<p>In recent
decades there has been great interest to produce novel bio-based composites to
reduce carbon footprint without sacrificing the necessities that society
demands. To achieve a more sustainable future, research in cellulose
biopolymers has risen to the forefront. Impressive mechanical, thermal and
optical properties along with its abundant biomass has made nanocellulose (NC)
the subject of intense research in the area of electronics, drug delivery,
sensors, selective filters, and structural materials, to name a few. The
practical utility of any cellulose-based materials requires a more complete understanding
of how the fundamental structure affects final performance. This thesis
examines several avenues to obtain novel materials by considering processing
parameters and preparation methods for working with raw nanocellulose
materials, and mechanochemical approaches for surface grafting to obtain
modified CNs with improved dispersion in organic media. Lastly, the synergy
between the two studies and its impact on advanced materials and nanocomposites
is discussed.</p>
<p>The low cost and
wide availability of cellulose nanofibers (CNF), a refined form of cellulose
microfibrils, make these an ideal starting material for our studies. However,
the aggregated states of freeze-dried CNFs hinder its use as an additive for
reinforcing polymer blends or functional films. The use of <i>tert</i>-butyl alcohol (TBA) as a stabilizer in pharmaceutical drugs
has been well studied for its effectiveness in facilitating redissolution and
extending product shelf life. Lyophilization of aqueous CNF slurries treated
with various amounts of TBA produced a more porous material that could be
redispersed with superior colloidal stability relative to untreated
freeze-dried CNFs. Furthermore, CNFs lyophilized from aqueous TBA mixtures
could be subjected to mild mechanochemical reactions (horizontal ball milling)
to produce esterified nanofibers with high degrees of substitution (DS) and
good dispersibility profiles in organic solvents. This solventless technique
allowed for a variety of carboxylic acids to be grafted onto CNF surfaces.
Finally, investigations of new materials with technological utility have been
explored using networks of CNFs modified with oleic acid. These can be cast
into superhydrophobic (SHP) films having a hierarchical structure
characteristic of a self-similar material, with a wettability comparable to
that of the lotus leaf. The SHP surface can also be regenerated after surface
fouling or physical damage. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8938295 |
| Date | 15 August 2019 |
| Creators | Miran Mavlan (6983801) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Engineering_Cellulose_Nanofibers_For_Better_Performance_as_Nanocomposites/8938295 |
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