Unidirectional Tape-Based Composites from Hemp and Pineapple Leaf Fiber: Mechanical Performance in Conventional and Bio-Based Matrices

Abstract

A newly developed unidirectional semi-finished product made from hemp or pineapple leaf fibers (PALF) is examined for its reinforcing potential in various polymer matrices, including epoxy, bio-based epoxy, polyhydroxyalkanoate (PHA), polybutylene adipate terephthalate (PBAT), and polylactide (PLA), at a fiber volume fraction of ≈40%. Compression-molded composites are characterized with respect to mechanical properties, interlaminar shear strength (ILSS), density, and void content. All systems show promising performance, with tensile strengths ranging from 110 MPa for PALF/PHA to 227 MPa for hemp/bio-based epoxy, and Young's moduli ranging from 9.8 to 22.7 GPa. At comparable ILSS levels, hemp-based composites exhibit higher strengths and stiffnesses, whereas PALF composites show increased void content. The observed microvoids appear less detrimental than macrovoids, supporting the materials’ suitability for lightweight structures. PALF composites demonstrate greater toughness than their hemp counterparts, with PALF/bio-based epoxy achieving an unnotched Charpy impact strength of 39 kJ m−2 compared with 29 kJ m−2 for hemp/bio-based epoxy. Although the full tensile strength potential of PALF cannot be realized—because the composites do not reach the fibers’ maximum elongation and therefore their maximum stress—the combination of low density and favorable mechanical behavior highlights both PALF and hemp-based composites as promisi ng candidates for structural lightweight applications.