Research On Ultrasonic Detection Of Polymer Thermodynamic Transition

Significant is understanding polymer thermodynamics transitions for exploring technological parameters and selections of equipment and materials as well as material modification. This thesis established on-line characterization of rubber vulcanization and polymer crystallization without interfering with the production or processing molding. The quantative expressions were suggested between ultrasonic velocity, crystallinity and polymer specific volume. The main content and achievements are as follows:(1) Ultrasonic velocity and natural rubber specific volume were synchronously detected in vulcanization process using PVT-ultrasonic wave testing device showing single corresponding relationship between them, which indicates that ultrasonic velocity can be monitored to obtain specific volume illustrating the material variation. Four groups of their quantitative relationships were developed through theoretical analysis and numerical fitting. Predicted results were in good agreement with experimental data. In addition, the master curve of ultrasonic velocity versus temperature was then formed using temperature-pressure equivalence principle. Their experiment data were fitted in linear equation and acoustic impedance method fitting expression.(2) Ultrasonic probes were mounted in the material cavity of rotorless rheometer as synchronous detection device of torque, axial force and ultrasonic. Quantitative ultrasonic characterization of vulcanization process was put forward after comparison of synchronous detection ultrasonic velocity curve, torque curve and axial pressure curve on the basis of rubber vulcanization testing standards, in which vulcanization characteristic parameters were defined before the curing kinetics equation was described. Subsequently, the variation in specific volume with time can be used to describe the vulcanization process when it is calculated from the expressions of specific volume with ultrasonic velocity. This was confirmed on two mbber materials.(3) PVT-ultrasonic synchronous detection device was used to conduct on-line characterization of crystallization process for specific volume and the corresponding ultrasonic velocity. Hereafter, quantitative relation between crystallinity and ultrasonic velocity was built. Thus, ultrasonic wave can quantitatively characterize crystallization process under different pressures. The non-isothermal crystallization kinetics of polypropylene and high density polyethylene was analyzed by Jeziorny method of modified Avrami equation and m0method presenting crystallization kinetics parameters and cooling rate functions. The resultant points were consistent with those by conventional PVT test, which showed the feasibility of this experimental approach.The formed on-line quantitative characterizations of rubber vulcanization and polymer crystallization can be further widened and deepened for other polymer thermodynamics and engineering applications.