Extraction of “green” cellulose nanocrystals (CNCs) from waste biomass is a sustainable strategy for high valued valorization in the view of socio-economic and environmental issues. Herein, for the first time, waste pencil chips (PC) as a potential source of cellulose, were used for the extraction of CNCs. CNCs were successfully extracted from PC wastes using alkali and bleaching chemical treatments to remove hemicellulose and lignin followed by acid hydrolysis using concentrated sulfuric acid. The products after each step were characterized in terms of crystallinity, chemical structures, thermal properties, and morphologies. The XRD results showed that the crystalline index increased about 16% from PC (75%) to CNCs (91%). The FTIR analysis confirmed the removal of the hemicellulose and lignin from PC after alkali and bleaching treatments. The TGA analysis showed that the thermal stability of the CNCs is affected mainly by the dehydration reaction caused by sulfate groups. The SEM and FE-SEM images showed that after chemical treatments, defibrillation of fibers occurs and CNCs have a needle/rod like structure. Also, the specific surface aera was greatly increased from 0.495 for PC to 486.430 m2/g for CNCs. Herein, for the first time, lignin-containing cellulose extracted from PC was replaced with sawdust (SRB) in the production of alumina refractory bricks (RBs), as a pore former/binder. Interestingly, the prepared RBs (PC–NaOH/RB) had a greater amount of alumina (83%) and a lower density (0.75 g/cm3) than SRB. The classification temperature increased from 1650 for SRB to 1717 ◦C for PC-NaOH/RB.

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