This Application Note shows that fast near-infrared spectroscopy (NIRS) accelerates quality control of polymer granulates and raw material identification. Polyethylene (PE) and polypropylene (PP) can be simultaneously identified. Additionally, the density of PE is determined in the same measurement.
Method description: The most commonly used polymers for daily life products are polypropylene (PP) and polyethylene (PE). These polyolefins are versatile and cheap in production costs. PP and PE are used in the same application fields, but due to a lower glass transition temperature, PE is unusable above 80 °C. The broad application possibilities of PE is based on the varying number of cross-links (branches) and therefore also on the density. Depending on its density, PE can be subdivided into:
- Low density (LDPE): 0.915 – 0.935 g/ cm3
- High density (HDPE): 0.936 – 0.970 g/ cm3
Normally, this parameter is determined according to ASTM D1505/ ISO 1183. Besides the quantitative characterization of PE, the raw material identification of PP, HDPE and LDPE needs to be assured, especially if the final product will be used as packaging material for food and drug products (regulated according to e.g. FDA and USP).
