The Viscoelastic Properties of Plastics

A general method has been devised to predict the viscoelastic behavior of plastics. A simplified model of the molecule is assumed and its general motion is treated by the method of normal coordinates. General equations have been developed such that when the manner of application of external forces to the molecule is known, the molecule's general behavior may be found in a convenient and straightforward fashion. This method has been used to obtain theoretical curves for the viscoelastic behavior of cross-linked polymers subjected to sinusoidal forces. Also, the similar problem for linear material has been solved together with the creep and stress relaxation problems. It is shown that the temperature-time superposition procedure of Ferry and Tobolsky has a firm theoretical basis. In general, the theoretical curves appear to agree with the limited experimental data available. The method is also applied to the case of dilute solutions and comparison is made with the result obtained by Rouse using a different approach.