โ Scribed by G. Titomanlio; F.P. La Mantia
No coin nor oath required. For personal study only.
Many properties of glassy polymers undergo significant changes upon annealing 1. These changes which may be reversed with a brief heating to above the glass transition temperature, have,been related to enthalpy and/or free volume relaxation.
As both enthalpy and free volume tend either increase or decrease depending on their values with respect to equilibrium at the annealing conditions, polymers starting with deficient values of free volume and enthalpy should be expected to show converse property changes with respect to those starting with excess values. In fact some evidence of this is already present in the literature 2.
On the other hand densified samples prepared by cooling under very high pressure from above the glass transition temperature showed properties very close to those of samples prepared under much lower pressure 3.
The effect of pressure, during cooling from above Tg, on the annealing behaviour of glassy polymers is further investigated in this work by means of dynamic mechanical and dielectric measurements performed on polycarbonate samples.
The material studied was polycarbonate Sinvet 301 manufactured by Anic. Samples 0.2 mm thick were prepared by compression moulding at 180"C under two values of pressure: 5 and 150 atm. A cooling rate of about 0.5ยฐC/sec was adopted down to room temperature. The samples were then subjected to annealing procedures at 1300C and 1 atm.
Dynamic mechanical data were collected on a Rheovibron DDV II C instrument at a frequency of 110 Hz.
Dielectric measurements were performed at 10 ~ Hz on disk shaped samples,
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