The polystyrene is a petroleum-derived polymer which, in its basic formula, is solid at room temperature, pasty at 120 ° C, liquid from 150 ° C and self-igniting around 490 ° C. Soluble in a wide variety of hydrocarbons and different essential oils, it is produced under pressure in airtight furnaces (autoclaves). This material is used in construction and public works, in 2 main forms: standard polystyrenes (PS) and polystyrene foams (PSE).
Characteristics of standard polystyrenes
The standard polystyrene is mainly available, for construction, in 3 variants:
- The Crystal polystyrene (PS), so called because of its original transparency, is the product that serves as the basis of this family. It is a crystalline material, rigid, but fragile and brittle.
- The impact polystyrene (SB) is a PS bonded with 3 to 25% synthetic rubber (polybutadiene). It loses in hardness, but acquires good impact resistance. This product is more opaque, less easy to weld, but thermoformable. Note that the ABS, little employed in the building, fall into this category.
- The heat polystyrene (SPS), polymerized in the presence of α-methylstyrene, resistant to high temperatures (up to 270 ° C).
Crystal, shock or heat, standard polystyrenes lend themselves to all shapes and reproduce, endlessly, the fine details of each molded part. They are stable over time. The material can be injected, vacuum formed or extruded. It can also be colored in the mass according to a wide range of colors and presented in smooth glossy or matt sandblasted finishes.
Use of standard polystyrenes
In the building industry, standard polystyrenes are used mainly in the composition of finishing materials, such as electrical devices and boxes, joinery accessories, etc.
Characteristics of Polystyrene foams
Construction companies mainly exploit the insulating properties of polystyrene foams, which are among the most popular thermal insulators and best known to the public. They are most often sold in sheets or rigid blocks. Thermoplastic, they can also constitute the formwork of concrete elements, or become architectural objects of the most varied forms.
Expanded polystyrene PSE (or PSE-M) is made from solid 0.2-0.3mm crystal PS beads containing a gas, most commonly Pentane or Butane. By treatment with steam, these balls swell 40 to 50 times their initial volume and then merge in a mold, under the effect of pressure. Composed of 95 to 98% gas, the rigid foam, white in color, closed cells thus obtained is a product of standard yield. The addition of graphite to the formulation increases its insulating capacities, but the product is very sensitive to UV. It is recognizable by its more or less dark gray color.
Calculation of thermal efficiency of EPS
The coefficient of thermal conductivity lambda (λ) EPS must be specified on the packaging. It varies between 0.040 W / (mK) and 0.030W / (mK). The higher the λ figure, the better the efficiency. Conversely, the insulation efficiency (R), increases with the thickness of the insulation. The calculation formula is simple: R = thickness in meters / lambda. Thus, for an EPS of lambda 0.040 in 10 cm thickness, the thermal resistance R = 0.10 / 0.040, or 2.5 m².K / W.
Use of expanded polystyrene
PSE is used for its thermal regulation powers, summer and winter. It is perfectly suited to lining flat walls, such as walls, roofs or basements. It is available in various forms:
- Raw, in plates of different sizes and thicknesses for lining interior and exterior walls.
- In sandwich panels, for roof insulation from the outside or the inside.
- In covered panels a protective film or siding for lining interior walls and partitioning.
- In concrete blocks or lost insulating formwork for poured concrete
- In bulk, to be injected into a confined volume.
- In aggregate intended for concrete of light screeds …
Benefits of expanded polystyrene
Main qualities of PES:
- It is cheap.
- Good thermal insulator, it reduces clutter layers of insulation.
- It is lightweight (less than 30 kg / m3), easy to handle and economical to transport.
- It is easy to implementre and cut using common tools (cutter, saw) or a thermal slicer.
- He takes the complex shapes, such as decorative patterns imitating stucco (profiles, rosettes, etc.).
- Rot-proof and Hydrophobic, it is suitable for humid environments
Disadvantages of expanded polystyrene
The PSE has its limits of use, but certain improved versions widen its spectrum of uses:
- Flammable, it releases black soot and toxic gases on burning. The so-called flame retardant productions delay this process.
- It’s a poor sound insulation. The plasticized variants (PSE-db, PSE ThA…) reduce this drawback.
- As it ages, it shrinks slightly (creep), releasing pentane, known to be harmless to health, but harmful for the ozone layer.
- Finally, it is a popular dish for small rodents.
Expanded polystyrene price
The price of expanded polystyrene varies depending on its thickness, density, thermal efficiency, shape, manufacturer and supplier. Price ranges inclusive of tax, excluding installation, per m², in R = 2.5:
- between 5 and 8 € for bare EPS
- between 15 and 18 € for uncoated graphite EPS
- between 12 and 15 € for a plaster / EPS lining complex
- between 18 and 20 € for a water-repellent or fire-retardant complex.
Note that some insulation work is eligible, subject to conditions, for aid from the state, local communities or public bodies.
Extruded polystyrene (XPS or PSE-E) is a variant of PSE which is distinguished by its method of manufacture. The original crystal PS is no longer in beads, but in crystals or fine pearls, mixed with additives:
- Carbon dioxide (CO²) for the current λ
- Hydrofluorocarbon (HFC) for high performance λ
The product, melted at high temperature in an extruder, forms a flexible paste. Thrust, under pressure through a die, then into a die in which it expands. It is finally cut to take its final shape. A foam with particular qualities is thus obtained.
Differences between expanded polystyrene and extruded polystyrene
Extruded polystyrene has the same characteristics and excels in all EPS applications, improving its performance:
- Also light, its closed cells are thinner and tighter.
- It offers better thermal and mechanical performance.
- It has smoother surfaces, less prone to ginning.
- It has better resistance to puncturing and compression.
- It is less prone to creep and more impermeable to moisture.
These characteristics naturally impose this material, for carrying out exterior insulation work, in humid environments or subjected to high pressures. It is ideal for insulating walls from the outside (ITE), concrete floor slabs on embankments, slab floor interjoists or swimming pool bench formwork.
Its price is about 20% higher than that of PSE.