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polystyrene
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What is polystyrene?
Polystyrene is a synthetic resin created through styrene polymerization. Its transparency results from bulky phenyl groups hindering crystalline arrangements, while these rings also restrict chain rotation, giving rigidity.
Industrially, styrene (CH_2=CHC_6H_5) is polymerized from styrene using free-radical initiators. Polystyrene is used in food packaging, disposable utensils, and cases. Polystyrene can be foamed for use in insulation.
Blending polystyrene with 5–10% polybutadiene improves impact strength, creating high-impact polystyrene (HIPS). Recycling faces challenges like contamination and property changes, leading to down-cycling into less demanding applications.
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What is polystyrene made from?
Polystyrene is a synthetic resin created through the polymerization of styrene. Styrene, a clear liquid hydrocarbon with the chemical structure (CH_2=CHC_6H_5), is produced by reacting ethylene with benzene in the presence of aluminum chloride to yield ethylbenzene. The benzene group in this compound is then dehydrogenated to yield styrene.
The presence of pendant phenyl ((C_6H_5)) groups gives polystyrene its properties. These large, ring-shaped molecular groups prevent the polymer chains from packing closely, making solid polystyrene transparent. The phenyl rings also restrict rotation of the chains around the carbon-carbon bonds, giving the polymer its rigidity.
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What are the main uses of polystyrene?
Polystyrene is a versatile synthetic resin with numerous applications. It is commonly used in the food-service industry for items like rigid trays and containers, disposable utensils, and foamed cups, plates, and bowls.
Polystyrene is also copolymerized or blended with other polymers, enhancing the hardness and rigidity of various plastic and rubber products. Foamed polystyrene is utilized in insulation, packaging, and food containers like egg cartons. Solid polystyrene is used in injection-molded eating utensils, videocassettes and audiocassettes, and cases for compact discs.
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What is the difference between solid polystyrene and foam polystyrene?
Solid polystyrene is a hard, transparent, and stiff synthetic resin. Its transparency and rigidity come from its molecular structure, specifically the pendant phenyl groups which prevent tight crystalline packing and restrict chain rotation.
Foam polystyrene is produced by foaming polystyrene with gases like pentane or carbon dioxide. It is widely used for insulation, packaging, and food containers. The process involves impregnating polystyrene pellets with a gas, then heating them to fuse together while the gas evaporates, creating the foam.
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Why does polystyrene take a long time to decompose in the environment?
Polystyrene's slow decomposition is due to its high molecular weight, crystalline regions, and dense cross-linking. The large, ring-shaped molecular groups hinder chain packing, preventing close, crystalline arrangements. Polystyrene's rigidity, caused by restricted chain rotation around carbon-carbon bonds, also contributes to its resistance to degradation. These properties make it difficult for organisms to break down the material into simpler components for assimilation and mineralization.
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What are the environmental issues and alternatives related to polystyrene use?
Polystyrene is a synthetic resin widely used in the food-service industry. Environmental concerns exist around polystyrene because it is not biodegradable and can break down into microplastics, which persist in the environment for hundreds of years.
Alternatives and remediation strategies include:
* Bioplastics Bioplastics can be made from renewable raw materials or petrochemicals with biodegradable additives.
* Recycling Polystyrene can be recycled into foamed insulation, though recycled plastics often have disadvantages compared to unrecycled ones.
* Microorganisms Certain species of bacteria and fungi can break down polystyrene and other microplastics.
* International cooperation Organizations such as the United Nations are engaged in educational campaigns and programs to address plastic and microplastic pollution.4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
polystyrene, a hard, stiff, brilliantly transparent synthetic resin produced by the polymerization of styrene. It is widely employed in the food-service industry as rigid trays and containers, disposable eating utensils, and foamed cups, plates, and bowls. Polystyrene is also copolymerized, or blended with other polymers, lending hardness and rigidity to a number of important plastic and rubber products.
Styrene is obtained by reacting ethylene with benzene in the presence of aluminum chloride to yield ethylbenzene. The benzene group in this compound is then dehydrogenated to yield phenylethylene, or styrene, a clear liquid hydrocarbon with the chemical structure CH2=CHC6H5. Styrene is polymerized by using free-radical initiators primarily in bulk and suspension processes, although solution and emulsion methods are also employed. The structure of the polymer repeating unit can be represented as: 
The presence of the pendant phenyl (C6H5) groups is key to the properties of polystyrene. Solid polystyrene is transparent, owing to these large, ring-shaped molecular groups, which prevent the polymer chains from packing into close, crystalline arrangements. In addition, the phenyl rings restrict rotation of the chains around the carbon-carbon bonds, lending the polymer its noted rigidity.
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The polymerization of styrene has been known since 1839, when German pharmacist Eduard Simon reported its conversion into a solid later named metastyrol. As late as 1930 little commercial use had been found for the polymer because of brittleness and crazing (minute cracking), which were caused by impurities that brought about the cross-linking of the polymer chains. By 1937 American chemist Robert Dreisbach and others at the Dow Chemical Company’s physics laboratory had obtained purified styrene monomer through the dehydrogenation of ethylbenzene and developed a pilot polymerization process. By 1938 polystyrene was being produced commercially. It quickly became one of the most important modern plastics, owing to the low cost of producing large volumes of styrene monomer, the ease of shaping the melted polymer in injection-molding operations, and the optical and physical properties of the material.
Polystyrene foam was formerly made with the aid of chlorofluorocarbon blowing agents—a class of compounds that has been banned for environmental reasons. Now foamed by pentane or carbon dioxide gas, polystyrene is made into insulation and packaging materials as well as food containers such as beverage cups, egg cartons, and disposable plates and trays. Solid polystyrene products include injection-molded eating utensils, videocassettes and audiocassettes, and cases for audiocassettes and compact discs. Many fresh foods are packaged in clear vacuum-formed polystyrene trays, owing to the high gas permeability and good water-vapour transmission of the material. The clear windows in many postage envelopes are made of polystyrene film. The plastic recycling code number of polystyrene is #6. Recycled polystyrene products are commonly melted down and reused in foamed insulation.
Despite its advantageous properties, polystyrene is brittle and flammable; it also softens in boiling water and, without the addition of chemical stabilizers, yellows upon prolonged exposure to sunlight. In order to reduce brittleness and improve impact strength, more than half of all polystyrene produced is blended with 5 to 10 percent butadiene rubber. This blend, suitable for toys and appliance parts, is marketed as high-impact polystyrene (HIPS).