DETERIORATION OF ORGANIC POLYMERS 



1087 



Oxygen 



The degradative agent of most general attack and of greatest economic 

 importance is oxygen, which is capable sooner or later of bringing about 

 change in almost any organic material. Even disregarding the oxidation of 

 dead organic matter in nature, which is aided by bacteria and fungi, one 

 finds many examples of oxidation familiar to the layman. The development 

 of rancidity in foods is a common one. The production of sludge-forming acids 

 in engine oils, and the spontaneous combustion of rags soaked with hnseed 

 oil are others. The loss of strength of cotton cloth after a few years of service 

 is very largely due to oxidation although mildew or other fungus attack 

 may have played a part depending on circumstances.^^- ^^' ^^ That changes 



lig. 9 — A Ldpc-wiappcu splice after 6-weeks of exposure outdoors. An example of the 

 acceleration of the ozone reaction by heat. 



in polymers are indeed the result of oxidation is easily demonstrated in the 

 laboratory by exposing samples to heat or to ultraviolet light in the presence 

 and in the absence of oxygen The results of such an experiment are shown 

 in Table I, in which solution viscosity is used as a measure of molecular 

 weight. It is seen that in nitrogen neither heat nor light brought about any 

 serious loss of molecular weight. 



Similar work has been reported with natural rubber with the conclusion 

 that in an inert atmosphere rubber would retain its original properties 

 "for at least thirty years". ^^ 



Gross Effects of Oxidation of Polymers 



Severe oxidation of organic polymers results in the drastic changes men- 

 tioned in the introduction and is easily detected. Photo-oxidation of poly- 



