Presentation on theme: "Packaging Materials An overview. Main Packaging Materials Metals Paper and Board Glass Polymers This session will concentrate on the first three."— Presentation transcript:
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