The interchange reaction between poly(ethylene terephthalate) and poly(m‐xylylene adipamide)

The interchange reaction in blends of poly(ethylene terephthalate) (PET) and poly(m‐xylylene adipamide) (MXD6) has been characterized in terms of changes observed in spectra obtained with a 600‐MHz ¹H‐NMR. The selective degradation of PET components in the blends was carried out in the NMR tubes prior to evaluation. Results indicate that there is no chemical reaction between the PET and MXD6 in the absence of sodium p‐toluenesulfonate catalyst. The presence of the catalyst activates the interchange reaction between these two resins. A mathematical method was applied to calculate the degree of randomness of PET‐MXD6 copolymer. In addition, the reaction degree was found to be affected by exposure temperature, time, shear rate, and catalyst concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of shearing on crystallization behavior of poly(ethylene terephthalate)

The shear‐induced crystallization behavior of PET was investigated by measuring the time‐dependent storage modulus (G′) and dynamic viscosity (η′) with a parallel‐plate rheometer at different temperatures and shear rate. The morphology of shear‐induced crystallized PET was measured by DSC, X‐ray, and polarizing optical microscopy. When a constant shear rate was added to the molten polymer, the shear stress increased with the time as a result of the orientation of molecular chains. The induction time of crystallization is decreased with frequency. Moreover, the rate of isothermal crystallization of PET was notably decreased with increasing temperature. The shape of spherulites is changed to ellipsoid in the direction of shear. In addition, aggregation of spherulites is increased with increasing frequency. Particularly, the row nucleation morphology could be observed under polarized light for ω = 1. From the results of DSC, the melting point and enthalpy have a tendency to decrease slightly with increasing frequency. The crystallite size and perfectness decreased with frequency, which was confirmed with X‐ray data. The unit length of the crystallographic unit cell of the PET increased and the (1 0 3) plane peak increased with increasing frequency. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2640–2646, 2001     

PEN/PET共混物结晶行为研究

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。     

The complicated influence of branching on crystallization behavior of poly(ethylene terephthalate)

The randomly branched poly(ethylene terephthalate) (BPET) was prepared by bulk polycondensation from dimethyl terephthalate (DMT) and ethylene glycol (EG), with 0.4–5.0 mol % (with respect to DMT) of glycerol (GL) as a branching agent. The glass transition and crystallization behavior was studied by differential scanning calorimetry (DSC). It was found that the glass transition temperature of BPET reduced with the increasing content of GL until 1.2 mol %, and then increases a little at high degrees of branching. When compared with a linear PET, the crystallization temperature of BPET from the melt shifted to higher temperature as GL content was smaller than 1.2 mol %, and then became lower while GL load was added. Nonisothermal crystallization kinetics was studied through the modified Avrami analysis. It was revealed that the overall crystallization rate parameter of BPET became larger when the GL content was less than 1.2 mol %, then turned to lower at higher branching degree. This indicated that low degree of branching could enhance the overall crystallization of poly(ethylene terephthalate) (PET), whereas high degree of branching in the range of 3.5–5.0 mol % would block the development of crystallization. On the basis of Hoffman's secondary crystallization theory, the product σσ_e of the free energy of formation per unit area of the lateral and folding surface was calculated. According to the change of the product σσ_e with the degree of branching, a possible explanation was presented to illuminate this diverse effect of different degrees of branching on crystallization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

聚(对苯二甲酸乙二醇酯-co-对苯二甲酸异山梨醇酯)等温结晶行为研究

以对苯二甲酸(PTA)、乙二醇(EG)、异山梨醇(ISB)为原料,通过直接熔融缩聚法合成聚(对苯二甲酸乙二醇酯-co-对苯二甲酸异山梨醇酯)(PEIT)共聚酯。利用差示扫描量热法(DSC)研究了共聚酯的结晶行为,采用Avrami方程分析了共聚酯的等温结晶动力学。结果表明,PEIT共聚酯结晶行为受共聚组成和结晶温度影响。随着ISB用量的增加或结晶温度的降低,共聚酯半结晶周期t1/2增加、结晶速率变慢;ISB摩尔分数超过20%,共聚酯无法结晶。     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Morphology and crystallization of poly(ethylene terephthalate)

The melting behaviour and the morphology of poly(ethylene terephthalate) crystallized from the melt are reported. In general, dual or triple melting endotherms are seen, and single endotherms are seen when the samples are crystallized above 215°C for long times. The location of the uppermost endotherm was found to be constant below T_c = 230°C, and above that temperature the location depends on T_c. Therefore, we have shown that samples of PET which are crystallized above T_c = 230°C contain perfect crystals only; below T_c = 230°C, they contain perfect and imperfect crystals. Scanning electron microscopy showed that the perfect crystals are the dominant lamellae in the spherulitic structure, while the imperfect crystals are the subsidiary lamellae in the spherulitic structure, The amorphous regions are located between individual lamellae.     

Compatible and crystallization properties of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and dynamic mechanical analysis (DMA) properties of poly(lactic acid)/ poly(butylene adipate‐co‐terephthalate) (PLA/PBAT) specimens suggest that only small amounts of poor PLA and/or PBAT crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature and onset re‐crystallization temperature values of PLA/PBAT specimens reduce gradually as their PBAT contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA analysis reduce to the minimum value as the PBAT contents of PLA_xPBAT_y specimens reach 2.5 wt %. Further morphological and DMA analysis of PLA/PBAT specimens reveal that PBAT molecules are miscible with PLA molecules at PBAT contents equal to or less than 2.5 wt %, since no distinguished phase‐separated PBAT droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/PBAT specimens, respectively. In contrast to PLA, the PBAT specimen exhibits highly deformable properties. After blending proper amounts of PBAT in PLA, the inherent brittle deformation behavior of PLA was successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tensile properties of PLA/PBAT specimens are proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystalline and thermal behavior of poly(ethylene terephthalate)/polyphenoxy blends

Poly(ethylene terephthalate) (PET)/polyphenoxy blends were prepared by melt blending. Crystalline and thermal behaviors of PET/polyphenoxy blends were verified by use of DSC. The experiment results show that the initial temperature, peak temperature, and ending temperature of cold crystallization increase with increasing phenoxy content. On the contrary, the onset melting temperature, finishing melting temperature, and peak temperature in the first heating and the secondary heating processes decrease with increasing phenoxy content. The crystallization enthalpy and melting enthalpy, as well as the crystallization rate, decrease with increasing phenoxy content. Avrami exponents of the blends are slightly higher than that of pure PET and almost independent of phenoxy content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 878–885, 2005     

Effect of poly(ethylene glycol) on the solid‐state polymerization of poly(ethylene terephthalate)

Poly(ethylene glycol) (PEG) and end‐capped poly(ethylene glycol) (poly(ethylene glycol) dimethyl ether (PEGDME)) of number average molecular weight 1000 g mol^?1 was melt blended with poly(ethylene terephthalate) (PET) oligomer. NMR, DSC and WAXS techniques characterized the structure and morphology of the blends. Both these samples show reduction in T_g and similar crystallization behavior. Solid‐state polymerization (SSP) was performed on these blend samples using Sb₂O₃ as catalyst under reduced pressure at temperatures below the melting point of the samples. Inherent viscosity data indicate that for the blend sample with PEG there is enhancement of SSP rate, while for the sample with PEGDME the SSP rate is suppressed. NMR data showed that PEG is incorporated into the PET chain, while PEGDME does not react with PET. Copyright © 2005 Society of Chemical Industry     

Rheological and thermal properties of blends of modified poly(ethylene terephthalate) with p‐acetoxybenzoic acid and poly(butylene terephthalate)

Blending of thermotropic liquid crystalline polyesters (LCPs) with conventional polymers could result in materials that can be used as an alternative for short fiber‐reinforced thermoplastic composites, because of their low melt viscosity as well as their inherent high stiffness and strength, high use temperature, and excellent chemical resistance and low coefficient of expansion. In most of the blends was used LCP of 40 mol % of poly(ethylene terephthalate) (PET) and 60 mol % of p‐acetoxybenzoic acid (PABA). In this work, blends of several copolyesters having various PABA compositions from 10 to 70 mol % and poly(butylene terephthalate) (PBT) were prepared and their rheological and thermal properties were investigated. For convenience, the copolyesters were designated as PETA‐x, where x is the mol % of PABA. It was found that PET‐60 and PET‐70 copolyesters decreased the melt viscosity of PBT in the blends and those PBT/PETA‐60 and PBT/PETA‐70 blends showed different melt viscosity behaviors with the change in shear rate, while blends of PBT and PET‐x having less than 50 mol % of PABA exhibited totally different rheological behaviors. The blends of PBT with PETA‐50, PETA‐60, and PETA‐70 showed the morphology of multiple layers of fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1797–1806, 1999     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005     

Synthesis and characterization of copolymers of poly(m-xylylene adipamide) and poly(ethylene terephthalate) oligomers by melt copolycondensation

Poly(m-xylylene adipamide)/poly(ethylene terephthalate)(MXD6/PET) copolymers are synthesized by melt copolycondensation with 1–5 wt% low molecular weight PET oligomers into the MXD6 oligomers at 260 °C.FR-IR and1 H NMR analysis results indicate that the interchange reaction has occurred between MXD6 oligomers and PET oligomers. The thermal behavior of copolymers shows that the melting temperature of MXD6/PET copolymers decreases with the increasing of amount of PET oligomers, while the crystallization temperature accordingly increases. And the equilibrium temperature Tm0 is evaluated to be 251.8 °C for the copolymers with5 wt% PET oligomer adding, which is very close to that of neat MXD6. The tensile and impact strength of MXD6/PET copolymers are significantly improved than that of pure MXD6 by mechanical properties test, and the microfibril structure in the impact fracture sample's surface reveals the feature of ductile fracture.     

聚酯固相缩聚等温结晶特性的研究

聚酯(PET)固相缩聚(SSP)中切片的结晶性能及其演变影响固相缩聚反应,采用差示扫描量热仪(DSC)和热台偏光显微镜研究了固相缩聚反应前后PET切片的等温结晶特性。结果表明:PET切片在DSC中的等温结晶符合Avrami 方程,等温结晶温度升高,结晶速率常数K值减小,即结晶速率降低;热台偏光显微镜中不同等温结晶温度下形成了不同的球晶形态:黑十字消光图以及环形消光图;随着PET特性粘数(平均分子质量)增大,结晶速率常数K值减小,球晶生长速率减小,Avrami指数n值增大,形成更加复杂的消光图。对于固相缩聚前PET基础切片,球晶最大结晶速率在190℃左右。     

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25-110 °C) and strain rates (.005-1.0 s⁻¹). The stress-strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature (θ_g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress-strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub-θ_g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress-strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.     

Poly(ethylene terephthalate‐co‐isophthalate) copolyesters obtained from ethylene terephthalate and isophthalate oligomers

A series of poly(ethylene terephthalate‐co‐isophthalate) copolyesters containing upto 50%‐mole of isophthalic units were prepared by polycondensation from ethylene terephthalate and ethylene isophthalate fractions of linear oligomers containing from 5 to 6 repeating units in average. The polyesters were obtained in good yields and with high‐molecular‐weights. The microstructure of the copolyesters was studied as a function of reaction time by ¹³C‐NMR showing that a random distribution of the comonomers was achieved since the earlier stages of polycondensation. The melting temperature and enthalpy of the copolyesters decreased with the content of isophthalic units so that copolyesters containing more than 25% of these units were amorphous. Isothermal crystallization studies made on crystalline copolyesters revealed that the crystallization rate of copolyesters decreased with the content in isophthalic units. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Relationship between the crystallization behavior of poly(ethylene glycol) and stereocomplex crystallization of poly(L‐lactic acid)/poly(D‐lactic acid)

Poly(l ‐lactic acid) (PLLA) is a good biomedical polymer material with wide applications. The addition of poly(ethylene glycol) (PEG) as a plasticizer and the formation of stereocomplex crystals (SCs) have been proved to be effective methods for improving the crystallization of PLLA, which will promote its heat resistance. In this work, the crystallization behavior of PEG and PLLA/poly(d ‐lactic acid) (PDLA) in PLLA/PDLA/PEG and PEG‐b‐PLLA/PEG‐b‐PDLA blends has been investigated using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both SCs and homocrystals (HCs) were observed in blends with asymmetric mass ratio of PLLA/PDLA, while exclusively SCs were observed in blends with approximately equal mass ratio of PLLA/PDLA. The crystallization of PEG was only observed for the symmetric blends of PLLA_39k/PDLA_35k/PEG_2k, PLLA_39k/PDLA_35k/PEG_5k, PLLA_69k/PDLA_96k/PEG_5k and PEG‐b‐PLLA_31k/PEG‐b‐PDLA_27k, where the mass ratio of PLLA/PDLA was approximately 1/1. The results demonstrated that the formation of exclusively SCs would facilitate the crystallization of PEG, while the existence of both HCs and SCs could restrict the crystallization of PEG. The crystallization of PEG is related to the crystallinity of PLLA and PDLA, which will be promoted by the formation of SCs. © 2017 Society of Chemical Industry     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

Recycled poly(ethylene terephthalate)/linear low‐density polyethylene blends through physical processing

Poly(styrene‐ethylene/butylene‐styrene) (SEBS) was used as a compatibilizer to improve the thermal and mechanical properties of recycled poly(ethylene terephthalate)/linear low‐density polyethylene (R‐PET/LLDPE) blends. The blends compatibilized with 0–20 wt % SEBS were prepared by low‐temperature solid‐state extrusion. The effect of SEBS content was investigated using scanning electron microscope, differential scanning calorimeter, dynamic mechanical analysis (DMA), and mechanical property testing. Morphology observation showed that the addition of 10 wt % SEBS led to the deformation of dispersed phase from spherical to fibrous structure, and microfibrils were formed at the interface between two phases in the compatibilized blends. Both differential scanning calorimeter and DMA results revealed that the blend with 20 wt % SEBS showed better compatibility between PET and LLDPE than other blends studied. The addition of 20 wt % of SEBS obviously improved the crystallizibility of PET as well as the modulus of the blends. DMA analysis also showed that the interaction between SEBS and two other components enhanced at high temperature above 130°C. The impact strength of the blend with 20 wt % SEBS increased of 93.2% with respect to the blend without SEBS, accompanied by only a 28.7% tensile strength decrease. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009