The blowing agent used since EPS Foam was first introduced in 1952 by BASF 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.
It is contemplated that various blowing agents may be used in the present invention, including physical blowing agents such as hydrocarbons. The preferred physical blowing agents for this invention are organic chemical compounds that have boiling points less than about 37° C. These organic compounds include, but are not limited to, fully hydrogenated hydrocarbons and partially fluorinated hydrocarbons that are considered to be flammable. Flammable as defined herein generally includes those materials having flashpoints less than about 37.8° C.
The preferred fully hydrogenated hydrocarbon blowing agents include the initial members of the alkane series of hydrocarbons that contain up to five carbon atoms and which are not regulated by governmental agencies as being specifically toxic to human or plant life under normal exposure. These fully hydrogenated blowing agents include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane and blends thereof.
The most preferred fully hydrogenated hydrocarbon blowing agents are C2 to C4 compounds and blends thereof An example of a preferred blend is a blend of approximately 67 weight percent n-butane and approximately 33 weight percent isobutane, which is commonly referred to in the industry as an A21 butane blend. This blend may be added at a rate of from about 1 to about 20 weight percent of the total extruder flow rate, and preferably added at a rate of from about 3 to about 20 weight percent of the total extruder flow rate.
It is contemplated that auxiliary blowing agents may be used in the present invention in amounts less than about 40 weight percent of the total blowing agent. The preferred auxiliary blowing agent are partially fluorinated hydrocarbon blowing agents that have molecules containing up to three carbon atoms without any other halogen atoms, and those considered flammable. For example, this includes 1,1-difluoroethane (HFC-152a), and 1,1,1-trifluoroethane (HFC-143a), with the most preferred auxiliary blowing agent being HFC-152a. It is also contemplated that 1-1-chlorofluoroethane (HFC-142b) and 1-1-dichloro-2-fluoroethane (HFC-141b) may be added as auxiliary blowing agents for non-regulated insulation applications.
In addition, water may optionally be added at a low concentration level as an auxiliary blowing agent. The water quality should be at least adequate for human consumption. Water containing a high level of dissolved ions may cause excessive nucleation, so therefore deionized water is preferred. The preferred rate for water addition is from about 0.05 to about 0.5 parts water to 100 parts of the polymeric composition (0.05 to 0.5 phr). The most preferred rate of adding water is from about 0.2 to about 0.3 phr.
What is EPS
Polystyrene is one of the most widely used kinds of plastic. It is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is a thermoplastic substance, it melts if heated and becomes solid again when cool.
Polystyrene is most commonly found in three forms. Rigid Polystyrene (PS), Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS).
Rigid polystyrene has many applications including disposable cutlery, cd cases, video/casette casings, components for plastic model toys as well as some margarine and yoghurt containers. Extruded polystyrene foam has good insulating properties making it important as a non-structural construction material. XPS is sold under the trademark Styrofoam by Dow Chemical, however this term is often used informally for other foamed polystyrene products.
How to produce foam?
Expandable Polystyrene / EPS:
This is PS Foam that uses Pentane gas (C5H12) as the blowing agent. During the material production process called “Polymerisation” 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. The next step in the process is moulding process where expanded foam bead will be heated again with steam then they expand further until they fuse together, forming as foam products.
There are mainly 2 types of EPS moulding machines;
- Shape moulding machine that produce various shapes of foam products according to the molds such as icebox, helmet and packaging foam.
- Block moulding 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.
Polystyrene Paper (PSP):
This is a PS Foam which is 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 is then extended as sheet then rolled as paper roll, that is why it is commonly known as “Polystyrene Paper”. The polystyrene foam sheet or polystyrene paper can be produced as many shape according to the mould by thermal forming process such as food tray, cups, bow, and food box.
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 in its 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 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 moulders 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:
- 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.
- Mixing the crushed bead with cement to reduce the weight and increase insulation properties.
- 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 PS:
Since both EPS and PSP Foam are made of Polystyrene, which is thermoplastic, so that it will become again a polystyrene plastic when recycled. AMEPS members 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 moulding process.