The cold crystallization and melting of poly(ethylene therephthalate) (PET), poly(ethylene 2,6-naphthalene dicarboxylate)
(PEN) and their blends were studied using temperature modulated differential scanning calorimetry (TMDSC) at underlying heating
rates of between 1 and 3 K min-1 and periods ranging from 30 to 90 s. The amplitude of modulation was selected in order to give an instantaneous heating rate
β≥0. Heat flow is analyzed by the total heat flow signal o, which is equivalent to the conventional DSC signal, and the reversing
heat flow oREV, which only detects the glass transition and the melting processes. The dependence of the melting region in the reversing
heat flow on the frequency of modulation is analyzed. The use of the so-called non-reversing heat flow oNREV (=o-oREV)) and the effect of frequency and amplitude on the complex heat capacity are also studied. The results show the complexity
of these magnitudes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Transreactions of PET and PEN melt‐mixed in a twin‐screw extruder are investigated. The extruder is modeled and characterized in the frame of a tubular system of closed type. The kinetic modeling is based on a modified second‐order reversible reaction equation, which allows the dispersion equation to be solved analytically. The analysis shows a good agreement between the model and experiment. The axial dispersion model is employed to predict the extent of transesterification reactions (X) and degree of randomness (RD). 1H NMR measurements are performed to estimate X and RD. Theoretical and experimental data are in good agreement. The model can thus be exploited to describe the effects of processing parameters, mixing time, mixing temperature, and blend composition on X and RD.
Monte–Carlo kinetic simulations are performed to study exchange reactions in PET/PEN blends. Chain distribution of the blend is simulated at various mixing conditions. The average length of PET and PEN repeating units decreases with increasing exchange reactions. Derivative of heat flow is modeled at Tg region during mixing. Two peaks are observed on the derivative of heat flow curve at the early stages of mixing, indicating formation of an immiscible blend. With increasing mixing time, miscibility between two phases increasea and the peaks converge toward each other and finally form a single peak. The Monte–Carlo simulation results are in fine agreement with experimental data obtained from different systems.
Thermoplastic elastomers based on PET glycolysates were synthesized in the molten state according to a multistep process. Their chemical structures were studied (1H NMR, triple detection, steric exclusion chromatography) as well as their thermal properties (ATG, DSC) and their morphology (AFM). Influence of hard segments composition on the different properties was investigated with the same ratio soft/hard segment. DSC study showed that these compounds had thermal properties similar to those of conventional thermoplastic elastomers (low Tg and high Tm). The association of PET with PBT segments seemed to harm the hard segments crystallization. SEC analyses showed that the compounds obtained had low molecular weights. Two factors seemed to explain the difference in properties between the compounds with and without glycolysate: a lower molecular weight of the TPE containing glycolysate, and a lower organization for materials containing both PET and PBT segments in respect to copolymer without glycolysate and containing solely PBT segments.Dielectric measurements showed properties close to those usually encountered for insulators used in electrical engineering. Glycolysate-free materials exhibited the best properties (high resistivity, low loss factor, slight variation of permittivity) and the materials exhibited interesting insulating properties (breakdown voltage up than 35 kV/mmRMS, resistivity around 109 Ωm). An improvement of the synthesis methodology with the use of catalyst might result in a significant enhancement of the dielectric properties, already promising for this type of materials. 相似文献
