Ozone discolorations

Blends of diene and backbone-saturated mbbers are frequently used in appHcations where discoloration by chemical antiozonants caimot be tolerated, yet where cost is stiH a primary consideration (eg, white sidewalls of tires). Disadvantages are that physical properties have to be compromised and the two mbbers usually differ greatly in their rates of vulcanization. Usually, at least a 25% replacement by the ozone-resistant mbber is needed for an appreciable enhancement in ozone protection (6). 

Materials The damage that air pollutants can do to some materials is well known ozone in photochemical smog cracks rubber, weakens fabrics, and fades dyes hydrogen sulfide tarnishes silver smoke dirties laundry acid aerosols ruin nylon hose. Among the most important effects are discoloration, corrosion, the soiling of goods, and impairment of visibility. 

The first level of treatment, with sand filters and chlorination to remove suspended matters and disinfection of pathogens, may be good enough for the low-cost water. The removal of discoloration and bad smell is accomplished by activated charcoal absorption. Ozone and ultraviolet treatments are much more expensive for the removal of microbes and organic matter, and should be considered only when necessary to solve a technical problem, or to satisfy an advertisement need. Reverse osmosis is the most effective method used to recover clean water from brackish water, and to remove inorganic minerals such as sodium, copper, iron, and zinc. The removal of calcium and magnesium ions can be accomplished by the method of ion exchange with sodium, which would also increase the sodium concentration, and could cause objections. Different levels of treatment require a variety of costs, and can produce different levels of customer satisfaction. 

One factor contributing to crop losses caused by ozone is the development of abnormal pigments which are viewed as discolored areas on foliage of ozone-sensitive cultivars. Such discoloration is esthetically unacceptable on leafy food crops and probably causes a reduction in the nutritional value of all foliar components used for food and feed. Biochemical and physiological reactions responsible for ozone-induced discolorations have not... 

Ozone stimulates the synthesis of anthocyanins 2, caffeoyl derivatives ( ), and total phenols ( ) in plant foliage. It induces necrotic lesions and localized discolored areas of yellow, red or brown on foliage of plants of many species. The size and number of lesions and the intensity of color are related to plant cultivar, maturity of foliage, cultural conditions, concentration of ozone and duration of time after exposure. 

Synthetic operations involving ozonolysis lead to formation of aldehydes, ketones or carboxylic acids, as shown in Scheme 16, or to various peroxide compounds, as depicted in Scheme 7 (Section V.B.5), depending on the nature of the R to R substituents and the prevalent conditions of reaction no effort is usually made to isolate either type of ozonide, but only the final products. This notwithstanding, intermediates 276 and 278 are prone to qualitative, quantitative and structural analysis. The appearance of a red-brown discoloration during ozonization of an olefin below — 180°C was postulated as due to formation of an olefin-ozone complex, in analogy to the jr-complexes formed with aromatic compounds however, this contention was contested (see also Section V1I.C.2). 

One of the earliest indications of ozone injury on several plant species is an upper surface discoloration with a waxy appearance. This symptom often disappears completely a few hours after exposure is terminated. High dosages of ozone cause permanent necrotic lesions on susceptible leaf tissue. Permeability of cell membranes is apparently disrupted, and cell contents are allowed to leak into the intercellular spaces producing a water-soaked appearance. Upon drying, the tissue will totally collapse and turn white or various shades of brown. Lesions which extend through the entire thickness of the leaf are commonly referred to as bifacial... 

Almost all commercial polymers are susceptible to the attack of oxygen or traces of ozone in the atmosphere. Oxidation is the major cause of their discoloration, impairment of mechanical properties, and subsequent failure. It is accelerated by heat or sunlight. Antioxidants and antiozonants are added to the polymers to extend their useful temperature ranges and service lives and to allow outdoor application. Their 1967 consumption for various polymers is given in Table II. 

PVA oxidation has been studied by several groups, and it has been observed that the degree of polymerization decreases when PVA is oxidized with hydrochloric acid (I), potassium permanganate (2-4) potassium bichromate (3,5,6), hydrogen peroxide (7,8), periodic acid, and ozone (9). However, only a limited number of studies have been performed on the oxidation of PVA by molecular oxygen. Shiraishi and Matsumoto (10) observed that it is oxidized by molecular oxygen in alkaline aqueous solution, which causes discoloration and a decrease in... 

Body-centered tetragonal crystals, sublimes at 120°. d 5,55. Very sensitive to moisture, discolors quickly in moist air. Violent reaction with water forming BiFa and ozone. Reids with liqnid petrolatum above 50. ... 

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