Sustainable biocomposites from Nylon 6 and polypropylene blends and biocarbon - Studies on tailored morphologies and complex composite structures

The ability of irregular and polydisperse sustainable biocarbon (BC) particles to deform a binary immiscible blend in composites formulations was investigated at different particle polarity. Herein, up to 40 wt% of biocarbon particles with size of similar to 1.80-2.00 mu m were melt-compounded with polyamide 6 (PA6) and polypropylene (PP) at 80/20 and 20/80 (w/w). A high affinity of biocarbon for the PA6 phase over the PP phase was observed and was not affected by the polarity. A critical filling ratio (phi(BC) in PA6 or phi(PA6+BC) in PP) marking the formation of a 3-dimensional percolated network between the particles was estimated at similar to 0.26-0.31, yielding a fractal network of dimension d(f) similar to 1.7-2.0. This critical ratio was assessed by measuring the droplet size, material viscosity, and yield stress. In addition, a transition from a droplet suspension to funicular morphology was observed at (phi(PA6 +BC) similar to 0.36 in PP. It was furthermore found that solid- or liquid-like behavior in such morphologies was induced by a high or low biocarbon surface functionality as a result of low or high biocarbon pyrolysis temperature. As such this work gives new insight on morphology development and properties of complex composite structures with heterogeneous particles.