Oxidation rubber

Thermoanalytical techniques such as differential scanning calorimetry (DSC) and thermogravi-metric analysis (TGA) have also been widely used to study rubber oxidation [24—27]. The oxidative stability of mbbers and the effectiveness of various antioxidants can be evaluated with DSC based on the heat change (oxidation exotherm) during oxidation, the activation energy of oxidation, the isothermal induction time, the onset temperamre of oxidation, and the oxidation peak temperature. 

Protective Systems. As in the case of sulfur vulcanization, there have been many research workers in the field of natural rubber oxidation and its protection (39,40). The principal problem has always been to find an antioxidant that provides protection against flex-cracking, and yet does not stain. None has been found as of the mid-1990s, hence it is best to categorize the various types according to their capabilities. 

See Nitric acid Lead-containing rubber Oxidants... 

Unsaturated and Vulcanized Rubbers. Oxidation occurs most readily at polymers with structural double bonds, such as natural rubber, polybutadiene, or polyisoprene. Aromatic amines and sterically hindered phenols are effective antioxidants. From the rubber antioxidants, 96.8 million pounds were amines, and 20 million pounds were phenols. Amines act also as antiozonants whereas phenols are not effective. Furukawa shows that amines have a lower oxidation potential which is a prerequisite for antiozonant action. 

Later the mechanism of the rubber oxidation was studied extensively by Bolland and coworkers (1946-1950), who mainly used model substances. In his first publication Bolland proposed the following mechanism for the propagation reaction ... 

Rubber oxidation products able to undergo redox and/or condensation reactions must be considered in particular as reactive partners with antiozonant species. Analogies in the reactivity with low molecular weight organics are mostly considered. Limits controlling polymer-analogous reactions cannot however, be omitted in particular restrictions of the reactivity by physical environmental factors in the solid matrix. 

LP-lOO, 200, 300, 400. [ e-Picher] Lead dioxide catalyst, curing agent for polysulfide, butyl and polyisoprene rubber oxidizer for mfg. of dyes. 

Nitrodiphenylamine Octylphenol o-Phenylphenol Squalene intermediate, rubber oxidants Paraldehyde... 

Selecting the correct combination of antioxidants is specific to the elastomer polymer type as well as the compound formulation and the end use application. It is important to note that many of these materials may be considered toxic or hazardous in nature. Chemical specific Material Safety Data Sheets (MSDS) should be consulted for safe handling practices. Particular attention should be given to the proper selection and use of personal protective equipment, including proper ventilation and/or the use of respiratory protection. The MSDS will also provide information on how to handle spills and proper disposal procedures. Disposal methods should not be overlooked since these chemicals are all regulated, and hence waste disposal must conform to EPA and local disposal regulations. Refer to Rubber Oxidation. (Source Handbook of Polymer Science and Technology Volume 2 - Performance Properties of Plastics and Elastomers, N. P. Cheremisinoff - editor, Marcel Dekker Inc., New York, 1989). 

Polymers related to natural rubber include ebonite, chlorinated rubber, oxidized rubber, cyclized rubber, and gutta-percha and balata. 

The oxidation of rubbers is substantially accelerated by salts of metals of variable valence (iron, copper, manganese, cobalt, etc.). Figure 169 presents the kinetic oxidation curves illustrating ttie premise stated [23]. Homogeneous catalysis of the chain reaction of rubber oxidation occurs as a result of the reduction of tiie activation energy of initiation, as well as the decomposition of stable peroxide. 

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