Recovery and characterization of cellulose nanocrystals (CNCs) from Phalaris aquatica L. energy crop: towards the Mediterranean biorefinery sustainability and biodiversity valorisation

Phalaris aquatica L., a perennial Mediterranean species with potential as a sustainable energy crop, represents an underexplored lignocellulosic resource for advanced bio-based material production. This study investigated the feasibility of converting P. aquatica biomass into cellulose nanocrystals (CNCs) through sequential alkaline treatment (4% w/v NaOH, 80°C for 2 h), bleaching (1.7% w/v sodium chlorite under reflux at 80°C for 4 h), and sulfuric acid hydrolysis (65% w/w H 2 SO 4 at 50°C for 40 min). Chemical fractionation substantially enriched the cellulose fraction, increasing cellulose content from 43.1 ± 3.1% (w/w) in the raw biomass to 77.7 ± 1.8% after alkaline treatment and 90.5 ± 1.5% following bleaching, with an overall CNC recovery of 15.7%. Fourier-transform infrared spectroscopy (FTIR) verified the progressive removal of hemicellulose and lignin, while X-ray diffraction (XRD) revealed an increase in crystallinity index from 59.1 ± 1.6% to 76.1 ± 2.8% following processing. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated changes in thermal decomposition behaviour associated with chemical purification and acid hydrolysis. Dynamic light scattering (DLS) yielded a mean hydrodynamic particle size of 165.2 ± 15.4 nm, indicating aggregated CNC structures. Atomic force microscopy (AFM) confirmed nanoscale surface features attributable to CNC aggregates rather than individual nanocrystals. Collectively, these findings establish P. aquatica lignocellulosic biomass as a promising feedstock for cellulose-rich nanostructured materials and support its integration into Mediterranean biomass valorisation and biorefinery strategies. Future research should prioritise process optimisation, reduced chemical and energy consumption, techno-economic assessment, environmental evaluation, and scale-up.