The use of cellulose nanofibres to reduce the wet strength polymer quantity for development of cleaner filters

Abstract

Polyamideamine-epichlorohydrin resin (PAE) is one of the most commonly used wet strength agents in the papermaking industry. However, adsorbable organic halogens (AOX) are known to be a toxic side product of the PAE manufacturing process; therefore, the use of PAE is restricted by regulation for food and medical applications. In this study, we investigated partially replacing the indirect food additive, PAE, with a renewable, biodegradable material, cellulose nanofibres (CNF), in order to drastically reduce the amount of PAE used while maintaining the same wet tensile strength. The concept is to replace covalent bonds by hydrogen bonds and to drastically increase bonding area. Depth-type filters were prepared with cellulose (30%), perlite (70%) and lesser amounts of PAE via papermaking technique. A small fraction of cellulose fibre composition was substituted with CNF while the PAE amount was gradually decreased. The substitution of positively charged PAE for negatively charged cellulose nanofibres switched the overall charge of the system from cationic to anionic. Therefore, two cationic polyelectrolytes, CPAM or PEI, were investigated to control the overall charge and adsorption performance of the filter system.The substitution of CNF enabled PAE dosage to be reduced by over 95% while retaining the wet strength properties of the filters. The wet strength obtained from the small quantity of wet strength polymer could be further improved by increasing the curing temperature to 150 °C with a much shorter curing period. The filters with reduced PAE dosage have also improved adsorption of positively charged contaminants. However, for negatively charged contaminants a very minor amount (around 20 mg/g) of cationic polymer addition would be required to maintain the performance. Our study shows that partial replacement of conventional papermaking fibres with cellulose nanofibres allows us to reduce the quantity of wet strength polymer remarkably and achieve a sustainable and environmentally-friendly concept for filter manufacturing or for any paper product requiring wet strength.