Lead scavengers, solubility

FIGU RE 4.16 Relative solubilities of BTEX, MTBE, and the lead scavengers EDC and EDB. 

Magnesium oxide is a typical acid scavenger for chlorinated mbbers. Compounds containing zinc oxide or magnesium oxide may tend to swell upon immersion in water. These inorganic salts have some water solubility and osmotic pressure causes the vulcanizates to imbibe water to equalize pressure (8,9). As such, vulcanizates tend to swell more in fresh (distilled) water than in salt water. To minimize water swell, insoluble salts such as lead oxides can be substituted. Because of the health concerns associated with lead, there is much mbber industry interest in other acid acceptors, such as synthetic... 

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... 

Water insolubility and resistance to hydrolysis water solubility could lead to more reaction in the aqueous phase and wall fouling. Other expedients to reduce aqueous phase reactions include use of a water-soluble free-radical scavenger or a chelating agent to minimize redox reactions in the aqueous phase. (Such water-soluble chelating agents include salts of oxalic acid and ethylene diamine tetraacetic acid.)... 

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