Pinecone Powder as a Functional Biofiller for Natural Rubber Composites: Structure-Property Relationships and Potential Applications

Green rubber biocomposites provide a sustainable alternative to conventional rubber by incorporating natural fillers with lower environmental impact. This study examines pinecone powder from Scots Pine (Pinus sylvestris) as a renewable filler for natural rubber (NR). Pinecones were ground using a ball mill, and the resulting powder was added to NR at 5–30 phr through two-roll milling followed by vulcanization at 160°C. SEM analysis revealed cylindrical, rough-surfaced particles that promote mechanical interlocking with the matrix. Despite limited interfacial adhesion, the filler caused reinforcement with appropriate loadings. The composite containing 15 phr pinecone powder exhibited the highest torque increase (3.6 dNm) and cross-link density (1.78 × 10−4 mol/cm3). Tensile strength was optimal at 5–15 phr (17.16–19.22 MPa). Pinecone powder improved barrier properties but also increased water absorption and surface wettability. Overall, it shows promise as a sustainable filler for NR biocomposites, providing mechanical and barrier improvements, though moisture sensitivity and matrix compatibility remain challenges that may be addressed through filler modification.