Lead Stabilisers

The lead compounds used as heat stabilisers include dibasic lead carbonate and phthalate, dibasic and neutral lead stearate, tribasic and tetrabasic lead sulphate, dibasic lead phosphate and phthalate, liquid lead carboxylates and tetrabasic lead fiunarate. Lead stearates are added to other lead compounds because some combinations show a synergistic effect. 

Lead chloride is formed in the first stages of degradation by the reaction of some of the above compoimds with hydrogen chloride. The convenient insolubility of lead chloride in water means that lead-stabilised PVC can be used in electrical applications. 

Most lead stabilisers have the side effect of making the products opaque, except for the lead carboxylates. They also react with any sulfur present, producing brown lead sulfide. 

Chapter 5 discusses the current usage of lead stabilisers and the implications of their voluntary phase-out over the next few years. 

---

It is briefly reported that the European Commission will issue a White Paper on PVC within the next couple of months. The Paper will probably be a mix of both legislation and voluntary commitments. A Green Paper on PVC was adopted by the EC in July 2000. This raised six issues to be addressed substitution, production process, cadmium stabilisers, lead stabilisers, phthalates and waste management. 

Primarily used extensively for PVC-U applications in Europe and the Far East viz. pipe, fittings and profile, lead stabilisers have been very cost effective heat stabilisers. For similar reasons, plus good insulation resistance, lead stabilisers have also been used in PVC-P in wire and cable across the world. Their toxicity hazards have been well known and controlled, particularly in relation to worker exposure. 

However the EU classification of lead stabilisers as reprotoxic, harmful, dangerous for the environment and danger of cumulative effects and their presence (heavy metal) causing issues in waste management strategies, resulted in their agreed phase-out in Europe (see Section 7). 

Under the Voluntary Commitment (Section 7) there is an agreement to phase out lead stabilisers (159) and suitable alternatives are being introduced. 

As the reader has observed in this review, the innovation process is thriving within this new environment. The focus has been on more cost effective polymerisation plants with an improved environmental profile, the replacement of lead stabilisers, scientific studies and support for phthalates, a greater understanding of and an increasing role for impact modifiers, recycling techniques and waste management possibilities. 

The characteristics of organic based heat stabilisers used in PVC are outlined and a comparison is made of the performance of an organic based stabiliser one-pack with a traditional lead stabiliser one-pack in the injection moulding of an unplasticised PVC pipe compound. Spiral flow and colour development during injection moulding are discussed and the results of customer trials on a large... 

Lead stabilisers have been used in a variety of PVC as well as other polymers for many years. In some halogenated polymers, such as chlorinated PE (CPE), chlorosulphonated polyethylene (CSM), polychloroprene (CR) and epichlorohydrin (ECO), dibasic lead phthalate and dibasic lead phosphite are used to scavenge HC1 arising from crosslinking as well as from degradation. In some of these cases, the metal may participate in crosslink formation. With lead-based stabilisers, the result is typically a product with greater water and chemical resistance than if a light metal, with more soluble halide salts, were used instead. In other cases, lead stabilisers may be used solely for function in metal oxide... 

Risk reduction is a world wide problem and of course a concern to the field of PVC stabilisers. The replacement of lead stabilisers in wire and cable applications is demonstrated. Newly developed non-lead stabilisers (RUP-series) are shown to offer excellent heat stability, electrical and mechanical properties compared with traditional wire and cable formulations. The overall processability is shown with experimental and actual results. The gradual increase in use of ADKs and other non-lead stabilisers in the USA and Japan demonstrates industry s concern for the public demand in saving the environment without direct laws banning the use of lead. JAPAN... 

IR and NMR spectra of basic lead carboxylates used as heat stabilisers for halogenated polymers, e.g. PVC, indicated that these salts were not complexes, or double compounds of lead oxide, as suggested in most textbooks, but unique compounds of interesting structure. Stabilisers studied included monobasic lead phthalate, tribasic lead maleate, tetrabasic lead fumarate, dibasic lead phthalate and dibasic lead stearate. Lead stabilisers probably functioned in these polymers by converting hydrogen chloride to water, interfering with acid catalysis of the elimination reaction. 6 refs. 

Processing aids are usually based on high molecular weight acrylic copolymers (for PVC). They modify the rheology and processing characteristics of the melt. Lubricants are processing aids that function to ease the process and are of two types either internal lubricants (that influence the viscosity, such as calcium stearates) or external lubricants (such as oxidised polyethylene wax). Lead-stabilised PVC lubricants are a part of the stabiliser system. They are important in PVC foam formulations. 

As a final note on PVC, it is worth mentioning Vinyl 2010, which is an EU voluntary commitment study on the PVC industry initiated in 2001 for the following 10 years, including mid-term revisions of targets in 2005 and definition of new objectives in 2010. The plan includes for full replacement of lead stabilisers by 2015, in addition to the replacement of cadmium stabilisers by March 2001 [27, 30]. Also in Vinyl 2010, the following values are put forward for maximum permissible VCM concentrations in the final PVC products ... 

The EU initiated studies to control and stop completely the use of lead stabilisers in plastics by the year 2015. 

Edge M, Liauw CM, Allen NS, Herrero R. Surface pinking in titanium dioxide/lead stabiliser filled PVC profiles. Polym Degrad Stab 2010 95 (10) 2022-2040. 

The high level of interest in reducing lead concentrations also raised some questions about the leaching of lead-based stabiliser compounds from PVC pipe. A number of European pipe manufacturers have already moved to non-lead stabiliser systems and it is likely that such moves will be completed by voluntary action before legislation is introduced [40]. 

Members of the European Stabiliser Producers Association (ESPA) have made a voluntary commitment to phase out all lead stabilisers in Europe by 2015. Since lead is the commonest type in use today, this is a considerable commitment. There is expected to be a 50% reduction in lead stabiliser usage between 2001 and 2010. It is possible that individual national regulatory authorities will press for a more rapid elimination of lead from specific end products. Cadmium was phased out some time ago. 

Since the consumption of PVC worldwide is about 30 M tonnes ear, it should be reasonable to assume a global heat stabiliser consumption of approximately 750,000 t/y. There is expected to be a decline in lead stabiliser consumption, however, and a 3%/y growth in the tin type, with 4% growth in mixed metal stabilisers. As an example, the lead previously used in wire and cable and in window and door profiles is being replaced by mixed metal stabilisers. Tin is expected to remain the most important PVC heat stabiliser in North America for some time. 

Employee numbers at Akcros in the UK and Emope were about 1000 three or four years ago, but were reduced by about 30% when the lead stabiliser business was sold in a management buy-out and now, after further deals, the lead stabiliser operation is owned by Chemson. 

Another factor leading to acquisitions has been the turmoil in the heat stabiliser business. In 2001 Akcros Chemicals agreed a management buy-out of its lead stabiliser manufactming operations, since lead was to be phased out. The lead business became known as Allstab, but two years later Chemson bought it. By this time it had a turnover of 60 M euros and 210 employees. The plan was that Chemson would ultimately move its own operations to one of the old Allstab sites at Diiren. 

Heavy metals in PVC compoimds, including tin from stabilisers or biocides, have also attracted attention. The implications for heat stabilisers have already been discussed. A decision was made by the Emopean Stabilisers Producers Association to phase out lead stabilisers by 2015. The central issues in the medium-term future are likely to be (a) the rate at which lead is phased out and (b) the future attitude of regulatory authorities to organotin. Organotin stabilisers represented 9% of the Emopean stabiliser market in 2002. (Greenpeace opposes organotin compoimds in PVC products intended for children, as well as lead.)... 

The European Union has legislated to reduce the permitted lead contents in potable water. Denmark banned lead in certain PVC applications, including pipes, from the end of 2003, and the UK banned lead in potable water pipes by the same date. Wire and cable insulation materials for use in vehicles has had to be lead-free in Europe since 2003. Sweden implemented a ban on lead stabilisers from January 2002. The Netherlands has followed a voluntary coiuse, with Norway expected to ban lead by 2010. In practice not much lead stabiliser is used in Scandinavia, but other parts of Europe still depend on this type of product. 

Japan banned lead based stabilisers from water pipes as long ago as 1993, replacing them by organotin, and may soon even replace existing pipes that contain lead stabilisers, as well as encouraging the voluntary phase out of lead from sewerage pipes. 

The EU put forward following key milestones as regards to control and diminishing the use of lead stabilisers in plastics by the year 2004, completion of initial risk assessment on lead stabilisers will be accomplished by 2005 15% (to reach 100 Kt), and by 2010 50% rednction target of their use (reaching 60 Kt), and by 2015, it will be 100% off for use of lead stabilisers [33]. 

---