Payal Polyplast Trioctyl Trimellitate (TOTM)

When TOTM Replaces DINP in 105°C Continuous-Service Automotive Wire Insulation

Formulation development for thin-wall automotive primary wire begins with suspension PVC having a K-value of 70. TOTM is added at 50–70 phr after the resin reaches 70–80°C in a high-speed mixer, followed by Ca-Zn stabilizer at 5–7 phr, acid scavenger at 1–2 phr, and antioxidant at 0.3–0.8 phr. The batch is dropped at 125–135°C and cooled under agitation to 40°C before feeding a counter-rotating twin-screw extruder with L/D 36:1, compression ratio 2.5:1, and barrel zones of 150°C, 160°C, 170°C, and 175°C. At 50–70 phr TOTM, melt viscosity is higher than DINP at equal loading; breaker-plate pressure typically reaches 130–180 bar at a screw speed of 20–30 min⁻¹. The higher molecular weight of TOTM demands greater shear to produce a homogeneous melt, but barrel temperatures above 195°C initiate dehydrochlorination in unstabilised zones. Vent vacuum is therefore held below -0.08 MPa and die temperature is capped at 185°C.

Thermal endurance is evaluated against ISO 6722-1 for class B and class C automotive cable. Insulation extruded to 0.35 mm wall thickness on a crosshead die at 150–200 m/min must retain at least 70% of original elongation after 3,000 h at 125°C when tested per ISO 188. TOTM-based compounds typically show Shore A hardness of 80–85 per ISO 868 and tensile strength of 18–22 MPa per ISO 37. Volume resistivity after 7 days at 85°C and 85% relative humidity remains above 1×10¹² Ω·cm per ASTM D257 when the stabilizer level is maintained at 5–7 phr. These values are production-compounding ranges and are not guaranteed batch data for every PVC lot. During wire extrusion, conductor preheat is set to 120–140°C to prevent die-entry freezing. The pressure drop through a 0.35 mm wall crosshead is higher with TOTM than with DINP; line speed on single-screw extruders with L/D 24:1 is reduced by 5–15% unless screw temperature is increased. The resulting insulation passes low-temperature winding at -40°C according to ISO 6722-1 without cracking when the compound is free of residual moisture.

Reprocessing of TOTM-based wire compound is limited to 10–20% in the virgin dry blend. Heat-exposed recyclate increases fusion time and reduces volume resistivity because partially degraded PVC absorbs plasticizer unevenly. On a Brabender Plastograph EC fitted with a W 50 E mixer, TOTM at 65 phr extends fusion-torque equilibrium by 20–40% compared with DINP at the same loading when tested at 175°C and 40 rpm. Strand pelletizer calibration must account for higher melt tack; die-face temperatures above 180°C cause sticking and discontinuous pellet geometry. Inkjet marking adhesion is generally improved on TOTM surfaces because trimellitate plasticizer does not bloom as readily as low-molecular-weight phthalates, but adhesion remains batch-dependent and requires corona pre-treatment above 38 dyn/cm.

Why Is TOTM Specified for Blood-Contact PVC Tubing and Cytotoxicity-Screened Sets?

Medical-grade PVC compound is prepared in a clean compounding area using suspension PVC with K-value 70–72 and residual vinyl chloride monomer below 1 ppm. TOTM is added at 40–55 phr with epoxidised soybean oil at 3–5 phr, Ca-Zn stabilizer at 1–3 phr, and processing aid at 0.1–0.3 phr. The dry blend is fed to a single-screw extruder with L/D 30:1 and a barrier screw, operating at 20–40 min⁻¹ with barrel zones of 155°C, 165°C, 170°C, and 175°C. Head pressure is maintained below 200 bar. The die is set at 180°C to produce 3.0 mm outer diameter tubing with 0.5 mm wall thickness. Solvent bonding of TOTM-based tubing shows no surface stress cracking after exposure to cyclohexanone for 5 minutes in standard production checks.

Plasticizer migration is evaluated under ISO 10993-18. TOTM demonstrates lower extraction than DEHP in n-hexane and ethanol/water media because its higher molecular weight and branched alkyl chains restrict diffusion. Cytotoxicity is assessed per ISO 10993-5 using L929 mouse fibroblast cells, and irritation is assessed per ISO 10993-10. A chemical characterisation report must be generated for each stabilizer combination because leachable metal ions and organotin degradation products influence the overall biological evaluation. Mechanical properties after steam sterilisation at 121°C for 30 minutes remain within specification: elongation at break above 250% per ISO 37, Shore A hardness 65–75 per ISO 868. Gamma sterilisation at 25–40 kGy produces dose-dependent yellowing but does not introduce additional cytotoxic leachates from TOTM at levels that fail ISO 10993-5 in most formulations.

Ethylene oxide sterilisation at 55°C with 600 mg/L EO and 60% relative humidity requires aeration at 50°C for at least 12 h. Residual EO in TOTM-based tubing is removed more slowly than in DEHP-based tubing due to lower gas permeability. This constraint applies to blood bags and dialysis sets that must meet ISO 3826. TOTM is not indicated for long-term implantable devices; the material remains plasticised PVC and retains a measurable leachable profile. Published data for specific TOTM-stabilizer combinations in implant-grade applications is limited.

In automotive instrument panel skin production, calender or cast-film lines use TOTM to reduce interior fogging. A typical paste resin formulation contains 100 phr PVC with K-value 70, 65–75 phr TOTM, 3–5 phr epoxidised soybean oil, and 1–3 phr Ca-Zn stabilizer. The film is fused in a hot-air oven at 190–200°C for 3–5 minutes before embossing. Fogging is measured according to DIN 75201 method B or ISO 6452; TOTM-based formulations typically show reflectance values above 90% and gravimetric condensate below 1.0 mg. These results are batch-dependent and must be verified with the selected stabilizer package. Calender roll temperatures are held 5–10°C higher than DIDP-based material. Roll temperatures below 175°C produce visible unmelted resin particles and surface streaks; above 195°C, the compound yellows if thermal stabilizer is insufficient. Vacuum forming over a polyurethane foam substrate at 120–140°C requires sufficient low-temperature flexibility to avoid whitening at grain lines. The low fogging result establishes reduced volatile loss but is not interpreted as zero emission.

Extraction Resistance in Fuel-Contact Hose and Static Seal Compounds

For low-pressure fuel return lines and pump suction lines, PVC/NBR hose compounds are produced with TOTM at 40–60 phr, NBR at 15–25 phr, and PVC with K-value 70. Immersion testing per ASTM D471 in IRM 903 oil at 100°C for 70 h shows lower volume swell than DOP-based equivalents; the actual percentage is strongly influenced by NBR ratio and filler content. Compounds with Shore A 70–80 are extruded on a pin-type crosshead at 140–160°C. TOTM maintains plasticizer retention after fuel contact but is not suitable in high-aromatic gasoline service where nitrile rubber content above 40 phr is required for elastomeric sealing. Published data for this specific hose configuration is limited.

Gelation Temperature, Solvency, and High-Shear Viscosity in TOTM Loaded Plastisols

High-shear mixing of PVC paste resin with TOTM begins at 25°C liquid phase. TOTM has a Brookfield viscosity of approximately 250–350 mPa·s at 25°C using spindle #3 at 20 rpm. Paste resin with K-value 75 is charged into a dissolver at 1,500–2,000 rpm for 15–20 minutes and then vacuum-deaerated at -0.09 MPa for 30 minutes. At 60 phr TOTM, the plastisol has an initial Brookfield viscosity above 3,000 mPa·s; at 80 phr, viscosity falls to 1,500–2,500 mPa·s. Viscosity stability over 7 days at 23°C is better than branched phthalates, but room-temperature solvency is lower, requiring a co-solvent if extended pot life is specified.

Fusion in a forced-air oven uses a two-stage profile: 140°C for 3 minutes to gel the film and 195°C for 5 minutes to form a dense continuous matrix. Dipped steel parts are preheated to 150°C. Insufficient gelation time at 140°C results in interlayer porosity and loss of adhesion per ASTM D413. The final coating has Shore A 75–85, tensile strength 12–16 MPa, and elongation 250–350% per ASTM D638. TOTM reduces tensile strength slightly relative to low-molecular-weight plasticizers at equal hardness because it increases free volume without increasing network density. Corrosion resistance of dipped coatings on phosphated steel is tested per ISO 9227; TOTM-based plastisols show no blistering for 500 h when edge coverage is complete.

Outdoor exposure of single-ply PVC roofing membranes places simultaneous heat, UV, and mechanical stress on the plasticizer system. TOTM is used at 60–70 phr with PVC K-value 70–73 and liquid Ba-Zn or Ca-Zn stabilizer at 4–6 phr. The melt is processed on a calender at 165–185°C and drawn into 1.2 mm, 1.5 mm, or 2.0 mm sheet before embossing. Dimensional stability is tested according to EN 1107-2 at 100°C for 6 hours; the change in length must be below 0.5% for mechanically fastened systems. Cold flexibility is tested per EN 495-5 at -20°C; TOTM-based membranes show no cracking at -20°C, but published data for temperatures below -20°C is limited. Accelerated xenon-arc exposure per ISO 4892-2 at 0.35 W/m² and 340 nm with black-standard temperature 65°C and 18/102 min water spray shows retention of elongation above 80% after 5,000 h only if a UV screening package is present. Plasticizer volatility measured by activated carbon method per ISO 176 is below 1%, but this test is not a substitute for long-term service. Hot-air welding at 400–450°C produces seam strength of 80–90% of sheet tensile strength per EN 12317-2. TOTM is not suitable for membranes in contact with bitumen or coal tar products because aromatic oils extract trimellitate plasticizers.