Carbon fiber composite wire for enhancing durability of 3D printed part and preparation method

Abstract

The invention relates to the technical field of composite materials, and discloses a carbon fiber composite wire for enhancing the mechanical strength and durability of a 3D printed piece and a preparation method, the wire comprises the following components: 60-70 wt% of matrix resin, the length of short carbon fiber is 1-5 [mu] m, and the length of carbon fiber is 1-5 [mu] m. 5-8 wt% of thermal response regulation particles, the particles are a PCL-g-PNIPAm copolymer, and the particle size of the particles is 200-500 nm; 2-5 wt% of a dynamic cross-linking agent precursor; and 0.5-1 wt% of an interface coupling agent. Through a reversible acetalation mechanism of a dynamic cross-linking agent precursor, a fracture-recombination function of a chemical bond is realized in a composite system, and the interface bonding strength and network continuity are remarkably improved, so that a more compact synergistic structure is formed between a reinforced phase and matrix resin.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, specifically to a carbon fiber composite wire for enhancing the durability of 3D printed parts and a preparation method thereof. Background Art

[0002] In recent years, to meet the demands of high-performance manufacturing, researchers have developed a carbon fiber composite filament and its preparation method for enhancing the mechanical strength and durability of 3D printed parts. This method uniformly disperses chopped carbon fibers in a thermoplastic resin matrix to produce a printing filament with excellent rigidity and load-bearing capacity. During conventional melt extrusion and cooling and solidification, the carbon fibers provide significant reinforcement for the printed parts, effectively improving interlayer bonding strength and overall structural stability, and providing a feasible approach for the rapid prototyping of high-strength functional parts.

[0003] In existing technologies, most carbon fiber composite wire preparation methods focus on optimizing fiber length, content, and matrix melt fluidity, often using surface treatment or coupling agent modification to enhance the interfacial bonding between the fiber and the resin. However, these methods often rely on permanent chemical bonds or physical entanglement, and are unable to achieve dynamic adjustment and adaptive repair of interfacial bonding during processing and use. This leads to problems such as interfacial debonding and fatigue crack propagation under long-term cyclic loading or thermal cycling conditions, which restricts the durability and reliability of printed parts.

[0004] Current carbon fiber composite wires often experience bond fracture and network discontinuity due to irreversible damage to the interface structure under multiple thermal cycles or mechanical fatigue. A durable and recoverable synergistic structure cannot be established between the reinforcement phase and the matrix, which leads to a decrease in the strength of the printed components and a shortened lifespan. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon fiber composite wire and a preparation method for enhancing the mechanical strength and durability of 3D printed parts, which solves the problems of interface bonding strength degradation and crack propagation in carbon fiber composite materials under multiple thermal cycles and mechanical loads in the prior art.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: a carbon fiber composite wire for enhancing the mechanical strength and durability of 3D printed parts, the wire comprising the following components: 60–70 wt % of a matrix resin, wherein the matrix resin is selected from polyethylene terephthalate or polylactic acid; 25–30 wt% surface-modified chopped carbon fibers, wherein the chopped carbon fibers have a length of 1–5 μm and are surface-functionalized with maleic anhydride grafts; 5–8 wt% of thermally responsive controlled particles, wherein the particles are PCL-g-PNIPAm copolymers with a particle size of 200–500 nm; The dynamic crosslinker precursor is 2-5 wt%, composed of aromatic aldehydes and diol monomers, which can form a reversible Schiff base network structure; the interfacial coupling agent is 0.5-1 wt%, which is a silane coupling agent with a bifunctional group; The matrix resin has a melt index range of 3-15 g / 10 min, a glass transition temperature of not less than 55° C., and a molecular weight distribution index between 1.5 and 2.5.

[0007] The chopped carbon fibers have a moisture content of no more than 0.2 wt% before surface modification and a specific surface area of 0.5-2.0 m 2 / g, the grafted substance is a polyolefin polymer with anhydride groups, and is treated with the carbon fiber surface by melt coating at a treatment temperature range of 170-200°C.

[0008] The mass ratio of ε-caprolactone to N-isopropylacrylamide in the thermally responsive regulating microparticles is 1:1 to 3:1. The microparticles are prepared by emulsion polymerization, are spherical or quasi-spherical, and have a polydispersity index of particle size distribution of ≤0.3.

[0009] The thermal response regulating particles are freeze-dried after copolymerization, and the residual moisture content thereof is ≤1.0wt%. The molar ratio of the aromatic aldehyde to the diol of the dynamic crosslinking agent precursor is 0.8:1 to 1.2:1.

[0010] The choice of matrix resin plays a crucial role in the basic performance of the entire composite material. Polyethylene terephthalate (PET) or polylactic acid (PLA) are common 3D printing materials. These resins have good melt processability and relatively stable physical properties, which can provide appropriate support for composite materials. Mechanistically, the flexibility and adaptability of the matrix resin provide an ideal carrier foundation for the distribution of thermally responsive particles and carbon fibers, ensuring that the various components are evenly dispersed during the printing process, while also providing a reliable carrier for subsequent self-healing functions. Surface-modified chopped carbon fibers further enhance the strength and rigidity of the composite material. Carbon fibers themselves, due to their excellent mechanical properties, play a core role in enhancing the load-bearing capacity of composite materials. Surface functionalization with maleic anhydride grafts can effectively enhance the interfacial adhesion between carbon fibers and matrix resins. After maleic anhydride grafting, the carbon fiber surface can provide active functional groups that can chemically react or form physical bonds with the matrix resin, thereby increasing the bonding between the two and avoiding the common problem of insufficient interfacial adhesion in traditional composite materials. Through this modification, the composite material can maintain structural stability for a longer period of time under higher loads; Thermally responsive control particles (PCL-g-PNIPAm copolymer) are one of the key innovations in this invention. The particles are thermally responsive and can undergo changes in physical properties at a specific temperature, thereby adjusting the structure and performance of the composite material. The particularity of PCL-g-PNIPAm copolymers is that their particle size is between 200–500 nm, which allows them to be finely distributed in the composite material and automatically expand or contract when the external temperature changes. When the temperature rises, the particles can utilize their unique thermal responsive properties to locally expand at cracks or defects and fill gaps, thereby achieving self-repair function. This process is based on the adjustability of the particles, which greatly enhances the durability and reliability of the composite material in complex use environments; The introduction of dynamic cross-linking agent precursors enables the composite material to reconstruct its network structure through reversible chemical reactions under high temperature conditions. The precursor is composed of aromatic aldehydes and diol monomers, which can form a reversible Schiff base network structure. The reversibility of the Schiff base means that when the material is heated, some of the bonds in the cross-linked network can be broken, and as the temperature drops, new chemical bonds are re-formed. This process not only enhances the self-healing ability of the composite material, but also ensures the structural stability and performance recovery of the material after long-term use. The introduction of a dynamic cross-linking network can automatically adjust the structure of the material according to the ambient temperature or external stress conditions, so that it can still maintain high mechanical properties under multiple thermal cycles or mechanical fatigue; The role of the interfacial coupling agent in the material is to further strengthen the bond between the carbon fibers and the matrix resin. In particular, the bifunctional design of the silane coupling agent allows it to chemically react with both the resin matrix and the carbon fibers simultaneously, forming a stronger interfacial connection. This approach effectively eliminates problems such as insufficient interfacial bonding or uneven fiber dispersion, providing the composite with stronger fatigue and crack growth resistance.

[0011] The present invention also provides a method for preparing a carbon fiber composite wire for enhancing the mechanical strength and durability of a 3D printed part, comprising the following steps: Step 1: Mixing the matrix resin, surface functionalized chopped carbon fibers, thermally responsive particles, a dynamic crosslinking agent precursor, and an interfacial coupling agent in proportion to obtain a premix; Step 2: feeding the premix into a twin-screw extruder for melt blending at a temperature in the range of 160–220° C. to simultaneously complete a dynamic crosslinking reaction; Step 3: Cooling and pelletizing the blend to obtain a composite masterbatch; Step 4: melt-extrude the composite masterbatch and control the wire diameter to be 1.75 mm or 2.85 mm to form a composite wire.

[0012] Preferably, the step 1 includes the following sub-steps: The surface functionalized chopped carbon fibers are dried at a temperature of 80-110°C for 1-3 hours. The matrix resin and the thermally responsive particles are pre-mixed in separate containers, and then the chopped carbon fibers, the dynamic crosslinking agent precursor, and the interfacial coupling agent are added in sequence. Use a high-speed mixing device for stirring and mixing. The mixing time is 3-6 minutes, and the stirring speed is maintained at 500-1000 rpm during the process.

[0013] Preferably, the step 2 includes the following sub-steps: The premix was fed into the feed port of the twin-screw extruder at a feed rate of 10–30 kg / h; In the feeding section of the twin-screw extruder, the screw speed is set to 150–250 rpm and the temperature is controlled at 160–200°C to ensure good material feeding and initial heating; In the melting section of the extruder, the temperature is raised to 200–220°C and the screw speed is adjusted to 250–400 rpm to ensure that the materials are fully mixed and dynamically cross-linked under appropriate shear forces. In the discharging section, a stable pressure is maintained and the discharging rate is 20-40kg / h to ensure smooth discharge of materials.

[0014] Preferably, the step three includes the following sub-steps: After the blend is discharged from the twin-screw extruder outlet, it is immediately sent to the cooling water tank for preliminary cooling; In the cooling water tank, keep the water flow continuous and evenly distributed to ensure that the surface of the blend solidifies quickly; The cooled blend is conveyed to the pelletizer inlet via a conveyor belt, ready for pelletizing operation; In the pelletizer, the cooled material is cut into pellets, and the cutting speed is ensured to be stable to avoid pellets that are too large or too small. After pelletizing, the pellets are sent to the drying equipment to remove excess moisture to ensure that the pellets are dried evenly.

[0015] Preferably, the step 4 includes the following sub-steps: Continuously feed the dried composite masterbatch to the feed section of the single-screw or twin-screw extruder; During the screw advancement process, the feeding rhythm is controlled to be synchronized with the screw pushing speed to avoid material stagnation or blockage; After being heated and melted, the melt is guided through a forming die to form a continuous wire; A take-off device is installed at the die exit to stabilize the pulling speed and ensure continuous wire forming; The extruded wire passes through the sizing sleeve and cooling trough in turn for shaping and solidification, and is finally collected by the winding device.

[0016] In summary, the present invention includes at least one of the following beneficial technical effects: 1. The present invention realizes the breaking-recombination function of chemical bonds in the composite system through the reversible acetalization mechanism of the dynamic crosslinker precursor, significantly improving the interfacial bonding strength and network continuity, and forming a closer synergistic structure between the reinforcing phase and the matrix resin.

[0017] 2. The thermally responsive particles of the present invention can migrate along crack or defect interfaces and fill gaps when triggered by temperature. Combined with the chemical reconstruction of the dynamic network, a multi-scale, coupled self-repair strategy is realized, enabling the material to maintain high self-repair efficiency throughout multiple damage-repair cycles.

[0018] 3. The material of the present invention can effectively relieve stress concentration through slip and reconstruction of the microstructure under the action of external force, significantly improving the elongation at break and toughness performance, demonstrating the effect of the material of the present invention in optimizing overall mechanical properties and extending service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0020] The following is combined with Figure 1 , the present invention is described in further detail.

[0021] Example 1 In this embodiment, PLA is used as the matrix resin to prepare a reinforced carbon fiber composite wire. The specific preparation steps are as follows: Raw material ratio: Polylactic acid (PLA): 65wt%; Surface-modified chopped carbon fiber: 28 wt%; Thermally responsive regulated microparticles (PCL-g-PNIPAm): 5wt%; Dynamic crosslinker precursor (aromatic aldehyde / diol): 2 wt%; Interfacial coupling agent (bifunctional silane): 0.5 wt%.

[0022] Step 1: Premix preparation Chopped carbon fibers modified with maleic anhydride-grafted polyolefin were dried at 90°C for 2 hours. PLA and PCL-g-PNIPAm microparticles were pre-dispersed by stirring in separate containers. The carbon fibers, dynamic crosslinker precursor, and interfacial coupling agent were then added in sequence. A high-speed mixer was used to stir at 800 rpm for 5 minutes to form a homogeneous premix.

[0023] Step 2: Twin-screw extrusion The premix was fed into a twin-screw extruder, and the feed section temperature was set at 180°C, the melting section temperature was 215°C, and the discharge section temperature was 210°C; the screw speed was changed from 180 rpm to 320 rpm from the feed section to the melting section to complete the blending and dynamic cross-linking reaction.

[0024] Step 3: Granulation The extrudate is rapidly cooled in a cooling water tank, and after solidification, it is conveyed to a pelletizer to be cut into uniform cylindrical particles, and then enters a hot air dryer for processing to remove residual moisture.

[0025] Step 4: Melt extrusion molding The composite masterbatch is fed into a single-screw extruder with a die set to form wire with a diameter of 1.75 mm. Shaping and winding are completed through a stable pulling and cooling process.

[0026] Example 2 PET was used as the matrix, and the ratio of microparticles to cross-linking agent was appropriately adjusted to verify the adaptability of the components.

[0027] Raw material ratio: Polyethylene terephthalate (PET): 62 wt%; Surface-modified chopped carbon fibers: 27 wt%; Thermally responsive regulated microparticles (PCL-g-PNIPAm): 6 wt%; Dynamic crosslinker precursor: 4 wt%; Interfacial coupling agent: 1 wt%.

[0028] Step 1: Premix preparation The chopped carbon fibers were dried at 100°C for 1.5 hours. The PET and microparticles were added to the mixing vessel after being processed separately. The dynamic crosslinker precursor and silane coupling agent were then added. The mixture was stirred at 750 rpm for 4 minutes to form a premix.

[0029] Step 2: Twin-screw blending The temperature of the feeding section was set at 170°C, and that of the melting section was increased to 220°C. The screw speed was 160 rpm in the feeding section and increased to 350 rpm in the melting section. The blend stayed in the shear section for about 45 seconds, and a dynamic network was generated in situ.

[0030] Step 3: Cooling and granulation After the material is discharged, it directly enters the water bath for cooling, and then the whole solidified material enters the pelletizing mechanism to obtain medium-sized composite masterbatch; it is treated by low-temperature air drying to control the moisture content.

[0031] Step 4: Extrusion The composite masterbatch enters the twin-screw extrusion system, and the die head adjusts the output to produce 2.85mm wire. A constant speed traction device is used to ensure uniform wire thickness, and the wire is wound after cooling.

[0032] Example 3 Optimize the microparticle to crosslinker ratio, control the upper limit of fiber loading, and evaluate the impact of high carbon fiber content on the molding process.

[0033] Raw material ratio: PLA: 60wt%; Surface modified chopped carbon fiber: 30wt%; Thermally responsive particles: 5wt%; Dynamic crosslinker precursor: 4 wt%; Interfacial coupling agent: 1 wt%.

[0034] Step 1: Premixing The carbon fiber drying temperature was controlled at 105°C, and the PLA and microparticles were dispersed and added separately. The high-speed stirring equipment was set to a speed of 900 rpm and the stirring was continued for 3 minutes to complete the mixing of the raw materials.

[0035] Step 2: Melt blending The extruder feed temperature was 185°C, the melting zone temperature was 215°C; the screw speed was 180 rpm in the initial stage, increased to 360 rpm in the middle and later stages, and the residence time was extended in the shear enhancement stage.

[0036] Step 3: Granulation and drying The temperature is lowered by a cooling water tank and a rotary knife pelletizer is used to prepare the masterbatch. The dehydration and drying temperature is controlled to be no higher than 60°C to keep the masterbatch shape stable.

[0037] Step 4: Composite wire extrusion The wire is formed by a single screw extruder. The wire drawing ratio is adjusted synchronously with the die flow rate to ensure the radial dimension stability during the wire forming process. The wire is cooled in a liquid cooling tank and then wound into a roll-shaped feeding product.

[0038] Comparative Example 1: Compared with Example 1, the difference is that no thermal response regulating particles are added, and the other components and operating steps are the same.

[0039] Comparative Example 2: Compared with Example 1, the difference is that no dynamic cross-linking agent precursor is added, and the other components and steps are the same.

[0040] Comparative Example 3: Compared with Example 1, the difference is that the maleic anhydride grafted modified chopped carbon fibers are replaced by chopped carbon fibers without any surface treatment, and the other conditions are the same.

[0041] Test Example 1: Testing the Effect of Thermally Responsive Controlled Particles on Composite Structure Stability Experimental steps: Sample preparation: Example 1: A composite material containing thermally responsive regulated particles (PCL-g-PNIPAm) was prepared according to the formula.

[0042] Comparative Example 1: Preparation of a composite material without thermally responsive particles.

[0043] The samples were prepared using the same equipment and conditions to ensure that only the components differed.

[0044] Extrusion molding: The raw materials of Example 1 and Comparative Example 1 were respectively put into a twin-screw extruder.

[0045] The extruder was set at 180°C in the feed section, 215°C in the melting section, and 210°C in the discharge section, with a screw speed of 200 rpm.

[0046] Observe the fluidity and molding stability of the two materials during the extrusion process, and pay special attention to whether there are phenomena such as flow instability and jetting during the melting process.

[0047] Cooling and observation: The extruded composite material is immediately cooled through a water cooling tank and fed into a pulling device to ensure the stability of the wire after forming.

[0048] Data Records: Record the molding stability, particle distribution consistency, and mechanical properties test results of each experimental sample.

[0049] According to Table 1 above, we can see that: In this experiment, thermally responsive particles have a significant effect on the molding stability and structural uniformity of the composite material. By introducing such particles, the temperature responsiveness of the particles enables them to be better dispersed and stabilized in the matrix resin under appropriate temperature conditions in the molten state of the composite material. Compared with materials without thermally responsive particles, the composite material with the addition of thermally responsive particles has significantly more stable fluidity during the melting process, reducing uneven material flow and jetting. This stability can be attributed to the phase change effect of the thermally responsive particles during the heating process. They are better compatible with the resin matrix at high temperatures and help to enhance the viscosity of the molten material, thereby improving the processing controllability of the composite material.

[0050] In addition, the introduction of thermally responsive particles not only improves the fluidity of the composite material, but also effectively improves the dispersion of the particles. During the extrusion process of the composite material without the addition of the particles, the particle aggregation problem is serious, resulting in an uneven structure within the material. The thermally responsive particles can adjust their morphology under high temperature conditions, reduce aggregation, and promote a more uniform distribution of the material during the molding process. The realization of this mechanism is due to the temperature response characteristics of the thermally responsive particles. During material processing, the particles can adjust their morphology and size in time to ensure their uniform distribution in the composite system, avoiding the dispersion problem of traditional fillers in the resin matrix due to poor surface affinity.

[0051] Finally, the improvement of the mechanical properties of composite materials by thermally responsive particles is also reflected in their promotion of interfacial interactions. The introduction of thermally responsive particles not only improves the flow and dispersibility of the composite material, but also enhances the interfacial adhesion between the resin matrix and the reinforcement phase. When the temperature rises, the volume change of the particles and their interaction with the matrix resin help to form a stronger interfacial connection, thereby improving the tensile strength and elongation at break of the composite material. This mechanism shows that thermally responsive particles not only improve the uniformity of the material at the physical level, but also promote the bonding of the reinforcement phase and the matrix through chemical and physical effects, thereby significantly improving the mechanical properties of the material.

[0052] Experiment 2: Testing the Effect of Dynamic Crosslinker Precursors on Structural Network Formation Experimental steps: Sample preparation: Example 1: A composite material containing a dynamic crosslinking agent precursor (aromatic aldehyde / diol) was prepared according to the recipe.

[0053] Comparative Example 2: Preparation of a composite material without a dynamic crosslinking agent precursor.

[0054] Both samples were prepared using the same starting materials and equipment, ensuring that the only difference was the addition of the dynamic cross-linker precursor.

[0055] Pre-mixing treatment: According to the designed ratio, the matrix resin, reinforcing phase (such as carbon fiber), thermally responsive particles, and dynamic crosslinking agent precursor (for Example 1) were premixed separately. For Comparative Example 2, the dynamic crosslinking agent precursor was skipped and the other components were premixed.

[0056] During the mixing process, a high-speed stirrer (speed of 800 rpm, stirring time of 5 minutes) was used to ensure that the components were fully dispersed.

[0057] Twin-screw extrusion: The premixed materials were fed into a twin-screw extruder, and the set temperatures were: 180°C in the feeding section, 220°C in the melting section, 215°C in the discharging section, and the screw speed was 200 rpm.

[0058] Observe the fluidity and molding stability of the two groups of samples in the molten state, and record whether there is uneven flow or jetting.

[0059] Cooling and forming: The extruded composite material is cooled to room temperature through a water cooling tank to ensure its stable molding.

[0060] Use the pulling device to stretch and form the wire and complete the wire coiling.

[0061] Test method: Molding stability test: Observe the fluidity of the two groups of samples during the extrusion process and whether there are bubbles or unevenness.

[0062] Mechanical properties test: The tensile strength and elongation at break of the formed wire are tested using a tensile tester to evaluate the differences in mechanical properties.

[0063] Data Records: Record the molding stability, particle distribution, structural uniformity and tensile strength data of each test sample in the experiment.

[0064] According to Table 2 above, we can see that: The experimental results show that the introduction of dynamic crosslinker precursors into the material system can induce the formation of a dynamic, reversible crosslinked network structure in situ during melt processing, thereby effectively improving the molding stability of the composite material. This mechanism is based on the dynamic covalent chemical mechanism. Specifically, the introduced aldehyde / diol crosslinker precursor undergoes a reversible acetalization reaction at a certain temperature, forming dynamic crosslinks. This provides the material with a certain network structure support during the thermal processing stage, thereby maintaining the integrity and uniformity of the internal structure during the heated shear flow process, significantly reducing the occurrence of phenomena such as spraying and material blockage.

[0065] Microstructural observations reveal that in composite materials containing crosslinker precursors, the particles and reinforcing components can be more evenly dispersed during processing. This is because the dynamic network provides a self-regulating confined environment during the melting phase, which not only ensures good material fluidity but also spatially constrains the components, preventing localized aggregation. Furthermore, the network exhibits a certain degree of recoverability. When microscopic perturbations occur in the molten system, the dynamic bonds can break and reorganize, thereby enhancing the composite material's structural recovery during the perturbation and contributing to the formation of a more stable and uniform three-dimensional interpenetrating network structure.

[0066] In terms of mechanical properties, the presence of a dynamic cross-linked network also provides support for improving the strength and toughness of composite materials. On the one hand, the presence of a cross-linked structure enhances the synergistic effect between interfaces, allowing a tighter interface bond to form between the thermally responsive particles and the matrix resin, thereby improving the overall load transfer capacity. On the other hand, the reversibility of the dynamic bond can achieve moderate slippage and reconstruction of the microstructure when subjected to external forces, effectively alleviating local stress concentration, thereby improving the elongation at break and overall tensile properties of the material. This result confirms the ability of the dynamic network to achieve self-regulation and steady-state maintenance in the material system, and is an important mechanistic basis for improving the performance of composite structures.

[0067] Experiment 3: Testing the behavior of thermally responsive composite structures during controlled desorption Experimental steps: Sample preparation: Example 1: Preparation of a composite material containing thermoresponsive microparticles (such as PCL-g-PNIPAm) and a dynamic crosslinker precursor.

[0068] Comparative Example 3: Preparation of a composite material containing neither thermally responsive particles nor cross-linking agent precursor.

[0069] Heating treatment: Each sample was placed on a controllable heating platform and slowly heated from room temperature to 60, 80, and 100°C according to the set heating curve, and kept warm for 10 minutes.

[0070] After each temperature point, samples were quickly taken and cooled to room temperature.

[0071] Structural inspection after heating: Optical microscopy and scanning electron microscopy were used to analyze the samples after treatment at different temperatures to observe whether the particles desorbed, aggregated, or migrated.

[0072] The thermal response behavior of the sample was detected by a DSC thermal analyzer to confirm the response state of the particles at each temperature point.

[0073] Reversibility test: After the sample was heated to 100°C and cooled to room temperature, the microstructure was observed again to see whether it could be restored and to evaluate its structural reversibility.

[0074] If recovery is evident, record the interface recombination or particle redistribution.

[0075] Data recording and organization: Record the changes in particle position, interface structure integrity and morphology of each sample at different temperature points.

[0076] According to Table 3 above, we can see that: Experimental results show that the composite material exhibits significant structural response characteristics during heating. In particular, in a system containing thermoresponsive particles and a dynamic crosslinker precursor, its interfacial structure undergoes temperature-induced, controllable changes. This behavior can be attributed to the phase transition of the thermoresponsive particles at a specific temperature. When the temperature exceeds the phase transition threshold, the particles transition from a hydrophilic to a hydrophobic state, resulting in a decrease in the interfacial bonding between them and the surrounding matrix, thereby enabling controlled desorption of the particles in localized areas. This process allows the composite material to undergo stress release and microstructural loosening at the structural level after heating, facilitating subsequent structural adjustment and reversible recovery.

[0077] Further observations revealed that in the presence of a dynamic crosslinker precursor, the structural desorption caused by heat is not irreversible, and the system can achieve partial self-repair of the structure during the cooling phase through the breakage-recombination mechanism of dynamic covalent bonds. In this mechanism, the reversible acetal bonds formed by the crosslinker precursor under the action of heat provide network support. When the temperature drops, these bonds can be reformed, prompting the particles that were originally slightly desorbed or had loose interfaces to reposition and fix, thereby restoring the composite structure to a state close to its initial state. This reversible behavior was not observed in the comparative samples that did not contain dynamic crosslinking components, indicating that the construction of a dynamic network is a key factor in achieving controllable and self-repairing behavior.

[0078] Furthermore, a comparison of the interface morphologies after treatment at different temperatures reveals that the responsive particle system exhibits strong interface regulation and structural flexibility. Under heat, this type of composite structure can undergo partial deconstruction, facilitating stress relief; and during the temperature drop, the structural integrity can be gradually restored with the help of the "remodeling effect" of the dynamic network. This dynamic regulation and reversible response mechanism is the core foundation for the design of composite materials to achieve functional integration (such as thermally triggered release and structural self-regulation), and is also an important manifestation of the present invention in terms of multi-scale structural control.

[0079] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A carbon fiber composite wire for enhancing the durability of 3D printed parts, characterized in that: The wire comprises the following components: 60-70 wt % of a matrix resin, wherein the matrix resin is selected from polyethylene terephthalate or polylactic acid; 25–30 wt% of surface-modified chopped carbon fibers, wherein the chopped carbon fibers have a length of 1–5 μm and are surface-functionalized with maleic anhydride grafts; 5–8 wt% of thermally responsive controlled particles, comprising PCL-g-PNIPAm copolymers with a particle size of 200–500 nm; Dynamic cross-linker precursors (2–5 wt%) are composed of aromatic aldehydes and diol monomers, which can form a reversible Schiff base network structure; The interfacial coupling agent is 0.5–1 wt%, which is a silane coupling agent with a bifunctional group.

2. The carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The matrix resin has a melt index range of 3-15 g / 10 min, a glass transition temperature of not less than 55° C., and a molecular weight distribution index between 1.5 and 2.

5.

3. The carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The chopped carbon fibers have a moisture content of no more than 0.2 wt% before surface modification and a specific surface area of 0.5–2.0 m 2 / g, the grafted substance is a polyolefin polymer with anhydride groups, and is treated with the carbon fiber surface by melt coating at a treatment temperature range of 170-200°C.

4. The carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The mass ratio of ε-caprolactone to N-isopropylacrylamide in the thermally responsive regulating microparticles is 1:1 to 3:

1. The microparticles are prepared by emulsion polymerization, are spherical or quasi-spherical, and have a polydispersity index of particle size distribution of ≤0.

3.

5. The carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The thermally responsive regulating particles are freeze-dried after the copolymerization reaction, and the residual moisture content thereof is ≤1.0wt%. The molar ratio of the aromatic aldehyde to the diol of the dynamic crosslinking agent precursor is 0.8:1 to 1.2:

1.

6. A method for preparing a carbon fiber composite wire for enhancing the durability of a 3D printed part, according to the carbon fiber composite wire for enhancing the durability of a 3D printed part according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Mixing the matrix resin, surface functionalized chopped carbon fibers, thermally responsive particles, a dynamic crosslinking agent precursor, and an interfacial coupling agent in proportion to obtain a premix; Step 2: feeding the premix into a twin-screw extruder for melt blending at a temperature in the range of 160–220° C. to simultaneously complete a dynamic crosslinking reaction; Step 3: Cooling and pelletizing the blend to obtain a composite masterbatch; Step 4: melt-extrude the composite masterbatch and control the wire diameter to be 1.75 mm or 2.85 mm to form a composite wire.

7. The method for preparing a carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The step 1 includes the following steps: Drying the surface functionalized chopped carbon fibers at a temperature of 80-110° C. for 1-3 hours; The matrix resin and the thermally responsive particles are placed in separate containers and pre-mixed, and then the chopped carbon fibers, the dynamic crosslinking agent precursor and the interfacial coupling agent are added in sequence; Use a high-speed mixing device for stirring and mixing. The mixing time is 3-6 minutes, and the stirring speed is maintained at 500-1000 rpm during the process.

8. The method for preparing a carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The second step includes the following sub-steps: The premix was fed into the feed port of the twin-screw extruder at a feed rate of 10–30 kg / h; In the feeding section of the twin-screw extruder, the screw speed is set to 150–250 rpm and the temperature is controlled at 160–200°C to ensure good material feeding and initial heating; In the melting section of the extruder, the temperature is raised to 200–220°C and the screw speed is adjusted to 250–400 rpm; In the discharging section, a stable pressure is maintained and the discharging rate is 20-40kg / h to ensure smooth discharge of materials.

9. The method for preparing a carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The step three includes the following sub-steps: After the blend is discharged from the twin-screw extruder outlet, it is immediately sent to the cooling water tank for preliminary cooling; In the cooling water tank, keep the water flow continuous and evenly distributed to ensure that the surface of the blend solidifies quickly; The cooled blend is conveyed to the pelletizer inlet via a conveyor belt, ready for pelletizing operation; In the pelletizer, the cooled material is cut into pellets and the cutting speed is kept stable to avoid pellets that are too large or too small. After pelletizing, the pellets are sent to the drying equipment to remove excess moisture to ensure that the pellets are dried evenly.

10. The method for preparing a carbon fiber composite wire for enhancing the durability of 3D printed parts according to claim 1, characterized in that: The step 4 includes the following steps: Continuously feed the dried composite masterbatch to the feed section of the single-screw or twin-screw extruder; During the screw advancement process, the feeding rhythm is controlled to be synchronized with the screw pushing speed to avoid material stagnation or blockage; After being heated and melted, the melt is guided through a forming die to form a continuous wire; A take-off device is installed at the die exit to stabilize the pulling speed and ensure continuous wire forming; The extruded wire passes through the sizing sleeve and cooling trough in turn for shaping and solidification, and is finally collected by the winding device.

Images