Abstract
Fused filament fabrication (FFF) is a widely used additive manufacturing (AM) technology due to its cost-effectiveness, material efficiency, and the ability to produce complex geometries. However, the mechanical limitations of thermoplastic materials limit their use in broader functional applications. In this study, PLA and ABS thermoplastics were reinforced with 1%, 3%, and 5% carbon fiber (CF) and glass fiber (GF) to improve their mechanical performance. The results showed that 3% reinforcement provided the most balanced performance overall. The highest tensile strength was 29.67 MPa in the ABS + 3%CF samples, while the highest tensile strength among the PLA composites was measured as 17.47 MPa in the PLA + 3%GF samples. The highest impact strength was obtained with 1% reinforcement for ABS and 5% reinforcement (0.47 J) for PLA-GF. While GF reinforcement increased stiffness in PLA, 5% reinforcement in both matrices caused a performance decrease due to fiber agglomeration. SEM–EDS and FTIR analyses supported optimal binding and dispersion at 1–3% reinforcement ratios. The increased strength, toughness, and structural integrity of the resulting 3% reinforced composites suggest that these materials are potential candidates for applications requiring lightweight and durable parts, such as those in the defense industry. Future studies are recommended to evaluate long-term performance criteria such as fatigue and environmental resistance, and to improve fiber distribution for higher reinforcement ratios.
Keywords: Additive manufacturing, Fused filament fabrication, Carbon fiber, Glass fiber, Composite filament
Subject terms: Engineering, Materials science
Introduction
Fused filament fabrication (FFF), a type of additive manufacturing (AM) technology, enables the production of objects by melting thermoplastic filaments and bonding them layer by layer1,2. Polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are the two main thermoplastic matrices frequently used in the FFF process. PLA stands out for its biodegradability and low cost, while ABS is preferred for its high mechanical strength and heat resistance. However, the limited mechanical performance of these thermoplastics makes them insufficient, particularly for engineering and defense applications3–5. Therefore, attempts are being made to overcome these limitations by reinforcing them with reinforcement materials such as carbon fiber (CF) and glass fiber (GF)6. CF has been extensively studied for its ability to enhance the mechanical properties of thermoplastics in FFF applications, thanks to its excellent strength to weight ratio and suitability for structural components in the aerospace and transportation sectors7–10. In contrast, GF has attracted attention as a cost effective reinforcement material, particularly in applications requiring thermal insulation and improved toughness in the defense and automotive industries11,12.
Previous studies have shown that the mechanical properties of thermoplastics used in the FFF method can be significantly improved by fiber reinforcement. Surface modified short carbon fiber (HCF) strengthened the fiber matrix interface in ABS composites and increased the tensile strength13. Similarly, up to 30% short glass fiber (SGF) reinforcement improved both impact resistance and surface quality14. Process parameters such as nozzle diameter have been shown to directly affect the performance of carbon fiber reinforced ABS composites by affecting interlayer adhesion and microstructure15. Optimum tensile properties, along with minimum void ratio and homogeneous distribution, were achieved with the use of 1–3% carbon fiber, indicating that these reinforcements are suitable for lightweight structural applications16. However, at high reinforcement ratios such as 5%, porosity increased, adhesion weakened, and mechanical efficiency decreased17. The effect of the printing direction on the mechanical behavior has also been emphasized, and it has been shown that the highest tensile strength is obtained at certain printing angles18. In addition, nanocomposite and hybrid structures such as carbon nanofiber reinforced polypropylene19, carbon fiber reinforced PLA20, and cement based composites containing recycled carbon fiber21 have also been investigated for high performance applications. While electrical conductivity was significantly increased in graphene reinforced ABS composites, a decrease in tensile strength was observed, suggesting that performance trade-offs should be taken into consideration in multifunctional composites22.
Studies in the literature have mostly been limited to a single fiber type and matrix material, and systematic comparisons of different matrix reinforcement combinations have been neglected. In this study, CF and GF reinforcements were applied to both PLA and ABS matrices at 1%, 3%, and 5%, and all samples were evaluated under the same production and testing conditions. Granular matrix materials and powdered reinforcement materials were extruded into composite filament form, and test samples were produced using an FFF type Y682 functional 3D printer. Tensile, hardness, impact, surface roughness, FTIR, and SEM–EDS analyses were performed on the resulting samples, respectively. The production process and experimental stages are shown in Fig. 1. The effects of fiber type and ratio on mechanical and microstructural properties were investigated in a direct comparative manner, presenting a unique and innovative approach that considers different matrix and reinforcement types together, determines optimum reinforcement ratios, and includes comprehensive characterization. This study, unlike similar studies, makes a significant contribution to the literature by evaluating the multiple matrix-multiple fiber structure and demonstrating its application potential through comprehensive analyses23,24. It is thought that these composites developed using FFF technology can find application areas especially in sectors such as defense, automotive and aerospace.
Fig. 1.
Production process and experimental method in this study.
Material and method
Material
In this study, in order to improve the mechanical properties of PLA and ABS thermoplastic materials in granular form, composite filaments were produced by reinforcing 80 µm ground CF and 100 µm ground e-GF in powder form at different percentages (1%, 3% and 5%). Test samples were produced from the obtained composite filaments using the FFF type Y682 model functional 3D printer, and mechanical and microstructural analyzes of the samples were carried out. The physical and mechanical properties of the materials used in this study are given in Table 1.
Table 1.
Physical and mechanical properties of PLA, ABS, CF and GF materials.
| Material | Tensile strength (MPa) | Modulus of elasticity (MPa) | Hardness (Shore D) | Impact Energy (J) | Density (g/cm3) | Melting Temp. (°C) | |
|---|---|---|---|---|---|---|---|
| PLA (Pure) | 9.5 | 140 | 42.0 | 0.18 | 1.24 | 200 | |
| ABS (Pure) | 8.8 | 250 | 58.0 | 0.45 | 1.10 | 230 | |
| CF-PLA | 16.3 | 2270 | 53.8 | 0.23 | 1.27 | 200 | |
| GF-PLA | 17.5 | 1520 | 64.8 | 0.47 | 1.28 | 200 | |
| CF-ABS | 29.7 | 3540 | 54.8 | 0.36 | 1.22 | 230 | |
| GF-ABS | 23.4 | 3610 | 63.2 | 0.50 | 1.26 | 230 | |
The CF and GF powders used in this study were obtained from the company "Kompozit Pazarı", and the PLA and ABS granules were obtained from the “Filameon” brand. Technical information about these CF and GF powders used in the study is given in Table 2.
Table 2.
Technical information of CF and GF powders.
| Material | Product code | Mean fiber length milled (μm) | Filament diameter (μm) | Single filament resistivity (μΩm) | Bulk density (g/l) | Sizing type |
|---|---|---|---|---|---|---|
| CF | M80-3 | 80 | 7 | 22 | 380 | Unsized |
| GF | FIL100 | 100 | 13 | Insulating | 2620 | Silane-based |
The chemical nature and surface treatment of the reinforcement fibers used in this study played a critical role in the interfacial interactions between fiber and matrix. According to the supplier data, the GF used in this study were sized with a silane based coupling agent, while the CF were unsized (Table 2). Silane based sizings are commonly used to improve the adhesion between glass fibers and polymer matrices by forming covalent and hydrogen bonds with the functional groups in the polymer chains16. These silanes typically contain reactive organofunctional groups such as epoxy, methacryloxy, or amino groups that can interact with hydroxyl or carboxyl groups in polymers like PLA, enhancing fiber–matrix compatibility12,17. In contrast, unsized CF lacks surface functionalization, which may limit its chemical affinity with certain polymer matrices, particularly polar matrices like PLA. The difference in surface chemistry between GF and CF has a significant impact on the mechanical properties and interfacial bonding performance of the resulting composites.
In order to protect the materials from moisture and environmental factors that may occur during the working process, they were kept in vacuum bags and in the laboratory environment to ensure that they were minimally affected by environmental factors. In addition, 10% and 15% reinforcement ratios have been tried in the production of carbon and glass fiber composite filament, and it has been accepted that the optimum reinforcement range should be 1–5% due to the fact that powders create blockages in the nozzle section at the exit of the extruder device. It is thought that the reason why high reinforcement rates cannot be achieved is that the extruder machine works with a single screw and the micron (µm) values of the preferred powder reinforcement materials cannot meet the high reinforcement rates.
Method
In the study, PLA and ABS granules were reinforced with 1%, 3% and 5% CF and GF in powder form (80 µm and 100 µm sizes, respectively). The homogeneity of the composite mixtures was ensured through mechanical mixing in a temperature controlled single screw extruder system. Prior to processing, all raw materials (matrix and reinforcement fibers) were dried to remove moisture and then manually fed into the hopper. The granule-powder mixture was melted by resistive heating within the extruder, and homogeneous dispersion of the reinforcement fibers was achieved through continuous mixing in the screw chamber, resulting in the production of composite filaments. Figure 2 shows the mixture of granules and powder that forms this composite filament.
Fig. 2.
Granule and powder mixture.
After the homogeneous granule and powder mixture was formed, PLA + CF, PLA + GF, ABS + CF and ABS + GF composite filaments with a diameter of 1.75 mm were obtained from the nozzle exit. Figure 3 shows the extruder device used to produce composite filaments, and Fig. 4 shows the form of the composite filaments produced. The 1%, 3% and 5% reinforcement ratios used in the study were determined by the mass ratio of the reinforcement fibers to the matrix material. All raw materials were weighed separately with a precision balance and mixed in dry form according to these ratios.
Fig. 3.
Extruder device.
Fig. 4.
Composite filament formed.
Table 3 and Table 4 inculude the technical properties and process parameters of the extruder device used in the study, respectively.
Table 3.
Technical properties of the extruder device.
| Properties | Values |
|---|---|
| Extruder machine size | 1957 × 25x56 mm |
| Nozzle diameter | Ø 1.75 mm |
| Extrusion screw diameter | Ø 22 mm, L = 40 mm |
| Engine | 12 N/m, 4.2 A, angle of pitch 1.8o |
| Heater | 500 W, 220 V |
Table 4.
Process parameters of the extruder device.
| Properties | Values |
|---|---|
| Extrusion temperature | 190o (PLA), 210 °C (ABS) |
| Mixing time | 8 min |
| Screw speed | 100 rpm |
| Injection rate | 1500 rpm |
| Extrusion rate | 2500 rpm |
| Winding rate | 500 rpm |
| Cooling conditions | Forced air cooling (with fan) |
1%, 3% and 5% reinforced PLA + CF, PLA + GF, ABS + CF and ABS + GF composite filaments were produced on the FFF type Y682 model functional 3D printer. Figure 5 shows the Y682 model functional 3D printer, and Table 5 gives the technical properties of this printer.
Fig. 5.
Y682 model functional 3D printer.
Table 5.
Technical properties of the Y682 model functional 3D printer.
| Properties | Values |
|---|---|
| Model | Y682 functional 3D printer |
| Manufacturer | Custom-designed prototype |
| Country of origin | Turkey |
| Printing technology | FFF type |
| Software | Ultimaker Cura |
| Printer dimensions | 310 × 310 × 210 mm |
| Filament diameter | 1.75 mm |
| Nozzle diameter | 0.4 mm |
| Nozzle material | Titanium |
| Nozzle temperature | 220 °C (PLA composites), 240 °C (ABS composites) |
| Magnetic build plate | Aluminum |
| Build plate temperature | 60 °C (PLA composites), 75 °C (ABS composites) |
| Slicer settings | 0.2 mm layer height, 20% infill, 60 mm/s speed, grid pattern |
The G-code run on the device was sliced using the Ultimaker Cura program. In the Ultimaker program, 100% internal filling and 0.3 mm layer spacing were set for the samples. Since table temperature control was ensured, no edge gluing was applied to the samples. The printing type was grid type and the samples were produced one by one at a printing speed of 60 mm/sec. Acceleration and speed control is provided with the Core XY structure. Figure 6 shows the printing of test samples. For optimum printing of PLA + CF and PLA + GF composite filaments, the nozzle temperature was determined as 220 °C and the table temperature was determined as 60 °C, and that of ABS + CF and ABS + GF composite filaments was determined as 240 °C and 75 °C, respectively.
Fig. 6.
Printing of test samples.
In this study, tensile, hardness, impact, surface roughness, FTIR and SEM–EDS analyzes were carried out to examine the mechanical and microstructural properties of 3D printing samples. Tensile test samples were manufactured according to ASTM D638-Type 1. The same samples were used for tensile testing. Impact test samples were manufactured according to ISO 179. The same samples were used for surface roughness, FTIR, and SEM–EDS analyses.
Tensile tests were carried out on a Mohr&Federhaff brand 7079 model 100 kN load capacity tensile device. Tensile force was applied to the fixed samples at a speed of 5 mm/min. Hardness tests were carried out on a Pepisky Durometer brand Type D model hardness measuring device by applying a load in the range of 0–44.5 N. For hardness measurement, the samples were placed on a flat surface and 3 measurements were taken from each sample surface and the average hardness values were determined in Shore D. Figure 7 shows the printed tensile test samples.
Fig. 7.
Tensile test samples.
The impact tests were performed on a Karl Frank GmbH type 53,580 (300 J'luk) impact tester. Figure 8 shows the printed impact test samples. Also, standard deviation values were calculated for hardness, tensile and impact test. ANOVA analysis evaluates the relative influence of each factor, allowing a more precise determination of the optimum combination of process parameters. In this study, ANOVA was conducted using MINITAB 15 software at a significance level of 5% to evaluate the contribution of individual factors. Each independent variable in the model is associated with a p-value in the ANOVA table. If the p-value is less than 0.05, the corresponding factor is considered statistically significant. Surface roughness tests were carried out on an AEP brand Nanomap 1000WLI model device. Sample surfaces were measured with 0.01 nm precision in an area of 150 mm2. FTIR analysis was performed on a Bruker Optics brand TENSOR II model test device with a resolution of 4 cm-1. SEM–EDS analyzes were carried out on a Zeiss brand EVO LS 10 model device. Measurements were made in line and area scans by applying conductive coating at magnifications of 5.000x – 10.000x. Qualitative and quantitative elemental analyzes were carried out in local regions.
Fig. 8.
Impact test samples.
Results and discussion
Tensile test
Three samples of each sample were produced for the tensile test. Table 6 and Fig. 9 were created by averaging the results of these three test samples.
Table 6.
Tensile test results.
| Sample | Force (N) | Tenstile stress (MPa) | Standard deviation (MPa) | Modulus of elasticity (GPa) | Strain (mm/mm) |
|---|---|---|---|---|---|
| PLA (Pure) | 790 | 9.5 | 0.70 | 1.40 × 10–3 | 4.20 |
| %1 GF-PLA | 843 | 10.79 | 0.89 | 1.63 × 10–3 | 4.91 |
| %3 GF-PLA | 1366 | 17.47 | 1.12 | 1.52 × 10–3 | 6.36 |
| %5 GF-PLA | 896 | 11.48 | 0.77 | 2.38 × 10–3 | 3.51 |
| %1 CF-PLA | 1270 | 16.25 | 0.92 | 0.85 × 10–3 | 4.65 |
| %3 CF-PLA | 793 | 10.16 | 0.88 | 2.27 × 10–3 | 3.02 |
| %5 CF-PLA | 843 | 10.77 | 1.23 | 2.04 × 10–3 | 2.77 |
| ABS (Pure) | 800 | 8.8 | 0.65 | 2.50 × 10–3 | 2.00 |
| %1 GF-ABS | 823 | 19.72 | 0.83 | 3.01 × 10–3 | 2.28 |
| %3 GF-ABS | 900 | 21.70 | 1.34 | 1.81 × 10–3 | 3.15 |
| %5 GF-ABS | 970 | 23.40 | 1.03 | 3.61 × 10–3 | 3.74 |
| %1 CF-ABS | 916 | 22.07 | 1.25 | 2.17 × 10–3 | 3.67 |
| %3 CF-ABS | 1233 | 29.67 | 0.67 | 3.54 × 10–3 | 3.96 |
| %5 CF-ABS | 940 | 22.52 | 1.26 | 1.24 × 10–3 | 9.25 |
Fig. 9.
The graph of maximum tensile stress.
CF reinforcement in ABS matrix provided high strength, but performance degradation was observed at 5% reinforcement ratio (22.52 MPa). GF showed a steady increase in strength as the reinforcement ratio increased in the ABS matrix. GF is more effective than CF in the PLA matrix, and the 3% GF-PLA sample showed optimum tensile strength (17.47 MPa). CF reinforced into PLA matrix negatively affected the tensile strength. Figure 10 shows fractured samples after tensile testing. The fracture surface of the sample shows that the CF reinforcement has high rates of compatibility problems with the matrix and creates brittleness. This causes the samples to lose elasticity. Homogeneity and regularity on the fracture surface indicate that GF reinforcement is more compatible in the ABS than in the PLA.
Fig. 10.
Fractured samples after tensile test (a) PLA-GF, (b) PLA-CF, (c) ABS-GF ve (d) ABS-CF.
Especially in PLA matrix samples, 3% GF reinforcement provided optimum tensile strength (17.47 MPa) due to the uniform distribution of glass fiber and good bonding with PLA matrix. The glassy structure of GF and the physical bonds it formed with the amorphous regions of PLA increased the strength by facilitating load transfer. On the other hand, PLA samples containing 1% CF reinforcement increased the strength due to the homogeneous distribution of low carbon fiber and sufficient bond formation at the fiber-matrix interface, but as the ratio increased (especially 5%), brittle fracture behavior was observed due to fiber accumulation and matrix incompatibility. In ABS-based composites, 3% CF reinforcement showed the highest tensile strength (29.67 MPa). This can be attributed to the viscoelastic nature of ABS creating a better bond with carbon fiber and more effective load transfer. In 5% CF reinforcement, a decrease in mechanical performance was observed because sufficient interfacial bonding between fibers could not be provided. In GF-reinforced ABS composites, tensile strength increased up to 3% reinforcement, but performance deteriorated due to microstructural deterioration at 5%.
As a result, 3% reinforcement rate generally gave the optimum results for PLA and ABS matrices. Reinforcement rates of 5% caused performance degradation due to homogeneity and bonding issues. The 3% CF-ABS sample showed the highest strength in the tensile test with a value of 29.67 MPa. In addition, elastic modulus values are higher in ABS-based samples than PLA, which shows that ABS offers a rigid structure. Surface treatments (such as chemical etching, pre-heat treatment, surface coating, micro-roughening and oxidation) and binding agents can be applied to the created composite samples to increase the reinforcement and matrix bonding. Although CF is an expensive reinforcement material with high strength and stiffness potential, these properties can only be fully realized when effective fiber-matrix interfacial bonding is achieved. In this study, the silane-treated GF formed stronger chemical interactions with the matrix, particularly in polar polymers such as PLA, resulting in superior mechanical performance compared to CF. These findings demonstrate that higher cost materials do not necessarily guarantee superior performance; rather, interfacial bonding quality and the homogeneity of fiber dispersion are equally critical factors influencing composite behavior.
Table 7 shows that the p-value of all three factors is less than 0.05, that is, highly significant at 95% confidence interval. It can be observed that ratio (35.14%) is the main contributing factor, followed matrix (34.21%) and finally reinforcement (15.35%) and affects the tensile strengt of these composites.
Table 7.
ANOVA analysis for tensile strength.
| Factor | DoF | F | p Value | Pc (%) |
|---|---|---|---|---|
| Matrix (A) | 1 | 132.27 | 0.0 | 34.21 |
| Reinforcement (B) | 1 | 59.36 | 0.0 | 15.35 |
| Ratio (C) | 2 | 67.93 | 0.0 | 35.14 |
| A (Polymer type)*B (Fiber type) | 1 | 8.92 | 0.00765 | 2.31 |
| A (Polymer type)*C (wt.%) | 2 | 7.02 | 0.00341 | 3.63 |
| B (Fiber type)*C (wt.%) | 2 | 1.81 | 0.18095 | 0.94 |
| A*B*C | 2 | 4.29 | 0.02139 | 2.22 |
| Error | 24 | 0.319 | - | - |
Hardness test
Hardness test results of the samples are given in Table 8 and Fig. 11. For each sample, measurements were taken from 3 different regions and average hardness values were determined.
Table 8.
Hardness test results.
| Sample | Hardness (Shore D) | Standard deviation (Shore D) |
|---|---|---|
| PLA (Pure) | 42.0 | 0.70 |
| %1 GF-PLA | 45.5 | 0.73 |
| %3 GF-PLA | 57.3 | 1.08 |
| %5 GF-PLA | 64.8 | 0.79 |
| %1 CF-PLA | 53.8 | 1.22 |
| %3 CF-PLA | 52.8 | 0.44 |
| %5 CF-PLA | 47.5 | 1.01 |
| ABS (Pure) | 58.0 | 0.75 |
| %1 GF-ABS | 60.5 | 0.76 |
| %3 GF-ABS | 64.5 | 0.85 |
| %5 GF-ABS | 63.2 | 1.34 |
| %1 CF-ABS | 50.2 | 0.82 |
| %3 CF-ABS | 54.8 | 1.11 |
| %5 CF-ABS | 49.2 | 0.67 |
Fig. 11.
The graph of hardness (Shore D).
According to the hardness test results, the positive effect of GF reinforcement on the hardness of the PLA matrix is seen and the material performance increases as the reinforcement ratio increases. CF reinforcement has a negative effect on hardness at high reinforcement rates for PLA. GF reinforcement in the ABS matrix generally increased the hardness values, but after 3% the effect of the reinforcement became saturated. While CF reinforcement contributed positively to the ABS matrix at low rates, it reduced mechanical performance at high rates.
As a result, optimum hardness results were obtained in the case of 3% CF reinforcement in PLA and ABS matrices (52.8 and 54.8 Shore D, respectively). However, 5% reinforcement reduced the material hardness in both matrix types. While GF offers a more effective performance in the PLA matrix; CF provided maximum hardness of 3% in the ABS matrix. This situation is associated with the fact that the bonding capacity of CF with the polymer matrix may be lower than that of GF. High reinforcement rates (5%) may have caused brittleness or inhomogeneous structure, often due to excessive filling, and had a negative impact on hardness. In the study, the most optimum result in terms of hardness was obtained at 5% reinforcement ratio in PLA-GF samples with a Shore D value of 64.8. It can be said that GF is a compatible reinforcement to the PLA matrix (forming a good mechanical bond) and exhibits a homogeneous distribution.
Table 9 shows that the p-value of all three factors is less than 0.05, that is, highly significant at 95% confidence interval. It can be observed that ratio (76.88%) is the main contributing factor, followed reinforcement (4.69%) and finally matrix (0%) and affects the hardness of these composites.
Table 9.
ANOVA analysis for hardness.
| Factor | DoF | F | p Value | Pc (%) |
|---|---|---|---|---|
| Matrix (A) | 1 | 0.00035 | 0.0 | 0.0 |
| Reinforcement (B) | 1 | 5.85 | 0.0237 | 4.69 |
| Ratio (C) | 2 | 191.52 | 0.0 | 76.88 |
| A (Polymer type)*B (Fiber type) | 1 | 6.61 | 0.0174 | 5.29 |
| A (Polymer type)*C (wt.%) | 2 | 8.15 | 0.0024 | 6.55 |
| B (Fiber type)*C (wt.%) | 2 | 0.58 | 0.5684 | 0.23 |
| A*B*C | 2 | 1.09 | 0.3539 | 0.44 |
| Error | 24 | 1.253 | - | - |
Impact test
Three samples of each sample were produced for the impact test. Impact test results of the samples are given in Table 10 and Fig. 12.
Table 10.
Impact test results.
| Sample | Impact energy (J) | Standard deviation (J) |
|---|---|---|
| PLA (Pure) | 0.18 | 0.04 |
| %1 GF-PLA | 0.20 | 0.05 |
| %3 GF-PLA | 0.26 | 0.06 |
| %5 GF-PLA | 0.47 | 0.09 |
| %1 CF-PLA | 0.23 | 0.04 |
| %3 CF-PLA | 0.37 | 0.07 |
| %5 CF-PLA | 0.23 | 0.05 |
| ABS (Pure) | 0.45 | 0.06 |
| %1 GF-ABS | 0.60 | 0.08 |
| %3 GF-ABS | 0.53 | 0.06 |
| %5 GF-ABS | 0.50 | 0.07 |
| %1 CF-ABS | 0.53 | 0.06 |
| %3 CF-ABS | 0.36 | 0.05 |
| %5 CF-ABS | 0.36 | 0.06 |
Fig. 12.
The graph of impact energy.
The highest impact energy values in CF and GF reinforced ABS matrices were obtained at 1% reinforcement ratio with values of 0.53 and 0.6 J, respectively. As the reinforcement ratio increased in ABS-CF and ABS-GF samples, the impact energy, that is, the fracture resistance, decreased. This may be due to the fact that at high reinforcement rates, CF is not distributed homogeneously in the ABS matrix or makes the material brittle, while GF weakens the bonding force in the ABS matrix or creates micro defects. The highest impact energy in PLA-CF samples was obtained with a value of 0.37 J at a 3% reinforcement ratio. It is thought that this medium level of reinforcement strengthens the homogeneous distribution and bonding in the PLA matrix, while the high amount of reinforcement makes the material brittle. In PLA-GF samples, the impact energy constantly increased as the reinforcement ratio increased. The mechanisms in the tensile test results were also observed in the impact and hardness test results. In the PLA matrix GF reinforced samples, the distribution of GF became homogeneous with increasing rates, and the impact energy and hardness were positively affected. In the ABS matrix CF reinforced samples, low rate reinforcements (especially 1% and 3%) increased both the bond strength with the matrix and the energy absorption capacity. However, in high rate reinforcements (5%), brittleness increased due to fiber clustering and interface voids.
As a result, GF increased the impact strength in the ABS matrix more than CF. The highest impact energy value of 0.6 J was observed in the 1% GF-ABS sample. High percentage reinforcements (5%) reduced the impact strength for both GF and CF in the ABS matrix (0.36 J and 0.5 J, respectively). This can be attributed to the deterioration of the homogeneous distribution of the reinforcement and the formation of microcracks. GF provided more effective impact resistance in the PLA matrix than CF. In particular, the 5% GF-PLA sample reached the maximum impact energy. 5% CF-PLA sample gave optimum results in CF reinforcements, but 5% reinforcement increased material brittleness and reduced impact strength. The fact that the material is resistant to breakage is associated with the fact that it has established a strong bond between the matrix and fiber reinforcement. In terms of impact resistance, the increase in the reinforcement phase in the matrix material negatively affected ABS, while it positively affected PLA. As in the tensile test results, surface treatments can be applied to increase the bonding of composite samples between reinforcement and matrix.
Table 11 shows that the p-value of all three factors is less than 0.05, that is, highly significant at 95% confidence interval. It can be observed that ratio (68.98%) is the main contributing factor, followed reinforcement (3.07%) and finally matrix (1.09%) and affects the impact energy of these composites.
Table 11.
ANOVA analysis for impact energy.
| Factor | DoF | F | p Value | Pc (%) |
|---|---|---|---|---|
| Matrix (A) | 1 | 3.29 | 0.0826 | 1.09 |
| Reinforcement (B) | 1 | 9.24 | 0.0057 | 3.07 |
| Ratio (C) | 2 | 207.97 | 0.0000 | 68.98 |
| A (Polymer type)*B (Fiber type) | 1 | 8.14 | 0.0091 | 2.70 |
| A (Polymer type)*C (wt.%) | 2 | 8.28 | 0.002 | 5.49 |
| B (Fiber type)*C (wt.%) | 2 | 1.47 | 0.2526 | 0.49 |
| A*B*C | 2 | 5.09 | 0.0151 | 3.37 |
| Error | 24 | 1.33 | - | - |
The variation in the optimal reinforcement ratio across different matrix and fiber combinations can be attributed to differences in fiber-matrix interfacial compatibility, dispersion quality, and load transfer efficiency. In PLA-based composites, 3% GF provided the best tensile strength, likely due to the enhanced chemical bonding facilitated by the silane treated surface of GF, which is more compatible with the polar PLA matrix. However, in the case of impact strength, 5% GF in PLA showed the highest value, which suggests that a higher volume of energy absorbing fiber content can be beneficial for dynamic loading conditions despite the onset of some agglomeration. For ABS based systems, 3% CF resulted in the highest tensile strength. This could be due to ABS’s relatively non-polar, amorphous structure, which allows more uniform stress distribution even with unsized CF. Interestingly, 1% Reinforcement, both CF and GF, provided the highest impact strength in ABS composites. At higher reinforcement ratios (especially 5%), fiber agglomeration and the resulting microvoids likely act as stress concentrators, reducing the overall toughness. These trends confirm that each mechanical property (tensile strength, impact resistance, hardness) responds differently to reinforcement levels, depending on the polymer’s molecular structure and the fiber’s surface chemistry and dispersion behavior.
Surface roughness test
The mechanical profilometer test for surface roughness shows Ra (average roughness) values. Figure 13 (a, b, c) showed that as the reinforcement ratio increased in PLA-GF samples, the decreasing Ra values increased the material homogeneity. In Fig. 13, Ra values in ABS-GF samples increased as the reinforcement ratio increased and increased approximately 6 times at the highest reinforcement ratio (5%). This increase was associated with the decrease in the homogeneity of GF for the ABS matrix composite. A homogeneous mixture was achieved in the 5% GP-PLA sample, creating the smoothest surface in this study.
Fig. 13.
Surface roughness test results (a) %1 GF-PLA, (b) %3 GF-PLA, (c) %5 GF-PLA, (d) %1 GF-ABS, (e) %3 GF-ABS, (f) %5 GF-ABS.
FTIR analysis
The FTIR spectrum given in Fig. 14 reveal the characteristic functional groups of the respective matrices (PLA and ABS) and reinforcements (GF and CF). Peaks observed at 3000–2945 cm–1 and 2920–2930 cm–1 are attributed to C-H stretching vibrations in PLA and ABS matrices, respectively, while the peak at 1750 cm–1 in PLA composites corresponds to C = O stretching of ester groups, and peaks at 1190–1095 cm–1 represent C–O–C stretching vibrations. Characteristic reinforcement specific peaks, such as 1150 cm–1 for CF in PLA-CF and 960 cm–1 for CF in ABS-CF, indicate the presence of CF within the composites. Similarly, the peaks at 2230 cm–1 (C≡N vibration) and 700 cm–1 (benzene ring deformation) in ABS-GF confirm the chemical structure of the ABS matrix and GF interactions12,16,17,24,25.
Fig. 14.
FTIR analysis (a) GF-PLA, (b) CF-PLA, (c) GF-ABS and (d) CF-ABS.
According to the results, the distinct and narrow peaks observed in the FTIR spectrum at 1% and 3% reinforcement ratios indicate better bonding between the matrix and reinforcement and homogeneous distribution. This is directly related to the higher mechanical performance observed in tensile and impact tests. On the other hand, spectral changes observed at the 5% reinforcement ratio may reflect variations in local chemical environments caused by fiber agglomeration and insufficient dispersion within the matrix; this interpretation is supported by the performance decreases observed in the mechanical tests. This effect is especially evident in regions such as C = O stretching in PLA composites and C = C stretching in ABS composites15,16. In this context, a clear causality has been established between the peak changes detected in the FTIR analysis and the differences in mechanical properties.
In the FTIR analysis of PLA and ABS matrix composites reinforced with GF and CF, the characteristic bands of the organic structure of PLA and ABS (such as C-H, C = O, and C = C) were observed. However, the influence of the reinforcement materials (GF and CF) on the spectrum has led to structural changes, such as signal weakening or broadening in certain bands. Especially at 5% reinforcement ratio, the weakening of matrix reinforcement compatibility is due to peak changes and decreases in signal intensity (low transmittance). In addition to FTIR analysis, techniques such as SEM–EDS and XRD must be used to evaluate the effect of GF and CF reinforcements on the chemical structure. Thus, possible peak changes and signal weakening observed in FTIR can be better interpreted and the general structural properties of the composite materials can be evaluated more comprehensively. In addition, the superior mechanical performance observed in the PLA-GF composites, particularly at 3% reinforcement, can be attributed to the silanization of the glass fiber surface, which significantly enhances the interfacial bonding with the PLA matrix. PLA, a polar polymer with functional groups such as carbonyl (C = O) and hydroxyl (-OH), interacts favorably with the silane-treated GF, which contains organofunctional groups that form strong chemical bridges with the polymer chains. This enhanced chemical affinity promotes better stress transfer across the fiber–matrix interface, resulting in increased tensile strength and impact resistance. In contrast, the unsized CF lacks such functional surface groups, limiting the effectiveness of bonding with PLA and contributing to fiber pull-out and interfacial failure, especially at higher reinforcement ratios. These findings are consistent with the FTIR results, which showed sharper and stronger absorption peaks at 3% GF loading, and the SEM images, where more uniform fiber distribution and fewer voids were observed in PLA-GF composites compared to PLA-CF ones.
SEM–EDS analysis
The SEM analysis images were taken from the fracture surface at 1000 × magnification with a 50 µm scale. In Fig. 15, GF at 1% reinforcement ratio was homogeneously distributed in the PLA matrix, and the fiber powder particles did not create any obvious heterogeneity on the surface. The 3% reinforcement ratio becomes more evident on the GF surface. Fiber particles show better bonding with the matrix, but microscopic aggregates were observed in certain regions. Fiber powder particles with 5% reinforcement ratio are more clearly clustered on the matrix surface. Homogeneous distribution was weakened and gaps formed on the surface that could cause bonding problems12,15–26. CF at 1% reinforcement ratio is homogeneously distributed in the PLA matrix. There is no visible clustering or separation on the surface. The CF of 3% reinforcement ratio has become more evident on the surface and there are cluster impressions in some regions. CF clusters were observed on the surface in 5% reinforcement ratio. This indicates that matrix reinforcement homogeneity is impaired. The fiber powder particles appear not to be well bonded to the matrix in some areas. GF at 1% reinforcement ratio is homogeneously distributed in the ABS matrix. The GF of 3% reinforcement ratio has become more evident on the surface and there are cluster impressions in some regions. The matrix reinforcement homogeneity has deteriorated in 5% reinforcement ratio. CF at 1% reinforcement ratio is homogeneously distributed in the ABS matrix. No significant voids are observed on the surface. The CF of 3% reinforcement ratio has become more evident on the surface and there are local condensation impressions in some regions. Matrix reinforcement compatibility was weakened and voids and bonding problems were observed on the surface in 5% reinforcement ratio.
Fig. 15.
SEM–EDS analysis.
The results show that 1% and 3% reinforcement rates provide optimum results for both PLA and ABS matrices. This was supported by lower Ra values (smoother surfaces) in the surface roughness results. Reinforcements at the rate of 5% negatively affected the matrix reinforcement compatibility, causing a decrease in mechanical and chemical performance27–29. At 5% reinforcement rates, surface roughness increased significantly, indicating that reinforcement homogeneity within the matrix decreased and confirming the SEM analysis findings. C, Si, Ca, O and Fe elements were determined as the basic components of GF and CF in EDS analyses (Fig. 15). All these results reveal that the GF and CF reinforcement ratio should be carefully optimized and improvements should be made to ensure homogeneous distribution within the matrix in the production processes, especially at 5% rates30–32.
Conclusion
In this study, composite filaments were produced by reinforcing PLA and ABS matrices with CF and GF at 1%, 3%, and 5% ratios. Test samples were prepared using an FFF type Y682 model functional 3D printer. Tensile, hardness, impact, surface roughness, FTIR and SEM–EDS analyzes were carried out to evaluate the mechanical and microstructural properties of the produced composites.
According to the results, the 3% reinforcement ratio provided the most balanced performance for both matrices. Specifically, the highest tensile strength was achieved with 3% CF reinforcement in the ABS matrix at 29.67 MPa, and with 3% GF reinforcement in the PLA matrix at 17.47 MPa. Performance loss was observed at 5% reinforcement due to fiber clustering and poor fiber matrix adhesion. The impact strength of the CF-ABS and GF-ABS composites reached a maximum at 1% reinforcement and decreased significantly at 5%. The impact strength of the GF-PLA composites increased steadily as the reinforcement ratio increased, with the 5% GF-PLA sample exhibiting the highest impact energy of 0.47 J. In the CF-PLA samples, the impact strength peaked at 3% and decreased at 5% due to brittleness.
Surface roughness (Ra) analyses showed that as the reinforcement ratio increased in PLA-GF composites, the roughness decreased and the homogeneity increased. In contrast, in the ABS-GF and CF-ABS samples, the roughness values increased at 5% reinforcement, and it was observed that the fibers were not homogeneously distributed. FTIR analyses revealed stronger functional group signals and bonding characteristics at 1% and 3% reinforcement, while signal attenuation and peak broadening were observed at 5%. SEM images also supported these findings. While homogeneous fiber distribution and strong interfacial bonding were observed at 1–3% reinforcement, voids and clusters were observed to disrupt the matrix reinforcement compatibility at 5%. EDS analyses confirmed the presence of C, O, Si, Ca, and Fe, the main elements of GF and CF, and showed their distribution within the matrix.
Furthermore, the findings of this study are consistent with previous research on fiber-reinforced thermoplastics. The literature has reported that 3% carbon fiber reinforcement in PLA significantly increases tensile strength, which is consistent with the optimal mechanical performance observed in this study8,9. It has also been demonstrated that reinforcement ratios of 5% and above lead to matrix-fiber incompatibility and brittleness, which is consistent with the performance degradation seen in the 5% reinforced samples in our study5–14. The better compatibility of CF in ABS and GF in PLA is also supported by studies in which researchers emphasized the influence of the interaction between fiber type and matrix on the mechanical behavior of the composites12–33. These comparisons show that the obtained results are consistent with the literature.
The findings of this study emphasize the importance of fiber surface treatment in enhancing the performance of fiber reinforced thermoplastic composites produced via FFF. In particular, silane treated GF demonstrated superior compatibility with the PLA matrix due to the improved interfacial bonding facilitated by chemical interactions, leading to enhanced mechanical properties at optimal reinforcement levels. Conversely, unsized CF exhibited limited bonding efficiency, especially in polar matrices like PLA, resulting in reduced structural performance. Based on these observations, future studies are recommended to explore the use of surface treatments, such as silanization, oxidation, or plasma activation, on CF and other reinforcement fibers to improve their compatibility with thermoplastic matrices. Moreover, optimizing mixing and extrusion conditions to prevent fiber agglomeration at higher reinforcement ratios will be essential to ensure homogeneous fiber dispersion and maximize composite performance.
In conclusion, the type and ratio of reinforcement play a critical role in determining the mechanical integrity and performance of thermoplastic composites produced with FFF. A 3% reinforcement ratio for both matrices provided the optimal balance in terms of strength, toughness, and structural stability. However, it was also observed that some mechanical properties peaked at different reinforcement ratios, depending on the matrix and fiber type used. The 5% reinforcement ratio negatively affected material performance, particularly due to loss of homogeneity and clustering problems. GF exhibited better compatibility in the PLA matrix, while CF exhibited better compatibility in the ABS matrix. These results highlight the importance of adding the reinforcement material at appropriate ratios within the matrix. Future studies are recommended to develop production methods to increase the homogeneous distribution of reinforcements and optimize matrix reinforcement compatibility. Surface treatments such as chemical etching, oxidation, or coating can be applied to enhance matrix-reinforcement bonding. Furthermore, optimizing the extrusion and mixing processes can achieve a more homogeneous distribution of reinforcements within the matrix.
Acknowledgements
This study was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) 2209-A University Students Research Projects Support Program, with project number 1919B012208965. The authors would like to thank TUBITAK for support supporting the project.
Author contributions
All authors have contributed to, read, and approved the manuscript in its current form. The conceptualization and manuscript were conducted by D.A.G. Literature, material and method, results were completed by D.A.G and B.D.A.
Funding
This study was financially supported by The Scientific and Technological Research Council of Turkey (TUBITAK), Project Number 1919B012208965.
Data availability
The raw data can be obtained on request from the corresponding author.
Declarations
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
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Data Availability Statement
The raw data can be obtained on request from the corresponding author.