What rubber process oil does
Rubber process oil (RPO) is a refined petroleum oil added to natural or synthetic rubber during mixing. It softens the compound so fillers disperse evenly, shortens mixing time and lowers energy use, improves extrusion and moulding, and extends the rubber polymer.
It is used in tyres, automotive tubes, retreads, reclaim rubber, extrusion profiles and moulded or extruded rubber products.
Aromatic, naphthenic and paraffinic oils
Process oils are classified by the share of aromatic (Ca), naphthenic (Cn) and paraffinic (Cp) carbon in the oil, determined by ASTM D2140. The aniline point (ASTM D611) is a quick indicator: the lower it is, the more aromatic the oil and the higher its solvency for rubber.
| Type | Character | Typical use |
|---|---|---|
| Aromatic (DAE) | High aromatic content, high solvency, high PAH | Traditional tyre oil — restricted in EU tyres |
| Low-PAH aromatic (RAE, TDAE) | Aromatic solvency with PAH below EU limits | Tyre and rubber compounds with SBR and natural rubber |
| Naphthenic | Balanced solvency, low PCA, lighter colour | Tyres, tubes, retreads, extruded and moulded goods |
| Paraffinic | Highest aniline point, lowest aromatic content | Rubbers that need low-aromatic oils |
Key test values on a process oil COA
| Property | Test method | What it tells you |
|---|---|---|
| Kinematic viscosity | ASTM D445 | Oil thickness at 40 °C or 100 °C |
| Specific gravity / density | ASTM D1298 | Indicator of oil type |
| Aniline point | ASTM D611 | Aromaticity and solvency |
| Viscosity-gravity constant (VGC) | ASTM D2501 | Oil type (higher = more aromatic) |
| Flash point | ASTM D92 | Handling and processing safety |
| Pour point | ASTM D97 | Lowest temperature the oil flows |
| PCA (DMSO extract) | IP 346 | Screening for PAH content (< 3 %) |
| PAH content | EN 16143 | Direct measurement of regulated PAHs |
EU REACH PAH limits
EU REACH Annex XVII, entry 50, prohibits extender oils for tyres containing more than 1 mg/kg benzo(a)pyrene or more than 10 mg/kg for the sum of eight listed PAHs. Low-PAH grades — residual aromatic extract (RAE), treated distillate aromatic extract (TDAE) and naphthenic oils — are used instead of DAE.
Petroseal Enterprises supplies rubber process oil all over Pakistan and exports low-PAH grades from Karachi to European buyers, in steel drums or bulk. Every batch ships with a Certificate of Analysis stating its PAH or PCA content.