PACKAGING OF DAIRY PRODUCTS

Module 2. Packaging materials

Lesson 13
FOILS AND LAMINATES - CHARACTERISTICS AND IMPORTANCE IN FOOD INDUSTRY

13.1 Introduction

This lesson covers topics related to foils and laminates, composite cans and barrier properties of different packaging materials in detail.

13.2 Aluminum Foil

Aluminum foil is sheet metal of a very thin gauge. It is produced by the cold reduction process through which pure aluminum is pressed to reduce its thickness to less than 0.152 mm and annealed to give folding properties. Aluminum foil is used in the form of cups and trays, laminated foil pouches as alternatives to cans or jars, collapsible aluminum tubes for pastes, and aluminum barrels.

13.2.1 The advantages of foil as a packaging material

1. Good appearance

2. Excellent dead-folding properties

3. Ability to reflect radiant energy

4. Excellent barrier to moisture, gases, and odors

5. Nonabsorbent and nontoxic

Foil (> 0.015 mm thick) is totally impermeable to moist gases, light, and microorganisms. It is widely used for wraps (bottle caps [0.05 mm]), and trays for frozen and ready meals (0.06 mm). Foil trays are coated with vinyl epoxy compounds to make them suitable for microwave heating without damage to the magnetron. The disadvantages of aluminum foil are:

1. Low strength due to its thin gauges

2. Readily attacked by high-acid products

3. Not heat-sealable

To overcome these problems, the foil is often laminated on the outside paperboard (to increase its strength) and with low-density polyethylene on the inside to impart resistance to high-acid products and to develop heat-sealant characteristics. Aluminum is also used to metallize flexible films.

13.3 Composite Containers

• Recently due to development of laminates with metalized films which are having similar properties of a metal container with less cost, the use of metal containers is decreasing.

• Therefore, cans made from a combination of paperboard, foil, and plastic are now used in place of metal cans.

• Kraft paper is the main component in the can body. The inside of the can is plastic (low-density polyethylene, polypropylene, or ionomer) often backed by foil for added barrier properties. End closures can be made of metal, plastic, paper, or a combination of these materials.

• Composite cans are manufactured by a spin convolute wound method, with spiral cans dominating the market due to their superior barrier characteristics.

• Composite cans are widely used to package shortening, powdered and dehydrated baby foods, aseptically packaged single-strength fruit juices, and frozen dough.

13.4 Barrier Properties of Packaging Materials

Many materials can be selected for packaging food products. When choosing the appropriate packaging material, the following factors should be considered:

1. Gas barrier properties

2. Moisture barrier properties

3. Antifog properties

4. Machinability

5. Mechanical strength

6. Sealability

7. Performance vs. cost

One of the most important characteristics is the barrier properties to both oxygen and moisture vapor, which varies greatly from material to material. Because tin plate and glass are excellent gas barriers, examples of the barrier properties of various flexible films only are shown in Table 13.1 and Table 13.2 respectively. Examples of laminated structures and their barrier properties are shown in Table 13.3.

• High-barrier materials usually provide high barriers to both moisture and oxygen, e.g., glass, tin plate, and aluminum foil.

• However, the barrier properties to oxygen and moisture may be different and may also vary as a function of the relative humidity and temperature of the storage conditions.
• E.g. EVOH, a hygroscopic film that is an excellent oxygen barrier at low relative humidity. At higher relative humidity, it absorbs moisture that has a plasticizing effect and reduces the barrier characteristics to oxygen.

• Some films have mixed barrier properties, i.e., low oxygen barrier characteristics and high-moisture vapor barriers. E.g. LDPE, which explains why this film is selected for packaging fresh meat and produce and for frozen stored products to prevent freezer burn.

Table 13.4 Multilayer films used for dairy products packaging