Shandong Qilu Trioctyl Trimellitate (TOTM)

Shandong Qilu trioctyl trimellitate (TOTM, tris(2-ethylhexyl) trimellitate, CAS 3319-31-1) is introduced into high-temperature PVC insulation compounds as a branched C8 triester with a molecular weight of 546.78 g/mol. The ester’s three 2-ethylhexyl groups bonded to the aromatic trimellitate core reduce vapour-phase plasticizer loss compared with shorter-chain phthalates, making it a technical candidate for appliance wiring and automotive primary wire where thermal ageing is evaluated by UL 1581 and ISO 6722 schedules. A typical suspension PVC resin of K value 70 to 75 is dry-blended with 45 to 65 phr TOTM, 5 to 8 phr Ca/Zn stabilizer, 0.5 to 1.0 phr antioxidant, and 10 to 20 phr calcined clay or calcium carbonate. The high-speed mixer is run until the batch reaches 115 °C to 125 °C, then the dry blend is transferred to a cooling mixer and brought below 45 °C to prevent agglomeration and premature stabilizer reaction. Extrusion on a single-screw line with an L/D ratio of 30:1 and a compression ratio of 2.5:1 is carried out over a barrel zone range of 140 °C to 175 °C, with a screen pack of 40/60/100 mesh installed to raise melt pressure and remove unmelted resin particles. Published plasticizer comparison data under ASTM D1203-22 activated carbon absorption show that TOTM loses substantially less weight than DINP at equivalent loadings, while oil-extraction data measured under ASTM D471-16a indicate lower extractable loss in mineral oil than linear phthalates. Laboratory tensile tests conducted on press-cured plaques according to ASTM D638-14 typically place elongation at break above 300 % for 60 phr TOTM compounds; tensile retention after thermal ageing remains above 70 % where stabilizer loading is adequate. The compound is not subject to phthalate restrictions for electrical and electronic equipment under Directive (EU) 2015/863, because TOTM is a trimellitate rather than a DEHP, BBP, DBP, or DIBP ester.

During extrusion of TOTM wire insulation formulations, the main processing constraint is melt-temperature control. When the melt temperature exceeds 185 °C to 195 °C, the PVC backbone can begin dehydrochlorination, leading to colour shift from light amber to dark red and plate-out on the die lip. For this reason, screw cooling on the feed section is often set to 40 °C to 60 °C, and the head pressure is maintained below 350 bar. In high-speed extrusion lines for thin-wall primary wire, line speeds of 300 m/min to 800 m/min require a low-viscosity compound; TOTM’s higher molecular weight relative to DOP raises compound viscosity at equivalent loading, so formulators may reduce filler loading or increase process temperature by 5 °C to 10 °C to maintain equivalent output. Production-line audits have recorded that careless addition of recycled trimellitate-containing regrind above 20 wt% without re-stabilization produces surging and surface roughness, a batch-to-batch variance that is controlled by limiting regrind ratio and by preblending regrind with fresh compound for 30 min in a low-speed ribbon blender.

How Does TOTM Shift the Gelation-Fusion Window in Automotive Plastisol Formulations?

Automotive plastisol formulators evaluate trimellitate plasticizers primarily through the temperature interval between initial solvation and complete fusion. In a PVC paste resin with a K value of 72 to 80, TOTM raises the gelation onset relative to DINP because its higher molecular weight and branched ester structure slow solvent diffusion into the polymer particles. Rheological measurements on a Brookfield RVT spindle viscometer at 20 rpm and 25 °C typically show initial plastisol viscosity between 3,000 mPa·s and 8,000 mPa·s at 50 phr TOTM, with moderate shear-rate dependence. Gelation is measured on a Bohlin controlled-stress rheometer at 1 Hz during a temperature ramp; the crossover of storage modulus G′ and loss modulus G″ occurs 10 °C to 20 °C higher than with DINP of equivalent weight. This shift is not a formulation failure but a processing parameter requiring fusion-oven zone temperatures of 180 °C to 210 °C for TOTM-containing plastisols, compared with 170 °C to 195 °C for many phthalate controls. The higher fusion temperature must be balanced against the thermal stabilizer package because prolonged exposure at 220 °C or above produces HCl release and viscosity rise before full tensile development. In production knife-over-roll coating, a gap of 0.15 mm to 0.35 mm is used, and the film passes through a three-zone tunnel oven with zone temperatures set at 140 °C, 175 °C, and 200 °C. TOTM’s low vapour pressure supports compliance with DIN 75201 method B fogging and VDA 278 VOC limit values; measured fogging condensate under DIN 75201 method B is lower for TOTM than for DOP at 100 °C over 16 h. In underbody sealants, the plasticizer selection also affects adhesion to electrocoat substrates; TOTM’s lower migration reduces interfacial plasticizer bloom after humidity ageing under ISO 6270-2.

Medical PVC tubing and fluid-contact components require plasticizer permanence under aqueous and lipid exposure because plasticizer loss changes device mechanical behaviour and introduces extractables into the contact medium. TOTM is formulated into suspension PVC with K value 67 to 72 at loadings of 40 to 60 phr, together with epoxidized soybean oil or another secondary plasticizer at 3 to 10 phr, Ca/Zn stabilizers, and processing lubricants. The molecular weight of 546.78 g/mol and the branched C8 structure lower the diffusion coefficient of TOTM in plasticized PVC relative to DEHP under ISO 10993-18 extractables profiling; migration into lipophilic simulants is reduced but not eliminated. Haemodialysis tubing, enteral feeding lines, and respiratory circuits have been evaluated with TOTM as a non-phthalate alternative where DEHP exposure is restricted. Mechanical properties for medical-grade compounds are tested according to ASTM D638-14 or ISO 527-2, with tensile strength typically exceeding 14 MPa at 50 phr TOTM and elongation at break above 280 %. After steam sterilisation at 121 °C for 30 min or gamma irradiation up to 25 kGy, hardness drift is typically less than 5 Shore A units when stabilizer is adequate. Tubing extrusion is run on a single-screw extruder with an L/D of 24:1 to 30:1, vacuum sizing, and a melt temperature below 180 °C to limit degradation. Compatibility with parenteral contact must be validated under ISO 10993-5 and ISO 10993-10, and the final device must be assessed for leachables according to ISO 10993-18; TOTM is not automatically acceptable for all body-contact classifications merely by replacement of DEHP.

When Cable Jacketing Compounds Must Meet ISO 6722 Class D Thermal Aging

In ISO 6722 Class D automotive cable jacketing, the compound is exposed to long-term heat ageing at 150 °C for up to 3,000 h, and the retention of tensile strength and elongation is a pass/fail criterion. TOTM is selected in this class because its high molecular weight and low vapour pressure reduce plasticizer evaporation from the jacket surface, while its aromatic ester structure improves migration resistance to engine-bay fluids. A typical jacket formulation contains 100 phr PVC suspension resin with K value 70 to 75, 50 to 70 phr TOTM, 5 to 10 phr Ca/Zn or mixed-metal stabilizer, 20 to 50 phr aluminium hydroxide or magnesium hydroxide, 3 to 8 phr antimony trioxide, and 5 to 10 phr zinc borate for flame and smoke control. The choice of antimony trioxide and ATH creates a processing conflict: ATH decomposes above 180 °C, while TOTM-formulated PVC often requires melt temperatures near 175 °C to 185 °C for efficient fusion. Therefore, barrel temperature settings must be profiled so the melt zone does not exceed 180 °C, and the head/die zone is held at 175 °C to 185 °C only briefly. Extruders with an L/D of 30:1 and vacuum venting are used, and the compound is predried at 70 °C for 2 h when ambient relative humidity exceeds 60 % to prevent surface porosity. Flame testing under UL 1581 VW-1 or IEC 60332-1-2 requires the jacket to self-extinguish; antimony-chlorine synergy from PVC itself contributes to char formation. Published data for the exact ATH decomposition kinetics in TOTM-plasticized PVC are limited, and production trials are required to verify the thermal window by differential scanning calorimetry. The compound is outside phthalate restrictions under Directive (EU) 2015/863 because the plasticizer is a trimellitate, but the full cable construction must still comply with REACH Annex XVII restrictions and OEM materials standards.

Industrial hose and gasket compounds processed on single-screw extrusion lines with a 24:1 L/D ratio use TOTM where extraction resistance to mineral oil, dilute acids, and alkaline cleaning solutions is a service requirement. At 60 phr TOTM, PVC compounds show Shore A hardness values from 78 to 85 according to ASTM D2240-15e1, tensile strength above 14 MPa under ASTM D638-14, and brittleness temperatures between −20 °C and −30 °C under ASTM D746-21. The brittleness range is a limitation relative to linear phthalate plasticizers, which typically provide better low-temperature flexibility at equivalent loading; this boundary must be considered for gaskets on refrigeration or outdoor automotive applications below −30 °C. Plasticizer permanence is tested by ASTM D3291-15 compression set under plasticizer extraction conditions, and by ASTM D471-16a after immersion in ASTM IRM 902 oil at 70 °C for 70 h. In TOTM formulations, mass change in IRM 902 is lower than with DOP or DINP, but the compound still swells in aromatic fuels and chlorinated solvents; nitrile rubber blends or fluoropolymer liners are required for aggressive solvent service. Gasket profiles are extruded through a die at melt temperatures of 150 °C to 170 °C, and vacuum calibration is adjusted to maintain dimensional tolerance. Because TOTM increases compound viscosity, the extruder current draw can rise by 5 % to 10 % relative to an equivalent DOP formulation; screw speed is reduced or barrel temperature is increased by 5 °C to 10 °C to compensate. At press-cured test plaques, plasticizer exudation under ASTM D3291-15 is considered acceptable when no oil film appears after 72 h at 70 °C under compression.

Low-Temperature Property Cliffs in Trioctyl Trimellitate-Plasticized Gasket Compounds

TOTM-plasticized gasket compounds exhibit a nonlinear cold-flexibility response when plasticizer loading is varied. At 40 phr TOTM, ASTM D746-21 brittleness temperature is typically in the range of −5 °C to −15 °C, which is unacceptable for outdoor sealing in northern European or North American winter conditions. Increasing the plasticizer to 50 phr shifts the brittleness point by approximately 10 °C to 15 °C, while 60 phr TOTM brings the value to −20 °C to −30 °C. At 70 phr TOTM, the brittleness temperature can reach −35 °C to −45 °C, but the tensile strength under ASTM D638-14 can fall below 12 MPa, and Shore A hardness can drop below 75, creating a property cliff for compression set resistance under ASTM D395-18 method B. The processing window is also constrained by plasticizer absorption limits: when TOTM exceeds 70 phr in a suspension PVC K-value 67 to 70 resin without a polymeric plasticizer, dry-blend absorption slows and the compound may require a two-stage mixing cycle or longer preheating in the mixer to avoid free plasticizer during extrusion. Published data for this specific formulation window are limited, and production validation with differential scanning calorimetry and capillary rheometry is required to define the exact free-plasticizer threshold for a given batch source. In service, gaskets used in contact with polished polycarbonate or ABS surfaces require migration testing because TOTM has lower migration than phthalate plasticizers but can still produce contact staining under high compressive load at elevated temperatures.

At voltages below 1,000 V AC, dip-moulded PVC insulating boots and connector caps formulated with TOTM provide high-temperature dielectric stability and low volatile loss, but the dip-moulding process imposes rheological constraints. The plastisol is compounded from a PVC paste resin with K value 75 to 82, TOTM at 50 to 65 phr, an epoxidized co-plasticizer at 3 to 5 phr, and a Ca/Zn stabilizer. Initial viscosity at 25 °C is adjusted to 800 to 2,000 mPa·s so that the preheated mandrel can accept a uniform deposit without dripping. Mandrel temperature is maintained at 120 °C to 180 °C, dwell time is 10 s to 60 s, and fusion is completed in a tunnel oven at 180 °C to 210 °C. Dielectric strength for a fused film of 1 mm thickness is tested under ASTM D149-20 and typically exceeds 20 kV/mm; volume resistivity tested under ASTM D257-14 is maintained above 10¹² Ω·cm after standard conditioning. Flame-retardant grades use antimony trioxide and zinc borate to achieve UL 94 V-0. Because the final part is often installed in engine compartments or high-current electrical enclosures, heat ageing is evaluated at 125 °C for 168 h with retention of tensile strength and dielectric strength measured under ASTM D149-20. TOTM provides lower outgassing than DOP in enclosed electrical connectors, but surface cleanliness is still critical before dip moulding; residual release agents, moisture, or polar contaminants can reduce wetting and create pinholes that degrade dielectric withstand performance.