Abstract
In order to study the viscoelastic behaviour of high polymers, an apparatus is required which enables the measurement of dynamic modulus and loss factor in a wide range of frequency and temperature. An apparatus was constructed for this purpose, which covers a range from 0.01cps to 20cps of frequency, from 20°C to 160°C of temperature, and from about 107 to 1011 dynes/cm2 in the value of dynamic Young's modulus.
The forced vibration of specimen was used in stead of resonant vibration, because the measurement could be carried out at any desirable frequency. The dynamic Young's modulus E' and loss factor tan δ can be obtained from the amplitude ratio and phase difference between stress and strain in the specimen, which is subjected to longitudinal vibration.
In practice, the displacement of one end of the film-shaped specimen was detected by a wire strain gauge which was fixed to the driving clamp of specimen. The force was similarly detected by another strain gauge, which was fixed to the other clamp, having much higher stiffness as compared to the stiffness of specimen.
The electrical outputs from two strain gauges, which are proportional to the displacement and force respectively, are amplified and lead to the horizontal and vertical axes of afterglow cathoderay oscillograph. From the Lissajous' figure thus obtained the elastic modulus E' and loss factor tan δ can be easily calculated. The two amplifiers were constructed identically, so that the electrical phase lag and temperature variation of sensitivity cancelled each other.
When the frequency is higher, both electrical outputs are led into a specially devised circuit by which the values of E' and tan δ can be measured directly from the reading of the dial in potentiometer and of voltmeter. The observation of the Lissajous' figure in cathod-ray tube was also useful for watching the state of movement and the distribution of tension in the specimen.
The specimen was surrounded by a cylindrical metal tube and heater element and the temperature of the atmosphere around specimen was controlled in the accuracy of 0.1°C by a saturable core reactor system.
The dynamic Young's modulus and loss factor of polyvinylacetate-styrene graft copolymers (29% and 37% styrene) have been measured over the temperature range of glass transition. Master curves for these specimens could be obtained following the ordinary reduced variable method.
