Civil Engineering Reference
In-Depth Information
as well as the thermal and mechanical properties. Also noteworthy was the covalent
link between BC and the synthetic grat s which prevented leaching during use which
is a common limitation for many composites. h ey also proved the living nature of
the system by the growth of the second PBA block, which opened a variety of possi-
bilities to tune the phobic behavior of such materials, their mechanical properties, pH,
and temperature responsive behavior, and even bioapplication potential upon adequate
modii cation of the grat end groups with molecules with biological activity. Hence, it
was envisaged that these novel nanostructured porous materials could i nd potential
applications in several i elds, namely, in controlled release of drugs or other bioactive
compounds.
5.5.4
Surface Coating Applications
A series of new waterborne polyurethane (WPU)/cellulose nanocrystal (CN) compos-
ites were successfully synthesized via
in-situ
polymerization by Cao
et al.
[64] . A series
of WPU/CNs nanocomposites were prepared via one pot polymerization, surface grat -
ing, and processing. Some of the pre-synthesized WPU chains were successfully grat ed
to CNs through the reaction between the isocyanates of the WPU prepolymers and
hydroxyls of CNs. h ese grat ed-WPU chains were able to form a crystalline structure
on the surface of CNs, and thus induce the crystallization of the matrix which created
a co-continuous phase. As a result, very good dispersion and strong interfacial adhe-
sion between CNs and WPU were obtained. h erefore, the incorporation of CNs in
WPU resulted in a signii cant improvement in the thermal stability and the mechanical
properties. Such waterborne polyurethane-cellulose nanocrystal nanocomposites with
improved properties can i nd widespread applications in a range of commodity prod-
ucts such as elastomers, foams, paints, and adhesives.
Nanocellulose-reinforced acrylate latex can also be an interesting material for the
surface coating industry. Mabrouk
et al.
[57] used an one-step miniemulsion polymer-
ization method to prepare stable aqueous nanocomposite dispersions based on cellulose
whiskers extracted from the rachis of the date palm tree and a poly (styrene-co-2-ethyl
hexylacrylate) copolymer. A reactive silane, i.e., methacryloxypropyl triethoxysilane
(MPS) was added to stabilize the dispersion and favor the anchoring of the whiskers on
the polymer particles. h e particle size of the polymer dispersion ranged between 90
and 160 nm for a whisker content varying from 1 to 5 wt%.
Analysis of the nanocomposite i lms obtained by the casting/evaporation of the
nanocomposite dispersions revealed a quasi constant value of the Tg of the matrix and
a specii c heat increment (ΔCp) regardless of the i ller content indicating that the incor-
poration of the whiskers into the matrix did not bring about any restriction of the chain
mobility. h e DMA analysis showed a notable enhancement of the storage modulus
in the rubbery state of the matrix on adding cellulose whiskers, which is in agreement
with the well-known reinforcing ef ect of the cellulose whiskers. However, above 3 wt%
whiskers the reinforcing ef ect was highly inl uenced by the MPS content, shown in
Figure 5.11 .
It was evident that with 1 wt% MPS, the reinforcing aptitude of the whiskers was
much higher than that reached when using 3 wt% MPS. At such a level, the presence of
MPS prevented the formation of a rigid percolating whiskers network through strong
