Antti Tynys, Cristian Hedesiu
Papers # 2014 Chicago
In the Middle East propylene random copolymers (PP-R) are commonly used for heating, plumbing and domestic water systems in large, prestigious high rise buildings. These buildings may contain more than 60-80 floors and be over 300 metres in height, which demands many kilometres of pipe in sizes up to 160 mm in diameter. Good processability is therefore essential to manufacture these large diameter pipes efficiently and economically without forfeiting any of the materials excellent properties which pushes the design of the existing materials to the limit. Some specific projects in the Middle East are described to illustrate this situation. Initially, unimodal PP-R grades were widely used but due to limitations in the balance between mechanical performance and processability they have been largely replaced by second generation bimodal PP-R grades, which are now widely used in Europe and the Middle East. To address the higher demands for large diameter pipes, further development has led to a third generation multi-modal PP-R material, which shows an excellent balance between mechanical properties and processability. This improved material enables higher output for pipe extrusion and injection moulding fittings whilst maintaining good quality and surface appearance of final product. The authors describe the effect of polymer modality on pipe and fittings performance and processability. In the second part of the paper the authors examine the benefits of alpha nucleation on these materials. It is shown that adding an alpha nucleator during the polymerisation process significantly changes the crystallisation speed and shrinkage behaviour of the polymer. Faster crystallisation enables the cycle time to be reduced in injection moulding fittings which is particularly beneficial for the production of larger diameter fittings. The shrinkage of the products also becomes far less dependent on the colour additives, which enables faster colour changes during pipe extrusion without the need to make adjustments to the processing conditions.
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