Experimental–Numerical Framework for Evaluating the Mechanical Response of Cornus sanguinea L.-Reinforced Polypropylene Biocomposites

Polypropylene (PP) biocomposites reinforced with Cornus sanguinea L. (CS) pruning-waste particles were investigated using a combined experimental mechanics and finite element (FE) validation framework to support model-based design with an under-utilized lignocellulosic feedstock. Two particle-size fractions (<100 µm, LF1; 100–250 µm, LF2) were produced by grinding and sieving and incorporated into PP at 5–20 wt% via melt compounding and compression molding. Tensile and three-point bending properties were measured in accordance with ASTM D638 and ASTM D790. PP exhibited a tensile strength of 23.63 ± 0.51 MPa and a tensile modulus of 868 ± 21 MPa. Incorporation of LF1 particles increased tensile modulus monotonically, reaching 1020 ± 137 MPa at 20 wt%, while tensile strength decreased with filler content; by contrast, the 20 wt% LF2 formulation showed a pronounced strength reduction to 16.30 ± 0.25 MPa, indicating a disadvantageous size–loading interaction. In flexure, strength was comparatively insensitive to reinforcement (PP: 39.5 ± 0.34 MPa; reductions typically ≤7%), whereas flexural modulus increased to 2152 ± 27 MPa (LF1) and 2110 ± 34 MPa (LF2). FE models calibrated using true stress–true plastic strain data accurately reproduced tensile responses across the full strain range and flexural behavior within the pre-contact-dominated regime, demonstrating the suitability of PP/CS biocomposites for stiffness-driven applications.