Valorization of cotton waste into cellulose nanocrystals and their incorporation into electrospun poly (vinyl alcohol) nanofibrous membranes with enhanced thermal and structural properties

Abstract

Cellulose nanocrystals (CNCs) were extracted from cotton waste using alkaline treatment, bleaching, and sulfuric acid hydrolysis. Increasing the sulfuric acid concentration from 40% to 62% was associated with an increase in CNC yield from approximately 19.20 ± 3.9% to 41.30 ± 3.1%, indicating the influence of acid concentration on the recovery of the nanocrystalline fraction under the conditions employed. Energy-dispersive X-ray spectroscopy (EDX) showed carbon and oxygen as the predominant elements, at 62.39 and 34.33 wt%, respectively, with trace amounts of sulfur and sodium. Scanning electron microscopy (SEM) revealed snowflake-like aggregated structures composed of branched rod-like features, with an average width of 56.5 ± 8.7 nm . Atomic force microscopy (AFM) showed broadly consistent nanoscale morphological features, with snowflake-like structures ranging from approximately 120–200 nm and protruding branches of approximately 63.2 ± 10.9 nm in diameter. Fourier-transform infrared spectroscopy (FTIR) showed characteristic cellulose bands, including the band at 872.9 cm⁻¹ associated with β-(1→4)-glycosidic linkages. CNCs were incorporated into poly (vinyl alcohol) (PVA) nanofibrous membranes at concentrations of 0–40 wt% via electrospinning. Field-emission scanning electron microscopy (FESEM) of the 40 wt% CNC membrane revealed a relatively uniform fibrous network with a mean fiber diameter of 104.3 ± 38.6 nm, with CNCs distributed on the fiber surfaces. FTIR analysis of the prepared nanofibers showed the characteristic 916 cm⁻¹ band, supporting the presence of the cellulose component. Thermogravimetric analysis (TGA) showed an increase in residual mass with increasing CNC content, from 1.28% for the neat PVA membrane to 24.88% for the 40 wt% CNC membrane. Derivative thermogravimetry (DTG) indicated changes in thermal degradation behavior with increasing CNC content. The 40 wt% CNC formulation exhibited the highest residual mass among the studied formulations. The study highlights the successful conversion of cotton waste into CNCs and their incorporation into PVA nanofibrous membranes, with potential applications in advanced packaging and biomedical membranes.