Packaging Materials An overview

Main Packaging Materials  Metals  Paper and Board  Glass  Polymers This session will concentrate on the first three

Metals  Metals are elements which generally share a range of properties to a greater or lesser degree including  Strength  Malleability  Ductility  Metallic “sheen”  Conduct electricity

Metals (2)  The metals most widely used with foods are  Steel  Usually found in the form of tinplate  Aluminium

Steel  Steel is an alloy of iron & carbon plus small quantities of other metals  Its advantages are its  strength,  malleability and ductility  Carbon steel is relatively easily corroded, so for food it is usually coated with tin (tinplate)  The major use of tinplate is for canning - a process which has been in use for about 200 years.

Aluminium  Aluminium is a soft white metal which is less dense, but more corrosion resistant than steel.  For food applications aluminium is usually alloyed with up to about 4% other elements to give it more strength.  Aluminium is used for three major food applications  Beverage cans  Foil containers  Aerosol cans

Can manufacture  Cans are produced in two major forms  Three piece with rolled and soldered side seams and two separate end enclosures  Two piece in which sides and one end are formed from flat sheet and are seamless. There is only one end enclosure.  The ends are sealed by a double seal which is purely mechanical  The interior of cans is usually coated with a suitable “enamel” to protect against tainting the food.

Glass  Glass results from the fusing together of oxides of silicon, sodium and calcium to form a hard, brittle, clear material.  It is neither truly solid, nor truly liquid, but is referred to as a “vitreous” material.  Small quantities of oxides of other elements can be added to the glass mix to vary the properties of the glass

Properties of glass  Glass is a hard brittle material which is easily shattered by a sharp blow.  Sudden heating and cooling (thermal shock) can cause glass to crack, though grades of glass with improved heat resistance are available (e.g. borosilicate glass)  It is widely compatible with foods  It can be cleaned and re-used and also recycled.

Paper and board  Paper is produced by separating then re-bonding vegetable fibres (mainly cellulose)  Vegetable materials (mainly wood pulp) are treated chemically to form a pulp  A dilute solution of the pulp is filtered through a wire mesh to produce the basic paper  This is then hot pressed and dried to produce paper.  Various finishes are then applied to produce the desired grades of paper

Grades of paper  Kraft paper; a strong paper often used for paper sacks  Vegetable parchment; a paper specially treated with acid to give it a closer, smoother texture  Sulphite paper; a lighter, weaker paper than kraft paper - often used as paper bags and sweet wrappers  Greasproof paper; produced from sulphite pulp where the fibres are more thoroughly beaten to give a closer texture. It is resistant to oil and grease  Tissue; is a soft resilient paper used for protection.

Properties of paper  Of moderate mechanical strength  Loses its strength when wet  Can easily be folded and laminated to produce stronger structures  Can be coated, e.g. with wax to produce water resistance for liquid containers  Low cost, light weight, flexible and recyclable

Aseptic packaging  Aseptic packaging is a process where the food is sterilised then filled into sterile containers under conditions which will prevent recontamination.  It differs from in-pack sterilisation in that the containers and food are sterilised separately  This enables HTST processes to be used as the centre of the packaging does not have to be heated to sterilisation temperature.

Aseptic processing (2)  The shorter processing times possible mean the food is less processed leading to less destruction of vitamins and loss of flavours.  Because the packaging does not have to be heated, a wider range of packaging is available  However, care must be taken to ensure sterility during the packaging operation  Aseptic processing permits longer shelf life at normal temperatures with higher quality products

The End