Technical Specifications

Material properties of polyethylene (PE) and polypropylene (PP)

Rendifield supplies Polyolefin pipes from high-quality raw materials supplied by providers certified in terms of the standards of ISO 4427. The pipes and fittings are fabricated in accordance with national and international standards that guarantee their quality.

Polypropylene (PP)- is an excellent option when the medium to be disposed of by the piping system has a high temperature or contains particularly aggressive substances, e.g. in the case of industrial wastewater. As in the case of polyethylene, pipes made of this material are sized and deployed in observance of the applicable specifications derived from internal pressure creep curves and creep modulus data.

Abrasion resistance- Wastewater directed through sewage systems often flows at high velocity. What is more, it frequently contains an extremely high level of solids. This leads to a considerable abrasive load in systems made of conventional materials, particularly at the bottom of the sewers. The result: an increased risk of pipe wear. Owing to their high abrasion resistance, PE pipes are particularly well suited to applications within this area, as highlighted by comparative tests conducted on the basis of the Darmstadt method.

Creep under internal pressure- One of the most important methods of verifying the service life of PE pipes is to determine creep under internal pressure, also referred to simply as “creep”. Even after 100 years of a continuous service temperature of 20 °C no thermooxidative processes will occur in PE 80 or PE 100 pipes. The tests conducted within this area provide comparative data used for the purpose of design/sizing pipes to be exposed to sustained loading (up to 100 years).

Time-dependent modulus of elasticity (creep modulus) Data relating to the modulus of elasticity is essential when it comes to performing stability analyses, e.g. in the case of buried pipes exposed to soil loads, live loads or groundwater. In the case of pipes made of thermoplastic materials, the time-dependent modulus of elasticity is of par ticular impor tance. Scientific tests and practical experience have provided longterm dimensional parameters, ensuring that the design of the piping system is technically sound and suitable for sustained operation.

Table 5.1: Technical Specifications PE 100 (black)

Tables 5.1 provide a general description with the technical specifications for the most commonly used Polyolefin grades, namely PE 100 (Black).

Melt Flow Index (MFI)

Generally used to categorize the molecular mass and is therefore a very important indicator of the type and properties of a polymer. MFI is determined as the mass of polymer extruded in a certain time through a standard die under a pre-determined load and temperature. Low MFI indicates that a polymer is very viscous and of a high MM. Lowering the MFI has the following positive effects on polymers by increasing:

• Tensile strength
• Elongation at break
• Impact resistance
• Resistance to creep
• Toughness
• Environmental stress crack resistance

It should however be noted that as MFI decreases the processing extrusion capabilities of the material are negatively affected.

Melt Flow Index Molecular Mass (MM)

A very important concept in plastics which describes the viscosity of a polymer and hence its flow and conditions for processing. A high MM has a more viscous melt and does not flow as easily as one with lower MM.