<p>Cellulose
nanocrystals (CNCs) and its composite coatings may impart many benefits in
packaging, electronic, optical, etc. applications; however, large-scale coating
production is a major engineering challenge. To fill this knowledge gap, a
potential large-scale manufacturing technique, roll-to-roll reverse gravure
processing, has been described in this work for the manufacture of CNC and
CNC-poly(vinyl alcohol) (PVA) coatings on a flexible polymer substrate. Various
processing parameters which control the coating structure and properties were
examined. The most important parameters in controlling liquid transfers were
gravure roll, gravure speed, substrate speed, and ink viscosity. After successful fabrication, coating
adhesion was investigated with a crosshatch adhesion test. The surface
roughness and morphology of the coating samples were characterized by atomic
force microscopy and optical profilometer. The Hermans order parameter (S) and
coating transparency were measured by UV–Vis spectroscopy. The effect of
viscosity on CNC alignment was explained by the variation of shear rate, which
was controlled by the micro-gravure rotation. Finally, the CNC alignment effect
was investigated for gas barrier and thermal management applications.</p>
<p>In
packaging applications, cellulose nanomaterials may impart enhanced gas barrier
performance due to their high crystallinity and polarity. In this work, low to
superior gas barrier pristine nanocellulose films were produced using a
shear-coating technique to obtain a range of anisotropic films. Induction of
anisotropy in a nanocellulose film can control the overall free volume of the
system which effectively controls the gas diffusion path and hence, controlled
anisotropy results in tunable barrier properties. The highest anisotropy
materials showed a maximum of 900-fold oxygen barrier improvement compared to
the isotropic arrangement of nanocellulose film. The Bharadwaj model of nanocomposite
permeability was modified for pure nanoparticles, and the CNC data were fitted
with good agreement. Overall, the oxygen barrier performance of anisotropic
nanocellulose films was 97 and 27 times better than traditional barrier
materials such as biaxially oriented poly(ethylene terephthalate) (BoPET) and
ethylene vinyl alcohol copolymer (EVOH), respectively, and thus could be
utilized for oxygen-sensitive packaging applications. </p>
The
in-plane thermal conductivity of CNC -
PVA composite films containing different PVA molecular weights, CNC loadings
and varying order parameters (S) were investigated for potential application in
thermal management of flexible electronics. Isotropic CNC - PVA bulk films with
10-50 wt% PVA solid loading showed significant improvement in thermal
conductivity compared to either one component system (PVA or CNC). Furthermore,
anisotropic composite films exhibited in-plane thermal conductivity as high as
~ 3.45 W m-1 K-1 in the chain direction, which is higher than most polymeric
materials used as substrates for flexible electronics. Such an improvement can
be attributed to the inclusion of PVA as well as to a high degree of CNC
orientation. The theoretical model was used to study the effect of CNC
arrangement (both isotropic and anisotropic configurations) and interfacial
thermal resistance on the in-plane thermal conductivity of the CNC-PVA
composite films. To demonstrate an application for flexible electronics,
thermal images of a concentrated heat source on both neat PVA and CNC-PVA
composite films were taken that showed the temperature of the resulting hot
spot was lower for the composite films at the same power dissipation.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8028773 |
| Date | 10 June 2019 |
| Creators | Reaz Chowdhury (6623510) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/ROLL-TO-ROLL_FABRICATION_OF_CELLULOSE_NANOCRYSTAL_NANOCOMPOSITE_FOR_GAS_BARRIER_AND_THERMAL_MANAGEMENT_APPLICATIONS/8028773 |
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