Study On The Measurement Of Polymer Melt Dynamic Density By Ultrasonic

At present many domestic and foreign ultrasonic measurement of polymer melt density depend on offline methods. It means through the ultrasonic transmission sound speed oscillogram, measuring the wave amplitude pad value. Use related parameter to obtain the melt acoustic impedance value. Through the acoustic impedance, the sound speed and the density relation, the melt density can be obtained indirectly. Because of its hysteresis and low efficiency, it is not suitable for melt density measurement continuously in the polymer formation process.This article introduced one kind of ultrasonic online measuring polymer melt density under the different temperature and the pressure, and the method divides into three steps:First step, based on the PVT theory of polymer melt, a Melt Flow Rates Tester was modified with a dial indicator for the measurement of the micro distance. With the modified instrument, polymer melt density can be measured under any pressure and melting temperature. By further analyzing the result, the data of the melt density is agreed with the free volume theory, that is, the polymer melt density decreased with the higher temperature and increased with the higher pressure. Moreover, this method also to be able to survey the polymer melt bulk modulus, by analyzing the result, the melt the bulk modulus also elevates along with the temperature reduces and increases along with the pressure increases.Second step, uses the equipment designed and manufactured by ourselves to survey polymer melt transmission sonic speed under different temperature and pressure. With analysis of result, the rule that transmission sonic speed maintains consistent with the polymer melt dynamic density changing was discovered.Third step, depending on polymer melt dynamic density and the corresponding condition melt transmission sonic speed, uses the Least square polynomial method to establish the melt density measurement mathematical model. With the curve the melt density can be obtained directly.This method has a simple operation, and the test equipment is easy to design and manufacture, and the data is more accurate. Later period if the corresponding data software system can be created, the melt density will be obtained through the transmission sonic speed, then the online measurement can be realized.