Polymer Materials and Their Barrier Functions in Food Packaging

Polymers, more commonly known as plastics, are among the most widely used materials in modern food packaging. Their popularity stems from their ability to act as effective barriers that control the movement of gases, vapors, and moisture. These barrier properties are essential for preserving the quality, safety, and shelf life of many food products. Because of their versatility, polymers have increasingly replaced traditional packaging materials such as metal, glass, and paper. Lighter in weight, easier to shape, and often more cost-effective, plastics offer superior functionality across a wide range of applications.

A polymer’s permeability—its tendency to allow substances to pass through—depends on several key molecular characteristics. Free volume within the plastic allows small molecules to move more easily, while crystallinity makes the structure tighter and less permeable. Tacticity, or how side groups are arranged along the polymer chain, also influences barrier strength. Additional factors such as cross-linking, molecular orientation, and the thickness of the material play important roles in determining how well a polymer can keep moisture in and contaminants out.

Food-grade polymers appear in many forms. Thin films are used for wrapping snacks, produce, and baked goods, while more rigid plastics serve as bottles for beverages or cartons for dairy products. Regardless of form, a major requirement is effective protection—preventing food from drying out while blocking the entry of unwanted odors, environmental gases, or pollutants.

Some of the most common plastics in food packaging include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). Each offers a different combination of flexibility, clarity, strength, and cost. However, one challenge with plastic packaging is migration: small amounts of unreacted monomers or additives may slowly move from the packaging into the food, especially when exposed to heat or prolonged storage.

For applications demanding the highest barrier performance, specialized polymers such as polyvinylidene chloride (PVDC) and ethylene vinyl alcohol (EVOH) are widely used. These materials excel at blocking oxygen and moisture, making them essential in products where freshness and extended shelf life are critical.
Polymer Materials and Their Barrier Functions in Food Packaging

The Role of Plastic Films in Food Preservation

The preservation of food products packaged in plastic films relies heavily on maintaining their original quality by shielding them from external factors that cause deterioration. This protection is primarily achieved through the barrier properties of the packaging material, which control the transfer of gases, vapors, and moisture that could compromise the freshness and safety of the food.

Since the early 1960s, polymer films have become the dominant packaging material in the snack food, bakery, and confectionery industries. Their popularity stems from their versatility, cost-effectiveness, and ability to preserve product quality. Most plastic films are naturally transparent and do not easily take on color through dyeing or pigments. To produce opacity or a matte appearance, manufacturers often “cavitate” the films during production, introducing tiny voids that scatter light and give a white or opaque look.

Plastic films offer several practical advantages. They are heat-sealable, which allows for airtight and tamper-evident packaging, and they possess excellent resistance to grease and oil, protecting the contents from contamination. Depending on the specific product requirements, protection can be provided by a single polymer layer or enhanced through multilayered films that combine different polymers, coatings, and even metal foils. These composite structures are carefully designed to balance strength, flexibility, and barrier performance.

The effectiveness of a film largely depends on its permeability to gases and vapors. For example, exposure to oxygen can lead to oxidation and spoilage, while water vapor loss may cause undesirable drying, negatively affecting texture and taste. For this reason, materials with superior moisture and oxygen barrier properties are crucial, particularly for products like chips, cookies, and chocolate. Special coatings can further enhance the oxygen barrier, extending shelf life and preserving flavor.

Typically, packaging films are less than 100 micrometers thick. They are used to wrap individual products, overwrap packages, and form sachets, bags, and pouches. In many cases, they are laminated with other materials to improve strength, sealability, or visual appeal. Through continuous innovation, plastic films have become an indispensable tool in modern food preservation, ensuring that products remain fresh, safe, and appealing from factory to consumer.
The Role of Plastic Films in Food Preservation

Primary packaging: Packaging System Overview

Packaging constitutes a coordinated system that employs various materials for the preparation of goods, covering containment, protection, transportation, handling, distribution, delivery, and presentation. It consists of three primary categories: a) primary, b) secondary, and c) distribution (shipping) packages. Additionally, some authors identify other types like d) convenience packaging and e) wasteful packaging.

Primary packaging refers to materials in direct contact with the final product and the packaging surrounding it during consumer purchase. Essentially, it serves as the initial layer containing the product and is designed with consideration for both the product and any existing secondary layers of packaging.

This initial layer houses the finished product, such as a plastic pouch enclosing whole-grain cereal or the cardboard box containing the cereal pouch. Geared towards end-users, primary packaging has diverse applications influenced by product, transit, and storage variables. Its fundamental purpose is to protect and preserve the product from damage, external interference, contamination, spoilage, and chemical imbalances.

Moreover, primary packaging facilitates the storage of products over extended periods. Historically, it has been used to count items that were challenging to tally individually when unpacked, using the package as a unit of measurement (e.g., bottles, boxes, bags).

The selection of primary and/or secondary packaging materials depends on factors such as the required level of protection, compatibility with contents, filling method, and cost considerations.
Primary packaging: Packaging System Overview

Food packaging

Packaging has become an integral part of the processing, preservation, marketing and even the cooking of foods.

Initially, packages served simply to contain products and to protect them from outside contamination. However, there has been tremendous growth in the development and design of new packages to fit specific needs.

While there has been adaptation of many of the traditional packaging materials, e.g paper, glass, and metals (tin, steel, and aluminium), much of the growth has been due to development of plastic or flexible packaging materials.

Packaging materials may be composed of single component (usually one chemical substance polymeric, building block form) or they may be composed of multiple components, consisting of the variety of materials, usually laminated in layers, offering many advantages not provided by single components.
Food packaging 

Packaging: various definitions and meaning

Packaging plays a key role in protecting the product from contamination by external sources, and reducing damage during its transportation and handling in the supply chain from the producer and manufacturer to the consumer.

Packaging has been defined as a socio-scientific discipline which operated in society to ensure delivery of goods to the ultimate consumer of those goods in the best condition intended for their use.

Packaging is a medium between product manufacturers and consumers aiding the maintenance of original quality of the packaged products and providing information and characteristics of the packaged products to the consumers. Legal definitions of packaging are in the EC Directive on Packaging and Packaging Waste in which packaging is defined as ‘all products made of any materials of any nature to be used for the containment, protection, handling, delivery and presentation of goods, from raw materials to processed goods.

Other definitions of packaging include a coordinated system of preparing goods for transport, distribution, storage, retailing and end-user a means of ensuring safe delivery to the ultimate consumer on sound at optimum cost and a techno commercial function aimed at optimizing the costs of delivery while maximizing sales.

For food products packaging has an important role to preserve food quality. It has to act as an barrier to moisture and gas, microbial infection and insect infestation, other chemical and biological contamination light.

In most cases packaging reduces the cost of goods, because its role as protector means reduced product damage. The use of proper packaging materials and methods to minimize food losses and to provide safe and wholesome food products has always been a primary focus of food packaging.
Packaging: various definitions and meaning