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Why do we use different polymer types in plastic packaging?

December 06, 2022
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Plastic packaging serves several important functions in our modern lives, which are the primary reasons we rely on it:

Protection: protects vulnerable products from damage whilst in transit and from contamination or damage by moisture, humidity, gases, microorganisms, insects and light.

Preservation: preserves products for longer, which reduces waste by giving people more time to use or consume them before it is no longer suitable to do so.

Prevents waste: products kept together and spillages avoided.

Transportation: Allows transport over great distances, so that we have access to a wide variety of non-local produce that, in turn, encourages trade. It also saves space through stacking objects which make transporting more efficient.

Displays information: important information about the product, such as nutritional content or allergy advice, is displayed on packaging.

 

Why do we use different polymer types in plastic packaging?

 

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.