Influences on main thermal and mechanical parameters of plasticized sisal fiber-reinforced PLA: An experimental approach

• Sisal fiber and acetyl tributyl citrate (ATBC) increased the crystallization tendency of poly(lactic acid) PLA, with ATBC acting as a nucleating agent in addition to plasticizing by lowering melting and glass transition temperatures while boosting crystallinity. • The addition of sisal fiber raised the thermal conductivity of PLA composites, with a slight further increase when ATBC was added. Conductivity increased up to 50°C but decreased beyond that temperature. • Incorporating sisal fiber enhanced the stiffness of PLA composites, whereas ATBC reduced stiffness and storage modulus. • All PLA composites exhibited shear-thinning behavior, with viscosity decreasing at higher shear rates and temperatures, but increasing with greater fiber content at lower shear rates. Composites based on poly(lactic acid) (PLA) and sisal fiber were prepared using extrusion and injection molding processes with the addition of acetyl tributyl citrate as a plasticizer. The raw materials and the formulated composites were characterized through thermal and rheological analyses to evaluate effects of fiber and plasticizer content on the final thermal properties of the composites. Differential scanning calorimetry results showed that PLA crystallinity increased with the addition of both fiber and plasticizer, although the increase due to fiber content alone was relatively small. The incorporation of the plasticizer also reduced the glass transition temperature of the PLA. In addition, thermal property analysis revealed that both fiber content and processing temperature significantly influenced thermal conductivity: thermal conductivity increased with increasing fiber content and temperature up to 50°C, but decreased at temperatures above 50°C. Furthermore, the dynamic mechanical analysis indicated that the storage and loss moduli of the composites varied with temperature. The storage modulus increased with fiber content but dropped sharply near the glass transition temperature. Rheological characterization further demonstrated that fiber-fiber and fiber-matrix interactions were relatively effective, with good fiber dispersion within the PLA matrix. This resulted in stable shear viscosity across the entire range of shear rates for different capillary dimensions. Moreover, viscosity increased with increasing fiber content but decreased with the addition of the plasticizer. Temperature also played a critical role, as viscosity decreased with increasing melt temperature.