DOP lowers the glass transition temperature of PVC, and with it hardness, tensile strength, modulus and melt viscosity, while elongation at break, impact resistance and low-temperature flexibility rise as the loading goes up. Its molecules sit between the PVC chains in the amorphous regions and weaken the attraction between them, so the chains move at lower temperatures. Plasticizers make PVC flexible this way, and DOP is the general-purpose plasticizer.
Permanence and insulation get worse. The compound slowly loses DOP by evaporation and migration, and dielectric loss rises.
Mechanical Properties
Hardness
Hardness barely moves up to about 10 phr of DOP, then falls steadily as loading rises. Compiled producer data put a 50 phr DOP compound at Shore A 80; in a separate compilation, a 67 phr compound read 69.
DOP is the usual reference for plasticizing efficiency. In the 50 phr data, DINP gives Shore A 84 against DOP’s 80, so a DINP compound needs more phr to reach the same hardness.
Tensile Strength
Tensile strength falls as DOP loading rises, after a slight rise at the lowest loadings. In one study across three PVC grades, it peaked at 5–10 phr and began to drop sharply at about 20 phr.
Unplasticized PVC runs 40–70 MPa; in a 2020 study, a 40 phr DOP compound measured 17.7 MPa. Young’s modulus falls along with tensile strength.
Elongation at Break
Elongation at break stays near rigid-PVC levels up to about 10 phr of DOP, then jumps by 20 phr and keeps rising almost linearly with loading. The figures below are averages from the same three-grade study, across its stabilizer systems.
Impact Strength
A small amount of DOP can make PVC more brittle, an effect known as antiplasticization; impact resistance climbs only once the loading is high enough to make the compound flexible. In a study of PVC/PMMA blends, it increased up to 30% DOP by weight of the PVC, and at 50% the specimens no longer broke.
Thermal Properties
Glass Transition Temperature
DOP lowers the glass transition temperature by about 2.45 °C for each mass percent in the compound, from close to 80 °C for unplasticized PVC. The rate comes from dynamic mechanical thermal analysis (DMTA), without a stated loading range.
The reading also depends on the test method. In a 2022 study, one 50 phr DOP compound showed its glass transition at −50.5 °C by DSC and at about −10 °C by the DMA tan δ peak, some 40 °C apart.
Low-Temperature Flexibility
Raising the DOP loading lowers the cold-flex temperature along with Tg, but at a given hardness DOP leaves the compound stiffer in the cold than an adipate does. A 48 phr DOP compound with 4 phr ESBO reached its cold-flex temperature at −20 °C in the ISO 458-1 torsion test, while a DOA compound of the same Shore A hardness measured below −40 °C.
Processability
DOP lowers PVC’s melt viscosity and the temperature at which the compound gels and fuses, so the more DOP, the lower the processing temperature. It also gels at a lower temperature than heavier phthalates: at 50 phr, compiled producer data put the gelling temperature of a DOP compound at 109 °C against 118 °C for DINP.
Its effect on thermal stability is mixed: processing at a lower temperature puts less heat into the resin, but a 2026 review notes that the extra chain mobility tends to lower thermal stability, and that low plasticizer levels can speed dehydrochlorination.
Migration and Volatility
DOP stays in PVC less well than heavier phthalates. Over the service life it evaporates from the surface and migrates into whatever the compound touches.
In one comparison of esters at 67 phr in the same resin, the DOP compound lost 4.5% in a day at 87 °C over activated carbon, against 2.1% for the DINP compound. Water extracted 0.01% and kerosene 44%, so oils and fuels are where a DOP compound loses plasticizer fastest.
Heat Aging and Weathering
Under heat, a DOP compound ages mainly by losing DOP. The higher the temperature, the faster the ester evaporates, and the compound hardens and eventually turns brittle.
For cable with a high temperature rating, heavier phthalates and trimellitates have become the first choice over DOP, because they evaporate far less. In car interiors, the same volatility shows up as fogging: DOP evaporating from warm trim condenses on the inside of the windscreen.
Outdoors, sunlight degrades the PVC itself. Weather resistance comes mainly from the stabilizers and UV protection in the compound, though the choice of plasticizer also affects it.
Electrical Properties
DOP makes PVC a poorer insulator: as the loading rises, dielectric constant and dielectric loss go up and breakdown voltage comes down.
One study measured dielectric constant and tan δ to ASTM D150 at 30 kHz, and breakdown voltage to ASTM D149, at three DOP levels:
| DOP (%, basis not stated) | Dielectric constant | tan δ | Breakdown voltage (kV/cm) |
|---|---|---|---|
| 20 | 2.73 | 0.035 | 228 |
| 30 | 2.88 | 0.065 | 212 |
| 40 | 3.50 | 0.096 | 203 |