# Need good aproximation to the atomic composition of late 1980's expanded polystyrene foam

I'm not a chemist and what little I know about expanded polystyrene (EPS) foam has been found by looking at articles on the internet. At work I need an approximation to the atomic composition (at %) of foam that dates to the late 1980's up to early 1990's. Beyond the fact that it's 'EPS,' I have a density of 0.05g/cc, and that is it. It is important to get a reasonable estimate of higher Z elements for this foam.

I've read that EPS is 95-98% air. Therefore, when I look on the Pharosproject.net at the common material EPS Insulation, I am confused in that air components, $$N_2$$, $$O_2$$, and $$Ar$$ seem not to be in the list. I'll stop at the top three components by weight percent in that list and suitably approximated: (polystyrene=$$CH_2$$, 96%), (flame retardant containing bromide, 1.0%), (3 blowing agents, 2%) This totals 99%, and for the sake of the ensuing calculation, let the extra 1% fall in the category of blowing agents. The lack of the atmospheric components seems suggestive that this is some kind of pellet that has yet to undergo a chemical process. I don't know a chemical formula for the bromide-containing flame retardant, but let's take HBCD (hexabromocyclododecane) with formula $$C_{12}H_{18}Br_{6}$$. I'm assuming a closed-cell foam. I'm guessing that some of the blowing agent and all of the flame retardant ends up in the cells, along with the air. Someone with expertise might be able say how much blowing agent ends up in the cells.

Now in the 1980's through the early 1990's, I've read that hydrochlorofluorcarbons were the blowing agents. Therefore assume 3% $$CF_3 CH_2 F$$ (refrigerant R134a) to replace the blowing agents of the previous paragraph. If this is a bad assumption, please correct it.

Assume air is, in vol %, ($$N_2$$,78.08%), ($$O_2$$,20.95%), (Ar, 0.93%), ($$CO_2$$, 0.04%) where the $$CO_2$$ percentage has been made to take up the slack in trace elements so the total for air is 100% by volume.

I want a table in atomic percent for each element for a block of EPS. The elements are C, H, N, O, Ar, Br, F. I especially want feedback if the assumptions are way out-of-line.

ADDED: Here is a quote that suggest the blowing agent, or at least part of it, stays in the foam. As stated, the foam is meant to be 'old' as in late 1980's to early 1990's. 'A wide range of concentrations of CFC-12 (dichlorodifluorocarbon) was detected in styrofoam ware. It fluctuated between a low of 32 ppm and a high of 35471 ppm in two different samples of styrofoam plates.' In abstract of Environ Monit Asses. 1991 Oct; (1-3): 413-22 'The determination of chlorofluorocarbons and extractives in the expanded and disposable polystyrene ware' by C.T. Sam & T.H. Chua.

It should be mentioned that contemporary blowing agents, like that found on Pharosproject, seem to be $$CH_2$$ based, like pentane. Since the vast majority of atoms of the styrene foam will be C and H, these kind of blowing agents are not of a concern to me, and they may well completely diffuse out.

• The blowing agent has long diffused out of the foam.The only heavy element in there is bromium, and the air inside has the same composition as outside. ... What do you want to do with this?
– Karl
Aug 24 at 12:02
• @Karl Thanks for response. I have a potential identification process that depends on <Z^2>. Therefore I want an estimate of common impurities in EPS or 'styrofoam' of the late 80's - early 90's. I have added one reference that suggests that chlorine might be present. When you say Br remains, does it stay in its unit of $C_{12}H_{18}Br_6,$ or is the C&H driven off in the foam-making process? Aug 24 at 15:40
• $\ce{C_12H_18Br_6}$ is a moleculear compound. And I should probably have said could have diffused out. How much still resides in there depends on a lot of things. Blowing agents e.g. do not diffuse through a metallic layer. Size of the EPS item, environmental conditions in the past 40 yrs, ... Even the flame retardant could be leached out, potentially, although unlikely. Why don't you just run the analysis? Then you'll know.
– Karl
Aug 24 at 16:28
• @Karl I'm doing a simulation and no product is available. I think you are right about too many unknowns. I guess I should figure the composition with no assumed Cl, F, or Br; then assume 1 part/thousand (taken out of the C &H) for each and run a sim; then 10/thousand for each and do a sim, and see if makes any difference. (The sims are expensive however.) Thanks for your comments. Aug 24 at 16:47
• What kind of a simulation is that?
– Karl
Aug 24 at 19:33

You do not explain the context of your analytical problem. One cannot go to an analytical chemist/analysis service and state that tell me all the compounds which are present in this foam. This can take a year. So you have to simplify the problem.

(i) If you are solely interested in atomic compositions, all you have to do is to request elemental combustion analysis for

Carbon, H, Nitrogen, Oxygen, Sulfur and Halogens. This is a standard process. They will burn a small amount of your sample and tell you the percentages of these elements.

(ii) If you interested in other elements of the periodic tabke, you will have to request inductively coupled plasma with mass spectrometric analysis. You can find what elements are there up to Z=90 (or perhaps even higher).

(iii) The third problem is the most difficult one. What compounds are present? like the halogenated compounds mentioned in your post. This may require specialized gas chromatography-mass spectrometry analysis with targeted analysis. One has to specify what the analyst should look at.

(i)-(iii) will cost a lot.

From the comments, you mentioned simulations without having a real sample?? What is the basis of those simulations. You do need some starting real data and real data can only come from the actual analysis.

• Thanks for your answer; I've accepted it. I agree with your points. Unfortunately, I don't have a time machine to go back and get a sample. As mentioned in a correspondence with Karl, I think I'm forced to take a reasonable guess, and then 10 times the amount to see if it matters in my simulation. Aug 25 at 18:48
• I am still unsure of what the actual problem was with the foam from the 80s. Were you concerned due to health issues? What were you modelling or simulating? Aug 25 at 23:41