Rheological,thermal, and mechanical properties of poly(ethylene naphthalate)/poly(ethylene terephthalate) blends

Structural, Theological, thermal, and mechanical properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) obtained by melt blending were investigated using capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) observation, tensile testing. X-ray diffraction, and ¹H nuclear magnetic resonance (NMR) measurements. The melt Theological behavior of the PEN/PET blends was very similar to that of the two parent polymers. The melt viscosity of the blends was between that of PEN and that of PET. Thermal properties and NMR measurement of the blends revealed that PEN is partially miscible with PET in the as molded blends, indicating that an interchange reaction occurs to some extent on melt processing. The blend of 50/50 PEN/PET was more difficult to crystallize compared with blends of other PEN/PET ratios. The blends, once melted during DSC measurements, almost never showed cold crystallization and subsequent melting and definitely exhibited a single glass transition temperature between those of PEN and PET during a reheating run. Improvement of the miscibility between PEN and PET with melting is mostly due to an increase in transesterification. The tensile modulus of the PEN/PET blend strands had a low value, reflecting amorphous structures of the blends, while tensile strength at the yield point increased linearly with increasing PEN content.     

BLENDS OF THERMOTROPIC LIQUID CRYSTALLINE POLYESTER AND POLY(ETHYLENE TEREPHTHALATE)

Two kinds of blends of thermotropic liquid crystalline polymers (LCPs) and poly(ethylene terephthalate) (PET) were prepared by solution and melt blending, respectively. Crystallization behavior of the blends was observed by differential scanning calorimetry (DSC). The LCP in both blends considerably decreased the cold crystallization temperature of PET and increased the crystallization rate in the low-temperature region, but did not show any significant effect on crystallization in the high-temperature region. Phase behavior of samples prepared by melt blending was investigated with the scanning electronic microscope (SEM). It was found that LCP/PET blends display a biphasic structure with an aromatic unit-rich phase as a dispersed domain, and a highly oriented fibrous structure was formed on the fracture surface of the blends. During the melt blending process, PET reacted with LCP through transesterification, as indicated by both DSC and SEM measurements.     

Aromatic poly(ester carbonate)/poly-(ethylene terephthalate) alloys

When mixtures of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) containing up to two-thirds of the latter are melt extruded, they produce a single-phase amorphous “alloy.” This alloy is characterized by a sharp, single, composition-dependent glass transition temperature, T_g. When annealed below T_g, the alloy remains unaltered, but when annealed above its T_g, the alloy separates into minute pure-PET crystallites and an amorphous PEC/PET phase. The thermal and dynamic mechanical behavior, crystallization kinetics, and SAXS patterns all strongly suggest the PEC-rich alloys to be solid solutions in which the PET molecules are dispersed individually or in small aggregates containing only a few PET molecules each. Calculations of the interaction parameter and assumed interfacial layer thickness tend to support this suggestion. Use of appropriate solvents allows one to selectively dissolve the PEC and recover from the alloys both PET and PEC in the original purity and molecular weights. Diffusion constants of PET molecules through the amorphous alloys were obtained from studies of PET crystallization above T_g of the alloys. The magnitude of the constants are in the range of expectation. The mechanical properties of the amorphous alloys in the glassy state do not deviate greatly from simple additivity of the respective properties of the parent polymers. However, the melt viscosity of the PEC-rich alloys and their plateau modulus above T show drastic decreases from straight additivity. A qualitative, but not quantitative, explanation of these observations is offered.     

Sequential Structure,Crystallization, and Properties of Biodegradable Poly(ethylene Terephthalate-Co-Ethylene Oxide-Co-Lactide) Copolyester

The sequential structure, isothermal crystallization, tensile property, and degradation behavior of poly(ethylene terephthalate-co-ethylene oxide-co-lactide) (ETOLA) copolyester based on melt transesterification of poly(ethylene terephthalate) with poly(ethylene oxide) and oligo(lactic acid) was investigated. The degree of randomness was calculated to be 0.38, showing the incorporation of poly(ethylene oxide) (PEO) blocks into the homogeneous sequences of ethylene terephthalate (ET) and lactide (LA) units. The isothermal crystallization kinetics results revealed that the crystallization activation energy of the copolyester calculated using the Arrhenius’ equation was lower than that reported for poly(ethylene terephthalate) (PET), indicating that the addition of PEO and LA units into PET retarded the crystallization of PET. The copolyester exhibited the same crystal structure at different crystallization temperatures, similar to that of PET homopolymer, based on wide angle X-ray diffraction results. The size of the spherulites of ETOLA increased with crystallization temperature. The increase of crystallization temperature reduced the elongation at break of the copolyesters, as well as the enzymatic degradation.     

Calorimetric study of polyethylene terephthalate)/poly(butylene terephthalate) blends

Poly(ethylene terephthalate)/poly(butylene terephthalate) blends [xPET/(l-x)PBT] were prepared by ultraquenching of the melt between two metal rolls rotating in a liquid nitrogen bath. Both DSC and WAXS studies indicate that immediately after preparation, the blends are amorphous regardless of the composition. Two glass transition temperatures are found for the as-quenched 0.5 PET/0.5 PBT blend. The activation energies determined from the dependence of each glass transition temperature on the heating rate are approximately the same. Furthermore, they are equal to the mean activation energy for the overall crystallization. This can be explained in terms of the percolation threshold theory.     

Transport properties of poly(ethylene terephthalate)/Rodrun 3000 blends

The transport properties of incompatible blends of poly(ethylene terephthalate) (PET) and a thermotropic liquid crystalline polymer (TLCP) composed of 40 mol% of PET and 60 mol% of p-hydroxybenzoic acid (Rodrun 3000) have been investigated using dichloromethane as permeant. Films, obtained by a blown film extrusion process, were analyzed and compared with the same samples stored 2 and 15 days at 60°C. With respect to the as-blown films, blends submitted to physical aging show a decrease in permeability by a percentage that increases with the amount of the LC phase present and a larger contribution derived from the polymeric matrix. The decrease of permeability is essentially attributed to a lowering of sorption because diffusional behavior for the different samples is the same.     

Molecular dynamics of poly(ethylene 2,6-naphthalate)-polycarbonate composite by nuclear magnetic resonance

The aim of the work was to examine molecular dynamics of a series of poly(ethylene 2,6-naphthalate)-polycarbonate blends with changing weight ratio of copolymers by off-resonance nuclear magnetic resonance technique. It was shown that this technique provides information about the correlation times of the internal motions. The spectral density function amplitudes were estimated on the basis of the dispersion of the spin-lattice relaxation time off-resonanceT _lp^off. The measurements were performed for two series of blends which had been injection moulded with and without compatibilizer. The new polymer materials were also characterized using differential scanning calorimetry. Samples obtained after injection moulding and annealing became amorphous, which indicates that a reaction of transesterification process between the two polymers occurred.     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T _p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t _1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.     

Thin-layer chromatography of copolyesters from blends of poly(ethylene terephthalate)/polycarbonate

Copolymers made by ester exchange reaction have been obtained from poly(ethylene terephthalate) (PET)/poly(bis-phenol-A carbonate) (PC) blends during melt mixing. The copolyesters were isolated by thin-layer chromatography (TLC) and identified by infrared spectroscopy. It was found that the quantity of copolymer formed was increased by the temperature and duration of melt mixing. The PET/PC blend was found to react at 270°C within 10 min, as detected by TLC. After 60 min, the pure PC had disappeared. The miscibility of PET/PC blends was found to be markedly aided by the addition of as little as 2% of the copolymer isolated by TLC.     

The Effect of Microwave Irradiation on the Crystallization Behavior of PET/PEN Blends

The crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ethylene‐ 2,6‐naphthalate) (PEN) blends before and after microwave irradiation for different time intervals has been investigated by means of wide angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques. It was found that microwave irradiation could greatly affect the crystallization behavior of PET/PEN blends and significantly enhance their degree of crystallinity. For the PET/PEN (90/10) blends, the degree of crystallinity increased from 15 to 45%; for the PET/PEN (60/40) blends, the degree of crystallinity significantly increased, from 1 to 36%. However, with increasing irradiation time, the degree of crystallinity didn't continually increase. It reached a maximum at certain time point. The cold crystallization enthalpy △Hcc gradually decreased as microwave irradiation time increased and the melting enthalpy △Hm vis‐à‐vis the long time interval of such irradiation was decreased. In addition, the mechanism for microwave irradiation affecting the crystallization behavior of polymers is discussed.     

Antistatic performance and morphological observation of ternary blends of poly(ethylene terephthalate), poly(ether esteramide), and Na-neutralized poly(ethylene-co-methacrylic acid) copolymers

Blends of poly(ethylene terephthalate) (PET) and poly(ether esteramide) (PEEA), which is known as an ion conductive polymer, were prepared by melt mixing using a twin screw extruder. Antistatic performance of the molded plaques of the binary blends was investigated and the effects of adding sodium ionomer, Na-neutralized poly(ethylene-co-methacrylic acid) (E/MAA) Copolymers, in comparison with NaI, were also investigated. We found Na-neutralized E/MAA significantly improved static dissipation performance when blended with above PET/PEEA system whereas NaI was only effective when PEEA amount was larger than 25 wt%. Morphological study of these ternary blends system was conducted by using TEM and it was observed that PEEA domain formed platelet structure in PET matrix when PEEA content was 30%. The domain shape changed from sphere particle to platelet structure via string shape with the increase of PEEA content. And the thickness of the PEEA layers was confirmed as thin as 10 nm. Specific interaction between PEEA and Na-neutralized E/MAA was found by TEM. The Na-neutralized E/MAA domain was encapsulated by PEEA, which could increase the surface area of PEEA in PET matrix. This encapsulation effect explains the unexpected synergy for the static dissipation performance on addition of Na-neutralized E/MAA to PET/PEEA blends.     

Size effect of nanostructured formations on scattering of optical phonons in poly(ethylene terephthalate)

The temperature dependence of the half-width of the infrared (IR) absorption band at a frequency of 971.5 cm^?1 in the spectra of poly(ethylene terephthalate) (PET) is investigated for crystallized and amorphous PET samples in which the lengths of trans sequences are approximately equal to 4–7 and 2–3 nm, respectively. The observed increase in the half-width with increasing temperature is explained by inelastic scattering of phonons of stretching vibrations of the macromolecular skeleton by other phonons. The half-width of the band at 971.5 cm^?1 in the IR spectra of the amorphous polymer is approximately 1.5 times larger than that in the spectra of the crystallized polymer. This is associated with the violation of the wave-vector selection rules due to a small length of the trans sequences in the amorphous sample.     

The Suppression of Isothermal Cold Crystallization in PET Through Nano‐Silica Incorporation

Isothermal crystallization from the glassy state of pure poly(ethylene terephthalate)(PET) and PET/Silica nanocomposites films was studied. The results showed that addition of nano‐silica increased the crystallinity of filled PET compared to pure PET, suggesting that nano‐silica is an effective nucleating agent. However, the induction period prior to crystallization was prolonged and the overall crystallization rate decreased through nano‐silica incorporation. This is a result of the cold crystallization rate being primarily controlled by diffusion of PET chains, rather than being controlled by the nucleation rate. The strong interaction between the nanoparticles and PET chains confined the movement of the macromolecular chains and decreased the cold crystallization rate.     

Compatibilization by Olefin Block Copolymer (OBC) in Polypropylene/Ethylene-Propylene-Diene Terpolymer (PP/EPDM) Blends

The compatibilization by olefin block copolymer (OBC) in the blends of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) and the phase morphology of the ternary blends were investigated by rheology, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements. It was found that the PP/EPDM blends exhibited enhanced mechanical properties in the presence of OBC. The addition of OBC had a significant influence on the phase separation behavior of the blends. For the PP/EPDM-50/50 heterogeneous blends, the addition of 15 phr OBC enabled the two-phase morphology to change from a droplet-matrix structure to a co-continuous one. In the temperature range of 150 to 200 °C, OBC was shown to have a better compatibility with PP than EPDM. The changes in viscosity ratio of the dispersed phase to matrix phase caused by adding OBC might be the dominant factor in controlling the coalescence of the dispersed phase domains. For the crystallization behavior of PP/EPDM/OBC ternary blends, OBC was found to have an induction effect on the formation of β-crystals of PP that was not proportional to the volume of OBC addition. In addition, DSC results showed that PP could induce the OBC crystallization and improve the crystallization temperature of OBC. The existence of simultaneous crystallization behavior between PP and OBC was also observed. A possible mechanism of phase evolution induced by crystallization was proposed.     

Transesterification-Induced Evolution of Structure and Morphology in Poly(trimethylene terephthalate)/Poly(butylenes succinate) Blends

The evolution of the structure and morphology in poly(trimethylene terephthalate)/poly(butylene succinate) (PTT/PBS) blends induced by transesterification between PTT and PBS at different blending temperatures for 2 h and various times at 270°C was investigated. By control of the extent of transesterification, the degree of randomness, crystallization, morphology, and tensile properties of the blends could be modulated. The results indicated that the degree of randomness of the blends increased by increasing the blending temperature above 260°C and blending time, leading to the formation of copolyesters. The crystallization of the blends was restricted by the increase of blending temperature and time, shown by broad reflection peaks in X-ray spectra and less perfect spherulites as observed by polarized optical microscopy (POM), which was due to the increase of the degree of randomness. The elongation at break increased by increasing the blending time and temperature, accompanied by a decrease of tensile strength and elastic modulus, showing a dependence on the degree of randomness caused by the transesterification.     

Miscibility, Crystallization, and Rheological Behavior of Solution Casting Poly(3-hydroxybutyrate)/poly(ethylene succinate) Blends Probed by Differential Scanning Calorimetry, Rheology, and Optical Microscope Techniques

应用差示扫描量热、流变及偏光显微镜等方法研究了聚3-羟基丁酸酯/聚丁二酸乙二醇酯(PHB/PES)共混体系的相容性、结晶和流变行为．相图显示该共混体系有两个玻璃化转变,但PHB的熔点随其含量的减少而降低,这个结果证明该共混体系是部分相容的,同时应用偏光显微镜观察体系结晶形态的发展证实了这个结论．依赖于结晶温度和组成,PHB和PES能同时结晶,也能分步结晶,且PHB的球晶生长速率随PES含量的增加而增大．对于部分相容的聚合物共混体系,共混组成对球晶生长速率的影响也做了详细地讨论．     

Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (K_g) – the lowest value of K_g was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be ?260 kJ/mol for pure PEO, ?538 kJ/mol for PEO/lauric acid blend, and ?387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and ?135,6 kJ/mol, ?114,5 kJ/mol, and ?92,8 kJ/mol, respectively, for nonisothermal crystallization.     

Study of Miscibility in Polymer Blends Obtained from Binary Inclusion Complexes of γ-Cyclodextrin and Polycarbonate/Poly(Ethylene Terephthalate)

In this work the synthesis and characterization of the nanostructure of polymer blends of polycarbonate (PC) and poly(ethylene terephthalate) (PET) obtained from their inclusion complexes with γ-cyclodextrin are reported. The blends prepared by this method present differences in their miscibility compared with those blends obtained by conventional methods like solution casting, coprecipitation, or melt blending. In order to understand the influence of molecular weight in the inclusion complex process, PCs of M_w = 64,000 and 28,000 g/mol were used. The analysis of the nanostructured blend by Fourier transform infrared (FTIR), ¹H-nuclear magnetic resonance (¹H-NMR), wide-angle X-ray diffraction (WAXD), differential scanning colorimetry (DSC), and thermogravimetric analysis (TGA) suggests the existence of specific intermolecular interactions between PC and PET that promote miscibility in this normally immiscible polymer blend. Studies by FTIR confirm that the miscibility found was not due to a transesterification reaction during DSC analysis. There were also differences in the morphology of the blends, observed by optical microscopy, obtaining a more homogeneous phase for blends formed in inclusion complexes. The results obtained strongly suggest an improvement in miscibility of the PC/PET blends.     

Crystallization of poly(phenylenesulfide)/amorphous polyamide blends: DSC and microscopic studies

Poly(phenylenesulfide) (PPS) is a high-performance engineering thermoplastic with exceptional thermal and chemical resistance. The results of crystallization behavior of blends of PPS with amorphous polyamide (PA) are presented. The melting and crystallization behavior was studied using differential scanning calorimetry (DSC), and the crystalline morphology was studied using optical microscopy. The results of thermal analysis indicate that the blends exhibit composition-dependent melting point depression. Optical microscopy studies showed the uniform distribution of amorphous nylon in PPS spherulites. The presence of amorphous nylon enhanced the growth rate compared to that for the neat polymer. The observed changes in the equilibrium melting point crystallization behavior, and spherulitic growth rate are explained.