Amount of pressure needed for polystyrene (PS) compaction

[CasualCause]

Hi all!

 

 

I may not have the necessary knowledge in chemistry to calculate such seemingly easy problem.

How much pressure is needed to compact 30kg/m3 density PS into a 330kg/m3 one? Can someone please explain me this through equations?

 

Hope I am not to be expelled for my noobness

[CaptainPanic]

You first need to define the starting pressure of your PS (polystyrene foam, I assume). The final answer depends on that. By default, it would be "atmospheric pressure", or 1.01325 bar, but it would be best if you confirm this.

 

And maybe you can solve the question now that you know what piece of important information was missing so far?

 

 

Mod comment: also, I moved your post, at your request.

[CasualCause]

Indeed.

Atmospheric pressure is Po. On To=24-30 Celsius room temperature. (I am giving the temperature in case if temperature will count as a factor in pressurizing material, i.e. will overheat & overheat has to be calculated?)

I am aware of compressing solid PS (non-foam) may require a huge amount of pressure.

I recently found some documentation on this subject, namely:

A Static and Dynamical Properties of PS
http://pubs.acs.org/doi/abs/10.1021/ma60073a024

And a book of high pressure Chemistry and Physics of Polymere

http://books.google.de/books?id=6IwG_5hqgGkC&dq=polystyrene+compressibility&source=gbs_navlinks_s

 

 

I will return with a solution proposal later, after I read these a bit .

[CaptainPanic]

As a first approximation, I would just calculate as if you are compressing gas. (After all, a foam is mostly small gas bubbles).

 

No equations in this link, but it is a fun read anyway (and not too long).

[CasualCause]

As a first approximation, I would just calculate as if you are compressing gas. (After all, a foam is mostly small gas bubbles).

 

No equations in this link, but it is a fun read anyway (and not too long).

Thank you for the article

 

I am interested in fact the recycling cost of Polystyrene (any kind of it). Knowing its high recycling value as pellets, compressed to 330kg/m3 or the EPS (Expanded Polystyrene-foam polystyrene) as insulation sheets.

 

There is certainly a reason why isn't accepted as recyclable material, and the reason may be in the cost of pressurizing it.

 

 

[CaptainPanic]

I do not think that the foam should be compressed (in the sense of gas compression) to increase the density if you want to recycle. When you compress it, and you compress it for a short period, it will actually just decompress just as you release the pressure, meaning that the volume will increase again. You should somehow get the density to increase permanently. Unfortunately, the PS decomposes before it melts, otherwise you could just melt it down. I think I'd like to find out first what it decomposes into (perhaps that can be recycled too).

 

Maybe you can dissolve the foam (I believe it dissolves into acetone). The trick would be to use as little solvent as possible (and preferably a non-toxic one). It's not ideal either, because obviously you would have to separate the solvent out again, and you would have recycling trucks going up and down with solvent (a high risk liquid, which makes it expensive).

 

I think there is a reason why even in Germany, where recycling is mandatory, the PS recycling isn't taking off.

 

Also, I believe that you got your values from wikipedia? The values of 30 kg/m³ to 330 kg/m³ are bulk density - not actual material density. (Bulk means if you take 330 kg of polystyrene scrap, and you pour all those pieces into a container, it should fit in 1 m3, including all the pockets of air in between those pieces). Therefore, the actual material density should be even more.

[CasualCause]

Indeed, I forgot to link wiki though I intended to.

Understanding the bulk notion, I can't see the problem with compressing scrap PS. I find it easily feasible to pressure out air from that 1m³ until 330kg fits in there instead of 30kg. This is just packing problem from my perception. Therefore if its that valuable in this ultra-packaging, I cannot see the problem with recycling it. This is certainly not maintaining huge MPa-s for minutes long to melt them into a reusable material, battling with temperature levels.
Collecting it is the same procedure as collecting pet, or glass.