Identifier

etd-10232013-142737

Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

Regenerated cellulose nanoparticles (RCNs) including both elongated fiber and spherical structures were prepared from microcrystalline cellulose (MCC) and cotton using 1-butyl-3-methylimidazolium chloride followed by high-pressure homogenization. The RCN has a two-step pyrolysis, different from raw MCC and cotton that had a one-step process. The crystalline structure of RCNs was cellulose II in contrast to the cellulose I form of the starting materials. Also, the RCNs have decreased crystallinity and crystallite size. The elongated RCNs produced from cotton and MCC had average lengths of 123 ± 34 and 112 ± 42 nm, and mean widths of 12 ± 5 and 12 ± 3 nm, respectively. The average diameter of spherical RCNs from MCC was 118 ± 32 nm. Cellulose nanocrystals and cellulose nanofibers with I and II crystalline allomorphs (designated as CNC I, CNC II, CNF I, and CNF II) were isolated from bleached wood fibers by alkaline pretreatment and acid hydrolysis. The effects of concentration, particle size, surface charge, and crystal structure on the lyophilization-induced self-assembly of cellulose particles in aqueous suspensions were studied. Within the concentration range of 0.5 to 1.0 wt %, cellulose particles self-organized into lamellar structured foam composed of aligned membrane layers with widths between 0.5 and 3 ì m. At 0.05 wt %, CNC I, CNF I, CNC II, and CNF II self-assembled into oriented ultrafine fibers with mean diameters of 0.57, 1.02, 1.50, and 1.00 ì m, respectively. Cellulose nanoparticle (CNP) reinforced Polyvinyl alcohol-borax (PB) hydrogels were prepared through a facile approach in an aqueous medium. The obtained stiff, high-water-capacity (~96%), low-density (~1.1g/cm3), translucence hydrogels exhibited birefringence textures. These free-standing, high elasticity and mouldable hydrogels also exhibited self-recovery under continuous step strain and thermo-reversibility under temperature sweep. The rheological tests and compression measurements confirmed the incorporation of well-dispersed CNPs to PB system significantly enhanced the compressive strength, viscoelasticity and stiffness of the hydrogels. Highly-crystalline CNPs not only tangled with PVA chains though numerous hydrogen bonds, but formed chemically crosslinked complexes with borax ions as well, thus acting as multifunctional crosslinking agents and nanofillers to physically and chemically bridge the 3D network hydrogels.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Wu, Qinglin

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