Metal smoke retarders for poly(vinyl chloride)

This article provides an overview of smoke‐;retarding rigid PVC using metal compounds. It shows that a large variety of metals from throughout the Periodic Table can form compounds which are smoke retarders for PVC. These metals act to change the thermal degradation pattern of the PVC and promote the formation of char. Most of the active metals are transition metals, although many of the post‐;transition metals and a few of the pretransition metals also are active. The activity of metal smoke retarders primarily is determined by the choice of metal and the environment surrounding the metal ion. Since most of the effective smoke retarders are transition metal compounds, the ability to undergo redox reactions may be important. The initial oxidation state, however, appears to be relatively unimportant. Particle and dispersion characteristics are secondary factors. Increasing the concentration of a smoke retarder can increase, decrease, or have no effect on its effectiveness. It is impossible to predict the influence of a tin stabilizer on a metal smoke retarder, but for many smoke retarders there is little effect. Transition metal compounds are the most effective metal smoke retarders. Smoke‐;reducing synergisms result when molybdenum trioxide is combined with certain compounds of copper, iron, and tin.