EPS foam — Common packaging insulation

下载EPS(expanded polystyrene) foam is among the largest commodity polymer. It’s also one of the main choice in my thesis.

EPS is consisted of closed cells which are glued together. It is rigid and tough and has good thermal insulation and damping property.

It is often used as packagings because of it can prevent damage and its thermal insulation required for food and medical transportation. It’s also used in building insulation.

The thermal conductivity of EPS varies from 0.032 to 0.038 W/(m·K) depending on its density. Recently the thermal conductivity has reached 0.029 to 0.034 W/(m·K) by adding graphite, aluminum and carbons as fillers and such EPS has grey or black color different from the normal white color.

images (3)It is normally produced by two meganism: 1. Polystyrene beads are expanded to little balls(pre-expanded polystyrene) with blowing agent like pentane. 2. The little balls are glued together with hot steam. In my thesis, we choose to use ready made pre-expanded polysyrene, because it’s easy to pour the little balls into the little cells of the panel.

There is another polystyrene foam called XPS(Extruded polystyrene). It offers higher surface roughness and stiffness. It has a reduced thermal conductivity between 0.029 and 0.039 W/(m·K). It has a higher water vapour diffusion resistance, which makes it more suitable in wet environment than EPS. One disadvantage of XPS is the use of hydrofluorocarbons(HFC) as blowing agent which has very high global warming potential.

There are two famous trade names of EPS. Styrofoam is a brand of XPS but is refered to EPS packaging in United States and Canada. Thermacol is another tradename originated from BASF.

There are a few disadvantages. It is non-biodegradable, but it’s recyclable although the recylcling program can be limited. It is flammable like other organic compounds. There will be rough panel edges and dust when cut, when XPS is cut clean and straight. It’s not water proof as XPS.  It has a very low flexual strength while XPS has exellent flexual breaking strength.

Here is the reference link: http://www.wisegeek.com/what-is-a-polystyrene-foam.htm

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8 thoughts on “EPS foam — Common packaging insulation

  1. As the structural stiffness is provided by the Econcore itself, I would think that the only criterion for the insulation material is the thermal conductivity. Keeping that in mind, nitrogen would seem an interesting option. We use it in scuba diving as thermal insulation gas in drysuits. A quick wiki search shows me that the thermal conductivity is 0.026 W/(m·K). The main advantage though, is that it is nearly the best recyclable insulating material available (normal air consists of about 78% nitrogen 😉 ), and it isn’t flammable.

      • You’re right, my mistake. Of course the thermal conductivity of air is about the same as nitrogen. It’s argon that’s used as insulating gas (0,016 W/(m*k)), which is less suitable for your application because of its price.

  2. If you compare the thermal conductivity of air (0.025 W/mK) and the one of EPS (0.029-0.034 W/mK), you could conclude that air is a better thermal isolator than EPS. So I was wondering how effective it is too fill up the air-cores in the panels with EPS?

    • I think the convection of air [not trapped in a small matrix] makes it a less efficient insulator compared to, i.e. EPS, in which there’s almost no convection at all.

      Nevertheless I too am curious to know if there’s any measurable difference in overall thermal conductivity between air filled and EPS filled Econcore.

      • You are right, convetion but also radiation is reduced by the EPS filler.
        The experimental result is not coming out yet.
        But by simulation, the air filled is reduced by 1/6 to 1/4 by EPS filler.

  3. You state that the thermal conductivity decreases when the foam is enriched with graphite, which makes it more dark. But I always thought that houses for example were painted white to give better insulation against heat. Do you know the mechanism behind the lower thermal conductivity of dark foam?

    • It’s different mechanism. Houses are painted white to reflect radiation, while adding graphite is to reduce conduction and convection and dark is just a side effect.The mechanism of dark foam may be caused by the smaller scale spherical pores that limit the convection in air pockets.

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