Assessing upcycling of waste bioplastics for production of sustainable carbon black substitute

Carbon black is a product with multiple applications, including use as an additive for tyres or plastics, as well as ink or toner. Current methods of carbon black production are based on incomplete combustion of fossil fuels, followed by quenching, resulting in a high carbon footprint and related emissions. Even though unintended, biodegradable bioplastics at the end of life still pose problems to waste management plants. Most notably, the time required for bioplastics to biodegrade is longer than the typical residence time in state-of-the-art processes, such as anaerobic digestion and composting. This causes incomplete degradation and reduces the efficiency of waste treatment facilities. This work provides an experimental evaluation of a novel method of production of carbon black, using bioplastic waste (namely, cellulose acetate) as a feedstock. The proposed system consists of hydrothermal carbonisation (HTC) and subsequent pyrolysis of separated solid products. The novel product exhibits morphology and structure similar to commercial carbon black and high thermal stability. BET surface area as high as 175 m²/g can be achieved by combining hydrothermal carbonisation performed at 250 °C followed by pyrolysis at 600 °C. Further increase in pyrolysis temperature provided no additional benefits and resulted in collapse of the pores within the mesoporous range, with detrimental influence on BET surface and pore volume.