Title page for ETD etd-06062011-143639


Type of Document Master's Thesis
Author Yue, Yiying
Author's Email Address yyue3@lsu.edu
URN etd-06062011-143639
Title A Comparative Study of Cellulose I and II and Fibers and Nanocrystals
Degree Master of Science (M.S.)
Department Renewable Natural Resources
Advisory Committee
Advisor Name Title
Wu, Qinglin Committee Chair
de Hoop, Cornelis Committee Member
French, Alfred D Committee Member
Negulescu, Ioan Committee Member
Keywords
  • Cellulose
  • mercerization
  • nanofiber
  • nanocrystal
Date of Defense 2011-04-20
Availability unrestricted
Abstract
The influence of sodium hydroxide treatment on the structure of cotton fibers was studied. Compared to raw cotton fibers, the entire bundles of mercerized fibers were converted into a swollen and roughened state. Fourier transform infrared spectrometry (FTIR) indicated that intermolecular hydrogen bonding was enhanced by mercerization treatment. Wide-angle X ray diffraction (WXRD) results showed decreased fiber crystallinity after mercerization. The structure of cellulose II fibers was more thermally stable than cellulose I fibers. Mechanical properties of cotton fiber-reinforced polyethylene oxide (PEO) composites demonstrated that both raw and mercerized cotton fibers enhanced their tensile strength of the PEO matrix, but both made the composites more brittle due to poor fiber dispersion in the PEO matrix.

Cotton nano crystals (CNCs) were fabricated from both raw and mercerized cotton fibers by sulfuric acid hydrolysis combined with a high-pressure homogenization technique. Stable aqueous suspensions from both raw and mercerized CNCs were formed. Transmission electron microscopy (TEM) suggested that there was no obvious change in crystal morphology from raw and mercerized cellulose. Dry mercerized crystals had a much larger bulk density than the dry raw crystals. FTIR and WXRD data showed a clear transition from cellulose I (raw) to II (mercerized) cellulose crystal structure. TGA curves showed that cellulose II CNCs had better thermal stability properties. The storage modulus of cellulose II CNC suspensions at all temperatures were obviously larger than those of cellulose I crystal suspensions at the same concentration level. Cellulose II CNC suspensions/gels were shown to be more thermally stable in response to temperature changes. Dilute cellulose II crystal suspensions formed an ordered liquid phase displaying chiral nematic orientation in the direction of the vector director at a much lower concentration level compared with cellulose I crystal suspension. Both cellulose I CNC /PEO and cellulose II CNC/PEO composites showed increased tensile strength and elongation at break compared with these of the pure PEO. However, composites with cellulose II crystals exhibited larger tensile strength, and elongation at break than those from composites with raw crystals due to the enhanced hydrogen bonding. Thus, cellulose II nano crystals provide better reinforcement materials for manufacturing advanced nano-composites.

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