ADDITIVES | ANTIOXIDANTS/UV STABILISERS
Figure 4: Retained OIT of HDPE geomembrane samples produced with custom stabiliser systems by Everspring - oven aged at 85°C in air Source: Everspring
Figure 5: Retained OIT of HDPE geomembrane samples produced with custom stabiliser systems by Everspring – hot water aged at 85°C Source: Everspring
Everspring has worked closely with a converter to develop an improved stabilisation system for geomembranes. The Geosynthetic Research Institute (a US-based consortium of organisations involved with geosynthetics) has defined test methods with minimum specifications for various membranes. For HDPE types, for example, one of the requirements is that the membrane should retain more than 55% of its original oxidative stability (as measured by OIT with a minimum initial induction time of 100 minutes at 200°C) after 3 months oven ageing at 85°C in air. “Working closely with a customer who was developing a new HDPE membrane, Everspring was able to provide a customised solution which not only fulfilled this demanding standard but could surpass this requirement even after ageing in water at 85°C for 6 months,” Marshall says (Figures 4 and 5). “The reference product could not even achieve comparable performance after three months ageing in water – water can leach or hydrolyse certain commonly used antioxidants – showing the limitation of standard solutions in this demanding long service life application.” Solvay has this year commercialised two new advanced stabilisers for polyolefins: Cyasorb Cynergy Solutions M535 Light Stabilizer for moulding applications and Cyasorb Cynergy Solutions B878T Light Stabilizer for construction materials that require long-term UV and heat stability for harsh conditions. Cyasorb Cynergy Solutions M535 Light Stabilizer imparts a very low initial colour in natural HDPE (Figure 6). “Because M535 can be used at lower loadings than competi- tive solutions, a colour concentrate producer can add more pigment or other additives to the formulation in lieu of stabiliser, allowing formula- tion flexibility and helping to maximise value,” says Marketing Director Landuzzi. The stabiliser also delivers good colour stability in
natural HDPE, with ΔE staying below 2.0 after 10,000 hours of Xenon weathering. It is also especially effective in preventing photo-induced colour change and surface degradation (as measured by loss of gloss) in pigmented systems (Figure 7). The current ASTM UV specification for TPO
sheet roofing is no cracking/crazing on a mandrel after 10,080 kJ/(m2
·nm) radiant exposure at 340nm
Figure 6: Initial colour of HDPE containing Cyasorb Cynergy M535 from Solvay against competitive stabiliser systems Source: Solvay
48 COMPOUNDING WORLD | September 2017
and the oven specification calls for 5,376 hours at 116°C. Cyasorb Cynergy Solutions B878T Stabilizer shows no cracking or crazing over a mandrel at three times the radiant energy of the ASTM UV specification. Another commercial formulation is reported to have failed this test after around 27,500 kJ/m2
.
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