Lactoprene EV Elastomer - Effects of Plasticizers

Abstract

The films, after orientation, are anisotropic with regard to their mechanical properties. An oriented film has a higher modulus of elasticity along the axis of orientation than perpendicular to this axis. At an intermediate angle, the modulus has an intermediate value.It is, of course, well known that plasticized polyvinyl chloride becomes somewhat anisotropic in certain forming operations such as calendering, extrusion, etc. However, in such operations there is ordinarily an opportunity for a considerable amount of the orientation to relax before the structure is frozen in, so that only a residual effect is observed. Much larger variations in mechanical properties can be achieyed by temperature and stress sequences such as those used here. It is not unlikely that such recrystallization operations could find industrial application.A set of experiments was carried out to study the recrystailization under constant load in some detail. The plasticized films were first subjected to a stress at 30.0°C. After 60 minutes the samples were slowly heated to 90.0°C .; the heating cycle was 2 hours. On reaching 90.0°C ., the samples were cooled to 35.0°C. This cycle being completed, the samples were reheated to 90.0 °C. and the resulting contraction, due to melting of the crystalline structure, was followed. A typical diagram of the compliance (strain per unit stress) as a function of temperature, is presented in Figure 4. Here it is noted that process A, the initial upheat, is nonreversible. On cooling, curve B results. Process B, the cook ing process, on the other hand, is essentially reversible, since, on reheating, curve C results. There is some hysteresis during this process, but it is small. This curve is typical of the curves obtained with all the samples examined. If the load is removed at a low temperature-for example, 30°or 40°C .-only a small amount of recovery occurs.The samples retain their elongated, oriented form permanently, as far as-these experiments can show. (Samples stored for 6 weeks showed no signs of further recovery.) Of course, if the oriented samples are heated to a temperature of 90°C ., slow recovery to the original, unstressed length will take place, and the anisotropic properties will disappear. SUMMARY AND CONCLUSIONSPlasticized polyvinyl chloride and plasticized Vinylite VYNW exhibit a three-dimensional gel structure, the cross links of which are crystallites. The mechanical properties of a given formulation can be markedly altered by suitable recrystallization procedures.