Brief introduction of Lead stabilizer
“Like tin and iron, lead is among the longest-known metals, and was made mention of already in the Old Testament”, the famous chemist Dr J. Jakob Berzelius, a professor at the Royal Swedish Academy of Sciences, wrote in his chemistry textbook in 1824.
Lead is easy to mine and both pure lead and lead alloys have favourable mechanical properties. In addition, lead can be formed into many different compounds and has therefore always been extensively used across a wide range of applications.
For example, it is a well-known fact that lead compounds are used as pigments, such as minium, white lead and patent yellow or lead chromates in a variety of shades from yellow to fiery red.
Lead and PVC
Lead compounds were among the first materials to be used as Stabilizers to prevent the decomposition of PVC.
A Union Carbide patent from 1934 describes the use of lead oxide as a heat stabilizer for vinyl resin enamels.
Only compounds derived from bivalent lead are relevant in practice, with basic primary lead stabilizers and lead soaps being the most commonly used PVC Stabilizers.
Typical applications of lead Stabilizers include recyclable PVC profiles, pipes and cables with a long service life.
Primary lead Stabilizers are generally used in conjunction with lead soaps, calcium soaps, lubricants and antioxidants.
•Excellent long-term heat stability
•Pigmenting effect of basic primary lead Stabilizers beneficial in light coloured applications
•Low solubility in water, no leaking into the environment
•No odour during processing and in the final product
•No detrimental effects on the Vicat softening temperature of rigid PVC
•Lead compounds in biologically available form are chronically toxic (as explained in the notes on precautions in handling lead products).
•Discolouration in contact with sulphur-containing compounds (sulphur staining)
Principle of action
Basic lead compounds are excellent HCl scavengers and are able to bind substantial amounts of hydrogen chloride during the decomposition of PVC. The resulting lead chloride is very stable, insoluble in water and does not encourage the decomposition of PVC.