Oxidation aging

Some biphenylene end-capped polyquiaolines have been used to make carbon-fiber rekiforced composites (102). However, properties of these composites dropped off significantly when oxidatively aged for 50—100 h at 316°C. 

FIGURE 34.22 Log (strain ratio) versus log (modulus) for field and oven-aged SUV/Minivan-A tires. Both sets are linear indicating oxidative aging, but the slopes are different indicating a change in composition of the wedge rubber. 

The effectiveness of tea polyphenols as antioxidants in elastomeric mixes was evaluated and comparison was made with standard styrenated phenol-based antioxidant [45]. The data showed that thermal and oxidative aging resistance was comparable for both natural and synthetic antioxidants. 

Recently, these researchers, again using a combination of TGA and TGA-MS, published further studies on the thermo-oxidative ageing of POM, including determining various activation energies [108]. 

A radical which can exist in the free or uncombined state. Such radicals are extremely reactive with themselves and with other neighbouring molecules. Free radicals are considered to take part in many reactions of importance to the rubber industry - vulcanisation, oxidation, ageing, polymerisation, etc. 

Oxidative ageing of rubbers is limited by the rate of diffusion of oxygen into the rubber product and is usually confined to the outer 3 mm. Antioxidants are used to protect rubbers from the effects of thermal oxidation and the vast majority of compounds will contain one or more. Peroxide vulcanisates are usually protected with dihydroquinolines. Other antioxidants react adversely with the peroxide inhibiting the crosslinking reaction. 

Ford, R.G., Bertsch, P.M., Farley, K.J. 1997. Changes in transition and heavy metal partitioning during hydrous iron oxide aging. Environmental Science and Technology, 31, 2028-2033. 

SEES is chosen for a better oxidation, ageing and weathering resistance a broader rigidity range and better retention of properties when the temperatures rise above the glass transition of polystyrene. 

Amorphous isoprene largely 1,4 isomer good chemical inertness, low gas permeability, high viscoelastic response to stresses, less sensitive to oxidative aging than most isoprene rubbers better ozone stability than NR good solvent resistance... 

Butyl rubber is produced by a process in which isobutylene is copolymerized with a small amount of isoprene using aluminum chloride catalyst at temperatures around — 150° F. (20). The isoprene is used to provide some unsaturation, yielding a product that can be vulcanized (43). Vulcanized Butyl rubber is characterized by high tensile strength and excellent flex resistance furthermore, as a result of its low residual unsaturation (only 1 to 2% of that of natural rubber) it has outstanding resistance to oxidative aging and low air permeability. These properties combine to make it an ideal material for automobile inner tubes (3), and Butyl rubber has continued to be preferred over natural rubber for this application, even when the latter has been available in adequate supply. 

IV. CHANGES IN THE CHEMICAL COMPOSITION OF SHERRY WINES DURING THE BIOLOGICAL AND OXIDATIVE AGING... 

Some of the most important chemical changes that occur during the biological and /or oxidative aging of sherry wines are reviewed below. 

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