Nanocellulose production by ultrasound-assisted TEMPO oxidation of Kraft pulp on laboratory and pilot scales

Production of cellulose nanofibres from native cellulose has been the subject of intensive investigation during the past decade. In the pulp and paper industry, it is generally believed that this new product will open new market and increase profitability. Cellulose nanofibres can be successfully produced using a TEMPO-Sodium bromide-Sodium hypochlorite system followed by mechanical treatment. This system can be further optimized with the use of low frequency ultrasound. However, these laboratory trials are not suitable for mass production. For this reason, trials using a full scale flow-through sonoreactor which is compatible with such an oxidation system were carried out with limited sets of experiments. The objective of this study was to compare the laboratory oxidation results at various chemicals dosages to those obtained from the full scale flowthrough sonoreactor under an optimal ultrasound condition in order to further optimize the reaction conditions. The results clearly indicated that the ultrasonic efficiency of the sonoreactor was greater than that of the laboratory ultrasonic bath in terms of carboxylate content. This benefit was rather unclear basing on the rheological curves. However, the viscosity measurements suggested that it is possible to conduct the oxidation with reduced TEMPO and NaBr (3/5) using a sonoreactor and obtain similar end product. With the chemicals dosage and ultrasonic conditions now optimized in the sonoreactor, we can now produce up to 1 kg of nanocellulose per day.