PVC stabilization

Halogenated polymers, and polyvinyl chloride (PVC) in particular, are so special that they deserve to be treated separately from other polymers. With annual worldwide production exceeding 40 million tonnes, PVC is today one of the most widely used and versatile polymers to be found in every aspect of everyday life. Yet PVC is also the most difficult polymer to process, and particularly difficult to stabilize due to the complex nature of its degradation processes. Stabilization of this unique polymer has traditionally been more of an art than a science, and is based on the concept of pseudo-empirical formulation with other additives required for processing. Given the diversity of PVC applications, the stabilizers used are numerous, and their choice depends as much on the processing method envisaged as on the final application. Changes in regulations, particularly at European level, have contributed considerably to the diversification of PVC stabilizers.

The mechanisms of PVC degradation are still the subject of controversy, and the literature continues to see an increasing number of publications. This article presents the main stages generally recognized by specialists, covering the structural defects responsible for PVC instability, the autocatalytic aspect of dehydrochlorination and the radical aspect of thermooxidation.

The choice of the various major families of PVC stabilizers takes into account not only the technical aspects of application, but also the advantages and disadvantages of each technology in terms of application and regulations. Each family of stabilizers has its own mechanism of action, and it is not possible to differentiate PVC stabilization from its complete formulation. Costabilizers and other additives affect PVC stabilization at dosages that are relevant to the material's application and service life. The evolution of regulations on chemical products is leading to the gradual disappearance of certain technologies and threatening others. Faced with the considerable economic impact of banning stabilizers now considered toxic, the search for stabilizers containing no heavy metals, or in other words all-organic stabilizers, continues to drive industrial and university research laboratories.