What is EPS

“Foam” is generally known everywhere but in fact its’ meaning is so wide. According to translation “Foam” means, “expand” or “blow”.

Herewith we concern “Foam” as the expanded plastics. There are many kinds of plastics in the world, any plastics when react with the Blowing Agent will become “Foam” which generally called “Foam Plastics”.

The example of well -known foam plastics is sponge, food box, foam sheet, spray foam for insulation and etc. These foam plastics are produced from different kinds of plastics.

We will only mention about foam that produced from Polystyrene / PS (C8H8) plastic. PS Foam or so-called “Expanded Polystyrene” are made for food box, ice box, packaging for television and floating Krathong foam.

There are two kinds of Polystyrene Foams:
1. Expandable Polystyrene / EPS usually use as packaging for many kind of products such as television, electrical appliances, helmet, ice box, sheet foam and block foam for road construction.
2. Polystyrene Paper / PSP so called Extruded Polystyrene / XPS which use to produce food tray and food box.

How to produce foam?

1. Expandable Polystyrene / EPS is PS Foam that use Pentane gas (C5H12) as the blowing agent. During the material production process called “Polymerization” the polystyrene resin granules impregnated with the blowing agent. EPS production processes begin in the pre-expansion process where the EPS bead will expand by the heat of steam usually 50 times in volume. Next step is molding process where expanded foam bead will be heated again with steam then they expand further until they fuse together, forming as foam products.

foam1

There are mainly 2 types of EPS molding machines;

1.1 Shape molding machine that produce various shapes of foam products according to the molds such as icebox, helmet and packaging foam.

1.2 Block molding machine that produce block foam and sheet foam Expanded EPS foam bead contains 98% air per volume, only 2% is plastic. This make EPS foam very light weight, has low thermal conductivity because air is the best insulation, high compressive strength and excellent shock absorption. These properties make EPS to be ideal material for packaging and construction.

2. Polystyrene Paper (PSP) is a PS Foam which produced by extruding process as another plastic. Production process start when put polystyrene resin pellets into the extruder that heated by electric. Foaming process occur at the end of extruder where the blowing agent, butane (C4H10) gas react with the melt plastic then become foam. The melted polystyrene foam then extended as sheet then roll as paper roll, that is why commonly known as “Polystyrene Paper”. The polystyrene foam sheet or polystyrene paper can be produced as many shape according to the mold by thermal forming process such as food tray, cups, bow, and food box.

There’s no any CFC’s in PS foam

foam2

Both EPS and PSP contain 95 -98 % air another 2-5% is polystyrene which is pure hydrocarbon. CFC’s is Chlorofluorocarbons which is totally different chemical structure from polystyrene. CFC’s has very low blowing point and uneasy to be maintained in EPS beads. Therefore, EPS Foam never use CFC’s at any stage of its production. The blowing agent used since EPS Foam was first introduced in 1952 by BASF of Germany is Pentane gas which, does not contain any chlorine atoms as CFC’s. PSP Foam in the beginning used CFC’s as blowing agent. In the past two decades CFC’s are gradually phased out from plastics and refrigerator industries. PSP molders in Thailand already use Butane (C4H10) as the blowing agent since the last 15 years. Butane gas is the gas that we use at home for cooking. The blowing agents that use in producing PS Foam are Pentane and Butane, which are pure hydrocarbon as polystyrene. They belong to the same chemical family, the paraffin series as methane, ethane, and propane gas.
How to manage the EPS foam waste

Apart from recycling by melting and compacting, there are many ways to manage the EPS waste as the followings:

1. Crush in to small particle and mix with soil. Foam waste will improve ventilation in the soil, organic substances in the soil will become easier the humus.

2. Mixing the crushed bead with cement to reduce the weight and increase insulation properties.

3. Combustion at 1000 C with sufficient air supplies in to generate heat. Burning EPS require no any additional fuel, in fact EPS can replace the fuel normally required for combustion, l kg of EPS saves 1 kg = 1.2 – 1.4 Litre of fuel oil.

The Recycling of PSSince both EPS and PSP Foam are made of Polystyrene, which is thermoplastic, so that it will become again a polystyrene plastic when recycled. We recycle both EPS and PSP Foam by first crushing into small particle then melting or compacting it. Melting can be done by heated roller, disk or screw extruders, where the regrind scraps is heated usually by electrical power for some time above the melting temperature. Compacting can be done by rotary compactors where pressure and frictional force create heat below melting temperature to soften the regrind scraps for only few seconds. This method also called “agglomeration”.

PS pallet from recycled foam will be produced in various kinds of plastic products e.g. video and tape cassette and ruler. The other way to reuse EPS Foam is to mix the regrind beads with the new expanded bead for re-production in molding process.

By Apiwat Hiranpradit