This study presents an effective approach for compatibilizing thermoplastic polyolefin, a polymer blend comprising polypropylene, polyethylene, and ethylene propylene diene monomer domains, with aramid fibers. It addresses the long-standing challenge of poor interfacial adhesion between non-polar matrices and inert fibers. Aramid fibers were modified using medium and high radio frequency (RF) power air plasma, which increased surface roughness and introduced amines and other polar functional groups. These functionalities enabled covalent bonding with polypropylene-graft-maleic anhydride (PP-g-MA), a compatibilizer, through stable amide linkages at the fiber-matrix interface. This compatibilization strategy leveraged both mechanical interlocking from surface roughness and chemical coupling through interfacial interactions. Combining these two mechanisms led to greater reinforcement than either approach alone. Mechanical testing revealed that the compatibilized composites exhibited significantly improved tensile and flexural strength and stiffness compared with both uncompatibilized systems and previously reported aramid/polyolefins composites. Dynamic mechanical analysis and rheological measurements confirmed enhanced stress transfer and energy dissipation, while differential scanning calorimetry indicated increased crystallization temperature and thermal stability. Scanning electron microscopy of fractured surfaces revealed distinct composite failure mechanisms between untreated fibers, plasma-treated fibers (mechanical interlocking only), and treated fibers with PP-g-MA (both mechanisms), with extensive fiber defibrillation observed only in the last case. To the best of our knowledge, this is the first study on this dual-mechanism compatibilization strategy based on plasma surface treatment. The findings establish a scalable and effective strategy for developing high performance, durable, and thermally stable composites from non-polar polymers and inert fiber systems.
