Doctoral Dissertations

Date of Award

12-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Natural Resources

Major Professor

Siqun Wang, Timothy G. Rials

Committee Members

David P. Harper, Kevin M. Kit

Abstract

A novel process using high-intensity ultrasonication (HIUS) was developed to isolate fibrils from cellulose fibers. The geometrical characteristics of the fibrils were investigated using polarized light microscopy (PLM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results show that small fibrils with diameter ranging from about thirty nanometers to several micrometers were peeled from the fibers. The degree of fibrillation of the fibers was significantly increased. The crystallinities or molecular structures of most of the cellulose materials were changed by HIUS treatment.

To evaluate the fibrils degradation by HIUS, a method using AFM was modified and developed to measure the elastic modulus of single cellulose fibrils. The results indicated that it was necessary to consider the penetration of AFM tips to the cellulose fibril surfaces. In the diameter range of 150 to 300 nm, the elastic moduli of Lyocell fibrils did not have significant differences between the HIUS treatment time of 30 min and 60 min. The modulus of Lyocell fibrils with diameters from 150 to 180 nm was evaluated about 98 GPa and it decreased dramatically when the diameter was more than 180 nm. The elastic moduli of cellulose fibrils were not significantly different between isolation methods of HIUS and high-pressure homogenizer for pure cellulose fiber, between different cellulose sources of pulp fibers treated by homogenizer. The elastic modulus of fibrils from regenerated cellulose fibers was higher than that of natural fibers.

The treated fiber and separated fibrils were used to reinforce poly(vinyl alcohol), poly(lactic acid), and polypropylene by film casting or compression molding. Both of the tensile modulus and strength of nano-biocomposites reinforced with treated fiber and separated fibrils were higher than those of the untreated fiber reinforced composites. The morphological characteristics of the nanocomposites were investigated with SEM, AFM, and PLM. The dispersion of fibrils was not perfect, and the adhesions between the polymer and fibrils were not good without further modification of the fibrils. The fibrils on the fibers and isolated from the fibers may be the role that the tensile modulus and strength of the treated fiber and separated fibril reinforced composites were higher than those of the untreated fiber.

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