Deterioration of Organic Polymers 



By B. S. BIGGS 



(Manuscript Received July 9, 1951) 



This paper is a general review of deterioration processes in polymers. It is 

 pointed out that changes in properties with aging are usually the result of chemi- 

 cal reaction with components of the atmosphere. The mechanisms of these reac- 

 tions and some methods of preventing or retarding them are discussed. 



ORGANIC compounds v^^hich have enough inherent strength to be 

 used as structural materials — e.g. rubbers, plastics, textiles, and sur- 

 face coatings — belong to a class called polymers. The deterioration of these 

 materials in service is a serious problem, probably equal in dollar value to 

 corrosion of metals, and one or another aspect of it has been under study in 

 the Laboratories for years.^ Everyone is familiar with the tendering of 

 cotton cloth and with the loss of strength of rubber with time, but except 

 among people who work with them there is not a wide recognition of the 

 fact that plastics also suffer extensive damage from the weather. This is 

 probably because organic corrosion is usually not visible in its early stages 

 even though deep-seated changes may be taking place throughout the body 

 of the material. In its advanced state, however, such deterioration is easily 

 observable, manifesting itself in loss of strength, erosion, warpage, develop- 

 ment of cracks, loss of transparency, or in other ways depending on the 

 material and the application. These changes are of obvious importance in 

 most engineering uses, particularly in the Bell System where apparatus fre- 

 quently is expected to last thirty or forty years, and it is therefore desirable 

 that they be understood. It is the purpose of this article to review in a rather 

 general way the causes and mechanisms of deterioration. 



Even casual consideration reveals that both chemical and physical changes 

 may occur. The loss of plasticizer from a plastic, for example, can induce 

 warping and embrittlement without a change having occurred in the chemi- 

 cal nature of any of the component molecules. Alternate periods of high and 

 low humidity can cause swelling and shrinking in such hydrophilic materials 

 as nylon and cellulose acetate and if stresses are present this can result in 

 permanent distortion^ (Fig. 1). The swelling of rubber in contact with oils is 

 another example of physical change (Fig. 2). These phenomena are generally 

 well understood and are taken into account in careful engineering. The effect 

 of chemical changes can be even more striking as illustrated in Figs. 3, 4 

 and 5, but their mechanisms are more obscure and require more detailed 

 discussion. 



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