Civil Engineering Reference
In-Depth Information
nanocrystals on the barrier properties of thermoplastic polymers. Reductions of 34%
in water vapor permeability were obtained for i lms with 1 wt% of modii ed crystals
and good oxygen barrier properties were obtained for all nano-biocomposites high-
lighting the success of the solvent casting procedure and the reinforcement ef ect of
cellulose [150]. Yano and Nakahara used accessory polysaccharides to form composites
with wood MFC. h e disintegrated wood celluloses were mixed with starch as a binder
and then hot pressed between porous metal plates. Using a starch content of 2 wt%,
the bending strength reached 310 MPa, compared to 250 MPa for unmodii ed i bers.
Concurrently, the Young's modulus decreased from 16 to 12.5 GPa. When the starch
content was 20 wt%, the bending strength decreased to 270 MPa. [151]. Okahisa
et al.
(2009) fabricated an organic light-emitting diode on l exible, low coei cient of thermal
expansion and optically transparent wood/cellulose nanocomposites. At the same i ber
content, the nanocomposites using lower Young's modulus matrix resin exhibited lower
coei cient of thermal expansion values than using higher Young's modulus matrix res-
ins. It led to the development of nanocomposites with a very low coei cient of thermal
expansion while having high l exibility and ductile properties which open up many
possibilities for the application of OLEDs in l exible, transparent displays [152]. h e
preparation, characterization, and application of BC-based composites with a variety
of plastic materials were recently reviewed [27] in a summary report describing the
considerable progress that has been made in the ef ective liberation/formation of the
cellulosic nanoi brillar structures. h ese can be considered as ways to improve the com-
patibility of the cellulose structures with a variety of synthetic polymers as composite
partners, and the resulting innovation potential for the use of CR in a wide range of
high-tech applications. Composites can be formed by
in-situ
modii cation of BC, that is,
by the addition of the composite partners to the culture medium, or by post-processing
of BC synthesized conventionally. Typical composite partners are organic compounds,
such as bioactive agents and polymerizable monomers, polymers, such as polyacrylates,
resins, polysaccharides, and proteins, as well as inorganic substances, such as metals
and metal oxide [24]. h e depositing of BNC onto natural i bers, to create hierarchical
i ber-reinforced nanocomposites, has also been described. h e coating of sisal i bers
with BNC during fermentation leads to better adhesion properties without af ecting
the strength and biodegradability of the composite materials and enables the extended
application of natural i bers in renewable composites [15]. h e nanostructured network
and morphological similarities with collagen make BNC very attractive for cell immo-
bilization, cell migration, and the production of extracellular matrices. In-vitro and
in-vivo evaluation showed that the BNC implants did not elicit any foreign-body reac-
tion. Fibrosis, capsule formation, or giant cells were not detected around the implants,
and connective tissue was very nicely integrated with the BNC structures. Although
BNC had been shown not to be cytotoxic or genotoxic, the properties of isolated BNC
nanoi bers on cells and tissues had never been analysed. Generally, the recent develop-
ment of BC implants has been characterized by a broad patenting of these materials.
However, these patent claims are frequently based on insui cient background investi-
gations to determine the manufacture-dependent structure of the material and its func-
tion and stability in the body. h e same is true for BC scaf olds for tissue engineering.
In particular, the in-growth of living cells requires further investigation and a deeper
understanding [24] .
