Khalil Jradi

Grafting of Polycaprolactone on Oxidized Nanocelluloses by Click Chemistry

The main objective of this work is the grafting of polycaprolactone diol (PCL) on the surface of oxidized nanocelluloses (ONC) in order to enhance the compatibility between the hydrophilic cellulose nanofibres and the hydrophobic polymer matrix. This grafting was successfully realized with a new strategy known as click chemistry. In this context, the oxidized nanocelluloses bearing alkyl groups (ONC-PR) were prepared by reacting amino groups of propargylamine (PR) with carboxyl groups of ONC. In parallel, PCL was converted into azido-polycaprolactone (PCL-N3) in two steps: (i) tosylation of polycaprolactone (PCL-OTs) and (ii) conversion of PCL-OTs into PCL-N3 by nucleophilic displacement using sodium azide. Finally, ONC-PR was reacted with PCL-N3 in heterogeneous conditions through click chemistry in order to prepare polycaprolactone grafted oxidized nanocellulose (ONC-g-PCL), which could be suitable for improving the interfacial adhesion in the composite materials. The grafted samples were characterized by transmission electron microscopy and by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR) spectroscopic techniques.

Study of the Effect of Grafting Method on Surface Polarity of Tempo-Oxidized Nanocellulose Using Polycaprolactone as the Modifying Compound: Esterification versus Click-Chemistry

Esterification and click-chemistry were evaluated as surface modification treatments for TEMPO-oxidized nanocelluloses (TONC) using Polycaprolactone-diol (PCL) as modifying compound in order to improve the dispersion of nanofibers in organic media. These two grafting strategies were analyzed and compared. The first consists of grafting directly the PCL onto TONC, and was carried out by esterification between hydroxyl groups of PCL and carboxyl groups of TONC. The second strategy known as click-chemistry is based on the 1,3-dipolar cycloaddition reaction between azides and alkyne terminated moieties to form the triazole ring between PCL and TONC. The grafted samples were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Thermogravimetry analysis (TGA). Further, the effects of the two treatments on the surface hydrophobization of TONC were investigated by contact angle measurements. The results show that both methods confirm the success of such a modification and the click reaction was significantly more effective than esterification.

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.