Yellowness Index of Plastics: Understanding Laboratory Testing Methods

The Yellowness Index of plastics is a key indicator of color quality and stability in manufacturing and material science

by | Apr 24, 2024

The Yellowness Index (YI) is a numerical indicator used to assess the degree of yellow discoloration in white or transparent plastics. This index is critical for quality control in industries where aesthetic consistency and clarity are essential, such as in automotive, packaging, and consumer electronics. The following article explores the importance of the Yellowness Index, how it is measured, and the laboratory techniques employed to ensure precise results.

What is the Yellowness Index?

The Yellowness Index is a calculated number representing the change in color of a plastic material from clear or white to yellow. This change is often due to aging, chemical exposure, or irradiation. The index helps manufacturers ensure that their products meet certain color specifications over time, thus maintaining quality and consumer satisfaction.

Laboratory Testing of the Yellowness Index

Testing for the Yellowness Index is typically carried out in a controlled laboratory setting, where precise conditions can be maintained to ensure consistent and accurate measurements. The process involves several key steps and technologies:

  1. Sample Preparation: Prior to testing, plastic samples must be prepared according to standardized dimensions and surface conditions. This may involve cutting, polishing, or conditioning the samples to mimic the effects of aging or environmental exposure.
  2. Spectrophotometry: The primary method for measuring the Yellowness Index is spectrophotometry. This technique involves the use of a spectrophotometer to measure the intensity of light passing through a sample or reflected from its surface at specific wavelengths.
    • Instrument Calibration: Before measurements, the spectrophotometer is calibrated using standard white plates to ensure accuracy.
    • Measurement: The sample is placed in the spectrophotometer, and measurements are taken across the visible spectrum. The Yellowness Index is calculated based on the absorption at specified wavelengths, typically around 420 nm to 570 nm, where yellow light is absorbed.
  3. Colorimetry: As an alternative or supplementary method, colorimetry can be used. Colorimeters, like spectrophotometers, assess color based on light absorption but are generally simpler and less expensive. However, they provide less comprehensive data.
  4. Data Analysis: The data collected from these instruments are analyzed to calculate the Yellowness Index. The calculation often involves a formula that integrates the measurements of blue light absorption, which correlates directly with the yellow tint of the plastic.

Quality Control and Standards

To ensure reliability and industry-wide consistency, the testing of the Yellowness Index follows specific standards such as ASTM E313 and ISO 17223:2014. These standards define the methodology for measuring color and yellowness in plastics and ensure that the results are comparable across different laboratories and production batches.

Importance of Quality Assurance and Standards

Measuring the Yellowness Index of plastics is a vital process in maintaining product quality and meeting industry standards. Through precise laboratory testing, manufacturers can monitor the stability and consistency of their plastic materials against yellowing, thereby safeguarding both the product’s aesthetic qualities and its performance in the market. This testing not only helps in quality control but also assists in research and development by providing insights into the effects of various additives and processing conditions on the color stability of plastics.

Future Outlook

As material science advances and environmental considerations become more pressing, the methods for testing and improving the color stability of plastics are likely to evolve. Ongoing research in polymer stabilization and enhanced analytical techniques will continue to play a crucial role in addressing the challenges associated with plastic discoloration.

Do You Require Yellowness Testing of a Product?

Contract Laboratory assists manufacturers in accessing specialized labs for Yellowness Index (YI) testing, adhering to ASTM E313 and ISO 17223:2014 standards. This service is crucial for ensuring the quality and regulatory compliance of plastic products, particularly in industries where aesthetic consistency is vital. Through, companies can quickly find and partner with qualified labs to evaluate the color stability of their materials. To find a lab, simply Submit a Test Request.

Related Content


Editor's Choice