Sustainable Fabrication of FDM-Printed Jute/PLA Biocomposites: Effect of Fiber Volume Fraction on Mechanical and Thermal Performance

Technical Summary: Sustainable Fabrication of FDM-Printed Jute/PLA Biocomposites

Problem Statement
The rapid accumulation of non-biodegradable plastic waste and the depletion of petroleum-based raw materials have necessitated the development of sustainable alternatives in additive manufacturing. While Poly (lactic acid) (PLA) is a leading biodegradable thermoplastic derived from renewable feedstocks, it suffers from inherent limitations, including high brittleness, a low heat deflection temperature (55–60 °C), and thermal degradation at processing temperatures above 200 °C. Although blending PLA with natural fibers like jute offers a pathway to improve stiffness, strength, and thermal stability, the specific effects of fiber volume fraction ($V_f$) and post-processing thermal curing on the thermo-mechanical performance of Fused Deposition Modeling (FDM)-printed jute/PLA biocomposites remain insufficiently understood. Furthermore, the hydrophilic nature of jute fibers often leads to poor interfacial adhesion with the hydrophobic PLA matrix, resulting in void formation and debonding.

Methodology
The study employed a systematic approach to fabricate and characterize jute/PLA biocomposites using FDM.

• Materials: Commercial PLA (NatureWorks 3052D) served as the matrix, while untreated short jute fibers (4–6 mm length) were used as reinforcement.
• Fabrication: Composite filaments were produced via twin-screw extrusion at target fiber volume fractions of 10, 20, and 30 vol.% (with characterization extending to 50% in results). Specimens were printed using an FDM printer with a 0.40 mm nozzle, 100% infill, and a ±45° raster angle.
• Post-Processing: A controlled thermal curing process was applied in a hot-air oven at temperatures ranging from 160 °C to 180 °C to investigate interfacial integrity and crystallinity.
• Characterization: The study utilized a comprehensive suite of analytical techniques:
  • Mechanical: Tensile, flexural, and hardness testing (ASTM standards).
  • Physical: Density and water absorption measurements.
  • Thermal: Differential Scanning Calorimetry (DSC) for melting temperature and crystallinity; Thermogravimetric Analysis (TGA) for thermal stability and residual char.
  • Microstructural/Molecular: Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), and X-Ray Diffraction (XRD).
  • Modeling: Theoretical calculations based on the Rule of Mixtures and finite element modeling concepts were used to validate experimental data.

Key Contributions
This research establishes a robust processing-structure-property correlation for FDM-printed jute/PLA biocomposites. Key contributions include:

1. Optimization of Fiber Volume Fraction: The study identifies an optimal fiber loading range (25–35 vol.%) that maximizes mechanical performance while minimizing defects such as agglomeration and porosity.
2. Thermal Curing Effects: It demonstrates that post-curing at 160–165 °C significantly enhances interfacial bonding, crystallinity, and thermal stability compared to higher curing temperatures which may induce thermal relaxation.
3. Multiscale Characterization: The paper provides a detailed analysis linking molecular interactions (hydrogen bonding between cellulose hydroxyls and PLA ester groups) to macroscopic mechanical properties and surface morphology.
4. Quantitative Metrics: The work quantifies improvements in tensile strength, flexural modulus, and crystallinity, offering specific data points for the design of sustainable structural components.

Key Results

• Mechanical Performance: The optimum mechanical performance was achieved at 25–35 vol.% fiber content with curing at 160–165 °C.
  • Tensile Strength: Increased by approximately 14% to a maximum of 72 MPa (at 30% $V_f$, 160 °C) compared to 63 MPa for neat PLA.
  • Flexural Strength: Showed a dramatic improvement, rising from 100 MPa (neat PLA) to a peak of 315 MPa at 35% $V_f$ and 160 °C.
  • Modulus: Young's modulus increased by ~10% (to 3.85 GPa), and flexural modulus more than doubled (from 4.0 GPa to 8.5 GPa) at optimal conditions.
  • Hardness: Barcol hardness peaked at 38 for 25–30% fiber content at 160 °C.
• Microstructural Observations:
  • Dispersion: SEM and TEM revealed uniform fiber dispersion and good matrix wetting at intermediate loadings. However, fiber agglomeration, voids, and debonding were observed at high loadings (≥45–50%), leading to reduced performance.
  • Surface Roughness: AFM analysis indicated a reduction in surface roughness ($R_a$) from 37.8 nm to 20.0 nm as fiber content increased, suggesting better consolidation.
  • Interface: TEM and FTIR confirmed the formation of a distinct interphase region with hydrogen bonding, facilitating effective stress transfer.
• Thermal Properties:
  • Crystallinity: XRD and DSC results showed an increase in PLA crystallinity from 22.3% to 27.5% with higher fiber loading, attributed to the heterogeneous nucleation effect of jute fibers.
  • Melting Temperature: The melting temperature of the composite increased from 162.5 °C to 165.1 °C with increased fiber content.
  • Thermal Stability: TGA showed an increase in residual char from 8.2% to 15.1% as fiber content rose, indicating improved thermal stability, although the onset of degradation is influenced by the natural fiber's lower thermal stability compared to PLA.
• Water Absorption: Water absorption increased monotonically with fiber content due to the hydrophilic nature of jute, rising from 0.5% (neat PLA) to 22% at 50% $V_f$. Higher curing temperatures partially mitigated this by reducing void content.

Significance
The paper concludes that jute/PLA biocomposites fabricated via FDM represent a viable, lightweight, and environmentally sustainable alternative to conventional synthetic fiber-reinforced polymers for structural engineering applications. The study elucidates the critical balance required between fiber volume fraction and thermal processing parameters to achieve high-performance biocomposites. By confirming that moderate fiber loadings (25–35%) and controlled curing (160–165 °C) optimize mechanical strength, thermal stability, and interfacial integrity, the work provides essential guidance for the design of next-generation biodegradable materials. The findings support the development of high-performance, eco-friendly components without relying on synthetic reinforcements.