Polystyrene In Packaging

Polystyrene compounds are a thermoplastic polymer made from the aromatic monomer styrene, a hydrocarbon that is commercially manufactured from petroleum. Polystyrene is one of the most widely used plastics and is the base for foam plastic as well as PVC.

Polystyrene compounds are used in the production of various packaging materials. One of the most important features of this type of material in the context of packaging is that it has moderate to good barrier properties to liquids, making it suitable for holding beverages and warm foot products (like fast foods). Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and similar knickknacks. It is also be the basis for one of the most popular 'foamed' plastics called 'styrene foam' or 'Styrofoam'.

Below is a description of some of the common polystyrene polymers used in various forms for packaging.

General Purpose Polystyrene - Styrofoam - (GPPS)

The material is brittle and very rigid, transparent, has low shrinkage, is easy and cheap to produce, has excellent X-ray resistance and is free from any odor or taste. Polystyrene has low barrier properties and is therefore not useful for long term packaging.

This material is widely used in disposable party glasses/ fast food boxes (like McDonalds or Burger King) and is a recyclable material. The foam can be formed into all shapes through heat-stamping or injection molding processes.

Expanded Polystyrene & Extruded Polystyrene (EPS & XPS)

- Expanded Polystyrene (EPS - 'bead foam')

EPS is usually white and made of expanded polystyrene beads. This is a foam type material; it is brittle and not suitable for use at high temperatures. It is commonly produced and packaged as rigid panels (size 4' by 8' or 2' by 8' square feet in the United States) also known as 'bead-boards'.
This material is generally used to contain fresh meat or fast foods (short term storage) as it has poor barrier properties. Other uses include packing 'peanuts' (common loose-fill packing material for fragile objects) and molded packing material for cushioning fragile items inside boxes.

- Extruded Polystyrene (XPS - 'Foamcore')

XPS has air inclusions in its structure which give it moderate flexibility, low density, and good insulation.
Foamed between two sheets of paper, it makes a more uniform substitute for corrugated cardboard and is used as such to make shock absorbent packaging containers.

High Impact Polystyrene / Toughened Polystyrene - Bextrene (HIPS / TPS)

Pure polystyrene is brittle, but hard enough that a fairly high-performance product can be made by combining it with polybutadiene rubber during polymerization. The resulting compound is a copolymer (also known as high-impact plastic) which is hard, rigid, translucent, has good impact strength (7 times greater than GPPS), low shrinkage, is cheap and easy to process, X-ray resistant, free of odor or taste, has very good resistance to dilute acids and alkalis, alcohols, oils and greases.

HIPS is used in product casings and thermoformed trays and is unsuitable for use at high temperatures (i.e. microwave heating / ovens). It's a material widely used to store fresh produce (e.g. mushrooms, strawberries etc.). It has poor barrier properties and is recyclable.

Polypropylene / Orientated Polypropylene/ Expanded Polypropylene (PP, OPP & EPP)

These are thermoplastic polymers and are a semi-rigid, translucent, have good chemical and fatigue resistance, are tough, steam sterilizable and recyclable, possesses good heat resistance, and are resistant to dilute acids, alkalis and alcohols with moderate resistance to oils and greases. If biaxialy orientated (OPP), they have moderate barrier properties to gasses and are a good barrier to water vapor. PP and OPP are moderately expensive to produce.

When thermoformed it is suitable for use at temperatures up to 110° C, therefore it is suitable for use in microwave ovens, in this instance it is widely used to store bakery/confectionery products. It is durable, dirt resistant and is highly colorfast, meaning it can be colored in variety of ways and colors and is thus ideal of retail packaging.

- PP is also used to make closures (a very versatile packaging material).

- OPP is generally used for a wide variety of products and parts, including storage and packaging boxes (from sheet form), bottles and bottle caps.

- EPP has good impact characteristics due to low stiffness and rigidity, allowing it to resume shape after impact. It is used as a shock absorbent in packaging.