Physical and chemical properties of cork

The uniqueness of cork is due to both its impermeable properties, filled
air of cells, and z 35% fatty acid, who is in them
is located. Each cork cell is waterproof and flexible. In its
cork cells are an excellent insulating material, resistant
on liquids. This is undoubtedly an adaptive response to the harsh environment
natural, in which the trunk of a cork oak needs protection from changing
influenced by weather conditions – including before summer
heat and drying winds.

Lightness
Air poses 90% the volume of the cork and approx 50% its mass, making,
that its specific gravity is in the range of 190 do 250 kg/m3.
Therefore, cork is a material five times lighter than water, and because
does not soak up water (only accepts from 18 do 20% water) is the material
practically unsinkable. This property of it was known earliest
and it was used thousands of years ago, e.g.: as buoys to the net
fishing.
And nowadays, there are also floats and cork lifebuoys.

Impermeability to liquids and gases
Suberin, which is a complex mixture of fatty and heavy acids
organic alcohols, states from 39 do 45% cork mass. Her presence
makes, that the cork is impermeable to gases and liquids (including
for water and alcohol). also, thanks to the presence of tannins and the lack of protein
cork is not susceptible to the harmful effects of moisture, and most importantly
on rot. Amphorae with wine sealed with a cork were found lying by
hundreds of years sunk in the sea where the cork stoppers have not deteriorated.
Another property of cork is related to impermeability – namely
its low hygroscopicity, i.e. no absorption of water vapor. There is
this feature is extremely important, especially when installing cork coverings
on walls or ceilings. It occurs in all rooms
some moisture, which may settle down especially in poorly insulated places
or in the corners. In damp places, floating dust quickly settles
up in the air, and mold develops over time. The formation of moisture
the hygroscopicity of the substance may be very conducive, from which made
there are coatings of walls and ceilings. This does not happen with the application
above. Cork has the lowest, and therefore the best hygroscopicity (factor
water vapor permeability) among the materials traditionally used
for building walls. So it is the least likely, that on the traffic jam
they will become dirty streaks of wet dust. In addition
fungus or mold will never settle on the stopper. In many countries, the traffic jam
it is even used to protect against fungus. Mushy walls
after drying, it obscures itself with a cork, for it is almost
an insurmountable biological obstacle for at least several years.
Another additional factor is related to the impermeability of the cork
advantage – cork flooring can effectively isolate the interior
housing from the harmful effects of certain building materials,
like for example.: blast furnace slag.

Chemical indifference
The cork is chemically inert. The cork mass is not only tight
liquids and gases without being damaged, but also does not come in
with them in chemical reactions, has no taste or smell, it is harmless
for one's health. Hence the traditional use of a stopper
bottles, because it not only tightly and permanently clogs the dishes, but also
it does not spoil the substances contained in them. This way you can be sure,
that the wine, despite being aged for many years, will not taste like the cork.

Flexibility and compressibility
Cork cell membranes are very pliable, making, that it is compressible
and flexible, returns to its previous shape, when it ceases to be subject to
pressure. When the cork is subjected to high forces, compresses
gas in its cells and their volume decreases. After the pressure is gone
the cork returns to its original shape and shows no signs of deformation.
When fully compressed, the cork immediately returns to 85% initial
volume, in three hours it expands to 90%, a po 24 hours
takes already 94% previous volume. It uses this property
when closing bottles. You choose plugs like this, that the inner diameter
the neck of the bottle accounted for 85% plug diameter. Then a cork plug
are squeezed in a suitable device and put into a bottle. After being released
pressure, the stopper immediately expands tightly filling the neck
bottles. The same cork property is retained for parquet floors
cork. Sometimes buyers are concerned, that high heels, for example
will leave them permanent, deep dents in the cork floor.
Well, you should remember, that cork parquets are manufactured according to modern standards
technology, which provide them with high resistance to pressure and abrasion
and, of course, they do not easily get bent, but even very much
with a large squeeze, the cork cells will expand quickly and the floor will be crushed
will rise without leaving any traces of deformation. With flexibility
cork has an interesting story. At the beginning of our century
a cork was placed on a pile driven into the ground during the construction of the bridge in Neustadt
fired from the champagne. Then for an hour from a height 2 meters
the pile was struck by a steam hammer of the weight 2,4 tony. It turned out, that
the cork not only did not change in volume, but he carved a stake in the wood
a hole with a depth 1 cm. ( based on: German wine newspaper, no.
7 with 1907 year )

Poor thermal conductivity
The thermal conductivity of materials depends on two essential parameters:
on their specific weight (bulk density) and from their inner
structures. Basically, the lower the specific weight, the weaker the conductivity
thermal, i.e. better thermal insulation. On the other hand, because
the air thermal conductivity coefficient is many times lower
on the coefficient of thermal conductivity of solids, materials
with a porous structure, that is, filled with air, they are less conductive
warm. So we see, that cork is an ideal thermal insulator,
because, first of all, it has a very low specific gravity, and second, it has structure
porous (it's made up of lots of closed cells, impermeable
and filled with air). A given thermal conductivity coefficient
material is not constant and depends, among other things, on the moisture content.
Many good insulation materials lose their properties, if
becomes wet, because water conducts heat perfectly. Jam
in this respect, it is a very resistant material, because it does not break down
under the influence of water, does not absorb water and does not pass water vapor. As they prove
research materials such, like polystyrene or mineral wool have a smaller one
specific gravity from cork, but no material has better
(smaller) thermal conductivity coefficient (0,045 W/m*K). Big
the advantage of cork is also this, that with a relatively light weight
has a very high specific heat. Therefore, to warm the cork
by 1 ° C it needs to be supplied with much more heat, than for example
glass wool or mineral wool (the same property also applies to
cooling the cork – to reduce its temperature you have to take it from him
much more heat than other materials). High specific heat
it constitutes the so-called high thermal inertia of the cork. In contrast
cork retains its insulating properties for other materials
a very wide temperature range. In this respect, it far exceeds
for example, polystyrene, which evaporates under the influence of high temperatures.
The cork is always warm due to its low thermal conductivity
in touch, because it neither lets in nor absorbs the heat of our body
and makes an impression, as if he had an inner warmth (as if it kept us warm).

The ability to absorb vibrations
Due to its specific structure, the cork does not transmit vibrations, but
it amortizes them.. Its flexibility and compressibility have a great influence on it
and cellular structure, resembling a shock absorber
car. Therefore, cork cells are a great absorbing material
sound waves and vibrations.

Antistatic
No electric charges accumulate on the cork surface, that is, others
words, the cork is not electrifying. Therefore, it neither attracts nor absorbs
course, and therefore parquet and cork paneling do not cause
allergies or risk to asthmatics.

It is hardly flammable
Due to the high saturation of suberin, the cork is difficult and slow to burn. Not
it also deals with the flame and does not keep the fire going, but it only burns
on the surface and only with high oxygen availability.

Durability
Cork practically does not age and does not lose its own despite the passage of time
properties, even if it is not specially impregnated. W 1956
In the year, perfectly preserved wine was found in Indre et Lorie, France
with 1789 year. The wine tasted good, which proves its excellent durability
closing the bottle with a stopper by 167 years. Similar finds do not belong
to a rarity. Many very old ones have survived to our times
cork products, for example, amphora cork plugs derived
from the beginning of our era. Cork is certainly one of the most
persistent organic materials, and modern technological processes
they additionally strengthen its longevity.