Effect of Thermal Treatment on the Mechanical Behavior of 3D-Printed Carbon Fiber-Reinforced PLA Composites

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Tensile, compressive, and flexural tests were conducted on samples annealed at three different temperatures (80°C, 100°C, and 120°C) with varying holding times (30, 60, and 90 minutes). The mechanical performance was analyzed, and fracture morphology was inspected using Field Emission Scanning Electron Microscopy (FESEM). Results demonstrated significant improvements, particularly in HTPLA, with enhanced inter-layer bonding and reduced voids. FESEM analysis confirmed these observations, highlighting structural differences in fracture surfaces. These findings provide insights into optimizing post-processing conditions for improving the strength of CF-PLA composites, making them suitable for load-bearing applications. Bioplastic Fused Deposition Modeling PLA CF-PLA Tensile Strength Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. INTRODUCTION In recent years, the demand for sustainable materials has surged, driven by environmental concerns and the need to reduce dependence on fossil-based resources. Bioplastics, sourced from renewable materials, have gained attention as a sustainable alternative to conventional plastics, offering biodegradability, reduced environmental impact, and broad applicability. Among these, Polylactic Acid (PLA) has gained considerable attention in additive manufacturing, mainly in Fused Deposition Modeling (FDM), owing to its ease of processability, cost-effectiveness, and environmental compatibility [ 1 ], [ 2 ], [ 3 ]. However, the comparatively low thermal and mechanical strength of PLA limit its application in high-performance and load-bearing scenarios [ 4 ] [ 5 ]. To address these challenges, significant efforts have been directed towards enhancing PLA’s performance through modifications that improve its mechanical strength and thermal stability [ 6 ]. Studies have shown that incorporating nanoparticles such as nano-ZnO or layered silicate particles can boost PLA’s tensile strength, elastic modulus, and thermal properties [ 7 ], [ 8 ], [ 9 ]. For example, nanoparticle reinforcement has been explored to not only enhance strength but also introduce additional functionalities, such as antibacterial properties [ 10 ], [ 11 ]. Fiber reinforcement has emerged as another effective strategy for improving PLA performance. Natural fibers, as well as synthetic fibers such as glass and carbon fiber, have been successfully integrated into PLA to create high-strength composites [ 12 ], [ 13 ], [ 14 ], [ 15 ]. Research has demonstrated that fiber-reinforced PLA composites exhibit notable improvements in tensile strength, dimensional stability, and flexural properties. Innovative combinations of reinforcement materials, such as mixing GF and CF, have further advanced the mechanical capabilities of PLA-based composites [ 16 ], [ 17 ]. The Annealing heat treatment is extensively recognized as an effective method for modifying the molecular structure of polymers, leading to enhanced material properties. This process promotes an increase in the crystallinity of the polymer matrix, which subsequently improves its viscoelastic performance and enhances mechanical strength. Additionally, annealing contributes to better thermal stability and electrical conductivity [ 18 ], [ 19 ], [ 20 ]. In the realm of 3D printing, annealing aids as a critical post-processing step that promotes increased polymer crystallinity and cross-linking, eventually refining the mechanical, thermal, and structural properties of the printed components [ 20 ], [ 21 ]. Several studies have explored the relationship between the mechanical properties and crystallinity of PLA. Harris and Lee [ 22 ] examined the effects of varying process parameters, particularly the extension of annealing time in injection-molded PLA, on its crystallinity and subsequent mechanical performance. Their findings indicated that refining the molding cycle and incorporating nucleating agents significantly improved crystallinity by 37%, leading to a 25% enhancement in flexural strength, along with an increase in heating by 30°C. Notably, annealing ensured uniform crystallinity throughout the fabricated components [ 23 ]. Similarly, Wang et al. [ 24 ] demonstrated that the higher crystallinity of 3D-printed PLA produced through FDM technology corresponded with improved impact strength. In addition, Drummer et al. [ 25 ] examined the manufacture of PLA composites reinforced with tricalcium phosphate via FDM. They reported that elevating the extruder temperature contributed to enhanced crystallinity, primarily because the heat from newly extruded layers reheated previously deposited layers, thereby promoting further crystallization. This thermal effect was also found to positively influence the tensile strength of the printed samples. While modifications using nanoparticles and fiber reinforcements have achieved significant improvements, the optimization of FDM printing parameters remains a critical area for further exploration [ 26 ], [ 27 ]. Parameters such as layer height, printing speed, and infill density pointedly affect the mechanical properties of printed components. For instance, optimized layer heights and nozzle temperatures have been shown to enhance tensile and bending strength, while higher infill densities improve compression and tensile performance [ 28 ], [ 29 ]. Continued research into these parameters, combined with advanced simulation and experimental methods, is essential to unlock the full potential of PLA and its composites in FDM applications. This research explores the influence of annealing treatment effect on the strength of 3D-printed CF-PLA. While these composites are stronger than standard PLA, they often become brittle and lose interlayer strength due to crystallization. By adjusting heat treatment factors such as temperature and time, the study aims to improve tensile, compressive, and flexural strength while also analyzing shrinkage and dimensional accuracy. The findings highlight how heat treatment can enhance the performance and precision of 3D-printed parts. 2. MATERIALS AND METHODS 2.1. Experimental Procedure This study utilized carbon fiber reinforced polylactic acid (C-PLA), commonly referred to as PLA + filament, procured from eSun, China. C-PLA is a combination of 10% weight high-purity carbon fiber and high-performance PLA with no pigmentation and a 1.75 mm nominal diameter. The C-PLA has low odor, non-toxic, renewably-sourced characterises [ 30 ]. The material was 3D printed using a Creality 3 Pro 3D printer (manufactured by Flashforge, China) (Fig. 1 b). A 100% infill density was selected to achieve an optimal balance between the strength and weight of the printed samples. The printer's operational parameters, listed in Table 1 , were chosen to ensure high-quality printing results. Table 1 Printing parameters of the 3D printing Sl. No Parameter Range 1 Nozzle Diameter 0.4 mm 2 Layer height 0.18 mm 3 Infill Density 100% 4 Printing Temperature 210 0 C 5 Bed Temperature 60 0 C 6 Printing Speed 30 mm/s 7 Annealing Temperature 80, 100 and 120 0 C 8 Holding time 30, 60 and 90 min The Critical steps in sample preparation involved identifying and resolving issues such as non-manifold geometries, intersecting faces, or other design errors that could affect the print. The digital models were created using SolidWorks software and processed with FlashPrint slicer software to generate the necessary G-code for printing. Proper bed preparation was a key aspect of the process. Adhesives like glue or hairspray were applied to the print bed to prevent deformation or detachment of the printed part during the printing process. Additionally, accurate bed leveling was performed to ensure that the initial layer adhered well and subsequent layers were deposited effectively. In this present study, annealing temperature and holding temperature were considered for investigating the annealing behaviour of the 3D printed specimens. To analyse the influence of these parameters, three different annealing temperature levels (80°C, 100°C, and 120°C) and three distinct holding times (30, 60 and 90 minutes) were chosen. Nine samples with different combinations of annealing temperature and holding time were selected, as presented in Table 2 . The final printed specimens, including tensile, compressive, and flexural test samples, are shown in Fig. 1 . All prepared samples were subjected to mechanical testing, which included tensile, compressive, and flexural assessments. The selected temperature limits were determined based on preliminary trial experiments and a comprehensive literature survey. The annealing process was carried out using a hot air oven, where the 3D-printed specimens were subjected to different heat treatment conditions, as shown in Fig. 2 . Table 2 Experimental factors and levels Exp. No Annealing Temperature ( 0 C) Holding Time (Minutes) 1 80 30 2 80 60 3 80 90 4 100 30 5 100 60 6 100 90 7 120 30 8 120 60 9 120 90 Mechanical testing was accomplished using a universal testing machine, following standardized procedures for tensile, compressive, and flexural assessments. The tensile tests were conducted by ASTM D638 Type I, utilizing a specimen with a 25-mm gauge length, a 6-mm-wide narrow section, 19-mm-wide shoulders, an overall length of 115 mm, and a thickness of 3.6 mm. For compressive testing, ASTM D695 was followed, which specifies commonly used cylindrical specimens. Among the available configurations, the selected design had a diameter of 12.7 mm and a length of 25.4 mm, making it compact yet effective for evaluating compressive strength and modulus. A crosshead speed of 15 mm/min is applied up to the sample height is reduced by half to determine the maximum compressive strength. Flexural testing was performed using a three-point bending setup based on ASTM D790-10. Having a cuboidal shape, measuring 3.6 mm in thickness, 19 mm in breadth, and 115 mm in total length, the specimens made it possible to accurately evaluate their bending properties. To enhance statistical accuracy, each experimental condition was tested three times, and the average of the three measurements was considered for additional statistical analysis and discussion. 3. RESULTS AND DISCUSSION 3.1 Effect of annealing treatment on the tensile strength The influence of annealing on the tensile strength of C-PLA under different combinations of heat treatment parameters is presented in Table 3 . The tensile testing was conducted using a universal testing machine, with the specimen held securely between the upper and lower jaws, as shown in Fig. 3 a. Among the tested conditions, experimental Run 3 (annealed at 100°C for 90 minutes) exhibited the peak tensile strength of 90.6 MPa. Conversely, the lowermost tensile strength, 64.98 MPa, was observed in experimental Run 6, which was also subjected to 100°C for 90 minutes. This value is lower than the tensile strength of untreated carbon fiber samples, which had a strength of 67.43 MPa. The variation in tensile strength across different annealing conditions is visually represented in the bar chart (Fig. 3 b), providing a clear contrast of the effects of annealing on 3D-printed CF-PLA specimens. As illustrated in the bar chart (Fig. 3 b), the tensile strength of the samples rises to a specific temperature (100°C) before declining with more heating. This reduction cab be attributed to the softening of the polymer matrix at elevated temperatures. Tensile strength was greatly affected by the holding duration at each temperature. Only at 80°C does a longer holding period increase the strength due to the strengthening of the interfacial bond. Achieving optimal mechanical performance requires a precise mixture of heat treatment parameters to minimize fiber and matrix degradation while maximizing polymer chain diffusion. Table 3 Tensile strength results obtained under different heat treatment parameters. Exp. No Annealing Temperature ( 0 C) Holding Time (Minutes) Average Tensile Strength (MPa) 1 80 30 84.93 2 80 60 82.65 3 80 90 90.63 4 100 30 83.334 5 100 60 77.292 6 100 90 64.98 7 120 30 71.934 8 120 60 74.67 9 120 90 73.188 Figure 4 presents the FESEM images of the fracture surfaces of tensile-tested samples printed at an annealing temperature of 100°C with a duration of 90 min, which exhibited lower tensile strength. The annealing process contributed to partial healing of gaps as the temperature increased; however, the material became more brittle, as evidenced by the presence of interlayer cracks and incomplete fusion between layers. The FESEM analysis indicates the role of annealing in reducing voids and improving interlayer adhesion, as depicted in Fig. 4 . Figure 5 displays the fracture surface of sample 3, which exhibited its maximum strength after heat treatment at 80°C for 90 minutes. The microstructural examination results are shown in Fig. 5 reveals a well-organized layer arrangement with strong adhesion, although minor traces of voids remain. This sample exhibits ductile characteristics, contributing to its superior strength. Furthermore, the analysis confirmed improved layer bonding, minimal porosity in the CF-PLA matrix, validating the effectiveness of the selected heat treatment conditions [ 31 ]. 3.2 Effect of annealing treatment on the compressive strength The compressive strength of the 3D-printed CF-PLA samples was evaluated using a universal testing machine under a constant crosshead speed until failure. The experimental setup for the compression test is illustrated in Fig. 6 a, where the specimen is positioned vertically between two compression platens. This configuration ensures uniform axial loading during the test. The post-test appearance of the specimens, showing different deformation patterns based on annealing conditions, is presented in Fig. 6 b. Table 4 lists the average compressive strength values of the fabricated composite samples under different annealing conditions. The heating conditions significantly influenced the compressive strength of the composites. In the experimental results, it is experiential that the compressive strength varied with changes in heating conditions. At 80°C, the compressive strength decreased as the holding time increased from 30 minutes (86.3 MPa) to 60 minutes (79.4 MPa), followed by a slight recovery at 90 minutes (84.0 MPa). A similar trend was observed for the samples annealed at 100°C, where the compressive strength increased from 81.7 MPa at 30 minutes to 88.6 MPa at 90 minutes. Notably, at 120°C, the highest compressive strength of 90.9 MPa was achieved after 60 minutes of annealing. However, a further increase in the holding time to 90 minutes resulted in a decline in compressive strength to 81.7 MPa, suggesting possible thermal degradation or structural relaxation beyond the optimal conditions. The highest compressive strength is obtained by annealing at 120°C for 60 minutes and then retaining the material for that length of time, suggesting an optimal condition for enhancing the mechanical properties of the composite material. Table 4 Compressive strength results for different heat treatment parameters Exp. No Annealing Temperature ( 0 C) Holding Time (Minutes) Average Compressive Strength (MPa) 1 80 30 86.3 2 80 60 79.4 3 80 90 84.0 4 100 30 81.7 5 100 60 87.4 6 100 90 88.6 7 120 30 81.7 8 120 60 90.9 9 120 90 81.7 To correlate the mechanical performance with internal structural changes, Figs. 7 and 8 present micrographs of the samples with the lowest and highest compressive strengths, respectively. Figure 7 presents the fracture surface of the sample annealed at 80°C for 60 minutes, which showed the lowest strength (79.4 MPa). The image reveals poor interlayer adhesion, visible microvoids, and weak bonding interfaces, all of which contribute to the diminished load-bearing capacity. These defects indicate that at this specific annealing condition, the heat treatment was insufficient to enhance bonding between layers, leading to a weakened internal structure. Such voids act as stress concentrators, accelerating failure under compressive loads. Identifying these deficiencies is crucial in understanding the factors that degrade material integrity and performance. In contrast, Fig. 8 shows the microstructure of the sample annealed at 120°C for 60 minutes, which exhibited the highest compressive strength (90.9 MPa). The micrograph indicates dense layer fusion, minimal porosity, and strong interfacial bonding, leading to enhanced structural integrity and mechanical performance. The enhanced layer adhesion indicates that the selected annealing conditions facilitated better polymer chain mobility, allowing for improved interlayer bonding and reduced internal defects [ 32 ]. Moreover, the micrograph demonstrates that interlayer gaps are shallow, further confirming that the heat treatment at this temperature and duration optimizes the material’s structural integrity. These observations affirm the critical role of optimized annealing in improving interlayer cohesion and minimizing internal defects in 3D-printed CF-PLA composites. 3.3 Effect of annealing treatment on the flexural strength The influence of annealing parameters on the flexural strength of 3D-printed CF-PLA samples is illustrated in Fig. 9 , with corresponding values presented in Table 5 . The samples were subjected to three different annealing temperatures (80°C, 100°C, and 120°C), each for holding times of 30, 60, and 90 minutes. At 80°C, the samples maintained relatively high flexural strength values, ranging from 65.28 MPa to 66.79 MPa, with the highest strength observed after a 90-minute holding period. As the temperature increased to 100°C, a slight decline in strength was noted, with values between 62.45 MPa and 63.63 MPa. Further temperature elevation to 120°C resulted in more pronounced reductions in strength, with the lowest value of 60.29 MPa recorded at 60 minutes. However, the strength partially recovered to 64.47 MPa at 90 minutes, possibly due to improved polymer chain mobility at extended exposure. These results indicate that lower annealing temperatures, particularly 80°C, are more effective in retaining flexural strength. Higher annealing temperatures may negatively affect interlayer bonding and fiber-matrix interaction due to polymer softening or thermal degradation [ 33 ]. Therefore, optimizing heat treatment parameters is essential for preserving mechanical integrity in CF-PLA composites. Table 5 Flexural strength results corresponding to different heat treatment parameters Exp. No Annealing Temperature ( 0 C) Holding Time (Minutes) Average flexural strength (MPa) 1 80 30 66.48 2 80 60 65.28 3 80 90 65.61 4 100 30 66.79 5 100 60 62.45 6 100 90 63.63 7 120 30 65.02 8 120 60 60.29 9 120 90 64.47 The FESEM images (Figs. 10 and 11 ) provide critical insights into the fracture behavior and microstructural integrity of the annealed CF-PLA samples after flexural testing. The morphology of these fracture surfaces revealed the effects of heat treatment parameters on layer bonding, void healing, and overall mechanical performance of the fabricated material. Figure 10 shows the fracture surface of the sample annealed at 120°C for 60 minutes, which demonstrated the lowest flexural strength. The image reveals significant defects, including interlayer voids, cracks, delamination, and fiber pull-outs [ 34 ]. These features indicate insufficient thermal bonding, poor polymer reflow, and weak fiber-matrix adhesion, all of which contribute to stress concentration and premature failure under bending loads. This lack of adhesion leads to stress concentration points, reducing the overall flexural strength [ 35 ], [ 36 ]. The detachment of carbon and the matrix suggests weak fiber-matrix bonding, which diminishes the reinforcing effect of the fibers, ultimately lowering the flexural strength. In contrast, Fig. 11 depicts the microstructure of the sample annealed at 100°C for 30 minutes, which exhibited the highest flexural strength. The smooth and continuous interface between layers indicates that the material underwent effective thermal reflow, enhancing interlayer adhesion. This improved bonding reduces stress concentration and enhances load transfer across layers. Unlike the previous sample, fiber pull-out is significantly reduced, indicating better fiber-matrix adhesion [ 37 ]. These observations underscore the importance of controlling heat treatment conditions to enhance the structural and functional performance of 3D-printed composites, particularly for applications requiring high flexural durability. 4. CONCLUSION This study systematically evaluated the effect of annealing on the tensile, compressive, and flexural properties of carbon fiber-reinforced PLA (CF-PLA) using FDM 3D-printing. Experimental findings revealed that heat treatment significantly altered the mechanical behavior of the composites, with optimized parameters improving interlayer bonding and structural integrity. The annealing process was found to expand the strength of 3D printed CF-PLA, as confirmed by FESEM analysis of the fracture surfaces. The high-strength samples exhibited dense, uniform microstructures with minimal porosity, while the low-strength samples exhibited weak interfacial bonding, voids, and brittle fracture characteristics. These results confirm that heat treatment must be carefully optimized to balance mechanical performance and structural stability. Overall, this study offers a critical understanding of the post-processing effects on CF-PLA composites, thereby aiding in their application for load-bearing and structural components. Future work can explore additional reinforcement strategies, alternative annealing techniques, and extended aging studies to further enhance material performance and longevity. Declarations Data Availability: The authors confirm that the data supporting the findings of this study are available within the article. Funding : This research received no external funding. Ethics approval and consent to participate: Not applicable Consent for publication: Not applicable Clinical trial number: Not applicable Author Contribution S.S. and D.V. designed the experiments and coordinated the research work. J.B. and S.Su. conducted the mechanical testing and data collection. 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Suresh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYLACxgYgbmc+AGRKyJCgpZktAaSFh3gtDMw8BiA2YS3yM3IfPvy5gyGauZnn86sbNRY8DOyHj27Ap8XgRrqxMe8ZhtzGZt5t1jnHgA7jSUu7gVeLRBqbNGMbRItxDhtQiwSPGV4t8jPS2H/+BGvheWac848ILQw30tgYeCFamB/nthGhxeDMM2Zp3jYJoBY2M+bcPgkeNkJ+kW9PY/z4s80md2N78+PPOd/q5PjZDx/D7zAIkGAwbGBgkwAx2YhQDrUOGJkfiFY9CkbBKBgFIwoAABQrQgzL4PLZAAAAAElFTkSuQmCC","orcid":"","institution":"Erode Sengunthar Engineering College","correspondingAuthor":true,"prefix":"","firstName":"S","middleName":"","lastName":"Suresh","suffix":""},{"id":471846591,"identity":"8d6ad995-1025-4af9-bca0-d8e9294f8ac9","order_by":1,"name":"D Velmurugan","email":"","orcid":"","institution":"Muthayammal Engineering College","correspondingAuthor":false,"prefix":"","firstName":"D","middleName":"","lastName":"Velmurugan","suffix":""},{"id":471846592,"identity":"33788bb4-6833-4160-be3f-2d96f6656964","order_by":2,"name":"J Balaji","email":"","orcid":"","institution":"Erode Sengunthar Engineering College","correspondingAuthor":false,"prefix":"","firstName":"J","middleName":"","lastName":"Balaji","suffix":""},{"id":471846593,"identity":"c4b30bf4-b30a-4166-a053-f38d7a93c464","order_by":3,"name":"S Sudhagar","email":"","orcid":"","institution":"Kalaignarkarunanidhi Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"S","middleName":"","lastName":"Sudhagar","suffix":""},{"id":471846594,"identity":"3536237f-ea67-489a-81a0-22c78bef33a5","order_by":4,"name":"R Elayaraja","email":"","orcid":"","institution":"Vellore Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"R","middleName":"","lastName":"Elayaraja","suffix":""}],"badges":[],"createdAt":"2025-05-28 10:53:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6767342/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6767342/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1177/00952443261427226","type":"published","date":"2026-02-16T00:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84803453,"identity":"19297417-062c-4bad-90ad-0f896f8ec224","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":230094,"visible":true,"origin":"","legend":"\u003cp\u003e(a) 3D model of test specimens prepared in FlashPrint slicer, (b) FDM 3D printer used for fabrication, and (c) final 3D-printed specimens.\u003c/p\u003e","description":"","filename":"1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/0a57bda2e82cc9a8303260cb.jpeg"},{"id":84803454,"identity":"406bc4bf-5e2e-44ce-9896-fe2354f43644","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":181013,"visible":true,"origin":"","legend":"\u003cp\u003ea) Hot air oven, and b) specimens undergoing annealing treatment.\u003c/p\u003e","description":"","filename":"2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/56f5ae91c753eb13b680c8e6.jpeg"},{"id":84803455,"identity":"fca62f8c-709f-4d9f-9eeb-199d38b3f590","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":142167,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Tensile testing setup showing the specimen mounted between the upper and lower jaws, and (b) Comparison of the tensile strength under different heat treatment parameters\u003c/p\u003e","description":"","filename":"3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/6639bb6c87d2e378963505eb.jpeg"},{"id":84803457,"identity":"5737946a-df27-46f5-92cf-aef62d6146de","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":278723,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of the fracture surfaces of tensile tested sample \u0026nbsp;(\u003cstrong\u003eAnnealed at 100°C for 90 min\u003c/strong\u003e)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/ce32cfbdad0a966a67eb312d.png"},{"id":84805321,"identity":"71bc81f0-722c-49d4-8e45-795339f34cb8","added_by":"auto","created_at":"2025-06-17 13:57:48","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":263030,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of the fracture surfaces of tensile tested sample \u0026nbsp;\u0026nbsp;(\u003cstrong\u003eAnnealed at 80°C for 90 min\u003c/strong\u003e)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/f8975f09727661e4e7aec270.png"},{"id":84805678,"identity":"e18c9238-bb27-456f-aaf8-6b54178618da","added_by":"auto","created_at":"2025-06-17 14:05:48","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":163861,"visible":true,"origin":"","legend":"\u003cp\u003ea) Experimental setup for the compression test and (b) Compression-tested samples\u003c/p\u003e","description":"","filename":"6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/406d4c6ff5bb03e439b441f5.jpeg"},{"id":84803465,"identity":"d7548480-14a2-4a24-a466-412647a1e57f","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":216899,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM image of the fracture surface of CF-PLA sample annealed at 80 °C for 60 minutes, showing weak interlayer bonding and visible porosity\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/d5f7fb362f7ac43ec048c806.png"},{"id":84803459,"identity":"9ed23fea-0dd2-4282-8724-5f8c49c65ee0","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":207228,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM image of the fracture surface of CF-PLA sample annealed at 120 °C for 60 minutes, showing strong interlayer adhesion and reduced porosity\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/f955de25baf7154b96a1a329.png"},{"id":84805320,"identity":"e7c2d9e1-6d6d-4a1c-abe5-2b09ccf7fb3a","added_by":"auto","created_at":"2025-06-17 13:57:48","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":35215,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the flexural strength under different heat treatment parameters\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/9175cecfacf33e8bd7459545.png"},{"id":84803470,"identity":"be147305-b56b-4992-a897-03a3a41f0c40","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":262566,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of fracture surfaces of flexural tested sample (\u003cstrong\u003eAnnealed at 120°C for 60 min\u003c/strong\u003e)\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/56be09b406eb9d19168366fc.png"},{"id":84803478,"identity":"4a9f65bd-fe9d-4bd5-90d3-d39be3ea3ec6","added_by":"auto","created_at":"2025-06-17 13:41:48","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":229804,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of fracture surfaces of the flexural samples (\u003cstrong\u003eAnnealed at 100°C for 30 min\u003c/strong\u003e)\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/82946bddaff580102f356456.png"},{"id":105218953,"identity":"f8cfff07-938d-4e5a-b5e1-385a05b8a7a7","added_by":"auto","created_at":"2026-03-23 15:13:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3321976,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6767342/v1/b905c39d-5520-4fe9-94a2-3dc7e5667683.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Thermal Treatment on the Mechanical Behavior of 3D-Printed Carbon Fiber-Reinforced PLA Composites","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eIn recent years, the demand for sustainable materials has surged, driven by environmental concerns and the need to reduce dependence on fossil-based resources. Bioplastics, sourced from renewable materials, have gained attention as a sustainable alternative to conventional plastics, offering biodegradability, reduced environmental impact, and broad applicability. Among these, Polylactic Acid (PLA) has gained considerable attention in additive manufacturing, mainly in Fused Deposition Modeling (FDM), owing to its ease of processability, cost-effectiveness, and environmental compatibility [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, the comparatively low thermal and mechanical strength of PLA limit its application in high-performance and load-bearing scenarios [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo address these challenges, significant efforts have been directed towards enhancing PLA\u0026rsquo;s performance through modifications that improve its mechanical strength and thermal stability [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Studies have shown that incorporating nanoparticles such as nano-ZnO or layered silicate particles can boost PLA\u0026rsquo;s tensile strength, elastic modulus, and thermal properties [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. For example, nanoparticle reinforcement has been explored to not only enhance strength but also introduce additional functionalities, such as antibacterial properties [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Fiber reinforcement has emerged as another effective strategy for improving PLA performance. Natural fibers, as well as synthetic fibers such as glass and carbon fiber, have been successfully integrated into PLA to create high-strength composites [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Research has demonstrated that fiber-reinforced PLA composites exhibit notable improvements in tensile strength, dimensional stability, and flexural properties. Innovative combinations of reinforcement materials, such as mixing GF and CF, have further advanced the mechanical capabilities of PLA-based composites [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Annealing heat treatment is extensively recognized as an effective method for modifying the molecular structure of polymers, leading to enhanced material properties. This process promotes an increase in the crystallinity of the polymer matrix, which subsequently improves its viscoelastic performance and enhances mechanical strength. Additionally, annealing contributes to better thermal stability and electrical conductivity [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In the realm of 3D printing, annealing aids as a critical post-processing step that promotes increased polymer crystallinity and cross-linking, eventually refining the mechanical, thermal, and structural properties of the printed components [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeveral studies have explored the relationship between the mechanical properties and crystallinity of PLA. Harris and Lee [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] examined the effects of varying process parameters, particularly the extension of annealing time in injection-molded PLA, on its crystallinity and subsequent mechanical performance. Their findings indicated that refining the molding cycle and incorporating nucleating agents significantly improved crystallinity by 37%, leading to a 25% enhancement in flexural strength, along with an increase in heating by 30\u0026deg;C. Notably, annealing ensured uniform crystallinity throughout the fabricated components [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSimilarly, Wang et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] demonstrated that the higher crystallinity of 3D-printed PLA produced through FDM technology corresponded with improved impact strength. In addition, Drummer et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] examined the manufacture of PLA composites reinforced with tricalcium phosphate via FDM. They reported that elevating the extruder temperature contributed to enhanced crystallinity, primarily because the heat from newly extruded layers reheated previously deposited layers, thereby promoting further crystallization. This thermal effect was also found to positively influence the tensile strength of the printed samples.\u003c/p\u003e \u003cp\u003eWhile modifications using nanoparticles and fiber reinforcements have achieved significant improvements, the optimization of FDM printing parameters remains a critical area for further exploration [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Parameters such as layer height, printing speed, and infill density pointedly affect the mechanical properties of printed components. For instance, optimized layer heights and nozzle temperatures have been shown to enhance tensile and bending strength, while higher infill densities improve compression and tensile performance [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Continued research into these parameters, combined with advanced simulation and experimental methods, is essential to unlock the full potential of PLA and its composites in FDM applications.\u003c/p\u003e \u003cp\u003eThis research explores the influence of annealing treatment effect on the strength of 3D-printed CF-PLA. While these composites are stronger than standard PLA, they often become brittle and lose interlayer strength due to crystallization. By adjusting heat treatment factors such as temperature and time, the study aims to improve tensile, compressive, and flexural strength while also analyzing shrinkage and dimensional accuracy. The findings highlight how heat treatment can enhance the performance and precision of 3D-printed parts.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Experimental Procedure\u003c/h2\u003e \u003cp\u003eThis study utilized carbon fiber reinforced polylactic acid (C-PLA), commonly referred to as PLA\u0026thinsp;+\u0026thinsp;filament, procured from eSun, China. C-PLA is a combination of 10% weight high-purity carbon fiber and high-performance PLA with no pigmentation and a 1.75 mm nominal diameter. The C-PLA has low odor, non-toxic, renewably-sourced characterises [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The material was 3D printed using a Creality 3 Pro 3D printer (manufactured by Flashforge, China) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). A 100% infill density was selected to achieve an optimal balance between the strength and weight of the printed samples. The printer's operational parameters, listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, were chosen to ensure high-quality printing results.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePrinting parameters of the 3D printing\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSl. No\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRange\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNozzle Diameter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.4 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLayer height\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.18 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInfill Density\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePrinting Temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e210 \u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBed Temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60 \u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePrinting Speed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 mm/s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnnealing Temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80, 100 and 120 \u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHolding time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30, 60 and 90 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe Critical steps in sample preparation involved identifying and resolving issues such as non-manifold geometries, intersecting faces, or other design errors that could affect the print. The digital models were created using SolidWorks software and processed with FlashPrint slicer software to generate the necessary G-code for printing. Proper bed preparation was a key aspect of the process. Adhesives like glue or hairspray were applied to the print bed to prevent deformation or detachment of the printed part during the printing process. Additionally, accurate bed leveling was performed to ensure that the initial layer adhered well and subsequent layers were deposited effectively.\u003c/p\u003e \u003cp\u003eIn this present study, annealing temperature and holding temperature were considered for investigating the annealing behaviour of the 3D printed specimens. To analyse the influence of these parameters, three different annealing temperature levels (80\u0026deg;C, 100\u0026deg;C, and 120\u0026deg;C) and three distinct holding times (30, 60 and 90 minutes) were chosen. Nine samples with different combinations of annealing temperature and holding time were selected, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The final printed specimens, including tensile, compressive, and flexural test samples, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All prepared samples were subjected to mechanical testing, which included tensile, compressive, and flexural assessments. The selected temperature limits were determined based on preliminary trial experiments and a comprehensive literature survey. The annealing process was carried out using a hot air oven, where the 3D-printed specimens were subjected to different heat treatment conditions, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental factors and levels\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExp. No\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnnealing\u003c/p\u003e \u003cp\u003eTemperature (\u003csup\u003e0\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHolding Time\u003c/p\u003e \u003cp\u003e(Minutes)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eMechanical testing was accomplished using a universal testing machine, following standardized procedures for tensile, compressive, and flexural assessments. The tensile tests were conducted by ASTM D638 Type I, utilizing a specimen with a 25-mm gauge length, a 6-mm-wide narrow section, 19-mm-wide shoulders, an overall length of 115 mm, and a thickness of 3.6 mm. For compressive testing, ASTM D695 was followed, which specifies commonly used cylindrical specimens. Among the available configurations, the selected design had a diameter of 12.7 mm and a length of 25.4 mm, making it compact yet effective for evaluating compressive strength and modulus. A crosshead speed of 15 mm/min is applied up to the sample height is reduced by half to determine the maximum compressive strength.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFlexural testing was performed using a three-point bending setup based on ASTM D790-10. Having a cuboidal shape, measuring 3.6 mm in thickness, 19 mm in breadth, and 115 mm in total length, the specimens made it possible to accurately evaluate their bending properties. To enhance statistical accuracy, each experimental condition was tested three times, and the average of the three measurements was considered for additional statistical analysis and discussion.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Effect of annealing treatment on the tensile strength\u003c/h2\u003e \u003cp\u003eThe influence of annealing on the tensile strength of C-PLA under different combinations of heat treatment parameters is presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The tensile testing was conducted using a universal testing machine, with the specimen held securely between the upper and lower jaws, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. Among the tested conditions, experimental Run 3 (annealed at 100\u0026deg;C for 90 minutes) exhibited the peak tensile strength of 90.6 MPa. Conversely, the lowermost tensile strength, 64.98 MPa, was observed in experimental Run 6, which was also subjected to 100\u0026deg;C for 90 minutes. This value is lower than the tensile strength of untreated carbon fiber samples, which had a strength of 67.43 MPa. The variation in tensile strength across different annealing conditions is visually represented in the bar chart (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), providing a clear contrast of the effects of annealing on 3D-printed CF-PLA specimens.\u003c/p\u003e \u003cp\u003eAs illustrated in the bar chart (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), the tensile strength of the samples rises to a specific temperature (100\u0026deg;C) before declining with more heating. This reduction cab be attributed to the softening of the polymer matrix at elevated temperatures. Tensile strength was greatly affected by the holding duration at each temperature. Only at 80\u0026deg;C does a longer holding period increase the strength due to the strengthening of the interfacial bond. Achieving optimal mechanical performance requires a precise mixture of heat treatment parameters to minimize fiber and matrix degradation while maximizing polymer chain diffusion.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTensile strength results obtained under different heat treatment parameters.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExp. No\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnnealing\u003c/p\u003e \u003cp\u003eTemperature (\u003csup\u003e0\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHolding Time\u003c/p\u003e \u003cp\u003e(Minutes)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAverage Tensile Strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e84.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e82.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e90.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e83.334\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e77.292\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e64.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e71.934\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e74.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e73.188\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the FESEM images of the fracture surfaces of tensile-tested samples printed at an annealing temperature of 100\u0026deg;C with a duration of 90 min, which exhibited lower tensile strength. The annealing process contributed to partial healing of gaps as the temperature increased; however, the material became more brittle, as evidenced by the presence of interlayer cracks and incomplete fusion between layers. The FESEM analysis indicates the role of annealing in reducing voids and improving interlayer adhesion, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the fracture surface of sample 3, which exhibited its maximum strength after heat treatment at 80\u0026deg;C for 90 minutes. The microstructural examination results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e reveals a well-organized layer arrangement with strong adhesion, although minor traces of voids remain. This sample exhibits ductile characteristics, contributing to its superior strength. Furthermore, the analysis confirmed improved layer bonding, minimal porosity in the CF-PLA matrix, validating the effectiveness of the selected heat treatment conditions [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Effect of annealing treatment on the compressive strength\u003c/h2\u003e \u003cp\u003eThe compressive strength of the 3D-printed CF-PLA samples was evaluated using a universal testing machine under a constant crosshead speed until failure. The experimental setup for the compression test is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, where the specimen is positioned vertically between two compression platens. This configuration ensures uniform axial loading during the test. The post-test appearance of the specimens, showing different deformation patterns based on annealing conditions, is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e lists the average compressive strength values of the fabricated composite samples under different annealing conditions. The heating conditions significantly influenced the compressive strength of the composites. In the experimental results, it is experiential that the compressive strength varied with changes in heating conditions. At 80\u0026deg;C, the compressive strength decreased as the holding time increased from 30 minutes (86.3 MPa) to 60 minutes (79.4 MPa), followed by a slight recovery at 90 minutes (84.0 MPa). A similar trend was observed for the samples annealed at 100\u0026deg;C, where the compressive strength increased from 81.7 MPa at 30 minutes to 88.6 MPa at 90 minutes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNotably, at 120\u0026deg;C, the highest compressive strength of 90.9 MPa was achieved after 60 minutes of annealing. However, a further increase in the holding time to 90 minutes resulted in a decline in compressive strength to 81.7 MPa, suggesting possible thermal degradation or structural relaxation beyond the optimal conditions. The highest compressive strength is obtained by annealing at 120\u0026deg;C for 60 minutes and then retaining the material for that length of time, suggesting an optimal condition for enhancing the mechanical properties of the composite material.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCompressive strength results for different heat treatment parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExp. No\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnnealing\u003c/p\u003e \u003cp\u003eTemperature (\u003csup\u003e0\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHolding Time\u003c/p\u003e \u003cp\u003e(Minutes)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAverage Compressive Strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e86.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e79.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e84.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e87.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e88.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e90.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e81.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo correlate the mechanical performance with internal structural changes, Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e present micrographs of the samples with the lowest and highest compressive strengths, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the fracture surface of the sample annealed at 80\u0026deg;C for 60 minutes, which showed the lowest strength (79.4 MPa). The image reveals poor interlayer adhesion, visible microvoids, and weak bonding interfaces, all of which contribute to the diminished load-bearing capacity. These defects indicate that at this specific annealing condition, the heat treatment was insufficient to enhance bonding between layers, leading to a weakened internal structure. Such voids act as stress concentrators, accelerating failure under compressive loads. Identifying these deficiencies is crucial in understanding the factors that degrade material integrity and performance. In contrast, Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the microstructure of the sample annealed at 120\u0026deg;C for 60 minutes, which exhibited the highest compressive strength (90.9 MPa).\u003c/p\u003e \u003cp\u003eThe micrograph indicates dense layer fusion, minimal porosity, and strong interfacial bonding, leading to enhanced structural integrity and mechanical performance. The enhanced layer adhesion indicates that the selected annealing conditions facilitated better polymer chain mobility, allowing for improved interlayer bonding and reduced internal defects [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Moreover, the micrograph demonstrates that interlayer gaps are shallow, further confirming that the heat treatment at this temperature and duration optimizes the material\u0026rsquo;s structural integrity. These observations affirm the critical role of optimized annealing in improving interlayer cohesion and minimizing internal defects in 3D-printed CF-PLA composites.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Effect of annealing treatment on the flexural strength\u003c/h2\u003e \u003cp\u003eThe influence of annealing parameters on the flexural strength of 3D-printed CF-PLA samples is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, with corresponding values presented in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The samples were subjected to three different annealing temperatures (80\u0026deg;C, 100\u0026deg;C, and 120\u0026deg;C), each for holding times of 30, 60, and 90 minutes. At 80\u0026deg;C, the samples maintained relatively high flexural strength values, ranging from 65.28 MPa to 66.79 MPa, with the highest strength observed after a 90-minute holding period. As the temperature increased to 100\u0026deg;C, a slight decline in strength was noted, with values between 62.45 MPa and 63.63 MPa. Further temperature elevation to 120\u0026deg;C resulted in more pronounced reductions in strength, with the lowest value of 60.29 MPa recorded at 60 minutes. However, the strength partially recovered to 64.47 MPa at 90 minutes, possibly due to improved polymer chain mobility at extended exposure.\u003c/p\u003e \u003cp\u003eThese results indicate that lower annealing temperatures, particularly 80\u0026deg;C, are more effective in retaining flexural strength. Higher annealing temperatures may negatively affect interlayer bonding and fiber-matrix interaction due to polymer softening or thermal degradation [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Therefore, optimizing heat treatment parameters is essential for preserving mechanical integrity in CF-PLA composites.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFlexural strength results corresponding to different heat treatment parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExp. No\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnnealing\u003c/p\u003e \u003cp\u003eTemperature (\u003csup\u003e0\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHolding Time\u003c/p\u003e \u003cp\u003e(Minutes)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAverage flexural strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e66.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e65.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e65.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e66.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e62.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e63.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e65.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e60.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e64.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe FESEM images (Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e) provide critical insights into the fracture behavior and microstructural integrity of the annealed CF-PLA samples after flexural testing. The morphology of these fracture surfaces revealed the effects of heat treatment parameters on layer bonding, void healing, and overall mechanical performance of the fabricated material. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the fracture surface of the sample annealed at 120\u0026deg;C for 60 minutes, which demonstrated the lowest flexural strength. The image reveals significant defects, including interlayer voids, cracks, delamination, and fiber pull-outs [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. These features indicate insufficient thermal bonding, poor polymer reflow, and weak fiber-matrix adhesion, all of which contribute to stress concentration and premature failure under bending loads. This lack of adhesion leads to stress concentration points, reducing the overall flexural strength [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The detachment of carbon and the matrix suggests weak fiber-matrix bonding, which diminishes the reinforcing effect of the fibers, ultimately lowering the flexural strength.\u003c/p\u003e \u003cp\u003eIn contrast, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e depicts the microstructure of the sample annealed at 100\u0026deg;C for 30 minutes, which exhibited the highest flexural strength. The smooth and continuous interface between layers indicates that the material underwent effective thermal reflow, enhancing interlayer adhesion. This improved bonding reduces stress concentration and enhances load transfer across layers. Unlike the previous sample, fiber pull-out is significantly reduced, indicating better fiber-matrix adhesion [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. These observations underscore the importance of controlling heat treatment conditions to enhance the structural and functional performance of 3D-printed composites, particularly for applications requiring high flexural durability.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. CONCLUSION","content":"\u003cp\u003eThis study systematically evaluated the effect of annealing on the tensile, compressive, and flexural properties of carbon fiber-reinforced PLA (CF-PLA) using FDM 3D-printing. Experimental findings revealed that heat treatment significantly altered the mechanical behavior of the composites, with optimized parameters improving interlayer bonding and structural integrity.\u003c/p\u003e \u003cp\u003eThe annealing process was found to expand the strength of 3D printed CF-PLA, as confirmed by FESEM analysis of the fracture surfaces. The high-strength samples exhibited dense, uniform microstructures with minimal porosity, while the low-strength samples exhibited weak interfacial bonding, voids, and brittle fracture characteristics. These results confirm that heat treatment must be carefully optimized to balance mechanical performance and structural stability.\u003c/p\u003e \u003cp\u003eOverall, this study offers a critical understanding of the post-processing effects on CF-PLA composites, thereby aiding in their application for load-bearing and structural components. Future work can explore additional reinforcement strategies, alternative annealing techniques, and extended aging studies to further enhance material performance and longevity.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability:\u0026nbsp;\u003c/strong\u003eThe authors confirm that the data supporting the findings of this study are available within the article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: This research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.S. and D.V. designed the experiments and coordinated the research work. J.B. and S.Su. conducted the mechanical testing and data collection. R.E. carried out the FESEM analysis and contributed to interpreting the microstructural data. S.S. wrote the original draft of the manuscript. All authors contributed to reviewing and editing the manuscrip.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJavaid M, Haleem A, Singh RP, Suman R, Rab S. Role of additive manufacturing applications towards environmental sustainability. 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Iran Polym J. 2024;33(8):1065\u0026ndash;74. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s13726-024-01315-8\u003c/span\u003e\u003cspan address=\"10.1007/s13726-024-01315-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Bioplastic, Fused Deposition Modeling, PLA, CF-PLA, Tensile Strength","lastPublishedDoi":"10.21203/rs.3.rs-6767342/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6767342/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the impact of optimized Fused Deposition Modeling (FDM) parameters and post-process heat treatment on the mechanical, thermal, and dimensional properties of carbon fiber reinforced polylactic acid (CF-PLA). Tensile, compressive, and flexural tests were conducted on samples annealed at three different temperatures (80\u0026deg;C, 100\u0026deg;C, and 120\u0026deg;C) with varying holding times (30, 60, and 90 minutes). The mechanical performance was analyzed, and fracture morphology was inspected using Field Emission Scanning Electron Microscopy (FESEM). Results demonstrated significant improvements, particularly in HTPLA, with enhanced inter-layer bonding and reduced voids. FESEM analysis confirmed these observations, highlighting structural differences in fracture surfaces. These findings provide insights into optimizing post-processing conditions for improving the strength of CF-PLA composites, making them suitable for load-bearing applications.\u003c/p\u003e","manuscriptTitle":"Effect of Thermal Treatment on the Mechanical Behavior of 3D-Printed Carbon Fiber-Reinforced PLA Composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-17 13:41:43","doi":"10.21203/rs.3.rs-6767342/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"26ac33e5-fae5-40ab-822f-12fcc82e4e9c","owner":[],"postedDate":"June 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-23T15:12:19+00:00","versionOfRecord":{"articleIdentity":"rs-6767342","link":"https://doi.org/10.1177/00952443261427226","journal":{"identity":"journal-of-elastomers-and-plastics","isVorOnly":true,"title":"Journal of Elastomers \u0026 Plastics"},"publishedOn":"2026-02-16 00:00:00","publishedOnDateReadable":"February 16th, 2026"},"versionCreatedAt":"2025-06-17 13:41:43","video":"","vorDoi":"10.1177/00952443261427226","vorDoiUrl":"https://doi.org/10.1177/00952443261427226","workflowStages":[]},"version":"v1","identity":"rs-6767342","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6767342","identity":"rs-6767342","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}