The polystyrene is a polymer derived from petroleum 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 sealed ovens (autoclaves). This material is used in building and public works, in 2 main forms: standard polystyrene (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 forms the basis of this family. It is a crystalline material, rigid, but fragile and brittle.
- The high impact polystyrene (SB) is a PS bonded with 3-25% synthetic rubber (polybutadiene). It loses hardness, but acquires good impact resistance. This product is more opaque, less easy to weld, but thermoformable. Note that the ABSlittle used in construction, fall into this category.
- The polystyrene heat (SPS), polymerized in the presence of α-methylstyrene, resists high temperatures (up to 270°C).
Crystal, shock or heat, standard polystyrene lends itself to all shapes and reproduces, to infinity, 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 tinted in the mass according to a wide color chart and presented in smooth shiny or matt sanded finishes.
Use of standard polystyrenes
In construction, standard polystyrenes are mainly used in the composition of finishing materials, such as electrical appliances and boxes, carpentry accessories, etc.
Characteristics of polystyrene foams
Building 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 marketed in rigid sheets or blocks. Thermoplastics, they can also constitute the formwork of concrete elements, or become architectural objects in the most varied forms.
expanded polystyrene PSE (or PSE-M) is made from 0.2 to 0.3 mm crystal PS solid beads containing a gas, usually Pentane or Butane. By treatment with water vapour, these beads swell to 40 to 50 times their initial volume and then fuse in a mould, under the effect of pressure. Composed of 95 to 98% gas, the rigid foam, white in color, with closed cells thus obtained is a product with 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 (l) of EPS must be specified on the packaging. It varies between 0.040 W/(mK) and 0.030W/(mK). The higher the λ number, the better the performance. 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
EPS is used for its thermal regulation powers, summer and winter alike. 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 panelsfor the insulation of roofs from the outside or the inside.
- In covered panels protective film or siding for lining interior walls and partitioning.
- In breeze blocks or insulating lost formwork for shuttered concrete
- in bulkto be injected into a confined volume.
- In aggregate intended for the concrete of light screeds…
Advantages of expanded polystyrene
Main qualities of EPS:
- He is cheap.
- Good thermal insulator reduces clutter layers of insulation.
- He is light (less than 30 kg/m3), easy to handle and economical to transport.
- He is easy to implementre and cut using common tools (cutter, saw) or a thermal slicer.
- He takes the forms complexessuch as decorative motifs imitating stucco (profiles, rosettes, etc.).
- rot-proof et Hydrophobicit is suitable for humid environments
Disadvantages of expanded polystyrene
The PSE has its limits of use, but some improved versions widen its spectrum of uses:
- Inflammable, it gives off black soot and toxic gases when burning. So-called fireproof productions delay this process.
- It’s a poor sound insulation. Plasticized variants (PSE-db, PSE ThA, etc.) reduce this drawback.
- As it ages, it shrinks slightly (creep), releasing pentane, reputed to be harmless to health, but harmful to the ozone layer.
- Finally, it is a dish appreciated by small rodents.
price of expanded polystyrene
The price of expanded polystyrene varies depending on its thickness, density, thermal performance, shape, manufacturer and supplier. Price ranges including VAT, 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 certain insulation works are eligible, under certain conditions, for aid from the state, local authorities 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 balls, but in crystals or fine pearls, mixed with additives:
- Carbon dioxide (CO²) for the current λ
- Hydrofluorocarbure (HFC) for high performance λ
The product, melted at high temperature in an extruder, forms a soft paste. Thrust, under pressure through a die, then into a matrix in which it expands. It is finally cut to take its final shape. A foam with special qualities is thus obtained.
Differences between expanded polystyrene and extruded polystyrene
Extruded polystyrene takes on the characteristics and excels in all the applications of EPS whose performance it improves:
- Also light, its closed cells are thinner and tighter.
- It offers better thermal and mechanical performance.
- It has smoother surfaces, less prone to shattering.
- It has better resistance to puncture and compression.
- It is less prone to creep and more impervious to moisture.
These characteristics naturally impose this material, for the realization of external insulation works, in humid environments or subjected to strong pressures. It is ideal for the insulation of walls from the outside (ITE), concrete floor slabs on earth, interjoists of slab floors or formwork for pool shuttering.
Its price is about 20% higher than that of EPS.