Oxidative modification of cellulosic substrates

Oxidized polysaccharides derived from starch or cellulose find manifold applications as gelling agents, binders, complexing agents or superabsorbing media. Introduction of oxidized functions such as aldehyde, keto or carboxyl groups lead to significant changes in the hydrolytic stability of the polymers as well induce loss of brightness and fibre strength, but may also be exploited for fibre surface modification. A fluorescence label with high affinity towards these oxidized structures was developed employing selectively oxidized model saccharides as well as oxidized industrial and laboratory pulps. The high sensitivity of the fluorescence label made it possible to detect very low concentrations of oxidized functionalities and, for the first time, a profile of carbonyl groups relative to the molecular weight of native and oxidized pulps was established. The new method was validated for the analytical characterization of dissolving and low Mw paper pulps. Various oxidation procedures (Swern oxidation of cellulose 2.5 acetates, TEMPO-oxidation and higher oxidative systems) were shown to lack pronounced selectivity for the introduction of oxidized functions even under optimized conditions. NMMO, which is used as a solvent in industrial fibre production, rapidly produced chromophores upon reaction with carbonyl groups. Polyglucuronic acids were generated with TEMPO as oxidant, which may be of interest for the application as absorbers or as wound dressing materials.