Effect of alkaline treatment on the thermal and mechanical properties of sugar palm fibre reinforced thermoplastic polyurethane composites

This study examines the impact of alkaline treatment on the mechanical, thermal, and morphological properties of sugar palm fiber (SPF)-reinforced thermoplastic polyurethane (TPU) composites. SPF fibers (250 μm) were treated with sodium hydroxide (NaOH) solutions of 0%, 2%, 4%, and 6% (w/w) for 90 min at room temperature. These fibers were then mixed with TPU in an extruder at 180-200 °C and molded into composite sheets using compression molding at 190 °C, 10 MPa pressure, and a 10-minute holding time. X-ray diffraction (XRD) revealed increased crystallinity in the composites, peaking at 1589 cps with 6% NaOH. Fourier transform infrared (FTIR) spectra showed improved fiber-matrix compatibility, most evident with 2% NaOH. SEM analysis indicated cleaner and rougher fiber surfaces post-treatment, though cracks were observed at higher concentrations. Energy-dispersive X-ray (EDX) confirmed increased oxygen content and sodium residue at elevated NaOH levels, reflecting lignin removal. Thermogravimetric analysis (TGA) demonstrated enhanced thermal stability, with the highest residue mass of 599.16 °C at 6% NaOH. Alkaline treatment notably enhanced SPF/TPU composites, with 2% NaOH providing optimal flexural strength and 6% NaOH maximizing impact strength and thermal stability.