Advanced Bio-Based Nanocomposites and Manufacturing Processes

The aim of the PhD thesis concerns with the modification of cellulose nanocrystals (CNCs) via esterification or a radical grafting "from" approach to achieve polymeric nanocomposites of exceptional properties (Chapters 1 to 4). In addition to CNCs modification, other green routes have been introduced in this thesis in order to environmentally friendly polyester-based materials, i.e. Chapters five and six.;The second chapter focuses on expanding on a one-pot cellulose acid hydrolysis/Fischer esterification to produce highly compatible CNCs without any organic solvent. It consists of modifying CNCs with acetic- and lactic- acid and exploring how such surface chemistry has an effect of dispersion in the case of polylactide (PLA)-based nanocomposites. The degree of substitution for AA-CNCs and LA-CNCs, determined by FTIR, are 0.12 and 0.13, respectively. PLA-based materials represent the best bioplastics relating to its high stiffness and biodegradability, but suffer from its poor thermal performances, namely its Heat Deflection Temperature (HDT). To improve the HDT of PLA, nanocomposites have been therefore prepared with modified cellulose nanocrystals (CNCs) by melt blending. After blending at 5 wt-% loading of CNCs, LA-CNCs gives superior reinforcement below and above the glass temperature of PLA. An increase in PLA's heat deflection temperature by 10°C and 20°C is achieved by melt-blending PLA with 5 and 20 wt-% LA-CNCs, respectively.;Chapter three concerns with expanding this process to a series of hydrophilic and hydrophobic acids yielding functional CNCs for electronic and biomedical applications. Hydrophilic acids include citric-, malonic- and malic acid. Modification with the abovementioned organic acids allows for the introduction of free acids onto the surface of CNCs. Modification with citric-, malonic- and malic- acid is verified by Fourier Transform Infrared Spectroscopy and 13C solid state magic-angle spinning (MAS) NMR experiments. The degree of substation of modified CNCs is determined by quantitative direct carbon MAS NMR for malonate CNCs, malate CNCs and Citrate CNCs are found to be 0.16, 0.22 and 0.18, respectively. Re-hydrolysis experiments are performed and the yield of citrate CNCs was increased to 55% with little effect on CNC crystallinity or morphology. Citrate CNCs are then used for a myriad of applications such as polymer reinforcement (polyvinyl alcohol (PVOH) and bio-temptation of inorganic nanoparticles. Introduction of just 1% citrate CNCs results in a 40°C increase in PVOH's thermal stability (T50%). Appendant citrate groups are used for the direct reduction of silver nanoparticles without any external reducing agents. Finally citrate CNCs are used to reinforce collagen hydrogels.;Chapter four builds on "grafting from" reactions of poly(methyl methacrylate) (PMMA) onto the surface of CNCs to further increase the HDT of PLAs above 100°C. Taking advantage of the PMMA-PLLA miscibility, the presence of PMMA grafts on the CNC surface clearly improves CNC dispersion in PLLA, and reduces CNC aggregation thus enhancing the PLAs HDT. Herein "grafting from" reactions of poly(methyl methacrylate) (PMMA) on the surface of CNCs was is performed by free-radical grafting in water using two different redox initiators: Fe2+/H2O2 (Fenton's reagent) and ceric ammonium nitrate (CAN). The amount of grafted PMMA could be easily tuned according to the initiator and CAN clearly represents the most efficient initiator. From rheological data, high grafting levels favor the percolation of CNC with the development of a long-range 3D network. PLA's (HDT) higher was increased to over 130°C.;Chapter five reports blending PLA with another renewable poly(o-hydroxytetradecanoic acid) (PC14).The goal of this chapter is to enhance the poor brittleness of PLA by blending with a rubbery polymer such as PC14. Like most polymer blends, PLA and PC14 are however found to be immiscible by simple blending. To achieve this goal, a fully bio-sourced PLA based polymer blend is conceived by incorporating small quantities of poly(o-hydroxytetradecanoic acid) (PC14). PC14 is produced by polycondensation, thus we explore ring opening polymerization of poly(w-pentadecalactone) using enzymatic reactive extrusion.;The final chapter of this thesis concerns the feasibility of conducting an enzymatic ring-opening polymerization on the basis of lipase enzymes by reactive extrusion (REX) at high shear and temperature conditions. The ability of lipases to catalyze ring-opening and condensation polymerizations at relatively low temperatures (e.g. 70--90°C) is advantageous to reduce energy input and to preserve thermally sensitive chemical moieties. However, when high molecular weight polymer synthesis is desired, corresponding diffusional constraints must be overcome by either running reactions at higher temperatures (e.g. 150--220°C) or by adding solvent. Reactive extrusion (REX) has been used to overcome the aforementioned problems of bulk polymerizations that slows chain growth.;In the chapter using immobilized Candida antarctica Lipase B (CALB) as catalyst at temperatures ranging from 90 to 130°C is investigated. (Abstract shortened by UMI.).