Please consider attending the following: MATERIALS ENGINEERING SEMINAR "Effect of Nanocellulose Reinforcement on the Properties of Polymer Composites" By Shikha Shrestha Purdue MSE Ph.D. Final Exam Advisor: Professor Jeffrey P. Youngblood ABSTRACT Polymer nanocomposites are envisioned for use in many advanced applications, such as structural industries, aerospace, automotive and electronic materials, due to the improved properties like mechanical strengthening, thermal and chemical stability, easy bulk processing, and/or light-weight instigated by the filler-matrix combination compared to the neat matrix. In recent years, due to increasing environmental concerns, many industries are inclining towards developing sustainable and renewable polymer nanocomposites. Cellulose nanomaterials (CNs), including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), have gained popularity due to their excellent mechanical properties and eco-friendliness (extracted from trees, algae, plants etc.). However, to develop CN-reinforced nanocomposites it is necessary to understand impact of hygroscopic swelling, aspect ratio, and content of CNs on the overall performance of nanocomposites; and overcome the low dispersibility of CNs and improve their compatibility with hydrophobic matrix. In this work, we attempt to understand the influence of single nanocrystals in the hygroscopic response exhibited by nanostructured films; effect of CNCs on the properties of CNC-reinforced fibers; and hydrophobized CNFs using a facile, aqueous surface modification to improve interfacial compatibility with epoxy. To evaluate the effect of CNC alignment in the bulk response to hygroscopic expansion, self-organized and shear-oriented CNC films were prepared under two different mechanisms. The coefficient of hygroscopic swelling (CHS) of these films was determined by using a contact-free method of Contrast Enhanced Microscopy Digital Image Correlation (CEMDIC) that enabled the characterization of dimensional changes induced by hygroscopic swelling of the films. By calculating the CHS values of CNC, it was determined that hygroscopic swelling is highly dependent on the alignment of nanocrystals within the films, with aligned CNC films showing dramatically reduced hygroscopic expansion than randomly oriented films. Next, to study the effects of different aspect ratios of CNCs on intrinsic properties of polyvinyl alcohol (PVA) fibers, CNCs extracted from wood and cotton were reinforced into PVA to produce fibers by dry-jet-wet spinning. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5 - 15 wt. %) at the expense of their strain-to-failure. The mechanical properties of fibers with cotton CNC were higher than the fibers with wood CNC when the same amount of CNCs were added due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, to improve the dispersibility and compatibility of CNFs with epoxy, CNFs were modified by a water-based method where tannic acid (TA) acts as a primer with CNF and reacts with hexadecylamine (HDA). The modified (-m) and unmodified (-um) CNFs were filled into hydrophobic epoxy resin. Better dispersion and stronger adhesion between fillers and epoxy were obtained for m-CNF than the um-CNF, resulting in better mechanical properties of nanocomposites at the same loading. Thermal stability and the degradation temperature of m-CNF/epoxy improved when compared to neat epoxy. Date: Friday, April 12, 2019 Time: 2:00 P.M. Place: ARMS 1028