Hemp Granule Size and Mass Fraction Effects on the Rheological, Thermal, and Mechanical Behavior of PLA-Based Biocomposites for Thermoforming

In this work, polylactic acid (PLA) biocomposites reinforced with hemp granules of different sizes (1 mm and 2 mm) and contents (10, 20, and 30 wt.%) were systematically investigated. The study aimed to elucidate how granule size and concentration affect the rheological, thermal, and heat-transfer properties of the composites, with a focus on rheological parameters relevant to thermoforming. The results showed that increasing filler content enhanced stiffness, storage modulus (G′), and complex viscosity (η*), with smaller granules providing better reinforcement due to improved dispersion and interfacial adhesion. Thermal analyses confirmed a nucleating effect of hemp, slightly increasing crystallinity, while higher contents reduced thermal stability. The effect of filler content and size on heat transfer was discussed with respect to heating and cooling sensitivity during thermoforming, a key aspect of processability. The originality of this work lies in its integrated characterization strategy, which highlights the combined effect of granule size and concentration on the viscoelastic response and processing-relevant parameters of PLA-based biocomposites. These insights contribute to the development of sustainable biocomposites with improved potential for thermoforming applications.