Ultrasonic non-destructive evaluation of natural rubber latex suspensions.
This thesis describes the development of wide bandwidth ultrasonic pulse
transmission and pulse echo comparison spectrometer methods to measure the ultrasonic
phase velocity and absorption in natural rubber latex. Details of the quantitative design and
construction of simple prototype test rigs include the mechanism of: variable path length
pulse transmission, variable path length reflected pulse echo, and dual transducers reflected
pulse echo. Special signal processing of experimental data, including transducer impulse
response correction routines to calculate the acoustical parameters, are outlined.
Measurements made using the constructed prototype test rigs are compared with
each other and with data available in the pulished literature. A selection of methods to suit
varying requirements for acoustical measurements in natural rubber latex samples is
made. Calibration curves relating the measured ultrasonic absorption and phase velocity
with the dry rubber content (d.r.c.) at temperatures of 20 to 30°C were constructed.
Experiments to test the usefulness of these calibration curves were undertaken to determine
if there was any deviation from the Standard Laboratory Method.
A comparison between the experimental results obtained using the dual transducer
reflected pulse method and the simulation of the Allegra and Hawley model with multiple
scattering is presented. Good agreement was obtained between the experimental and the
theoritical approaches up to 40% d.r.c. The feasibility of the detection of adulterant
materials in natural rubber latex concentrates by using an ultrasonic method is discussed.
Finally, the dual transducers reflected pulse echo technique is found be an alternative
method to determine d.r.c. in natural rubber latex and could be used as a real time
monitoring system for liquids and suspensions in a production environment.