Plastic: a versatile and handy material

Plastics represent the most wide-ranging materials used for food packaging and kitchenware. In many cases they have replaced other traditional materials but they have also added a myriad of novel forms and functions. The widespread use of plastic in food packaging is justified by its low cost, ease of processability, plasmability, chemical resistance, and a variety of physical properties. Here you will learn about the most common plastics being used for food packaging and Food Contact Materials (FCM), their intended uses and their disposal.

Types of plastic – their use – their disposal Polyolefins and polyesters, that you see in the picture below, are the most common materials. Low-density (LD) and high density (HD) polyethylene are extensively used due to their lightweight, malleability, strength, stability, processability, reusability and resistance to chemicals and moisture. Milk, juices and water bottles, grocery and garbage bags, bags for bread and frozen food are some of the uses of polyethylene

Polypropylenes (in the figure below) are used when heat resistance is needed. Yogurt containers and margarine tubs are applications of polypropylene. Trays, yogurt cups, frozen food bags and cake boxes are applications of polystyrene

Polyethylene Terephthalate, or PET (see below) is a plastic that plays an important part of your everyday life. Because it is an excellent water and moisture barrier material, bottles made from PET are widely used for mineral water and carbonated soft drinks.

Other commonly used packaging materials are the Polyvinylidene Chlorides (PVDC), that you see in the picture below. These have been used as a barrier in fresh meat packaging for decades, but increasing environmental concerns are urging packaging producers around the world to revisit its use and develop alternative. EVOH copolymers are the most widely used polymers to provide barrier to packages for food and beverage requiring a very low permeability to gases (like oxygen or carbon dioxide) and organic vapors for its conservation.

Two main drawbacks of plastic as packaging material The first main drawback deriving from high plastic consumption is associated with environmental problems due to the slow degradation of most commonly used polymers, most of them being petroleum-based materials. Although the stability of containers during product shelf-life is an advantage, it becomes a disadvantage because they are rarely reused or recycled, thereby generating large volumes of residues. Furthermore, reusing or recycling are not fully suitable methods to manage all packagings, especially in the case of food packaging materials, since they often consist of several different materials (blends of plastics or multilayer systems) to achieve optimum properties. Therefore, there is growing interest in the development and implementation of “bioplastics”. Bioplastics, also called biopolymers, include both polymers from renewable resources such as plants and microorganisms, as well as biodegradable polymers from renewable or non-renewable resources. You will learn more about this in week 4.

The second main drawback is shown in the picture below. Plastics are permeable to low molecular weight compounds, thus having limited barrier properties. This causes various mass transport phenomena in the package/food/environment scenario. Permeation is the movement of gases, vapors or liquids from the outside through packaging materials and may significantly impact the shelf life of foods. Migration is the diffusion of substances, originally present in the polymer, into the food. Sorption is the uptake of components such as flovour aromas, lipids and moisture from the food into the package and subsequent diffusion, resulting in loss of food flavor (and loss of the packaging initial appearance and properties). Multilayered systems or nanostructured additives have been developed to overcome these problems and to generate high barrier materials or modify its properties. However, these high barrier options are not always used and are mainly constrained to high-value applications.

Active packaging These are packagings that change the condition of the packed food to extend the shelf-life or/and to improve food quality and safety. The drawbacks of conventional plastics are balanced by the advent of a new concept of packaging that exploits food-packaging interactions, named active packaging. The idea is to have materials that change the condition of the packed food to extend its shelf-life or/and to improve its quality and safety. For example some materials are able to remove O2, emit CO2, emit ethanol, adsorb ethylene, regulate moisture, remove taint, or even release antimicrobial substances.