Authors:Mingxin Ye, Xiaohui Wang, Weishi Huang, Jiulan Hu, and Haishan Bu
The crystallization of poly(ethylene terephthalate) (PET) was studied in the presence of nucleating agents and promoters. The effect of both by themselves and in concert was investigated using differential scanning calorimetry. The aim of this work is to find conditions of fast crystallization of PET. Sodium benzoate(SB) and Surlyn® (S) substantially increase the crystallization rate of PET at higher temperature owing to a reduction in the energy barrier towards primary nucleation, but they accelerate crystallization even more at lower temperature with an additional improvement of the molecular mobility of PET chains. Chain scission of PET caused by the reaction with the nucleating agents was proven by determination of molecular weight. The addition of S alone led to a lower reduction in molecular weight. A series of N-alkyl-p-toluenesulfonamides (ATSAs) were shown to effectively promote molecular motion of the PET chains, leading to an increase in crsytallization rate at lower temperature. A remarkable acceleration of crystallization of PET was attained at lower temperature when S and ATSA were added together. When the content of ATSA is low, S has the dominant influence due to its dual effect of decreasing energy barrier towards nucleation and promoting molecular motion of PET chains. A further increase of crystallization rate of PET was found only after an addition of ATSA of above 5 wt.%.
Volumetric thermal analysis of semicrystalline poly(ethylene terephthalate), PET, with different content of crystalline phase
was carried out using mercury-in-glass dilatometry. The effect of crystals on the thermal properties of amorphous phase (glass
transition temperature, Tg, thermal expansion coefficients, α) were determined. At cold-crystallization (106°C, up to 4 h), crystalline content of 2.4–25.3
vol.% was achieved. Increasing content of crystalline phase broadens the glass transition region and increases Tg. The change of thermal expansion coefficient during glass transition is lower than that predicted by the two-phase model,
which indicates the presence of a third fraction — rigid amorphous fraction (RAF), whose content steadily increases during
crystallization. However, its relative portion (specific RAF) is significantly reduced. Further significant decrease in specific
RAF appears after annealing at a higher temperature.
Confinement of the glass-forming regions in the nanometer range influences the α-relaxation which is associated with the glass transition. These effects were investigated for semicrystalline poly(ethylene terephthalate) by dielectric spectroscopy and differential scanning calorimetry. The results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of glass transition. Both experiments showed a dependence of the glass transition on the mean thickness of the amorphous layers. For the dielectric relaxation, the loss maximum was found to shift to higher temperatures with decreasing thickness of the amorphous layers, but no differences were observed in the curve shape for the differently crystallized samples. For the calorimetric measurements, in contrast, there was no correlation for the glass transition temperature, whereas the curve shape did correlate with the layer thickness of the mobile amorphous fraction. From the structure parameters, a characteristic length of approximately (2.5±1) nm was estimated for the unconfined glass relaxation (transition).
Authors:Sulene Araújo, Antonio Araujo, Nedja Fernandes, Valter Fernandes, and Massao Ionashiro
Poly(ethyleneterephthalate), in powder form (50 mesh), was obtained from Recipet of Brazil. The kinetic parameters for decomposition of the PET alone and with catalyst (PET/MCM-41) were determined in a simultaneous TG/DTA (model 2960, TA Instruments
Authors:Jacek Przepiórski, Justyna Karolczyk, Tomoki Tsumura, Masahiro Toyoda, Michio Inagaki, and Antoni W. Morawski
Post consumer poly(ethyleneterephthalate) (PET) is a material causing environmental problems. Therefore, much effort has been put to investigate methods to utilize it. One of the ways widely studied is converting
The optical transmittance of poly(ethylene terephthalate) foils has been investigated using the linear heating as well as the isothermal heating. It was found out that transmittance records obtained at linear heating show the crystallisation and melting processes distinctly. These results are in accordance with those achieved by DSC measurements. The isothermal heating was especially applied to investigate PET cold crystallisation. In its course the optical transmittance first decreases to a certain minimal value, regaining some of the transmittance in the final period of crystallisation (crystal growth). The used method is suitable for investigating crystallisation processes of polymers accomplished at very slow rates.
A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which
was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking.
The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal
parameters studied were the glass transition temperature (Tg), the cold-crystallization temperature (Tcc), the melting temperature (Tm), the enthalpy (ΔHm) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension
time, the higher Tgand Tcc, but the lower Tmand ΔHm, i.e. the more amorphous the chain-extended samples, as also shown by density measurements.
Behaviours of drawn semi-crystalline poly(ethylene terephthalate) films are investigated by DSC, X-ray diffraction and birefringence
measurements. The comparison of the different results confirms the coexistence of two structures into the amorphous part of
the material: a completely disordered amorphous phase and a mesomorphic amorphous one. Moreover, for the strongest draw ratio,
the calorimetric results show that the drawing effect on the strain induced crystalline structure proceeds by a better orientation
of this structure rather than by nucleation and growth of new oriented crystallites.
Authors:A. Aboulkas, K. El Harfi, A. El Bouadili, and M. Nadifiyine
Investigations into the pyrolytic behaviours of oil shale, poly (ethylene terephthalate) (PET) and their mixture have been
conducted using a thermogravimetric analyzer. Experiments were carried out dynamically by increasing the temperature from
298 to 1,273 K with heating rates of 2–100 K/min under a nitrogen atmosphere. Discrepancies between the experimental and calculated
TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation
temperature of each component in the mixture was higher than those the individual components; thus an increase in thermal
stability was expected. The kinetic processing of thermogravimetric data was carried out using Flynn–Wall–Ozawa (FWO) method.