The viscoelastic behaviour of plasticized and “antiplasticized” polyvinylchloride

Abstract

SEVERAL papers have appeared recently in which the question of increase in the elasticity modulus and strength of plasticized polymers as the concentration of plasticizer is increased, is discussed [1-8]. Jackson and Caldwell [1-4] have called this phenomenon antiplasticization and have formulated the basic requirements of low-molecular additives to a polymer, for its strength and elastici ty modulus to be increased. For this purpose they investigated the behaviour of a large number of low-molecular substances (mainly containing phenyl groups), which they mixed with a polycarbonate, and divided them into two classes. Those low-molecular organic substances that cause lowering of the strength and elasticity modulus when added to the polymer they assign to the first class (plasticizers). Low-molecular organic substances that raise the elasticity modulus and strength were assigned to the other class (antiplasticizers). This division of substances into plasticizers and antiplasticizers has more recently been confirmed by a number of authors [7, 8]. I t should be mentioned that effects analogous to antiplasticization, relating to anomalous effects of addition of small amounts of substances on the strength and deformational characteristics of polymers had been observed a considerable time before [9, 10]. When the concentration of plasticizer was large however the strength and elasticity modulus decreased as the concentration of plasticizer was increased [9, 10]. This has complicated ideas about the specific effect of low concentrations of a plasticizer. In references [5] and [6] it was stated that it is not correct to compare the properties of polymers containing different concentrations of the same plasticizer at an arbitrarily chosen (usually room) temperature. In such a comparison it could prove to be that the compositions containing different quantities of the plasticizer are in different physical states. For example at a given temperature a polymer containing a low concentration of plasticizer could be in the glassy state and one with a high concentration of plasticizer in the high-elastic state. I t is understandable that such a comparison would not lead to discovery of the mechanism of the effect of a plasticizer on the physical properties of polymers. For this reason it was proposed [5, 6, 11] tha t the properties of polymers should