The polymer will produce a lot of smoke during the combustion process, and the smoke produced by the combustion of some polymers is toxic. Alfa Chemistry provides low-valence transition metal additive as smoke suppressant, which is one of the ways to solve the problem of smoke suppression of polymer materials.
Some low-valent transition metal-containing additives can promote polymer crosslinking through the reductive coupling mechanism of polymer chains and play a role in smoke suppression. Typical products include phosphites and other monovalent copper clathrates, a range of low-valent transition metal carbonyls, formates and oxalates, monovalent copper halides, etc.
Copper is one of the most effective additives for PVC smoke suppression using a reductive coupling mechanism. In addition, cuprous and copper compounds can be used as weak acid catalysts to facilitate the alkylation of Friedel-Crafts reactions.
Take the smoke suppression mechanism of a series of transition metals such as oxalate and formate as smoke suppressants for PVC as an example. First, zero-valent metals are formed through reduction reactions. Cross-linking can occur in solid-state PVC below 200 °C when additives with transition metals suppress fumes through a reductive coupling mechanism of polymer chains that promote cross-linking. The equations for the reduction and coupling reactions of simple allyl halides and benzyl halides promoted by low-valent organometallic clathrates are shown in the figure below. 
Smoke suppression effect of transition metal oxides
Zhoumei Xu et al. developed a series of carbon-coated transition metal oxide particles, including Cu@C, Fe2O3@C, and Cu2O@Fe2O3@C, and studied their related smoke suppression mechanism for RPUF. In this work, the smoke suppression mechanism of metal oxides can be mainly attributed to the reductive coupling mechanism: the catalytic effect of Cu2O or Fe2O3on the coupling reaction of polyurethane molecular chains. Under this action, many degradation products are transformed into a dense and continuous carbon layer, which inhibits the heat and mass exchange process, thereby preventing the further decomposition of the internal foam structure. 
Schematic illustration for the mechanisms of smoke suppression 
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