TEMPO-Oxidized Cellulosic Material from Agro-Industrial Purple Corn Cob Waste: Extraction, Characterization

Peru’s agro-industrial activities generate lignocellulosic residues that can be valorized as sources of cellulose-based materials. This study aimed to obtain TEMPO-oxidized cellulosic material (T-OCM) from bleached purple corn cob pulp. Spent purple corn cob (SPCC) was characterized and conditioned through washing, drying, grinding, and sieving, followed by treatment with acidified ethanol (0.01% HCl) to remove anthocyanins. Cellulose was obtained via alkaline delignification (6% NaOH) and bleaching with 4% H2O2. T-OCM was then produced using TEMPO-mediated oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl, 98%) with NaBr, testing NaClO concentrations of 10, 20, and 30 mmol/g over a 6 h reaction time. Characterization included FTIR, particle size analysis (zeta sizer), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry (TGA). SPCC showed 5.76 ± 0.08% moisture, 1.66 ± 0.06% ash, 2.62 ± 0.02% extractives, 41.81 ± 0.34% cellulose, 36.06 ± 0.34% hemicellulose, and 17.85 ± 0.05% lignin, comparable to unprocessed samples. The cellulose reached a purity of 91.05%, while the maximum yield of T-OCM was 58% at 20 mmol of NaClO/g, with a carboxylate content of 1.60 mmol/g, which increased with the dosage. The resulting T-OCM exhibited zeta potential −45.1 mV and hydrodynamic particle diameter 134.12 nm. The crystallinity index increased from 65.53% in cellulose to 73.7% in the T-OCM. In conclusion, SPCC can be valorized to obtain highly purified cellulose and TEMPO-oxidized cellulosic material.