ASTM D7399 Standard Test Method for Determination of the Amount of Polypropylene (PP) in Polypropylene/LDPE Mixtures using Infrared Spectrophotometer.
The amount of polypropylene (PP) in polypropylene/LDPE mixtures using an infrared spectrophotometer can be determined using the standard test method in ASTM D7399. Thin films representing a typical portion of the material are analyzed with an IR spectrophotometer using two absorbance bands-one characteristic for PP and one for low density polyethylene (LDPE). The ratio of these two absorbances is used to assess the presence of polypropylene.
Scope:
ASTM D7399 covers the determination PP presence that has been physically mixed with LDPE by an infrared approach. This method is usually used for recycling purposes. In recycling PP and LDPE, it is important to the product properties as well as the processing conditions to know what the purity of the mixture is.
Test Procedure:
Film specimens used in ASTM D7399 give absorbances of 1.5 units or less on IR scan. In addition, with thickness of approximately 0.025 mm (1 mil). The specimen is placed in the infrared spectrophotometer. A spectral resolution of 4 cm-1 and a Beer-Norton medium or Happ-Genzel apodization function have been found to be appropriate. The infrared spectrum from 4000 cm-1 to 500 cm-1 is recorded. The absorbance of bands at 1373 cm-1 and 1465 cm-1 is one of the characteristics for PP and LDPE, respectively. Several standards with known concentrations of PP are needed to develop a calibration curve. The absorbance ratio of 1373 cm-1 versus 1465 cm-1 is plotted against PP concentration from which the PP content of the unknown sample is obtained. For quantitative determinations, several standards with known concentrations of PP in LDPE bracketing the range of interest are needed to develop a calibration curve. The presence of materials other than PP or LDPE in a sample might cause an error in measurement. An inhomogeneous sample is known to cause false readings. It is recommended to verify sample homogeneity by measuring different areas of the sample.
Sample size:
Thickness: 0.025 mm (1 mil).
Absorbencies: 1.5 units or less.
Spectrophotometer with: 4 cm-1 spectral resolution.
Conclusion: ASTM D7399 covers the presence determination of PP that is physically mixed with LDPE by an infrared approach.
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