Processing and structural characterization toward all-cellulose nanocomposites

Abstract

Cellulose is the most abundant biopolymer on the planet and is used in a variety of industry sectors including paper, coatings, medicine, and food. A deep understanding of cellulose is important for its development as an alternative polymer to those based on petroleum. This work focuses on two cellulose systems. The first of these, cellulose nanofibers, are the basic structural elements of naturally-occurring cellulosic materials; they exhibit excellent mechanical characteristics due to high crystallinity and a dense network of hydrogen bonding. These fibers can be separated from bulk cellulose via a TEMPO oxidation reaction followed by mechanical homogenization into a suspension in water. In this work, the production of these fibers is investigated by monitoring the change in structure of cellulose as a function of TEMPO reaction time and mechanical homogenization using small angle neutron scattering, atomic force microscopy, and optical microscopy. The second cellulose system is a molecular solution of cellulose formed using a binary solvent mixture consisting of ionic liquid and an aprotic solvent. Cellulose is difficult dissolve due to a dense hydrogen bonding network, and ionic liquids have been shown to be an effective alternative to more hazardous and energy-intensive dissolution methods for cellulose currently used in industry. The phase behavior of these solutions has been investigated using small angle neutron scattering as a function of temperature. The process of regenerating cellulose from these solutions is also investigated, as dense gels of cellulose and ionic liquid were produced with a unique multiscale ordered structure. The ultimate goal of this work is to combine cellulose nanofibers and molecular cellulose solutions in order to create all-cellulose nanocomposite films. These films are characterized using tensile testing, atomic force microscopy, and water uptake measurements in order to understand the interaction between cellulose nanofibers and molecular cellulose solutions, water resistance and tunability of mechanical properties.