Oxidative degradation chain scission

Finally, mention must be made of a study on PS-PP blends in which PP was a minority component (20wt%). When the blends were yirradiated at low doses (<70kGy) [95], EPR data relating to the concentration of trapped radicals indicated that in these systems the PP was protected against a strong oxidative degradation (chain scission). 

Above 420 C, methane and carbon monoxide are produced from the degraded material but not from the undamaged sample. Carbon dioxide yield is also much higher from the degraded material, and the yield of monomer is significantly reduced. The results are consistent with formation of free radicals by mechanical action, followed by oxidation and chain scission reactions. The extent of the effect is proportional to the amount of mechanical degradation, and that is responsible for our poor reproducibility. 

Corrosive wear is due to the gradual degradation of the plastic surface through oxidation and chain scission. The embrittled layer is removed quickly at the wear interface. Unlike metals, hydrolytically induced corrosive wear is not a problem in plastics. 

Nuclear magnetic resonance (NMR) spectroscopy is one of the most useful methods for the study of degradation (chain scission and crosslinking) and photo-oxidative degradation (disappearance and the formation of new groups which contain protons deutrons carbon C isotopes and fluors The theory of NMR spectroscopy of polymers and experimental methods have been described in many excellent monographs [5,6,295,608,1206,1223, 1327,1699,1885,2064,2111,2221]. 

Exposure of poly(alkylene oxide)s to high-energy radiation, such as electrons from electron beam or gamma radiation from cobalt-60 sources, will alter the structure of the polymers. The main structure alterations involved are degradation, chain scission, and crosslinking. The relative importance of these alteration processes depends on a variety of factors, such as physical state (solid or solution state), dosage, oxygen concentration, and water or moisture content. 

The natural aging of UHMWPE leads to oxidation and chain scission provoking embrittlement and degradation of its mechanical properties. The chain scission process allows crystal growth to occur, increasing the degree of crystallinity of aged UHMWPE [90]. 

The effect of oxidative irradiation on mechanical properties on the foams of E-plastomers has been investigated. In this study, stress relaxation and dynamic rheological experiments are used to probe the effects of oxidative irradiation on the stmcture and final properties of these polymeric foams. Experiments conducted on irradiated E-plastomer (octene comonomer) foams of two different densities reveal significantly different behavior. Gamma irradiation of the lighter foam causes stmctural degradation due to chain scission reactions. This is manifested in faster stress-relaxation rates and lower values of elastic modulus and gel fraction in the irradiated samples. The incorporation of O2 into the polymer backbone, verified by IR analysis, conftrms the hypothesis of... 

When this decomposition occurs the degradation does not give high monomer yields (compared with un-zipping) the products tend to be low MW products. The chain scission and propagation is inhibited by free radical traps (see anti-oxidants). 

In the supercritical wet oxidation, the concentration of oxygen in the reactive system is high and the contact between the reactants is more intimate, thus making chain scission reactions much more active. This appears to be a major reason for more rapid degradation of PVC in an oxygen environment and production of monomers and dimers. 

The effect of photodynamic degradation on the viscosity of DNA132 was shown to be the result initially of single chain breaks, followed eventually by double chain scission this is in agreement with the idea that guanine oxidation is the cause of the viscosity change. 

Other additives such as waxes and polyethylene glycols melt at relatively low tem-peratnres and vaporize over a more narrow temperatnre range. Oxidation of the binder canses the temperature to increase more rapidly. For the thermolysis of polyethylene glycol (PEG) in air, decomposition occnrs by the mechanism of chain scission and oxidative degradation. 

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