ADDITIVES | PVC FORMULATION
Songwon says its SONGSTAB CZ-SA20 calcium-zinc (CaZn) stabiliser helps reduce discolouration caused by amine migration Source: Songwon
says: “We tested two tin-based stabilisers (mostly used in North America) and three calcium organic stabilisers (COS) mostly used in Europe, each with 7 and 9 phr of titanium dioxide concentration. Each extruded sample was exposed five times, each for four years, in a severe climate (EN 12608-1 ), starting in four different seasons and the same season for two consecutive years. [At the study’s conclusion] we did not have evidence of a starting season that particularly negatively affects ageing, neither comparing colour change (Delta E) at end exposure nor the overall speed of the colour change over the whole exposure time frame. The evaluations evidenced a similar performance of all stabilisers, with COS technology proven to be a valid and, in many instances, outperforming alternative to tin-based stabilisers.”
Tin replacement Tin-based stabilisers for PVC, predominantly used in rigid, often transparent, calendered film and foamed profiles and sheets, have long been the focus of regulatory bodies due to environmental concerns. Calcium-based stabilisers are seen by many as a viable alternative and are already being utilised in many applications such as plasticised film or rigid compact and foam sheet extrusion. Conventional tin stabilisers offer limited lubrication but provide good transparency, heat stability, and high transparency. All these properties and more need to be provided by the alternatives. German additive manufacturer Baerlocher has developed various calcium-based grades for rigid calendered film, such as Baerostab NT 1883 P or Baerostab NT 1929 P-series, which can cope with
34 COMPOUNDING WORLD | June 2024
demand for high transparency, good initial colour, and maintaining a stable calendering process due to adjusted low lubricity. For foam profile and foam sheet formulations used in continental Europe, calcium-based stabiliser systems are designed in a conventional way as they are used in rigid PVC profile extrusion. Care must be taken when fine-tuning co-stabiliser systems and lubricants for foam extrusion to achieve proper surfaces and colour. Not all aspects are related strictly to stabilisation, and the company is a big advocate of making necessary formulation adjustments after close communication with converters. At NPE 2024 in Florida in May, US-based performance additive producer SI Group show- cased Weston 705, a phosphite stabiliser free of nonylphenol which can be used in a variety of polymer systems including PVC. Weston 705 reduces both plate-out and gel formation by a factor of ten, and has been developed as an alternative to TNPP or for use in applications with nonylphenol restrictions. Adam Watson, Senior Sales Director, Polymer Solutions – North America at SI Group, said: “Our presence at NPE under- scores our dedication to driving positive change within the plastics industry, advancing towards a more sustainable and circular future.” As in other areas of plastic production and manufacturing, sustainability is now considered a high priority in PVC formulation and a lot of PVC materials such as building materials, film, and wire and cable, are being developed in accordance with these concepts. Japanese additive manufacturer Adeka has long been involved in the development of environmentally friendly stabilisers to meet
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