The yield and properties of cellulose nanocrystals extracted from HCl vapor-Prehydrolyzed torch ginger stem cellulose

Torch ginger (Etlingera elatior) stem is a valuable non-wood biomass source for nanocellulose production, due to its high cellulose content and widespread availability. This study examined the yield and properties of cellulose nanocrystals (CNCs) of cellulose extracted from torch ginger stems, comparing the H₂SO₄ hydrolysis of samples with and without HCl vapor prehydrolysis. The cellulose extraction was performed using the Alkaline Hydrogen Peroxide-Peracetic Acid (AHP-PAA) method (CO1), followed by a 24-h pretreatment with HCl vapor (CO2). Optimal hydrolysis conditions were determined through Response Surface Methodology-Central Composite Design (RSM-CCD), focusing on three key parameters: H₂SO₄ concentration (58-62 wt%), reaction time (30-90 min), and temperature (40-50 °C). Results indicated that HCl vapor prehydrolysis enhanced the crystallinity of cellulose via partial hydrolysis and subsequent crystallization. The cubic polynomial regression model derived from RSM-CCD effectively captured the interaction terms (X₁²X₃ for CO1 and X₁X₂² for CO2), allowing for accurate predictions of CNC yields under equivalent hydrolysis conditions. The analysis revealed that CNCs derived from CNC-O1 yielded a higher percentage (44.4 %) compared to those from CNC-O2 (41.6 %). CNC-O1 showed an aspect ratio of >150, comparable to CNCs sourced from bacterial cellulose, tunicates, and several non-wood biomass, while CNC-O2 exhibited an aspect ratio of ∼50, analogous to wood-derived CNCs. Furthermore, CNC-O2 demonstrated enhanced crystallinity, thermal stability, and surface charge compared to CNC-O1. HCl vapor prehydrolysis enhances cellulose accessibility rather than directly affecting crystallinity, indicating its potential to optimize CNC characteristics through improved substrate accessibility.