Research On Ultrasonic Detection Of Polymer Rheological Properties

Polymer flows into mold cavity under a certain pressure after being molten. In such complicated flow or deformation, such material viscoelasticities as viscosity, melt flow index and normal stress difference coefficients will change. Testing rheological properties are significant in designing processing machine and setting technological parameters. Traditional off-line rheological measurement can be hardly used in the polymer process. In contrast, on-line detection is an effective way to monitor polymer processing. This paper is going to conduct simultaneous testing viscoelastic properties and ultrasonic characteristics in polymers (crystalline polymer, glassy polymer and their blends as well as filled systems) to establish their specific relationships and on-line detection method. The main content and achievements are as follows,1. Ultrasonic wave was detected through melt in capillary equipment as one simultaneous measurement of polymer viscoelasticity and ultrasonic signal for on-line characterization research.2. Three sets of quantitative relationships between ultrasonic velocity and melt viscosity are built on basis of equation of state and the developed specific volume-ultrasonic velocity in considering Doolittle viscosity function, Arrhenuis equation and relaxation time-ultrasonic velocity from the definitions of unfilled space and free volume. The detection wa conducted on materials of HDPE、PS and PP. The small error between the predicted values of these models and experimental data prove their applicability.3. Such on-line detection was successfully applied to blends of HDPE/PP、HDPE/PS and filled composite PP/CaCO3as well as natural rubber mixture. Some variable expressions considering component effects were introduced into viscosity-ultrasonic velocity models. Experimental data proved that ultrasonic velocity of blend was approximately composition percentage-exponential addition of those of components while that of particle-filled composite was expressed as that of matrix multiplied by filler concentration function. The viscosity-ultrasonic velocity curves for the complex systems at different composition were almost shifter into master one showing the similarity in alalysis from ultrasonic amplitude.4. Flow rate was detected mathematically by ultrasonic velocity as viscosity considering that velocity was affected by specific volume variation when viscosity corresponds to flow rate at constant pressure (showing constant stress). Thus, melt flow index can be characterized on-line by ultrasonic wave. The largest error between the prediced values by models and experimental data is below15%for pure polymer melt at different loads. The linear model fits at lower temperature against exponential model for higher temperature and power law model for wider range. The relationships were suggested for blends and composites quantatifying the effects of composition and filling content, which was verified.5. Ultrasonic wave and normal stress difference coefficient were simultaneously measured on one planar die-rheometer. Their quantative relationships were proposed for polymers, blends and filled systems. The effects of compositon and filler content were analyzed quantitatively. The curves of normal stress difference coefficient versus ultrasonic velocity were shifted to one master curve at different pressures and temperatures, which showed a certain rationality of the models.In all, the proposed on-line detection way and the models for rheoligical property-ultrasonic characteristics fits to polymer melt processing. It should be noticed that the models must be checked for optimization at high shear rate in dynamic conditions.