Hydrophobic Modifications of Cellulose Nanocrystals for Anticorrosion and Polymer Coating Applications
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Date
2020-04-20
Authors
Ly, Malin
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Cellulose nanocrystal (CNC) is a robust, renewable and green nanorods, which has a
potential as an excellent reinforcing and multi-functional filler for polymers used in coating and
other applications. CNC contains abundant surface hydroxyl (-OH) groups, making it highly polar
and hydrophilic nanomaterial. As a result, its interfacial interaction and dispersibility in several
non-polar polymers, such as epoxy and polyurethane, is limited. These limitations severely
constrain it from transferring its intrinsic properties (e.g. loading bearing capabilities) to polymeric
materials. The main goal of this thesis was to investigate the surface chemical modifications of
CNCs with hydrophobic molecules to enhance its compatibility with epoxy and polyurethane
matrices for coating applications.
In the first part of the study, ammonium cationic surfactant modified CNC was produced.
First, the -OH group of CNC was oxidized to carboxylic CNC using 2,2,6,6-Tetramethyl-1-
piperidinyloxy (TEMPO) as a catalyst. Then, three differentiated cationic ammonium surfactants:
cetyltetramethylammoniumbromide (CTAB, C16 single chain), dimethyldidodecylammonium
bromide (DDAB, C12 double chains), and dimethyldihexadecylammonium (DHAB, C16 double
chains) were used to modify the surface of carboxylate CNCs. The modifications were confirmed
using Fourier-Transform Infrared Spectroscopy (FTIR) and elemental analysis. X-ray diffraction
(XRD) and thermogravimetric analysis (TGA) of the samples revealed that the crystallinities and
the thermal stabilities of the modified CNCs were preserved. Corrosion protection studies of epoxy
nanocomposite coatings containing the native and surfactant modified CNCs were conducted using
model steel specimens via salt spray and electrochemical test methods. The results indicated that
the use of surfactant modified CNCs resulted in an enhanced dispersibility in the epoxy matrices
as compared to native CNCs. The improved dispersion assisted in retardation of the penetration of
electrolyte that caused a remarkable improvement in the metal corrosion protection performance,
as compared to unfilled or native CNC filled epoxy coatings.
The second investigation focused on the modifications of CNCs for polyurethane polymer
coating. It involves surface grafting of varying levels of epoxy functionalized silane (ES) on
surface of CNCs. The effect of reaction time and concentration of ES on the level of grafting were
also investigated. The level of modifications was evaluated using Fourier Transform Infrared
Spectroscopy (FTIR), Elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), water
contact angle measurement (WCA) and dispersibility test. It was found that prolonged reaction
time and high mole ratio of ES to CNC improved the thermal properties and material wettability
of the modified CNC. The highest modified sample has WCA of 72.5º as compared to 25.6º for
CNCs. The incorporation of modified CNC in polyurethane not only improved mechanical
properties but also reduced the water absorption properties of the PU composites, which could be
attributed to the improvement in the dispersion and enhanced interfacial adhesion between the
nanoparticle and the PU matrix. Salt spray and electrochemical impendence spectroscopy (EIS)
study that were carried out on mild steel coated with PU/ES-CNC nanocomposite exhibited
excellent corrosion protection against salt solution compared to pure polyurethane.
As a result of these two studies, knowledge of modification of CNC through cationic
surfactant and epoxide functionalized silane agent have been advanced. The tailoring of CNC
surfaces via a facile and green process that maintained their desired crystallinity and nanostructure
while enhancing their compatibility with hydrophobic polymer matrices could further expand their
application in several advanced multi-functional material platforms.
Description
Keywords
hydrophobic modification, cellulose nanocrystals, corrosion resistant, nanocomposites
LC Keywords
Hydrophobic surfaces, Cellulose nanocrystals, Cellulose, Chemistry, Nanocomposites (Materials)