Full-biodegradable material based on carbon fibers and preparation method of full-biodegradable material

Abstract

The invention provides a full-biodegradable material based on carbon fibers and a preparation method of the full-biodegradable material. The full-biodegradable material comprises the following raw materials in parts by mass: 100 parts of polylactic acid, 15-30 parts of poly (butylene adipate-co-terephthalate), 5-15 parts of modified bio-based carbon fibers, 1-5 parts of a plasticizer and 0.1-1 part of an antioxidant. Wherein the modified bio-based carbon fiber is obtained by carbonizing soluble metal salt and nitrogen-containing compound modified plant fiber. By introducing the plant-derived carbon fibers which are synergistically modified by the metal salt and the nitrogen-containing compound, the interface bonding capacity of a reinforcement phase and biodegradable polymers such as polylactic acid is remarkably improved, the mechanical property and the structural stability of the composite material are improved, and meanwhile, it is ensured that the system has good biodegradation synergy.

Description

Technical Field

[0001] The present application belongs to the technical field of polymer materials, and specifically relates to a fully biodegradable material based on carbon fiber and a preparation method thereof. Background Art

[0002] Carbon fiber is widely used in high-performance composite materials such as aerospace, automobiles, and electronics due to its excellent specific strength, specific modulus, and thermal stability. Introducing carbon fiber into polymer matrix materials can significantly improve their mechanical properties, dimensional stability, and heat resistance. However, traditional carbon fibers are mostly made from polyacrylonitrile (PAN) or asphalt as precursors and are carbonized in a high-temperature inert atmosphere. Not only is the preparation process energy-intensive and environmentally burdensome, but the resulting carbon fibers are dense and stable in structure and extremely difficult to degrade under natural conditions, limiting their application in sustainable development and environmentally friendly material systems.

[0003] On the other hand, in recent years, biodegradable polymers (such as polylactic acid, polybutylene adipate / terephthalate, etc.) have gradually attracted attention as environmentally friendly materials. However, the mechanical properties, thermal stability, and barrier properties of these materials are generally low, making it difficult to meet the requirements of structural materials or high-load applications. Therefore, researchers generally try to introduce carbon fibers into biodegradable polymer systems to construct composite structures that are both "degradable" and "high-performance."

[0004] However, there are still some problems when introducing carbon fiber as a reinforcing phase into degradable polymers in the existing technology. For example, the traditional carbon fiber has a low content of surface functional groups and weak polarity, and lacks effective interfacial bonding with the biodegradable polymer, resulting in problems such as interface peeling and delamination, which seriously affect the overall performance of the composite material; conventional carbon fiber itself is non-degradable and remains in the soil, compost or ocean for a long time, and easily forms microfiber pollution after the composite material is degraded, making it impossible to achieve the overall environmental friendliness of the composite structure; the source and preparation process are not green: traditional carbon fiber uses petroleum-based polymers as raw materials, and the preparation process requires high temperature, inert atmosphere and complex control, with high carbon emissions and strong resource dependence, which is contrary to the development goal of "fully biodegradable and renewable raw materials".

[0005] Therefore, how to develop a bio-based carbon fiber material based on renewable plant fibers, with adjustable structure, good interfacial reactivity and certain environmental degradation ability, and construct a composite system with good compatibility and balanced performance with degradable polymers, is a key technical problem that needs to be solved urgently in the field of fully biodegradable composite materials. Summary of the Invention

[0006] The present application provides a carbon fiber-based fully biodegradable material and a preparation method thereof, aiming to solve the problems of existing carbon fiber-reinforced biodegradable materials such as poor interface compatibility, low reinforcement efficiency, and insufficient degradation synergy.

[0007] In the first aspect, the present application provides a fully biodegradable material based on carbon fiber, comprising the following raw materials in parts by mass: 100 parts of polylactic acid, 15 to 30 parts of polybutylene adipate / terephthalate (PBAT), 5 to 15 parts of modified bio-based carbon fiber, 1 to 5 parts of plasticizer, and 0.1 to 1 part of antioxidant; wherein the modified bio-based carbon fiber is obtained by carbonizing plant fibers modified with soluble metal salts and nitrogen-containing compounds.

[0008] According to this application, by introducing plant-derived carbon fibers synergistically modified with metal salts and nitrogen-containing compounds, the interfacial bonding ability between the reinforcing phase and biodegradable polymers such as polylactic acid is significantly improved, the mechanical properties and structural stability of the composite material are improved, and at the same time, good biodegradation synergy is ensured in the system.

[0009] Specifically, the material utilizes pretreated and modified bio-based carbon fibers as the reinforcement phase. During the preparation process, the plant fibers react with soluble metal salts and nitrogen-containing compounds to form a highly dispersed metal-nitrogen ligand precursor structure on the fiber surface. This structure is further transformed into a carbon skeleton rich in defects, heteroatom doping, and coordination structures during the carbonization process, giving the carbon fiber surface high polarity and reactivity.

[0010] When the modified carbon fiber is compounded with a polar polyester matrix (such as PLA and PBAT), it is easy to form adsorption, interpenetration and anchoring structures at the interface, establishing a denser and more stable interface interaction area; at the same time, the active sites on its surface are conducive to the directional attachment and chemical anchoring of coupling agent molecules, thereby significantly improving the interface bridging efficiency and mechanical stress transmission ability. Compared with unmodified carbon fiber, the reinforcement effect is more significant.

[0011] Furthermore, the structural defects and doping element distribution formed on the surface of these carbon fibers can regulate the degradation behavior of the interface. Their microstructures help them become degradation initiation sites under microbial or hydrolytic conditions, while also possessing a certain degree of hydrophilicity and oxidation-inducing ability, thereby promoting the controlled disintegration of the overall system. This synergistic degradation mechanism, brought about by the intrinsic regulation of the reinforcing phase structure, works in conjunction with the hydrolysis of the polymer backbone to achieve a balance between the stability of the composite material during service and its rapid degradation after service.

[0012] Therefore, this application constructs a modified bio-based carbon fiber with strong interfacial activity and structural and functional synergy, and compounds it into a fully biodegradable polyester system. While achieving mechanical enhancement, it ensures the coordination of the overall degradation behavior. It is suitable for the preparation of degradable high-performance composite materials in the fields of green packaging, bio-based equipment, etc.

[0013] In some embodiments, the modified bio-based carbon fiber is prepared by the following steps:

[0014] S10: dispersing the plant fiber, the soluble metal salt, and the nitrogen-containing compound in water, so that the plant fiber, the metal salt, and the nitrogen-containing compound are complexed with each other to obtain a precursor material;

[0015] S20: Carbonizing the precursor material to obtain modified bio-based carbon fiber.

[0016] In some of the above embodiments, the soluble metal salt and the nitrogen-containing compound in step S10 are physically adsorbed and complexed with the hydroxyl or carboxyl structure on the surface of the plant fiber to form a metal-ligand-fiber ternary composite precursor, which can induce a metal-nitrogen structure (MN) during the carbonization process. x , M is a metal) is stably constructed on the carbon fiber surface while inhibiting the complete removal of surface functional groups. Compared to direct carbonization of plant fibers or the introduction of metal salts or nitrogen-containing compounds alone, this synergistic pretreatment scheme can more stably introduce heterogeneous atom doping sites and surface defects on the carbon skeleton surface after carbonization, enhancing the binding activity of the carbon fiber surface to coupling agents or polar polyester matrices.

[0017] Furthermore, during the carbonization process, due to the presence of nitrogen sources and metal ions, some metals will catalyze the carbonization path of cellulose, making the carbonization process more directional and the carbon yield higher. At the same time, by stabilizing the structural orientation, nitrogen doping and defect generation are promoted, improving the microstructural regularity and uniformity of the interfacial activity distribution of the final carbon fiber. These structural characteristics give the resulting carbon fiber better interfacial anchoring ability, stronger mechanical reinforcement effect, and the ability to more easily stimulate the controlled degradation of the polyester matrix.

[0018] Therefore, this application enhances the structural orientation and interfacial functionalization of plant-derived carbon fibers during carbonization by introducing a metal salt-nitrogen compound synergistic system before carbonization, thereby constructing a biodegradable composite material with high interfacial bonding strength, high mechanical properties, and good degradation coordination. Furthermore, this method has mild process conditions, an environmentally friendly treatment process, and is suitable for industrial scale-up.

[0019] In some embodiments, S10 includes: ultrasonically dispersing 100 parts of plant fiber, 10-20 parts of soluble metal salt, and 5-15 parts of nitrogen-containing compound in 800-1200 parts of water, and stirring for 1-3 hours at a pH of 6.5-7.5 to obtain a precursor material.

[0020] In some of the above embodiments, the process design enables the metal salt and the nitrogen-containing compound to form a stable complex structure in the aqueous phase and to be fully adsorbed on the surface of the plant fiber. Under the above pH conditions, the residual carboxyl and hydroxyl structures on the surface of the plant fiber maintain an active state and can undergo electrostatic adsorption or weak coordination with the metal ions. It is also beneficial for the nitrogen-containing compound to exist in an unprotonated form, thereby improving its chelation efficiency for metal ions. Ultrasonic dispersion improves the contact efficiency between the three components, avoids local concentration of metal salts or ligands in the system, and helps to achieve a uniform distribution of the complex structure of the precursor.

[0021] In the fully stirred precursor system, the metal ion-nitrogen ligand complex structure is uniformly adsorbed on the fiber surface and embedded into the fiber structure through physical adsorption and weak coordination, laying the foundation for heteroatom doping, defect induction, and surface polar structure construction during the subsequent carbonization process. Compared to simple mixing methods or pretreatment methods without pH control, this embodiment can achieve a higher density and more stable distribution of functional sites on the surface of the modified carbon fibers, thereby achieving stronger interfacial bonding and better mechanical reinforcement effects in the composite material.

[0022] In some embodiments, the soluble metal salt includes an iron salt and an aluminum salt, and the mass ratio of the iron salt to the aluminum salt is 1:0.8-1.2.

[0023] In some of the above embodiments, the synergistic use of iron salts and aluminum salts not only improves the loading efficiency of metal ions in the precursor, but also significantly improves the functionalized structure of the subsequent carbon fiber surface. Among them, iron ions have strong coordination ability and are easy to form stable Fe-N complexes with nitrogen-containing compounds. Such structures can be converted into defect-rich carbon regions doped with Fe heteroatoms during high-temperature carbonization, which helps to improve the polarity and interfacial activity of the carbon fiber surface. Aluminum ions, as a typical Lewis acid, can assist the rearrangement of hydroxyl groups on the surface of plant fibers through complexation in the precursor dispersion system, thereby adjusting their microstructure and coordination orientation.

[0024] By introducing iron salt and aluminum salt at a mass ratio of 1:0.8 to 1.2, a more stable distribution of metal ions can be achieved during the composite adsorption stage, thereby forming a carbon fiber surface structure with uniform heteroatom doping and regular defect morphology during the carbonization conversion process. Compared with single metal salt doping, this synergistic structure can significantly improve the wettability and anchoring ability of the composite carbon fiber in the polyester matrix, thereby improving the interfacial shear strength and overall mechanical properties of the composite material.

[0025] In addition, Fe 3+ With Al 3+ The metal-nitrogen ligand structure constructed by complex combination also has a significant effect on the degradation behavior of the composite material. 3+ Doping can form Fe-Nx Active sites, these structures have certain oxidation catalytic ability under composting or wet heat conditions, which can promote the scission reaction of polyester chains and form the "triggering point" of interface degradation; at the same time, Al 3+ The high hydrophilicity of the carbon fiber promotes the formation of hydrophilic structures such as hydroxyl or carbonyl groups on the carbon fiber surface, which helps to initiate water swelling and localized hydrolysis. The synergistic effect of these two factors makes the carbon fiber-polyester interface the first region of composite degradation, inducing layer-by-layer decomposition and coordinated decomposition of the material on a macroscale.

[0026] In contrast, although copper salts and zinc salts also have certain coordination capabilities, they tend to form heterogeneous metal oxide clusters after carbonization, with poor doping uniformity and weak surface polarity, which can easily lead to a decrease in interface binding ability; while alkaline earth metal ions such as calcium salts have weak coordination capabilities and are easily deactivated during the carbonization process, which is not conducive to the construction of stable defect structures and the formation of functional sites. Therefore, in this embodiment, Fe 3+ With Al 3+ The combined combination can show better synergistic effects in structure induction, interface polarization and degradation initiation.

[0027] In some embodiments, the nitrogen-containing compound includes urea and polyethyleneimine with a number average molecular weight of 1500 to 2500, and the mass ratio of the urea to the polyethyleneimine is 1:0.4 to 0.6.

[0028] In some of the above embodiments, the coordinated use of urea and polyethyleneimine (PEI) can construct a molecular-scale complex structure on the surface of the cellulose precursor. Urea, as a low molecular weight, highly diffusible small molecule nitrogen source, can quickly react with Fe 3+ or Al 3+ The reaction between the metal ions and the polyethyleneimine forms a uniform small molecule complex, which helps to establish an initial adsorption layer on the fiber surface. Polyethyleneimine has a branched polyamine structure, and the primary amine and secondary amine groups on its main chain and side chain can form stable chelates with multiple metal ions, further enhancing the spatial stability and directional control ability of the complex configuration.

[0029] Under the action of metal ions, this complex system can synergistically induce the formation of a composite precursor network stabilized by hydrogen bonds, coordination bonds, and electrostatic interactions. During the subsequent carbonization process, urea partially decomposes to produce volatile components such as NH3, which can regulate the micro-local alkaline environment and promote uniform heteroatom doping. At the same time, the PEI skeleton structure is transformed into heterocyclic structures such as pyrrolic nitrogen and pyridinic nitrogen, forming nitrogen-doped carbon microdomains, which endow the carbon fibers with higher polarity, defect density, and interfacial activity.

[0030] In this composite system, urea and PEI, under the action of metal ions, synergistically induce the formation of a composite precursor network stabilized by hydrogen bonding, coordination bonding, and electrostatic interactions. During carbonization, urea partially decomposes to produce volatile components such as NH3, which helps regulate the microlocal alkaline environment and promote heteroatom doping. The PEI backbone structure is then transformed into structurally stable doping sites such as pyrrolic and pyridinic nitrogen. This synergistic effect significantly improves nitrogen doping density and uniformity, thereby enhancing the polarity, defect density, and interfacial adsorption capacity of the carbon fiber surface.

[0031] More importantly, the urea + PEI composite structure also has a significant positive effect on the degradation performance of the composite material. The surface pores generated by urea during carbonization and the nitrogen-doped regions induced by PEI synergistically construct an "interfacial degradation activation zone," which can enhance the material's hydrophilicity and initial degradation response in composting, hydrolysis, or microbial environments. This interfacial structure can accelerate the hydrolytic cleavage or enzymatic depolymerization of polyester chain segments such as polylactic acid and PBAT, driving the synergistic degradation of the composite material, which gradually expands from the interface to the interior.

[0032] Compared with other commonly used nitrogen-containing compounds such as melamine and chitosan, the urea + PEI system performs better in terms of complexation efficiency and dispersion stability. Although melamine has a triamine structure, it has poor water solubility and weak dispersibility in neutral or weakly alkaline environments. It easily forms granular residues during carbonization, which is not conducive to the formation of a uniform active structure. Although chitosan has a natural amino skeleton, its molecules are highly rigid and easily gelled, which limits the carbonization doping efficiency. In contrast, the combination of urea and polyethyleneimine not only has a flexible configuration and uniform complexation, but also can effectively induce the formation of functional microstructures during the carbonization process, thereby achieving dual optimization of the material's mechanical properties and degradability.

[0033] In some embodiments, the carbonization treatment conditions include: heating to 200-300°C at 0.5-1.5°C / min in an air atmosphere and keeping warm for 1-2 hours; then heating to 550-650°C at 4-6°C / min in a nitrogen atmosphere and keeping warm for 1.5-2.5 hours.

[0034] In some of the above-mentioned embodiments, the segmented carbonization treatment design helps to improve the stability of the fiber structure and the efficiency of the formation of the surface active structure of the carbon material. Among them, the first stage is carried out in an air atmosphere, and the temperature is controlled in the range of 200-300°C, which is conducive to the slow dehydration, removal of volatile groups and pre-oxidation reactions of the plant fiber raw materials, promoting the stabilization of the internal structure, while inducing the cross-linking and curing of some functional groups to avoid excessive shrinkage or structural collapse during high-temperature carbonization. This stage can also enhance the anchoring of metal salts and nitrogen-containing compounds in the fiber structure and inhibit migration or agglomeration.

[0035] The second stage is completed in a nitrogen atmosphere. The heating rate, holding temperature and time are optimized to maximize the preservation of the precursor morphology while promoting the transformation of the cellulose structure into a carbon-rich skeleton, and inducing the decomposition of nitrogen-containing compounds to produce active nitrogen sources, which are doped into the carbon skeleton to form heteroatom structures such as pyrrole nitrogen and graphitic nitrogen, thereby improving the surface polarity and electronegativity distribution of the carbon fiber.

[0036] In addition, the carbonization temperature of 550-650°C can not only ensure the nitrogen doping efficiency, but also avoid the agglomeration of carbon structures or the conversion of metal salts into uncontrollable cluster structures caused by excessively high temperatures, which is conducive to the formation of more surface defects and reactive sites, thereby enhancing its interfacial adhesion ability with polar polyester matrices such as polylactic acid or PBAT.

[0037] Compared with traditional one-step carbonization methods or high-temperature rapid carbonization processes, the fine control of the atmosphere and temperature program in this embodiment significantly improves the structural order and functionalization uniformity of the carbon material. The resulting modified bio-based carbon fiber exhibits better surface activity and interfacial affinity while maintaining morphological integrity, thereby exerting higher reinforcement efficiency and better degradation synergy in the composite material.

[0038] In some embodiments, in step S20, after the carbonization treatment, the further step includes: crushing the material obtained by the carbonization treatment through a 150-300 mesh sieve, and then treating it with an aminosilane coupling agent to obtain modified bio-based carbon fiber.

[0039] In some of the above embodiments, by performing particle size screening on the carbonized bio-based carbon fibers, the dispersion uniformity thereof in the polylactic acid and PBAT matrices can be effectively improved, thereby avoiding local agglomeration and causing weak interface areas in the composite structure, thereby improving the mechanical properties consistency and enhancement efficiency of the composite material.

[0040] The surface is then functionalized by introducing an aminosilane coupling agent, which creates a polar functional layer on the carbon fiber surface, enhancing its interfacial adsorption and stability with the polyester matrix. The polar functional groups in the coupling agent molecules further enhance the stability and density of the interfacial bond, effectively reducing interfacial stress concentration between the reinforcement phase and the matrix, and improving the overall structural integrity and mechanical strength of the composite material.

[0041] In addition, the coupling agent treatment also helps to improve the interfacial environment of the modified carbon fiber in the composite material, so that the interface layer has higher hydrophilicity and initial response ability in a humid and hot or composting environment, thereby helping to promote the preferential degradation of the composite material along the interface direction and improving the overall environmental adaptability and controllable degradation ability of the material.

[0042] In some embodiments, the treatment with an aminosilane coupling agent includes: dispersing 20 parts of the carbonized and crushed material in 300 to 500 parts of an ethanol aqueous solution, adding 2 to 5 parts of γ-aminopropyltriethoxysilane, and heating under reflux at a pH of 4.5 to 5.5 and 70°C for 1 to 3 hours to obtain modified bio-based carbon fiber.

[0043] In some embodiments, the plant fiber is obtained by crushing a biomass raw material, soaking it in alkali solution, and ultrasonically treating it before drying; the biomass raw material includes at least one of wood fiber, bamboo fiber, and straw fiber.

[0044] In some of the above embodiments, the plant fiber pretreatment process helps to improve the purity and structural uniformity of the carbon fiber precursor. The crushing step can break the crude fiber material into smaller particles or short fiber forms, increase its specific surface area, and facilitate the penetration and homogenization of subsequent processing reactions; alkali solution soaking can effectively remove lignin, hemicellulose, wax and other non-cellulose impurities in the raw materials, thereby improving the purity and crystallinity of the resulting cellulose components. Combined with ultrasonic treatment, the fiber bundle structure can be further broken up, the fiber surface layer can be stripped off, and the penetration and diffusion of alkali solution can be promoted, making the de-impurity process more thorough and uniform. This method is particularly suitable for raw materials with denser natural sources or uneven fiber distribution (such as bamboo fiber, straw fiber, etc.), and can significantly improve the homogeneity and controllability of the precursor raw materials.

[0045] After drying, the pretreated plant fibers have higher structural stability and reactivity, which helps to form uniform complex precursors with metal salts and nitrogen-containing compounds, and generate more uniform and defect-controllable modified carbon fiber structures during the carbonization process, thus laying the foundation for subsequent interface reinforcement, structural induction and degradation synergistic effects.

[0046] In some embodiments, the plant fiber is obtained by the following method: crushing the biomass raw material into powder with a particle size of less than 0.5 cm, then mixing it with 5wt% to 10wt% sodium hydroxide aqueous solution at a solid-liquid ratio of 1g:8-12mL, treating it at 90-100°C for 4-6h, washing it to neutrality and then dispersing it in water to obtain a slurry with a solid content of 0.5wt% to 2wt%, transferring it to a high-speed homogenizer and mechanically shearing it at 8000-12000rpm for 10-20min, then ultrasonically treating it for 20-40min, and drying it to obtain the plant fiber.

[0047] In some embodiments, the weight average molecular weight of the polylactic acid is 100,000 to 140,000. Based on the above embodiments, polylactic acid with a higher molecular weight can improve the mechanical strength and thermal stability of the material while maintaining its processability, making the service performance of the composite material more stable in application.

[0048] In some embodiments, the weight average molecular weight of the polybutylene adipate / terephthalate is 120,000 to 200,000. Based on the above embodiment, the PBAT with the above molecular weight has better ductility and elasticity, can effectively alleviate the interfacial stress concentration problem caused by the brittleness of polylactic acid, and cooperate with the carbon fiber reinforcement phase to improve the impact resistance and overall flexibility of the composite material, making it suitable for biodegradable products requiring high flexibility and toughness.

[0049] In some embodiments, the plasticizer includes at least one of tributyl citrate and acetyl tributyl citrate. Both ester plasticizers have good biodegradability and compatibility with polyester resins, can effectively lower the glass transition temperature and melting temperature of polylactic acid and PBAT, improve their processing performance and flexibility, and do not significantly negatively affect the thermal stability and structural integrity of the composite system.

[0050] In some embodiments, the antioxidant includes at least one of antioxidant 1010 and antioxidant 1076. Based on the above embodiments, this type of antioxidant can inhibit the oxidative breakage of polymer chains during high-temperature extrusion processing or use, delaying the thermal oxidative aging process, and improving the storage stability and service life of the composite material. It is particularly suitable for use in fully biodegradable products exposed to air or moderate temperature environments for long periods of time.

[0051] In a second aspect, the present application provides a method for preparing a fully biodegradable material based on carbon fiber, comprising: providing the raw materials included in the fully biodegradable material described in any embodiment of the first aspect;

[0052] The raw materials are mixed, extruded and injection-molded to obtain a fully biodegradable material.

[0053] According to the present application, the method achieves efficient dispersion and interface composite of modified carbon fiber and polyester degradable matrix in a molten state through an integrated processing technology, while maintaining degradability, significantly improving the mechanical properties and interface stability of the composite material, and is suitable for large-scale continuous preparation process.

[0054] In some embodiments, the method comprises:

[0055] Polylactic acid, polybutylene adipate / terephthalate, modified bio-based carbon fiber, plasticizer and antioxidant were weighed according to a preset ratio and pre-mixed in a low-speed mixer for 2 to 5 minutes to ensure that the modified carbon fiber was initially evenly distributed in the resin matrix.

[0056] The mixed raw materials are melt-blended in a twin-screw extruder, the extrusion temperature is set to 140-150°C, 155-165°C, 155-165°C, 165-175°C, 165-175°C, and 175-185°C in stages, the screw speed is 80-120rpm, and a water-cooled strand pelletizing method is adopted to obtain composite modified pellets.

[0057] The obtained pellets are dried at 80-100° C. for 6-8 hours and then sent to an injection molding machine for molding. The injection molding temperature is 170-200° C., the mold temperature is controlled at 40-60° C., the holding time is 5-15 seconds, and the pressure is 60-100 MPa to obtain a fully biodegradable material.

[0058] Compared with the prior art, the present invention has the following advantages:

[0059] (1) By introducing a synergistic modification strategy of soluble metal salts and nitrogen-containing compounds during the carbon fiber preparation stage, the obtained bio-based carbon fibers have good surface polarity structure and interfacial activity, thereby significantly improving the interfacial bonding strength and reinforcement efficiency between them and biodegradable polyester matrices such as polylactic acid and PBAT; not only effectively making up for the poor interfacial adhesion and insufficient dispersion of traditional carbon fibers in biodegradable materials, but also giving the composite materials excellent mechanical strength and stability;

[0060] (2) The defective areas, heteroatom-doped areas and surface polar sites induced by the modified carbon fibers help the interface layer to respond first to degradation reactions under conditions such as microorganisms and hydrolysis, promote the gradual deconstruction of the polyester matrix, and enable the composite material provided by the present application to establish effective synergy between mechanical properties and biodegradability, thus solving the technical problem of poor degradation coordination of existing carbon fiber reinforced degradable materials, and having good prospects for industrial application and ecological sustainability. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0062] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0063] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0064] In this application, unless otherwise specified, "parts" refer to "parts by mass".

[0065] The scheme of the present application is described below with reference to the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0066] Preparation of bamboo-based plant fiber: Take dry bamboo chips and pre-crush them using a high-speed grinder to control the particle size to less than 0.5 cm. Add the above powder to an 8wt% sodium hydroxide aqueous solution at a solid-liquid ratio of 1g:10mL, stir and react at 95°C for 5 hours, and after the reaction, wash with distilled water several times until the pH of the filtrate is close to neutral. Suspend the neutralized bamboo fiber in pure water, adjust the system to 1.0wt% solid content, transfer it to a high-speed homogenizer, and shear it at 10,000rpm for 15 minutes; the sheared slurry is then transferred to an ultrasonic cleaner with a power of 300W, a frequency of 40kHz, and a treatment time of 30 minutes; the treated fiber suspension is filtered, dehydrated by suction, and then dried in a vacuum drying oven at 60°C for 12 hours to obtain bamboo-based plant fiber with a clean surface and loose structure.

[0067] Preparation Example 1

[0068] Preparation of modified bio-based carbon fibers:

[0069] Take 100 parts of dry bamboo-based plant fiber and disperse it in 1000 parts of water. Add 6 parts of ferric chloride hexahydrate and 6 parts of aluminum chloride hexahydrate as soluble metal salts in sequence. Then add 6 parts of urea and 3 parts of polyethyleneimine with a number average molecular weight of 1800 as nitrogen-containing compounds. After mixing, adjust the pH to 7±0.2. After stirring for 2 hours, filter and collect the filter cake. Dry it in a vacuum drying oven at 80°C for 12 hours to obtain a precursor dry powder. The dry powder is placed in an atmosphere-controlled tubular furnace and subjected to a two-step carbonization treatment: in an air atmosphere, heat it to 250°C at 1.0°C / min and keep it warm for 1.5 hours; switch to a nitrogen protective atmosphere, heat it to 600°C at 5°C / min, keep it warm for 2 hours, and naturally cool it to room temperature to obtain a black and loose carbonized product.

[0070] The carbonized product was ground and passed through a 200-mesh sieve. 20 parts of the carbonized product were dispersed in 400 parts of an ethanol-water solution (the volume ratio of ethanol to water was 7:3). 4 parts of γ-aminopropyltriethoxysilane were added, and the pH was adjusted to 5. The mixture was heated under reflux at 70°C for 2 hours. After the reaction, the mixture was centrifuged and washed three times, and then dried to obtain the modified bio-based carbon fiber.

[0071] Preparation Example 2

[0072] Preparation of modified bio-based carbon fibers:

[0073] The process is substantially the same as Example 1, except that 12 parts of ferric chloride hexahydrate are used as the soluble metal salt.

[0074] Preparation Example 3

[0075] Preparation of modified bio-based carbon fibers:

[0076] The process is substantially the same as Example 1, except that 12 parts of aluminum chloride hexahydrate are used as the soluble metal salt.

[0077] Preparation Example 4

[0078] Preparation of modified bio-based carbon fibers:

[0079] The process is substantially the same as Example 1, except that 12 parts of calcium chloride hexahydrate are used as the soluble metal salt.

[0080] Preparation Example 5

[0081] Preparation of modified bio-based carbon fibers:

[0082] The process is substantially the same as Example 1, except that 6 parts of ferric chloride hexahydrate and 6 parts of calcium chloride hexahydrate are used as soluble metal salts.

[0083] Preparation Example 6

[0084] Preparation of modified bio-based carbon fibers:

[0085] The process is substantially the same as Example 1, except that 9 parts of urea are used as the nitrogen-containing compound.

[0086] Preparation Example 7

[0087] Preparation of modified bio-based carbon fibers:

[0088] The process is substantially the same as Example 1, except that 9 parts of polyethyleneimine with a number average molecular weight of 1800 is used as the nitrogen-containing compound.

[0089] Preparation Example 8

[0090] Preparation of modified bio-based carbon fibers:

[0091] The process is substantially the same as Example 1, except that 6 parts of urea and 3 parts of melamine are used as nitrogen-containing compounds.

[0092] Preparation Example 9

[0093] Preparation of modified bio-based carbon fibers:

[0094] Take 100 parts of dry bamboo-based plant fiber and disperse it in 1000 parts of water. Then add 6 parts of ferric chloride hexahydrate and 6 parts of aluminum chloride hexahydrate as soluble metal salts, and then add 6 parts of urea and 3 parts of polyethyleneimine with a number average molecular weight of 1800 as nitrogen-containing compounds. After mixing, adjust the pH to 7±0.2, stir and mix for 2 hours, then filter and collect the filter cake. Dry it in a vacuum drying oven at 80°C for 12 hours to obtain a precursor dry powder. The dry powder is placed in an atmosphere-controlled tubular furnace for a one-step carbonization treatment: in a nitrogen protective atmosphere, heat it to 600°C at 5°C / min, keep it warm for 3 hours, and cool it naturally to room temperature to obtain a black and loose carbonized product.

[0095] The carbonized product was ground and passed through a 200-mesh sieve. 20 parts of the carbonized product were dispersed in 400 parts of an ethanol-water solution (the volume ratio of ethanol to water was 7:3). 4 parts of γ-aminopropyltriethoxysilane were added, and the pH was adjusted to 5. The mixture was heated under reflux at 70°C for 2 hours. After the reaction, the mixture was centrifuged and washed three times, and then dried to obtain the modified bio-based carbon fiber.

[0096] Comparative Preparation Example 1

[0097] Preparation of modified bio-based carbon fibers:

[0098] Take 100 parts of dry bamboo-based plant fiber and disperse it in 1000 parts of water. Adjust the pH to 7±0.2, stir and mix for 2 hours, then filter and collect the filter cake. Dry it in a vacuum drying oven at 80℃ for 12 hours to obtain a precursor dry powder. The dry powder is placed in an atmosphere-controlled tube furnace and subjected to a two-step carbonization treatment: in an air atmosphere, heat it to 250℃ at 1.0℃ / min and keep it at that temperature for 1.5 hours; switch to a nitrogen protective atmosphere, heat it to 600℃ at 5℃ / min and keep it at that temperature for 2 hours. Then cool it naturally to room temperature to obtain a black and loose carbonized product.

[0099] The carbonized product was ground and passed through a 200-mesh sieve. 20 parts of the carbonized product were dispersed in 400 parts of an ethanol-water solution (the volume ratio of ethanol to water was 7:3). 4 parts of γ-aminopropyltriethoxysilane were added, and the pH was adjusted to 5. The mixture was heated under reflux at 70°C for 2 hours. After the reaction, the mixture was centrifuged and washed three times, and then dried to obtain the modified bio-based carbon fiber.

[0100] Comparative Example Preparation Example 2

[0101] Preparation of modified bio-based carbon fibers:

[0102] Take 100 parts of dry bamboo-based plant fiber and disperse it in 1000 parts of water. Add 6 parts of ferric chloride hexahydrate and 6 parts of aluminum chloride hexahydrate as soluble metal salts in sequence. After mixing, adjust the pH to 7±0.2. After stirring for 2 hours, filter and collect the filter cake. Dry it in a vacuum drying oven at 80℃ for 12 hours to obtain a precursor dry powder. The dry powder is placed in an atmosphere-controlled tubular furnace and subjected to a two-step carbonization treatment: in an air atmosphere, heat it to 250℃ at 1.0℃ / min and keep it warm for 1.5 hours; switch to a nitrogen protective atmosphere, heat it to 600℃ at 5℃ / min, keep it warm for 2 hours, and naturally cool it to room temperature to obtain a black and loose carbonized product.

[0103] The carbonized product was ground and passed through a 200-mesh sieve. 20 parts of the carbonized product were dispersed in 400 parts of an ethanol-water solution (the volume ratio of ethanol to water was 7:3). 4 parts of γ-aminopropyltriethoxysilane were added, and the pH was adjusted to 5. The mixture was heated under reflux at 70°C for 2 hours. After the reaction, the mixture was centrifuged and washed three times, and then dried to obtain the modified bio-based carbon fiber.

[0104] Comparative Preparation Example 3

[0105] Preparation of modified bio-based carbon fibers:

[0106] Take 100 parts of dry bamboo-based plant fiber and disperse it in 1000 parts of water. Then add 6 parts of urea and 3 parts of polyethyleneimine with a number average molecular weight of 1800 as nitrogen-containing compounds. After mixing, adjust the pH to 7±0.2, stir and mix for 2 hours, then filter and collect the filter cake. Dry it in a vacuum drying oven at 80℃ for 12 hours to obtain a precursor dry powder. The dry powder is placed in an atmosphere-controlled tubular furnace and subjected to a two-step carbonization treatment: in an air atmosphere, heat it to 250℃ at 1.0℃ / min and keep it warm for 1.5 hours; switch to a nitrogen protective atmosphere, heat it to 600℃ at 5℃ / min, keep it warm for 2 hours, and naturally cool it to room temperature to obtain a black and loose carbonized product.

[0107] The carbonized product was ground and passed through a 200-mesh sieve. 20 parts of the carbonized product were dispersed in 400 parts of an ethanol-water solution (the volume ratio of ethanol to water was 7:3). 4 parts of γ-aminopropyltriethoxysilane were added, and the pH was adjusted to 5. The mixture was heated under reflux at 70°C for 2 hours. After the reaction, the mixture was centrifuged and washed three times, and then dried to obtain the modified bio-based carbon fiber.

[0108] Example 1

[0109] Preparation of fully biodegradable materials based on carbon fiber:

[0110] The raw materials were weighed according to the following mass parts: 100 parts of PLA (weight average molecular weight of about 120,000); 25 parts of PBAT (weight average molecular weight of about 150,000); 10 parts of the modified bio-based carbon fiber obtained in Preparation Example 1; 3 parts of tributyl citrate (TBC); 0.3 parts of antioxidant 1010;

[0111] PLA, PBAT, modified bio-based carbon fiber, and antioxidant were first mixed in a high-speed mixer. TBC was then slowly added and mixed for 5 minutes to obtain a premix. The mixture was then dried in a vacuum oven at 80°C for 12 hours to remove moisture and residual solvent.

[0112] The dried mixture was melt-blended and extruded in a twin-screw extruder under the following process conditions: temperature from feed port to die: 145°C / 160°C / 160°C / 170°C / 170°C / 180°C, screw speed of 60 rpm, and the discharged material was water-cooled and pelletized to obtain masterbatch;

[0113] The granulated masterbatch was vacuum-dried at 80°C for 4 hours and then molded on an injection molding machine to produce a fully biodegradable material. The injection molding process conditions were as follows: injection temperature: 190°C; mold temperature: 45°C; pressure: 80 MPa; and holding time: 10 seconds.

[0114] Example 2

[0115] Preparation of fully biodegradable materials based on carbon fiber:

[0116] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 2 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0117] Example 3

[0118] Preparation of fully biodegradable materials based on carbon fiber:

[0119] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 3 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0120] Example 4

[0121] Preparation of fully biodegradable materials based on carbon fiber:

[0122] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 4 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0123] Example 5

[0124] Preparation of fully biodegradable materials based on carbon fiber:

[0125] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 5 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0126] Example 6

[0127] Preparation of fully biodegradable materials based on carbon fiber:

[0128] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 6 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0129] Example 7

[0130] Preparation of fully biodegradable materials based on carbon fiber:

[0131] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 7 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0132] Example 8

[0133] Preparation of fully biodegradable materials based on carbon fiber:

[0134] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 8 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0135] Example 9

[0136] Preparation of fully biodegradable materials based on carbon fiber:

[0137] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Preparation Example 9 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0138] Comparative Example 1

[0139] Preparation of fully biodegradable materials based on carbon fiber:

[0140] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Comparative Preparation Example 1 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0141] Comparative Example 2

[0142] Preparation of fully biodegradable materials based on carbon fiber:

[0143] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Comparative Preparation Example 2 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0144] Comparative Example 3

[0145] Preparation of fully biodegradable materials based on carbon fiber:

[0146] Compared with Example 1, the only difference is that the modified bio-based carbon fiber obtained in Comparative Preparation Example 3 is used instead of the modified bio-based carbon fiber obtained in Preparation Example 1.

[0147] Test section

[0148] The tensile stress at break (MPa) of the fully biodegradable materials obtained in each embodiment and comparative example was tested according to GB / T 1040-2006. The mass loss (%) of the fully biodegradable materials obtained in each embodiment and comparative example under standard composting conditions at 58°C on day 45 was tested according to GB / T 19277-2003. The results are shown in Table 1.

[0149] Table 1

[0150] Tensile breaking stress (MPa) Mass loss rate (%) Example 1 38.2 63.5 Example 2 35.6 57.4 Example 3 33.9 53.7 Example 4 32.3 51.6 Example 5 34.1 55.9 Example 6 36.5 57.9 Example 7 34.8 53.0 Example 8 37.1 58.2 Example 9 36.7 60.1 Comparative Example 1 26.2 37.5 Comparative Example 2 30.7 46.3 Comparative Example 3 28.1 42.8

[0151] According to Table 1, each embodiment shows higher tensile breaking stress and higher mass loss rate under composting conditions after 45 days compared with comparative examples 1 to 3, indicating that the carbon fiber-based fully biodegradable material provided in the present application can significantly improve the mechanical properties of the material while enhancing its biodegradability, taking into account both high strength and environmental performance, and has excellent comprehensive performance. The possible reasons are: in Comparative Example 1, no metal salts and nitrogen-containing compounds were introduced to pretreat the plant fibers, and the resulting carbon fibers lacked interfacial polar sites and structural defect areas, resulting in poor interfacial bonding ability with the polyester matrix and limited reinforcement efficiency. In addition, the carbon fiber surface was highly hydrophobic, which limited the occurrence of interfacial degradation reactions and exhibited poor mechanical properties and degradation properties. In Comparative Example 2, only metal salts were used without introducing nitrogen-containing compounds, resulting in a lack of effective nitrogen source doping and defect-induced structure in the carbon fibers, and limited improvement in the polarity of the carbon skeleton, which affected the interfacial adsorption efficiency and the formation of degradation active sites, resulting in poor mechanical properties and degradability. In Comparative Example 3, only nitrogen-containing compounds were used without introducing metal salts, and the doped nitrogen atom structure in the carbon fibers lacked stable coordination framework support, the structural construction efficiency during the carbonization process was low, and the interfacial reaction activity and degradation responsiveness were not ideal, resulting in poor mechanical properties and degradability.

[0152] According to Examples 1 to 5, as the types of metal salts change, the performance of the carbon fiber reinforced phase constructed also has significant differences. In Example 1, the composite coordination structure formed by the synergistic effect of ferric chloride and aluminum chloride is the most stable, and the degree of heteroatom doping and defect construction after carbonization are optimal, so the tensile fracture stress and degradation rate are both optimal. In contrast, there is a certain performance degradation when using iron salts (Example 2) or aluminum salts (Example 3) alone, and the mixed iron salt and calcium salt (Example 5) also perform slightly worse, indicating that the design of the metal salt type has a significant impact on the final carbon fiber performance.

[0153] According to Examples 1, 6 to 8, the type of nitrogen-containing compound also has a significant impact on the carbon fiber modification effect. The complex system formed by the combination of urea and PEI in Example 1 has both dispersibility and structure-directing capabilities, and can construct a more stable and uniform doping precursor. Therefore, it is better than the modification effect obtained by using only urea (Example 6) or PEI (Example 7), as well as the modification effect obtained by combining urea and melamine (Example 8), indicating that the "urea + PEI" proposed in this application is a more optimal nitrogen-containing modification system.

[0154] According to the comparison between Example 1 and Example 9, under the same other conditions, simplifying the two-step carbonization process into a one-step carbonization treatment can simplify the process, but it will lead to a decrease in the structural control ability of the carbonization process. The modified carbon fiber finally formed is slightly inferior in doping uniformity and structural integrity, which is manifested as a slight decrease in mechanical properties and degradation ability, indicating the important role of the two-step carbonization path adopted in improving material performance.

[0155] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the principles of the present application should be included in the scope of protection of the present application.

Claims

1. A fully biodegradable material based on carbon fiber, characterized in that: Including the following raw materials by weight: 100 parts of polylactic acid, 15-30 parts of polybutylene adipate / terephthalate, 5-15 parts of modified bio-based carbon fiber, 1-5 parts of plasticizer, 0.1-1 parts of antioxidant; The modified bio-based carbon fibers are obtained by carbonizing plant fibers modified with soluble metal salts and nitrogen-containing compounds.

2. The fully biodegradable material according to claim 1, characterized in that: The modified bio-based carbon fiber is prepared by the following steps: S10: dispersing the plant fiber, the soluble metal salt, and the nitrogen-containing compound in water, so that the plant fiber, the metal salt, and the nitrogen-containing compound are complexed with each other to obtain a precursor material; S20: Carbonizing the precursor material to obtain modified bio-based carbon fiber.

3. The fully biodegradable material according to claim 2, characterized in that: The S10 includes: 100 parts of plant fiber, 10-20 parts of soluble metal salt, and 5-15 parts of nitrogen-containing compound are ultrasonically dispersed in 800-1200 parts of water, and stirred for 1-3 hours at a pH of 6.5-7.5 to obtain a precursor material.

4. The fully biodegradable material according to claim 3, characterized in that: The soluble metal salt includes iron salt and aluminum salt, and the mass ratio of the iron salt to the aluminum salt is 1:0.8~1.

2.

5. The fully biodegradable material according to claim 3, characterized in that: The nitrogen-containing compound includes urea and polyethyleneimine with a number average molecular weight of 1500-2500, and the mass ratio of the urea to the polyethyleneimine is 1:0.4-0.

6.

6. The fully biodegradable material according to claim 2, characterized in that: The carbonization treatment conditions include: heating to 200-300° C. at 0.5-1.5° C. / min in an air atmosphere and keeping the temperature for 1-2 hours; then heating to 550-650° C. at 4-6° C. / min in a nitrogen atmosphere and keeping the temperature for 1.5-2.5 hours.

7. The fully biodegradable material according to claim 2, characterized in that: In the step S20, after the carbonization treatment, the method further includes: crushing the material obtained by the carbonization treatment through a 150-300 mesh sieve, and then treating it with an aminosilane coupling agent to obtain modified bio-based carbon fiber.

8. The fully biodegradable material according to claim 1, characterized in that: The plant fiber is obtained by crushing biomass raw materials, soaking them in alkali solution, ultrasonically treating them, and then drying them; the biomass raw materials include at least one of wood fiber, bamboo fiber, and straw fiber.

9. The fully biodegradable material according to any one of claims 1 to 8, characterized in that: The fully biodegradable material meets at least one of the following conditions: 1) The weight average molecular weight of the polylactic acid is 100,000 to 140,000; 2) The weight average molecular weight of the polybutylene adipate / terephthalate is 120,000 to 200,000; 3) The plasticizer includes at least one of tributyl citrate and acetyl tributyl citrate; 4) The antioxidant includes at least one of antioxidant 1010 and antioxidant 1076.

10. A method for preparing a fully biodegradable material based on carbon fiber, characterized in that: include: Providing raw materials comprising the fully biodegradable material according to any one of claims 1 to 9; The raw materials are mixed, extruded and injection-molded to obtain a fully biodegradable material.