Date

6-2015

Degree Name

BS in Materials Engineering

Department

Materials Engineering Department

Advisor(s)

Trevor Harding

Abstract

Atom level computer simulations of the arabinan and cellulose interface were performed to better understand the mechanisms that give arabinan-cellulose composites (ArCCs) their strength with the goal to improve man-made ArCCs. The molecular dynamics (MD) software LAMMPS was used in conjunction with the ReaxFF/c force field to model the bond between cellulose and arabinan. A cellulose nanocrystal with dimensions 51 x 32 x 8 Å was minimized with various weight percent of water, 0%, 3%, 5%, 8%, 10%, and 12%. After the system was equilibrated for at least 100,000 femtoseconds, an arabinan molecule composed of 8 arabinose rings was added close to the cellulose's surface and equilibrated until fully adsorbed. A straightening force was applied to the arabinan during adsorption so the arabinan would lay flat on the {200} plane of the cellulose. A simulated AFM pull was performed to measure the force needed to desorb the arabinan from the cellulose. Due to computational resource limits, the pull speed was much faster than physical experiments, 500 m/s and 50 m/s. In general, the force needed for desorption increased with increasing water content with the force plateauing at 8wt% water. This increase in strength is probably due to water forming bridging hydrogen bonds between the relatively flat cellulose and crimped arabinan. Without water, fewer hydrogen bonds would form between cellulose and arabinan. This is an effect that will probably only be seen at high strain rates. Pull speeds of slower than 0.5 m/s must be performed to get accurate results.