All aluminum cans are lined, but the term “plastic” is a generalized term for the sophisticated protective coating applied to the interior surface. This thin, lacquer-like layer is a polymer resin engineered to separate the can’s contents from the metal packaging. Without this coating, beverages would quickly react with the aluminum, making the product undrinkable and the can structurally unsound.
The Essential Role of the Can Liner
The internal coating’s primary function is to prevent chemical reactions between the can’s contents and the aluminum metal. Many canned beverages, such as sodas, beers, and fruit juices, have a naturally acidic pH level. This acidity would corrode the bare aluminum over time, potentially leading to pinhole leaks and a reduced shelf life.
The lining acts as a physical barrier, preventing aluminum from leaching into the beverage. If the metal were to dissolve even in trace amounts, it could alter the taste and raise potential health concerns for consumers. This protective polymer ensures the integrity of the packaging is maintained until it is opened.
The liner also preserves the intended flavor profile of the beverage. Aluminum is a reactive metal, and direct contact with the liquid would impart an unpleasant, metallic taste. The coating maintains flavor stability, ensuring that the consumer experiences the taste the manufacturer intended.
What Material Lines the Can?
The term “plastic” simplifies the various polymer resins used as can coatings, which are sprayed into the can and cured with heat. For many years, the industry standard was a coating based on epoxy resins, offering excellent adhesion and barrier properties. These traditional epoxy linings typically contained Bisphenol A (BPA), a chemical component that became a subject of consumer concern regarding its potential health effects.
In response to consumer demand and regulatory pressures, the packaging industry has shifted toward alternative materials. Today, many manufacturers utilize Bisphenol A non-intent (BPANI) linings, meaning the substance is not intentionally added to the formulation. These BPANI alternatives are divided into different chemical families to suit various canned products.
One common category of non-BPA coatings is based on acrylic polymers, sometimes referred to as Generation 1 BPANI. Newer formulations, often called Generation 2 BPANI, are epoxy-based but chemically altered to remove the BPA component, offering performance properties closer to the traditional liners. Other materials used include polyesters and specialized oleoresins derived from natural oils and resins.
The choice of liner is highly dependent on the contents of the can, as a highly acidic product requires a more robust coating. The Food and Drug Administration (FDA) and other global regulatory bodies oversee the safety of these coatings. This oversight ensures that materials used are safe for food contact and do not migrate into the contents above established safety thresholds.
Impact on Recycling and Sustainability
The internal polymer coating does not disrupt the highly efficient process of aluminum recycling. Aluminum cans are prized because the metal is infinitely recyclable without losing quality. The recycling process involves melting the shredded aluminum scrap in a high-temperature furnace.
During smelting, the organic polymer lining is exposed to temperatures far exceeding its breakdown point. Aluminum melts at approximately 1,220 degrees Fahrenheit. At this heat, the thin coating undergoes pyrolysis, where it combusts and vaporizes, effectively burning off the lining and leaving behind pure aluminum metal.
While the burning process does produce emissions, recycling facilities are equipped with sophisticated pollution control systems to manage and filter these byproducts. The energy saved by recycling aluminum, which requires up to 95% less energy than producing new metal from raw ore, vastly outweighs the complications introduced by the thin organic lining. The can lining is therefore a non-issue in the final recovery of the metal.