Experimental Evaluation of Thermal and Mechanical Performances of Plasticized Sisal Fiber–Reinforced Polylactic Acid Composites under Variable Conditions

Abstract

Recently, the focus of global researchers is on the development and characterization of natural fiber-reinforced bio-based polymer composites for various engineering applications. In this study, composites of PLA and sisal fiber were fabricated using injection molding, with acetyl tributyl citrate added as a plasticizer. Composites were characterized through mechanical, thermal and rheological analyses to assess the effects of the fiber content and the plasticizer on the mechanical, thermal and rheological properties of the composites. In addition, differential scanning calorimetry test results indicated that PLA crystallinity increased with the addition of both fiber and plasticizer, although the contribution of fiber alone was relatively limited. The inclusion of the plasticizer also led to a reduction in the glass transition temperature of PLA. Thermal property analysis further revealed that fiber content and processing temperature had a significant influence on thermal conductivity of composites. Thermal conductivity increased with rising fiber content and temperature up to 50°C but decreased at temperatures above this threshold. Dynamic mechanical analysis showed that the storage and loss moduli of the composites were temperature-dependent. The storage modulus increased with fiber content but declined sharply near the glass transition temperature. Rheological characterization demonstrated effective fiber–fiber and fiber–matrix interactions, resulting in good fiber dispersion within the PLA matrix. This contributed to stable shear viscosity across a wide range of shear rates for different capillary dimensions. Viscosity increased with higher fiber content but decreased with plasticizer addition. Temperature also played a critical role, as viscosity decreased with increasing melt temperature.

 Keywords: Composite; mechanical properties; PLA; sisal fiber; thermal behavior.