Green Solution for PE-Xb in Drinking Water and Beyond

Session 3A
4:30

Dieter Scholz, Silon International GmbH
François de Buyl and Michal Hrebičík, Dow Corning Europe s.a.
Josef Křivánek, Polymer Institute Brno spol.s.r.o.

The green revolution for a cleaner world continues to gain significant momentum. It is therefore time to revisit the Sioplas® process discovered in the late sixties by Dow Corning to bring the technology a step forward by improving PE-Xb performance for applications such as plastic pipes used in cold and hot water piping systems.

Silon, one of the major producers of silane-crosslinked-polyethylene compounds (PE-Xb) for pipe applications has worked in partnership with Dow Corning and the Polymer Institute of Brno (CZ) in developing a new generation of PE-Xb compounds. The new product that has evolved from this co-operation shall offer the pipe extruders the opportunity to bring pipes with excellent organoleptic properties (e.g., Threshold Odor Number, Total Organic Content, and olfactometry profile) to the market and meet the most stringent European standards applicable to drinking water. In addition to improved organoleptics the new PE-Xb compound is able to crosslink and attain the specified minimum gel content of 65% without requiring the use of any tin-catalyst masterbatch during the pipe extrusion processing step.

These green and consumer friendly benefits are in perfect agreement with the more and more severe classifications applied to certain organotin species, which shall dramatically restrict their use in consumer applications in a near future.

Alternatively to the tin-free solution which needs to be cured in hot water another PE-Xb system has been designed in the joint development work to show its benefits without any post treatment after pipe production. In this case a tin-catalyst masterbatch is used during extrusion process. Doing so crosslinking the final product can be achieved by storage under ambient conditions.

Along the way of developing the new PE-Xb compound, a new test method was also established using the Dynisco Viscosity-Transition-Modulus® (VTM®) rheometer. Presented already at Plastic Pipes XIV in Budapest, the new method was proven being able to dramatically improve the efficacy to determine the rate of crosslinking and the final crosslinking density of the new PE-Xb material in comparison to standard vinylsilane-PE-Xb material. A good correlation was established between the measurements made on the VTM® rheometer with gel content measurements made using the standard xylene extraction method (e.g., ISO10147 or ASTM D2765). Crosslinking kinetics of various PE-Xb compounds as a function of temperature, silane type and concentration grafted to polyethylene resin, and the presence or absence of tin catalyst will be discussed.