Degradation of Polymers: Chemical
Course Module for ME 5XX - The Degradation of Polymers
Types of Degradation - Chemical
The chemical degradation of polymers is really an encompassing topic that can refer to thermal degradation or oxidative degradation as well. The basic issue in reference to chemical degradation is solvolysis.
Solvolysis is concerned with the breaking of C-X bonds were X is a non-carbon atom, mostly O, N, P, S, Si, or a halogen. Solvolysis agents, such as water, alcohols, ammonia, etc., rupture the main chain of the polymer and break it down. A common solvolysis reaction is hydrolysis, in which one of the degradation products is water. Water soluble polymers succumb easily to hydrolysis, while water insoluble polymers are degraded only on the surface of the specimen.
Different kinds of chemical agents can attack polymers. Those with the most practical application to study from a corrosive point of view are atmospheric pollutants. Other agents that can degrade polymers include ozone, acids, alkalies, and halogens.
Atmospheric pollutants, such as nitrogen dioxide (NO2) and sulfur dioxide (SO2), nearly always react with polymers in the presence of air in this practical application of outdoor exposure. Simultaneous scission and crosslinking occurs when unsaturated polymers with accessible linear sections, where the rate of raection is dependent upon the temperature and partial pressure of oxygen. A mechanism is set forth for the interaction between polyethelene and NO2 by Schnabel, with a similar proposal for SO2. Ozone is another atmospheric pollutant that can degrade polymers, notably natural rubber, by the oxidation of its double bonds. Car tires usually have antiozonants that saturate the rubber in order to inhibit premature breakdown.
This page prepared by Kimberly Farrell for Professor Sisson of WPI, for use in ME XXX, Corrosion and assorted fun times.