Bacterial Cellulose For Use in: Hierarchical Composites, Macroporous Foams, Bioinorganic Nanohybrids and Bacterial-Based Nanocomposites

Abstract

The growing environmental awareness and the not so distant scarcity of fossil feedstocks are promoting nowadays a renewed interest in the use of renewable raw materials derived from biomass, i.e., cellulosic products. Recently, a relatively novel type of cellulose product namely, bacterial cellulose, biosynthesised by cellulose-producing bacteria Gluconobacter xylinus, has appeared as a promising raw material for the development of advanced renewable (nano-) materials owing to its outstanding properties such as inherent nanosize (width: 1 to 25 nm; length: 1 to 9 m), high degree of crystallinity (70% to 90%) and impressive mechanical properties (Young's modulus: 78 to 155 GPa). This thesis describes the preparation of different types of renewable (nano-) materials composed of bacterial cellulose, which includes all-cellulose hierarchical composites, macroporous cryogel microspheres, functional bioinorganic nanohybrids and entirely bacterial-based nanocomposites. Bacterial cellulose was deposited around the surface of sisal fibres by Gluconobacter xylinus, which resulted in a dense bacterial cellulose coating of the surfaces of sisal fibres. Furthermore, the bacterial cellulose coated sisal fibres obtained after surface modification of fibres enhanced the mechanical performance of all-cellulose hierarchical composites owing to an improvement of the quality of the sisal fibres-regenerated cellulose matrix interface. Bacterial cellulose manofibrils were dissolved in DMAc/LiCl cosolvent, then templated into a microsphere shape, regenerated in H2O and freeze-dried to obtain highly porous cryogel microspheres composed exclusively of regenerated bacterial cellulose, which possessed a Brunauer-Emmet-Teller (BET) surface area ranging from 55 m2/g to 123 m2/g. Thioether functionalised bacterial cellulose nanofibrils were synthesised using a "grafting from" approach during the free radical grafting polymerisation of a monomer containing thioether moieties, namely 2-(methylthio)ethyl methacrylate. The thioether moieties grafted from the bacterial cellulose (MTEMA-g-BC) nanofibrils subsequently enabled the preparation of optically functional bioinorganic nanohybrids, where either gold nanoparticles or cadmium telluride quantum dots were chemisorbed onto the thioether moieties functionalised bacterial cellulose nanofibrils. Hydrophobised bacterial cellulose nanofibrils were also synthesised using the same "grafting from" approach using free radical grafting polymerisation of a hydrophobic caprolactone-based macromonomer, caprolactone 2- (methacryloyloxy)ethyl ester. Then, entirely bacterial-based nanocomposites composed of caprolactone grafted bacterial cellulose (PCLMA-g-BC) nanofibrils reinforced poly(3- hydroxy- butyrate) (PHB) matrix were produced by solution casting. The tensile strength and Young's modulus of bacterial-based nanocomposites reinforced with PCLMA- g-BC nanofibrils (i.e., nanofiller content of 10 wt./wt.%) increased by 101% and 170%, respectively, as compared to the neat PHB lm. The findings reported in this thesis highlight the potential and versatility of bacterial cellulose to produce novel and innovative types of renewable advanced (nano-) materials and composites.