| Popis: |
The manipulation, assembly, and control of matter at the nanometer scale enable the fabrication of nanomaterials that could revolutionize the industry and impact our society. Various bacterial species such as K. xylinus or K. rhaeticus already manufacture nanocellulose directly at the nanometric scale. The resulting cellulose, called bacterial nanocellulose (BNC), is secreted in its purest form, with high crystallinity (up to 90%) and a high degree of polymerization. This bottomup approach to production comes with many advantages over traditional wood-based nanocellulose. In addition to growing without lignin, hemicellulose, or pectin, which eliminates the extraction step, BNC also does not need any mechanical separation or hydrolysis processes to become nano. Moreover, the formation of cellulosic microfibrils occurring during biosynthesis is influenced by many factors such as culture medium, temperature, pH, agitation, and oxygen level, which can be modified according to the desired properties. Today, there are some challenges that slow down the entry of this material into the industrial scene. The first is the optimization of production yield and cost of the raw materials used for cultivation. The second is its hard processability such as the dissolution process, which limits its scope of applications. In this study, three experimental parts have been conducted to measure the issues holding back BNC from developing on an industrial scale. The first part focuses on the parameters influencing the productivity and the quality of the BNC. Each parameter is analyzed by calculating the production yield and the water loss of the bacterial nanocellulose. The highest production yield of 12.85 g/L was obtained over a period of 20 days in a 0.5% w/v green tea and 10% w/v sucrosebased culture media. However, coffee showed impressive results with a yield of 7.08 g/L over a culture of 7 days. 32°C was found to be the optimal growing temperature. A pH set at 2.9 gave a higher yield than at pH 3.2. Fructose gave the highest production yield of all carbon sources. More results are discussed in depth in the conclusion of Chapter 1. The second part evaluates which is the best method of purification in order to preserve the unique characteristics of BNC. Morphological analysis is conducted using scanning electron microscopy (SEM), and the mechanical properties of the bacterial nanocellulose are tested via tensile strength. Other tests such as contact angle, water absorption, and bending test are evaluated. The optimal treatment was attributed to the two-step purification treatment using a low concentration of 2.5% w/v NaOH and 2.5% w/v NaOCl for 1h/1h immersion time at room temperature. The last part is dedicated to the study of dissolution mechanisms between BNCs and AmimCl ionic liquids. Attempts at regeneration by electrospinning are discussed. Finally, the performances of a series of BNC nanopapers are compared to standard cellulosic papers. Nanopapers were demonstrated to outperform the mechanical properties of standard papers |
