Processing issues with colorants

In many cases where color differences exist, it may be necessary to evaluate the magnitude and the nature of the color shift. The use of delta E value alone will not provide any diree-tional color information. But information such as hue versus angle of measurement ean help to provide the insight to resolve particular color issues. With all the processing steps involved and process variable influence it is necessary that the measurement instrument offer the ability to provide selectable information to assist in identifying problem areas. 

Alternatively polycarbonate can be made in a melt process using diphenyl carbonate in lieu of phosgene. Mainly due to some issues with inferior properties such as color and thermal aging, the melt process was not used commercially to any significant extent until the early 1990s when these problems were solved. A 1 1 molar ratio of BPA and diphenyl carbonate is combined and heated in the presence of a catalyst. The BPA dissolves in the molten diphenyl carbonate and phenol is generated by a transesterification reaction. Vacuum is applied and removal of phenol shifts the equilibrium to the polycarbonate. The molten polycarbonate is extruded through a die and pelletized. 

All leafy horticultural commodities show high transpiration rates due to their large surface areas and this poses the additional problem of accelerating senescence. Therefore, a great challenge of most processes has been the maintenance of the original food color along with other characteristics perceived as quality issues by consumers. 

The stabilizer or stabilization system used depends on the heat and shear likely to be experienced by the polymer during processing, the end use application requirements, such as clarity or color, and the health concerns. A major health issue has been identified with the lead salts and soaps, because of their relative solubility and their corresponding potential to leach into water. For this reason, lead stabilizers currently find use only when other stabilizer systems do not provide the necessary stabilization or end use properties. Wire and cable sheathing is the only remaining application where the use of the lead stabilizer systems is widespread. Since most humans do not chew on wires (though mice, rats, and squirrels do) and lead-based stabilizers provide superior electrical properties, lead salts persist in this application. 

A considerable amount of nitrous acid is present in the spent acid. /J-Nitroethyl nitrate is feebly acidic and dissolves in dilute alkali solutions with a yellow color. It is not sufficiently stable for use in commercial explosives. On digestion with warm water or on slow distillation with steam it undergoes a decomposition or sort of hydrolysis whereby nitrous acid and other materials are produced. Numerous patents have been issued for processes of procuring pure nitroglycol from the Kekule oil. One hundred parts of the last-named material yield about 40 parts of nitroglycol, and the economic success of the Process depends upon the recovery of valuable by-products from the 0-nitroethyl nitrate which is destroyed. ... 

This chapter is designed to provide a basic understanding of the synthetic resin (plastics) processing that is necessary to improve or alter the properties of various synthetic resin materials so these resins may be turned into more desirable and useful consumer products. It also discusses the health, safety, and environmental issues associated with the industrial processes used to formulate colorant and additive products. 

---