Civil Engineering Reference
In-Depth Information
emitting diode (OLED) display, satisfying the criteria for the substrate of OLED with
an additional feature of l exibility [190]. Due to the hydrophilic nature of CNR, some
other studies also focused on thermosetting nanocomposites based on hydrophilic
matrices: in the specii c case of polycondensation systems, prepolymers are compatible
and reactive towards cellulose, and on this basis, they should be excellent candidates
to develop cellulose nanocomposites. Moreover, CNR might be readily dispersed in
the starting prepolymer leading to the formation of an interpenetrating network upon
further polycondensation and resin cure; specii cally, in the case of polycondensation
between phenol and formaldehyde, chemical reaction between the phenolic prepoly-
mers and CNR is theoretically possible, with consequent modii cation of rheology and
curing behavior of phenol formaldehyde resole resin [191-193]. Phenolic resin-based
nanocomposites were also produced by Cherian
et al.
[194] , incorporating cellulose
micro and nanoi brils extracted from banana macro i bers and chemically modii ed
using sodium hydroxide, formic acid, 3-methacryloxy propyltrimethoxy silane in phe-
nol formaldehyde. h e most important class of thermosetting systems in which the
use of cellulose nanostructures was investigated was the one related to epoxy matrices:
Eichhorn
et al.
[195, 196] investigated the stif ness of cellulose whisker/epoxy system
using Raman spectroscopy and highlighted the importance of the interface between
matrix and nanoi ller. Lu
et al.
[197] reported that the modulus showed approximately
a six-fold increase upon incorporation of 5% (w/w) microi brillated cellulose (but not
cellulose whiskers) into an epoxy matrix, Matos Ruiz
et al.
[183, 184] studied water-
borne epoxy coatings into which low concentrations of tunicate whiskers were incor-
porated, while in Tang
et al.
[183] solvent exchange process from aqueous into organic
(DMF) dispersions was adopted as a suitable method to ei ciently mix an oligomeric
diglycidyl ether and an multifunctional amine crosslinker. In Takagi
et al.
[198] , the
preparation and characterization of a new type of natural i ber-based nanocomposite,
which is composed of bacterial cellulose nanoi ber and epoxy resin, was reported. In
Lee
et al.
[199], the surface and bulk properties of nanoi brillated cellulose and bacte-
rial cellulose, as well as their reinforcing ability in nanocomposites manufactured by
impregnating the nanocellulose paper with an epoxy resin using vacuum assisted resin
infusion, was investigated.
Few examples of nanocomposites in which the cellulosic nanostructure is used in
biobased thermosets can be also found. Due to the fact that these environment friendly
composites suf er from several limitations, such as low mechanical properties due to
low strength in reinforcement plus inadequate interfacial strength, and that cellulose
nanostructures have been shown to have signii cant potential as a reinforcement, the
possibility of using cellulose nanoi bers as reinforcements in a bio-derived resin was
revised. In Masoodi
et al.
[200] , cellulose nanoi bers were used as reinforcements in
the forms of layered i lms, while in Lee
et al.
[201] the stability of the gas-soybean oil
foam templates and the mechanical properties of the polymer nanocomposite foams
are enhanced upon the addition of bacterial cellulose nanoi brils. Other examples of
biobased thermosets containing cellulosic nanoreinforcements are the work of Shibata
[202] in which the use of a biobased epoxy was revised, and systems in which cellu-
lose nanocrystals are incorporated in biobased polyurethanes [203, 204]. Few examples
exist also in the literature on the polymerization of furfuryl alcohol in presence of CNR
[205, 206]; in these papers, the authors established the feasibility of producing furfuryl
