Biochar as a renewable carbon additive for biodegradable plastics

Abstract

Biochar - a carbon material produced from pyrolysis of biomass - is a promising alternative to petroleum-derived filler materials in biobased and biodegradable plastics. In this application, biochar can replace materials such as carbon black, with a material that is compatible with end-of-life degradation of bioplastics, while reducing costs and improving material properties. Specifically, high electrical conductivity biochar has the potential to be applied to create highly electrically conductive and biodegradable biochar-bioplastic composite materials. Herein, two critical gaps to development of biochar-bioplastic composites are addressed: the high variation in biochar electrical conductivity and poor thermal interactions between bioplastics and biochar that reduce the bioplastics molecular weight and mechanical properties. To this end, biochars are produced from a variety of feedstocks and their chemical structure and electrical conductivity are extensively characterized. The relationship between feedstock chemical properties, biochar chemical properties, and biochar electrical conductivity is examined. Feedstock oxygen and inorganic content are found to play a critical role in developing highly electrically conductive biochar. The impact of these biochars on the thermal behavior of bioplastics is then examined in detail, and multiple hypotheses for the reduction in thermal behavior that have been proposed in past studies are tested. Biochar moisture content is found to have a limited impact on polymer thermal degradation, while alkali and alkaline earth metals present in biochar reduce the thermal degradation temperature of common bioplastics. A simple washing method was developed to remove these metals and improve the thermal stability of biochar-bioplastic composites. Finally, the environmental benefits of biochar-plastic composites are examined with life cycle assessment methodology, and the developed biochar is examined as a conductive additive in lithium-ion batteries. This work addresses two critical issues that limited the potential of biochar to reduce environmental impacts of rapidly growing classes of materials, as well as demonstrating its applicability in critical applications of petroleum-derived materials. Biochar-bioplastic composites show a unique combination of high electrical conductivity and biodegradability, with strong potential for development of applications in diverse industries from agriculture to biomedical applications.