Organic materials, oxidative stability

Oxygen has nevertheless been used successfully during thermal pretreatment of biological sample matrices to both facilitate decomposition of organic material and stabilize the analyte (aluminum, cadmium, lead, selenium) in oxide format active sites. However, the pretreatment temperature must be accurately controlled to prevent oxidation of graphite. 

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). 

In thick samples, a boron oxide/boron carbide crust has been detected on the surface of the polymer. This inorganic surface layer has a shielding effect on the inner polymer layers, further enhancing the thermal stability of the material. Poly(m-carborane-siloxane)s have therefore been considered as surface coatings for organic materials, providing protection from erosion effects. 

It is a very powerful oxidant, but of low stability, which reacts explosively with organic materials [1] such combinations should be avoided [2],... 

AN is a very stable materia even at 150° as indicated by the Vacuum Stability Test at that temp. It can be heated at 100° for 100 days without appreciable decompn. This does not appear to begin until the compd melts. At 220° there are formed nitrous oxide, water and nitrogen, and this reaction is used for the manuf of nitrous oxide. If an organic material such as cellulose is present, decompn of the mixt begins at 100° and is pronounced at 120°. Admixture with TNT has little, if any, effect on the stability of AN at temps lower than 120°... 

A minor explosion in the use of gaseous acetyl hypofluorite was caused by inadvertent contact of the gas inlet tube with a cooling bath, which condensed liquid hypofluorite which subsequently exploded on contact with organic material or air [ 1 ]. More detail on the isolation of this compound of limited stability, particularly in the liquid phase, is given [2]. See other ACYL HYPOHALITES, OXIDANTS... 

---