PET is a very strong transparent glossy film, which has good moisture and gas barrier properties. It is commonly used for carbonated drinks and boil-in-bags. Polyester is a transparent exceptionally strong oriented film. It is mainly used for packaging processed meats, cheese, candy and coffee.
Uncoated polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC)
PVC and PVDC are closely related plastics that are a part of the group of polymers more commonly known as “vinyl”. Its uses include “film” wrap for meats and water and cooking oil bottles. As a packaging material, PVC is most commonly formed into very thin plastic “film” (such as that used to wrap meat) and as thicker plastic “sheet,” which is molded into some type of rigid container. PVDC films are fat resistant and do not melt in contact with hot fats, making it suitable for ‘freezer-to-oven’ foods. It is also used as a coating for films and bottles to improve the barrier properties.
Nylon (PA) polyamides and polyethylene modifications
Nylon is a strong transparent film made of two principle polymers namely type 6 and 66 and has a combination of properties which make it suitable for a variety of industrial applications. It can be printed, laminated or extrusion coated. Nylon alone is a poor moisture barrier therefore must be coated with surlyn.
Surlyn (SU) is a versatile film which is sometimes covered over polyethylene due to some unique properties such as excellent moisture barrier, high melt strength, good clarity, low temperature sealability and toughness. It is commonly used for packaging processed and fresh meats.
Laminated films are commonly made by the lamination of two or more films. Lamination of two or more films improves the barrier properties and/ or mechanical strength of a package. For example- laminates of nylon-LDPE, nylon-PVDC-LDPE are commonly used for non-respiring products. In such a combination, the nylon provides the strength to the pack, whereas PVDC provides the correct gas and moisture barrier properties and LDPE gives heat reliability. For products like bakery items, snack foods, confectionary, etc., the plastic based laminate in three or four layer are commonly used in order to meet the requirement of barrier properties against moisture, oxygen and light.
Coextrusion is the simultaneous extrusion of two or more layers of different polymers to form a single film. There are three main groups of polymers which are used in co-extruded films- olefins (low density and high density polyethylene and polypropylene), styrenes (polystyrene and acrylonitritebutadiene-styrene) and polyvinyl chloride polymers. These types of films have got extensive application for the packaging of fresh milk and edible oil.
Plastic woven sack
Available in laminated or non-laminated forms.
Metal is used to form rigid metal containers as well as foils to be used as rigid and flexible packaging material, respectively.
Rigid metal containers
Rigid forms of metal containers include metal cans which could be made either from aluminum, tin plate or tin free steel. But the tin plate containers and aluminum containers have got extensive application in packaging. The former being the most popular form of metal containers used in food packaging.
Tin containers were traditionally used for heat-sterilized products and are made of the plate, with a base sheet of low carbon steel with coating of tin-applied by hot dipping or electrolytic processes. Corrosion resistance, good lacquering adhesion and sole durability are the advantages of tin plate.
There are two types of tin plate containers namely open top container and general line container.
Open top containers are also called as open top sanitary (OTS) cans and are essentially round in shape . A standard open top can is supplied by can making company with bottom seamed to the body and the top ends are supplied as loose. The processed food manufacturer fill the content into the tin can and then seam with the top lid by using a machine called seamer and then the filled tin cans are subjected to heat process. This can is also called as 3-piece can. Open top sanitary cans are widely used for processed food and beverages. With the advent of easy open end, cans are now fitted with “ring pull tab” for ease of opening a can. Recently “Drawn and Wall Ironing” can (DWI can) has been developed, which is also called two piece can as the cylindrical body and bottom become single piece and lid is separate. E.g. pressurised beer and beverage cans.
General line containers are containers range of tailor made sizes and may be round as well as un-round (known as irregular) and are filled with various kinds of fitments made from tinplate, aluminum and plastics. These containers do not have much application for processed foods, rather bakery products, hydrogenated oils and confectionery items are packed in them.
However, due to shortage of metallic tin and its import costs, expensiveness, tin free steel (TFS) and aluminum containers have been developed. These are used for processed fruit and vegetable products, meat and fish and dairy products. New types include:
- High tin fillet (HTF): Developed in USA for canning type foods like green asparagus, tomato products, dried prunes, green beans, carrots etc.
- Low tin coated steel (LTS): Nominal coating of tin is used. Used for canning beer, carbonated beverages, vegetable and meat products.
- Tin free steel cans (TFS): Developed by replacing tin with chromium metal, therefore also called as Chromium steel can. Used for vegetable and meat products, milk powder, vanaspati, edible oils, which are low acid products.
- Aluminum cans: Developed as an alternative to the plating. Used for packaging carbonated beverages, beer, vegetable and meat products.
Metal containers have a number of advantages over other types of containers which are as under:
- Provide total protection of the contents
- Convenient for ambient storage and presentation
However, the high cost of metal and high manufacturing costs make them expensive. They are heavier than other materials, except glass, and therefore have higher transport costs.
Important food packaging foils consist of pure aluminum. It has the best barrier performance against moisture, gases, light, aroma, etc. compared to any of the material; therefore it has been established as the best flexible packaging material. No other flexible material can match the characteristics of aluminum because foil retains all metallic properties of aluminum. The important properties of aluminum foil are impermeability, non-toxic, stable, barrier against light and heat, tasteless and odourless.
Because of its impermeable nature it is extensively used for lamination. On its own, aluminum foil is not strong, hence needs to be laminated to a stronger material to reinforce it and make it efficient as a barrier to water-vapour and oxygen. Common reinforcement is paper. Others include regenerated cellulose, polyester, polyethylene, polypropylene.
The important applications of aluminum foils include bag , decorative label, confectionery, biscuit wrappers, milk products, multilayer laminates, stand up pouches, tea chest lining etc.
Glass is an important package media, which has been used since many centuries. This packaging material is used for almost all types of products like liquid, powder, paste, granules, etc. Packaging properties of glass are moldability, inertness, transparency and strength etc. A variety of closures made of metal, plastic, cork or rubber, depending up on the requirement, can be chosen with glass containers. Recent development is the use of very thin glass encased in a plastic exterior providing inertness of interior surface with resistance to abrasion by the exterior surface. The advantages and disadvantages of glass packaging are presented in following text.