This article briefly describes the properties of different packaging materials. It however, only notes the technical properties of the different materials and actual use will depend mostly on the cost and availability in your particular area. Furthermore, there may be particular marketing reasons for choosing a certain type of package and although these are very important in package selection, they are outside the scope of this technical brief.
The importance of packaging can be summarized as follows:
- Adequate packaging aids distribution.
- Rapid and reliable distribution helps reduce malnutrition, removes local food surpluses and allows the consumer more choice in the foods available.
- Packaging and distribution reduce post harvest losses, this together with a larger market allows producers to increase their income.
Therefore, inadequate packaging in developing countries has profound effects on the whole pattern and total amount of food consumed.
Functions of Packaging
Packaging is a means of providing the correct environmental conditions for food during the length of time it is stored and/or distributed to the consumer. A good package has to perform the following functions:
- It must keep the product clean and provide a barrier against dirt and other contaminants.
- It should prevent losses. Its design should provide protection and convenience in handling, during transport, distribution and marketing. In particular, the size, shape and weight of the packages must be considered.
- It must provide protection to the food against physical and chemical damage (e.g. water and water vapor, oxidation, light) and insects and rodents.
- It must provide identification and instruction so that the food is used correctly and have sales appeal.
Textile containers have poor gas and moisture barrier properties and have a poorer appearance than plastics. Woven jute sacks, which are chemically treated to prevent rotting and to reduce their flammability, are non-slip, have a high tear resistance, and good durability. They are used to transport a wide variety of bulk foods including grain, flour, sugar and salt.
Calico is usually a closely woven, strong, plain, cotton fabric which is inexpensive and is satisfactory as a wrapper for flour, grains, legumes, coffee beans and powdered or granulated sugar. It can be re-used as many times as the material withstands washing and is easily marked to indicate the contents of the bag.
Muslin and cheesecloth are open-mesh, light fabrics used to wrap soft foods, which they help hold together in the desired shape. Processed meats, smoked shoulders of ham, etc, are tightly wrapped in cheesecloth, before being packaged into cellophane, wax paper etc.
Both muslin bags and cheesecloth wrappers have to be cut open and can seldom be re-used. It is a very cheap material, made in huge quantities because of its multiple applications, but it gives very little protection to food, and simply holds it together.
The kenaf plant grows in Central Asia, India, Africa and Cuba. It is chiefly used for making ropes and string but can be spun into a yarn which is fine enough to make a coarse canvas. In India, it is known as ambari or deccan hemp and in Africa, lipatam or gombo.
Sisal is a fiber that comes from the agave family of plants. Sisal is resistant to salt water and therefore makes an ideal natural material from which to make rope. The nets in which hard fruits are transported are often hand-made from vegetable fiber.
Wooden shipping containers have traditionally been used for a wide range of solid and liquid foods including fruits, vegetables, tea and beer. Wood offers good mechanical protection, good stacking characteristics and a high weight-to-strength ratio. However, plastic containers have a lower cost and have largely replaced wood in many applications. The use of wood continues for some wines and spirits because the transfer of flavor compounds from the wooden barrels improves the quality of the product.
Wooden tea chests are produced more cheaply than other containers in tea-producing countries and are still widely used. Wooden crates are imported for transporting fresh fruit and vegetables, fish etc. They are used to hold foods together and protect them from crushing, but otherwise offer little protection.
Traditional Packaging Materials
In general these materials are used to hold foods but they offer little in the way of barrier properties needed for a long shelf life. The exception is glazed pottery, which although heavy, has excellent properties.
Banana or plantain leaves are the most common and widespread leaves used for wrapping foods, such as certain kinds of cheese and confectionery (guava cheese). Corn husk is used to wrap corn paste or block brown sugar, and cooked foods of all sorts are wrapped into leaves. ‘Pan’ leaves are used for wrapping spices (India), they are an excellent solution for products that are quickly consumed, as they are cheap and readily available.
These natural raw materials are converted into fibers to produce the yarn, string or cord for packaging materials. Such materials, although categorized by the nature of the constituent fiber, have certain common characteristics. They are very flexible, to some extent resistant to tearing and permeable to water and water vapor. Their lightweight is an advantage in handling and transport.
The rough surface makes stacking easier in comparison to man-made fiber sacks, which slide due to their smooth surface. Another difference with man-made fibers is that the natural raw materials are bio-degradable when left in their pure state. However, they rot when moist limiting the number of times that they can be re-used.
Bamboo and Rattan
These are widely used materials for basket making. Bamboo pots, cut out of the bamboo stem are also found.
Green coconut palm and papyrus leaves are frequently woven into bags or baskets, which are used for carrying meat and vegetables in many parts of the world. Palyra palm leaves are used to weave boxes in which items such as cooked foods are transported.
Leather has been used for many centuries as a non-breakable container or bottle. Water and wine are frequently stored and transported in leather containers (camel, pig and kid goat hides). Manioc flour and solidified sugar are also packed in leather cases and pouches.
Earthenware is used worldwide for storage of liquids and solid foods such as curd, yoghurt, beer, dried food, honey, etc. Corks, wooden lids, leaves, wax, plastic sheets, or combinations of these are used to seal the pots. If well sealed, it is a gas, moisture and lightproof container. Unglazed earthenware is porous and is very suitable for products that need cooling e.g. curd. Glazed pots are better for storing liquids e.g. oils, wine, as they are moisture proof and airtight, if properly sealed. All are lightproof and if clean, restrict the entry and growth of micro-organisms, insects and rodents.
One should ensure that the glazing of the earthenware does not contain lead. Most traditionally glazed pots do have lead glazings which, although they are not really harmful for serving coffee or soup, should not be used for acid drinks and other products which are to be stored for a long time.
Metal cans have a number of advantages over other types of container, including the following:
- they provide total protection of the contents
- they are convenient for ambient storage and presentation
- they are tamperproof.
However, the high cost of metal and the high manufacturing costs make cans expensive. They are heavier than other materials, except glass, and therefore have higher transport costs.
Glass containers have the following advantages:
- they are impervious to moisture, gases, odours and micro-organisms
- they are inert and do not react with or migrate into food products
- they are suitable for heat processing when hermetically sealed
- they are re-usable and recyclable
- they are resealable
- they are transparent to display the contents
- they are rigid, to allow stacking without container damage.
The disadvantages of glass include:
- higher weight which incurs higher transport costs than other types of packaging
- lower resistance than other materials to fractures, scratches and thermal shock
- more variable dimensions than metal or plastic containers
- potentially serious hazards from glass splinters or fragments in foods.
In general, flexible films have the following properties:
- their cost is relatively low
- they have good barrier properties against moisture and gases
- they are heat sealable to prevent leakage of contents
- they have wet and dry strength
- they are easy to handle and convenient for the manufacturer, retailer and consumer
- they add little weight to the product
- they fit closely to the shape of the food, thereby wasting little space during storage and distribution.
A summary of the different types of flexible films is as follows:
Plain cellulose is a glossy transparent film which is odorless, tasteless and biodegradable (within approximately 100 days). It is tough and puncture resistant, although it tears easily. However, it is not heat sealable and the dimensions and permeability of the film vary with changes in humidity. It is used for foods that do not require a complete moisture or gas barrier.
Polypropylene is a clear glossy film with a high strength and is puncture resistance. It has moderate permeability to moisture, gases and odors, which is not affected by changes in humidity. It stretches, although less than polyethylene.
Low-density polyethylene is heat sealable, inert, odor free and shrinks when heated. It is a good moisture barrier but has a relatively high gas permeability, sensitivity to oils and poor odor resistance. It is less expensive than most films and is therefore widely used.
High-density polyethylene is stronger, thicker, less flexible and more brittle than low-density polyethylene and has lower permeability to gases and moisture. It has higher softening temperature (12º C) and can therefore be heat sterilized. Sacks made from 0.03 – 0.15mm high-density polyethylene have a high tear strength, penetration resistance and seal strength. They are waterproof and chemically resistant and are used instead of paper sacks.
Polystyrene is a brittle clear sparkling film which has high gas permeability. Polyvinylidene chloride is very strong and is therefore used in thin films. It has very low gas and water vapor permeabilities and is heat shrinkable and heat sealable. However, it has a brown tint which limits its use in some applications. Nylon has good mechanical properties a wide temperature range (from 60 to 200°C). However, the films are expensive to produce, they require high temperatures to form a heat seal, and the permeability changes at different storage humidities.
Films are coated with other polymers or aluminum to improve the barrier properties or to import heat sealability. For example, nitrocellulose is coated on one side of cellulose film to provide a moisture barrier but to retain oxygen permeability. A nitrocellulose coating on both sides of the film improves the barrier to oxygen, moisture and odors and enables the film to be heat sealed when broad seals are used. A coating of vinyl chloride or vinyl acetate gives a stiffer film which has intermediate permeability. Sleeves of this material are tough, stretchable and permeable to air, smoke and moisture. They are used, for example, for packaging meats before smoking and cooking.
A thin coating of aluminum produces a very good barrier to oils, gases, moisture, odors and light.
Lamination of two or more films improves the appearance, barrier properties or mechanical strength of a package.
This is the simultaneous extrusion of two or more layers of different polymers. Coextruded films have three main advantages over other types of film:
- They have very high barrier properties, similar to laminates but produced at a lower cost.
- They are thinner than laminates and are therefore easier to use on filling equipment.
- The layers do not separate.
Paper & Cardboard
‘Sulphate’ paper is strong and hence used for paper sacks for flour, sugar, fruits and vegetables. ‘Sulphite’ paper is lighter and weaker and is used for grocery bags and sweet wrappers, as an inner liner for biscuits and in laminations. Greaseproof paper is sulphite paper made resistant to oils and fats, for meat and dairy products. Glassine is a greaseproof sulphite paper which is given a high gloss. It is resistant to water when dry but loses its resistance once it becomes wet. Tissue paper is a soft paper used for example to protect fruits against dust and bruising.
Many papers are also treated with wax to provide a moisture barrier and allow the paper to be heat sealed. However, a simple wax coating is easily damaged by folding or by abrasive foods. This is overcome by laminating the wax between layers of paper and/or polyethylene. Waxed papers are used for bread wrappers and inner liners for cereal cartons.
Boards are made in a similar way to paper but are thicker to protect foods from mechanical damage. The main characteristics of board are thickness, stiffness, the ability to crease without cracking and the degree of whiteness. White board is suitable for contact with food and is often coated with polyethylene, polyvinyl chloride or wax for heat sealability. It is used for ice cream, chocolate and frozen food cartons. Chipboard is made from recycled paper and is not used in contact with foods (for example the outer cartons for tea and cereals). It is often lined with white board to improve the appearance and strength. Other types include paperboard and moulded paperboard trays (for example egg cartons).
Further information can be obtained about local costs and availability of different types of packaging from the following institutions:
Packaging Institute of the Philippines
Unit 725, 7/F Cityland Shaw Tower
St. Francis Ave. cor. Shaw Blvard.
Tel: (02) 687-3051, 687-3143
Association of Flexible Packaging Manufacturers of the Philippines
c/o Flexo Manufacturing Corporation, 275 Mabini St., Caloocan City
Tel: (02) 809-8489
Fax: (02) 809-1435
source: www.practicalaction.org, photo from greatlittlebox.com