A polycaprolactone filament for FDM 3D printing and its preparation method

Abstract

The application discloses a modified polycaprolactone wire for FDM 3D printing and a preparation method thereof, and aims to solve the problems of slow cooling, wire drawing, warping and low interlayer strength of the existing PCL wire. Through the synergistic effect of the introduction of ionizing reagent, nucleating agent and elastomer, and the low-temperature cooling process with structural memory effect, the melt strength, cooling speed and size accuracy of the wire are significantly improved, and the nucleation activity is continued to the FDM printing process, which effectively promotes the rapid crystallization of the printing layer, thereby enhancing the interlayer bonding force and reducing the warping of the printed part. The embodiment shows that the tensile strength of the wire is greater than or equal to 45 MPa, the warping deformation amount is less than or equal to 0.5 mm, the MFR is greater than or equal to 6.5 g / 10 min, the wire drawing does not occur in the printing process, the printed part has high crystallinity and high interlayer bonding strength, and the key material support is provided for high-precision FDM printing.

Description

Technical Field

[0001] This invention relates to the field of polycaprolactone filament preparation technology, specifically to a polycaprolactone filament that can be used for FDM 3D printing and its preparation method. Background Technology

[0002] Polycaprolactone (PCL), a biodegradable aliphatic polyester, has shown broad application prospects in biomedical scaffolds, tissue engineering, and personalized 3D printing due to its good biocompatibility, low-temperature processability, and controllable degradation rate. However, its inherent material properties and processing defects severely limit its practical application in fused deposition modeling (FDM) technology. First, PCL's low melting point leads to slow melt cooling during printing, prolonging interlayer bonding time and resulting in insufficient interlayer adhesion and decreased model mechanical properties, especially noticeable in high-precision complex structures, where the printed product is prone to delamination and collapse. Second, PCL has poor melt flowability and low melt strength, easily causing stringing during high-speed extrusion, severely affecting the surface finish of the printed product. Furthermore, excessive melt residence time at the nozzle can lead to thermal degradation, generating bubbles and impurities, further reducing printing accuracy. Furthermore, during the cooling and solidification process, PCL suffers from slow crystallization rates and uneven shrinkage, resulting in internal stress that is difficult to release. This leads to a significant increase in model warping deformation. For example, when printing large-area planar or thin-walled structures, edge warping typically exceeds 1.5 mm, making it difficult to meet the dimensional tolerance requirements of medical implants or precision devices. Existing technologies attempt to improve melt flowability by adding plasticizers, but these plasticizers have limited compatibility with PCL and easily migrate to the material surface, not only reducing mechanical properties but also causing yellowing and a severe decrease in whiteness. On the other hand, some studies use nanofillers to enhance the rigidity of PCL, but the agglomeration of nanoparticles exacerbates the non-uniformity of melt flow, increasing the filament breakage rate by more than 30% during printing, and the high amount of filler added significantly increases costs. In terms of process optimization, existing technologies mostly rely on adjusting printing temperature and layer thickness to balance flowability and cooling rate. However, simply lowering the printing temperature further deteriorates interlayer bonding, while increasing the temperature exacerbates thermal degradation, creating a "process parameter contradiction" that makes it difficult to overcome performance bottlenecks. It is worth noting that although some patents propose solutions for compounding plasticizers and stabilizers, the component ratios are wide-ranging and lack precise control over intermolecular synergistic effects. In practical applications, the problem of not being able to simultaneously achieve melt strength and cooling rate remains. For example, when adding 3wt% acetylthiol tributyl citrate, although the melt flow rate increases from 4.0 g / 10 min to 5.5 g / 10 min, the tensile strength decreases to 28 MPa, and the cooling time is only shortened by 10%, failing to fundamentally solve the warping deformation problem. In addition, existing technologies have relatively limited exploration of cooling processes, usually employing room temperature natural cooling or air cooling. Insufficient cooling rates lead to grain coarsening, further weakening the material's toughness. More importantly, even if the filament achieves fine crystals through nucleation and cooling control during the fabrication process, it often loses its nucleation advantage during the subsequent secondary melting process in FDM printing due to complete melting of the crystal nuclei. The printed product still needs to undergo a slow crystallization process again, resulting in poor interlayer bonding and warping deformation problems that remain prominent.In summary, while existing technologies have achieved partial improvements in individual performance aspects, they have failed to achieve synergistic enhancements in cooling rate, melt strength, dimensional stability, and overall mechanical properties of PCL filaments through systematic innovation in material formulation and process design. In particular, the lack of a full-process crystallization control mechanism from filament to printed product results in significant technical barriers to its application in high-precision FDM printing. A solution that can overcome multiple objectives and combine high efficiency with economy is urgently needed. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention significantly improves the melt strength, cooling rate, and printing accuracy of wires by introducing the synergistic effect of ionizing reagents, nucleating agents, and elastomers, combined with a low-temperature cooling process.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing modified polycaprolactone filaments for FDM 3D printing includes the following steps: (1) Mix polycaprolactone with ionizing reagent, nucleating agent and elastomer; (2) The mixture is melt-extruded to form a wire; (3) Perform low-temperature cooling treatment on the wire; (4) Rewind the cooled wire.

[0005] Preferably, the mass ratio of each component in step (1) is: Polycaprolactone: 100 parts; Ionizing reagent: 1-10 parts; Nucleating agent: 1-10 parts; Elastomer: 1-20 parts.

[0006] Preferably, the ionizing agent is zinc stearate or sodium sulfate with a particle size of 100-500 nm.

[0007] Preferably, the nucleating agent is talc or nano-silica with a particle size of 50-200 nm.

[0008] Preferably, the elastomer is thermoplastic polyurethane (TPU) or hydrogenated styrene-butadiene-styrene block copolymer (SEBS), with TPU having a molecular weight of 2000-10000, SEBS having a molecular weight of 50000-100000, and the powder particle size ≤100μm.

[0009] Preferably, in step (2), the melt extrusion temperature is 120-160℃ and the screw speed is 50-150rpm.

[0010] Preferably, in step (3), the low-temperature cooling temperature is -10 to 20°C and the cooling rate is 5 to 15°C / min.

[0011] Preferably, step (4) further includes ultrasonic vibration-assisted cooling, specifically including: First stage: Liquid nitrogen spray cooling at -10~0℃ (rate 50℃ / min), lasting 3 seconds; Second stage: Cooling with 20℃ cold air, and simultaneously applying ultrasonic vibration (frequency 20kHz, amplitude 10μm).

[0012] Preferably, the wire diameter is 1.75±0.05mm, the tensile strength is ≥45MPa, and the warpage is ≤0.5mm.

[0013] The low-temperature cooling and ultrasonic vibration treatment of the present invention not only significantly improves the dimensional stability of the wire, but also, through the formation of structural memory effect, allows the nucleating agent to retain some activity or redisperse as heterogeneous nucleation points after printing and melting, thereby promoting rapid crystallization of the melt during the printing process and improving the interlayer bonding strength and product dimensional accuracy. Beneficial effects

[0014] This invention achieves a systematic improvement in the melt strength, cooling rate, mechanical properties, and dimensional accuracy of PCL filaments through a four-dimensional innovative system of ionization enhancement, nucleation acceleration, elastic toughening, and temperature-controlled shaping. It resolves existing multi-objective performance contradictions and provides crucial material support for high-precision FDM printing, especially for biomedical scaffolds and precision devices. Its effects far exceed those of single modifications or process adjustments, possessing broad industrial application value. Low-temperature cooling combined with ultrasonic vibration not only refines the filament grains and releases internal stress but also enables the nucleating agent to form a stable dispersion and partially oriented structure within the PCL matrix. This structure exhibits a memory effect during the subsequent secondary melting in FDM printing, effectively guiding rapid heterogeneous nucleation of the melt and significantly improving the crystallization rate and uniformity of the printed layer. This extends the crystallization advantages of the filament stage to the final product, achieving a full-chain performance improvement from materials to molding processes. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] Example 1: Preparation of a modified polycaprolactone filament for FDM 3D printing: zinc stearate, talc, TPU modification Raw material preparation Polycaprolactone (PCL): 100g, dried in an oven at 40℃ for 4h to remove moisture, then cooled with liquid nitrogen and ground to obtain PCL powder with an average particle size of 50μm.

[0017] Zinc stearate (ionizing agent): 5g, particle size 200nm, pretreated using an air jet mill until uniformly dispersed.

[0018] Talc powder (nucleating agent): 5g, particle size 100nm, surface modified with silane coupling agent (KH-550) (modification time 30min, temperature 60℃).

[0019] Thermoplastic polyurethane (TPU, elastomer): 10g, molecular weight 5000, cut into 2mm granules for later use.

[0020] Preparation steps Gradient blending: First mixing: Add PCL powder and zinc stearate to a high-speed mixer (SHR-10A) and stir at 55°C and 1500 rpm for 20 minutes to allow the ionizing reagent to be uniformly adsorbed on the surface of the PCL particles.

[0021] Secondary mixing: Add talc powder and continue mixing at 55℃ and 1200 rpm for 15 minutes to form PCL-ionizing reagent-nucleating agent premix.

[0022] Three-stage mixing: Add TPU particles and mix at a low speed of 60℃ and 800rpm for 30 minutes to avoid excessive shear degradation of the elastomer.

[0023] Melt extrusion: Parameters of the twin-screw extruder (LSL-35): Feed section temperature: 120℃, screw speed: 100rpm (for conveying materials); Plasticizing section temperature: 140℃ (main heating zone), screw speed: 100rpm (melt mixing); Homogenization section temperature: 135℃, screw speed: 120rpm (melt homogenization); Head temperature: 140℃, die diameter: 1.75mm (controlling wire diameter).

[0024] During the extrusion process, the wire diameter is monitored in real time using a laser diameter gauge (LDM-200), and the traction speed is adjusted to 1.75±0.03mm.

[0025] Low temperature cooling: -5℃ liquid nitrogen spray, 3s; 20℃ air cooling; 25kHz ultrasonic vibrator, 10μm.

[0026] End of issue: The automatic winding machine has a tension control of 5N and a roll diameter of 500mm. The finished wire is sealed in an aluminum foil bag with a humidity of <20% RH.

[0027] Example 2: Preparation of a modified polycaprolactone filament for FDM 3D printing: high nucleating agent ratio, talc-reinforced crystallization. Raw material preparation PCL: 100g, dried at 50℃ for 3 hours, then ground to 70μm.

[0028] Zinc stearate: 3g, particle size 200nm.

[0029] Talc powder: 8g, particle size 100nm (unmodified, ready to use).

[0030] TPU: 15g, molecular weight 8000, crushed into 5mm particles.

[0031] Preparation steps Gradient blending: First mixing: PCL + zinc stearate, mix at 55℃ and 1800 rpm for 25 min.

[0032] Secondary mixing: Add talc powder and mix at 60℃ and 1500rpm for 20min (high shear promotes the dispersion of nucleating agent).

[0033] Three-stage mixing: TPU particles, mixed at 60℃ and 600rpm for 40 minutes (low speed to protect the elastomer).

[0034] Melt extrusion: Extruder parameters: The feed section is 130°C, the plasticizing section is 160°C, the homogenizing section is 150°C, the die head is 155°C, and the screw speed is 120 rpm.

[0035] Wire diameter: 1.75mm, traction speed: 6m / min.

[0036] -5℃ liquid nitrogen spray, 3s; 20℃ air cooling; 25kHz ultrasonic vibrator, 10μm.

[0037] Example 3: Preparation of a modified polycaprolactone filament for FDM 3D printing: low-temperature high-speed cooling, limiting process window Raw material preparation PCL: 100g, dried at 45℃ for 5h, then ground to 60μm.

[0038] Zinc stearate: 7g, particle size 300nm (slightly larger particle size increases melt viscosity).

[0039] Talc powder: 3g, particle size 150nm.

[0040] TPU: 5g, molecular weight 3000 (low molecular weight improves flowability).

[0041] Preparation steps Gradient blending: First mixing: PCL + zinc stearate, mix at 55°C and 1000 rpm for 15 min (low shear to avoid decomposition of ionized reagents).

[0042] Secondary mixing: talc powder, mix at 60℃ and 900rpm for 10min.

[0043] Three-stage mixing: TPU particles, 60℃, 500rpm for 50min (long-term low-speed dispersion).

[0044] Melt extrusion: Extruder parameters: Feeding section 100℃, plasticizing section 120℃, homogenizing section 115℃, die head 120℃, screw speed 80rpm (low speed ensures uniform melt).

[0045] -5℃ liquid nitrogen spray, 3s; 20℃ air cooling; 25kHz ultrasonic vibrator, 10μm.

[0046] The key difference between Comparative Example 1 and Example 1 is that the nucleating agent is absent, and only PCL, zinc stearate, and TPU are used. Raw materials and steps Differences: Talc powder is removed from the raw materials, and the remaining proportions are 100 parts PCL, 5 parts zinc stearate, and 10 parts TPU.

[0047] Mixing steps: Add PCL + zinc stearate + TPU directly to the mixer at once, mix at 70℃ and 1000rpm for 40min (no secondary nucleating agent mixing step).

[0048] Cooling process: The same as in Example 1 (but the crystallization rate decreases due to the absence of a nucleating agent).

[0049] The key difference between Comparative Example 2 and Example 1 is that Comparative Example 2 lacks an elastomer and only contains PCL, zinc stearate, and talc. Raw materials and steps Differences: TPU is removed, and the remaining proportions are 100 parts PCL, 5 parts zinc stearate, and 5 parts talc.

[0050] Mixing steps: omit the third mixing step (no elastomer added), and directly extrude after the second mixing step.

[0051] Extrusion parameters: Same as in Example 1, but due to the absence of an elastomer, the melt brittleness increases.

[0052] The key difference between Comparative Example 3 and Example 1 is that Comparative Example 3 was cooled at room temperature, while Example 1 was naturally cooled at 25°C. Raw materials and steps Difference: The cooling process has been changed to room temperature (25℃) natural cooling.

[0053] Cooling rate: approximately 1°C / min (natural convection), cooling time > 30s.

[0054] The key difference between Comparative Example 4 and Example 1 is that Comparative Example 4 involves a one-time mixing process without gradient mixing. Raw material ratio Same as Example 1 (ensuring a single variable: only the mixing process is changed): Polycaprolactone (PCL): 100 parts Zinc stearate (ionizing agent): 5 parts (particle size 200nm) Talc (nucleating agent): 5 parts (particle size 100nm, unmodified) TPU (elastomer): 10 parts (molecular weight 5000) Preparation steps (difference: one-time mixing) Mixing process: PCL powder, zinc stearate, talc, and TPU granules are added to a high-speed mixer at once and stirred at 60°C and 1500 rpm for 40 minutes (traditional blending method, without staged mixing).

[0055] Melt extrusion: Same parameters as in Example 1 (140°C, screw speed 100 rpm).

[0056] Cooling and post-treatment: Same as the previous example.

[0057] The performance of the above-mentioned embodiments and comparative products was tested according to the methods listed in Table 1, and the results are shown in Table 2; ;

[0058] From the data above, we can see that: Zinc stearate plasma reagents form intermolecular ionic bonds with PCL through polar groups, increasing melt viscosity while providing anchoring sites for nucleating agents, resulting in a 50% increase in nucleation efficiency and a 60% reduction in grain size. This dual-functional modification of viscosity regulation and accelerated crystallization breaks through the limitation of traditional plasticizers that only adjust flowability, achieving a balance between high melt strength and rapid crystallization cooling. For example, in Comparative Example 1, which lacks nucleating agents, the crystallization efficiency remains low despite the presence of ionizing reagents.

[0059] Elastomers such as TPU / SEBS form a nanoscale dispersed phase within the PCL matrix, with a particle size ≤100nm. When microcracks occur between printing layers, the elastomer particles absorb energy through deformation, increasing the crack propagation resistance by a factor of three. In contrast, Comparative Example 2, without elastomers, shows a sharp drop in impact strength. Simultaneously, the elastomer network restricts excessive slippage of the PCL molecular chains, improving the internal stress dispersion efficiency during warpage deformation by 40%, achieving synergistic optimization of strength, toughness, and dimensional stability.

[0060] Low-temperature cooling precisely controls crystallization kinetics, increasing the proportion of β crystal form to 70%, while room-temperature cooling only accounts for 30%. The crystal form transformation of this invention results in a 15% increase in modulus. Ultrasonic vibration promotes stress release during cooling, significantly reducing residual stress inside the wire.

[0061] Zinc stearate (Zn) 2+ It forms a dynamic coordination network with PCL, which reduces the elastic modulus of the melt, achieving high fluidity and zero fiber drawing; SEBS / talc inhibits the slippage of PCL molecular chains through π-hydrogen bonds, greatly compressing the warpage.

[0062] This invention achieves breakthroughs in the following aspects through a four-dimensional innovative system of ionization enhancement, nucleation acceleration, elastic toughening, and temperature-controlled shaping: Synergistic performance improvement: tensile strength increased by 80%, warpage decreased by 73%, and impact strength increased by 100%, far exceeding the effect of single modification. For example, the strength of the solution with only elastomer added increased by 30%, and the warpage decreased by 40% with only temperature control and cooling.

[0063] Solving the process contradiction: MFR is controlled at 5-7g / 10min, which avoids the low strength of traditional PCL (MFR>8g / 10min) and solves the problem of fluidity deterioration caused by filler reinforcement (MFR<4g / 10min), achieving high-speed printing without stringing and high adhesion at low temperature.

[0064] Cross-scale mechanism: From intermolecular ionic bonds to grain refinement and wire stress release, the size ranges from nanometer to submicron to millimeter, forming a multi-scale synergistic effect. However, the comparative scale cannot achieve effective control of any link due to the lack of key components or processes.

[0065] Data shows that the technological improvements provided by this invention are not simply additive, but rather solve the core problem of PCL filament in FDM printing through deep coupling of material formulation and process parameters, and have broad industrial application value.

[0066] Print verification test: To verify the sustained effect of the wire modification of the present invention during the FDM printing process, standard test samples were printed from the wires obtained in Examples 1-3 and Comparative Examples 1-4 on the same FDM printer. The process parameters were: layer thickness 0.2 mm, printing temperature 180°C, substrate temperature 60°C, and printing speed 60 mm / s. The printed samples were then subjected to the following tests: ;

[0067] The above data demonstrate that the filaments prepared by the ionization-nucleation-elastic toughening-temperature-controlled shaping synergistic system of this invention still exert a significant crystallinity control effect during FDM printing. The crystallinity of Examples 1-3 after printing is all above 65%, with fine grain size (<100nm), high interlayer shear strength, and small warpage. This confirms that the low-temperature cooling and nucleating agent dispersion during filament preparation create structural memory, which continues to promote heterogeneous nucleation after printing and melting, thereby optimizing the crystallinity kinetics, interlayer bonding, and dimensional stability of the printed product. In contrast, Comparative Examples 1 and 3 show low crystallinity, coarse grains, and significant performance degradation after printing, further verifying the continuous positive impact of the process of this invention on the printing process.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing modified polycaprolactone filaments for FDM 3D printing, characterized in that, Includes the following steps: (1) Mix polycaprolactone with ionizing reagent, nucleating agent and elastomer; (2) The mixture is melt-extruded to form a wire; (3) Perform low-temperature cooling treatment on the wire; (4) Rewind the cooled wire.

2. The method according to claim 1, characterized in that, The mass ratio of each component in step (1) is as follows: Polycaprolactone: 100 parts; Ionizing reagent: 1-10 parts; Nucleating agent: 1-10 parts; Elastomer: 1-20 parts.

3. The method according to claim 2, characterized in that, The ionizing agent is zinc stearate or sodium sulfate, with a particle size of 100-500 nm.

4. The method according to claim 2, characterized in that, The nucleating agent is talc or nano-silica with a particle size of 50-200 nm.

5. The method according to claim 2, characterized in that, The elastomer is a thermoplastic polyurethane or a hydrogenated styrene-butadiene-styrene block copolymer with a molecular weight of 50,000-100,000.

6. The method according to claim 1, characterized in that, In step (2), the melt extrusion temperature is 120-160℃ and the screw speed is 50-150rpm.

7. The method according to claim 1, characterized in that, In step (3), the low-temperature cooling temperature is -10 to 20℃, and the cooling rate is 5 to 15℃ / min.

8. The method according to claim 1, characterized in that, Step (4) also includes ultrasonic vibration-assisted cooling, specifically including: First stage: Liquid nitrogen spray cooling at -10~0℃ for 3 seconds; Second stage: Cooling with 20℃ cold air while simultaneously applying ultrasonic vibration.

9. A modified polycaprolactone wire prepared according to any one of claims 1-8, characterized in that, The wire diameter is 1.75±0.05mm, the tensile strength is ≥45MPa, and the warpage is ≤0.5mm.

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