Expanded Polystyrene (EPS) is technically defined as:
“Cellular and rigid plastic Material made from the moulding of expandable polystyrene preexpandid pearls or one of their copolymers, which has a closed, air-filled cell structure”.
The abbreviation for EPS is derived del ingles Expanded PolyStyrene. This material is also known as Telgopor or White Cork.
CHEMICAL FORMULA
: C8H8
In 1831 a colourless liquid, styrene, was first isolated from a tree bark. Today it is mostly obtained from oil.
Polystyrene was first synthesized at an industrial level in 1930. Towards the end of the 1950s, the firm BASF (Germany), at the initiative of Dr. F. Stastny, developed and started the production of a new product: expandable polystyrene, under the Styropor brand. That same year it was used as an insulator in a construction inside the same BASF plant where the discovery was made. After 45 years in front of scribes and technicians from different European institutes, some of this material was raised and subjected to all possible tests and verifications. The conclusion was that the material after 45 years of Use kept each and every one of its properties intact.
Density
The products and articles finished in expanded polystyrene are characterized by being extraordinarily light but resistant. Depending on the application, densities range from 10kg/m3 to 35kg/m3.
Color
The natural color of expanded polystyrene is white, this is due to light refraction.
Mechanical strength
The density of the material is closely related to the mechanical resistance properties. The graphs below show the values achieved on these properties depending on the apparent density of expanded polystyrene materials.
Thermal insulation
The products and materials of expanded polystyrene have an excellent thermal insulation capacity. In fact, many of its applications are directly related with this property: for example, when it is used as an insulating material of the various enclosures of the buildings or in the field of packaging and packaging of fresh foods and perishables such as for example the boxes of fish.
This good thermal insulation capacity is due to the very structure of the material that essentially consists of occluded air within a cell structure made up of polystyrene. Approximately 98% of the material volume is air and only 2% is solid matter (polystyrene), the air at rest being an excellent thermal insulator.
The thermal insulation capacity of a material is defined by its coefficient of thermal conductivity than in the case of the products of EPS varies, as the mechanical properties, with the apparent density.
Water and water vapour behaviour.
Expanded polystyrene is not hygroscopic, unlike other materials in the insulation and packaging sector. Even by completely immersing the material in water, absorption levels are minimal with values ranging from 1% to 3% by volume (immersion test after 28 days).
To the contrary of what happens with the water in the liquid state, the water vapor can diffuse into the interior of the cellular structure of the EPS when between both sides of the material is set to a gradient of pressures and temperatures.
Dimensional stability.
EPS products, like all materials, are subject to dimensional variations due to thermal influence. These variations are evaluated through the coefficient of thermal expansion that, for the products of EPS, is independent of the density and is placed in the values oscillate in the range 5-7 x 10 -5 K -1 , that is to say between 0.05 and 0.07 mm . per metre long and Kelvin grade.
As an example, an expanded polystyrene thermal insulation plate of 2 meters long and subjected to a thermal jump of 20 ° C will experience a variation in its length from 2 to 2.8 mm .
Stability against temperature.
In addition to the phenomena of dimensional changes due to the effect of temperature variation described above, expanded polystyrene may suffer variations or alterations due to the effect of thermal action.
The temperature range in which this material can be used safely without its properties being affected has no limitation at the lower end (except dimensional variations by contraction). With respect to the upper end the use temperature limit is around 100 ° C for short-lived actions, and about 80 ° C for continuous actions and with the material subject to a load of 20 kPa.
Behaviour against atmospheric factors.
Ultraviolet radiation is practically the only factor of importance. Under the prolonged action of UV light, the surface of the EPS becomes yellowish and fragile, so that rain and wind can erode it. These effects can be avoided by simple measures in construction applications with paints, coatings and coatings.
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