Optimum alkaline treatment parameters for the extraction of cellulose and production of cellulose nanocrystals from apple pomace

Cellulose nanocrystals (CNCs) were produced from cellulose extracted from apple pomace (AP). In the alkaline treatment step for cellulose extraction, three variables, the NaOH concentration (6–12%), extraction time (30–240 min), and temperature (30–90 °C) were optimized through response surface methodology (RSM) for highest yield, highest purity (α-cellulose), and whiteness index (WI). The optimum conditions were determined as 10.23% NaOH, 69.82 °C, and 161.54 min, where the cellulose yield was found as 27.96 ± 0.78%, α-cellulose content was 85.31 ± 0.91% and WI was 47.79 ± 0.65%. The acid hydrolysis and ultrasonication treatments were applied to the cellulose to produce CNCs. Morphological analysis of CNCs was revealed the formation of a needle–like structure with averages of 7.9 ± 1.25 nm in diameter and 28 ± 2.03 nm in length. Meanwhile, the XRD diffraction and thermal analysis showed that CNCs have 78% crystallinity index higher than α-cellulose (69%), and is thermally less stable.