Tin stabilisers for PVC compounds are characterised by a central tin atom, surrounded by alkyl and acidic groups. Mixtures of mono and dialkyl tin salts are used in varying ratios depending on the performance and property requirements of the final product. The tin used in heat stabilisers for PVC accounts for about 3.5 % of the world’s total tin consumption.
Properties and applications
There are two main types of tin heat stabilisers for PVC. These are:
- (a) Thio acid half esters such as thio-glycollates often known as thiotins or mercaptides.
- (b) Dicarboxylic half esters, often referred to as maleates or carboxylates.
PVC tin stabilisers are always based on methyl, butyl or octyl groups. Methyl-based stabilisers are not generally used in Europe, but are commonly incorporated in a range of compounds, including potable water pipe formulations in the USA. Both butyl and octyl tin stabilisers are found in an extensive range of applications in Europe, but butyl tin stabilisers are now prohibited and uses of octyl tin stabilisers are restricted under the REACH Regulation. Following a risk assessment in 2010, the EU implemented in the same year risk reduction measures. These include a prohibition of butyl tin stabilisers by 2012, except for a few applications where use could have continued until 2015. Use of octyl tin is limited in a few applications where the products are in contact with the skin. When good outdoor weathering performance or low odor are especially required, it is normal to use maleates or carboxylates, while for all other applications the thiotins are commonly used. Both butyl and octyl tins provide very good heat stability and colour control, combined with the option of manufacturing crystal clear products. . PVC compounds incorporating tin heat stabilisers are used in a diverse range of applications including sheet, bottles, profiles, injection moulded fittings, credit cards, blister packs, food containers and display trays. The ‘Forschungszentrum für Umwelt und Gesundheit’ in Germany (GSF) on behalf of ORTEP has published a comprehensive review of the toxic and ecotoxic aspects of tin stabilisers. This concludes that tin stabilisers do not bioaccumulate in the environment or in the human body.
More information on stabilisers’ types and uses can be found on https://www.stabilisers.eu/stabilisers/.