Oxidation of ether linked thermoplastics

Studies have been made of the heat and light induced oxidation of ether linked commercial thermoplastics using a variety of analytical methods. Our studies on polyoxymethylene, polyphenylene oxide, and its blends with polystyrene are discussed here. Comparisons of heat and light stability are made with thermoplastics previously reported. Heat aging of polyoxymethylene causes a decrease in elongation and weight as well as volatile product formation and changes in the infrared spectrum indicative of chain scission. Exposure to ultraviolet light accelerates the oxidative reaction. Polyoxymethylene copolymer is more thermally stable but both polymers are rapidly degraded during light aging. Investigation of the heat and light induced oxidation of polyphenylene oxide shows that oxidation, in either case, leads to a crosslinking reaction resulting in embrittlement of the polymer. The process is difficult to retard. However, oxygen uptake results indicate that blends of polyphenylene oxide and polystyrene can be suitably stabilized against thermal oxidation. Preliminary results indicate that oxidation of these blends proceeds by a chain scission mechanism.     

Thermal oxidation and photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide)

The thermal oxidation and photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide) have been examined. Oxidation of the plastic results in the evolution of carbon dioxide, nitrogen and traces of hydrogen, the introduction of considerable crosslinking, and increased absorption in the hydroxyl and carbonyl regions of the infrared spectrum. A free-radical oxidation mechanism is postulated.     

Thermal oxidation of thermoplastics

Commercial thermoplastics may be classified by the types of rate curves obtained on thermal oxidation. The rate of oxidation of an acrylonitrile-butadiene-styrene plastic is affected by sample thickness and appears to be diffusion-controlled. Pigmentation increases the reaction rate of this compound in all the cases studied because of the catalytic effect of the metals present. Carbon black adversely affects the oxidation rate of stabilized polypropylene. The acetal plastics decompose under oxidative condition at 140°C. Of the thermoplastics examined, polytetrafluoroethylene, fluorinated ethyleneproplyne copolymer, poly(vinylidene fluoride), poly(ethylene terephthalate), and polysulfone are the most resistant to thermal oxidation at 140°C.