A novel green approach for the preparation of cellulose nanowhiskers from white coir

• It was developed an organosolv pretreatment for unripe coconut husk fiber.
• Agro-industrial residues from coconut can yield industrial biomacromolecules.
• The organosolv pretreatment resulted in cellulose nanocrystals.
• A greener and more eco-friendly approach was applied to coconut fibers.

The aim of this work was to optimize the extraction of cellulose nanowhiskers (CNW) from unripe coconut husk fibers (CHF). The CHF was delignified using organosolv process, followed by alkaline bleaching (5% (w/w) H2O2 + 4% (w/w) NaOH; 50 °C, 90 min). The CHF was subsequently hydrolyzed with 30% (v/v) sulfuric acid (60 °C, 360 min). The process yielded a partially delignified acetosolv cellulose pulp and acetic black liquor, from which the lignin was recovered. The CNW from the acetosolv pulp exhibited an average length of 172 ± 88 nm and a diameter of 8 ± 3 nm, (aspect ratio of 22 ± 8). The surface charge of the CNW was −33 mV, indicating a stable aqueous colloidal suspension. The nanocrystals presented physical characteristics close to those extracted from cellulose pulp made by CHF chlorine-pulping. This approach offers the additional advantage of extracting the lignin as an alternative to eradication.