UC Davis

Nanocelluloses, the crystalline domains isolated from native cellulose, have gained increasing attention due to their uniquely ultra-high elastic modulus, low axial thermal expansion coefficient, and biocompatibility. All nanocelluloses in the market are hydrophilic and incompatible with most organic liquids and most synthesized polymers, limiting their applications which stated in the 1st chapter. In the 2nd chapter one-pot synthesis of 2-bromopropionyl esterified cellulose nanofibrils (Br-CNFs) coupled with in-situ disintegration by ultrasonication was developed and streamlined in processing and/or matrix media. This coupled functionalization and ultrasonication approach has been optimized to prepare Br-CNFs with tunable levels of esterification in high yields and imaged by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The structures of Br-CNFs were further characterized by Fourier-transform infrared (FTIR) and liquid phase proton nuclear magnetic resonance (1H NMR) spectroscopy. Thermal properties and crystallinity of Br-CNFs were characterized by thermogravimetric analysis (TGA) and X-ray diffraction (XRD), respectively. In the 3rd chapter, the organic compatibility and reactivity of these Br-CNFs have been demonstrated in their polyol role in replacing soft segment or as chain extender in synthesizing polyurethanes with significantly improved modulus (3x), strength (4x), and strain (1.5x) at merely 0.3 w% as polyol or 1.8 w% as extender. The Br bearing esters of these high specific surface Br-CNFs make them excellent macroinitiators for atom transfer radical polymerization (ATRP) of defined lengths of surface polymer grafts on crystalline cellulose, all described in 4th chapter. Br-CNF-g-PLMA from ATRP surface grafting of polylauryl methacrylate (PLMA) have shown to exhibit combined shear thinning behavior of Br-CNF proved by flow behavior index n< 1 and drag reducing effects of PLMA with up to 21071x increased viscosity. Moreover, in the 5th chapter Br-CNFs have shown to be effective hydrophobic coatings on non-porous carbon and cellulose fabrics to respective water contact angles up to 105° and 88° as well as moderately improved the fabric’s modulus (1.4x) and strength (1.2x). The multiple functionalities of these one-pot synthesized Br-CNFs have shown to be excellent surface modifiers (thin films, coatings), reactants or precursors for polyurethanes (polyols, crosslinkers), and ATRP macroinitiators for polymer sheath-nanocellulose core viscosity modifiers and drag reducers for diverse applications.