Civil Engineering Reference
In-Depth Information
Solvent casting is currently the most commonly used for three main types of
polymers:
1.
water soluble polymers;
2.
polymer emulsions; and
3.
non-hydrosoluble polymers.
For polymer emulsions and non-hydrosoluble polymers, two dif erent routes were
studied to uniformly disperse cellulose nanoi llers in an adequate organic medium [3]:
1. To incorporate a shell on the surface of the cellulose nanocrystals (by
using surfactants having polar heads and long hydrophobic tails.
2.
To grat hydrophobic chains at the surface of cellulose nanocrystals.
Melt extrusion has also been explored to obtain cellulose-based nanobiocomposites
because this technique is the most industrially prevalent one used for polymer process-
ing [29, 66]. Nevertheless, it is really dii cult to use dried cellulose nanoi llers because
the nanoparticles create strong hydrogen bonds between amorphous parts and form
aggregates when they are dried. To overcome these limitations, several researchers
have tried to pump the cellulose nanocrystals during the melt extrusion of cellulose
nanowhisker-reinforced biodegradable matrices nanocomposites [31], and the results
indicate that the dispersion of cellulose nanoi bers were improved when they were
incorporated into the two-screw extruder with liquid feeding compared to dry mixing.
9.3
Future Perspectives and Concluding Remarks
Cellulose is the most abundant natural polymer on Earth, which is an almost inexhaust-
ible source of raw material for the increasing demand for environmentally-friendly and
biocompatible products. h erefore, cellulose-based materials have become one of the
most important bioresources of the 21st century. h is increasing relevance induced
investment in bionanocomposites research. h is also includes its purii ed, modii ed or
biodegradable constituents that are used as matrix or nanoreinforcements. It has been
shown that cellulose nanoi bres have an exciting potential as reinforcements in nano-
composites. h ey also, due to their size and ability to chemically modify their surface,
have great potential for a wide variety of applications; foams, adhesives, hierarchical
materials and electronic display materials. A number of methods have been reviewed
that enable cellulose nanoi bers to be extracted from either plants or animal sources. It
has to be remembered that in order to do this, some disruption of structure may occur,
and so ef orts to reduce damage during extraction are of paramount importance. It is
also worth noting that mechanical means of i ber separation require large amounts of
energy, and so ef orts to reduce this, either by enzymatic or chemical methods, will
become increasingly important. h e potential mechanical properties of cellulose nano-
i bers compete well with other engineering materials, and we have seen that this could
