Discolored Part

Oxidation. AH polyamides are susceptible to oxidation. This involves the initial formation of a free radical on the carbon alpha to the NH group, which reacts to form a peroxy radical with subsequent chain reactions leading to chain scission and yellowing. As soon as molten nylon is exposed to air it starts to discolor and continues to oxidize until it is cooled to below 60°C. It is important, therefore, to minimize the exposure of hot nylon to air to avoid discoloration or loss of molecular weight. Similarly, nylon parts exposed to high temperature in air lose their properties with time as a result of oxidation. This process can be minimized by using material containing stabilizer additives. 

Cla.riGers. Pool water may occasionally contain metallic impurities such as copper, iron, or manganese which enter the pool with the makeup water or by corrosion of metallic parts in the circulation system. These dissolved metals can discolor the water and cause stains. Chlorine oxidizes soluble Fe and to the highly insoluble Fe(OH)3 and MnO which can be removed by filtration. Water-soluble, high molecular weight polymers can be... 

When the highest resistance to corrosion and solvent fumes is needed, catalyzed paints are the answer. These come in two parts a clear or colored base finish and a catalyst. Since their pot life is limited (typically eight hours), they must be mixed just prior to use. Brochures with information on their chemical resistance can be obtained from companies that sell industrial finishes. Since the resistance to different chemicals varies from brand to brand, a planner should study several types to find one that will best suit the particular application. These finishes are of the high gloss type. For highest chemical resistance to fumes, a coat of clear finish should be applied on top of the colored one. While the vehicle in the finish is very resistant, the pigments may not be and therefore could discolor. 

Prior to semi-preparative HPLC, matrix compounds may be present that require a purification step. In some cases, high sugar or salt contents and also pectic-like substances may preclude concentration and isolation precipitation using 2-propanol or ethanol is then required. Subsequent filtration will yield a pigment solution and a colorless filtrate that may be rinsed with a mixture of one part water and two parts alcohol for complete discoloration. The filtrate volume will be reduced under vacuum before further purification. Usually, precipitation precedes desalting. 

Other antibiotics still require freeze drying, e. g. Na-Cephalotin (Na-CET). Takeda [ 1.32] showed, that thermal treatment of Na-CET was not sufficient to produce pure crystalline Na-CET, as the amorphous fraction discolors during storage and must be avoided. Takeda described the production of pure crystalline Na-CET by adding microcrystals of Na-CET to a saturated solution of Na-CET. If this mixture was frozen and freeze dried, then no amorphous or quasi-crystalline were found. Koyama et al. [3.35] described, that after thermal treatment for 24 h some parts remained incompletely crystallized. After adding 5 % (w/w) isopropylalcohol, a thermal treatment of 1 h was sufficient. Furthermore, the product could be dried at a higher pressure. Thus the drying time could be reduced and 100 % of the product could be used. 

Rotary or other distillation equipment with metal parts should not be used in concentrating the reaction mixture because not only will the corrosive vapors damage Che equipment, but also the resulting metal salts will discolor and partially decompose the product. The solution should not be heated any longer than is necessary to concentrate it excessive heading gives a dark-colored product. 

Hoang, E.M., Liauw, C.M., Allen, N.S., Pontan, E., and Lafuente, P. Effect of Metal Stearate Antacid on the Melt StahiUzation Performance of PhenoUc/Phosphite Antioxidants in Metallocene LLDPE. Part 2 Discoloration, /. Vinyl Addit. Technol, 10, 3, 144 (2004)... 

Symptoms New shoots turn yellow, wilt and die back. The inner bark on infected twigs may show black or reddish brown discoloration. Gummy cankers form on trunks and branches and increase in size until they girdle and kill the affected part... 

Symptoms Onions appear healthy when growing, but become soft after 8-12 weeks in store. Brown sunken lesions and a fluffy gray mold develop in the neck. The upper part of the bulb is soft when pressed, with brownish-black discoloration under the dry outer leaves. The fungus spreads downward through the bulb, which in severe cases may decay completely. 

During the early part of the distillation when a substantial amount of benzyl bromide is present, the still pot should not be heated above 140° to avoid serious discoloration. When the bulk of the benzyl bromide has been removed, the temperature of the still pot may be raised to 150-160° to facilitate distillation of the product. 

After stating that the red color of the blood might be due to the presence of iron, Macquer added An observation from practical medicine agrees well with this view namely that mineral water containing iron, iron itself, and all preparations of this metal, of which at least a considerable part passes into the blood, as the experiments of M. Menghini have shown, are the best remedy one can use for chlorosis, in which disease the red part of the blood is almost entirely decolorized or discolored (198). Macquer realized that the iron was not itself the coloring matter of the blood but perhaps that which binds this pigment and determines its action (198). 

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