A glossary of common packaging materials

Packaging materials

Ceramics Ceramics are made from natural materials such as clay, quartz and kaolin. Although these are considered inert, they may be contaminated with heavy metals and other inorganic chemical species, that could possibly migrate into food contained within, especially at high temperatures. Ceramics are mostly used as kitchenware.

Glass Glass is made from silica sand and is chemically inert, provides a great barrier wall against gasses and microorganisms. It can be sterilized, reused and recycled. Together with metal, glass is perhaps the oldest packaging material. Glass is heavy and it breaks, these are the main disadvantages Glass is a non-crystal solid built by silica and oxygen (Si-O-Si-) with pores that are too small for chemicals to pass through. Chemical diffusion through glass is minimal. Glass surface is not totally inert, since it is coated by silanol groups (Si-OH) that are capable of adsorbing chemicals, inks, lubricants and releasing them slowly.

Metals The most common metals used as Food Contact Material (FCM) are aluminium (soft-drinks, pet food), aluminium foil (wrap food, trays), tinplate (drink cans, processed foods) or tin-free steel (food cans, bottle caps, trays). Tin free steel can corrode, thus it needs to be coated with a protective layer. Aluminium is expensive and cannot be welded, so it can only be used as seamless containers. Metal is good combination of physical protection, barrier properties and recyclability. They can be heat-treated and sealed for sterility. Metal cans may either consist of tin plate (steel covered in a thin tin layer) or of aluminium and steel coated with a lacquer. Tinplate is good in preventing oxidation and flavour loss, however can dissolve into the product. Lacquers are polymers, such as epoxy resins – and may also migrate into the food.

Paper and board Paper and board are versatile materials made of natural fibers of bleached or unbleached cellulose or are recycled from recovered materials. Paper is a permeable barrier, therefore needs to be treated or coated with wax, lacquer or resin, if intended for food contact. Cardboard is commonly used for liquid and dry foods, frozen foods and fast food. Corrugated board finds application as FCM in pizza boxes. Low molecular weight and volatile additives can migrate from FCM into the food.

Plastics Plastics are synthetic polymers, cheap and versatile. Plastics are light, heat-sealable and microwavable. However, they are rather permeable to light and small compounds (gases or vapours) and it is highly polluting. Typical plastics are polyethylene (PE), High Density Polyethylene (HDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS) and polycarbonate (PC). The choice depends on the application, which may be bottles, containers, films or coatings. To make the final product sturdy, heat and shock resistant various substances may be added, such as UV filters, plasticisers and colorants. These additives may also have functions in protecting the quality of the food contained in the plastic packaging. Plastic monomers and additives such as plasticizers are the most known and worrying chemicals coming from packaging.

Silicones Silicones are a highly versatile group of polymers used in FCMs and they are applied as fluids, rubbers and resins. Unlike plastics, the backbone of any silicone is based on alternating silicon (Si) and oxygen (O) atoms. Some kitchen utensils contacting food are made of silicone rubber, for instance baking molds, spoons, spatula, containers and ice cube trays. Baby soothers and feeding teats are often made of silicone rubber. Silicone resins are commonly used as anti-adherent coatings on kitchenware and in the food industry.

Porcelain Some cooking vessels are covered with a porcelain surface. This creates a non-reactive, low-stick surface. Such pots are much lighter than most other pots of similar size, are cheaper to make than stainless steel pots, and do not have the rust and reactivity issues of cast iron or carbon steel. Enamel over steel is ideal for large stockpots and for other large pans used mostly for water-based cooking. Porcelain is a ceramic made by heating materials, generally including kaolin, to temperatures between 1,200 and 1,400 °C.

Stone Stone or granite cookware are not true chunks of rock, of course. Modern “stone” cookware or pans have a stainless-steel or aluminum core coated with a mineral-based surface. Fused at more than 1,000 °C, that surface may contain crumbles of stone, diamond, marble, ceramic, titanium or porcelain.

Wood Wood is mostly used in kitchenware, such as cutting boards and bowls, or as kitchen sideboards or table surfaces. In order to prevent rapid degradation due to contact with liquids or sharp objects, wood is often lacquered.