ASTM D7133-21 Tristimulus CIELAB Color and Yellowness Index of Liquids

ASTM D7133-21 Tristimulus CIELAB Color and Yellowness Index of Liquids

ASTM D7133-21 is used to determine the CIELAB color and Yellowness Index (YI) of liquid polyurethane raw materials using an instrument. The CIELAB and YI findings are obtained by manipulating CIE tristimulus values mathematically, according to Practices E308 and E313, respectively. The values expressed in SI units should be considered standard.

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    ASTM D7133-21 CIELAB is a visual-based scale used in the polyurethane industry to specify color and set color tolerances. The Yellowness Index indicates how far the sample has strayed from colorless to yellow. Clear liquids with yellow saturation (dominant transmission wavelength in the 570 to 580 nm region) suit this index. It’s used to establish tolerances for polyurethane raw ingredients.


    Firstly in ASTM D7133-21, a spectrophotometer measures the color of total transmitted light in CIE tristimulus values under CIE standard illuminant D65 and CIE 1964 supplemental standard observer, also known as the 10° ordinary observer. These values are then translated to the CIELAB color scale and the Yellowness Index using the relevant equations. Finally, The L*a*b* and YI values are given.

    Specimen size

    The test samples must be homogeneous and representative of the liquid under investigation.
    There are no units connected with the CIELAB values L, a, and b*.
    There is no unit associated with the Yellowness Index value, YI.

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    The instrument software should automatically calculate the L*a*b* values using the equations provided in Practice E308 and the YI value using the equation defined in Practice E313.


    The date of measurement, sample description, and identification should all be included in the final report. 

    Any deviations from the required parameters or conditions (e.g., sample temperature if not 23 6 2°C or 50 6 2°C for pure MDI, use of a liquid other than mineral oil for standardization) and L*a* b* values and YI value to two significant figures to the right of the decimal point are determined. 


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