Production of nanocellulose from cashew apple bagasse: the influence of pretreatment

Nanocelluloses are highly interesting structures due to a variety of inherent properties, such as high surface area and porosity; hence, there is a need to investigate new sources of raw materials for their production. From this perspective, this paper presents a study on the obtainment of nanocelluloses from the cashew apple bagasse by evaluating the influence of the biomass pretreatment on the properties of the obtained structures. The cashew apple bagasse (CAB) was previously submitted to alkaline and acid–alkali pretreatments and the solid named CAB-PTA and CAB-PT-HA, respectively. The nanocellulosic fractions were obtained by hydrolysis using sulfuric acid combined with an ultrasonic treatment under different reaction times (1 h and 5 h). The highest nanocellulose yield was achieved using CAB-PT-HA, and the nanocrystals were rod-shaped and presented diameters of 30 to 40 nm. In the production of nanocelluloses using CAB-PTA, reaction time influenced the shape and size of the nanostructures, and the chemical composition analysis indicated the presence of residual lignin in those structures, which showed higher thermal stability. All obtained nanocelluloses presented zeta potentials greater than 30 mV in absolute values, indicating stable suspensions. Thus, this study can confirm the feasibility of the use of CAB as a novel renewable source for producing cellulose nanocrystals that possess great potential to be used as valuable biomaterials to this end.