Polyolefins | materials feature
Polyolefins are extending their applications in everything from water and gas pipes to wood-plastic composites, through fundamental research – and new additives. Lou Reade reports
Additives help boost advances in polyolefins
The broad functionality of polyolefins makes them suitable for a wide range of applications – and this continues to increase as suppliers extend their capabilities. In addition, academic research is looking to understand the more fundamental aspects of these materials. Researchers at Kyoto Institute of Technology (KIT) in
Japan have analysed the crystallinity distribution in pipe grade polyethylene in order to determine its long-term resistance to hot water. In tests, a piece of PE-RT was immersed in hot water at 60, 90 and 120°C, and the change in tensile proper- ties was measured. The sample was subject to acceler- ated ageing for up to 12,000 hours. Raman mapping was used to determine the degree of crystallinity. A better understanding of the degradation mecha- nism of PE-RT in hot water will help to build higher durability pipes, said the researchers. Raman mapping found that the dispersion degree of
crystallinity increased over test time from the analysis of Raman peak intensity ratio (crystal to amorphous). The dispersion of 110°C test samples was increased, and showed distribution curves with multiple components. Tensile elongation at break did not vary much below 90°C, but at 110°C it was hugely reduced up to 12,000 hours. The elongation decrease was assumed to be
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caused by inhomogeneous crystallisation – which may yield to deformation or defects in the micro region structure of polyethylene, said the researchers. Tensile strengths increased compared with initial
conditions, and remained almost the same regardless of exposure times. The heat of fusion varied similarly with the tensile strength – suggesting thermal crystal- lisation.
“Mapping analysis by Raman is effective at clarifying
structural change – especially distribution of the crystal state of PE molecules correlated with the physical and thermal properties,” the researchers concluded. Separate to this, different KIT researchers have
studied how wood fibres of different lengths affect the performance of WPCs. The researchers used block PP as a matrix, and
compounded in five types of wood powder – with fibre lengths of 50-300 microns. Samples were then tested for toughness. The team concluded that elongation of the WPC was
better with shorter fibres. However, mechanical properties were more reliant on the use of additives that improved interfacial adhesion between the wood and polymer matrix. Both sets of results were presented in papers at last year’s Antec conference.
March 2017 | PIPE & PROFILE EXTRUSION 23
Sabic’s Supeer 8200RT grade is aimed at hot and cold water pipe applica- tions
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