Civil Engineering Reference
In-Depth Information
liquid-crystalline colloidal particles can be interesting, because they can be manipu-
lated/rotated in electrial i elds, many of them acting as sensors to determine rotational
dif usion in colloidal dispersions, others manifesting anisotropic interactions in colloi-
dal dispersions. Liquid-crystalline colloidal particles from ferroelectrical LC-materials
have a polar axis if the colloidal particle gets small enough (below the size of a single
domain). h is case is of interest in nematic phases, as a model system, and also in fer-
roelectrical LC-phases, because of the low symmetry of the resulting colloidal particles.
Study of the incorporation of cellulose nanocrystals in a polyurethane elastomer
shows the modii cation produced in the properties of the resulting material [154]. In
this context, the surface hydroxyl groups on cellulose are reacted to produce modii ed
cellulose crystals. h e study reveals a strong dependence of materials properties on the
cellulose content, a peculiar behavior appearing below the percolation threshold.
Reaction with a polymerizable mixture, giving nanoi bers covalently attached to
the polymer, has also been studied [155]. Dif erent techniques, including dynamic
mechanical analysis and positron annihilation spectroscopy show that interaction at
the nanoi ber-polymer interface produces radical changes in the glass transition of the
material. h e ef ect of the addition of cellulose nanocrystals on the properties of a poly-
urethane matrix are theoretically described by the free volume theory.
In the multitude of points covered in this chapter, it is appropriate to mention the
materials constituted from bacterial cellulose, characterized by their high water-hold-
ing capacity, high crystallinity, an ultrai ne i ber network and high tensile strength.
Literature demonstrates the production of a new interpenetrated polymer network
nanocomposite obtained through the incorporation, e.g., of poly(vinyl alcohol) on the
bacterial cellulose matrix, and evaluates the ef ect of oven drying on the morphological,
mechanical and mass transfer properties of the composite membranes [156]. Moreover,
complex structures of cellulose derivatives, such as bioi bers and the corresponding
biocomposites have many new applications, given that their properties can be appro-
priately controlled and tailored. h us, the capacity of these materials to not degrade
in the body can be exploited to produce dif erent materials, such as artii cial blood
vessels [157] .
14.2
Conclusions
In summary, this chapter rel ects the current state of knowledge of dif erent processes
in cellulose derivatives, including structural aspects, method of structural analysis,
and properties of modii ed structures by dif erent techniques. h e presented exposure
demonstrates that cellulose derivatives constitute the basis of production of dif erent
materials with excellent properties for obtaining particular morphology, degradability,
biocompatibility, etc., for a variety of structural arrangements in industrial applications.
Finally, it can be pointed out that this chapter is useful for students and scientists of
both academia and industry interested in new possibilities to explore additional appli-
cations of cellulose derivatives. New aspects, including cellulose technologies constitute
future aims, strategies, and perspectives of cellulose research for diverse applications.
