EPS Packaging

Environmentally Friendly

EPS has revolutionised the way growers and manufacturers have packaged their products, throughout New Zealand and across the world. This clean, lightweight and cost effective packaging medium has entrenched itself in the market place.

It is the best all-round transportable protection for goods which are fragile and/or require the product to retain its freshness throughout its journey, whether to a local or international destination.

In fact EPS is so versatile it can be moulded to shape for standard and large quantity items such as fish and fruit boxes, whiteware packaging etc, or can be cut from large blocks and hot wire cut to any shape or design.

This makes it the ideal choice for the smaller manufacturer producing niche market items. This factor has particular relevance for NZ conditions, where short run manufacturing is a common practice owing to our small economy. It should also be noted that since the introduction of EPS for packaging the cost of packaging and transportation of these goods has been significantly reduced. This is because the energy required to manufacture and transport EPS is much less than conventional materials such as timber, straw, cork or cardboard. Other positive attributes are the options available for recycling EPS packaging. Further details can be found in the link to the right for EPS and the Environment.

Chemical Resistance

EPS is unaffected by water, most acids and alkali solutions. If EPS has to be brought into contact with substances of unknown composition, the reaction of the material should first be checked.

The best way of doing this is to age a piece of EPS in close contact with the other material and observe what happens. The duration of the experiment can be reduced by raising the temperature.

The table below depicts the effect of a few common chemicals & solvents when placed in contact with EPS.

Chemical Resistance of Expanded Polystyrene
Chemical or Solvent
Salt solution (seawater)	+
Soaps and wetting agent solutions	+
Bleaching agent solutions, e.g. sodium hypochlorite, chlorine water and hydrogen peroxide	+
Dilute acids	+
Hydrochloric acid, 35%, nitric acid up to 50%	+
Anhydrous acids, e.g. fuming sulphuric acid, 100% formic acid	-
Caustic soda and caustic potash solutions. ammonia water	+
Organic solvents such as acetone, ethyl acetate, benzene, xylene, paint thinners and trichloroethylene	-
Saturated aliphatic hydrocarbons, surgical spirit, white spirit	-
Paraffin oil, vaseline	+-
Diesel fuel	-
Engine fuels (normal- and super grade petrol)	-
Alcohols, e.g. methanol and ethanol	+-
Silicone fluids	+
+ resistant: the foam is not attacked even after a long time + - limited resistance: the foam may shrink after prolonged exposure to the chemical, or its surface may be attacked - not resistant: the foam shrivels up more or less quickly or is dissolved

Advantages of EPS

Because of its excellent physical and chemical properties EPS offers the following advantages when used as a packaging material.

• Low density, therefore lightweight packages.
• High energy absorption when dropped or subjected to impact.
• Abrasion resistant, yet relatively soft surfaces protect packaged goods against dirt and damage.
• Low thermal conductivity protects contents against sudden temperature changes.
• Since the foam is unaffected by water and vapour, its mechanical properties remain intact.
• Chemically inert, so that it can be used for food packaging.
• Easy to mould and cut to shape.

Insulated Packaging

Insulated packaging is required whenever the temperature of the contents must be maintained above or below the ambient temperature, depending on the nature of the product, e.g. hot foods, ice cream and fresh seafoods, or pharmaceuticals.

These demands can be met by materials with a low thermal conductivity. This is a measure for the heat flow over a given temperature gradient under standard conditions (DIN 52612). It can be seen from the table below that the average thermal conductivity of expanded polystyrene is very much less than that of compact plastics.

In other words, expanded polystyrene is the ideal material for insulated packaging.

If the thermal conductivity and the transportation and storage conditions are known, polystyrene insulated packaging can be designed for a given application.

Hints on Usage

 Contents will maintain desired condition longer by: 

• Airtight fit between the upper and lower halves of the packaging, e.g. by close-fitting tongue-and-groove joints.
• Arrangement of the contents in a compact form, as cubic as possible, in order to obtain a low area/volume ratio.
• Placing the refrigerant (ice) at the highest point, if the pack is to be kept in a given position.
• If the position of the pack cannot be foreseen, the refrigerant should be distributed over at least 4 surfaces at the sides of the contents.
• The inclusion of internal ribs to allow better air circulation within the packaging and by designing packs with thicker walls, will ensure the temperature remain uniform.

Impact Protection

One of the key functions of packaging is to protect the contents from external impact. In this area expanded polystyrene is unsurpassed.

As seen in the table below, the value quoted for e indicates the potential energy of a dynamic load that must be applied to a cushioning material to obtain a given value of C.

It can be seen from this table that polystyrene foam is the best shock absorbing material of all, i.e. it has the lowest value of C.

Table of Impact Protection for Sample Materials

Material Substance	Density e Kg/m3	Cushioning factor C* -	Specific potential energy e* cN.cm/cm3
PE expanded beads	30	3.5	500
PUR soft polyether foams	30	3.1	125
PUR soft polyester foams	30	3.3	200
PUR semi-hard	30	2.8	350
Expanded Polystyrene	30	2.2	2400
PS loose-fill material	8	4	400
Foam rubber*	200	4.3	350
Coconut fibres* rubberized	80	3.8	70
Corrugated board* single corrugation	800 g/m2	2.4	530
Corrugated board* twin -corrugation	1050 g/m2	2.6	800
Air, 1 bar	1.29	5.11	650

Design Recommendations

The following points must be observed in the design of polystyrene packaging (in addition to ensuring that the compressive strength lies above the maximum permissible compressive load).

• The load bearing walls in polystyrene packs must guide the stacking forces vertically downwards in a straight line.
• Fillets of at least 1Omm radius must be on all edges and corners in the interior of the pack and in the recesses in the walls and base.
• The outer walls and edges must be rectangular and exactly perpendicular to the surface of the base in order to ensure that the load-bearing area is as large as possible.

The strength of EPS is completely retained even on direct contact with water. This demonstrates that moulded EPS shapes ensure secure and stable stacks in all stages of transportation, even under severe conditions.