Black Plastics, Temperature, and Food

Black plastics are a blend of polymers and a black dye. These black plastics are commonly utilized in food ware such as takeout containers, disposable utensils, straws, and trays. Polypropylene is a common type of black plastic and is also considered a thermoplastic. When a thermoplastic is heated, it softens and becomes pliable until it melts. This allows these plastics to be extruded or shaped into many objects including takeout containers, lids, and utensils as when the plastic cools down it resolidifies. You have probably noticed this effect when you have microwaved a plastic container or picked up a black plastic takeout container with hot food in it. The container itself feels softer as it is on its way to melting. Why does this matter? What happens with the black dye in the plastic?

A diagram of different types of food

Description automatically generated

The black dye in the plastic is also known as Carbon Black. This dye is created through the incomplete combustion of tar, oil, or vegetable matter. Most commonly, carbon black is used in car tires to give them that distinct black color and increased strength, however, it is also used in black plastics in electronics, and food containers and trays for UV protection and aesthetics. Carbon black also contains chemicals known as Polycyclic Aromatic Hydrocarbons or PAHs which are known carcinogens and found in processed meats¹, air pollution², and cigarettes³. PAHs are known carcinogens and mutagens⁴, are known to be endocrine disruptors⁵, linked to increased risk of cardiovascular disease⁶, and disruption of the reproductive process⁷. They are also known to bioaccumulate in the fat stores of animals and humans due to their lipophilic nature⁸.

Oils and fats are commonly found in foods and drinks that are placed within black plastic containers or in contact with utensils or lids. When hot or warm food is placed into a black plastic container, the hot food begins to heat up the surrounding container which then softens. When the container softens the individual polymer chains are not as in contact as they are at cooler temperatures. This results in more nanosized openings within the container that allow chemicals such as PAHs to move through and out of the container into the surrounding food. You may have heard that you should not microwave your food in plastic but should you also think twice about putting your hot food in contact with black plastic?