Biocarbon Reinforced Toughened Polypropylene Biocomposite for Improved Mechanical Properties and Environmental Sustainability

Pyrolysis, a thermochemical pathway for converting biomass to energy in biorefinery systems, generates a considerable amount of solid residue by-product (up to 35 wt.%) which mainly consists of renewable carbon (biocarbon). Unless a high-volume application exists for the biocarbon (BC), the significant amount of this by-product can challenge the long-term sustainability of pyrolysis units. In the present project, biocarbon is evaluated for its usage as a filler as well as a reinforcing material in producing biocomposites for automotive applications. The focus of this research is to engineer durable biocomposites with well-balanced mechanical properties which have the same or better performance as the current mineral filled composites used in the auto industry. The project consisted of several phases including biocarbon characterization, preliminary studies on the melt mixing of BC and rubber toughened polypropylene (t-PP), compatibilization and optimization of compatibilizer content, developing structure-properties relationship for the biocomposites and a durability studies on the long-term performance of the developed biocomposites. The initial characterization results confirmed that biocarbon could potentially be a suitable filler for polymer composite applications. Using several techniques, such as atomic force microscopy and thermal analysis, a high stiffness and thermal stability were observed in biocarbon particles. In the next step, biocomposites were prepared, and their performance was evaluated based on their stiffness and toughness balance. The effects of compatibilizers and different treatments on the biocarbon were quantified and optimized using a full factorial statistical design of experiments. Morphological and dynamic mechanical analysis were performed to analyze the BC-matrix interface and interaction between the biocomposite components. The results are conclusive that property improvement in such biocomposites happens only when a separate dispersion of the biocarbon and rubber phase exist. Filler hybridization by means of recycled short carbon fibers and β nucleating agents created an improved performance level for these biocomposites. Durability studies showed that hindered phenol antioxidants could successfully protect such biocomposites from thermo-oxidative degradation. Overall, the investigation of governing mechanisms resulted in a novel t-PP/biocarbon biocomposites with better performance characteristics, higher biobased content and lighter density as compared to the common mineral filled composites used in automotive industry.