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Long ago I bought myself some lentils from a major retailer of whole foods. They came in a clear, crinkly, sharp kind of plastic bag with colorful, crisp images.  The bag had no plastic code so I  set about researching the packaging. I phoned and asked the producer/ retailer but they couldn’t help me. So I had the packaging analyzed. I can now tell them that it was in fact a film consisting of a series of bonded layers including a 70 micron thick polypropylene and ethylene layer, laminated and printed. Or to put it more simply several layers of plastic each with different properties stuck together.

This method of making plastic films leads to a very versatile product that looks good and has a wide range of uses.

On the down side these films are difficult to recycle. Because they consist of different plastics bonded together it is difficult to know what they are and how to treat them and separating the films is tricky and so very expensive. Films therefore often don’t get recycled but burnt or landfilled.

Just to remind you

Another barrier to [plastic] recycling is the widespread use of dyesfillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more often. . Yet another barrier to removing large quantities of plastic from the waste stream and landfills is the fact that many common but small plastic items lack the universal triangle recycling symbol and accompanying number. From  Wikipedia on plastic recycling

So if you need to buy something in plastic, try avoid the film and go for easily recycled polythene. You can find some suppliers here….

Plastics used to package food include the following. Copied from practical action 

Films

Film Type

Coating

Barriers to Moisture

Air/Odours

Strength

Clarity

Normal Thickness Micrometers

Cellulose

*

***

*

***

21 – 40

Cellulose

PVDC

***

***

*

***

19 – 42

Cellulose

Aluminium

***

***

*

21 – 42

Cellulose

Nitro- cellulose

***

***

*

21 – 24

Polythene (low density)

**

*

**

*

25 – 200

Polythene (high density)

***

**

***

*

350 – 1000

Polypropylene

***

*

***

***

20 – 40

Polypropylene

PVDC

***

***

***

***

18 – 34

Polypropylene

Aluminium

***

***

***

20 – 30

Polyester

**

**

***

**

12 -23

Polyester

***

***

***

**

Polyester

***

***

***

20 -30

Table 1: Properties of selected packaging materials
* = low ** = medium *** = high. Thicker films of each type have better barrier properties than thinner films. PVDC = polyvinylidene chloride.

Laminated films

Lamination of two or more films improves the appearance, barrier properties or mechanical strength of a package.

Coextruded films

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.
    Examples of the use of laminated and coextruded films are as follows:

Type of laminate

Typical food application

Polyvinylidene chloride coated polypropylene (2 layers)

Crisps, snackfoods, confectionery, ice cream, biscuits, chocolate

Polyvinylidene chloride coated polypropylene- polyethylene

Bakery products, cheese, confectionery, dried fruit, frozen vegetables

Cellulose-polyethylene-cellulose

Pies, crusty bread, bacon, coffee, cooked meats, cheese

Cellulose-acetate-paper-foil- polyethylene

Dried soups

Metallised polyester-polyethylene

Coffee, dried milk

Polyethylene-aluminium-paper

Dried soup, dried vegetables, chocolate

Type of coextrusion

Application

High impact polystyrene- polyethylene terephthalate

Margarine, butter tubs

Polystyrene-polystyrene- polyvinylidene chloride-polystyrene

Juices, milk bottles

Polystyrene-polystyrene- polyvinylidene chloride-polyethylene

Butter, cheese, margarine, coffee, mayonnaise, sauce tubs and bottles

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