Crystallization and morphology of poly(ethylene succinate) and poly(β-hydroxybutyrate) blends

Summary The melting and crystallization behavior of poly(β-hydroxybutyrate) (PHB) and poly(ethylene succinate) blends has been studied by differential scanning calorimetry and optical microscopy. The results indicate that PHB and PES are miscible in the melt. Consequently the blend exhibits a depression of the melting temperature of both PHB and PES. In addition, a depression of the equilibrium melting temperature of PHB is observed. The Flory-Huggins interaction parameter (χ₁₂ ), obtained from melting point depression data, is composition dependent, and its value is always negative. Isothermal crystallization in the miscible blend system PES/PHB is examined by polarized optical microscope. The presence of the PES component gives a wide variety of morphologies. The spherulites exhibit a banded structure and the band spacing decreases with increase PES content. Received: 29 June 1998/Revised version: 31 August 1998/Accepted: 10 September 1998     

Melting behaviour of poly(butylene succinate) in miscible blends with poly(ethylene oxide)

The melting behavior of poly(butylene succinate) (PBSU) in miscible blends with poly(ethylene oxide) (PEO), which is a newly found polymer blends of two crystalline polymers by our group, has been investigated by conventional differential scanning calorimetry (DSC). It was found that PBSU showed double melting behavior after isothermal crystallization from the melt under certain crystallization conditions, which was explained by the model of melting, recrystallization and remelting. The influence of the blend composition, crystallization temperature and scanning rate on the melting behavior of PBSU has been studied extensively. With increasing any of the PEO composition, crystallization temperature and scanning rate, the recrystallization of PBSU was inhibited. Furthermore, temperature modulated differential scanning calorimetry (TMDSC) was also employed in this work to investigate the melting behavior of PBSU in PBSU/PEO blends due to its advantage in the separation of exotherms (including crystallization and recrystallization) from reversible meltings (including the melting of the crystals originally existed prior to the DSC scan and the melting of the crystals formed through the recrystallization during the DSC scan). The TMDSC experiments gave a direct evidence of this melting, recrystallization and remelting model to explain the multiple melting behavior of PBSU in PBSU/PEO blends.     

Spherulitic crystallization in blends of poly(ethylene oxide) and poly(methyl methacrylate)

The crystallization kinetics of binary blends of poly(ethylene oxide) and poly(methyl methacrylate) were investigated. The isothermal spherulitic growth rates were measured by means of a polarized light microscope. The temperature and composition dependence on the growth rates have been analysed. The temperature range studied was from 44° to 58°C. The introduction of poly(methyl methacrylate) into poly(ethylene oxide) resulted in a reduction of the spherulitic growth rate as the proportion of poly(methyl methacrylate) was increased from zero to 40% by weight. Results have been analysed using the theoretical equations of Boon and Azcue for the growth rate of polymer-diluent mixtures. The experimental results are in good agreement with this equation. The temperature coefficient is negative as is the case in the crystallization of bulk homopolymers.     

Effect of self‐nucleation on the crystallization of segmented copolymer poly(ether ester)

The effect of self‐nucleation on the nonisothermal and isothermal crystallization behaviors of the segmented copolymer poly(ether ester), based on poly(ethylene glycol) as the soft segment and poly(ethylene terephthalate) as the hard segment was investigated by means of differential scanning calorimetry (DSC) and depolarization polarized light (DPL) techniques, respectively. The results demonstrated that self‐nucleation could enhance the crystallization rate in both cases. The experimental conditions of the self‐nucleation procedure studied by DSC were discussed in detail. The isothermal crystallization was analyzed by the Avrami equation, and the Avrami parameters were dependent on the melting temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 498–504, 2001     

Preparation and biodegradation of copolyesters based on poly(ethylene terephthalate) and poly(ethylene glycol)/oligo(lactic acid) by transesterification

The poly(ethylene terephthalate‐co‐ethyleneoxide‐co‐DL ‐lactide) copolymers were successfully prepared by the melt reaction between poly(ethylene terephthalate), poly(ethylene glycol), and DL ‐oligo(lactic acid) without any catalysts. The transesterification between ethylene terephthalate, ethyleneoxide, and lactide segments during the reaction was confirmed by the ¹H NMR analysis. The effect of reaction temperatures and the starting feed ratios on the molecular microstructures, molecular weights, solubility, thermal properties, and degradability of the copolyesters was extensively studied. The values of crystallization temperature, melting temperature, crystallization, and melting enthalpy of the copolyesters were found to be influenced by the reaction temperatures, starting feed ratios, etc. The copolyesters showed good tensile properties and were found to degrade in the soil burial experiments during the period of 3 months. The morphology of the copolyester films were also investigated by scanning electron microscopy during soil burial degradation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Poly(ε-caprolactone)/poly(ethylene oxide) diblock copolymer. I. Isothermal crystallization and melting behavior

The isothermal crystallization and melting behavior of the poly(ε-caprolactone)(PCL)/poly(ethylene oxide)(PEO) diblock copolymer has been studied by WAXD, SAXS, and DSC methods. Only the PCL block is crystallizable; the PEO block of weight fraction 20% cannot crystallize, although its corresponding homopolymer has strong crystallizability. The long period, amorphous layer, and crystalline lamella of the PCL/PEO block copolymer all increase with the rise in the crystallization temperature, and the thickness of the amorphous layer is much larger than that of crystalline lamella due to the existence of the PEO block in the amorphous region. The isothermal crystallization of the PCL/PEO block copolymer is investigated by using the theory of Turnbull and Fischer. It is found that the amorphous PEO block has a great influence on the nucleation of PCL block crystallization, and the extent of this influence depends on crystallization conditions, especially temperature. The outstanding characteristics are the phenomenon of the double melting peaks in the melting process of the PCL/PEO block copolymer after isothermal crystallization at different temperatures and the transformation of melting peaks from double peaks to a single peak with variations in the crystallization condition. They are related mainly to the existence of the PEO block bonding chemically with the PCL block. In summing up results of investigations into the crystallization and melting behavior of the PCL/PEO block copolymer, it is interesting to notice that when the PCL/PEO block copolymer crystallizes at three different crystallization temperatures, i.e., below 0°C, between 0 and 35°C, and above 35°C, the variation of peak melting temperature is similar to that of overall crystallization rates in the process of isothermal crystallization. The results can be elucidated by the effect of the PEO block on the crystallization of the PCL block, especially its nucleation. © 1996 John Wiley & Sons, Inc.     

Phase Behaviour of Poly(ethylene oxide)/Poly(styrene-co-maleic anhydride) Blends

Thermal behaviour and morphology of blends of poly(ethylene oxide) (PEO) and poly(styrene-co-maleic anhydride) (SMA) prepared by the coprecipitation technique were studied by means of differential scanning calorimetry, optical microscopy and thermogravimetry. SMA containing 25wt% maleic anhydride (MA) was found to be miscible with PEO when the SMA content was greater than 80%. The melting temperature and crystallinity depended on the composition of the blend. SMA appears to segregate interlamellarly during the isothermal crystallization of PEO. The thermal stability of blends was enhanced and was higher than that of pure PEO and SMA. © of SCI.     

Melting,crystallization behaviors,and nonisothermal crystallization kinetics of PET/PTT/PBT ternary blends

The melting, crystallization behaviors, and nonisothermal crystallization kinetics of the ternary blends composed of poly(ethylene terephthalate), poly(trimethylene terephthalate) (PTT) and poly(buthylene terephthalate) (PBT) were studied with differential scanning calorimeter (DSC). PBT content in all ternary blends was settled invariably to be one‐third, which improved the melt‐crystallization temperature of the ternary blends. All of the blend compositions in amorphous state were miscible as evidenced by a single, composition‐dependent glass transition temperature (T_g) observed in DSC curves. DSC melting thermograms of different blends showed different multiple melting and crystallization peaks because of their various polymer contents. During melt‐crystallization process, three components in blends crystallized simultaneously to form mixed crystals or separated crystals depending upon their content ratio. The Avrami equation modified by Jeziorny and the Ozawa theory were employed to describe the nonisothermal crystallization process of two selected ternary blends. The results spoke that the Avrami equation was successful in describing the nonisothermal crystallization process of the ternary blends. The values of the t_1/2 and the parameters Z_c showed that the crystallization rate of the ternary blends with more poly(ethylene terephthalate) content was faster than that with the lesser one at a given cooling rate. The crystal morphology of the five ternary blends investigated by polarized optical microscopy (POM) showed different size and distortional Maltese crosses or light spots when the PTT or poly(ethylene terephthalate) component varied, suggesting that the more the PTT content, the larger crystallites formed in ternary blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of blend composition on crystallization behavior of polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

The influence of blend composition on crystallization behavior of a typical crystalline/crystalline blend, polyoxymethylene (POM)/poly(ethylene oxide) (PEO), during slow non-isothermal crystallization was investigated by polarized light microscope (PLM) connected with a THMS600 hot-stage, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The experimental results indicated that with increasing PEO content in the blend, the crystallization temperature of POM of the blends reduced and the multiple crystalline morphologies or structures including two kinds of interfibrillar or interlamellar structures were produced. The melting point of each component decreased with raising the content of the other constituent due to the inclusion and entanglement between POM and PEO molecules. The shoulder melting peak of POM appeared in DSC heating traces of the PEO-rich blend because the stronger inclusion and entanglement induced the imperfect crystallization of POM.     

Effect of self‐nucleation on crystallization and melting behavior of polypropylene and its copolymers

The effect of self‐nucleation on the crystallization and melting behavior of isotactic polypropylene (i‐PP) and low ethylene content propylene–ethylene copolymers were investigated. Isothermal crystallization kinetics were studied using the Avrami equation and Lauritzen‐Hoffman nucleation theory. It was found that self‐nucleation can enhance the crystallization. The surface free energy ς_e decreased for the self‐nucleated sample. The melting behavior was affected by the preselected temperature, T_s, at which the polymer was partially melted. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1559–1564, 1999     

PET-PTMG聚醚酯熔融与结晶行为的研究

采用熔融缩聚法合成了一系列聚对苯二甲酸乙二醇酯(PET)-四氢呋喃聚醚(PTMG)聚醚酯，用DSC、偏光显微镜表征了材料的熔融与结晶性能，讨论了组成对聚醚酯的熔点、结晶温度、结晶度、结晶形态的影响。结果表明，PET—PTMG聚醚酯的熔点与组成的关系符合Baur公式；其结晶度随着聚醚含量的增加呈现先升高后下降的趋势；并为明显的结晶与非结晶的两相结构形态。     

Isothermal crystallization of poly(vinyl alcohol–co–ethylene)

Isothermal melt crystallization of poly(vinyl alcohol–co–ethylene) with different ethylene contents was studied in the temperature range of 140°C–160°C. A differential scanning calorimeter was used to follow the energy of the crystallization process. The results were analyzed by Avrami and Hoffman–Laurizten methods. The Avrami exponent was close to 2, indicating two‐dimensional growth with a linear growth rate and crystals nucleating athermally. The equilibrium melting temperature was determined by the Hoffman–Weeks method. The rate of crystallization depended on ethylene content and temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1071–1077, 2003     

The crystallization morphology and melting behavior of polymer crystals in nano-sized domains

The crystallization morphology and the melting behavior of the phase-separating poly(?-caprolactone) (PCL) and poly(ethylene oxide) (PEO) blends were studied using atomic force microscopy. Two blends consisting of PCL and PEO with weight ratios of 10/90 and 90/10 were prepared to form the isolated spherical domains by the phase-separating process. The results show that the melting temperatures of the PCL and PEO lamellae in the confined domains increased as the lamellar length increased, and the melting behavior of the PCL and PEO lamellae in the matrix and confined domains was also studied.     

不同温度熔融条件下聚对苯二甲酸乙二醇酯的结晶与熔融行为

分别采用低黏度和高黏度的聚对苯二甲酸乙二醇酯(PET)树脂切片,利用差示扫描量热分析(DSC)的方法研究不同的熔融温度条件对PET结晶行为和熔融行为的影响。结果表明:和高黏度PET相比,低黏度PET的结晶过程对熔融温度的变化极其敏感,不同熔融温度将对它的结晶行为与熔融行为产生显著的影响;在同等条件下,低黏度PET结晶速率快且易生成稳定的结晶结构,其稳定结晶的熔融温度要比高黏度PET高数度;总体上,采用较低的熔融温度有利于提高PET结晶温度和结晶速率,而采用较高的熔融温度有利于提高PET结晶的稳定性。     

On the triple melting behaviour of poly(ethylene succinate)

The morphology of melt-crystallized poly(ethylene succinate) (PES) was investigated by optical microscopy and scanning electron microscopy, and the melting behaviour of PES was studied by differential scanning calorimetry (DSC). At low crystallization temperature imperfect crystals were formed which could melt and recrystallize during the DSC scan. Triple melting peaks were observed, and the melting behaviour was strongly dependent on crystallization time and scan rate. It was observed that crystallization at high temperature perfected the crystals (dominant and subsidiary lamellae in the spherulitic structure). Increasing the scan rate reduced the chance for reorganization. However, at high crystallization temperature two melting peaks were observed. The material formed was much more perfect, so that the melting process was not dominated by recrystallization. Accordingly, the cause of dual melting is the existence of two kinds of crystal perfection.     

Crystallization and melting behavior of poly(p‐phenylene sulfide) in blends with poly(ether sulfone)

Crystallization and melting behaviors of poly(p‐phenylene sulfide) (PPS) in blends with poly(ether sulfone) (PES) prepared by melt‐mixing were investigated by differential scanning calorimetry (DSC). The blends showed two glass transition temperatures corresponding to PPS‐ and PES‐rich phases, which increased with increasing PES content, indicating that PPS and PES have some compatibility. The cold crystallization temperature of the blended PPS was a little higher than that of pure PPS. Also, the heats of crystallization and melting of the blended PPS decreased with increasing PES content, indicating that the degree of crystallinity decreased with an increase of PES content. The isothermal crystallization studies revealed that the crystallization of PPS is accelerated by blending PPS with 10 wt % PES and further addition results in the retardation. The Avrami exponent n was about 4 independent on blend composition. The activation energy of crystallization increased by blending with PES. The equilibrium melting point decreased linearly with increasing PES content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1686–1692, 1999     

PET/PLA共混物相容性和结晶性能的研究

研究了相容剂钛酸四丁酯[Ti(OBu)4]含量、聚乳酸(PLA)含量对聚对苯二甲酸乙二醇酯(PET)/PLA共混物相容性的影响,探讨了共混物的熔融和结晶行为,并对其结晶形貌进行了观察。结果表明,Ti(OBu)4含量为PLA的4%(质量分数,下同)时,PET/PLA共混物的相容性良好,但当PLA含量超过30%时,共混物出现相分离;PLA的加入使PET的结晶峰变窄,结晶速率增加,且结晶峰温度向高温方向移动;PLA的加入使PET的晶粒尺寸大幅减小,晶粒数目大幅增加,结晶更加完善。     

Fibers from blends of PET and thermotropic liquid crystalline polymer

Blends of poly(ethylene terephthalate-Co-p-oxybenzoate), PET/PHB, with poly(ethylene terephthalate), PET, have been studied in the form of as-spun and drawn fibers. DSC melting and crystallization results show that the PET is compatible with LCP and the crystallization of PET decreases by the addition of LCP in the matrix. Upon heating above the crystal melting temperature of PET, the blend shows good dispersion of LCP in the PET matrix. Wide angle X-ray diffraction of drawn blended fibers show the possible formation of LCP oriented domains. The mechanical properties of drawn fiber up to 10 wt% LCP composition exhibit significant improvement in tensile modulus and tensile strength with values of 17.7 GPa and 1.0 GPa, respectively. Values of modulus are compared with prediction from composite theory, assuming the blend system as nematic domains of LCP. dispersed in PET matrix.     

Lithium ion conducting polymeric electrolytes based on poly(ethylene adipate)

We report the preparation and properties of polymeric lithium ion conducting films based on poly(ethylene adipate) with lithium trifluoromethanesulfonate and blends of poly(ethylene adipate) and poly(vinyl acetate) with lithium triflouromethanesulfonate.The conductivity/temperature behaviour of these films was found to be very similar to those based on poly(ethylene oxide), with Arrhenius behaviour above the crystalline melting point and slight hysteresis below this temperature.     

Microstructure and kinetics study of polymeric electrolytes precursor based on poly(ethylene oxide)/polyphosphazene blends

This work reports on the microstructural study of the system: poly(ethylene oxide) (PEO) and a poly(fluoroalkoxyphosphazene) (PPz) and comprises both isothermal and non-isothermal crystallization kinetics as a function of blend composition, as well as the analysis of spherulite growth, nucleating energy and nucleation density. In addition, compatibility studies were conducted based on glass transition temperature on the one hand, and on the other hand on the determination of the Flory-Huggins interaction parameter via melting point depression.