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| HS Code | 627778 |
| Chemical Formula | C9H4O5 |
| Cas Number | 552-30-7 |
| Molecular Weight | 192.13 g/mol |
| Appearance | White crystalline flakes |
| Melting Point | 165-168 °C |
| Boiling Point | 390 °C |
| Density | 1.68 g/cm³ at 20 °C |
| Solubility In Water | Reacts/hydrolyzes to form trimellitic acid |
| Flash Point | 227 °C |
| Autoignition Temperature | 580 °C |
| Vapor Pressure | Negligible at room temperature |
As an accredited Trimellitic Anhydride factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Supplied as 25 kg net in polyethylene-lined multiwall paper bags, sealed and palletized for safe industrial handling and storage. |
| Container Loading (20′ FCL) | Trimellitic anhydride, typically in powder form, is packed in bags or drums and loaded into a 20-foot FCL container. |
| Shipping | Ship Trimellitic Anhydride in dry, sealed containers to prevent moisture exposure. Pack in lined bags or drums, shielded from humidity and direct sunlight. Ensure containment is labeled for potential respiratory sensitization/irritation hazards. Use appropriate ventilation and PPE during handling, and follow local hazardous material transport regulations. Avoid incompatible materials and water ingress. |
| Storage | Store Trimellitic Anhydride in a tightly sealed container in a cool, dry, well-ventilated area. Protect from moisture and humidity, as water causes hydrolysis. Keep away from strong oxidizers, bases, and heat sources. Ensure containers are clearly labeled and inspect regularly for damage or leakage. Use appropriate personal protective equipment when handling. |
| Shelf Life | Shelf life: 12 months when stored sealed in a dry, cool area, protected from moisture and air. |
In high-temperature automotive cable and appliance wiring, flexible PVC compounds replace general-purpose phthalate plasticizers with triester plasticizers derived from trimellitic anhydride (TMA), most often trioctyl trimellitate (TOTM) or triisononyl trimellitate (TINTM). Esterification is run under nitrogen in a glass-lined reactor with a packed column and water separator; excess 2-ethylhexanol or isononanol is charged with an organotitanate catalyst and staged from 180 °C to 230 °C to limit foaming. The reaction is terminated after the acid value falls below 0.5 mg KOH/g, and excess alcohol is removed in a wiped-film evaporator at 180–200 °C under 2–5 kPa. In PVC compounding, the trimellitate is added at 35–75 phr, with 50–70 phr typical for 105 °C continuous service insulation. Dry blending is performed in a high-speed ploughshare mixer to 110–120 °C, followed by twin-screw compounding on a 40:1 L/D machine with barrel zones from 150 °C to 180 °C. The pelletized compound is extruded onto stranded or solid copper conductors at line speeds of 50–400 m/min, with the extruder screw configured for low shear to prevent frictional heat rise above 190 °C.
Material substitution is fixed by volatility, extraction, and aging constraints. Plasticizer retention is measured under ASTM D1203-23 Method A, and extraction resistance is assessed with ASTM D1239-14 or ISO 175:2010. Cable insulation and jackets are qualified by UL 1581 oven aging at 121 °C or 136 °C for 168 h, while automotive thin-wall cables are tested under ISO 6722-1 at the specified thermal class, often 100 °C or 125 °C. The main processing conflict is plasticizer exudation above 75 phr in low-K-value PVC, particularly on embossed jackets stored at 60 °C and 85% RH; in such formulations, partial replacement with a polymeric plasticizer is required instead of further increasing TOTM.
| Qualification parameter | Standard designation | Test condition |
|---|---|---|
| Plasticizer volatile loss | ASTM D1203-23 | 24 h, 70 °C, activated carbon |
| Plasticizer extraction resistance | ASTM D1239-14 | 24 h, 50 °C, soap solution |
| Insulation thermal aging | UL 1581 | 121 °C or 136 °C, 168 h |
| Tensile elongation retention | ASTM D638-14 | 50 mm/min, 23 °C |
Polyamide-imide wire enamel based on TMA is prepared by reacting trimellitic anhydride with 4,4′-diphenylmethane diisocyanate in a solvent blend of N-methyl-2-pyrrolidone and xylene, with carbon dioxide evolution. In the alternate chloride route, TMA is converted to trimellitoyl chloride and then condensed with an aromatic diamine to remove free isocyanate from later processing. The enamel is supplied at 20–35 wt% solids with viscosity of 0.5–1.5 Pa·s at 30 °C. On a vertical enamelling tower, copper conductor is annealed at 500–600 °C, then passed through shaped dies and a cure zone with oven temperatures from 300 °C in the evaporation section to 550 °C in the final cure section. 6–12 passes are required to build 20–50 μm of final film thickness on round wire. Thermal endurance is evaluated under IEC 60172:2020 at multiple temperatures, and the wire is qualified according to IEC 60317 and NEMA MW 1000 for the intended thermal class.
Production failure modes are concentrated in the evaporation zone. Blistering occurs when the surface cure rate exceeds solvent diffusion through the deposited film; it is controlled by graduated oven profiles and by maintaining solvent ratio below a defined upper limit. Residual NMP above 0.5 wt% in the cured film is measurable by gas chromatography after solvent extraction and is associated with reduced dielectric strength under IEC 60851 pinhole and breakdown-voltage testing. In inverter-duty motor winding, partial discharge resistance is evaluated with repetitive impulse stress, and the coating is expected to withstand the specified rise time and peak voltage without insulation breakdown. Because TMA is a respiratory sensitizer, enamel manufacturing is engineered as a closed system; powder handling is contained with local exhaust ventilation.
During the second-stage cook of a water-reducible polyester, TMA is withheld until the first-stage hydroxyl and acid functional monomers have formed a linear oligomer; charging TMA earlier produces a gelled batch because the anhydride acts as a trifunctional branching agent without controlled carboxyl placement. The first stage is run at 220–240 °C with neopentyl glycol, trimethylolpropane, isophthalic acid, and adipic acid to an acid value below 10 mg KOH/g. TMA is then added at 160–190 °C and held until the final acid value reaches 35–65 mg KOH/g. The solid resin is neutralized with N,N-dimethylethanolamine at 70–90 °C under high shear, then dispersed in deionized water to 30–40 wt% solids. After filtration through a 10–25 μm bag filter, the dispersion is combined with a methylated melamine-formaldehyde crosslinker at a polyester:melamine solids ratio of 80:20 to 70:30. The mix is spray-applied to zinc-phosphated steel as an anti-corrosion primer at 20–35 μm dry film thickness and cured in a forced-air oven at 140–160 °C for 20–30 min.
Salt-spray resistance is tested under ISO 9227:2022, and cross-cut adhesion after humid exposure is evaluated with ISO 2409:2020. The hydrolysis boundary is the governing constraint: TMA-derived carboxyl groups that are not neutralized or not consumed by melamine remain hydrophilic, and films exposed to 40 °C water for 240 h can blister when the pre-cure acid value exceeds 65 mg KOH/g. For food-contact metal packaging, the coating is additionally assessed under 21 CFR 175.300 and migration testing under EU 10/2011, with attention to residual melamine derivative levels and solvent extractables.
Rigid polyisocyanurate (PIR) boardstock and LNG pipe supports frequently use aromatic polyester polyols in which TMA is co-esterified with phthalic anhydride and a glycol mixture to raise aromatic ester content and improve char-forming behavior. The polyol is produced in a batch reactor at 200–230 °C with a total acid feed adjusted so that the stripped polyol has a hydroxyl number of 180–250 mg KOH/g, an acid number below 3.0 mg KOH/g, and a Brookfield viscosity at 25 °C of 1,500–6,000 mPa·s. TMA is charged at 2–10 wt% of the total reactor mass; levels above this range can produce gel-like viscosity creep, especially when water content is not held below 0.05 wt%. On a double-belt continuous laminator, the polyol is mixed with polymeric MDI at an isocyanate index of 180–300, a potassium octoate or potassium acetate trimerization catalyst, a compatibilizing polyether, and n-pentane as the blowing agent. The exothermic PIR reaction is controlled so that the core temperature remains below 120–140 °C to avoid friable cell struts and facing debonding. Fire performance is tested under EN 13501-1:2018, ASTM E84-23, and cone calorimetry under ISO 5660-1:2015; thermogravimetric analysis at 800 °C under nitrogen confirms char retention relative to non-aromatic polyols. The main incompatibility is with residual basic contamination in the glycol blend; even small amounts of sodium hydroxide darken the batch and accelerate viscosity build during TMA addition.
| Fire performance parameter | Standard designation | Measured parameter |
|---|---|---|
| Reaction to fire classification | EN 13501-1:2018 | Euroclass B–F |
| Surface burning characteristics | ASTM E84-23 | Flame spread index, smoke developed index |
| Heat release rate | ISO 5660-1:2015 | kW/m² at 50 kW/m² irradiance |
| Compressive strength | EN 826:2013 | kPa at 10% deformation |
In electrophotographic toner, branched polyester binders made with TMA are used to separate low-temperature fusing behavior from hot-offset resistance. TMA is introduced after the initial monomer mixture of bisphenol A propylene oxide adduct, terephthalic acid, and fumaric acid has reached a low acid value, and the polycondensation continues under vacuum below 1 kPa at 230–250 °C. The resulting binder has an acid value of 5–20 mg KOH/g, a glass transition temperature of 55–70 °C measured under ISO 11357-3:2018, and a softening point of 100–140 °C. The binder is melt-compounded with carbon black at 5–12 wt%, a polypropylene wax, and a charge-control agent in a twin-screw extruder at 110–130 °C; the cooled extrudate is pulverized in a jet mill and air-classified to a volume median particle diameter of 5.0–9.0 μm. The branched TMA-derived structure broadens the molecular weight distribution and raises the elastic modulus near the fusing nip, preventing printed image splitting during roller release. Fusing performance is checked on a laboratory roller rig at 140–180 °C with nip dwell time of 30–90 ms, while charge-to-mass ratio is measured by blow-off after conditioning at controlled humidity. The compliance boundary is RoHS 2011/65/EU and REACH; free TMA monomer in the final binder is restricted to avoid sensitization risk during cartridge handling.
Saturated polyester coil coatings are formulated from TMA-modified resins when a trifunctional aromatic monomer is needed to raise crosslink density without introducing solvent-heavy low-molecular-weight species. The resin is synthesized by charging neopentyl glycol, propylene glycol, isophthalic acid, and terephthalic acid to a reactor, then adding TMA near the end of the cook at 0.5–3.0 wt%. The final resin has an acid value of 2–8 mg KOH/g, a hydroxyl number of 20–50 mg KOH/g, a number-average molecular weight of 2,500–5,000 g/mol, and a glass transition temperature of 15–35 °C. The coating is applied to galvanized steel by reverse roll coater at line speeds of 30–120 m/min, with a peak metal temperature of 232–249 °C for 20–40 s. TMA increases the curing rate with hexamethoxymethylmelamine and reduces the solvent fraction required to reach application viscosity. Flexibility after forming is measured by the T-bend test under EN 13523-7:2014, and impact resistance is tested under EN 13523-5:2014. The operational limit is over-crosslinking: TMA additions above 3.0 wt% can reduce flow enough to produce orange peel and lower the reverse-impact result below the accepted minimum for exterior building panels.
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Trimellitic anhydride (1,2,4-benzenetricarboxylic anhydride, CAS 552-30-7) is a trifunctional aromatic anhydride supplied as white flakes, powder, briquettes, or molten bulk. The anhydride has the molecular formula C9H4O5 and a molecular weight of 192.13 g/mol. The melting range of commercial flake is 165–168 °C, and the acid value after complete hydrolysis is 870–876 mg KOH/g, equivalent to a carboxyl equivalent weight of 64.04 g/eq. The boiling point at 1.87 kPa is 240–245 °C. Production proceeds by liquid-phase air oxidation of pseudocumene in acetic acid over a cobalt/manganese/bromide catalyst, followed by crystallization of trimellitic acid and thermal dehydration in a rotary dryer or multi-tube heated vessel. Because no universal ISO grade numbering system applies, the product is typically specified by physical form, purity, acid value, water content, molten colour, and residual ash. Flake grade remains the dominant model for bagged solid handling, while molten trimellitic anhydride is transferred in heated tank trailers to downstream esterification and resin reactors.
| Parameter | Method/Standard | Typical specification |
|---|---|---|
| Appearance | Visual inspection | White flakes or powder |
| Purity | Gas chromatography-FID | ≥ 99.0 area% |
| Acid value | Alkaline titration after hydrolysis | 870–876 mg KOH/g |
| Melting range | ASTM E324 | 165–168 °C |
| Water content | ASTM E203 | ≤ 0.10 wt% |
| Molten colour | ASTM D1209 | ≤ 60 APHA |
The three carboxylic acid equivalents generated by hydrolysis of the anhydride ring distinguish TMA from phthalic anhydride, which supplies two equivalents, and from pyromellitic dianhydride, which supplies four. The acid value range of 870–876 mg KOH/g corresponds to 15.6 mol of acid equivalents per kilogram of TMA. In polyester reactors operating at 180–230 °C with xylene azeotropic water removal, TMA is introduced at 3–8 wt% of the non-volatile acid charge to raise the final acid value to a waterborne-alkyd target of 40–60 mg KOH/g measured under ISO 2114:2000. Addition timing is controlled because early introduction of TMA accelerates branching and can drive the batch toward gelation before the target acid value is reached.
Each kilogram of TMA added to a polyester formulation contributes both a phenyl ring and a third branch point; the molecular weight between branch points falls more rapidly than with phthalic anhydride at equivalent mass loading. In a synthesis kettle equipped with a vapour condenser and Dean-Stark trap, the end-point is determined by acid value titration, and the batch is discharged through a 200–250 µm filter to remove microgel particles. The anhydride ring reacts with hydroxyl groups faster than a free carboxylic acid under the same esterification conditions, so the feed strategy often involves late addition of TMA after the initial diol–acid condensation has reduced water release.
In the manufacture of trimellitate plasticizers, TMA is esterified with 2-ethylhexanol or mixed C8–C10 alcohols. One mol of TMA releases 2 mol of water during conversion to the triester: the first alcoholysis of the anhydride ring opens the ring without water release, and subsequent esterification of the two remaining carboxylic acid groups generates the water. The finished tri-(2-ethylhexyl) trimellitate has a molecular weight of 546.78 g/mol. Esterification is carried out in a stainless steel or titanium-lined reactor with overhead condenser, vacuum stripping at 1–5 kPa, and final batch temperature of 200–230 °C to achieve residual acid values below 0.5 mg KOH/g. The resulting plasticizer is used in PVC insulation compounds qualified under UL 1581 for 105 °C service; the higher molecular weight and branched triester structure reduce plasticizer loss under thermal ageing compared with dioctyl phthalate. Processing trade-offs include higher fusion temperatures in a twin-screw extruder with L/D 40:1 and barrel profile 150–180 °C, and a higher plasticizer demand at equal Shore A hardness.
Trimellitic anhydride is converted to trimellitic anhydride chloride or used as the anhydride acid chloride in polyamide-imide synthesis. The condensation with aromatic diamines in N-methyl-2-pyrrolidone or dimethylacetamide yields an amide-imide polymer that is applied as a 25–35 wt% solution in a vertical wire-coating tower. Magnet wire coated with polyamide-imide topcoat derived from TMA is specified under NEMA MW 1000 thermal classes 200 and 220. In comparison with pyromellitic dianhydride-based polyimide, the TMA-derived polyamide-imide has a lower peak crosslink density but is easier to process because the acid chloride route avoids the high-viscosity polyamic acid stage and its water-sensitive intermediates. Residual chloride in the acid chloride raw material is controlled at ≤ 50 mg/kg because free chloride promotes copper corrosion during enamel wire thermal ageing.
The substitution of a portion of pyromellitic dianhydride with TMA in wire enamel formulations adjusts viscosity build and film flexibility. The trifunctional nature of TMA leaves one less reactive site than PMDA, which can reduce gelation risk in the reactor. In a typical batch reactor with 500–2000 L capacity, the diamine is added at 0.98–1.02 molar ratio to acid chloride to maintain a relative viscosity of 2.0–4.0 measured at 25 °C in NMP. Films are cured through a multi-zone oven with temperatures between 350 °C and 520 °C.
In alkyd and polyester applications, the replacement of phthalic anhydride with TMA is not a drop-in substitution. Phthalic anhydride has a bifunctional equivalent weight of 74.06 g/eq and forms predominantly linear or lightly branched alkyd chains. TMA has a trifunctional equivalent weight of 64.04 g/eq and introduces a third condensation site on the same aromatic ring. In waterborne alkyds, the additional carboxylic acid group is neutralized with dimethylethanolamine or triethylamine to pH 7.5–8.5. The higher acid value from TMA permits water dispersibility without high cosolvent demand; however, residual amine must be removed during bake to avoid film softening. In coil coating primers cured with hexamethoxymethylmelamine at 130–150 °C, the acid functionality accelerates the etherification reaction. Over-baking can shift the hardness reading measured under ISO 1522 pendulum damping beyond the specified range.
TMA-modified alkyds are discharged with acid values in the 40–60 mg KOH/g range and then neutralized. In a 6 m³ reactor, the final water reduction to 40–50 wt% solids is performed at 70–80 °C after neutralization. Compared with solventborne linear alkyds, the TMA-branched resin can exhibit a 10–20 percentage-point reduction in cosolvent content at equal application viscosity, measured with a rotational viscometer under ISO 2555:2018. This property is used only where waterborne compliance is required; the acid-functional film must be formulated with amine-resistant pigments to avoid pH drift in storage.
In thermosetting powder coating polyesters, TMA is incorporated as a portion of the acid monomer to raise the acid value to the range used by TGIC or β-hydroxyalkylamide curatives. A typical TGIC-cured powder coating polyester has an acid value of 30–40 mg KOH/g and a glass transition temperature of 55–65 °C; TMA addition at 2–6 mol% of the acid charge increases acid group density without reducing storage stability below the sintering limit. The resin is processed on a ZSK 40 class twin-screw extruder at 90–110 °C barrel temperature, then chipped and milled to a particle size distribution with d50 ≤ 35 µm. In comparison with trimellitic anhydride-free terephthalic acid/neopentyl glycol systems, the TMA-modified powder coating exhibits shorter gel time on a hot plate at 200 °C and can reach impact resistance values specified under ASTM D2794 only if the cure schedule is not overdriven.
Because TMA is a solid with melting range 165–168 °C, powder coating resin synthesis uses staged addition with the reactor temperature held above the melting point of the monomer before the final vacuum stage. Addition of TMA too early in the esterification can create high local acid concentration and promote etherification of neopentyl glycol; the resulting change in hydroxyl number is detected under ASTM E222. In production, the TMA charge is often split into two portions: the first with the initial esterification step, the second after vacuum stripping has reached 70–80% conversion. This sequence is reported to reduce reactor wall fouling in 1000 L pilot kettles.
| Property | Phthalic anhydride | Trimellitic anhydride | Pyromellitic dianhydride |
|---|---|---|---|
| CAS | 85-44-9 | 552-30-7 | 89-32-7 |
| Molecular weight | 148.12 g/mol | 192.13 g/mol | 218.12 g/mol |
| Carboxyl equivalents | 2 | 3 | 4 |
| Equivalent weight | 74.06 g/eq | 64.04 g/eq | 54.53 g/eq |
| Melting range | 131–133 °C | 165–168 °C | 283–286 °C |
| Typical derivative | Dioctyl phthalate, linear alkyds | Trimellitate plasticizers, waterborne alkyds, polyamide-imide | Polyimide films |
Molten TMA is maintained at 170–180 °C in jacketed stainless steel transfer pipe. Exposure to sustained temperatures above 200 °C causes colour drift beyond APHA 60 and anhydride sublimation into vent lines. The flake is hygroscopic; at relative humidity above 60%, hydrolysis to trimellitic acid increases the apparent acid value and causes surface caking. Bulk silos are therefore blanketed with dry air or nitrogen at a dew point below −20 °C. Bagged flake is stored in unopened, sealed containers at ≤ 25 °C.
Process-scale failure modes are dominated by equipment fouling from sublimed anhydride and moisture-induced lump formation in screw conveyors and rotary valves. Conveying lines are specified with hardfaced surfaces and close clearances to manage pressure-sensitive caking. If water content rises above 0.10 wt%, the material may still be used in esterification after corrective acid value titration and stoichiometric adjustment, but molten viscosity and product acid value will deviate from the original certificate of analysis. Contact with strong bases, bulk water, or uncontrolled primary amines must be avoided; the intentional amine neutralization used in waterborne alkyd processing is a controlled exception conducted below 80 °C with jacketed cooling to dissipate the neutralization exotherm.
