The temperature-dependent change in volume of polystyrene can be measured with a dilatometer using a special cylinder as a sample holder.
Before the 1st heating, the sample was aged below Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transition temperature (Tg); the 2nd heating was conducted on the same sample after controlled cooling. The volume RelaxationWhen a constant strain is applied to a rubber compound, the force necessary to maintain that strain is not constant but decreases with time; this behavior is known as stress relaxation. The process responsible for stress relaxation can be physical or chemical, and under normal conditions, both will occur at the same time. relaxation for the 1st heating is clearly visible at the Tg, as is the change in slope at the Tg for the 2nd heating. (measurement with DIL 402 C)