Cellulose nanofibrils from Euterpe oleracea residue extracted by acid hydrolysis and ultrasonic processing

The large amount of waste generated by the exploitation of açaí (Euterpe oleracea) by the agro-industrial sector in the Amazon, when not managed correctly, can become a threat to the environment due to widespread accumulation in terrestrial and aquatic environments. Utilising this waste as raw material to obtain cellulose nanofibrils (CNF) could avoid the use of non-renewable resources and replace petroleum-based polymers. CNFs are usually obtained by mechanical processes that require large amounts of energy, which is a disadvantage of this processing route. In the present study, the açaí residue was purified by alkaline treatment with NaOH and acidified sodium chlorite to remove the non-cellulosic components, and the resulting cellulose fibres were used as a raw material to obtain CNFs by a two-step process in which the cellulose fibres were hydrolysed with sulphuric acid as a pre-treatment method for subsequent ultrasonic processing. The CNFs obtained had widths between 9.14 nm and 7.22 nm, a crystallinity index of 75.78 %, high thermal stability, with the onset of thermal degradation at around 228 ºC, and a zeta potential up to 43.97 m/V. The results indicated that the combination of the sulphuric acid hydrolysis and ultrasonic processing allows to obtain CNFs from açaí residues that can be used in the production of nanostructured green products.