Organotin compounds have long been known in the PVC industry for their excellent performance properties in almost every application. Over the past several years, a wide variety of health and environmental studies have been conducted which demonstrate the safe use of these performance chemicals as PVC heat stabilizers. This paper introduces the "risk equation" and then applies this equation to the foreseeable exposure risks involved with the use of organotin stabilizers during PVC processing. Further, migration of organotin species from PVC end-use articles is discussed with comparison to established long-term no-effect levels for these chemicals. The environmental fate of organotin compounds and their effects on some species of microorganisms is also addressed. The risk equation is used to fully evaluate all potential hazards to provide a fully informed risk assessment for the use of organotin stabilizers in PVC.

Halogenated polymers, particularly poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDE), require the use of heat stabilizers for effective processing. A variety of chemical classes are effective commercial heat stabilizers since they prevent the catastrophic degradation of these polymers at normal processing temperatures. The most effective class of heat stabilizers are the organotin mercaptides which can provide effective stabilization at dosages of the order of 1% or less of the PVC. Mixed metal products, consisting of combinations of calcium and zinc or barium, calcium and zinc soaps are used extensively in many flexible PVC applications. Heat stabilizers based on lead soaps and salts have been used commercially in PVC since the 1930s. During the past decade, completely new heat stabilizer technologies, based on organic compounds, have been introduced to the market for rigid PVC processing. All heat stabilizers must provide several functions to stabilize PVC. They must neutralize hydrogen chloride, react with “defect sites” on the polymer to replace weakened carbon–chlorine bonds, prevent autoxidation effects, and disrupt conjugated polyenes on polymer. Reactive mechanisms for the major classes of technologies are reviewed. The heat stabilizers must be very cost‐effective in a highly competitive marketplace. Several suppliers and their major products are highlighted. Health and safety concerns for the major classes of heat stabilizers are also presented.

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometallic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinylidene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. PVC is the most important class of halogenated polymers requiring these chemical additives. In normal operations, PVC resin is intimately mixed with the desired ingredients under high intensity shear mixing conditions to result in a homogeneous dry powder compound. The heat stabilizers can be either liquids or powders and are added early in the blending cycle to afford stabilizing action during this operation. Preheating the resin to about the glass‐transition temperature facilitates the adsorption of the liquid additives giving the final compound better powder flow properties and decreasing the bulk density. Post‐compounding operations, eg, extrusion pelletizing, can increase the overall heat history of the polymer, thus necessitating slightly higher levels of heat stabilizers to compensate for this. Organotin‐based heat stabilizers are the most efficient and universally used PVC stabilizers. These are all derivatives of tetravalent tin. The second most widely used class of stabilizers are the mixed metal combinations. These products predominate in the flexible PVC applications in the United States. The commercially important alkali and alkaline‐earth metals used in these stabilizer systems are based on the salts and soaps of calcium, zinc, magnesium, barium, and cadmium. Other organic compounds, such as phosphites, epoxides, polyols, and β ‐diketones, can also be added to enhance the performance further. Antimony mercaptan stabilizers are also used.

Halogenated polymers, particularly poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDE), require the use of heat stabilizers for effective processing. A variety of chemical classes are effective commercial heat stabilizers since they prevent the catastrophic degradation of these polymers at normal processing temperatures. The most effective class of heat stabilizers are the organotin mercaptides which can provide effective stabilization at dosages of the order of 1% or less of the PVC. Mixed metal products, consisting of combinations of calcium and zinc or barium, calcium and zinc soaps are used extensively in many flexible PVC applications. Heat stabilizers based on lead soaps and salts have been used commercially in PVC since the 1930s. Within the past few years. completely new heat stabilizer technologies, based on new organic compounds, have been introduced to the market for rigid PVC processing. All heat stabilizers must provide several functions to stabilize PVC. They must neutralize hydrogen chloride, react with “defect sites” on the polymer to replace weakened carbon–chlorine bonds, prevent autoxidation effects, and disrupt conjugated polyenes on polymer. Reactive mechanisms for the major classes of technologies are reviewed. The heat stabilizers must be very cost‐effective in a highly competitive marketplace. Several suppliers and their major products are highlighted. Health and safety concerns for the major classes of heat stabilizers are also presented.