer by melt process

Abstract

The invention relates to a method for providing a polyacrylonitrile polymer with thermoplastic properties, due to the structure of the polyacrylonitrile polymer, the decomposition temperature of which is lower than the theoretical melting temperature, and by means of which the polyacrylonitrile polymer can be molded by means of a melting process, thereby obtaining significant advantages in the existing fiber production processes and increasing the usability of the polyacrylonitrile polymer in different industries. The method is different from conventional production methods such as a dry method, a wet method or gas injection known in the field.

Description

Technical Field

[0001] This invention relates to a method for providing thermoplastic properties to polyacrylonitrile polymers. Due to the structure of polyacrylonitrile polymers, their decomposition temperature is lower than the theoretical melting temperature. This characteristic enables them to be molded by melt molding, thereby gaining significant advantages over existing fiber production processes and improving their availability in various industries, unlike traditional production methods such as dry processes, wet processes, or air jetting known in the art. Background Technology

[0002] Polyacrylonitrile (PAN) is a synthetic polymer. PAN is obtained through the polymerization of monomers containing nitrile groups. PAN is an important component in the production of low-density, high-temperature resistant fibers. PAN possesses good strength, high-temperature resistance, UV resistance, and chemical resistance. Due to these properties, it is widely used in many technical fields, such as fiber production in the textile industry, technical textiles, filtration systems, the automotive industry, and cable coating or paint industries.

[0003] The theoretical melting temperature of PAN is approximately 317°C (603°F). As is known in the art, PAN undergoes thermal decomposition before reaching its melting point. When exposed to air under atmospheric conditions, PAN thermally decomposes at approximately 200°C (392°F). Therefore, it is important to distinguish between its melting point and decomposition point during heat treatment.

[0004] Due to this structural characteristic, PAN is typically produced using traditional dry, wet, or dry-jet wet-spinning methods. PAN is not a thermoplastic, meaning it cannot be softened, remolded, or recycled, which necessitates stringent heat treatment during production and a difficult recycling process. Therefore, in related technical fields, PAN is a material that is not easily molded using simple, low-cost production methods such as extrusion and injection molding.

[0005] However, in this technical field, some research and development work has been carried out in order to provide thermoplastic properties in addition to the above-mentioned properties of PAN.

[0006] One of the studies is patent application number US2011 / 0024939A1, which relates to applying a two-step plasticizing process to impart thermoplastic properties to PAN. In the first process step, plasticizing takes place in an extruder, while in the second process step, PAN is shaped into the desired product. In this invention, glycerol is used as the primary plasticizing component, and triethylene glycol and monoethylene glycol are used as auxiliary plasticizers. As auxiliary chemicals, 3-chloro-1,2-propanediol, 1,3-dichloro-2-propanol, diethylene glycol (DEG), 2,3-chloro-1,2-propanediol, and sulfuric acid are used in all formulations in varying weight proportions. The proportions of these chemicals used are as follows:

[0007] Formula 1: 240g PAN (6% vinyl acetate (VA), Mw: 130,000g / mol) with 100g glycerin and 50g triethylene glycol (TEG); Formula 2: 240g PAN (6% VA, Mw: 130,000g / mol) with 120g glycerin and 40g ethylene glycol (MEG); Formula 3: 240g PAN (6% VA, Mw: 130,000g / mol) using 100g glycerin, 30g MEG, and 20g DEG; Formula 4: 240g PAN (20% MA, Mw: 160,000g / mol) with 100g glycerin and 60g MEG; Formula 5: 240g PAN (20% MA, Mw: 160,000g / mol) using 150g glycerol, 50g MEG, and 30g polyvinylidene fluoride (PVDF). Formula 6: 240g PAN (6% VA, Mw: 130,000g / mol) with 60g glycerin and 110g TEG.

[0008] In the formulation sharing, the amount of chemical compounds used in the process steps is at least 62.5% of the PAN weight. From this perspective, it can be seen that the amount of auxiliary chemicals used is far higher than in thermoplastic production, and due to the excessive plasticizer, this production method will become a major drawback.

[0009] Another research in this technical field is patent application number US3488336. The subject of this patent relates to a scheme for lowering the melting point by synthesizing low molecular weight PAN. To this end, the melting temperature is lowered by synthesizing PAN with a molecular weight between 9000 and 20000 g / mol, thereby achieving a PAN with a thermoplastic structure. However, the strength value of thermoplastic PAN with this molecular weight is insufficient.

[0010] Another study is patent application number WO03 / 009991A1. Within the scope of this patent, PAN is mixed with ethylene carbonate in a 60 / 40% ratio, extruded and plasticized at 160–175°C, and cooled to 110–135°C at the extruder exit to produce fibers that achieve mechanical strength through stretching. This patent attempts to maintain a low temperature during production to prevent EC evaporation, thus making fiber production more stable. Furthermore, a unique manifold design is provided for effectively cooling the fibers produced at the extruder exit. Within the scope of this invention, ethylene carbonate is used as a raw material. As is known in the art, ethylene carbonate has adverse environmental and process effects when used as a plasticizer.

[0011] Therefore, it is anticipated that by addressing existing technical problems and shortcomings in related technological fields and ensuring the thermoplastic properties of PAN, technical solutions and advantages can be provided to these fields, thereby achieving significant advantages in existing fiber production processes and improving its usability in various industries. Summary of the Invention The characteristic that distinguishes PAN from other thermoplastic or thermosetting polymers is the strong bonding between nitrile groups in its microstructure. It is known that in fibrillary structures with irregular amorphous and crystalline regions, PAN has more crystalline regions than amorphous regions, and the interactions of nitrile groups in these crystalline regions form a helical structure. This strong interaction causes PAN to decompose before melting. It has been determined that these strong structures formed by the interactions of nitrile groups can prevent the aforementioned decomposition by reducing the interactions between nitrile groups. To achieve this, research in related technical fields has focused on increasing the distance between nitrile groups in PAN by using external or internal plasticizers, thereby enabling the PAN polymer to melt without decomposition.

[0012] In existing technologies, plasticizers or other auxiliary components are used in high weight ratios in the formulation to impart thermoplastic properties to PAN. Using chemical compounds at such high weight ratios negatively impacts the strength and other properties of PAN. Furthermore, using these chemicals at such high weight ratios results in high processing time and costs for producing thermoplastic PAN.

[0013] In this regard, the present invention proposes a method for producing thermoplastic PAN in which high weight ratios of plasticizers or other chemicals are not required.

[0014] In existing technologies, to impart thermoplastic properties to PAN, premixes need to be prepared at high temperatures for extended periods during production. Clearly, production methods with this preparation process result in high costs, labor intensity, and a large carbon footprint.

[0015] In this invention, a method for producing thermoplastic PAN is proposed, wherein the process steps are carried out at low temperature and for a short time. Detailed Implementation

[0016] In this detailed description, the subject matter of the invention relates to a method for producing PAN with thermoplastic properties, and is explained only by way of examples that do not have any limiting effect in order to better understand the subject matter.

[0017] The method of the present invention includes two basic process steps. The first step is to produce an intermediate product in powder form through a plasticizing process, and the second step is to convert the intermediate product in plasticized granule form into PAN with thermoplastic properties.

[0018] i) Plasticizing process The method of the present invention preferably comprises at least one plasticizing compound for the plasticizing process. The function of the plasticizing compound is to increase the distance between the nitrile groups involved in the PAN chain and weaken their interactions. To achieve this, the method includes at least one selected from the group consisting of polyethylene glycol, ethylene glycol, propylene glycol, glycerol, low molecular weight polyethylene or polypropylene wax derivatives, fatty acids (such as dioctyl phthalate (DOP), dioctyl terephthalate (DOTP), stearic acid, and lauric acid), organic acid esters, various cellulose derivatives, and oil derivatives (such as palm oil or soybean oil) as a plasticizer.

[0019] In a preferred embodiment of the invention, glycerol is used as a plasticizer. By including a specified amount of glycerol, components with no environmental toxicity can be used to obtain the final product, while providing the intended technical solutions and advantages.

[0020] In a preferred embodiment of the invention, the plasticizer used in the plasticizing process is dissolved in at least one solvent to obtain a solution or mixture. Here, the solvent provides gaps between the strong chains in the PAN plasticizer. In this way, at least one plasticizer polymer can be included in the functional groups between the chain gaps induced by the solution. To achieve this objective, the method of the present invention comprises at least one of N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), N,N-dimethylformamide (DMF), propylene carbonate, ethylene carbonate, diethyl ether, dimethyl sulfoxide (DMSO), or N-methyl-2-pyrrolidone (NMP) as a solvent.

[0021] In a preferred embodiment, the mixture of at least one solvent and at least one plasticizer comprises at least one plasticizer in an amount of 2% to 8% (by weight). The main function of the plasticizer is to intercalate between polymer chains, making it easier for the chains to move relative to each other. If the amount of plasticizer is less than a specified amount, the chain interfaces cannot be coated, and the flowability cannot be promoted. If the amount of plasticizer exceeds a specified amount, the mechanical properties and viscosity will be lower than the desired levels. The fibers cannot be stretched, or even if they can be stretched, sufficient stretch cannot be provided. Therefore, the amount of plasticizer must be maintained within a specified range.

[0022] In a preferred embodiment, the mixture of at least one solvent and at least one plasticizer contains at least 10% to 28% (by weight) of solvent. On the other hand, the solvent system opens the gaps between polymer chains, allowing the mixture containing the plasticizer to enter the region where it functions. If the solvent structure is sufficiently coordinated but the quantity is insufficient, even if too much plasticizer is added, the plasticizer cannot penetrate between the chains, thus failing to achieve the desired properties. If the amount of solvent exceeds a specified limit, mechanical properties and fiber tensile strength will be lost. Therefore, the solvent system mixture must also be optimized within a specified ratio.

[0023] In a preferred embodiment of the invention, propylene carbonate is used as a solvent. By adding propylene carbonate in a specific amount, it is possible to use environmentally non-toxic components in the final product while providing the intended technical solutions and advantages.

[0024] In a preferred embodiment, the solvent-plasticizer mixture contains at least one stabilizer. The stabilizer improves the thermal stability of the mixture.

[0025] In a preferred embodiment, the mixture of at least one solvent and at least one plasticizer contains at least one antioxidant. The antioxidant improves the oxygen tolerance of the production process steps and the finished product.

[0026] The total amount of antioxidants and stabilizers in the mixture is between 1% and 2% by weight.

[0027] The mixture contains a PAN copolymer used to obtain the PAN polymer. The comonomer used to produce the copolymer is obtained by using one of vinyl methacrylate, vinyl acetate, itaconic acid, vinylidene chloride (VDC), or vinyl acetate (VAM). In a preferred embodiment, the PAN copolymer contains 1% to 15% by weight of VA (vinyl acetate).

[0028] In the most preferred embodiment, the mixture used in the production process for thermoplastic PAN comprises at least one plasticizer, at least one solvent, at least one stabilizer, at least one antioxidant, and a PAN copolymer.

[0029] In the most preferred embodiment, the mixture used in the production process for thermoplastic PAN comprises at least one plasticizer in a weight percentage of 3% to 6%, at least one solvent in a weight percentage of 10% to 28%, at least one stabilizer and at least one antioxidant in a total weight percentage of 1% to 2%, and the balance being PAN copolymer.

[0030] It is anticipated that the most important part of this invention is obtaining a mixture for subsequent processes. The components in the mixture and their weight proportions were determined after optimization studies. Therefore, this mixture can also be considered as a raw material for all processes.

[0031] Another innovation of this invention lies in the arrangement of the processing environment. The preferred processing medium is a twin-screw extruder. All vents and gas outlets within the twin-screw extruder are closed. This creates a completely isolated and specially arranged environment. The technical solution involves evaporating the solvent in the mixture and effectively mixing the vapors generated in the twin-screw extrusion system into the PAN chains. This efficient solvent mixing ensures greater penetration into the PAN chains. Due to all these arrangements, the plasticizing process can be performed in the processing medium without prolonged heating or extremely high temperatures.

[0032] In addition to the arrangement within the processing medium, the process temperature must be applied in the extrusion system with a gradually increasing temperature profile ranging from 90°C to 190°C to transform the mixture into a granular intermediate product. The temperature should be kept low to prevent the dry mixture consisting of PAN, solvent system, plasticizer system, and additives from becoming viscous or clumping, and to ensure that the product is easily removed from the feed section of the extruder. On the other hand, the melting point of the product is determined by methods such as dynamic mechanical analysis (DMA) or differential scanning calorimetry (DSC), and the process should be confined to this temperature range.

[0033] Due to the optimization of the mixture and arrangement in the processing medium, the method of the present invention can use chemicals such as plasticizers, antioxidants, and stabilizers, as well as solvents, at a lower weight ratio. As is known in the art, using high weight ratios of chemicals in the mixtures for preparing thermoplastic PAN, and performing these processes at high temperatures for extended periods, can introduce technical problems into the plasticizing process. The method of the present invention eliminates these technical disadvantages.

[0034] Through the entire process, a plasticized intermediate product can be obtained. The next step is to transform the plasticized intermediate product into the final product PAN.

[0035] ii) Converting plasticizing intermediates into the final product PAN In this process step, the processing medium is provided with an arrangement for obtaining the final product, thermoplastic PAN, from the plasticizing intermediate.

[0036] Therefore, a single-screw extrusion system is used as the process medium, and then a melt pump extrusion system is integrated into this single-screw extrusion system.

[0037] Another configuration option is to use an extrusion system as the process medium, which is integrated into a melt pump single-screw extrusion system. This melt pump single-screw extrusion system will have a fixed output rate and will work in conjunction with a pressure sensor located at the extruder head to fix the pressure and maintain a constant production rate.

[0038] The temperature of the processing medium is preferably between 150 and 250°C. If the operating temperature is below these values, the required mechanical strength cannot be achieved; if the temperature exceeds these values, there is a risk of decomposition.

[0039] Extrusion processes can produce at a constant speed.

[0040] After the extrusion process, the final product is preferably spun at the extruder outlet. During this process, a conventional fiber drawing head located at the extruder outlet is used, employing a channel through which the melt advances after exiting the drawing head. The temperature of this channel is constant, ranging from 100°C to 120°C. By applying additional temperature to the channel, the product is prevented from solidifying rapidly, thus achieving a very high spinning rate in the first spinning stage. Without this temperature, the fibrous product would solidify quickly, making the spinning process difficult, especially due to the high interaction of the nitrile groups. Increasing force to ensure the spinning process can lead to fiber breakage or permanent deformation. At higher temperatures, melting is likely to occur, causing fiber breakage; therefore, the sample must remain unmelted at this temperature, and the fiber should be at an optimal temperature to allow for stretching.

[0041] After the spinning process, it is best to stretch and cool the final product. The spinning process largely determines the quality of the final product. The stretching process in the other rollers is carried out at a lower speed and without applying additional temperature. Stretching at speeds ranging from 5% to 300% at each stage yields the final product.

[0042] In the method of the present invention, during the extrusion process used in step ii), the provided stretching speed is 10 to 2000 times the fiber exit speed and the resulting product. The rapid stretching parameters are determined based on the product's strength, elongation at break, crystallinity, and fineness values, depending on the resulting product.

[0043] The thermoplastic PAN obtained by performing process steps i) and ii) can be used as a raw material for the production of fibers, low-density polyethylene, and various elastomers. It can also be used to produce PAN-based products with medium hardness and mechanical strength properties, as well as high hardness and high mechanical strength properties. By arranging process step ii), the final product can be obtained from products belonging to the above categories.

[0044] If desired, bio-based thermoplastic PAN products can be obtained by using bio-based raw materials as feedstocks in the synthesis of PAN polymers.

[0045] Due to the optimized process steps of this invention, the amount of chemicals required to obtain thermoplastic PAN can be lower. Unlike known production methods in the art, this invention can use other chemical compounds besides PAN copolymers, and in lower weight proportions.

[0046] The thermoplastic PAN obtained by the method of this invention can be combined with other plastic materials known in the art, thereby enabling the production of new materials in the form of mixtures. In this case, the thermoplastic PAN can be mixed with other materials to be used in a certain weight ratio according to the chemical and physical properties of the product to be obtained. Other materials mentioned herein may be at least one of the following: polypropylene (PP), polyethylene (PE), polystyrene (PS), polycarbonate (PC), polyurethane (PU), acrylonitrile-butadiene-styrene copolymer (ABS), polymethyl methacrylate (PMMA), and polyethylene terephthalate (PET).

[0047] Depending on the desired final product, the thermoplastic PAN obtained by the method of the present invention may contain a mixture of one or more additives, such as heat stabilizers, light stabilizers, antibacterial agents, antiviral agents, deodorants, biocides, conductive enhancers, antioxidants, pigments, plasticizers, and antifungal agents.

[0048] To improve the chemical and physical properties of the obtained thermoplastic PAN, such as flame retardancy, strength, and moisture retention, other compounds may be added to the process steps of the production method of the present invention.

[0049] The method of this invention can yield thermoplastic PAN. The resulting thermoplastic PAN can be used as a raw material in the production of products across multiple industries. These industries include, but are not limited to, the automotive, textile, food, aerospace, 3D printing tool manufacturing, agricultural, packaging, and food industries.

[0050] The thermoplastic PAN obtained in this invention can also be used as a raw material for the production of underwear and outerwear products, fibers, interior decorations, carpets, outdoor textiles, carbon fibers, water and air filters, medical devices and implants, food and other packaging materials, hoses and similar tools and hardware, electrical insulation materials, vehicle interior and exterior parts in the automotive industry, self-reinforcing thermoplastics and bioplastics.

[0051] According to the method features of the present invention, the use of raw materials can be reduced due to the configuration of the processing media. Because of the lower consumption of these raw materials, a final product with less environmental impact can be obtained at a lower cost.

[0052] According to the method features of the present invention, due to the configuration of the processing media, the process steps can be completed in a short time. This helps to reduce labor and costs.

[0053] According to the method features of this invention, due to the configuration of the processing medium, components such as glycerin and propylene carbonate can be used. This reduces the carbon footprint of the final product, making it an environmentally friendly product.

[0054] According to the method features of the present invention, the plasticizing process can be carried out at low temperatures due to the configuration of the processing medium. This ensures that the product achieves thermoplasticity without decomposition, while avoiding high costs.

[0055] The scope of protection of this invention is clearly defined in the appended claims and is not limited to the description provided herein for illustrative purposes. Clearly, those skilled in the art can propose similar structures based on the foregoing without departing from the subject matter of this invention.

Claims

1. A method for providing thermoplastic properties to a polyacrylonitrile polymer, said polymer having a decomposition temperature below its theoretical melting temperature due to its structure, characterized in that, The process includes the following steps: - A mixture is obtained by dissolving at least one solvent and at least one plasticizer. - Add polyacrylonitrile copolymer to the resulting mixture. - The mixture obtained after adding the polyacrylonitrile copolymer is fed into a twin-screw extruder with all vents and outlets closed, and a plasticized intermediate product is obtained by extrusion at a temperature of 90°C to 190°C. - The resulting plasticized intermediate product is fed into a single-screw extruder and extruded at a temperature of 150°C to 250°C. - After the plastic product leaves the die head, it undergoes a spinning operation in a constant-temperature channel together with a conventional fiber drawing head located at the outlet of the extrusion system, with the temperature adjusted to between 100°C and 120°C. - Stretching treatment is applied to the spun plasticized products. - Apply cooling technology.

2. The method according to claim 1, characterized in that, The method includes using at least one of dimethylacetamide, tetrahydrofuran, dimethylformamide, propylene carbonate, ethylene carbonate, diethyl ether, dimethyl sulfoxide, and N-methyl-2-pyrrolidone as a solvent.

3. The method according to claim 2, characterized in that, The solvent is propylene carbonate.

4. The method according to any one of claims 1 to 3, characterized in that, The method includes using polyethylene glycol, ethylene glycol, propylene glycol, glycerin, low molecular weight polyethylene or polypropylene wax derivatives, dioctyl phthalate, dioctyl terephthalate, stearic acid, lauric acid, organic acid esters, cellulose, palm oil and / or soybean oil as plasticizers.

5. The method according to claim 4, characterized in that, The plasticizer is glycerin.

6. The method according to any one of the preceding claims, characterized in that, The plasticizer content in the mixture is 2% to 8% by weight.

7. The method according to any one of the preceding claims, characterized in that, The solvent content in the mixture is 10% to 28% by weight.

8. The method according to any one of the preceding claims, characterized in that, The mixture includes at least one stabilizer and / or at least one antioxidant.

9. The method according to claim 8, characterized in that, The stabilizer and antioxidant in the mixture are present in an amount of 1% to 2% of the total weight.

10. The method according to claim 9, characterized in that, The mixture comprises at least one plasticizer, at least one solvent, at least one stabilizer, at least one antioxidant, and a polyacrylonitrile copolymer, wherein the plasticizer is present in a content of 3% to 6% by weight, the solvent is present in a content of 10% to 28% by weight, the stabilizer and the antioxidant are present in a content of 1% to 2% by weight, and the balance is the polyacrylonitrile copolymer.

11. The method according to any one of the preceding claims, characterized in that, The wire drawing speed in the wire drawing head is between 10 and 2000 times.

12. The method according to any one of the preceding claims, characterized in that, The stretching process is performed by applying a stretch of 5% to 300% at each stage.

13. A polyacrylonitrile polymer with thermoplastic properties, obtained by the method according to any one of the preceding claims.

14. The polyacrylonitrile polymer according to claim 13, comprising 1% to 15% vinyl acetate by weight.

15. The use of the polyacrylonitrile polymer according to claim 13 or 14 as a raw material in the production of underwear and outerwear products, fibers, interior decorations, carpets, outdoor textiles, carbon fibers, water and air filters, medical devices and implants, food and other packaging, hoses and similar tools and hardware, electrical insulation materials, vehicle interior and exterior parts in the automotive industry, self-reinforcing thermoplastics and bioplastic materials.

16. Use of the polyacrylonitrile polymer according to any one of claims 13 to 15 in the production of a polymer-based material, wherein the polymer-based material is prepared by mixing the polyacrylonitrile polymer with at least one polymer material selected from the group consisting of polypropylene, polyethylene, polystyrene, polycarbonate, polyurethane, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate and polyethylene terephthalate.