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D3349-21 – Standard Test Method Technical Guide
ASTM D3349-21 provides a standardized method for measuring the light transmitted through films of ethylene polymer materials pigmented with carbon black. By calculating the absorption coefficient from this transmission data and film thickness, manufacturers can effectively evaluate the dispersion quality and concentration of the carbon black pigment.
📖 Scope and Significance
The scope of this test method is strictly limited to measuring the amount of light transmitted through a film of carbon black pigmented ethylene polymer. A critical outcome of this measurement is the calculation of an absorption coefficient, which serves as a reciprocal function of transmission after a correction for film thickness. This absorption coefficient is a key indicator used to judge the degree and uniformity of pigment dispersion, as well as the adequacy of the quantitative level of pigment addition. These factors are applied to predict the performance of the polymer material in response to prolonged exposure to ultraviolet (UV) light, as evidenced by minimal changes in specific material properties.
⚠️ Caution on Application: This test method was developed primarily to evaluate ethylene polymer materials pigmented with small particle size carbon blacks suitable for UV protection. The accuracy and reproducibility of the test for larger particle sizes (35 nm or greater) has not been fully determined. However, for larger sizes, such as furnace black at 275 nm, a loading of at least 5% or higher carbon black has been found to provide suitable UV protection.
⚙️ Apparatus and Reference Standards
Execution of D3349-21 requires specific equipment conforming to strict specifications. The core apparatus includes a spectrophotometer that complies with Practice E60, specialized molds, and calibration materials.
| 🟦 Component | 📏 Specification Requirement |
|---|---|
| 📐 Spectrophotometer | Must conform to ASTM Practice E60 for spectrophotometric analysis. |
| 🛠️ Mold | Made of Ketos steel (or equivalent), hardened to Rockwell C45. Surfaces must be chromium plated to a minimum thickness of 0.005 mm (0.0002 in.). |
| 🔲 Specimen Holder | Two concentric rings cut from phenolic-paper laminate (or other suitable material) as shown in Fig. 3, designed for a snug slip fit one within the other. |
| 🎯 Reference Material | A neutral density filter with an absorbance value of 1.0 to 1.2 at 375 nm. An M-type carbon 0.85 density filter laminated between cellulose acetate sheets has been found suitable. |
📊 Test Summary and Key Parameters
The procedure involves measuring the transmission of light of a specified wavelength through a thin film of the polymer. The film thickness is carefully measured, and the resulting absorption coefficient is calculated as a reciprocal function of transmission after correction for thickness.
| ⚡ Parameter | 📊 Details / Value |
|---|---|
| 🟦 Carbon Black Particle Size (Target) | Small particle size blacks suitable for UV protection (e.g., less than 35 nm). |
| 📏 Furnace Black (275 nm) Loading Threshold | ≥ 5% by mass for adequate UV protection. |
| 🎯 Reference Filter Absorbance | 1.0 to 1.2 at a wavelength of 375 nm. |
| ⚡ Primary Measured Property | Light transmission through the film. |
| ⚡ Calculated Property | Absorption coefficient. |