Crystallization of Gutta Percha Networks and Associated Elasticity

Abstract

The force exerted by an amorphous, stretched rubbery network held at constant length varies directly with temperature. But crystallizable networks exhibit deviations from force-temperature linearity once temperature falls below the melting temperature into the crystallization region. Incipient crystallization drives the force downward¹, sometimes sharply so². A select few networks display a resurgence of force as temperature continues to fall^3–5;. Polyethylene^3,4 and gutta percha⁵ are examples. Gutta percha exhibits the U- or V-shaped stress-temperature profile in a spectacular fashion. Upon cooling its stress falls precipitously to negative values, reemerges in the positive domain at still lower temperatures, and climbs back to a high level⁵.