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Title: Nanocellulose as building block for novel materials
Author: Lee, Koon-Yang
ISNI:       0000 0004 2715 1327
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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This thesis describes the fabrication of novel green materials using nanocellulose as the building block. Bacterial cellulose (BC) was used as the nanocellulose predominantly in this work. BC is highly crystalline pure cellulose with an inherent fibre diameter in the nano-scale. A single BC nanofibre was found to possess a Young’s modulus of 114 GPa. All these properties are highly favourable for using BC as a nanofiller/reinforcement in green nanocomposite materials. In this work, the surface of BC was rendered hydrophobic by grafting organic acids with various aliphatic chain lengths. These surface-modified BC was used as nanofiller for poly(L-lactide) (PLLA). Direct wetting measurements showed that the BC nanofibre-PLLA interface was improved due to the hydrophobisation of BC with organic acids. This led to the production of BC reinforced PLLA nanocomposites with improved tensile properties. Nanocellulose can also be obtained by grinding of wood pulp, producing nanofibrillated cellulose (NFC). The surface and bulk properties of one type of NFC and BC were compared in this work. Furthermore, the reinforcing ability of NFC and BC was also studied and it was observed that there is no significant difference in the mechanical performance of NFC or BC reinforced nanocomposites. A novel method based on slurry dipping to coat sisal fibres with BC was developed to modify the surface of natural fibres. This method can produce either (i) a densely BC coating layer or (ii) “hairy” BC coated sisal fibres. Randomly oriented short BC coated sisal fibre reinforced hierarchical composites were manufactured. It was found that hierarchical (nano)composites containing BC coated sisal fibres and BC dispersed in the matrix were required to produce composites with improved mechanical properties. This slurry dipping method was also extended to produce robust short sisal fibre preforms. By infusing this preform with a bio-based thermosetting resin followed by curing, green composites with significantly improved mechanical properties were produced. BC was also used as stabiliser and nano-filler for the production of macroporous polymers made by frothing of acrylated epoxidised soybean oil followed by microwave curing.
Supervisor: Bismarck, Alexander ; Mantalaris, Sakis Sponsor: Engineering and Physical Science Research Council (EPSRC) ; Deputy Rector's Award of Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral