Biomedical Engineering Reference
In-Depth Information
at the nanoscale will enable us not only to decrease the negative impact of moisture
on woody materials, but perhaps allow us to turn what is currently perceived as a
disadvantage into an advantage. In addition to the size of the nanofibrils, the angle of
orientation of the fibrillar bundles of nanofibrils relative to the long axis of the fiber
plays a major role in the dimensional stability of the fiber in response to moisture. The
degree of crystallinity (i.e. the ratio of the ordered regions to the amorphous regions
in the microfibrils) will also impact the response to moisture. Because of inter- and
intra-chain hydrogen bonding, crystalline regions are less accessible to moisture. These
characteristics, which vary with species, can be genetically manipulated within a given
species. Changing the conditions under which the trees are grown and even changing
the drying conditions, as moisture is removed from the fiber during processing, can also
impact features such as the degree of crystallinity. By studying and understanding the
nature of bonding within paper and wood structures at the nanoscale, it may be possible
to modify how each composite material responds to moisture. The ability to modify and
control mechanosorptive behavior may lead to improvements in existing products and
many potential new products based on the lignocellulosic biomass resource, in addition
to greatly improving the efficiencies of the processes by which current products are made.
Durability of wood and paper products is closely tied to their response to moisture as
well. An understanding of the interactions between moisture and woody materials at the
nanoscale may permit the development of new and innovative technologies which will
decrease or even eliminate degradation.
Control or modification of surfaces of composites based on lignocellulose using
nanocoatings or impregnation of nanoparticles could be used to provide physical/
chemical barriers to prevent or control the transfer of moisture. In addition, modification
of the topography and surface chemistry could be used to control attractive and repulsive
forces between cellulosics and other materials thus enhancing or decreasing wetting
and adhesion. For example, this could be used to increase the specific bond strength
of an interfiber bond thus permitting a lighter paper sheet with strength and optical
properties, equivalent to a heavier weight sheet.
Very large amounts of water must be handled in the making and drying of products
made from the forest. Such activities account for a very high percentage of the costs
of production. Using nanotechnology, the nature of the interactions between the ligno-
cellulosics and water can be manipulated to improve drainage during formation of the
paper and increase the efficiency of drying of both wood and paper. This could take the
form of nanomaterials that modify fiber surfaces or change the viscosity of water. Such
materials could also be used as coatings on paper machine wires and press felts thus
enhancing drainage rates of liquid water. They might also be used on paper machine
dryer felts and dryer cans to improve heat transfer, making drying more efficient.
Understanding and manipulating the interactions between water and wood/paper will
permit huge reductions in energy and water usage in processes by which products are
made from these complex materials. It most likely will result in the more economical
use of the raw materials in a broad base of new and existing products. It may also
enable the substitution of products based on a sustainable renewable resource for some
of the products derived from a more limited and less environmentally friendly material
such as petroleum. The relationships between water and lignocellulosic materials have
been studied extensively and a great body of literature exists. However, relatively little
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