WO2025106053A1

WO2025106053A1 - A filament for additive manufacturing and production method

Info

Publication number: WO2025106053A1
Application number: PCT/TR2024/051340
Authority: WO
Inventors: Alperen DOĞRU; Mehmet Özgür Seydi̇beyoğlu
Original assignee: Ege Ueniversitesi Idari Ve Mali Islerdaire Bsk
Current assignee: Ege Ueniversitesi Idari Ve Mali Islerdaire Bsk
Priority date: 2023-11-15
Filing date: 2024-11-15
Publication date: 2025-05-22
Anticipated expiration: 2026-05-15

Abstract

The invention relates to a filament with improved mechanical characteristics for use in additive manufacturing methods and the production method of this filament.

Description

A FILAMENT FOR ADDITIVE MANUFACTURING AND PRODUCTION METHOD

Technical Field of the Invention

State of the Art of the Invention

The introduction of engineering plastics in the additive manufacturing market and particularly their reinforcement with fiber reinforcements by forming matrices creates new areas of use. Additive manufacturing methods are increasingly being used in the production of prototypes, pre-test and test parts, and final products, particularly in the aerospace, automotive, defense, white goods, and marine sectors.

The use of pure polymers and standard polymers such as PLA and ABS in additive manufacturing methods limits the preference of these methods in applications that require performance. The low mechanical, thermal, and chemical properties of standard polymers, combined with the low bonding occurring in additive manufacturing in the direction where the layers join, lead to dysfunctional products. Although the production of anisotropic structures seems to be a positive aspect of additive manufacturing, the insufficiency of the bonding regions of the layers and, if any, the interface formed with the matrix in fiber reinforcements, creates many negative aspects, especially for mechanical properties. Although this situation is attempted to be eliminated by methods such as sintering and pressure application after various productions, when it falls below the melting temperature or even the glass transition temperature, these effects are very low.

Reinforcing pure polymers with fibers and/or nanoparticles is a method that has been applied for many years. These additives are applied to change various properties of polymers. Carbon fiber is the most preferred type of fiber to increase strength and is the one with the most positive results obtained. However, carbon fibers have a costincreasing effect due to production difficulties. Glass fibers, on the other hand, can in many cases be even cheaper to use for matrix than polymers. Products in which only carbon and only glass fiber are used as reinforcement in different ratios in the polyamide matrix are available in many industries. Formed as a filament shape and commercialized products are also available for additive manufacturing methods. The increase in the fiber ratio has positive results in terms of tensile strength, but reduces the impact strength.

Document with publication number US20200247995A1 discloses a thermoplastic composition comprising an amorphous polyamide polymer and a crystalline or semicrystalline thermoplastic polymer for 3D printing.

Document with publication number US9744722B2 discloses an additive manufacturing method. The method here uses a polyamide blend comprising at least one semicrystalline polyamide and at least one amorphous polyamide that is substantially miscible with at least one semi-crystalline polyamide.

Document with publication number CN105440560A, discloses carbon fiber composite material for fused deposition 3D printing and preparation method thereof. Said composite material comprises thermoplastic resin, carbon fiber, anti-oxidant, and processing aids. In order to obtain the carbon fiber used here, the carbon fiber was firstly boiled in nitric acid and then washed and dried. The obtained carbon fiber was coated with titanate.

As a result, all the above-mentioned problems have made it imperative to make an innovation in the relevant field.

Object and Summary of the Invention

The main object of the invention is to increase the mechanical properties, especially the high strength value, to optimize the cost, and to introduce easily formable structures in the filaments used in additive manufacturing.

The main object of the invention is to improve the interface between the matrix and the fiber in filaments used in additive manufacturing and thus to increase the mechanical strength, especially in multilayer structures. Thanks to its mechanical properties and cost optimization, the designed material offers significant opportunities in the production of parts with complex geometry, requiring mechanical and chemical resistance, having low production volume and/or at the prototype stage.

The present invention designed for achieving these objects introduces a filament composed of a fiber comprising a carbon or glass or a mixture thereof particularly surface-modified with cellulose nanofibrils and/or cellulose nanocrystals, as well as a thermoplastic material. This structure is unique in terms of improving the matrix fiber interface with a sustainable source and using the fibers in a hybrid form. The cellulose nanofibrils and/or cellulose nanocrystals also mentioned herein were exposed to citric acid prior to surface modification. Modifying glass and carbon fibers with cellulose nanofibril and improving the bonding of the interfaces of polyamide matrix and these fibers has a positive effect on their mechanical performance.

Descriptions of the Drawings Describing the Invention

The drawings and the related descriptions used in order to better describe the device designed with this invention are as follows.

Fig. 1. Schematic representation for the production of modified fibers.

Fig. 1a. Schematic representation of the production of the filament of the invention.

Fig. 2. Tensile test results of various embodiments of the filament of the invention and the graph thereof.

Fig. 3. The SEM image of the hybrid filament of the invention.

Fig. 4. The SEM image of the hybrid filament of the invention without surface modification

Detailed Description of the Invention

The subject of the invention relates to a filament with improved mechanical characteristics for use in additive manufacturing methods and the production method of this filament. Referring to Figure 1 ; for the production of the current filament, the surface modification of the fiber to be used is first carried out. Here, carbon fiber, glass fiber, or, if a hybrid structure is desired to be created, both fibers are selected as the fiber to be surface modified. Preferably, glass fiber and carbon fiber are subjected to surface modification separately. Alternatively, glass fiber and carbon fiber surfaces can be modified together if the ratios by weight have previously been determined.

It is preferably mixed with glass fibers or carbon fibers, or separately with cellulose nanofibrils and/or crystals of both, at a rate of 0.1 -2% by weight according to the total weight of nanofibrils and/or crystals.

Said surface modification process is carried out as follows. Preferably, fibril cellulose (nano) and/or cellulose nanocrystals are used as cellulose fibers for surface modification. The description here will be based on cellulose nanofibril, but it should be understood that cellulose nanocrystal alone or a mixture of cellulose nanofibril/cel lulose nanocrystal can also be used in the disclosed embodiments.

Cellulose, which is a hydrophilic material, is easily affected by moisture. For this reason, firstly, cellulose fiber is added to the citric acid (lemon salt) solution and mixed between 40-60 °C for 15-30 minutes, preferably at 50 °C for 20 minutes. Then, in order to disperse the cellulose fibers, they are mechanically stirred together with fibers in a solvent, preferably toluene solvent, for 30-90 minutes, preferably 60 minutes. What is meant by fiber here is either only glass fiber and carbon fiber or both glass fiber and carbon fiber. Finally, the fibers that have undergone surface modification are dried. Here, a vacuum oven is preferably used for the drying process, preferably between 70- 90 °C for 36-60 hours, particularly at 80 °C for 48 hours.

Preferably, carbon fiber reinforcement has a density in the range of 1.7-1.8 g/cm3, particularly 1.73g/cm3. Said carbon fiber here is preferably short carbon fibers with values of tensile strength of 4000- 4500 MPa, particularly 4200MPa, and preferably a tensile modulus of 220-260 GPa, particularly 240GPa, with a diameter of 7p and a length of 6mm.

Glass fiber reinforcement, on the other hand, has a density in the range of 2.5-2.6 g/cm3, particularly 2.55g/cm3. Said glass fiber here is preferably short e-glass fibers with values of a tensile strength of 3300-3500 MPa, particularly 3400MPa, and preferably a tensile modulus of 60-90 GPa, particularly 75GPa, with an average diameter of 11 p and a length of 4.5mm.

These dimensions of the fibers have been determined to avoid clogging in the 3D printer nozzle.

Said cellulose fiber has a high surface area. Preferably, cellulose fibers with a surface area of 150-600 m2/g are selected. Here, cellulose fibers are about 5-20 nanometers (nm) in diameter and 150-200 nanometers in length and have a density of 1.5g/cm3. Preferably, white colored and odorless cellulose fibers are used.

Referring to Fig. 1a, the surface-modified fibers are mixed with a thermoplastic polymer and then this mixture is extruded to obtain filaments. Here, the extruding process is preferably carried out by means of a twin-screw extruder. Preferably the nozzle temperature of the extruder is 240-260 °C, particularly 250°C, has a layer thickness of 0.1 mm and preferably a nozzle diameter of 0.4-0.6 mm, particularly a nozzle diameter of 0.6 mm.

In this study, the fibers to be extruded together with the thermoplastic matrix are between 10-20% by weight relative to the total weight. This 10-20% ratio can consist of only carbon fiber and glass fiber, or this ratio can be obtained with a mixture of these fibers.

As a thermoplastic matrix, preferentially polyamide, particularly polyamide 6 was used. PA6 is a translucent or opaque white, thermoplastic, lightweight material with good toughness, resistance to chemicals, and strong mechanical properties. Compared to other common polymers used in additive manufacturing methods, PA6 has high mechanical properties and can produce strong parts. In addition, when the properties of the 3D printer devices in the market were examined, it was seen that the PA6 was compatible with the system.

PA6 is preferred in many engineering applications, especially in the automotive industry. Thanks to its physical properties, PA6 is a polymer matrix that creates opportunities for thermoplastic composites. For all these reasons and due to its uniqueness, PA6 has been determined as the matrix material.

Preferably, as thermoplastic polymers, especially polyamide 6, materials with a density in the range of 1.1 -1.16 g/cm3, particularly 1.13 g/cm3, and a relative viscosity value preferably between 3-6, especially 4, were selected. These values were chosen because they are suitable for the extrusion process. The PA6 pellets used are preferably cylindrical in shape and have a size between 2-2.5mm.

All compositions were formed into filaments, each with a diameter of 2.85mm (- /+0.15mm), preferably with a single screw extruder for use in 3D printers. All compositions were dried at 80 °C for 4 hours before the process. Barrel and mold temperatures between 180-235 °C were used to ensure line continuity and to keep the diameter within tolerances. These values were determined by the results of DSC analysis.

Using filaments produced from all compositions, tensile test samples according to ASTM D638 standard and Charpy impact test samples according to ISO-179 standard were produced and tested. At least six of each sample were produced by considering the effects of different parameters.

In the preliminary trial studies, the effects of many different parameters on mechanical properties were investigated. Below the highest values obtained produced with the parameters determined after optimization are shown in Table 1 and Figure 2. In this table, Pure PA6 refers to an untreated filament, i.e. a filament using only polyamide 6 as the thermoplastic matrix, PA6CF10c refers to a filament obtained using 10% surface modified carbon fiber, PA6CF20c refers to a filament obtained using 20% surface modified carbon fiber, PA6GF10c refers to a filament obtained using 10% surface modified glass fiber, PA6GF20c refers to a filament obtained using 20% surface modified glass fiber, PA6HF10c refers to a filament obtained using 10% surface modified glass fiber-carbon fiber hybrid, PA6HF20c refers to a filament obtained using 20% surface modified glass fiber-carbon fiber hybrid.

Table 1 : Tensile Test Results of Modified Compositions

When the results are examined, cellulose fiber modification in glass fiber-reinforced PA6 (PA6GFxx) samples show very successful results. PA6GF10c composition (10 percent by weight glass fiber reinforced) samples have an increase in tensile strength values at a ratio of 72 to 88%. PA6GF20c samples have an increase in tensile strength values at a ratio of 41 to 52%. It is thought that the amorphous structure of glass fibers will increase the effect of surface treatment carried out with nanocellulose fiber.

The addition of nanocellulose has also shown successful results in carbon fiber- reinforced PA6 samples.

PA6CF10c samples have an increase in tensile strength values at a ratio of 51 to 63%. PA6CF20 samples have an increase in tensile strength values at a ratio of 5 to 11%.

Table 2: Impact Test Results

It has been observed that the impact resistance of pure PA6 is higher compared to those with fiber additives. Although the addition of fiber increases tensile strength, it reduces impact resistance. It also causes a decrease in ductility and the formation of a brittle structure. The increase in the ratio of fibers by weight in the matrix reduces the impact resistance. In all compositions, the impact resistance of samples produced with 7+45 orientation is higher than those with 0/90 orientation. The reason why glass fibers have higher impact resistance is that they are more flexible than carbon fibers. The total area of the matrix-fiber interface increases with the increase in the fiber ratio. This is the reason why the increase in fiber ratio causes a decrease in impact strength.

When the mechanical properties of all samples were examined, it was seen that modifying the fiber surfaces with cellulose nanofiber had a positive effect.

The modification carried out with nanocellulose fiber gives positive results in the final products and increases the mechanical properties. Information about commercially available PA6 matrix composite filaments is given in the table below.

Table 3: Comparison of Commercial Filaments

In the designed material configuration, with 118MPa, results were obtained above the values shared in the data documents of commercial products. In addition, the combined use of carbon and glass fibers creates a cost-reducing effect.

Fiber modification with cellulose nanofibril has positive effects on the matrix-fiber interface, which increases mechanical properties and results in products with higher performance.

The images obtained with SEM also show that cellulose nanofibril modification is effective in adhesions in matrix and fiber bonding regions. It has been observed by microstructure analysis that these processes are effective in adhesion in the matrix and fiber bonding regions, and when the SEM images are examined, it is seen that the matrix-fiber interface bonds are quite good and that the surface modification with cellulose nanofibril improves this. The obtained tensile strength data also confirms this result.

As a result, considering the amount of increase in tensile strength caused by nanocellulose fiber modification to glass fiber reinforced PA6 samples, it can be concluded that there is a small amount of increase in carbon fiber reinforced PA6 matrix samples. The surface modification of glass fibers with cellulose nanofibrils, which has even a lower cost than PA6 matrix material and reduces costs in proportion to the addition, creates a significant change in tensile strength. This will have the effect of increasing the use of low-cost fibers such as glass fiber instead of expensive additives such as carbon fiber.

The present invention produces high-performance products in the polymer and polymeric composite additive manufacturing sector. The achieved hybrid fiber form provides cost optimization and reduces the cost of raw materials in prototype and even final product production. In addition, the use of sustainable resources in value- added processes is ensured by applying carbon and glass fibers surface-modified with cellulose nanofibril into the polyamide matrix in different ratios in hybrid form.

Claims

1. A filament for additive manufacturing, characterized in that it comprises: thermoplastic matrix and 10-20% by weight of glass fiber, carbon fiber, or a hybrid mixture thereof, the surfaces of which are modified with cellulose nanofibrils and/or crystals.

2. An additive according to claim 1 , characterized in that said mixture comprises glass fibers modified with cellulose nanofibril and/or crystal and carbon fibers modified with cellulose nanofibril in equal parts by weight.

3. An additive according to claim 1 , characterized in that said thermoplastic matrix is polyamide.

4. An additive according to claim 1 , characterized in that said thermoplastic matrix is polyamide 6.

5. The production method of a filament for additive manufacturing, characterized by: mixing cellulose nanofibrils and/or crystals with citric acid between 40-60 °C for 15-30 minutes, achieving surface modification by mixing a mixture of cellulose nanofibrils and/or crystals mixed with citric acid, glass fibers or carbon fibers or both separately for 30-90 minutes, drying the obtained surface-modified fibers at 70-90 °C for 36-60 hours, and compounding and extruding 10-20 wt% surface-modified fiber-reinforced thermoplastic matrix.

6. A method according to claim 5, characterized in that said thermoplastic matrix is polyamide.

7. A method according to claim 5, characterized in that said thermoplastic matrix is polyamide 6.

8. A method according to any one of the claims 5-7, characterized in that the density of said thermoplastic matrix is between 1.1 -1.16 gr/cm³.

9. A method according to any one of claims 5-8, characterized in that the relative viscosity of said thermoplastic matrix is between 3-6.

10. A method according to any one of claims 5-9, characterized in that said carbon fiber has a density between 1 .7-1 .8 gr/cm³.

11. A method according to claim 5 or 10, characterized in that the tensile strength of said carbon fiber is between 4000-4500 MPa.

12. A method according to any one of claims 5, 10, 11 , characterized in that the tensile modulus of said carbon fiber is between 220-260 GPa.

13. A method according to claim 5, characterized in that the density of said glass fiber is between 2.5-2.6 g/cm³.

14. A method according to claim 5 or 13, characterized in that the tensile strength of said glass fiber is between 3300-3500 MPa.

15. A method according to any one of claims 5, 13, 14, characterized in that the tensile modulus of said glass fiber is between 60-90 GPa.

16. A method according to claim 5, characterized in that the density of said cellulose fiber is between 1 .4- 1 .6 g/cm³.

17. A method according to claim 5 or 16, characterized in that the surface area of said cellulose fiber is between 150-600 m²/g.

18. A method according to claim 5, characterized in that glass fibers or carbon fibers or both separately are mixed with cellulose nanofibrils and/or crystals at a ratio of 0.1-2% by weight, based on the total weight of nanofibrils and/or crystals.

19. A method according to claim 5, characterized in that said thermoplastic matrix is compounded and extruded in a twin screw extruder.