Litharge Curing System

Stearic acid and stearates may also be used as release agents, but NOT with a litharge cure system as scorching occurs and a short induction time during curing. Zinc stearates should be avoided in heat-resistant compounds as zinc chloride forms and lead to dehydro-halogenation of the polymer upon aging, or exposure to weather. 

In this rubber, the curing system involves magnesia, litharge, or both, or an epoxy resin. Another alternative cure system is tri-basic lead maleate with wood rosin (organic cure). 

Room temperature curing systems such as unsaturated polyesters and epoxies are frequently used to cement threaded bushings into wheels. Inorganic materials such as litharge and sulfur cements and low melting metals are used for anchoring and bonding operations. 

For optimum resistance to hot water and superheated steam, red lead (Pb304) or litharge (PbO) will perform better than zinc oxide (in curing systems in which the presence of lead is acceptable) because lead halides are insoluble in water and therefore inhibit water adsorption. Allowance may need to be made, especially in chlorobutyl compounds, for the lead oxides being less cure-active than zinc oxide. 

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