Plastic Expanded

A cellular plastic has been defined as a plastic the apparent density of which is decreased substantially by the presence of numerous cells disposed throughout its mass (21). In this article the terms cellular plastic, foamed plastic, expanded plastic, and plastic foam are used interchangeably to denote all two-phase gas—soHd systems in which the soHd is continuous and composed of a synthetic polymer or mbber. 

Until the end of World War II, coal tar was the main source of these aromatic chemicals. However, the enormously increased demands by the rapidly expanding plastics and synthetic-fiber industries have greatly outstripped the potential supply from coal carbonization. This situation was exacerbated by the cessation of the manufacture in Europe of town gas from coal in the eady 1970s, a process carried out preponderantly in the continuous vertical retorts (CVRs), which has led to production from petroleum. Over 90% of the world production of aromatic chemicals in the 1990s is derived from the petrochemical industry, whereas coal tar is chiefly a source of anticorrosion coatings, wood preservatives, feedstocks for carbon-black manufacture, and binders for road surfacings and electrodes. 

Pipework and other components should be insulated after the safety pressure test, but usually before prolonged running of the plant, since it is very difficult to remove water and frost once it has formed. Only the low-pressure piping is insulated, where it does not form part of the evaporator, i.e. after the expansion valve, where this may be outside the cooled space, and from the evaporator back to the compressor. Basic materials are cork and the expanded plastics. These are sufficiently rigid to be moulded to the correct shape, remain firmly in place, and support the external vapour barrier which is essential to prevent the ingress of water vapour (see also Chapter 15). 

An outstanding property of EPS is its extremely low density (when compared to other processes), that by alteration of the preforming treatment can be varied according to the end use. Other types of plastics are employed to produce expandable plastic foam (EPF), including PE, PP, PMMA, and ethylene-styrene copolymers. They can use the same equipment, with only slight modifications. These plastics have different properties from those of EPS and open up different markets. They provide improved sound insulation, resistances to additional heat deformation, better recovery of shapes in moldings, and so on. 

METHOD AND APPARATUS FOR EXPANDING PLASTIC TUBING Filed May 29,1963 2 Sheets-Sheet 1... 

FrP 1242324(1961) CA 56, 2628(1962) [Permissible expls prepd by substituting reed meal, peat NaCl by Al silicates (perlite type), kieselguhr, or by substances, of volcanic origin and by expanded plastic materials]... 

FOAMED PLASTICS. Foamed polymers, otherwise known as cellular polymers or polymeric foams, or expanded plastics have been important to human life since primitive people began to use wood, a cellular form of the polymer cellulose. Cellular polymers have been commercially accepted in a wide variety of applications since the 1940s. The total usage of foamed plastics in the United Stales has risen from 441 x 10 i in 1967 lo a projected 2.8xIO6 i in 1995. 

Syntactic foamed materials are classified as foamed plastics because they are formally similar in structure to cellular gas-expanded plastics in that they are heterophase, gas-solid systems. In general, however, they differ from ordinary foamed plastics in that they are not binary but tertiary systems because the filler and binder are made usually from different materials 3 5). 

In 1985 large holes were discovered in the ozone layer over Antarctica, Australasia and Europe (Figure 7.12). Scientists think that these holes have partly been produced by chemicals called chlorofluorocarbons or CFCs. CFCs were developed as refrigerants in fridges back in the 1950s. They have also been used in air conditioning systems, in aerosol cans (as propellants) and in the manufacture of expanded plastics such as polystyrene. CFCs are very unreactive molecules. They escape into the atmosphere and, because of their inertness, remain without further reaction until they reach the... 

Chemicals Manufacturing Functional Plastics PVC Piping Caustic Soda Specialty Fibers Electronics Products Expandable Plastic Products Food Products... 

Important that dry air be used. Moisture in the blowing air can cause pockmarks on the inside product surface. This defective appearance is particularly objectionable in thin walled items such as milk bottles. The air performs three functions it expands the parison or preform against the closed mold cavity, exerts pressure on the expanding plastic to... 

EPS molding generates pressures of less than 30 psi (2 kPa) in most mold applications. This low pressure allows the use of inexpensive molds such as aluminum. To process the other expandable plastic foams (EPFs), such as PE, PP, and PMMA, the equipment for EPS can be used with only slight modifications. 

Plastic foams can be called expanded plastics, cellular plastics or foamed plastics, and include both thermoplastic and thermosetting plastics. 

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