Scope:

The ASTM D4883 test method employs a modern ultrasonic wave propagation-based technique for determining the density of polyethylenes. For the identification and characterization of polyethylene, density measurements are quite useful. It’s typically used as a way to track physical changes in a sample or as a measure of sample uniformity. It is a critical physical characteristic in polymer engineering that influences the manufacturing process’s cost and profitability. This test procedure is intended to produce results with an accuracy of at least 60.08%. 

Procedure:

A pulser is used to generate a longitudinal wave propagating at a frequency of 2 MHz or 4 MHz for the ASTM D4883 test. A metallic buffer rod transmits the ultrasonic wave to the polymer melt. Ultrasonic transducers are protected by the buffer rod from a high-temperature plastic melt.  Because the metallic buffer and the polymer have differing acoustic impedances, some of the acoustic energy is transmitted and some is reflected back. The longitudinal wave reflection measures the time of flight of ultrasonic waves and the ultrasound velocity in the polymer melt.  These data are used to calculate the density. The measurements are performed in the temperature range of 165 °C – 188 °C.

Video 01: Ultrasonic testing

Specimen size:

A sample with a thickness of 1.9 ± 0.2 mm shall be used in order to be in compliance with the specifications of ASTM D4883. 

Data :  

The density recorded is in the range of (0.4-1.4) gm/cm³. 

The ASTM D4883 test technique is simple to apply, error-free, repeatable, and non-destructive.

Conclusion:

The ASTM D4883 test method employs a modern ultrasonic wave propagation-based technique for determining the density of polyethylenes.