Light-weight sustainable composite from virgin and recycled polypropylene blends and biocarbon for automotive part application

Virgin PP was blended with automotive recycled PP (rPP) at 70/30 and 50/50 ratios; the 50PP/50rPP blend exhibited the highest impact strength (31.54 J/m) with acceptable stiffness and was selected as the composite matrix. Incorporation of 24 wt% waste paper/plastic-derived biocarbon (BC) and 3 wt% PP-g-MA(MAPP) into the 50/50 blend increased tensile and flexural moduli by 36% and 33%, while maintaining density below 1.0 g/cm³ (0.977 g/cm³), thus maintaining a favorable stiffness-to-weight ratio.

Thermal stability was significantly improved: T10 increased by 33 °C in the compatibilized BC composite compared to the 50PP/50rPP blend, and HDT increased by 44%. Biocarbon acted as a nucleating agent, increasing crystallinity by 47% in the uncompatibilized composite. The Guth-Smallwood model predicted nearly two-fold increase in tensile and flexural moduli at a BC volume fraction of 0.19; experimentally, the BC composites reached ~67–82% of this theoretical upper bound, indicating effective but non-ideal reinforcement due to residual agglomeration and interfacial defects.