Compressibility, transition region polymer glasses

Before use, all the polymer pellets were dried at Ta +20 K for at least 48 h. Then, sheets of controlled thickness B were firstly compression molded under vacuum at Ta + 50 K and then cooled down slowly through the glass transition region. Next, samples of dimensions suitable for the SENB tests were cut from the sheets with a diamond saw, machined to produce the notch, and annealed once more at Ta +20 K for 72 h. The purpose of this thermal treatment is double first, it allows the elimination of the residual stresses induced by sample pressing and machining and secondly, it permits removal of eventual moisture which is known to affect dramatically the SAPA mechanical properties [12]. The pre-crack was produced in the samples just before testing. 

---