AMAZING MATERIALS: TRANSPARENT WOOD
§ The simple
process of replacing the organic polymer lignin with a special mix of epoxies
removes the coloring from wood and adds a new level of strength.
§ While many may
see transparent wood as something of a novelty material, the practical benefits
are immense.
§ Practical uses
include replacement windows, high-end sports equipment and integration into
solar panels and solar cells to name but a few.
Transparent
wood is a type of a composite material that has the potential to revolutionize
the fields of construction and the manufacturing of various products. It
combines the benefits of wood as a material and the achievement of making it
opaque. For now, transparent wood remains under development but
advancements in the science of materials suggest that it will be widely
available very soon.
The story of
transparent wood
Transparent
wood was created back in 1992 when German researcher Siegfried
Fink sought to reveal the specific cavities in wood for the
purpose of writing a book on a functional study of wood structure. This work
inspired engineers from the Swedish Royal Institute of Technology, who
collaborated with a research group at the University of Maryland, to start
exploring the possibilities of creating transparent wood for more widespread
use. The publication of the first results, as well as samples of transparent
wood blocks last year, sparked the interest of many architects and engineers
around the globe. The road to the final stages of development for this novel
material is coming to an end.
How to make
transparent wood
The
key concept is to remove the organic polymer called “lignin” from the wood,
which is the substance responsible for the wood’s brownish coloring. To achieve
this targeted chemical removal, while keeping the rest of the material intact,
the scientists follow a procedure that is similar to chemical pulping. This
involves immersing the wood piece in a solution of water, sodium hydroxide and
sodium sulphite and boiling it for about two hours.
Once
all lignin has been removed, the wood becomes transparent although it is also
very fragile. This is because lignin is what gives wood its rigidity since this
polymer is a primary element of the cell walls. To compensate for this loss,
scientists re-immerse the block in a new solution that consists of a special
mix of epoxies that fill the emptied microscopic channels of the wood. These
strengthen the wood while maintaining its transparency and biodegradability.
This process lasts for about an hour, with the pressure in the bath
interchanging from positive to negative in order to make sure that all wood
channels are completely filled with the epoxy.
Advantages and
possible applications
The
resulting wood composite is much stronger than natural wood and
allows up to 90% of light to pass through it. The material has the practical utilization
potential to replace glass and plastic materials in a myriad of possible
applications. Some of the most notable first application examples include:
§ Replace glass
windows on buildings – allowing the use of fewer frame elements since the
composite wood can withstand loads much better than glass does. In addition to
this, composite wood is immensely better in terms of thermal insulation when
compared to glass, so it will likely have a hugely positive effect on the energy
efficiency of buildings in the future.
§ Solar panels
and solar cells can be equipped with composite wood that has a high light
transmittance, better durability against environmental damage such as hail
and the capacity to implement “light trapping” properties that reflect light
back to the cells. This will reduce the rate of escaping rays and increase the
energy efficiency of the panels.
§ Since wood is
very light compared to steel, but also very strong with the addition of the
epoxies and polymers, transparent wood may also be utilized as a key structural
element by itself. We have already seen the implementation of a model house
with its ceiling and roof being made by transparent wood. This combines
unprecedented thermal insulation and structural integrity.
§ High-end sports
equipment such as archery bows, various sticks and clubs, tennis rackets, etc
can all potentially benefit from the added strength of transparent wood with no
additional weight.
§ Wood is already
a popular choice of material for fuselages and wings for small aircraft.
As transparent wood is so much stronger we will likely see many significant
developments in this field.
Current
drawbacks
The
main problem at this time is that development funding for transparent wood is
running low. As a consequence research teams are being forced to spend time
convincing potential investors about the usability potential of the material.
The fact it is also unclear how best to achieve mass production in a
cost-efficient manner is not helping at this point in time. However, when
balancing the benefits of transparent wood with production costs going forward
there are still high hopes for the future.
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