Expanded Polystyrene (EPS)
WHAT IS EPS?
Expanded Polystyrene (EPS) is a rigid, closed cell, thermoplastic foam material produced from solid beads of polystyrene, which is polymerised from styrene monomer and contains an expansion gas (pentane) dissolved within the polystyrene bead.
Each solid polystyrene bead contains small amounts of gas which expand when heat (in the form of steam) is applied, thus forming closed cells of EPS. These expanded cells occupy approximately 40 times the volume of the original polystyrene bead, and so with a second heat treatment using a mould, large EPS blocks can be moulded into specific customised shapes.
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The commercial development of polystyrene was initially started in Germany by IG Farben in 1929, and built on by US firm Dow Chemical Co. around 1935 (1). Though used in both Germany and the US throughout the Second World War, polystyrene foam was more widely introduced by Dow Chemical Co. in 1954 under the brand name 'Styrofoam'. 'Styrofoam' - invented by Dow scientist Ray McIntire - was a result of trying to make a new rubber by combining styrene and isobtylene (2), but by doing so he 'accidently' created a foam 30 times lighter and far more flexible than polystyrene (3).
| EPS Properties |
| Waterproof |
| Insoluble |
| Non-hygroscopic |
| High impact |
| Long-term stable thermal conductivity |
| Non-toxic |
| Chemically inert |
EPS can be moulded in a range of densities from as low as 12kg/m3 up to 50kg/m3 with the resulting properties, such as compressive strength, being determined by the manufactured density.
Products made from EPS are typically water resistant, tough and give very high impact resistance. The air-filled structure has long term stable thermal conductivity, is non-toxic and chemically inert.
Fungi and bacteria cannot grow on EPS due to it's properties.
The production of products made from EPS is done so in 3 stages...
1. Pre-Expansion
- A measured quantity of expanded polystyrene beads are put into a profoamer
- Steam is circulated through these beads as well as a small amount (usually around 5% by weight) of petane which is a blowing agent. The beads are subsequently expanded by around 40 times.
- The expanded polystyrene beads are transferred into a storage hopper...
2. Maturing
- The material cools and the pentane liquifies which creates a partial vacuum inside the bead
- The expanded polystyrene beads are stored for between 12-24 hours to aid the maturing and to allow air to diffuse into the beads
3. Final Forming
- The beads are then reheated using steam and the mould is filled with a pre-measured amount of expanded beads
- Steam is introduced into the mould circulating round the polystyrene beads, expanding them further by 10%.
- The steaming process stops and a vacuum is drawn to extract residual condensed water and heat. Additional water channels assist in cooling the mould
The video below shows the process...
As does this animation...
4. APPLICATIONS
4.1. PACKAGING
As EPS is made of 98% air, it is one of the lightest packaging materials in existance, and therefore adds very little weight to packaging, which means transport costs and fuel emissions are kept to a minimum.
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A Selection of Products Made from EPS |
Polystyrene foam is also tough, and the cellular matrix gives outstanding impact resistance and shock absorbency for the protection of products, making it an ideal packaging in many applications, includes protecting all kinds of electrical components, from mobile phones to fridge-freezers.
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| Expanded Polystyrene is Used to Package Goods to Protect them in Transit |
It is also widely used to protect food and avoid damage during various stages of food production and shipment due to its properties being unable to grow fungi and bacteria. Its low thermal conductivity is utilised largely in the fish industry for the packaging and transport of fish products, and also in the medical field to transport vital transplant organs.
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| EPS is Often Used for Fishboxes as it Protects the Fish and Keeps it Cold (more info: www.fishboxes.info) |
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| EPS Insultation Between Wall and Plaster |
Due to its high levels of thermal insulation (from its light weight closed-cell structure, enduring strength, and long term structural integroty) EPS has been used in construction applictions since before the 1970's.
EPS is widely used in walls, roofs, and floors, where its compressive strength can be tailored for specific systems such as beam and block construction, underfloor heating systems, and below concrete floor slabs.
It is also specified for void filling and, at higher densities, as a base for road or rail embankments where traditional fill materials are too heavy. The material has the advantage in city centres of reducing congestion and traffic with the delivery of large volumes of product more efficiently than hardcore.
Other specialist applications such as protection of foundations have also been developed.
EPS Floor Insulation Board: Technical Data
| Standard (White) | Low Iambda (Grey) | ||||
| Material | EPS70 | EPS100 | EPS150 | EPS 200 | EPS 70 |
| Compression Strength at 10% Deformation (kPa) | 700 | 100 | 150 | 200 | 70 |
| Thermal Conductivity (W/mK) | 0.038 | 0.036 | 0.035 | 0.034 | 0.030 |
5. EXPANDED POLYSTYRENE (EPS) & EXTRUDED POLYSTYRRENE (XPS): TWO POLYSTYRENE MATERIALS
There is sometimes confusion between Expanded Polystyrene and Extruded Polystyrene because they are both manufactured from polystyrene resin and have similar names. However, the two materials are manufactured in very different ways, and the end result is two unique materials that provide specific performance properties to the end user. The properties of Expanded Polystyrene (EPS) make it appropriate for use in construction and packaging applications, XPS is only used in construction applications.
5.1 Differences in manufacture
EPS is manufactured from Expandable Polystyrene, a raw material that, in its raw state, looks like salt and contains Pentane, a blowing agent. XPS is manufactured from GPPS (General Purpose Polystyrene) pellet, the blowing agent and colour dye are added by the product manufacturer.
The first stage for both products is pre-expansion, although in two different ways. The EPS manufacturer heats the raw material using steam, the beads soften and expand into non-connected voids that must be freely flowing to achieve the required pre-expansion.
The XPS manufacturer heats the pellets, so they melt and then injects the blowing agent at high pressure creating the foams cellular structure. This foam is immediately extruded, cooled and cut and profiled into boards. For the EPS manufacturer, the next stage is to store this pre-expanded bead in huge hoppers, usually for between 24-72 hours. In this time air enters the beads as the pentane escapes. The final stage is to mould these beads, either into huge blocks to be sliced into insulation boards or into boxes or bespoke packaging. The final EPS product is 98% air.
5.2 Sustainability Characteristics
Both EPS and XPS have excellent thermal properties are used for insulation board in the construction industry and significantly reduce the carbon use of buildings that they insulate.
A significant difference between the two is that EPS is available in a range of densities from very low to high, whereas XPS is only made in high densities. This makes EPS a very versatile, cost-effective and lightweight material that can be used across a wide range of applications and for civil engineering projects.
EPS maintains consistent R-values over time and across external temperature variations helping to reduce CO2 emissions. The thermal performance of XPS reduces over time as off-gassing occurs.
6. ENVIRONMENTAL FACTS
EPS has a low carbon impact because clean manufacturing technologies equate to minimal energy and water inputs with no production waste. The protective performance of EPS also helps to reduce wastage caused by goods that are broken or damaged in the supply chain, which saves energy, materials, and transportation costs.
The use of EPS also helps to prevent food wastage because due to its cellular nature, as it protects the food and avoids damage in the various stages of production and shipment from farm to fork, ensuring that many different foods reach the retailer or consumer in perfect condition.
EPS is HFC, CFC, and HCFC free, with Pentane used as its blowing agent. Pentane has a low Global Warming Potential (GWP) of less than five - meaning the EU does not register pentane as a substance hazardous to human health or the environment.
As EPS is extremely lightweight it helps to reduce fuel consumption - when goods are transported compared to other heavier packaging materials.
Styrene, used in the manufacture of EPS, occurs naturally in many commonplace products including strawberries, beans, nuts, beer, wine, coffee beans and cinnamon.
The manufacture of EPS is a low pollution process. As steam is the key ingredient, and the water is re-used many times. There is no waste in the process as all cut off or rejects are re-used.
Only 0.1% of total oil consumption is used to manufacture EPS.
The carbon footprint of EPS is lower than many other packaging materials in use today.
7. END OF LIFE
EPS can be successfully recovered and recycled wherever facilities for recycling of EPS exist, which are becoming more widely available from mechanical recovery to solvent treatments, returning the polymer back to raw materials. EPS, sourced from packaging waste, is an ideal material for recovery schemes. Today it only represents 0.1% of municipal solid waste (MSW), although many believe it’s a lot more due to its bulky nature! Where the infrastructure for recycling is not currently in place, it is the ideal candidate to be submitted to energy from waste schemes.
The key benefit of using EPS for EfW is that it has a high calorific value (46,000 kj/kg) not dissimilar to natural gas at 48,000 kj/kg. There are also no toxic emissions in this method of waste management of EPS, as it is incinerated in modern plants at very high temperatures. The biproducts are therefore only steam, carbon dioxide and very low levels of non-toxic ash, which are less contaminating than a typical campfire - and in fact there is no credible evidence that EfW schemes have any impact on public health.
EfW emissions are strictly controlled, and the UK Government’s ‘Waste Strategy for England 2007’ saw ‘no credible evidence of adverse health outcome’ from EfW emissions.
Sustainability of EPS
EPS is 100% recyclable and widely recycled with thousands of tonnes recycled every year from the UK. Data from 2023 showed 66% of EPS packaging disposed of in the UK was recycled (EPS Group, 2023 - calculated by collecting raw data from UK convertors alongside UK and EU recyclers of EPS. Raw data and estimates have been used by industry experts to calculate the total recycling rate.). Alongside this, EPS is currently recycled in at least 38 countries over four continents. Recent reports by Conversio and the European Commission’s Joint Research Centre (JRC) highlight the remarkable progress achieved. Mechanical recycling is the most common method to recycle EPS whereas an emerging chemical recycling industry in the UK provide further opportunities.
To drive recycling rates further the EPS Group recently announced the launch of our EPS Recyclers Map, making it easier than ever to locate facilities that recycle Expanded Polystyrene (EPS). Whether you’re a business, organisation or local authority, the map provides you with easy-to-navigate features to find drop-off locations and contact details. It is a step forward in reducing waste and promoting a circular economy. This tool is here to support your recycling efforts.
Click HERE to find out more.
If you are looking for a supplier of EPS (either moulded product or materials) complete the form below and the BPF will analyse your enquiry and send on directly to relevant companies within membership who be in touch.
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Moulding Expanded Polystyrene (from Plastipedia)
List of EPS Recyclers
Discover Channel: How It's Made Expanded Polystyrene
1) Plastic Historic Society: The History of IG Farbenindustrie
2) The Inventors: Polystyrene and Styrofoam
3) National Inventors Hall of Fame (Otis Ray McIntire)
