PVC (polyvinyl chloride) and PP (polypropylene) are both thermoplastic materials. PVC was invented at the beginning of the 20th century and has been used industrially since the 1930s. The invention of PP took place in the 1950s and industrial use began shortly afterwards.

Thermoplastics require about 3 times less energy in their production than iron-metallic materials. By using small amounts of additives, the material properties can be greatly changed and adapted to the intended application. Thermoplastics are resistant to many chemical substances such as various acids, alkalis and solvents. They resist corrosive influences, weathering and sunlight.

In addition, they can be shaped at relatively low temperatures and can thus be processed into a wide variety of workpieces. Last but not least, they can be completely recycled in an environmentally friendly way.

The material is used as rigid PVC (PVC-U) in ventilation and air-conditioning technology. The material can be used to produce pipes and shaped parts with different wall thicknesses. Even more complicated components such as throttle, control and lamella dampers are possible. This allows a supply and exhaust air system to be constructed entirely from PVC components. Due to its chemical resistance, this is suitable wherever aggressive media come into contact with the ventilation system. The material has a particularly high resistance to organic acids and alkalis.

A PVC pipe system is dimensionally stable with very low thermal expansion, has a comparatively low weight and high rigidity. The very smooth surface prevents incrustations in which pollutants and bacteria can settle. In addition, it is flame-retardant and extinguishes automatically when the pilot flame is eliminated.

PVC components are easy to install. The connection is possible by welding and up to 250 mm diameter also by gluing. As with all thermoplastic materials, any damage to PVC can also be easily repaired.

Its properties make it suitable for use in exhaust air systems in laboratories, sewage treatment plants, in the chemical and electroplating industries, in surface finishing, in the production and processing of chlorine as well as in hospitals and clean rooms. Metal ventilation ducts are simply unsuitable here or would have to be provided with very complex and expensive processes with resistant coatings or completely made of stainless steel.

The PVC components are mainly used indoors. They are only conditionally suitable for outdoor use. The relatively low operating temperature range of 0 to + 60 °C plays a role here.

Thermoplastic PP is used in ventilation and air-conditioning technology in its refined PPS (flame-retardant) version. PPS can also be used to produce low-cost pipes, shaped parts and other components. The chemical resistance of the material complements that of PVC, as it is particularly insensitive to solvents and alcohols. In addition, PPS is hydrolysis resistant, which means that it can also withstand hot water and steam in temperatures up to 90 °C. At temperatures below 0 °C, PPS becomes brittle and, like PVC, should not be used.

Otherwise, the mechanical properties are similar to those of PVC. PPS pipe systems are also easy to install as the material is even lighter than PVC. However, the connection of the components is only possible with appropriate welding processes.

Components made of PPS are used in exhaust air systems of laboratories, hospitals, clean rooms, in the chemical industry and in surface finishing.

As already described, there is no alternative to plastic pipe systems for applications with aggressive media because sheet steel does not meet the requirements for chemical resistance. However, plastic components are also frequently used for controlled ventilation of living spaces. Here, the advantage lies in the simple installation and the possibility of also being able to produce very flat ventilation ducts. In addition, a plastic duct in the living area does not look as “technical” as a sheet metal component and therefore fits in better.

A disadvantage compared to sheet steel is the relatively small temperature range of 0 to + 60 °C for PVC and 0 to + 90 °C for PPS. This means that these components cannot be used outdoors because temperatures below 0 °C can occur in winter. The same problem arises at higher temperatures as smoke extraction systems have to withstand in the event of fire. Plastic components are also unsuitable for such applications.

As described, both plastics have quite similar properties in ventilation applications. The most important criterion for the selection is therefore which aggressive substances are to be expected in the concrete application. If, for example, solvent vapours have to be extracted, the choice will fall on a PPS pipe system. If evaporation of acids or alkalis is to be expected in the exhaust air system, one rather uses a PVC pipe system.

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