Study of oxidation of cellulose by Fenton-type reactions using alkali metal salts as swelling agents

Cellulose from corn straw was oxidized by Fenton-type reagents (FeSO₄. 7H₂O or CuCl₂. 2H₂O) using alkaline metal salts (LiCl; NaCl). Cellulose pre-treatment using alkali metal salts (LiCl; NaCl) coupled with a high H₂O₂ loading (up to 500 kg per ton of pulp) are used as a novel approach to improve the oxidation rate of oxidized celluloses. The oxidation rate was determined by measuring the carboxylic acid and total carbonyl contents of the oxidized cellulose. The oxidized celluloses were characterized by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The results show that the oxidation efficiency was improved by using the metal salts and increasing the H₂O₂ loading for both catalytic systems (Fe²⁺ or Cu²⁺). The oxidization rate increased gradually with H₂O₂ loading up to a maximum 500 kg/t of pulp tested without a considerable loss of cellulose structure. The FTIR results revealed that oxidized celluloses exhibit almost similar predominant hydroxy-based structure as native cellulose with the presence of bands in the regions of 1640–1742 cm⁻¹ characteristic of aldehyde and carboxylic acid groups. The XRD results showed that the crystallinity index slightly decreased from 69.4 to 67–68 and 62–64% after oxidation of the cellulose. The equilibrium moisture contents of oxidized celluloses increased compared to the raw cellulose pulp. The moisture curves fit the page model and exhibits a sub-diffusion process. Graphical Abstract: (Figure presented.)