ASTM D6290 Standard Test Method for Color Determination of Plastic Pellets

Get Certified ASTM D6290 Testing for Reliable Plastic Pellet Color Measurement

ASTM D6290 testing provides a standardized approach for comparing the color of plastic resins in pellet form. No molding or extrusion of specimens is required, making it convenient to compare the color of pellets. Therefore, engineers can evaluate color attributes using the Yellowness Index, CIE X, Y, Z, Hunter L, a, b, or CIE L*, a*, b* values.

• Material type: Plastic pellets.
• Purpose: Instrumental determination of plastic pellet color.
• Primary property: Degree of yellowness or change in yellowness.
• Illumination: Daylight illumination.
• Material appearance: Nearly colorless, transparent or nearly white, translucent or opaque plastics.
• Measurement principle: Tristimulus color measurement.
• Instrumentation: spectrophotometer or tristimulus colorimeter.
• Color values: Yellowness Index (YI), CIE X, Y, Z, Hunter L, a, b, and CIE L*, a*, b*.
• Color system: CIE 1976 X, Y, Z and CIELAB 1976 color space.
• Units: SI units are the standard units where applicable.
• Comparison requirement: Samples should have similar pellet shape, size, texture, and degree of translucency.
• Application: Color comparison of resin in pellet form.

What are the Uses of ASTM D6290 Testing?

ASTM D6290 is used to compare the instrumental color properties of plastic pellets that have similar physical properties. The method provides quantitative color data without molding or extruding the pellets. The ASTM D6290 standard:

• Measures the degree of yellowness of plastic pellets.
• Compares the differences in yellowness between similar samples of pellets.
• Generates CIE X, Y, Z tristimulus values.
• Calculates the a, b color values and Hunter L of the color.
• Calculates CIE L*, a*, b* color values.
• Measures Yellowness Index based on Practice E313.
• Helps compare resin pellets.
• Permits color comparison without molding or extruding test specimens.
• Assists in making color comparisons between similar pellet samples.
• Assists instrumental characterization of plastic resins in terms of color.

Which materials can be tested under ASTM D6290?

ASTM D6290 is applicable to nearly colorless, transparent or nearly white, translucent or opaque plastic pellets that are homogeneous and nonfluorescent. The method should be used to compare pellets of similar shape, size, texture, and translucency since these can affect the color measured. So it’s important for technicians to compare samples that have similar physical appearance, not dissimilar forms of pellets.

Why is ASTM D6290 Important?

ASTM D6290 is significant because it offers a simple instrumental approach to comparing the color of plastic resins in pellet form. The method eliminates the need for specimen preparation (e.g., molding or extrusion), enabling the engineer to assess the color of the pellets directly. The actual pellet color measured does not, however, necessarily reflect the color of the final molded, cast, or extruded product, as processing conditions, pellet shape, and pellet size can influence the final product appearance.

ASTM D6290 Testing Process and Data Collection

ASTM D6290 testing starts with the color measurement instrument being standardized based on the manufacturer’s instructions. Technicians then fill a clear glass sample cup full of plastic pellets and place the cup in the middle of the sensor port. Later, the technicians cap the sample to prevent outside light from reaching it. Analysts take the necessary tristimulus measurements and calculate and/or record the corresponding color values. The specified combination of CIE illuminant and standard observer is used for Yellowness Index measurements. The method can also be used to deliver CIE X, Y, Z, Hunter L, a, b, or CIE L*, a*, b* values. This allows comparison of the color characteristics of tested pellets with similar shape, size, texture, translucency, and measurement conditions.

Common Challenges and Troubleshooting

Consistent pellet characteristics, instrument standardization, sample positioning, and light control are crucial to obtaining accurate ASTM D6290 results. Technicians should thus compare pellets of similar shape, size, texture and translucency. If there is a significant difference in the form of the pellets being compared, the color measurements may not be a meaningful comparison of materials. Externally applied light can affect measurements, too, especially if pellets are not protected from strong light sources prior to testing. Hence, the specified light-exclusion cover (opaque light) should be used and unnecessary exposure at the measurement port should be avoided. When results are compared between measurements, they should also be taken from similar optical groups.

• Yellowness Index (YI) may be reported for plastic pellets that are applicable.
• CIE X, Y, Z tristimulus values can be obtained for the analysts.
• Hunter L, a, b color values can be evaluated by the engineer.
• CIE L, a, b*** color values can be assessed by the engineer.
• To compare, technicians should strive to have similar shape, size, texture, and translucency of pellets.
• When comparing results, analysts should keep in mind that the results were obtained using the same type of instrument and optical geometry.
• Pellet color may not always be the same as the color of the final product (molded, cast, or extruded).

Link to ASTM D6290