Trioctyl Trimellitate (TOTM) — Frequently Asked Questions

Because of molecular weight. It carries three ester chains where a phthalate carries two, which raises molecular weight substantially, and plasticiser permanence scales directly with that. A larger molecule is more entangled in the polymer, has much lower vapour pressure and diffuses far more slowly, so it stays in the compound at temperatures that would drive a conventional plasticiser out.

PVC plasticised with TOTM holds its flexibility through continuous service at 105 and 125 degrees Celsius, where a DOP compound would embrittle as plasticiser volatilised away. That is why it is the standard for high-temperature electrical cable and for automotive under-bonnet wiring.

Because extraction into the fluid contents must be minimised. A plasticiser that leaches into blood or an infusion is both a patient exposure and a change in the article's properties. TOTM's high molecular weight means it is extracted far more slowly than DEHP, which is the material it commonly replaces in those applications.

Cost, processing and cold performance. It is considerably more expensive than general-purpose plasticisers, its higher viscosity makes plastisol handling and gelation harder, and its low-temperature flexibility is slightly poorer. Those trade-offs are accepted where the heat rating or the extraction resistance is the governing requirement.