Chemicals & Materials Now!
From basic to specialty, and everything in between
Is today’s non-stick cookware safe?
Posted on February 10th, 2017 by Laurence W. McKeen in New Materials & Applications
Nonstick coatings have been used on cookware for over 50 years. It’s amazing that its safety continues to be debated.
Consumers hear this from many news reports, TV ads, and blogs from “experts”. There are all sorts of comments, claims and opinions, some are laughable. This article is focused on safety not performance.
As a consumer I am more interested in the overall safety of all cookware that I use. That includes not only fry pans, but sauce pans and baking sheets. There are four cookware components one must consider when evaluating cookware safety; substrate, interior coating (if any), exterior coating (if any) and handles.
Most cookware is made of stainless steel, aluminum, cast iron, glass, pyroceram, and ceramic. Some bakeware is made from flexible silicone.
The metals are all safe. There is a belief expressed on the internet that scratched metal cookware leads to increased leaching of metal into foods. That is nonsense. There have been claims that aluminum ingestion increases the risk of Alzheiner’s disease. There is no scientific proof of this.
Glass bakeware comes in two types, soda lime and borosilicate. The health risk with glass cookware comes from shattering. Soda lime glass tends to shatter at lower temperatures than borosilicate. Otherwise there are no known health risks.
Pyroceram and ceramic are similar. The best known of this type cookware is Corningware, which has been made of either material. Pyroceram is able to withstand stovetop and broiler heating. Do not use ceramic in this manner. Neither has any known health risks.
Stoneware is a ceramic. It is fired at high temperature and glazed to provide color and a smooth finish. The main safety concern is with the glaze, because it contacts the food. Some glazes contain heavy metals which are health risks. This is not always easy to ascertain if the glaze is food-grade, as they can be made anywhere in the world and even by local artisans.
Flexible silicone bakeware is made from silicone rubber. Silicone is generally stable to 300°C (572°F). Home ovens would not be used at a temperature this high.
The material of the handles is critical in determining if the cookware is oven safe. Handles are made from stainless steel, silicone-over-steel, and phenolic plastic. Metal handles have no safety concerns except from burns. They are often made of steel, even on an aluminum pan, because they are strong and the thermal conductivity is much lower than aluminum, so they will remain cooler for a longer time. If they contain plastic then the temperature limit of the plastic is important. Silicone is stable to above 300°C (572°F), but T-fal suggests a limit of 204°C (400°F). Phenolic plastics are usually hard and black and T-fal suggests an oven limit of 175°C (350°F). When phenolic handles are overheated a distinct plastic/chemical odor may be noticed. These fumes can contain formaldehyde (a carcinogen) and phenol which is corrosive and poisonous.
Interior Non-stick Coatings
Non-stick coatings come in a wide range of chemistries:
- silicon polyesters
Fluoropolymers have a lot of negative exposure over PFOA fears and other issues. The main polymer in these coatings is polytetrafluoroethylene (PTFE), often called by the tradename Teflon®. It has a high melting point (315-340 ºC, 599-644°F), making it ideal for most cooking applications. When heated to temperatures above 350 ºC (662 ºF), PTFE begins to degrade, releasing fine particles and a variety of gaseous compounds that can give one polymer fume fever if they can breathe enough of them. Symptoms similar to a bad flu last for 24 hours. The chance of a human being affected in their kitchen is essentially zero. I am unaware of any documented case of a consumer getting polymer fume fever. I have seen it in laboratories or applicator shops where large numbers of pans are being baked at one time and operators have poor ventilation in their ovens. To heat a pan above 350°C one would have to put it on a burner at medium high heat without food. You should not blacken food on a fluoropolymer coated pan. What about oil? Even the most stable cooking oils (safflower) smoke at 265°C or lower, well below the decomposition temperature of PTFE. Birds are much more sensitive to what’s in the air and it is well known that the fumes from a hot fluoropolymer coated pan can kills birds, but so can fumes from burning foods.
Perfluorooctanoic acid (PFOA), also known as C8, was used in the process of making PTFE. It is no longer used or is removed by reputable manufacturers. PFOA’s boiling point is 189-192 °C (372-378 °F). When non-stick coatings are cured after being applied to new pans, the temperatures reach 380-438°C (715-820°F) for several minutes. This is well above the boiling point of PFOA. The coatings are thin, so if there were any PFOA in the coating it would diffuse out during curing leaving essentially no PFOA in the cookware. Therefore there is no chance of PFOA exposure from cookware containing PTFE.
PTFE is one of the most inert materials known to man. It reacts with nothing in the food or in your digestive tract. If flaked off coating is consumed it isn’t toxic because PTFE is inert. The only possible concern is for unbranded coating and cookware. The major coating manufacturers pay very close attention to indirect food compliance guidelines and regulations. However, it is fairly easy now to formulate a non-stick coating by consulting patents. I would have concerns about what goes into coatings formulated by small companies in China and the developing world.
Ceramics are the latest thing in cookware non-stick coatings. Who has not seen the infomercials on TV barking these? These pans are coated using a sol-gel coating. Sol-gel coating technology is a hybrid of organic and inorganic chemistry. The cured coating on the pan is essentially silica, commonly called silicon dioxide or sand. As Whitford, a fluoropolymer and ceramic coating producer, says on their website: “Coatings produced using sol-gel technology are more accurately described as ceramic-like; they feature many of the same characteristics as ceramic but to a lesser extent. Compared to PTFE, sol-gel coatings are harder and can function at higher temperatures (up to 450°C/840°F).” These coatings are also baked at high temperatures so any volatiles in the coating will be gone in the coater’s ovens. What happens when this type of coating decomposes? It likely turns to sand. A coating formulated by a reputable company is unlikely to have any health issues from direct food contamination or ingestion.
Hydrids are sol-gel coatings formed with some PTFE in the silica matrix. As a combination of the two previous coatings already discussed, one would expect the safety to be a combination also. Since both fluoropolymer and sol-gel coatings are safe on their own, this combination will be safe also.
Silicone based coatings are most often used on bakeware trays, bread pans and muffin tins. These coatings are polysiloxane or siliconized polyester coatings, similar to sol-gel but with more organic character. They are cheaper that other non-sticks and sometimes perform better for release when foods have high sugar content. Silicone has low chemical reactivity and will not support microbiological growth. Because it is used in bakeware and ovens are rarely set above 500°F, it is unlikely to see thermal decomposition. While there have been reports by some users of strange odors, these are probably from very low grade bakeware. Known branded coated cookware does not have this problem. These coatings are considered safe and in fact I own and use these pans, though I do prefer fluoropolymer coated bakeware.
Lastly, one needs to consider the exteriors if they are not plain metal. Aluminum exteriors may be finished by the process of anodization, enameled or painted with siliconized polyesters.
Anodization is a coating of oxide film generated in an electrochemical process in an acidic electrolyte solution. Thickness of anodizing coating is much higher than the natural aluminum oxide film on an aluminum surface. It is very hard and chemically inert. While the natural color of aluminum oxide anodization is attractive, color can be added by a dye process. There are pores in the anodized surface that can be filled with the dye simply by soaking in the dye solution. After coloring a sealing step is performed. There are no apparent concerns about the safety of this type of exterior.
A Circulon® pan with non-stick interior and anodized exterior
Another colored exterior is porcelain enamel. Porcelain is a glass-based, inorganic coating. The enamel is sprayed onto the cookware and fused to the substrate by heating it to 1500 °F. The enameled finish does not peel, flake or rust. There are no safety concerns on exterior enamel.
Ceramic glazes are also used as exterior coatings. Some glazes are direct food compliant and some are not. Since food is not cooked on the exterior of the pan the glaze does not have to be food grade. The main question about ceramics has to do with the pigmentation used to color them. Non-food grade glazes may have heavy metal pigments in them.
Siliconized polyester coatings are often used on the exteriors because they allow wide color possibilities. Note that the bottoms are not coated. That is because being a polyester based organic material it does not have the thermal stability to withstand direct contact with the heat source.
Cookware with a brightly colored siliconized polyester coated exteriors.
Overall all cookware made by reputable manufacturers using reputable coating systems is safe. One should only have concerns about low end low cost cookware made by unknown manufacturers.
All opinions shared in this post are the author’s own.
R&D Solutions for Chemicals & MaterialsWe're happy to discuss your needs and show you how Elsevier's Solution can help.
Laurence W. McKeen
Consultant Fluorocoatings, Plastics & Polymers
- Are You Building an Incident-Proof Reputation?
- Not in My House
- Dow and DuPont Approach Merger and Spin-Offs from Positions of Strength
- Next Step In Solid State Batteries
- Chemicals in Arizona: nanoparticles in sunscreen creams