Effect of particle size and loading of cherry tree branch fillers on the mechanical and viscoelastic properties of polypropylene composites

Lignocellulosic fillers derived from pruned cherry tree branches were studied relative to the mechanical and viscoelastic properties of polypropylene (PP) composites. Tree branches were collected from the orchard after pruning and the wood and bark parts were separated from each other. Both materials were processed into particles of different sizes (below 100 µm and between 100 and 250 µm) and filled into PP at different weight percentages (5%, 10%, 15%, and 20%). The mechanical performances of the biocomposites were evaluated through tensile tests, while their viscoelastic behavior was analyzed using dynamic mechanical analysis (DMA). Results revealed a decline in tensile strength with increasing filler content, which was attributed to poor interfacial adhesion between the PP matrix and fillers. However, tensile modulus increased with increasing filler content, with the highest values were observed at 20% filler loadings. The DMA showed enhanced storage and loss moduli, indicating improved stiffness and energy dissipation. Scanning electron microscopy (SEM) confirmed the presence of voids and filler agglomeration, further explaining the mechanical property reductions. These results demonstrate the potential of cherry tree pruning waste as a bio-filler for sustainable biocomposites with improved stiffness.