Effect of the Presence of an Ester of Montanic Acids With Multifunctional Alcohols in the Composites of Titanium Dioxide Nanoparticles With Poly (Ethylene Terephthalate) in Their Non-Isothermal Crystallization

The effect of the addition of an ester of montanic acid with multifunctional alcohols in the effectiveness of the dispersion and compatibility of TiO₂ nanoparticles when included as filler in poly(ethyleneterephthalate) for composite production is studied through the study of the non-isothermal crystallization by differential scanning calorimetry (DSC). The application of the Avrami method enables to evaluate the compatibility and the level of dispersion/aggregation of the nanofiller in the poly(ethyleneterephthalate) by the analysis of the temperature and enthalpy of crystallization, the kinetic parameters and the half-crystallization time.     

Non-isothermal crystallization kinetics of recycled PET-Si3N4 nanocomposites

Poly(ethylene terephthalate) (PET) is an important industrial material and has been widely applied in consumer products. Due to its slow crystallization rate, nanoparticles are incorporated into PET to function as heterogeneous nucleating agents. In this study, the non-isothermal crystallization behavior of recycled PET-silicon nitride (Si₃N₄) nanocomposites was investigated by differential scanning calorimetry (DSC). In the general analysis of the non-isothermal crystallization curves, it was found that the Si₃N₄ nanoparticles could effectively accelerate the nucleation of PET, but the crystal growth rate was slowed down when the Si₃N₄ content was more than 1 wt%. This might be attributed to the interaction between the PET chains and the surface-treated Si₃N₄ nanoparticles. Results obtained from Avrami and Mo treatments agreed well with the general analysis. Application of the Kissinger method and isoconversional method of Flynn-Wall-Ozawa also showed that Si₃N₄ nanoparticles had a good nucleation effect on the crystallization of PET, and the crystal growth was hindered by Si₃N₄ when the particle loading is higher than 1 wt%.     

Effect of ZnO nanofillers treated with triethoxy caprylylsilane on the isothermal and non-isothermal crystallization of poly(lactic acid)

The crystallization of PLA-silane surface-treated ZnO nanocomposites was investigated by DSC and compared to that of neat PLA. Several modes of crystallization were considered: isothermal and non-isothermal cold crystallization and also isothermal and non-isothermal melt crystallization. The kinetics of cold crystallization were studied using different methods, namely the Avrami and Ozawa-Flynn-Wall models, to calculate activation energies and kinetic constants. In contrast to what is typically observed when the foreign particles are added in a polymer matrix, the silane surface-treated ZnO delayed the crystallization of PLA and made it more difficult to start. The nucleation activity of the ZnO nanoparticles, ?, was calculated and found to be greater than 1 (? = 1.7). This indicated that ZnO played an anti-nucleating role in the crystallization of PLA nanocomposites. This effect has been linked mainly to the interactions between the silane groups onto the surface of nanoparticles and PLA macromolecules. These interactions which reduce the mobility of polymer chains have been evidenced by rheological experiments.     

Enhanced crystallization behaviors of poly(ethylene terephthalate) via adding expanded graphite and poly(ethylene glycol)

A compound additive system consisting of expanded graphite (EG) and poly(ethylene glycol) (PEG) was designed to enhance the crystallization of poly(ethylene terephthalate) (PET). In this additive system, EG acted as a heterogeneous nucleating agent to reduce energy barrier for nucleation, while PEG played as plasticizer to improve mobility of PET chains. Simultaneously adding EG and PEG resulted in faster crystallization kinetics than the cases of solely adding EG or PEG in both of non-isothermal and isothermal crystallization processes, indicating a synergistic effect of EG and PEG on enhancing PET crystallization. However, for non-isothermal crystallization process, in which crystallization occurred from a cooling melt, EG played a dominant role. As to isothermal crystallization process where crystallization took place in a super-cooling state, PEG seemed to be more important. Moreover, the chain conformation change among the semi-crystalline PET specimens was ascertained by Fourier transform infrared spectroscopy.     

Isothermal crystallization kinetics and melting behaviour of PET/ATO nanocomposites prepared by in situ polymerization

Neat poly(ethylene terephthalate) (PET) and PET/antimony doped tin oxide (ATO) nanocomposites were prepared by in situ polymerization. The study of the isothermal crystallization behaviors of neat PET and PET/ATO nanocomposites was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For neat PET and PET/ATO nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing ATO content. These suggested that the crystallization types related to the values of n in the Avrami theory could not be suitable for the crystallization of PET and its nanocomposites. The change of the n values indicated that the addition of ATO resulted in the increase of the crystallizing growth points. That is a heterogeneous nucleating effect of ATO on crystallization of PET. In the DSC scan after isothermal crystallization process, multiple melting behavior was found. And the multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae produced during different crystallization processes. The equilibrium melting temperature of PET in the nanocomposites increased with increasing the ATO content. Surface free energy of PET chain folding for crystallization of PET/ATO nanocomposites was lower than that of neat PET, confirming the heterogeneous nucleation effect of ATO.     

Estimating the activation energy for non-isothermal crystallization of polymer melts

The advanced isoconversional method can be used to determine the effective activation energy of non-isothermal crystallization of the polymer melts. The method has been applied to DSC data on crystallization of poly(ethylene terephthalate) (PET). The resulting activation energy increases with the extent of crystallization from -270 to 20 kJ mol^-1. The variation is interpreted in terms of the Turnbull and Fisher crystallization theory. This revised version was published online in July 2006 with corrections to the Cover Date.     

High speed spinning of poly(ethylene terephthalate)—II: Orientation induced mechanism of cold crystallization in pre-orientated yarns

The kinetics of the “cold crystallization” of poly(ethylene terephthalate) (PET) pre-orientated yarns are investigated both in isothermal and in non-isothermal dynamic conditions. The amorphous-crystalline, solid-solid transformation is analyzed in terms of the Avrami equation and of Ozawa's theory. The nucleation and growth mechanism is a function of PET amorphous molecular orientation and changes from a three dimensional (n = 4) to a two dimensional and one dimensional disc-like or rod-like growth. The molecular orientation may be defined as the best “nucleating agent” for PET overall rate of crystallization in the low temperature region.     

Isothermal and Non-Isothermal Crystallization Kinetics and Morphology of Poly(trimethylene terephthalate)/Multiwalled Carbon Nanotube Composites

Summary: Multiwalled carbon nanotubes (MWCNTs) synthesized using chemical vapor deposition method were dispersed in poly(trimethylene terephthalate) (PTT, Mv = 88,000) by melt compounding technique using DMS microcompounder. The nanocomposites consisting of varying amounts of MWCNTs were characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of carbon nanotubes on the crystallization behavior (under isothermal and non isothermal crystallization conditions) of PTT was studied using DSC. The presence of carbon nanotubes didn't show any significant effect on crystallization temperature of PTT matrix under non-isothermal conditions. Crystallization studies under isothermal conditions were carried out at different temperatures i.e 185, 190, 195 and 200 °C. Complete crystallization was observed within 60 sec at 185 °C whereas at 200 °C, longer time was required for complete crystallization. Crystal growth was also investigated using hot stage polarizing microscope (PLM). The effect of annealing time at 200 °C was investigated in the presence as well as in the absence of varying amounts of MWCNTs. Spherulitic growth was seen and the spherulite size in all the samples increased with annealing time. Morphological characterization using SEM and TEM showed a uniform dispersion of MWCNTs and poor compatibility with PTT matrix.     

水性聚氨酯/功能化石墨烯纳米复合材料的非等温结晶动力学

采用差示扫描量热法DSC研究了水性聚氨酯/功能化石墨烯(WPU/FGNs)纳米复合材料的非等温结晶行为,分别采用Ozawa方程、莫志深方程研究复合材料的非等温结晶动力学,并通过Kissinger方程计算了结晶过程中的活化能。 结果表明,石墨烯在复合材料的结晶过程中起到异相成核剂的作用,提高了复合材料的结晶起始温度、峰值温度和结晶速率;增加石墨烯的质量分数,复合材料的结晶维数增加;石墨烯增加至0.3%,复合材料的活化能从-47.74 kJ/mol降低至-53.60 kJ/mol,继续增加石墨烯至1.0%,复合材料的活化能增加至-41.74 kJ/mol。     

Thermal stability and flammability properties of heterophasic PP-EP/EVA/organoclay nanocomposites

A study on the thermal behavior and flammability properties of the heterophasic polypropylene-(ethylene-propylene) copolymer (PP-EP)/poly(ethylene vinyl acetate) (EVA)/montmorillonite nanocomposite is presented. Nanoclay nanocomposites were prepared using a twin screw extruder. Both the fluidity of the EVA phase and compatibility conditions between PP-EP and EVA were used in order to obtain the required nanocomposites. Therefore, no additional compatibilizer was required to achieve the clay dispersion. Products exhibited the partially exfoliated/intercalated nanoclay dispersion. Thermogravimetric analyses indicated that nanoclays retard thermal degradation depending on nanoclay concentration. The retarding process was assigned to the exfoliation and dispersion of the silicate layers which impeded heat diffusion to the macromolecules. Thermal studies, under non-isothermal crystallization, indicated the lack of influence of nanoclay on the thermal behavior. Flammability characteristics were however affected by the nanoclay layers which overall generated flame retardation both in the EVA host and in the complex nanocomposites.     

多孔二氧化硅对聚环氧乙烷结晶行为的影响

高分子化合物由于具有很长的分子链,不易进行规整排列,结晶速度通常很慢,为提高结晶速度,有时需要加入成核剂．多孔二氧化硅（ＳｉＯ２）具有较大的比表面积,故吸附作用较强,有可能作为成核剂影响部分结晶高聚物的结晶过程．聚环氧乙烷（ＰＥＯ）为部分结晶高聚物,其结晶行为对杂质较为敏感．本文目的在于通过结晶动力学及结晶与熔融行为的研究,探索多孔二氧化硅对ＰＥＯ结晶行为的影响．１　实验部分　　聚环氧乙烷（ＰＥＯ,Ｍｗ＝１×１０５）．两种多孔二氧化硅（ＳｉＯ２）按文献［１］方法制备,平均粒度为０．３μｍ,平均孔…     

Structure-properties correlations in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)/nanosilica mixtures: Interrelationship among phase behavior,morphology and non-isothermal crystallization kinetics

In this work, the effects of amorphous poly(styrene-co-acrylonitrile) (SAN) chains and hydrophilic and hydrophobic nanosilica at different loadings on the non-isothermal crystallization kinetics of PCL phase have been evaluated using different theoretical models including Avrami, modified Avrami, Ozawa and Mo equations. Using microscopic observations, the interrelations among the changes in the kinetics parameters and the morphology and phase behavior of PCL/SAN and PCL/SAN/nanosilica mixtures have been thoroughly investigated. Microscopic observations on the nanocomposites showed differences in the nanofiller dispersion and distribution state as well as preferential migration and localization state. These differences lead to contradictory trends in the effects of hydrophilic and hydrophobic nanosilica on the crystallization kinetics of pure PCL and PCL/SAN blends. The nanoparticle migration during non-isothermal DSC tests in PCL/SAN blends, the formation of nanoparticle agglomerates at higher loadings, the restrictions imposed on the molecular movements in the crystallization growth stage and slower phase separation and dissolution of PCL/SAN/silica mixtures result in the cooling rate dependence of the kinetics parameters.     

Plasticization and Crystallization of Poly(ethylene Terephthalate) Induced by Water

Commercial poly(ethylene terephthalate) (PET) was treated at R. H.>80% and room temperature for a set time. The glass transition temperature (Tg) decreases with the time of exposure to high humidity. The decrease in Tg is a result of plasticization. Our data indicate that the Tg of dry PET of 76-78°C may decrease to as low a temperature as 65-67°C when it is wet. Induced crystallization of PET in the presence of water reduces the cold crystallization temperature (Tc). The structure of water-induced crystals is imperfect and can be improved in perfection by annealing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reflection–absorption infrared spectroscopy investigation of the crystallization kinetics of poly(ethylene terephthalate) ultrathin films

Reflection–absorption infrared spectroscopy was used to study the crystallization behavior of poly(ethylene terephthalate) (PET) ultrathin films. The crystallinity of ultrathin films was estimated by the fraction of trans conformers of PET. The isothermal and nonisothermal crystallization kinetics of ultrathin films with different thicknesses were investigated. The thinner PET film showed slower kinetics during isothermal crystallization than the thicker film. Moreover, the final crystallinity of films with various thicknesses were reduced with decreasing thickness. An Avrami equation was used to fit the acquired results. The Avrami exponents decreased with the film thickness. As for the nonisothermal crystallization, the cold‐crystallization starting temperature shifted to a lower temperature as the film thickness increased. The influence of the substrate on the crystallization kinetics of the films was also studied. The half‐crystallization times and final crystallinities of ultrathin films adsorbed onto a self‐assembled‐monolayer‐treated surface and an untreated substrate were clearly different, although their thickness dependence was similar. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4440–4447, 2004     

Melt‐crystallization mechanism of poly(ethylene terephthalate)/multi‐walled carbon nanotubes prepared by in situ polymerization

A series of poly(ethylene terephthalate)/multi‐walled carbon nanotubes (PET/MWCNTs) nanocomposites were prepared by in situ polymerization using different amounts of multi‐walled carbon nanotubes (MWCNTs). The polymerization of poly(ethylene terephthalate) (PET) was carried out by the two‐stage melt polycondensation method. The intrinsic viscosity (IV) of the composites is ranged between 0.31 and 0.63 dL/g depending on the concentration of the MWCNTs. A decrease of IV was found by increasing MWCNTs content. This is due to the reactions taking place between the two components leading to branched and crosslinked macromolecules. These reactions are, mainly, responsible for thermal behavior of nanocomposites. The melting point of the nanocomposites was shifted to slightly higher temperatures by the addition till 0.55 wt % of MWCNTs while for higher concentration was reduced. The degree of crystallinity in all nanocomposites was, also, reduced by increasing MWCNTs amount. However, from crystallization temperature, it was found that MWCNTs till 1 wt % can enhance the crystallization rate of PET, whereas at higher content (2 wt %), the trend is the opposite due to the formation of crosslinked macromolecules. From the extended crystallization analysis, it was proved that MWCNTs act as nucleating agents for PET crystallization. Additionally, the crystallization mechanism due to the existence of MWCNT becomes more complicated because two mechanisms with different activation energies are taking place in the different degrees of crystallization, depending on the percentage of MWCNT. The effect of molecular weight also plays an important role. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1452–1466, 2009     

聚对苯二甲酸乙二醇酯/聚乙二醇醚插层嵌段共聚物的结晶性能

合成了不同用量、不同分子量的聚乙二醇醚(PEG)或聚丁二醇醚(PTMC)与聚对苯二甲酸乙二醇酯(PET)/蒙脱土(MMT)的嵌段共聚物。研究了MMT在共聚物中的分散状态及PEG或PTMG对PET/MMT插层聚合物结晶性能的影响。结果表明,MMT在共聚物中以纳米尺寸分散;加入PEG或PTMG增强了聚酯链段的柔顺性,使共聚物熔体降温过程的结晶温度提高,冷结晶温度降低,即插层嵌段共聚物的结晶速率提高;在合成的共聚物中,分子量为2000,用量为DMT的6%的PEG对插层共聚物结晶速率的促进作用最大     

Thermomechanical properties and crystallization behavior of layered double hydroxide/poly(ethylene terephthalate) nanocomposites prepared by in‐situ polymerization

Thermomechanical properties and crystallization behavior of poly(ethylene terephthalate) (PET) nanocomposites containing layered double hydroxide (LDH) were investigated. To enhance the compatibility between PET matrix and LDH, dimethyl 5‐sulfoisophthalate (DMSI) anion intercalated LDH (LDH‐DMSI) was synthesized by coprecipitation method, and its structure was confirmed by Fourier transform infrared (FTIR) spectrometer and X‐ray diffraction (XRD) measurements. Then, PET nanocomposites with LDH‐DMSI content of 0, 0.5, 1.0, and 2.0 wt% were prepared by in‐situ polymerization. The dispersion morphologies were observed by transmission electron microscopy (TEM) and XRD, showing that LDH‐DMSI was exfoliated in PET matrix. Thermal and mechanical properties, such as thermal stability, tensile modulus, and tensile yield strength of nanocomposites, were enhanced by exfoliated LDH‐DMSI nanolayers. However, elongation at break was drastically decreased with LDH loading owing to the increased stiffness and microvoids. The effect of exfoliated nanolayers, which acted as a nucleating agent confirmed by differential scanning calorimeter (DSC), on the microstructural parameters during isothermal crystallization, was analyzed by synchrotron small‐angle X‐ray scattering (SAXS). It is believed that nanocomposites could be crystallized more easily owing to the increased nucleation sites, which lead to the decrease of average amorphous region size and the long period with the increase of LDH‐DMSI content. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 28–40, 2007     

聚对二氧环己酮的合成及其结晶性能

以对二氧环己酮为原料,经开环聚合反应合成了聚对二氧环己酮（PPDO）。用DSC曲线研究了PPDO的非等温结晶以及非等温冷结晶性能。采用Ozawa方程拟合了PPDO的非等温结晶曲线。采用莫志深方程拟合了PPDO非等温冷结晶曲线。     

Influence of degree of intercalation on the crystal growth kinetics of poly[(butylene succinate)-co-adipate] nanocomposites

The influence of the degree of intercalation of polymer chains in the two dimensional silicate galleries on the crystallization behavior of poly[(butylene succinate)-co-adipate] (PBSA) is being reported on. The nanocomposites were prepared by melt-blending of PBSA and organically modified montmorillonite (OMMT) in a batch-mixer. Two different types of commercially available OMMTs, with different extents of miscibility of organic modifiers with PBSA, were used, leading to highly delaminated and stacked/intercalated nanocomposite structures as revealed by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) observations. The non-isothermal crystallization behavior of PBSA and the nanocomposite samples were studied by differential scanning calorimetry (DSC). Crystal growth kinetics studies showed that when silicate layers are highly delaminated into the PBSA matrix, nucleation behaviors decreased significantly, relative to the stacked/intercalated silicate layers. These observations indicate that the overall crystal growth kinetics retard in delaminated nanocomposites, opposed to increasing in the case of stacked/intercalated nanocomposites. Polarized optical microscopy (POM) observations and light scattering studies indicate that PBSA spherulites are fairly large and more perfectly grown in the case of delaminated nanocomposites, relative to the pure PBSA matrix. The effect of high levels of dispersion of silicate layers in the PBSA matrix on cold crystallization behavior was also studied.     

KINETICS OF NON-ISOTHERMAL CRYSTALLIZATION

A kinetic equation of non-isothermal crystamzation was derived by extending Avrami's equation to the non-isothermal situation. More crystallization information can be obtained from this kinetic equation. The curves of non-isothermal and isothermal crystallizations were analysed and compared for poly (ethylene terephthalate) (PET), and the results were discussed.