Foamed plastics commercial polymers

Cellular polymers have been commercially accepted in a wide variety of appHcations since the 1940s (10—19). The total usage of foamed plastics in the United States has risen from 441 X ICf t in 1967 to 1.6 x 10 t in 1982, and has been projected to rise to about 2.8 X 10 t in 1995 (20). 

Some other groups such as ester, ether, amide, or urea are present in the Polymer chain of commercial polymers. In 1937, O. Bayer found that reaction of diisocyanates with glycols fields polyurethanes which are useful as plastics, fibres, adhesives, rigid foams and surface coatings. 

Styrenic polymer foams have been commercially accepted in a wide variety of applications since the 1940s [1,4]. The total usage of polystyrene foams in the United States rose from about 4.10 x 105 metric tons in 1982 to an estimated 5.35 x 105 metric tons in 1987. It is expected to grow at a rate of 3-4% for the next several years [5]. For example, a recent Fredonia report on foamed plastics estimates that the 2008 volume will be 10.77 x 105 metric tons [6]. 

Foamed plastics can be prepared by various methods. The most widely used, called the dispersion process, involves the dispersion of a gaseous phase throughout a fluid polymer phase, and the preservation of the resultant state. Other methods of producing cellular plastics include leaching out solid or liquid materials dispersed in the plastic, sintering small dispersed particles, and dispersing small cellular particles in the plastic. The latter processes are relatively straightforward techniques of lesser commercial importance. 

What are the trends in the polymeric foam industry The production of foamed plastics on the basis of high polymers will continue to expand mainly utilizing common raw materials (polystyrene, poly(vinyl chloride), polyolefins and synthetic resins). Apart from that, one should expect a strong increase in the commercial pro-... 

Unique Properties of Foamed Plastics Structural Features of Foamed Plastics Leading Commercial Polymers Polyurethane Polystyrene Poly(vinyl chloride)... 

Polystyrene (PS) is prepared by the polymerization of styrene (CeHs—CH=CH2), also known as vinylbenzene. Commercial PS is mostly of the atactic variety and is therefore amorphous. The polymer, on decomposition, unzips and forms the monomer with some benzene and toluene. Its major defects are poor stability to weather exposure, turning yellow and crazing in sunlight. In spite of these drawbacks and its brittleness it has found wide use as molded containers, Uds, bottles, electronic cabinets. As a foamed plastic it is used in packaging and insulation. The thermal conductivity of the expanded PS foam is about 0.03 Wm K The foam can absorb aromatic hydrocarbons usually found in the exhaust of automobiles and buses, causing the foam to disintegrate after long periods of normal exposure to a polluted environment. 

Foamed plastics are also called cellular polymers and expanded plastics, and have played a great role in everyday life. Sponge is an open cellular polymer that is well known, but wood is the oldest form of foam. It is a naturally occurring foam of cellulose. The first commercial foam was sponge rubber that was introduced in thel910s.f Polymeric foams possess special characteristics that render them attractive for many industrial and household applications. 

Potential uses for photodegradable polymers, such as ethylene-carbon monoxide and Ecolyte polystyrene and poly(ethylene terephthalate), will exist wherever plastics littering occurs. It has been estimated that almost a billion pounds of plastics find their way into the world s waterways annually [35]. Because E-CO and foamed plastics float and are photodegradable when in water, there should be commercial opportunities for them in marine packaging, fishing gear, and similar applications. 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Lactomes may also be polymerized by ring-opening anionic polymerization techniques. While the five-membered ring is not readily cleaved, the smaller rings polymerize easily producing linear polyesters (structure 5.46). These polymers are commercially used as biodegradable plastics and in PU foams. 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

Burning may be considered another means of oxidation. Non-burning plastics are a must in commercial constructions according to building codes and are often required for automotive, electronic, and electrical applications. From the numerous thermoplastics, only the halogen-containing polymers, polyamides, polycarbonate, poly(phenylene oxide), polysulfone, and polyimides are self-extinguishing. Even these, such as poly (vinyl chloride), may become flammable when plasticized with a flammable plasticizer. Fire control can be the key to volume use of plastics. Polyester panels, urethane foam, and PVC tarpaulins account for nearly 90% of all fire retardants consumed. Consumption in 1967... 

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