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1.
The transesterification reaction of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends during melt‐mixing was studied as a function of blending temperature, blending time, blend composition, processing equipment, and different grades of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate). Results show that the major factors controlling the reaction are the temperature and time of blending. Efficiency of mixing also plays an important role in transesterification. The reaction kinetics can be modeled using a second‐order direct ester–ester interchange reaction. The rate constant (k) was found to have a minimum value at an intermediate PEN content and the activation energy of the rate constant was calculated to be 140 kJ/mol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2422–2436, 2001  相似文献   

2.
The glass‐transition temperatures and melting behaviors of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were studied. Two blend systems were used for this work, with PET and PEN of different grades. It was found that Tg increases almost linearly with blend composition. Both the Gibbs–DiMarzio equation and the Fox equation fit experimental data very well, indicating copolymer‐like behavior of the blend systems. Multiple melting peaks were observed for all blend samples as well as for PET and PEN. The equilibrium melting point was obtained using the Hoffman–Weeks method. The melting points of PET and PEN were depressed as a result of the formation of miscible blends and copolymers. The Flory–Huggins theory was used to study the melting‐point depression for the blend system, and the Nishi–Wang equation was used to calculate the interaction parameter (χ12). The calculated χ12 is a small negative number, indicating the formation of thermodynamically stable, miscible blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 11–22, 2001  相似文献   

3.
The phase structure of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends was studied in relation to the molecular weight. The samples were prepared by both solution blends, which showed two glass‐transition temperatures (Tg), and melt blends (MQ), which showed a single Tg, depending on the composition of the blends. The Tg of the MQ series was independent of the molecular weight of the homopolymer, although the degree of transesterification in the blends was affected by the molecular weight. The MQ series showed two exotherms during the heating process of a differential scanning calorimetry scan. The peak temperature and the heat flow of the exotherms were affected by the molecular weight of the homopolymers. The strain‐induced crystallization of the MQ series suggested the independent crystallization of PET and PEN. Based on the results, a microdomain structure of each homopolymer was suggested. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2428–2438, 2005  相似文献   

4.
Rosa M. Medina 《Polymer》2004,45(25):8517-8522
In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)-poly(ethylene naphthalene 2,6-dicarboxylate), PET-PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET-PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester-ester exchange mechanism for the reaction.  相似文献   

5.
The effect of electron beam (EB) irradiation on the properties and compatibility of poly(ethylene 2,6‐naphthalate) (PEN)/poly(ethylene terephthalate) (PET) blends was investigated. Upon EB irradiation, PEN/PET blends underwent transesterification reactions, resulting in the formation of more random copolymers from the original binary pair. The degree of transesterification increased with dose rate, and all of the irradiated blends exhibited a single glass transition temperature. This indicated that transesterification reactions promoted by EB irradiation led to the formation of a single phase. Transesterification reactions promoted by EB irradiation led to more random copolymers, and the reduced regularity in the irradiated blends decreased the melting temperature. A higher degree of randomness and lower number‐average sequence lengths for the blend systems indicated that a more random chain structure was formed in the blends. The rheological measurements demonstrated that the irradiated PEN/PET blends were miscible. EB irradiation could promote transesterification reaction, thus enhancing the compatibility of PEN/PET blends.  相似文献   

6.
Poly(ethylene‐octene) (POE), maleic anhydride grafted poly(ethylene‐octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE, PBT/mPOE, and PBT/mPOE/POE blends by a twin‐screw extruder. Observation by scanning electron microscopy revealed improved compatibility between PBT and POE in the presence of maleic anhydride groups. The melting behavior and isothermal crystallization kinetics of the blends were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter; the kinetics data was delineated by kinetic models. The addition of POE or mPOE did not affect the melting behavior of PBT in samples quenched in water after blending in an extrude. Subsequent DSC scans of isothermally crystallized PBT and PBT blends exhibited two melting endotherms (TmI and TmII). TmI was the fusion of the crystals grown by normal primary crystallization and TmII was the melting peak of the most perfect crystals after reorganization. The dispersed second phase hindered the crystallization; on the other hand, the well dispersed phases with smaller size enhanced crystallization because of higher nucleation density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

7.
To improve the barrier properties of poly(ethylene terephthalate) (PET), PET/poly(ethylene 2,6‐naphthalate) (PEN) blends with different concentrations of PEN were prepared and were then processed into biaxially oriented PET/PEN films. The air permeability of bioriented films of pure PET, pure PEN, and PET/PEN blends were tested by the differential pressure method. The morphology of the blends was studied by scanning electron microscopy (SEM) observation of the impact fracture surfaces of extruded PET/PEN samples, and the morphology of the films was also investigated by SEM. The results of the study indicated that PEN could effectively improve the barrier properties of PET, and the barrier properties of the PET/PEN blends improved with increasing PEN concentration. When the PEN concentration was equal to or less than 30%, as in this study, the PET/PEN blends were phase‐separated; that is, PET formed the continuous phase, whereas PEN formed a dispersed phase of particles, and the interface was firmly integrated because of transesterification. After the PET/PEN blends were bioriented, the PET matrix contained a PEN microstructure consisting of parallel and extended, separate layers. This multilayer microstructure was characterized by microcontinuity, which resulted in improved barrier properties because air permeation was delayed as the air had to detour around the PEN layer structure. At a constant PEN concentration, the more extended the PEN layers were, the better the barrier properties were of the PET/PEN blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1309–1316, 2006  相似文献   

8.
The isothermal crystallization and crystal morphology of poly(trimethylene terephthalate) (PTT)/poly (ethylene 2,6‐naphthalate) (PEN) blends were investigated with differential scanning calorimetry and polarized optical microscopy. The commonly used Avrami equation was used to fit the primary stage of isothermal crystallization. The Avrami exponents were evaluated to be in the range of 3.0–3.3 for isothermal crystallization. The subsequent melting endotherms of the blends after isothermal crystallization showed multiple melting peaks. The crystallization activation energies of the blends with 20 or 40% PTT was ?48.3 and ?60.9 kJ/mol, respectively, as calculated by the Arrhenius formula for the isothermal‐crystallization processes. The Hoffman–Lauritzen theory was also employed to fit the process of isothermal crystallization, and the kinetic parameters of the blends with 20 or 40% PTT were determined to be 1.5 × 105 and 1.8 × 105 K2, respectively. The spherulite morphology of the six binary blends formed at 190°C showed different sizes and perfect Maltese crosses when the PTT or PEN component was varied, suggesting that the greater the PTT content was, the larger or more perfect the crystallites were that formed in the binary blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3316–3325, 2007  相似文献   

9.
Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE (20 wt % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt % mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (TmI and TmII). TmI was attributed to the melting of the crystals grown by normal primary crystallization, and TmII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were delineated by kinetic models. The dispersed phase hindered the crystallization; however, the well‐ dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen–Hoffman equation, showed the same results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

10.
Amorphous, partially transesterified poly(ethylene terephthalate)/poly(ethylene naphthalate) (PET/PEN) blends of different levels of transesterification and blend composition were investigated in terms of resultant phase behavior, thermal transitions, and melt rheological properties. Intrinsic viscosities of the lowest transesterified material were found to be significantly below those of a physical blend of an identical composition, but at higher levels of transesterification, there was little difference. This was similarly found in melt rheometry measurements, where the zero‐shear rate viscosity of the low and highly transesterified mixtures were similar. Both solution and melt rheometry indicated that the molecular weight decreased by thermal degradation from processing. This is believed to play an important role in determining the final molecular architecture and properties. For similar levels of ester interchange, there was a minimum observed in zero shear melt viscosity at around 40 wt % PEN. This is likely due to competition between the slightly transesterified copolymer chains having poorer packing in the melt and reduced entanglement. Differential scanning calorimetry and dynamic mechanical thermal analysis were used to investigate the phase behavior of partially and fully transesterified blends. Results for the glass transition of the highly transesterified blends were compared with the theoretical values calculated from the Fox equation and were found to be close, although slightly lower. A correlation between the melting temperature of the blend and the degree of transesterification was shown to exist. This correlation can be used to estimate the degree of ester exchange reaction from these melting transitions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1556–1567, 2002  相似文献   

11.
The production and properties of blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) with three modified clays are reported. Octadecylammonium chloride and maleic anhydride (MAH) are used to modify the surface of the montmorillonite–Na+ clay particles (clay–Na+) to produce clay–C18 and clay–MAH, respectively, before they are mixed with the PET/PEN system. The transesterification degree, hydrophobicity and the effect of the clays on the mechanical, rheological and thermal properties are analysed. The PET–PEN/clay–C18 system does not show any improvements in the mechanical properties, which is attributed to poor exfoliation. On the other hand, in the PET–PEN/clay–MAH blends, the modified clay restricts crystallization of the matrix, as evidenced in the low value of the crystallization enthalpy. The process‐induced PET–PEN transesterification reaction is affected by the clay particles. Clay–C18 induces the largest proportion of naphthalate–ethylene–terephthalate (NET) blocks, as opposed to clay–Na+ which renders the lowest proportion. The clay readily incorporates in the bulk polymer, but receding contact‐angle measurements reveal a small influence of the particles on the surface properties of the sample. The clay–Na+ blend shows a predominant solid‐like behaviour, as evidenced by the magnitude of the storage modulus in the low‐frequency range, which reflects a high entanglement density and a substantial degree of polymer–particle interactions. Copyright © 2005 Society of Chemical Industry  相似文献   

12.
Blends composed of poly(ethylene terephthalate) (PET) as the majority component and poly(ethylene naphthalate)(PEN) as the minority component were melt-mixed in a single screw extruder at various PET/PEN compound ratios. Tensile and flexural test results reveal a good PET/PEN composition dependence, indicating that the compatibility of the blends is effective in a macrodomain. In thermal tests, single transitions for Tg, Tm and Tc (crystallization temperature), respectively, are observed from DSC as well as single Tg from DMA except for 50/50 blends. These results suggests that the compatibility is sufficient down to the submicron level. Moreover, isothermal DSC tests along with Avrami analysis indicate that PET's crystallization is significantly retarded when blended with PEN. Results in this study demonstrate that PEN is a highly promising additive to improve PET's spinnability at high speeds.  相似文献   

13.
A new miscible blend of all compositions comprising poly(4‐vinyl phenol) (PVPh) and poly(trimethylene terephthalate) (PTT) was discovered and reported. The blends exhibit a single composition‐dependent glass transition and homogeneous phase morphology, with no lower critical solution temperature (LCST) behavior upon heating to high temperatures. Interactions and spherulite growth kinetics in the blends were also investigated. The Flory–Huggins interaction parameter (χ12) and interaction energy density (B) obtained from analysis of melting point depression are negative (χ12 = ?0.74 and B = ?32.49 J cm?3), proving that the PVPh/PTT blends are miscible over a wide temperature range from ambient up to high temperatures in the melt state. FTIR studies showed evidence of hydrogen‐bonding interactions between the two polymers. The miscibility of PVPh with PTT also resulted in a reduction in spherulite growth rate of PTT in the miscible blend. The Lauritzen–Hoffman model was used to analyze the spherulite growth kinetics, which showed a lower fold‐surface free energy (σe) of the blends than that of the neat PTT. The decrease in the fold‐surface free energy has been attributed to disruption of the PTT lamellae exerted by PVPh in an intimately interacted miscible state. Copyright © 2004 Society of Chemical Industry  相似文献   

14.
15.
The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA) blends were studied. Four compositions of the blends [PET 25/PMMA 75, PET 50/PMMA 50, PET 75/PMMA 25, and PET 90/PMMA 10 (w/w)] were melt‐blended for 1 h in a batch reactor at 275°C. Crystallization peaks of virgin PET and the four blends were obtained at cooling rates of 1°C, 2.5°C, 5°C, 10°C, 20°C, and 30°C/min, using a differential scanning calorimeter (DSC). A modified Avrami equation was used to analyze the nonisothermal data obtained. The Avrami parameters n, which denotes the nature of the crystal growth, and Zt, which represents the rate of crystallization, were evaluated for the four blends. The crystallization half‐life (t½) and maximum crystallization (tmax) times also were evaluated. The four blends and virgin polymers were characterized using a thermogravimetric analyzer (TGA), a wide‐angle X‐ray diffraction unit (WAXD), and a scanning electron microscope (SEM). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3565–3571, 2006  相似文献   

16.
Copolymers of ethylene glycol with 4,4′‐bibenzoic acid and terephthalic acid are known to crystallize rapidly to surprisingly high levels of crystallinity. To understand this unusual behavior, the isothermal crystallization of poly(ethylene bibenzoate‐co‐terephthalate) in the molar ratio 55:45 (PETBB55) was studied. Poly(ethylene naphthalate) (PEN) was included in the study for comparison. The kinetics of isothermal crystallization from the melt and from the amorphous glass was determined using differential thermal analysis. The results were correlated with the crystalline morphology as observed with atomic force microscopy (AFM). Crystallization of PEN exhibited similar kinetics and spherulitic morphology regardless of whether it was cooled from the melt or heated from the glass to the crystallization temperature. The Avrami coefficient was close to 3 for heterogeneous nucleation with 3‐dimensional crystal growth. The copolymer PETBB55 crystallized much faster than did PEN and demonstrated different crystallization habits from the melt and from the glass. From the melt, PETBB55 crystallized in the “normal” way with spherulitic growth and an Avrami coefficient of 3. However, crystallization from the glass produced a granular crystalline morphology with an Avrami coefficient of 2. A quasi‐ordered melt state, close to liquid crystalline but lacking the order of a recognizable mesophase, was proposed to explain the unusual crystallization characteristics of PETBB55. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 98–115, 2002  相似文献   

17.
The crystallization process of poly(1‐butene) and its blends with hydrogenated oligocyclopentadiene was analyzed in dependence on composition. Both isothermal and nonisothermal crystallization processes were studied, and the isothermal crystallization process was investigated starting from both the glass and the melt states. Results revealed that spherulite growth rate, overall crystallization rate, and morphology are strongly dependent on crystallization conditions and blend composition. Nonisothermal crystallization data were analyzed according to the theories of Ozawa and Ziabicki. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1677–1690, 1999  相似文献   

18.
PEN/PET共混物结晶行为研究   总被引:1,自引:0,他引:1  
用差示扫描量热法(DSC)研究了不同共混比例PEN/PET共混物的熔体结晶行为,并进行了等温结晶动力学测定。结果表明:随着两种组分向中间比例(50/50)靠近,共混物的熔融温度越低,结晶速率也越慢。  相似文献   

19.
The isothermal and dynamic crystallization behaviors of polyethylene terephthalate (PET) blended with three types of liquid crystal polymers, i.e., PHB60–PET40, HBA73–HNA27, [(PHB60–PET40)–(HBA73–HNA27) 50 : 50], have been studied using differential scanning calorimetry (DSC). The kinetics were calculated using the slope of the crystallization versus time plot, the time for 50% reduced crystallinity, the time to attain maximum rate of crystallization, and the Avrami equation. All the liquid crystalline polymer reinforcements with 10 wt % added accelerated the rate of crystallization of PET; however, the order of the acceleration effect among the liquid crystalline polymers could not be defined from the isothermal crystallization kinetics. The order of the effect for liquid crystalline polymer on the crystallization of PET is as follows: (PHB60–PET40)–(HBA73–HNA27) (50 : 50); HBA73–HNA27; PHB60–PET40: This order forms the dynamic scan of the DSC measurements. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1383–1392, 1998  相似文献   

20.
The occurrence of transesterification reactions in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) blends prepared in presence of triphenyl phosphite (TPP) was investigated. When PEN was processed with TPP, which is a known chain extender for PET, chain extension reactions also took place. Torqueprocessing time curves obtained during preparation of 75/25 PET/PEN blends containing TPP, showed a build‐up profile followed by a fast decrease that was interpreted as chain extension between blend components and degradation due to phosphite residues formation, respectively. Although transesterification inhibition was expected, this type of reaction was not suppressed by TPP.  相似文献   

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