An improved thermoplastic compound and its method of manufacture therefor are disclosed. The thermoplastic compound comprises a semicrystalline polyolefin matrix, selected from polypropylene, high-density polyethylene, or blends thereof, reinforced with a renewable, lignocellulosic nutshell particulate and compatibilized via maleic anhydride grafting. In-situ or pre-grafted maleic-anhydride functionality effects covalent interfacial bonding between the polymer and bio-filler during reactive extrusion, yielding composites with significantly enhanced tensile strength, flexural modulus, and notched-impact resistance compared to unfilled or uncoupled resins. The use of agricultural-waste nutshells as a reinforcing filler reduces material density and carbon footprint while lowering cost relative to conventional mineral fillers. The composites readily molded or extruded into structural and semi-structural parts, making them a sustainable, high-performance alternative for applications in automotive, construction, packaging, and consumer goods.