Chemicals — continued packaging

A typical polyethylene molecule is made up of about 2500-25,000 ethylene molecules joined in a continuous structure. Over 30 billion pounds of polyethylene are produced annually in the United States. Its uses are as varied as any single substance known and include chemical equipment, packaging material, electrical insulation, films, industrial protective clothing, and toys. 

The formulation of a carrier depends on four considerations (/) the carrier-active chemical compound (2) the emulsifier (J) special additives and (4) environmental concerns. Additional parameters to be considered in the formulation of a carrier product with satisfactory and repeatable performance arise from the equipment in which the dyeing operation is to be carried out. The choice of equipment is usually dictated by the form in which the fiber substrate is to be processed, eg, loose fiber, staple, continuous or texturized filament, woven or knot fabric, yam on packages or in skeins (see Textiles). 

The polymer, like many fluorine-containing polymers has very good weathering resistance and may also be used continuously up to 150°C. Outside of the electrical field it finds use in fluid handling, in hot water piping systems, in packaging and in chemical plant. A widely used specific application for PVDF is in ultra-pure water systems for the semiconductor industry. 

With the growth of plastic use in containers and packages, requirements to make them more compatible or useful resulted in new developments occuring and continue to occur. The two major approaches for providing permeability resistance in plastic containers involve chemically modifying the plastics surfaces and, more important from a marketing standpoint, the use of barrier plastics with nonbarrier types to meet cost-to-performance requirements. This is achieved through coextrusion, coinjection, corotation, and other such processes (Chapter 8). 

In the past decades, polymer materials have been continuously replacing more traditional materials such as paper, metal, glass, stone, wood, natural fibres and natural rubber in the fields of clothing industry, E E components, automotive materials, aeronautics, leisure, food packaging, sports goods, etc. Without the existence of suitable polymer materials progress in many of these areas would have been limited. Polymer materials are appreciated for their chemical, physical and economical qualities including low production cost, safety aspects and low environmental impact (cf. life-cycle analysis). 

If both common law and statutory obligations incurred by a manufacturer of new chemicals are considered, there is a cradle to grave coverage with respect to health hazards, for obligations now arise with the birth of the chemical in the research laboratory and continue through its life in mass production, packaging, transportation, on to its final conversion into a new substance or final distribution or dissipation by the ultimate user. 

Analytical problems continue to arise in new forms. Demands for analysis at long range by instrument packages steadily increase. Space probes, borehole logging and deep sea studies exemplify these requirements. In other fields, such as environmental and clinical studies, there is increasing recognition of the importance of the exact chemical form of an element in a sample rather than the mere level of its presence. Two well-known... 

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