What is Yellowness Index?YI D1925,YI E313?
What is Yellowness Index?
Visually, the yellowness of a sample is associated with burning, staining, light degradation, chemical exposure, and processing, so the Yellowing Index ( YellownessIndex, YI ) is primarily used to determine the degree of yellowing of such phenomena.
Commonly used indexes to characterize the degree of yellowing are YI E313, YI D1925, Platinum-Cobalt, APHA, Hazen, Saybolt, Gardner, ASTM chromaticity. Applicable objects can be either clear, nearly colorless liquids or solids (transmission mode) or nearly white, opaque solids (reflection mode).
E313 Yellowness Index YI E313 Introduction
YI E313 is the yellowness index recommended by ASTM E313 for D65 and C standard light sources (also known as standard illuminants).The calculation formula adopted for 2020 is:
where X, Y, and Z are the CIE tri-stimulus values, and CX and CZ are the coefficients (whose values vary with the standard light source and the standard observer's angle, see table 1).
YI E313 is suitable for samples with primary wavelengths in the range of 570-580nm, or Munsell hues in the range of approximately 2.5GY-2.5Y. YI E313 can be used to compare samples of the same material and appearance, e.g., the samples should be closer in terms of luster, texture, thickness (for semi-transparent or transparent samples), and light transmission.
YI D1925 is the yellowness index recommended by ASTM D1925 (Test Method for Yellowness Index of Plastics), which was adopted in 1962 with the formula:
The formula was only used for C/2° and was withdrawn in 1995, but the formula still provides useful information.
Both YI E313 and YI D1925 can be used in the textile, paint, and plastics industries, as well as for near-white or near-colorless objects.
Measurement Methods
The main instruments used to measure the Yellowness Index include colorimeters, spectrophotometers, and color difference meters. These instruments must comply with the standards set by the International Commission on Illumination (CIE) to ensure accuracy and consistency. Common standards include ASTM E313-10 and ISO 2470.
Applications
The Yellowness Index is widely used to control product quality and evaluate the aging of materials. It is applicable to transparent and semi-transparent materials such as plastics, films, and chemical additives.
Measurement Considerations
Sample Preparation: Ensure the sample surface is clean and free of scratches.
Instrument Calibration: Regularly calibrate instruments to ensure the light source and reference plates meet standards.
Environmental Conditions: Maintain appropriate temperature and humidity during measurement, and avoid vibrations and direct air conditioning.
Influencing Factors
The measurement results of the Yellowness Index can be affected by:
The color of the resin
Measurement temperature and humidity
Calibration of the reference plate
Standardization of the light source
Uniformity and presence of bubbles in the sample
Conclusion
The Yellowness Index is a crucial indicator for assessing color changes in polymer materials, widely used in material science and industrial production. Accurate measurement and control of the Yellowness Index can significantly enhance product quality and durability.