In this thesis, a Nonlinear Acoustic Technique (NAT) has been used to do a non-destructive quality assurance of plasticized polyvinyl chloride (PVC) specimens. The response of the specimen to an ultrasonic wave is analyzed in order to characterize its material properties. The analysis focuses on finding out linear and non-linear properties of the propagated ultrasound wave, such as the second order non-linearity parameter (β) and the sound velocity. The outcomes agree well with the actual properties of specimens in terms of: degree of molecular dispersion of plasticizing agent, non-mixed granulates and the volume fraction of air in strands. As conclusion, it was shown that non-linear acoustic method can be used for predicting mechanical properties of extruded plasticized PVCs. Furthermore, acoustic measurements can be used as on-line measurements during the manufacturing process. It will lead to: increased profit, saved time, less energy and lower costs.

There are four questions which are base of this thesis: 1. Is it possible to use non-linear acoustic methods to detect non-mixed granulates within strands? If so, what are the limits? 2. Is it possible to evaluate the degree of molecular dispersion of plasticizing agent with non-linear acoustic methods? If so, what are the limits? 3. Is it possible to determine the volume fraction of air in strands with non-linear acoustics methods? 4. If acoustics methods are used for on-line measurements, what are the limitations and how is it possible to automate measurements with respect to the conceptual design of non-linear methods? The three first questions can be shortened in, investigating degree of non-mixed granulates, molecular dispersion and volume of air in extruded PVC materials. To investigate them, the second order non-linearity parameter (β) and velocity of propagated ultrasound wave in material are measured. β parameter which indicates nonlinear behavior of material is used to examine quality of different PVC samples (non-mixed granulates and molecular dispersion), with respect to each other. Moreover, sound velocity is used to compare volume of air in the samples. Attenuation measurement is also done to find out any correlation between attenuation (linear acoustic property) and β parameter (nonlinear acoustic property). Finally it is concluded that measurement plan which is used in laboratory-experiments also can be utilized in on-line measurement in production line.