There is a surprising amount of misinformation in circulation about polystyrene foodservice packaging, considering what a simple and common product it is.
Over the years, we have addressed many, many questions, some of which have attained "urban legend" status. There are other issues that go beyond the basics that we would also like to address.
CFCs and Blowing Agents
Chlorofluorocarbons (CFCs) are known to harm the earth's stratospheric ozone layer. Polystyrene foam foodservice products are not manufactured with chlorofluorocarbons (CFCs) or any other ozone-depleting chemicals. In fact, Dart never used CFCs in manufacturing molded foam cups. Those manufacturers of polystyrene foodservice products that employed CFCs in their manufacturing operations, ceased using them by 1990.* According to the U.S. Environmental Protection Agency (EPA), only two to three percent of CFCs used in the United States in the 1980s went toward production of polystyrene packaging products. Even so, polystyrene manufacturers exceeded government goals and timetables during the phase-out period of CFCs in the late 1980s and were at the forefront of US industry in switching to alternatives.†
Polystyrene foam products are about 90 percent air and only 10 percent polystyrene. When polystyrene foam packaging is produced, a "blowing" or "expansion" agent is used in the process.
Polystyrene foam products are now manufactured primarily using two types of blowing agents: Pentane and carbon dioxide. Carbon dioxide (CO2, or other hydrocarbons in some cases) is non-toxic, non-flammable, and does not contribute to low-level smog, nor does it deplete the stratospheric ozone layer. However, CO2 does have the potential to produce global warming. The carbon dioxide used for this technology is recovered from existing commercial and natural sources. As a result, the use of this blowing agent technology does not increase the net levels of CO2 in the atmosphere.
Pentane gas has no effect on the upper ozone layer, although, if not recovered, it can contribute to low-level smog formation. Where smog formation is a large concern, many manufacturers use state-of-the-art technology to capture pentane emissions. Most Dart plants recapture and reuse a substantial portion of the pentane released in the pre-production processes as fuel.
* Alexander, Judd H. In Defense of Garbage. Westport, CT: Praeger Publishers, 1993. 55.
† Natural Resources Defense Council Environmental Defense Fund Friends of the Earth. Statement of Support for The Foodservice Packaging Institute’s Fully Halogenated Chlorofluorocarbon Voluntary Phaseout Program. 12 April 1988.
More information on blowing agents is available at:
American Chemistry Council: How plastics are Made
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The question sometimes arises: Are the inks used to print messages on Dart foam products safe for humans and the natural environment? The answer is simple: Yes!
Four major classes of inks can be used for screenprinting on packaging and similar products: solvent-based, water-based, plastisols, and UV. The selection of ink for a printing application largely depends on the end use of the product, although environmental concerns increasingly are a factor. Solvent-based inks are the traditional ink of choice used by many manufacturers because such inks are versatile and can be employed in a wide variety of applications. Unfortunately, in recent years it has become clear that solvent-based inks emit volatile organic compounds (VOCs), which may harm employees' health in an industrial setting and can contribute to atmospheric pollution. Water-based inks are preferable to solvent-based inks, but increase drying time and may cause the shape of a product to change slightly as it dries. Plastisol inks contain polyvinyl chloride resins dispersed in a plasticizer that fuse with whatever ink is applied to when the ink is heated to approximately 320°F. Owing to the high temperatures involved, plastisol inks are not suitable for use on plastic foodservice products. They are generally used on textiles.
Dart chooses to use UV inks for our polystyrene products for several reasons. First, UV inks are well suited for plastic, vinyl, metal and paper products because they adhere to surfaces smoothly and evenly. Moreover, they contain no VOCs. As an added bonus, they will not dry on a press or screen, thereby substantially reducing the need for cleaning solvents. Finally, Dart's UV inks do not contain heavy metals that may harm human health or the natural environment. In short, the company believes that the use of UV inks on our products is the best choice considering all relevant factors, especially the suitability of the application and the environmental consequences.
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Kosher and Halal
In the manufacture of our cups and plates, Dart uses a lubricant in the extrusion process of our polystyrene resin pellets which contains zinc stearate. Zinc stearate (C36 H70 O4 Zn) is ultimately derived from tallow (animal fat). Because of the high temperature and purification steps, the tallow is, in effect, denatured (removed from the class of being "food"). Some religious authorities accept this idea and consider zinc stearate just another processing chemical.
Other religious authorities do not accept this argument of denaturing and further take the position that the presence of even small amounts of tallow-derived processing aids causes contained foods to lose Kosher/Halal status.
Since Dart does utilize these processing aids and given the current differences in theological opinion, we suggest that guidance is sought from your religious leader.
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Dart Container Corporation does not make any products containing latex (Natural Rubber Latex, or NRL), nor is latex used in any of our manufacturing processes. Our manufacturing procedures prohibit the use of latex gloves in our plants.
Allergic reactions or sensitivities can occur when some people come in contact with NRL, either through direct contact, or if the latex allergens are airborne and inhaled.
Natural latex is harvested from rubber trees, and then processed to make products. Many types of synthetic or man-made rubber resemble natural rubber, but these synthetics do not contain the allergy-causing proteins present in natural rubber. And some products use the word "latex" in their name, but are made from synthetic products. The most obvious example is latex paint.
Further information on this topic is available at:
- U.S. Dept. of Labor, Occupational Safety and Health Administration,
Safety and Health Topics: Latex Allergy
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The rind of some citrus fruits contains oils, including a naturally-occurring chemical called d-limonene. D-limonene can be found in lemons, oranges, grapefruit and in limes. In extremely high concentrations, the chemical is used in industrial cleaners and for paint stripping.
For decades, the plastics industry and the U.S. Food and Drug Administration (FDA), among others, have observed, studied, and reviewed the physical effect of d-limonene acting as a solvent for polystyrene. The phenomenon became a matter of public debate over 20 years ago, which was when the most-detailed studies were done. As a result of these studies, the FDA regards polystyrene foam beverage containers as very safe for human use.
When a wedge of lemon is cut or squeezed into a cup of liquid, limonene exudes to the surface of the liquid and eventually moves to the inside surface of the cup. At that point, limonene interacts with the polystyrene, breaking down its cellular structure and actually entering into solution in the cup wall. Given enough time undisturbed and enough limonene, a hole can develop in a foam cup. Because it is a physical, not a chemical, action, it is not at all like strong acids or bases burning a finger, or eating through paper. There is no danger to anyone drinking from the cup; however, continuing the practice of leaving the rind in the cup for a long time is not recommended as the integrity of the cup breaks down and may no longer hold the hot liquid.
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Microwave ovens help make life today more convenient, and because they are so efficient, they reduce our energy needs. The plastics packaging in which we receive much of our food and beverages provides convenience and energy savings. Because plastic packaging protects so well, it also reduces food waste.
There are plenty of stories surrounding microwaves, and some have attained "urban legend" status – "everyone" knows they're true, even though there is no supporting evidence. Once the science behind microwaves is understood, it is clear that the use of polystyrene plastic cups or containers is safe. As with any product, the best advice is to follow the directions on the packaging.
How does a microwave work?
Typically, microwaves agitate polar molecules (molecules that have magnetic properties), like water, into very rapid motion. The collisions between these rapidly moving molecules create frictional heat, first within the liquid water, which is then transferred to the entire food or beverage contents. Because polystyrene foam cups or containers themselves do not contain water within their molecular structure, they are "transparent" to the microwaves. The microwaves pass right through, and the container is unaffected. If the container's temperature changes, it is because of the increasing heat of the liquid or solids they contain.
How does a microwave work compared to conventional methods?
With the conventional method of heating water, the container (a metal teakettle, for example) absorbs the stove's heat, and then transfers it to the water it contains. By contrast, a microwave heats the water first, which then transfers its heat to the container.
What does a microwave oven do?
A microwave interacts with water molecules in foods or beverages. Through this interaction, foods or beverages are heated directly (without the delay or increased energy needs of heating the container) and, afterward, the foods or beverages transfer heat to the container.
What does a microwave oven not do?
- It does not interact in any significant way with a plastic container used in the oven, because the container itself has no water molecules.
- It does not chemically change the food, other than the normal changes which take place with any means of cooking or heating
- It does not irradiate the food, or destroy vitamins.
What about overheating?
- Most of our foods and beverages have a high water content. The boiling point of water is 212°F at sea level and one atmosphere of pressure.
- Food with a high sugar or fat content (or both) can raise the boiling temp to over 212°F. If cooked or heated too long, some foods can soften the container, leading to a mess in the microwave oven and danger of burns from hot food or liquid.
- The much-publicized phenomenon of "superheating" water in a microwave, which can occasionally cause an explosive release of the contents, usually occurs only in containers with an exceedingly smooth cellular structure, such as glass or glazed ceramics. Polystyrene foam cups or containers do not have that structure.
Microwave best practices
- Remember, the microwave oven heats the food or beverage first, and then the food or beverage heats the container.
- Do not use more heat or time in the microwave than you need. It only takes a few minutes (or less) to reheat or warm food that already has been cooked.
- Foods or beverages high in sugar and fat can get hotter than 212°F. Be careful not to heat too long.
- Follow directions on the packaging, particularly for cooking.
- Use a microwave with a turntable so food heats more evenly.
Additional information on Microwaves and Plastics in the Microwave is available at:
Bloomfield, Louis A. How Things Work: The Physics of Everyday Life. New York: John Wiley & Sons, Inc., 1997.
Breder, Charles V., PhD. Common-Sense Approach to the Use and Reuse of Food-Contact Plastics to Heat & Reheat food in Microwave Ovens. Washington, DC: American Plastics Council. (www.plastics.org, 2002)
Meadows, Michelle. "Plastics and the Microwave." FDA Consumer Magazine. Washington, DC: U.S. Food and Drug Administration, November-December 2002.
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Information Regarding the 12th Report on Carcinogens Issued by the National Toxicology Program
American Chemistry Council Press Release
Styrene is a clear, colorless liquid that is a component of materials used to make thousands of everyday products for home, school, work, and play. Styrene is used in everything from food containers and packaging materials to cars, boats, and computers, medical, health, and safety equipment, and even video games. Derived from petroleum and natural gas byproducts, styrene helps create thousands of remarkably strong, flexible, and light-weight products, representing a vital part of our health and well-being.
A naturally occurring substance, styrene is present in many foods and beverages, including wheat, beef, strawberries, peanuts and coffee beans. Also found in the spice cinnamon, its chemical structure is similar to cinnamic aldehyde, the chemical component that elicits cinnamon's flavor. It is naturally present to flavor foods, and is used as a flavoring additive to such foods as baked goods, frozen dairy products, soft candy, and gelatins and puddings, with permission from the U.S. Food and Drug Administration (FDA).*
Polystyrene meets stringent U.S. FDA standards for use in food contact packaging and is safe for consumers. Health organizations encourage the use of single-use food service products, including polystyrene, because they provide increased food safety.†
Some people confuse styrene, which is a liquid, with polystyrene, which is a solid plastic made from polymerized styrene. Styrene and polystyrene are fundamentally different. Polystyrene is inert, and has no smell of styrene. Polystyrene often is used in applications where hygiene is important, such as health care and food service products.
Styrene Information Research Center (SIRC) has invested many years of effort, and nearly $12 million in research funding, to develop the most thorough and accurate information about possible cancer effects resulting from styrene exposure. The results of extensive health studies of workers in styrene-related industries collectively show that exposure to styrene does not increase the risk of developing cancer, or any other health effect. Results of a two-year styrene inhalation study in rats, completed in 1996, also showed no increased incidence of cancer.
Further information on this topic is available at:
* See: FDA's Food Additive Regulation at 21 CFR 172.515
† "Disposables versus Reusables: A Study of Comparative Sanitary Quality." Dairy Food and Sanitation. January 1985.
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BPA is used in the production of polycarbonate containers. Polystyrene #6, Polypropylene #5, PET #1 and Bisphenol-A have nothing to do with one another. Bisphenol-A is not used, directly or indirectly, in the manufacture of any Dart products.
There is a misconception that “plastics in general are unsafe to use in the microwave.” Dart has literature (M-334) and a section of our website addressing best practices for use of plastics in a microwave oven.
Dart is a member of the Plastics Foodservice Packaging Group, which is a part of the American Chemistry Council. The American Chemistry Council has addressed the erroneous information in hopes of contradicting these unscientific assertions and untruths. A special website--www.factsonplastic.com--has been developed to assist in answering some of the questions that have been raised. Visit the website provided above to see the information that is available.
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