Eric Loranger

The Use of Weissler Method for Scale-Up a Kraft Pulp Oxidation by TEMPO-Mediated System from a Batch Mode to a Continuous Flow-Through Sonoreactor

The efficiency of cellulose oxidation mediated by the 4-acetamido-TEMPO radical under ultrasonic cavitation was investigated using two ultrasonic systems: a batch lab scale ultrasonic bath with a glass reactor and a semi-continuous flow-through sonoreactor. The main objective was to explore the possibility of scaling up the production of oxidized cellulose under ultrasound, from a lab scale process to a pilot plant process, which served as a precursor for producing nanofibrils cellulose. It was found that under acoustic cavitation, the efficiency of TEMPO-mediation oxidation of native cellulose was significantly improved, particularly in the flow-through sonoreactor. In comparison with the glass reactor, the flow-through sonoreactor reduce the applied energy by 88% while increasing 7.8 times the production rate of radicals. These results enable a possibility of producing oxidized fibers for industrial applications.

Mechanical and antibacterial properties of a nanocellulose-polypyrrole multilayer composite.

In this study, a composite film based on TEMPO-oxidized cellulose nanofibers (TOCN), polyvinyl alcohol (PVA) and polypyrrole (PPy) was synthesized in situ by a chemical polymerization, resulting in the induced absorption of PPy on the surface of the TOCN. The composite films were investigated with scanning electron microscopy, thermogravimetric analysis, contact angle measurements, mechanical tests, and evaluation of antibacterial properties. The developed composite has nearly identical Young modulus (3.4GPa), elongation (2.6%) and tensile stress (about 51MPa) to TOCN even if PPy, which as poor properties by itself, was incorporated. From the energy-dispersive X-ray spectroscopy (EDX) results, it was shown that PPy is mainly located on the composite surface. Results confirmed by an increase from 54.5 to 83° in contact angle, an increased heat protection (Thermogravimetric analysis) and a decrease in surface energy. The nanocomposites were also evaluated for antibacterial activity against bacteria occasionally found in food: Gram-positive Bacillus subtilis (B. subtilis) and Gram-negative bacteria Escherichia coli (E. coli). The results indicate that the nanocomposites are effective against all of the bacteria studied as shown by the decrease of 5.2logcolonyformingunits (CFU) for B. subtilis and 6.5logCFU for E. coli. Resulting in the total destruction of the studied bacteria. The perfect match between the resulting inhibition zone and the composite surface area has demonstrated that our composite was contact active with a slight leaching of PPy. Our composite was successful as an active packaging on meat (liver) as bacteria were killed by contact, thereby preventing the spread of possible diseases. While it has not been tested on bacteria found in medicine, TOCN/PVA-PPy film may be able to act as an active sterile packaging for surgical instruments.

Influence of High Shear Dispersion on the Production of Cellulose Nanofibers by Ultrasound-Assisted TEMPO-Oxidation of Kraft Pulp

Cellulose nanofibers can be produced using a combination of TEMPO, sodium bromide (NaBr) and sodium hypochlorite, and mechanical dispersion. Recently, this process has been the subject of intensive investigation. However, studies on the aspects of mechanical treatment of this process remain marginal. The main objective of this study is to evaluate the high shear dispersion parameters (e.g., consistency, stator-rotor gap, recirculation rate and pH) and determine their influences on nanocellulose production using ultrasound-assisted TEMPO-oxidation of Kraft pulp. All nanofiber gels produced in this study exhibited rheological behaviors known as shear thinning. From all the dispersion parameters, the following conditions were identified as optimal: 0.042 mm stator-rotor gap, 200 mL/min recycle rate, dispersion pH of 7 and a feed consistency of 2%. High quality cellulose gel could be produced under these conditions. This finding is surely of great interest for the pulp and paper industry.

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.

Impact of transducers configuration in a pilot sonoreactor used for nanocellulose production by ultrasound-assisted TEMPO oxidation

For the pulp and paper industry, it is generally believed that nanocellulose will open new market and increase mills profitability. Our research group as shown that the TEMPO - Sodium bromide - Sodium hypochlorite oxidation system, used in nanocellulose production, can be further optimized with the use of low frequency ultrasound. Therefore, a pilot scale flow-through sonoreactor (sonoreactor 1) compatible with such oxidation was developed and many publications were issued. In effort to further optimize the system; a new sonoreactor (sonoreactor 2) with variable transducer configuration was fabricated. The objective of this work is to study the sonochemical efficiency of the new transducer configuration and the impact on the oxidation efficiency. From the Weissler method (potassium iodine oxidation) experiments, free radicals production was found to be dependent on the transducers configuration. For a given frequency and power, the production rate is respectively greater for the star pattern, orthogonal and face to face configuration. However, the increased free radical production was found to have a more subtle effect on the oxidation efficiency, thus carboxylate content of the pulp.

Investigation on using two types of sonoreactors for Kraft lignin fractionation

For a decreasing conventional pulp and paper industry, new products from wood are needed. As lignin is the second most abundant polymer on earth (cellulose is the first), many studies are oriented toward her utilisation. Lignin is rich in many carbon based polymer, phenolic groups, alcohol groups but the highly 3 dimensional structure prohibit easy usage of this material. Ultrasonic modifications were tried by a few researchers but success and horror stories were reported. The objective of this work is to study the potential in ultrasound fractionation on Kraft lignin in two high power flow-through sonoreactor. From our work, we can conclude that lignin modification is indeed possible with ultrasound but will be dependant of the system. Indeed, successful conditions were found for the small sonoreactor while the same condition tried in the semi-pilot sonoreactor was unsuccessful. This duality of results, as found in the literature, is indicating that ultrasonic modification of lignin is not evident but that the process, under specific conditions, could be successful.

Effect of ultrasonic pre-treatment of thermomechanical pulp on hydrogen peroxide bleaching

Ultrasound pre-treatments of softwood TMP had been carried to evaluate its impact on the efficiency of hydrogen peroxide bleaching. The trials were performed after a factorial design of experiment using frequency, power and time as variables. The experiments were conducted in an ultrasonic bath and then bleached with hydrogen peroxide. Measurements such as brightness, L*A*B* color system coordinate, residual hydrogen peroxide and metal content were evaluated on bleached pulp. The results indicate that the effect of ultrasonic treatment on brightness was dependent on the ultrasound frequency used; the brightness increased slightly at 68 kHz and decreased at 40 and 170 kHz. These results were correlated to the ultrasound effect on the generation of transition metals (copper, iron and manganese) which are responsible for catalytic decomposition of hydrogen peroxide. The influence of metal interference was minimized by using a chelating agent such as diethylene triamine pentaacetic acid (DTPA). With the results obtained in this study we have identified a set of option conditions, e.g. 1000 W, 40 kHz, 1.5 % consistency and 0.2% addition of DTPA prior to the bleaching stage (after ultrasonic pre-treatment) who improve brightness by 2.5 %ISO.