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Physical & Chemical properties

Viscosity

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Description of key information

The viscosity of pure formaldehyde does not need to be determined  because the substance is a gas at 20 °C / 1013 hPa. 
The viscosity of aqueous formaldehyde solutions ranges from 2.083 to 2.835 mPa s at 20°C depending on formaldehyde concentrations (30.19 - 40.08% ) and methanol concentrations (0.95 - 11.95%).

Key value for chemical safety assessment

Additional information

Viscosity pure formaldehyde

The viscosity study does not need to be performed because the substance is a gas at 20 °C / 1013 hPa. The DIPPR Project (2013) does however report a viscosity of pure liquid formaldehyde of 1.56 mPa s at -118 °C and 0.26 mPa at -19.3 °C.

Viscosity of aqueous formaldehyde solutions

Four sources were identified concerning the viscosity of aqueous formaldehyde solutions. According to a study perfomed according to the DIN 51 562 guideline by BASF (1987, Key), the viscosity of aqueous formaldehyde solutions ranges from 2.083 to 2.835 mPa s at 20°C depending on formaldehyde concentrations (30.19 - 40.08% ) and methanol concentrations (0.95 - 11.95%). A solution containing 37.13% formaldehyde and 0.95% methanol had a viscosity of 2.562 mPa s at 20°C. These values were supported by Ullmans dictionary (2012) reporting 2.1 mPa s (37% formaldehyde at 25°C) and Walker (1967) reporting values of 2.45 mPa s (37 % aqueous formaldehyde solution with 6 % methanol at 25°C) and 1.87 mPa s (30% formaldehyde at 25°C). The Kirk-Othmer (2015) report a lower value of 0.1421 mPa s, but the concentration formaldehyde is unknown.