Valorisation of Pre- and Post-Consumer Cotton, Viscose and Bast-Fibre Textile Waste into Sodium Carboxymethyl Cellulose: A Comprehensive Study of Feedstock Type, Synthesis Route and Product Quality

Sodium carboxymethyl cellulose (Na-CMC) is among the most widely used water-soluble cellulose ethers, yet its industrial production still relies largely on virgin cotton linters and wood pulp. In this work, we systematically converted a broad panel of cellulose-bearing textile wastes—reference fabrics, pre-consumer sewing-room clippings and post-consumer garments made of cotton, viscose, flax, jute and their blends—into Na-CMC through heterogeneous alkalisation and etherification in an isopropanol–water medium. Five synthesis routes were compared, including single-step, stepwise-reagent, hydrogen peroxide (H2O2) bleaching/degrading, cross-linking (dichloroacetic acid) and sodium monochloroacetate (MCA-Na) variants. Fifty-five separate batch syntheses were characterised for degree of substitution (DS), 2% apparent viscosity, active-substance purity, pH and residual moisture. The mean DS was 0.48 ± 0.07 and did not differ significantly among feedstock classes; used garments yielded similar mean substitution levels to reference fabrics in the statistical comparison. Product purity, in contrast, was lower on average for post-consumer material (71.9%) than for reference fabrics (75.9%), with a broader post-consumer distribution. scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) examination of the feedstocks matched this trend, showing frayed, contaminated post-consumer fibres with sulfur signals and locally elevated aluminium on the fibre surface, which were not observed on the smooth pre-consumer cotton. DS showed moderate positive correlations with purity and log-viscosity. Apparent viscosities spanned four orders of magnitude (2.5–23,100 mPa·s), enabling a single, tunable process to deliver both low- and high-viscosity grades. The moderate DS (reagent efficiency ≈ 42%) is consistent with the monochloroacetate charge and reagent losses to hydrolysis rather than with the textile origin of the cellulose, and hydrogen peroxide lowered viscosity to 2.5–30 mPa·s without a significant loss of substitution. The results demonstrate laboratory-scale conversion of mechanically shredded textile waste into technical-grade CMC spanning a broad viscosity range.