Researchers from the Institute of Space Technology (IST) in Islamabad, in collaboration with the National University of Science and Technology (NUST) and Ajman University in the United Arab Emirates, have developed a new production setup for continuous fiber-reinforced polymer (CFRP) composite filament optimized for fused deposition modeling (FDM) 3D printing. The system enables precise integration of continuous E-glass fibers within a polylactic acid (PLA) matrix, maintaining fiber alignment and polymer encapsulation throughout the extrusion process. Mechanical testing showed the continuous glass fiber-reinforced PLA filament achieved an average tensile strength of 146.75 MPa and a Young’s modulus of 4.96 GPa, compared with 60 MPa and 3.68 GPa for neat PLA. The filament’s performance closely matched theoretical predictions, confirming its suitability for high-strength additive manufacturing applications.
The research addresses a persistent challenge in additive manufacturing: the limited mechanical properties of standard FDM thermoplastics. Although PLA offers ease of processing and dimensional stability, its relatively low strength restricts its use in structural components. Continuous fiber reinforcement can significantly enhance the strength-to-weight ratio of printed parts, but producing consistent, fiber-integrated filaments has been hindered by issues such as fiber breakage, misalignment, and weak matrix adhesion.
Developing a Reliable Composite Filament Process
To resolve these limitations, the IST-led team designed and fabricated a gear-driven production system consisting of four integrated subsystems—a winding unit, extrusion assembly, heating chamber, and pulling spool. The system synchronizes feed and extrusion speeds, ensuring uniform polymer winding on the fiber and consistent filament diameter. Optimized processing parameters included a feed motor speed of 30 rpm, extrusion motor speed of 74–75 rpm, heater temperature of 165 °C, and a spool rotation rate of 10 rpm. These values maintained steady material flow and minimized thermal degradation. The resulting continuous glass fiber–PLA composite filament measured 1.75 ± 0.05 mm in diameter with a smooth, void-free surface finish suitable for direct FDM use without printer modification.
Mechanical characterization was performed on three material types: neat PLA, continuous E-glass fiber, and the composite filament. The glass fiber exhibited the highest stiffness, with a tensile strength of approximately 3,508 MPa and a modulus of 74.3 GPa, while the composite’s intermediate values confirmed effective load transfer between matrix and reinforcement. The 2.4-fold increase in tensile strength and 1.35-fold increase in stiffness over neat PLA demonstrated that even at a low fiber volume fraction of 2.8%, substantial reinforcement can be achieved.
Mechanical Tests Confirm Strong Fiber Bonding
Microscopic and spectroscopic analyses confirmed strong interfacial bonding and uniform impregnation. Scanning electron microscopy revealed full fiber encapsulation by the polymer matrix and minimal void formation. Energy-dispersive X-ray spectroscopy showed a homogeneous carbon–oxygen composition corresponding to PLA, indicating complete polymer distribution around the glass fibers. Thermal evaluation using thermogravimetric analysis found negligible mass loss up to 291 °C, compared with neat PLA’s degradation onset near 212 °C, confirming improved thermal stability. The derivative thermogravimetric curve identified the PLA matrix’s main decomposition range between 291 °C and 437 °C, leaving a 7% char yield primarily composed of glass fibers. Differential scanning calorimetry showed a glass transition temperature near 59 °C and a melting temperature of 152 °C—slightly higher than those of neat PLA—indicating restricted polymer mobility and enhanced crystallinity from fiber reinforcement.
The experimental and theoretical Young’s modulus values, 4.96 GPa and 5.66 GPa respectively, were in close agreement, validating the filament’s mechanical efficiency. Researchers noted that small deviations likely resulted from minor fiber misalignment and low fiber volume fraction, though the filament’s integrity remained consistent under tension.
Continuous fiber reinforcement in additive manufacturing has been studied for more than a decade, but most experimental or commercial solutions have relied on complex multi-nozzle or co-extrusion systems. Early efforts, including those by Parandoush et al. and Ismail et al., demonstrated laser-assisted and sintering-based FDM techniques using glass and carbon fibers, but faced challenges with void formation and nozzle synchronization. Later research introduced ultrasonic-assisted and dual-extrusion systems, such as those reported by Zhang et al. and Heidari-Rarani et al., which improved adhesion but added hardware complexity. Commercial implementations, like the Markforged Mark Two 3D printer, have successfully produced carbon fiber–reinforced components yet depend on proprietary materials and controlled environments.
PLA remains a preferred thermoplastic for composite filament development due to its biodegradability, low melting point, and stable printability without requiring heated chambers. E-glass fiber, selected as reinforcement in this study, combines high tensile strength, stiffness, and corrosion resistance with low cost and non-conductive behavior—avoiding carbon fiber’s drawbacks such as nozzle abrasion and electrical conductivity. By employing a melt-impregnation-based single-filament process rather than dual-channel extrusion, the researchers eliminated fiber breakage and clogging issues common to previous methods, producing a continuous, structurally coherent filament suitable for mechanical applications.
The custom-designed production setup demonstrates a practical and scalable route to manufacturing continuous fiber-reinforced composite filaments for 3D printing. The combination of mechanical strength, process stability, and thermal resistance positions the glass fiber–PLA composite as a promising material for structural FDM components. While the study achieved a modest fiber volume fraction of 2.8%, the results confirm that higher fractions could further enhance mechanical properties if process control is maintained.
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Featured image shows Stress vs. Strain Depicting UTS (a) Polymer (b) Fiber (c) Composite. Image via Nature.
