Molybdenum Compound

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 molybdenum compounds as smoke suppressants, which is one of the more realistic ways to solve the problem of smoke suppression of polymer materials.

Typical Product

Molybdenum compounds are the best smoke suppressants discovered so far. The main varieties are molybdenum trioxide, ammonium octamolybdate, calcium molybdate, ammonium phosphomolybdate, calcium phosphomolybdate, zinc molybdate, etc.

Because molybdenum compounds are very expensive, which restricts their application in PVC formulations, they are generally compounded with other oxides, such as MoO₃-Cu₂O, MoO₃-Fe₂O₃, MoO₃-SnO₂, etc. These compounds can not only reduce costs, but can also take advantage of synergistic effects between components to improve smoke suppression and flame retardancy.

Smoke Suppression Mechanism

The molybdenum in molybdenum trioxide and ammonium molybdenum is hexavalent, and its oxidation state and coordination number can be easily changed, which makes molybdenum trioxide and ammonium molybdenum possible flame retardants and smoke suppressants in the solid phase instead of gas phase. The smoke suppression mechanism of molybdenum compounds is likely to be through the Lewis acid (LA) mechanism to promote the formation of a carbon layer, thereby reducing the amount of smoke. However, the exact smoke suppression mechanism of molybdenum compounds is still uncertain.

Take the smoke suppression effect of MoO₃ on PVC as an example. The smoke suppression effect of MoO₃ on PVC is believed to be mainly carried out in the condensed phase, and the mechanism is shown in the following figure. Previous studies have concluded that the smoke suppression effect of hexavalent molybdenum may be due to the catalytic effect of the following three reactions:

(1) PVC dehydrochlorides to form trans polyenoid

(2) Isomerization of cis polyene to form trans polyenoid

(3) Polyenes are crosslinked by Friedel-Crafts alkylation or Diels-Alder cyclization. Benzene production can be reduced when PVC is cracked to form large amounts of trans-polyenes.

Smoke suppression effect of MoO₃ on PVC [1]

Research Information

Synergistic smoke suppression of ferrocene and MoS₂

Keqing Zhou et al. investigated the synergistic effects of ferrocene and MoS₂ on the thermal stability, fire resistance, and smoke suppression properties of PS composites. In this work, the significant improvement in thermal stability, fire resistance and smoke suppression is mainly attributed to the good dispersion of the modified MoS₂ nanosheets, the synergistic effect between ferrocene and MoS₂ nanosheets, the physical barrier of MoS₂ effect. The presence of nanosheets and ferrocene and MoS₂ can simultaneously promote the formation of carbon. [2]

Carbon monoxide and SPR curves of PS composite samples [2]

References

1. Jianjun Li, et al. (2019). "7. The mechanism of smoke suppression". Theory of Flame Retardation of Polymeric Materials, pp. 195-210.
2. Keqing Zhou, et al. (2014). "Synergetic effect of ferrocene and MoS₂ in polystyrene composites with enhanced thermal stability, flame retardant and smoke suppression properties," RSC Advances 4, 13205-13214.