The majority of stabilisers in this group are liquid, mixed metal soaps which have similarities to some calcium/zinc stabilisers described earlier and are generally used in the form of a carboxylate. However, solid forms are also manufactured which are used to provide specific properties.
As in the case of calcium/zinc heat stabilisers, all these products require the addition of co-stabilisers to provide optimum performance. These are the same types of products as are used with calcium/zinc stabilisers. Solvents are also sometimes incorporated.
A group of specialised liquid soap stabilisers allied to barium/zinc soaps are zinc or potassium/zinc soaps. These are generally laurates or octoates and are used as PVC stabilisers and as activators (or ‘kickers’) for the blowing agent used in making the foamed layer in a number of plastisol applications.
Properties and Applications
PVC compounds incorporating barium/zinc stabilisers are used to make a range of paste PVC applications. They are the most commonly used stabiliser in flexible foils (eg: for membranes, stationery and automotive applications), flooring, wall covering, flexible tubing and footwear. The potassium/zinc materials are widely used in cushion flooring, foamed wallpaper and in foamed fabric coating. Depending on the stabiliser selected, it is possible to obtain a selection of properties including good clarity, good weatherability, good colour hold, good long-term stability, suitability for white pigmented applications, low migration, low odour and low volatility. Some products are specifically designed to meet just a few of these criteria but others can achieve a good compromise of all the above features.
Applications for Stabilisers - European Market
|Foil and Sheet||+||+||++|
|Tubes and Footwear||+||++|
|Food Packaging Film||++|
++ Major use
+ Minor use
(+) Occasional use
(1) Used for potable water pipe
(2) Used as a stabiliser/'kicker' for foamed layers in these products
Safety, Health and Environmental Issues
No specific hazards are likely with barium/zinc stabilisers when normal handling procedures are observed. Barium compounds are classified as ‘harmful’ and this type of product is not approved for food contact applications, toys or medical applications.
The types of products made from PVC compounds incorporating barium/zinc stabilisers are not expected to be in contact with a leachate such as water and no loss or migration is expected during the normal lifetime of the product. Some of the co-stabilisers are, however, classified as toxic and environmentally hazardous, although others are approved for food contact. Even when substituted for barium in this type of stabilising system, the co-stabiliser still requires a risk assessment. Most environmental attention has been focused on removing volatile organic compounds and phenols and more stabilisers free of such ingredients are reaching the market.