additives | PVC
popularity in flexible PVC formulations, Pelzl noted. These systems prevent the formation of onium salts which would otherwise affect colour and cause crosslinking. In addition, they absorb very little water and are suitable for transparent PVC applications. Hydrotalcites are also used in other diverse applications such as antacids and waste water treatment, so their health and safety credentials are well established. “Organic systems enable sustainable PVC stabilising
Figure 1: PVC stabiliser use in Europe by type, 2007-2016 (COS refers to Ca-Zn and Ca-organic Systems) Source: Reagens/ESPA
systems,” Pelzl said. “Performance and processability are equal to either mixed metal or tin systems [how- ever] some applications are at the moment still difficult to implement. Organic stabilising systems are right in the beginning of their development in flexible PVC compounds.” Chemson Product Manager Walter Fischer, who
works with Pelzl, says: “Solid organic type stabilisers are showing overall performance comparable to common systems based on mixed metals – either liquid or solid ones – as static and dynamic stability tests demonstrate. The usage of organic type stabiliser systems in rigid applications is based on the good heat stabilisation without heavy metals and the substantially delayed cross-linking of degraded polymers.” These claims are visualised in the colour charts in Figures 4 and 5. Pelzl and Fischer also point out further advantages
Figure 2: Global PVC stabiliser consumption by type and region, 2016 Source: Reagens/ESPA
of organic stabiliser systems in their very good compatibility with fibres and their low migration tendency compared to zinc soaps. “These facts are more important for flexible applications. But most of the organic type solid stabiliser systems are somehow weaker in transparency than liquid stabiliser systems. This is one of the main reasons that these types of stabiliser systems are used in only selected flexible applications today,” the pair say. “However, organic type stabilisers are developing
Figure 3: Global PVC stabiliser consumption by application and region, 2026 Source: Reagens/ESPA
16 PIPE & PROFILE EXTRUSION | July/August 2017
further. New systems are demonstrating improved performances regarding transparency for flexible and rigid sheet applications.” These next-generation systems are in advanced development, with formula- tions being tailored to production processes at PVC article producers. Clariant is another company supplying hydrotalcites, which the company markets under the Sorbacid brand. It says that they create new opportunities in processing and manufacturing of flexible, rigid and transparent PVC products. “Window profiles, high temperature cables, coated wires, pipes and a variety of other PVC products are already being stabilised using Sorbacid,” Clariant says. It adds that the product works best in conjunction with Ca/Zn stabiliser systems where it says it creates “an environmentally friendly, non-toxic and heavy-metal free alternative for PVC stabilisation.”
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