The Use of Polyvinylamine-supported TEMPO Oxidation in Wet-strengthening of Paper

Abstract

<p>Paper wet-strength is very important in many situations. Traditional wet strengthening agents such as formaldehyde-based resins and polyamide- epichlorohydrin (PAE) resins have been criticized to be a source of organochlorine compounds (l). This research aims at developing an efficient and environmental- friendly method to improve paper wet-strength. The new method combines the utilization of cellulose oxidation catalyzed by 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) and the application of a new commercialized polymer, polyvinylamine (PYAm).</p> <p>The TEMPO oxidation is known to introduce aldehyde and carboxyl groups on cellulose. In this research, an immobilized catalyst, polyvinylamine grafted TEMPO was synthesized and used for cellulose oxidation. The oxidation followed Anelli protocol, i.e. using NaCIO/NaBr as the primary oxidant. By using PVAm-TEMPO, we expect two advantages: a) upon adsorption onto fiber surfaces, PVAm-TEMPO could catalyze the oxidization locally and neighboring amines could then bond to the freshly formed aldehydes to impart strength. b) The oxidation catalyzed by immobilized TEMPO would be restricted to the exterior fiber surfaces because of the large size of PVAm-TEMPO. This will avoid the damage of fiber interior structures which is usually associated with free TEMPO oxidation and thus retain the fiber strength.</p> <p>Wet cellulose-to-cellulose adhesion was evaluated by measuring the force required to separate two wet cellulose films laminated with PVAm. Cellulose wet-strength could be improved from almost 0 to 40 N/m if oxidation and PYAm addition were combined in a proper way. Three methods were developed to do this, namely: direct coating method, adsorption method and one step method.</p> <p>Treatment conditions such as the optimum dosage of sodium bromide during oxidation and the best pressing temperature after PVAm application were investigated.</p> <p>The catalytic activity of PVAm-TEMPO was demonstrated by the oxidation of methylglyoxal (a water-soluble aldehyde) in a membrane catalyst reactor. The supported TEMPO showed high reaction activity.</p>