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Physical & Chemical properties

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Appearance

At ambient temperature and pressure, trimellitic anhydride (TMA) is an organic solid. TMA is commercially available as white to yellow flakes or tablets (Villa, 2010a, Park & Sheehan 1996).

Melting point

The melting point of trimellitic anhydride is 167.2 °C under standard atmospheric conditions (Villa, 2010b).

Boiling point

Trimellitic anhydride boils at around 390 degrees C under normal conditions (Arnold, 1961; Villa, 2010b).

Density

The density of trimellitic anhydride is 1.4867 g/mL at 20 °C (Barbieri, 2010a).

Granulometry

The particle size distribution of samples of trimellitic anhydride flakes and drops, typical of the commercial manufacturing, was characterised by a sieving method. As result, 95% of particles are larger than 400 microns and less than 1% are smaller than 50 microns.

Vapour pressure

Extrapolated (Clausius-Clapeyron equation) vapour pressures of TMA at 20 and 25 deg C were 0.0000653 and 0.0000738 Pa, respectively. (Barbieri, 2010c).

Partition coefficient

The octanol/water partition coefficient of trimellitic anhydride (TMA) has been determined experimentally by the HPLC method. The log Kow obtained in this way is 0.06 (Villa, 2010c). QSAR modelling performed with the KOWWIN program of the US EPA gives a log Kow estimate of 1.95 for TMA.

Trimellitic anhydride undergoes almost instantaneous hydrolysis on contact with water, to form trimellitic acid (TMLA).

The octanol/water partition coefficient of trimellitic acid (TMLA) has been determined experimentally by the Shake Flask method. The log Kow obtained in this way is 0.54 (Nichetti, 2014). QSAR modelling performed with the KOWWIN program of the US EPA gives a log Kow estimate of 0.61 for TMLA.

Water solubility

Trimellitic anhydride (TMA) undergoes practically instantaneous hydrolysis to trimellitic acid (TMLA) on contact with water. It is therefore not possible to determine the aqueous solubility of the parent anhydride and data are provided instead for the hydrolysis product TMLA. The measured aqueous solubility of TMLA is 24.4 g/L at 20 degrees C and pH 1.8 (Villa, 2010d) and a similar value of 2.1% (w/w) at 25 degrees C is indicated in published literature (Roehrscheid, 2005). On this basis, TMLA is classed as 'very soluble' in water.

Surface tension

In accordance with Column 2 adaptation statement of REACH Annex VII, information requirement section 7.6, this study does not need to be conducted if, based on structure, surface activity is not expected and no surface-active properties would be predicted for this compound. Surface activity is not a desired property of trimellitic acid or its hydrolysis product trimellitic acid (TMLA). Consequently, a test of the surface tension of TMA or TMLA in aqueous solution is not required.

Flash point

The flashpoint of trimellitic anhydride (TMA) is 227 °C (Park & Sheehan, 1996).

Autoflammability

Trimellitic anhydride (TMA) is a solid at atmospheric pressure and its relative self-ignition temperature was therefore investigated according to EU Method A.16. No ignition occurred at temperatures up to 400 degrees C, the highest temperature applied (Barbieri, 2010b). The relative self-ignition temperature of TMA therefore exceeds 400 degrees C at atmospheric pressure.

Flammability

A preliminary flammability screening test was performed by applying a flame to a loosely-packed linear pile of trimellitic anhydride (TMA) for two minutes. The pile failed to ignite. According to the UN Recommendations on the Transport of Dangerous Goods, TMA is therefore classified as a non-readily combustible solid of Division 4.1 and further flammability testing is not required (Atwal & Tremain, 2010).

Explosiveness

According to theoretical considerations based on chemical structure, trimellitic anhydride (TMA) does not possess explosive or oxidising properties. TMA is unlikely to undergo rapid decomposition accompanied by the evolution of gases or release of heat and therefore does not present a risk of explosion (Curl & Wright, 2010a).

Oxidising properties

According to theoretical considerations based on chemical structure, trimellitic anhydride (TMA) does not possess oxidising properties. TMA is unlikely to cause or contribute to the combustion of other material during transport, storage or use (Curl & Wright, 2010b).

Stability in organic solvents and identity of relevant degradation products

In accordance with REACH Annex IX column 2, this study does not need to be conducted because it is not expected that the stability of trimellitic anhydride (TMA) in organic solvents is critical.

Dissociation constant

A waiver is proposed for the parent monomer on the basis that trimellitic anhydride (TMA) hydrolyses almost instantaneously on contact with water and measurement of its dissociation constant(s) is therefore not technically feasible.

Dissociation constants are, however, available for trimellitic acid (TMLA), the hydrolysis product of TMA. At 20 degrees C, the pKa1, pKa2 and pKa3 values of TMLA are 2.91, 3.94 and 5.30, respectively.

Viscosity

In accordance with Section 2 of REACH Annex XI, information requirement section 7.17, this study cannot be conducted on solid materials or gases. According to ECHA Chapter 7 guidance, viscosity measurement is only relevant to liquids.