Civil Engineering Reference
In-Depth Information
dif erent lengths of the aliphatic chains (C
12
to C
18
) [153] have also been reported. Cetin
et al.
proposed a novel and straightforward process of acetylation of CNCs (obtained
from cotton linter) by transesterii cation of vinyl acetate using potassium carbonate.
Initially the surface of CNCs were modii ed, while their dimensions and crystallinity
were unaf ected, but as time increased, a higher level of acetylation and reduced dimen-
sions with lower crystallinity occurred. Further, the modii ed CNCs with increased
acetylation showed improved stability in THF (a solvent of low polarity) [154]. Lin
et
al.
developed a novel and facile functionalization process for CNCs through acetylation
by reaction with acetic anhydride and hydroxyl groups on CNCs surfaces. h e resultant
acetylated CNCs (ACNCs) showed improved dispersion in dif erent organic solvents
and reduced surface polarity as compared to unmodii ed CNCs, maintaining the same
crystalline structure as that of unmodii ed CNCs. h ermal characterization showed
higher decomposition temperature. h e ACNCs-reinforced PLA nanocomposite
showed superior mechanical properties and thermal stability [155]. Lin
et al.
prepared
new nanocomposite of castor-oil-based polyurethane matrix reinforced with acetylated
CNCs (ACNCs). In this advancement, an acetylated CNCs-reinforced castor-oil-based
polyurethane nanocomposite with high loading level of 25 wt% has been carried out
and the tensile strength and Young's modulus increase from 2.79 MPa to 10.41 MPa and
from 0.98 MPa to 42.41 MPa, respectively [156].
15.6.5
Silylation
h e silylation of CNCs involves the replacement of protons of hydroxyl (-OH) groups
and promotes dispersion ability in organic solvents and compatibility with polymer
matrix. Gousse
et al.
reported the partial silylation of CNCs (extracted from tunicate)
by using a series of alkyldimethylchlorosilanes having alkyl moieties ranging from iso-
propyl to longer lengths represented by n-butyl, n-octyl and n-dodecyl. h e silylated
CNCs became readily dispersible and formed stable suspensions in low polarity solvents
(such as THF), showing that birefringent behavior and morphology remained unaf-
fected when degree of substitution (DS) was between 0.6 and 1; but a higher silylation
degree (DS greater than 1) disintegrated the crystals due to silylation of core crystals
and, consequently, the loss of original morphology [157]. h e reduction in hydrophilic-
ity of CNCs (extracted from bacterial cellulose microi brils) was attempted by trimeth-
ylsilylation and further dispersed in cellulose acetatebutyrate followed by fabrication of
composite by using solvent casting. However, unmodii ed CNCs showed better rein-
forcement characteristics than the trimethylsilylated CNCs [41]. h e enhanced disper-
sion of CNCs (extracted from sisal i bers) coupling with N-octadecyl isocyanate (via
bulk reaction in toluene) in organic medium has also been reported. h e compatibil-
ity of obtained CNCs with polycaprolactone in nanocomposites signii cantly showed
improvement in the stif ness and ductility [158]. Recently, the partial silylation of
CNCs (extracted from cotton) was addressed by using n-dodecyldimethylchlorosilane
in toluene. h e obtained silylated CNCs formed stable suspensions in tetrahydrofuran
and chloroform. h e silylated CNCs-reinforced PLA nanocomposites were prepared
by using solvent casting and exhibited improvement in tensile modulus and tensile
strength values [159].
