Entrepreneur Jesús Ricardo Álvarez Gualtieri explains the differentiated processing of PVC and Polyethylene in the manufacture of pipes

The type of raw material influences the way in which the material must be processed and the final use that will be given to the resulting pipe, assures Jesús Ricardo Álvarez Gualtieri, general manager of Tubosa.

For the construction and infrastructure industry, the use of pipes manufactured under efficient and innovative conditions and methods that guarantee their functionality and high levels of quality is essential, as Jesús Ricardo Álvarez Gualtieri, general manager of Tubosa, assures.

In this sense, the manufacture of pipes through the extrusion of PVC (polyvinyl chloride) and polyethylene (PE) stands out. Although they are materials that share certain similarities, they have unique properties that generate key differences in the process that affect their application and performance. Jesús Álvarez has spent a decade leading the management of Tubosa S.A.S., a Colombian company with more than 30 years of experience specialising in the production and marketing of PVC/CPVC piping systems and fittings.

From this experience, Álvarez Gualtieri comments that with the extrusion process, pipes can be created by pushing the raw material, with an appropriate mix of force and pressure, through a die to mould the desired shape of the parts. That is why it is key to determine which raw material will be chosen, taking into account the final product to be obtained, because this also conditions the particular extrusion process to be used.

Prioritise characteristics and uses, emphasises Jesús Ricardo Álvarez Gualtieri

“The choice of raw material is crucial depending on the pipe to be manufactured. PVC and PE have different compositions that influence their characteristics and the extrusion process,” says Álvarez Gualtieri.

PVC or polyvinyl chloride is the result of using additives such as stabilisers, lubricants, impact modifiers and, in some cases, plasticisers, which is why it is a more rigid material in its natural state. On the other hand, PE or polyethylene, of which there are different types, does not require heat stabilisers or plasticisers, is more flexible and has greater resistance to impact.

These initial differences, explains Jesús Álvarez Gualtieri, make PVC ideal for applications that require robust structures, while PE is more suitable for applications where durability and adaptability are needed. For example, PVC pipes are more suitable for drinking water and sewerage pipelines, and PE pipes for gas networks, pressurised drinking water and buried pipes without the need for rigid anchoring. ‘The choice depends on the end use of the pipe’.

Apply differentiated processes

In the case of PVC, a screw extruder is used in the process. Today, there are twin-screw machines with high and gradual compression, under precise temperature control to avoid thermal degradation and a low pressure matrix due to the viscosity of the molten PVC itself. This, says Alvarez Gualtieri, requires the use of a vacuum system in the calibration, to maintain the shape of the pipe, and cooling in vacuum and water tanks to stabilise the dimensions.

With PE, on the other hand, a screw extruder with a low compression ratio screw and high mixing efficiency is used, with greater flexibility in temperature control due to the properties of the input, but with high pressure in the extrusion, due to the lower viscosity of the molten PE. Finally, water bath cooling and in-line calibration are used, with some variants depending on the dimensions of the pipes to be manufactured. This post-processing and cooling phase is critical to ensure the quality of the pipes, says Jesús Ricardo Álvarez Gualtieri.

Particular connectors

Alvarez Gualtieri, an expert in the PVC and CPVC industry, highlights the fact that the nature of the raw material not only influences the way the material is processed and the end use of the resulting pipe, but also determines the way in which the pipes are joined and connected.

Thus, PVC pipes are joined by cementing, using special glue or by rubber rings in pressure systems, which ensure strong and durable connections. In the case of PE pipes, the connection is made by thermofusion, electrofusion or mechanical jointing, which guarantees airtight joints, which is crucial for high pressure applications and gas networks.

Given these particularities, specialised processing is required. That is why a large part of Tubosa‘s innovation culture has focused on the acquisition of new technologies in extrusion and injection, says Jesús Ricardo Álvarez Gualtieri, as well as on improving the efficiency of all the machinery in use, in order to have an industrial plant that responds to the requirements of the national and international market and the best use of raw materials with sustainable criteria.

Technical aspects

The differences in processing lie in the composition of the raw materials themselves, the main ones to be taken care of are:

• Processing temperature: pvc is processed between 160 °C and 210°C , with precise control to avoid the release of hydrochloric acid, this is achieved with thermal stabilisers. Polyethylene can range from 120°C (LDPE) to 200°C and 300°C in HDPE.
• Additives: PVC requires stabilisers and lubricants and PE requires only antioxidant additives or pigments.
• Processing methods: both can be used in extrusion, injection and most commonly PE with blow moulding.
• Cooling: PVC cools fast and PE slower due to lower shrinkage.

Generally speaking, according to Jesús Álvarez, PVC is ideal when stiffness, chemical resistance and low cost properties are needed, such as pipes, windows, cables, but its processing is more complex. Polyethylene (PE) on the other hand is more versatile, easier to process and more environmentally friendly. It is better for flexible applications such as bags, packaging, films, pipes or toys.

‘In my experience, I recommend choosing PVC if mechanical resistance is a priority and PE if you are looking for ease of manufacture and less environmental impact,’ says Álvarez Gualtieri.