Production, characterization and performance of biochar co-pyrolyzed with red mud for conductive epoxy composites

The incessant development of new electronic devices and the persistent emission of electromagnetic signals lead to seek new electromagnetic interference (EMI) shielding materials. Due to the increasing global concern about climate change, it seems necessary direct the research on sustainable feedstocks. For the upon reasons, two different types of feedstocks have been chosen. First is lignocellulosic biomass, which is a renewable source. Three different types were investigated: kraft lignin, pine wood and hemp. Second is Red Mud, the major by-product of aluminum production process with big disposable problem. It is mainly composed of iron oxide and other metal oxides. The aim is to create an EMI shielding material where its bulk is made of Red Mud, cover by a conductive layer of graphitize carbon from biomass. To complete the aim, co-pyrolysis of the two feedstocks were performed in two steps, in order to generate a biochar with the required characteristics. First, feedstocks were co-pyrolyzed at 600°C with nitrogen gas into a stirred batch reactor. After, the biochar produced was activated into a furnace at 900°C using carbon dioxide. Different blends with Red Mud were investigated: 50% biomass content, 80%, 90%, 95%, 100%. To understand which is the best biomass and the best blend, multiple analysis were performed over both pyrolyzed and activated biochars. Proximate, ultimate, nitrogen adsorption characterized the biochars matrix, while Raman and electrical measurement in DC revealed electrical properties. The results show a better carbon organization with the increase of Red Mud content for every type of biomass. Moreover, activation treatment significantly increases the surface area of one order of magnitude. Also, electrical conductivity rose of two orders of magnitude, up to 90 S/m. If best temperature and blend were determined, best biomass type needs to be further investigated.