Oxidation of sugar-beet pulp dissociates parenchyma cells and chemically modifies cellulose, influencing the material’s viscosity

Sugar-beet pulp (SBP) when treated with H 2 O 2 followed by NaOCl produces an industrially useful, thixotropic, oxidised pulp (oP) product. Here we investigated how each of these two oxidants produces oPs differing in applicability, for example as thickening agents for bioplastics and paints. SBP was stirred with 41 mM H 2 O 2 (pH 6, 90°C, 360 min) and/or 76 mM NaOCl (pH 10, 60°C, 30 min), in some experiments followed by TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl+NaOCl. The various oP preparations generated were examined for intercellular adherency; viscosity; pectin solubilisation; oxo and carboxy content; and surface accessibility of the cellulose to tritium-labelled cellopentaitol (a cellulose-complementary oligosaccharide). H 2 O 2 alone yielded high-viscosity, well-disaggregated oPs, with much of the pectin solubilised, and 10% of the cellulose oxidised to an alkali-soluble (anionic) ‘hemicellulose-a’. H 2 O 2 also generated ‘hemicellulose-a’ from pure cellulose (filter-paper). NaOCl alone slightly enhanced viscosity, yielding cell-aggregates with little pectin solubilisation and only 2% cellulose oxidation. With both oxidants, the order of their application had little effect on the oPs’ composition or morphology. TEMPO dramatically increased carboxy group production. SBP had low surface accessibility to tritiated cellopentaitol, and this was unaffected by the oxidants; conversely, pure cellulose had high surface accessibility which was diminished by oxidation. We propose that H 2 O 2 solubilises pectin, shearing the SBP tissue into a viscous suspension of single-cell ‘ghosts’, and renders the cellulose anionic, giving stable thixotropy by electrostatic repulsion. The similarity of twice-oxidised oPs, regardless of order of application of the oxidants, suggests that each oxidant acts independently.