Engineered thermoplastic blends were fabricated using PA6 and poly (butylene terephthalate) (PBT) and, upon optimization, they were reinforced with biocarbon and other conventional fillers. A twin-screw extruder and injection molder were used to produce the blends compatibilized blends, and biocomposites. Analyses of the materials were completed through mechanical and thermal tests while the viscoelastic behaviour was investigated via dynamic mechanical analysis. Fourier transform infrared spectroscopy and nuclear magnetic resonance was also performed to understand the effect of blending PBT with PA6. Following optimization of the PA6 and PBT blends, a maleic anhydride grafted polyamide 11 compatibilizer was designed in order to increase the compatibility. Comparison of thermo-oxidative aging on a new emerging and sustainable filler was carried out against fillers used in the automotive industry. The thermal degradation of the different fillers was investigated under accelerated heat aging for 1000 h at 140 °C. The composite’s performances, before and after heat aging, were evaluated using mechanical and thermal tests.