Mechanical, Thermal, and Microstructural Evaluation of Bio‐Based Polyurethane Composites Reinforced With Woven Jute and Flax

ABSTRACT Natural‐fiber composites have gained attention as sustainable alternatives to synthetic‐fiber materials. However, their performance is still limited by fiber‐matrix adhesion, moisture sensitivity, and variability in mechanical properties. In this study, bio‐based polyurethane (PU) composites reinforced with woven jute and flax fabrics were manufactured using a vacuum‐assisted resin transfer molding (VARTM) process. The materials were characterized through density measurements, Fourier‐transform infrared spectroscopy (FTIR), X ‐ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical testing. Mechanical characterization was performed through tensile tests (ASTM D3039, ASTM D3518), where Digital Image Correlation (DIC) was employed to calculate elastic properties (, , , and ). Additional analyses included flexural testing (ASTM D790). Flax‐reinforced composites exhibited the highest tensile and flexural performance, while jute‐reinforced composites showed superior thermal stability. SEM analyses revealed interfacial voids and incomplete fiber wetting, consistent with the observed mechanical behavior. These findings demonstrate the feasibility of using castor oil–based PU with natural fiber reinforcements for eco‐friendly structural applications.