TY - JOUR A1 - Hardy, L. A1 - Stevenson, I. A1 - Fritz, A. A1 - Boiteux, G. A1 - Seytre, G. A1 - Schönhals, Andreas T1 - Dielectric and dynamic mechanical relaxation behaviour of poly(ethylene 2,6-naphthalene dicarboxylate). II. Semicrystalline oriented films N2 - The dielectric and dynamic mechanical behaviour of bi-stretched non-treated and annealed semicrystalline poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) films are studied as a function of different morphologies obtained by thermal treatments at temperatures close to the melting temperature of a semicrystalline film. Differential scanning calorimetry (DSC) shows that the glass transition temperatures do not change significantly with the thermal treatment for bi-stretched films. However, the melting temperatures and the degree of crystallinity increase with the value of annealing temperature. Both dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA) display three relaxation processes. In order of decreasing temperature, can be observed: the ?-relaxation due to the glass transition, the ?*-process assigned to cooperative molecular motions of the naphthalene groups which aggregate and the ?-relaxation due to local fluctuations of the carbonyl groups. The ?-relaxation process shifts to higher temperatures for the 250 and 260 °C treated bi-stretched semicrystalline samples compared to the sample thermally treated at 240 °C according to DRS data but shifts to lower temperatures according to the DMA measurements for the three annealed samples. This discrepency results from the different sensitivity of each methods with regards to the release of orientation. At a fixed frequency the temperature associated to ?*-relaxation is lower for the non-treated bi-stretched semicrystalline samples than for the treated ones using DMA but no difference can be seen in DRS. The associated apparent activation energies are rather high which suggest cooperative motions. It is assumed that the orientation of the samples prevents coupling between the naphthalene groups due to the stretched chain configuration in the amorphous phase. The activation energy for the ?-process given by DRS is independent of the thermal treatment and the value agrees with those found for poly(ethylene terephthalate) (PET) and amorphous PEN. Evidence of the decrease of orientation in the sample with thermal treatment can be seen via the onset of mobility, both by DRS and DMA. Thus, the orientation induces a greater change of properties compared to the crystalline samples obtained from the thermal treatment of an amorphous sample. Finally, a three phase model is proposed since there is evidence of a rigid amorphous phase present in PEN biaxially stretched samples which was favoured by the dependence of dielectric relaxation strengths on the degree of crystallinity for the ?*- and ?-relaxation. KW - Dielectric relaxation spectroscopy KW - Dynamic mechanical analysis KW - Poly(ethylene 2,6-naphthalene dicarboxylate) PY - 2003 U6 - https://doi.org/10.1016/S0032-3861(03)00332-X SN - 0032-3861 SN - 1873-2291 VL - 44 IS - 15 SP - 4311 EP - 4323 PB - Springer CY - Berlin AN - OPUS4-2604 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Hardy, L. A1 - Fritz, Andreas A1 - Stevenson, I. A1 - Boiteux, G. A1 - Seytre, G. T1 - Dielectric relaxation behaviour of poly(ethylene naphthalene 2,6 dicarboxylate) (PEN) N2 - Dielectric spectroscopy has been used to study poly(ethylene naphthalene 2,6 dicarboxylate) (PEN) samples of different morphologies obtained by thermally treating bi-axially stretched PEN films. Neat and thermally treated samples of PEN films have been characterised by differential scanning calorimetry in order to measure the glass transition and melting temperatures as well as the degrees of crystallinity. Dielectric analysis has allowed the observation of the evolution of molecular relaxation phenomena with morphology changes and has revealed three relaxation processes: ?-, ?*- and ?-relaxation (increasing temperature). The ?-relaxation is associated with local motions of ester and the ?*-relaxation with partially cooperative motions of naphthalene groups. The latter has been shown to be related to the morphology of the materials under study. The ?-relaxation associated to the glass transition of PEN corresponds to cooperative motions induced by conformational rearrangements of the main chain and depends also on the morphology of the PEN films. Dielectric relaxation behaviours were compared using the activation energies calculated from Arrhenius equation formalism for the two sub-glass processes. Vogel–Fulcher–Tammann fits were performed on the ?-relaxation. Our important contribution for the bi-axially stretched PEN films study is related to the assignment of the ?*-relaxation that can be attributed to naphthalene aggregates. PY - 2002 U6 - https://doi.org/10.1016/S0022-3093(02)01104-3 SN - 0022-3093 VL - 305 SP - 174 EP - 182 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-1570 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -