Why do we use different polymer types in plastic packaging?

2 November 2016

Consumption patterns today demand a wide variety of packaging to contain, protect and preserve products.

As the main use of packaging is in the grocery sector where typically the number of items stocked runs into multiples of  tens of thousands, it is no wonder that no one material can meet all needs. But also packaging is used to package electrical and durable goods and needs to protect goods in transit as they are transferred from where the goods are manufactured to central depots, to the retailers shops and ultimately to the consumer.

The uses that polymers are put to in modern packaging are many and varied and the requirements demanded of them include being able to:

• Withstand high temperatures when the food is placed in the oven or microwave either before distribution or in the consumers home.
• Maintain its properties in cold temperatures when the food is stored frozen or chilled and when thawed.
• Have high or low barriers depending on the product and its ability to breath or withstand the migration of odours, greases and fats and/or the absorption or loss of moisture or gases, depending on the food and how it needs to be stored to remain fresh and for how long it needs to be stored.
• Be formed into a rigid format or flexible form depending on use and function.
• Form a strong seal to protect contents.
• Have good puncture or scuff resistance.
• Have tear resistance or where required to have 'easy tear' functionality to aid opening.
• Resist chemicals, e.g. in the case of bottles for liquid bleach.
• Prevent the ingress of UV light.
• Be formed into a required shape and hold that shape.
• Snap or break — this is an important feature in multipacks e.g. use of PS in yoghurt pots to allow one pot to be separated from another.
• Be flexible and allow the contents to be squeezed out e.g. ketchup, toothpaste — here LDPE would tend to be used.
• Bend but not break, e.g. PP in dual chamber pots where the content of one chamber needs to be mixed into the other before eating.
• Provide protection as in the use of EPS in packaging electrical goods and in the protection of other durable products to ensure they arrive undamaged.
• Provide insulation to maintain the cool chain, as in boxes for fresh fish during distribution — this where EPS offers unique benefits.
• Provide transparency so that the contents of a pack can be inspected.
• Be recycled back into food contact applications or other applications.

Also, of course, the commercial advantages for a particular application plays a part.

Some examples:

PE has good sealing properties and is often used as a sealing layer in laminate layers in conjunction with other polymers that have better barrier properties such as aluminium, nylon or EVOH or as a sealing area on a rigid pot formed out of PET or PP etc.The use of barriers and laminate structures is widely in use in many areas, e.g. snack foods such as crisps where there is a need to keep moisture, air and light out; in packaging fresh coffee to provide a moisture barrier; in cat food to keep moisture in and oxygen out; in tooth paste to stop the paste from drying out and losing flavour. These are just some examples.

PET is used in rigid and flexible form in flexible form for bags and in laminate structures especially as a print layer and is widely used for the manufacture of bottles and trays, the latter for use in ovens up to 220 degrees centigrade. In bottles, PET is also used due to its gas barrier properties, which help carbonated drinks retain their gas.

HDPE is widely used in rigid form e.g. bottles for fresh milk, in drums and crates and in flexible form HDPE is used in bags.

LDPE as films in agriculture for silage and used in stretch film applications and flexible containers e.g. the latter including toothpaste, moisturizers and ketchup.

PVC for use in blisters and shrink sleeves

PP is widely used in containers e.g. butter, yoghurt pots, caps, BOPP used in a flexible form for packaging salads, cigarette packaging, labels etc.

PS and EPS are used in the packaging of CDs, multi-pots of yoghurt, cups for vending and insulted boxes for fresh fish, protection of electrical and household goods etc.

Which are the main polymers collected for recycling in the UK at present

From households this includes: PET, HDPE and PP

From industry this includes: HPDE, PVC, LDPE, PP, ABS, PA, PS, EPS

Right now, 98% of councils in the UK offer a kerbside service to collect bottles and 75% offer a service to collect pots tubs and trays. Some councils offer the collection of films and bags as well (source: RECOUP).

How to recycle laminates

Increasingly we are seeing developments that will allow us to recycle laminates with the use of compatibilisers to help bind mixed materials with minor fractions of other polymers into structures that will allow no loss of strength and function in the recycled material. Also, some of the performance characteristics that presently require laminate structures at present are likely to be served in the future by new single material structures.

Why focusing on resource efficiency and reducing food waste is far more important than the number of polymers or the recyclability of the polymers in use

Using the right material will ensure resources in use continue to be reduced and ensure that food waste is minimised.

One recent innovation in the packaging of meat, which has involved the move away from modified atmosphere packaging involving two components to a one-component vacuum pack, has resulted in:

• A dramatic 3x increase in shelf life
• Reducing the amount of packaging in use by up to 90%
• Reducing food waste by up to 50%

Source DuPont and Denkstatt

In Summary

Calls for the use of fewer polymers than at present — or to only use those that are currently widely recyclable — could risk far more environmental damage, as packaging is selected to protect and preserve both the contents of the pack and the packaging. If any polymer was discontinued it could and only should be as a result of there being an alternative that could replace it and offer no loss of function, performance or overall resource efficiency in the process.

Each of the many tens of thousands products to be packed have different requirements and the variable properties of different polymers are selected to meet that vast and varied range of requirements.

Also, the development of more consistent approaches in the UK to the collection of plastic from both households and business will enable more recycling of plastics in the future as well as technical developments that will enable the recycling of much more material in the future, even when it is highly contaminated. So focussed action in these areas is likely to be more rewarding from an environmental perspective than in simply trying to limit the range of materials in use.