Expanded Polystyrene Foam (EPF)
Writer：zhongji-it Source：Zhongji Click： Label：Expanded Polystyrene Foam
Introduction：Expanded polystyrene foam (EPF) is a plastic material that has special properties due
|Expanded polystyrene foam (EPF) is a plastic material that has special properties due to its structure. Composed of individual cells of low density polystyrene, EPF is extraordinarily light and can support many times its own weight in water. Because its cells are not interconnected, heat cannot travel through EPF easily, so it is a great insulator. EPF is used in flotation devices, insulation, egg cartons, flats for meat and produce, sandwich and hamburger boxes, coffee cups, plates, peanut packaging, and picnic coolers. Although it is generally called Styrofoam, Styrofoam is a trademark of Dow Chemical Company and refers specifically to a type of hard, blue EPF used mainly in boating.
During the late 1800s, researchers seeking materials suitable for making film, carriage windshields, and various small items such as combs produced early plastics out of natural substances and chemicals. In making these plastics, the scientists exploited the natural tendency towards polymerization, in which two or more small molecules, or monomers, combine to form chains that are often very long. The resulting molecular chains, or polymers, comprise repeating structural units from the original molecules. One of the most familiar natural polymers is cellulose, the string of glucose molecules that forms a primary component of plant cell walls, cotton, paper, and rayon. Polystyrene is among the best-known synthetic polymers (others include polyethylene, polypropylene, and polyester). Styrene, the liquid hydrocarbon from which EPF is made, was derived in the late nineteenth century from storax balsam, which comes from a tree in Asia Minor called the Oriental sweet gum. In the early nineteenth century, completely synthetic plastics were developed from hydrocarbons, whose structure is conducive to easy polymerization. Polystyrene, the polymer from which EPF is made, was invented in 1938.
Foaming plastics were discovered indirectly, because in the beginning no one could see their advantages. Dr. Leo H. Baekeland, the American chemist who developed the first completely synthetic plastic, bakelite, experimented with phenol (an acidic compound) and formaldehyde (a colorless gas) while trying to make a nonporous resin. When one of his mixtures unexpectedly began to foam, Baekeland tried to control the foam before realizing that it could have advantages. Following Baekeland's death in 1944, the first foamed phenolics were developed, soon followed by epoxy foam. A short time later, polystyrene was foamed. At first it was used mainly in insulation and flotation devices for boats, life preservers, and buoys. It was not until EPF replaced paper, kapok (made from the silky fibers that encase ceiba tree seeds), and other natural packaging protection that the substance became as popular as it is today. Its familiarity was furthered by the enormous growth of the fast food and takeout industries, which began to use EPF in burger boxes and coffee cups. Today EPF is easily the most recognized plastic.
However, despite EPF's popularity and unique features, it has recently come under attack because of the gaseous methane derivatives—chlorofluorocarbons (CFCs)—used to foam it. CFCs are inert, and harmless to humans and the environment upon their release. However, long after their first use, scientists realized that CFCs contribute to the depletion of the ozone layer as they decompose. The ozone layer is a layer of the atmosphere that protects the earth against harmful ultraviolet rays from the sun. In 1988 representatives from 31 nations signed the Montreal Protocol, a treaty with which they resolved to halve CFC production by 1998. This agreement brought EPF to the world's consciousness as a threat to the ozone layer. While foam packaging is responsible for less than three percent of the CFCs being released into the atmosphere, EPF reduction has been targeted as a way to lower CFC levels, and new technology that explores ways to produce EPF without CFCs has flourished. EPF has also been singled out by environmentalists because it is not being recycled. Action has been taken, however, and programs are under way to see that a greater percentage of EPF will be recycled in upcoming years.
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