Civil Engineering Reference
In-Depth Information
be up-scaled in industrial level. Once developed, this can dramatically increase the
industrial development of cellulose nanocomposite products.
In comparison with these conventional methods,
in-situ
polymerization of mono-
mers in presence of cellulose nanoi llers is advantageous in many ways:
a) Uniform dispersion of the cellulosic nanoi llers can be achieved in the
polymer matrix minimizing aggregation and increasing the interaction
with the growing polymer molecules.
b) Reducing the moisture absorption behavior of engulfed cellulosic
nanoi llers.
c) Enhancing the biodegradability in compost when required for specii c
applications like packaging.
h e main limitation of this technique is that it is applicable only when the polymer-
ization is carried out in liquid phase where the liquid monomer molecules are polymer-
ized in presence of the nanocellulose i ller.
h e properties of composites depend on many factors, such as, i ller content, size,
shape and aspect ratio, uniform dispersion of the i ller in the matrix, i ller/matrix inter-
facial bonding, and stress/transfer ei ciency through the interface [59]. h rough
in-situ
polymerization technique, a uniform i ller dispersion and ef ective interfacial bonding
can be achieved.
Some reports on cellulose nanocomposites are given below where
in-situ
compos-
ite fabrication techniques were adopted and novel materials were developed with new
application potential.
5.5
Novel Materials with Wide Application Potential
5.5.1
Bone Defect Repair and Bone Tissue Engineering
An interesting work was carried out by Zhou
et al.
[60] to prepare cellulose nanocrys-
tal (CNC)-reinforced polyacrylamide (PAM) hydrogels with enhanced properties that
can have a wide variety of applications in dif erent i elds. CNCs were isolated from
commercial microcrystalline cellulose (MCC) using a combined acid hydrolysis with
64% H
2
SO
4
and high pressure homogenization process. h e PAM-CNC nanocompos-
ite hydrogels were prepared by
in-situ
free-radical polymerization of AM in aqueous
suspensions of cellulose nanocrystals. h e compositions of cellulose nanocrystals were
varied between 1-10 weight percentages (w/w%) with respect to the weight of AM.
A schematic view of the
in-situ
polymerization and gelation mechanism is shown in
Figure 5.3 .
h e investigation on the gelation reaction of nanocomposite hydrogels by oscillatory
shear on a rheometer demonstrated the fact that the CNCs can accelerate the forma-
tion of hydrogels through the grat copolymerization of monomer acrylamide on the
surface of CNCs. h e results suggested that CNCs in the gelation process of nanocom-
posite hydrogels system acted as a multifunctional crosslinker. SEM micrographs of
freeze dried PAM and CNC-reinforced PAM hydrogels with dif erent CNC content are
shown in Figure 5.4.
