What is polypropylene?
Polypropylene (PP) is a thermoplastic made from the monomer propylene. It is the lightest of the common plastics — with a density around 0.9 g/cm³ it floats on water — and at the same time stays dimensionally stable to higher temperatures than polyethylene.
Properties
- Heat resistant. PP holds its shape to considerably higher temperature than PE; the melting point is in the order of 160 °C. That makes it suitable for hot waste water and, in the PP-R grade, for hot water pipework.
- Chemically resistant to acids, alkalis, salts and most household chemicals.
- Stiff and hard, but more brittle at low temperature than PE. Copolymer grades are impact-modified and suffer less from this.
- Not UV-resistant without stabilisers.
- Alkali resistant. Unlike polyester, PP tolerates an alkaline environment — which makes it the logical choice in and around concrete.
Applications in construction
- Above-ground drainage. Grey PP pipe is the standard for waste pipework inside the building. Acoustic grades exist with a weighted, multi-layer wall for pipes in or beside habitable rooms.
- PP-R pipework for hot and cold water and heating, joined by socket fusion welding: pipe and fitting are melted into a single piece with a heated tool.
- PP fibres in concrete. In two quite different roles. Fine fibres limit plastic shrinkage cracking in young concrete. Monofilament fibres at a dosage in the order of 1 to 2 kg/m³ are used to reduce explosive spalling in fire: at high temperature the fibres melt away and leave channels through which steam can escape. This is standard practice in tunnel concrete.
- Geotextiles and road separation fabrics, particularly where contact with lime or cement is expected.
- Chambers, gullies and drainage components.
- Strapping bands for packaging bricks and slabs.
Points to watch
- You cannot glue it. Like PE, PP does not take adhesive. Join with a fusion socket, a compression fitting or a rubber coupling.
- Thermal movement. PP waste pipe expands noticeably with hot discharge. Use the slip sockets provided and bracket it so there is one fixed point and the rest can move.
- Cold on site. Brittle material breaks. Do not drop PP pipe in frosty weather or drive over it.
- UV on site. Stored pipe and fabric should be covered.
Related terms
- Plastic
- Polymer
- Polyethylene
- Above-ground drainage
- Concrete fibre
- Geotextile
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