Polystyrene

Polystyrene is a synthetic plastic material used in many everyday products. It is second only to the plastic polyethylene in usage. Polystyrene comes in several forms that make it useful for many products. It can be manufactured in a clear form used for product wrapping and laboratory materials, and in a rigid form for use in goods such as computer housings and other electronic casings, vehicle parts, toys, gardening tools, and more. Polystyrene can also be turned into a foam product, where air is incorporated into the plastic material to create a light but firm material used for insulation, packing, and food service and storage. However, the use of some forms of polystyrene, especially those meant for single-use items such as beverage cups and food containers, has raised concerns about pollution.

Background

In 1839, a German apothecary named Eduard Simon was working with the resin of a sweetgum tree called Liquidambar orientalis when he distilled a substance he called styrol. When he looked at the sample a few days later, he saw that the once oily substance had thickened into a gel. Simon called the substance styroloxyd.

A few years later, in 1845, two chemists, John Blyth and August Wilhelm von Hofmann, made the same discovery and confirmed Simon's suspicion that this change occurred because of oxidation, or its combination with oxygen. They called their discovery metastyrol, and it was later found to be the same as styroloxyd. During research on the substance in 1866, another chemist, Marcelin Berthelot, determined that this substance was the result of polymerization, or a chemical process that combines molecules into a long chain. This eventually led to the substance receiving a new name, polystyrene.

During the 1930s, the IG Farben Company in Germany was looking for a product that could replace heavier and more expensive die-cast zinc in their manufacturing. They developed a way to force polystyrene through a long heated tube and cut it off as it came out of the end, resulting in small pellets of polystyrene. This created a lightweight product that could be formed in many different ways, making it useful in several different industries.

Ways were soon discovered to combine these lightweight beads under heat to allow them to hold more air. This led to the development of Styrofoam in 1941 by the Dow Chemical Company. This new, even lighter form of polystyrene had good insulation properties, making it popular for household insulation and for protecting food products, especially those that needed to remain hot. Many disposable coffee cups and the clamshell-shaped containers often used for takeout food are made of this form of polystyrene.

Overview

Styrol appears in nature in tree saps like that used by Simon and in some common foods such as coffee, strawberries, and cinnamon. However, the raw material used in the manufacture of contemporary polystyrene comes from crude oil. This is then treated by one of a number of processes, including distilling, dehydration, or special steam processes, to become styrene. Its molecules are then combined through the chemical process of polymerization. The resulting product is most often turned into pellets for shipping to companies for manufacture into many different products.

Polystyrene comes in three main forms that are reprocessed to make the common products used every day. These include high impact polystyrene (HIPS); general purpose polystyrene (GPPS), which is sometimes referred to as crystal polystyrene; and expandable polystyrene (EPS). HIPS is generally used in the manufacture of appliances and electronics, toys, drinking cups, and other similar items that call for its lightweight rigidity. GPPS is used where a lightweight clear product is needed; therefore, it is often part of the cases for video and audio cassettes and CDs, packing materials for cosmetics and similar items, refrigerator trays and other components, and light diffusers. EPS is a foam-like product created by steaming the polystyrene beads until they expand up to fifty times their original size before blowing them into molds where they are heated until they fuse together. It is used for packing materials, insulation, and other building materials such as moldings, disposable food and beverage containers, and other materials that can benefit from its characteristic light weight and ease of shaping, such as movie props and scenery.

In many cases, HIPS and GPPS are extruded into a flat sheet that is then cut or shaped into the needed size and shape, sometimes using heat to help create the final form. However, it can also be processed through injection molding. For this process, a mold with a cavity shaped like the desired finished product is created, and the polystyrene is forced into the mold under pressure to ensure all areas are filled.

While it is lightweight and easy to shape, color, and even paint, polystyrene also has some potential drawbacks. It is flammable; therefore, it is not suitable for uses where it might be exposed to high heat or open flame, as it might melt or burn. In the past, there was some concern about exposure to hazardous chemicals when people or animals used products containing polystyrene. However, new laws and manufacturing processes have largely eliminated this problem.

Although durability is a desirable quality for polystyrene for many uses, it has raised the concerns of environmentalists. They express particular objection to products manufactured from EPS for a single use, such as beverage cups and containers. In July 2015, New York City banned EPS products such as packing peanuts, food and beverage containers, and serving trays, but the ban was later overturned. The concern is that the material does not degrade in landfills. Additionally, it often ends up in waterways, where it is consumed by wildlife who mistake it for food. The foam then clogs the animal's digestive system, where it can hamper the animal's ability to live and even kill it. In 2019, the European Union voted to ban expanded polystyrene food packaging and cups. The ban went into effect in 2021.

In addition, opponents say that as the foam breaks down, it releases chemicals that are hazardous to wildlife and humans. There is also a risk of health issues from chemicals for people who consume sea life that may have eaten a quantity of foam. EPS is difficult to recycle, yet an estimated twenty-five billion polystyrene coffee cups are used each year in the United States alone. Researchers have been searching for a cost-effective, harmless way to recycle polystyrene. A chemist at Virginia Tech discovered that if the material is exposed to ultraviolet light and has a chemical catalyst added to it, a product called diphenylmethane (DPM) is created. DPM is extremely useful and is used in drug development and polymer manufacturing. It also has a market price that is ten times higher than other materials that can be made from recycled polystyrene. In 2024, researchers based at the University of Bath in the United Kingdom and the Worcester Polytechnic Institute in Massachusetts published a new technique for recycling polystyrene that had the potential to be both economical and energy-efficient.

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