[neptune]

Hello,

I have a rubber compound that consists of the following...

Carbon Black - 23.67%
Petroleum Hydrocarbon (CAS#64742-57-0) - 2.02%
Zinc Oxide (CAS#1314-13-2) - 1.38%
Stearic Acid - 0.28%
Limestone (CAS#1317-65-3) - 13.763%
Saret EPR - 1.18%  which consists of Zinc Diacrylic (CAS#14643-97-9) - 70%
                                                  Saponifide Glycerides Blend (CAS#61789-31-9) - <5%
                                                  Alkylated Phenol - 5%
Varox DCP - 2.75% which consists of Dicumyl Peroxide (CAS#80-43-3) - >40%
                                                  Carbonic Acid Calcium Salt (CAS#471-34-1) - >60%
Buna EPT - 4.13% which consists of Sodium Carbonate (CAS#497-19-8) - ~30%
                                                 Zinc 2-Mercaptotolylimidazole (ZMTI) (CAS#61617-00-3) - <5%
                                                 1-Octadecanamine (CAS#124-30-1) - <5%
Buna EPT4969 - 50.648% which consists of Petroleum Distillates, solvent refined heavy paraffinic (CAS#64741-88-4) - <51%
                                                             Petroleum Diatillates, solvent dewaxed heavy paraffinic (CAS#64742-65-0) - <51%     

This is a compound that we manufacture/produce.  I am trying to reverse engineer this.  I have started by running a 18hr reflux in acetone to pull off oils (This is an ASTM test method). 

I ran a TGA on the compound and found the following degredations...
0-300C - 6.28%
300-600C - 51.14%
600-900C - 29.93%
Ash - 11.48%

From the 18hr reflux I got around 20% oil extracted.  I am thinking I should have quite a bit more oil/additives extracted.  Basically the Buna 4969 is 50% heavy oil, not to mention the other additives.  I do not have a problem with the ash, that is obvious.  I am wondering if I should really crank the heat up for the 18hr. acetone extraction to extract some higher boiling point oils, or just try a different solvent??  I would like some direction to break this compound down and reverse engineer it to find all the components.  I will eventually run the extract through a GC/MS to determine what that consists of.  Any help/insight on this matter would be appreciated.  Thanks in advance!!!

[Dude]

1.  My experience with EPDM rubbers is that methyl ethyl ketone (2-butanone or MEK) is the best extraction solvent for hydrocarbon processing oils.   For good extraction results, the sample must be cut into small pieces to maximize the surface area.  The setup should be a Soxhlet extractor for continuous streams of fresh solvent.

An IR of the extracted oil (with the MEK rigorously removed), GPC (molar mass determination) and possibly elemental analysis (in particular S to specify group I, II or III base oil) might be useful.  One problem with the elemental analysis of the oil would be the possibility of crosslinking S leachants messing up the value.

2.  Digestion and ICP analysis or Xray fluorescence will yield the metals content (zinc, Ca, Na). 

3.  A separate extraction and run on a GC with an FFAP column might yield the stearic acid content (if it didn't react).

4.  The TGA sample size should be small (~ 10 mg) and the temp ramp rate should be low (5 C/min) with a ramp up to 800 C under nitrogen followed by a 30 minute isothermal run under air (gas switch function) at 800 C might allow clear separation of the rubber/oil from the carbon black from the metal oxides.

Working with crosslinked material is somewhat difficult.  That is about all I can think of the validate the formulation.