Crystallization Of PET Research Articles

Controlling sandwich‐structure of PET microcellular foams using coupling of CO2 diffusion and induced crystallization

AbstractControlling sandwich‐structure of poly(ethylene terephthalate) (PET) microcellular foams using coupling of CO2 diffusion and CO2‐induced crystallization is presented in this article. The intrinsic kinetics of CO2‐induced crystallization of amorphous PET at 25°C and different CO2 pressures were detected using in situ high‐pressure Fourier transform infrared spectroscopy and correlated by Avrami equation. Sorption of CO2 in PET was measured using magnetic suspension balance and the diffusivity determined by Fick's second law. A model coupling CO2 diffusion in and CO2‐induced crystallization of PET was proposed to calculate the CO2 concentration as well as crystallinity distributions in PET sheet at different saturation times. It was revealed that a sandwich crystallization structure could be built in PET sheet, based on which a solid‐state foaming process was used to manipulate the sandwich‐structure of PET microcellular foams with two microcellular or even ultra‐microcellular foamed crystalline layers outside and a microcellular foamed amorphous layer inside. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2512–2523, 2012

Preparation and Characterization of Polyethylene Terephthalate)/Boehmite Nanocomposites

The morphology, flame retardancy and non-isothermal crystallization behaviour of pure PET and poly(ethylene terephthalate)/nano-boehmite composites (PET/AlOOH) prepared in situ were characterized using several techniques. The morphology of the nanocomposites carried out using transmission electron microscopy (TEM) showed that the nano-boehmite particles were uniformly dispersed in the polymer matrix and formed crosslinked structures. Combustion behaviour and flammability were assessed using cone calorimetry (CONE). The results indicated that the total heat release (THR) and smoke production rate of PET/AlOOH were significantly less than those of pure PET. Study of the behaviour and kinetics of non-isothermal crystallization of pure PET and PET/AlOOH nanocomposites was accomplished by DSC analysis. The results showed that the AlOOH could act as an effective nucleation agent for the crystallization of PET, while the presence of boehmite decreased the crystallization rate and extended the time of crystallization of PET, which can be explained by the formation of partly-crosslinked structure of PET/AlOOH nanocomposites.

Non-Isothermal Crystallization Behavior of Poly(Ethylene Terephthalate)/Carbon Black Composite

Poly(Ethylene Terephthalate)(PET)/carbon black(CB) composite was prepared by melt blending using a separate feeding technique. The non-isothermal crystallization process of virgin PET and PET/CB composite were investigated by differential scanning calorimetry (DSC) and the different methods such as Jeziorny modified Avrami equation, Ozawa equation and the method developed by Mo were employed to analyze the non-isothermal kinetics of virgin PET and PET/CB composite. The results show that the CB particles dispersed in PET matrix act as heterogeneous nucleating agents, while CB particles hinder the movement of molecular chains of PET, meanwhile, the crystallization activation energy(⊿E) of PET/CB composite is much greater than that of virgin PET according to Kissinger formula, which is opposite to the low CB content condition. This indicates that CB particles reduce the rate of crystal growth. Whereas, the results obtained from the mentioned three methods simultaneously demonstrate the addition of CB greatly increases crystallization temperature and crystallinity and accelerates crystallization rate. Taking the two seemingly contradictory results, crystal growth has little effect on the crystallization rate and crystal nucleation dominate the crystallization process of PET/CB composite with very high CB content. According to Jeziorny method, the constant of crystallization rate (Zc) increases with the increment of cooling rate and Avrami index (n) doesn’t change significantly, but the Zc and n of PET/CB composite are greater than that of PET. Based on Ozawa method, lg[-ln(1-Xt)] and lgR don’t show a good linear relationship. The parameter F(T) increases significantly with the increasing of relative crystallinity and n is almost unchanged. Besides, the F(T) of PET/CB composite is less than that of PET, while a is greater than that of PET. Comparing with Ozawa and Avrami equation, Mo method can better describe the non-isothermal crystallization of PET and PET/CB composite.

Nonisothermal cold crystallization of poly(ethylene terephthalate)

Abstract

Reinvestigation of the M Emission Spectrum of Uranium-92

The M spectrum of the element uranium was reinvestigated by using both high-resolution wavelength dispersive (WD) spectrometry as well as energy dispersive (ED) spectrometry. Thereby we observed relative intensities that deviate from data in the literature. These discrepancies were not only observed for the weak U M lines but also for major lines. By measuring the Mα,β region of the spectrum with a PET crystal in second-order reflection, a sufficient energy resolution was achieved to separate Mα(2) (M(5)N(6)) from Mα(1) (M(5)N(7)). The intensity ratio I(M(5)N(6))/I(M(5)N(7)) was determined to be approximately 5%, which is in strong contrast to the data tabulated by White and Johnson [White, E.W. & Johnson, G.G. (1970). X-Ray and Absorption Wavelengths and Two-Theta Tables. ASTM Data Series DS37A, 2nd ed. Philadelphia, PA: American Society for Testing and Materials]. Furthermore M(5)N(7) was clearly observed as the strongest of the M lines that disagrees with data presented by Kleykamp [Kleykamp, H. (1981). Wavelengths of the M X-ray spectra of uranium, neptunium, plutonium, and americium. Z Naturforsch 36a, 1388-1390], who reported Mβ (M(4)N(6)) as the strongest line. Also, after White and Johnson (1970), the line M(2)N(4) should be more intense than M(3)O(5) by a factor of 5. Both our WD and ED spectra show clearly that M(3)O(5) is stronger than M(2)N(4). Altogether, we observed in our WD spectra 26 M lines. In some cases untypical large differences between the line energies given by Bearden [Bearden, J.A. (1967). X-ray wavelengths. Rev Mod Phys 39, 78-124] and measured by us were observed.

Influence of Transesterification on the Properties of PET/MAPE Blends Prepared by Reactive Extrusion

Blends based on maleic anhydride grafted polyethylene (MAPE) and poly(ethylene terephthalate)(PET) were prepared through reactive extrusion in the presence of titanium tetrabutoxide (Ti(OBu)4) as transesterification catalyst. Mechanical properties of PET/MAPE blends(70wt./30wt.) were evaluated by mechanical tests. The Effects of Ti(OBu)4 on the structure and melt crystallization behavior of the blends were investigated by Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The addition of Ti(OBu)4 to the blends could improve the compatibility between PET and MAPE as was evidenced by the SEM micrograph in which filaments connected to a network structure was observed. With increasing the contents of Ti(OBu)4, the impact strength of the blends increased obviously, the flexural strength and tensile strength of blends did not change significantly, while the degradation of PET was gradually significant as was evidenced by FTIR analysis. Small amount of Ti(OBu)4 could hinder the crystallization of PET and make its melt peak shifted to higher temperature.

Coupling between Crystal Melting and Rigid Amorphous Fraction Mobilization in Poly(ethylene terephthalate)

A thorough analysis of the melting behavior of poly(ethylene terephthalate) (PET) is detailed in this contribution. Isothermal crystallization at 190 °C followed by cooling to room temperature provides a three-phase structure composed of a mobile amorphous, a crystalline, and a rigid amorphous fraction. A close connection between multiple melting and devitrification of the rigid amorphous fraction in PET is revealed by conventional and temperature-modulated calorimetry. Rearrangements of PET crystals at high temperatures involve recrystallization/annealing/crystal perfection following partial melting, which can occur only if the amorphous chain portions coupled to the crystal/melt phase boundary have sufficient mobility. Such mobility can be achieved above the glass transition of the amorphous chain segments coupled with the just-melted crystals. Combined analysis of the reversing heat capacity monitored during quasi-isothermal modulation with the thermal properties of the resulting structure suggests tha...

Nonisothermal melt crystallization kinetics of poly(ethylene terephthalate)/Barite nanocomposites

AbstractPoly(ethylene terephthalate) (PET)/Barite nanocomposites were prepared by direct melt compounding. The nonisothermal melt crystallization kinetics of pure PET and PET/Barite nanocomposites, containing unmodified Barite and surface‐modified Barite (SABarite), was investigated by differential scanning calorimetry (DSC) under different cooling rates. With the addition of barite nanoparticles, the crystallization peak became wider and shifted to higher temperature and the crystallization rate increased. Several analysis methods were used to describe the nonisothermal crystallization behavior of pure PET and its nanocomposites. The Jeziorny modification of the Avrami analysis was only valid for describing the early stage of crystallization but was not able to describe the later stage of PET crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PET. A combined Avrami and Ozawa equation, developed by Liu, was used to more accurately model the nonisothermal crystallization kinetics of PET. The crystallization activation energies calculated by Kissinger, Takhor, and Augis‐Bennett models were comparable. The results reveal that the different interfacial interactions between matrix and nanoparticles are responsible for the disparate effect on the crystallization ability of PET. POLYM. COMPOS., 31:1504–1514, 2010. © 2009 Society of Plastics Engineers

Crystallization and Mechanical Properties of Recycled Poly(ethylene terephthalate) Toughened by Styrene–Ethylene/Butylenes–Styrene Elastomer

Recycled poly(ethylene terephthalate) (R-PET) was blended with 15–30 wt% of styrene–ethylene/butylenes–styrene (SEBS) block copolymer and maleic anhydride grafted SEBS (SEBS-g-MA). Effects of nucleation and toughening of the elastomers were evaluated systematically by study of morphology, crystallization, thermal and mechanical properties of the blend. The addition of 30 wt% SEBS promoted the formation of co-continuous structure of the blend and caused the fracture mechanism to change from strain softening to strain hardening. Addition of SEBS-g-MA resulted in significant modification of phase morphology and obviously improved the impact strength. The compatibilization reaction of PET with SEBS-g-MA accelerated the crystallization of PET and increased the crystallinity. The shifts in glass transition temperature of PET towards that of SEBS-g-MA and the higher modulus for R-PET/SEBS-g-MA (70/30) blend found by DMA are also indications of better interactions under the conditions of compatibilization and interpenetrating structure.

Morphology development and crystallization behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The spherulite morphology and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). The thermal analysis showed that PET and PTT were miscible in the melt over the entire composition range. The rejected distance of non-crystallizable species, which was represented in terms of the parameter δ, played an important role in determining the morphological patterns of the blends at a specific crystallization temperature regime. The parameter δ could be controlled by variation of the composition, the crystallization temperature, and the level of transesterification. In the case of two-step crystallization, the crystallization of PTT commenced in the interspherulitic region between the grown PET crystals and proceeded until the interspherulitic space was filled with PTT crystals. The spherulitic surface of the PET crystals acted as nucleation sites where PTT preferentially crystallized, leading to the formation of non-spherulitic crystalline texture. The SALS results suggested that the growth pattern of the PET crystals was significantly changed by the presence of the PTT molecules. The lamellar morphology parameters were evaluated by a one-dimensional correlation function analysis. The blends that crystallized above the melting point of PTT showed a larger amorphous layer thickness than the pure PET, indicating that the non-crystallizable PTT component might be incorporated into the interlamellar region of the PET crystals. With an increased level of transesterification, the exclusion of non-crystallizable species from the lamellar stacks was favorable due to the lower crystal growth rates. As a result, the amorphous layer thickness of the PET crystals decreased as the annealing time in the melt state was increased.

SU‐GG‐J‐145: PET Image Simulation of Isotopes Produced in Patient during Proton Therapy

Introduction — During proton therapy, positron emitting radio‐isotopes are produced along the track where incident proton beam interacts with human tissue. The isotope activity profile is related to the proton dose distribution and can be imaged using a PET scanner. Many factors affect the obtained PET images, such as various patient geometry, time interval between proton therapy and PET scan, the PET scan duration, and PET scanner design. In order to quantitatively relate the obtained PET image to the dose delivered in patient, an understanding of these factors in the PET image is necessary. This work is to develop a simulation pathway to facilitate such study. Method — The simulation starts with proton beam irradiating the patient geometry, obtains isotopes distribution, records in list‐mode gammas from positron annihilations arriving at PET ring geometry, and finally reconstructs the PET images. The patient DICOM CT are input to GEANT4 code to construct the geometry. Experimental isotope cross‐section data are built into the simulation. The positron emitter 3D map is used as the source in the PET scanner simulation. The PET scanner geometry, crystal detector type and its cross‐section are the input parameters. The received signals in PET crystals are output in list‐mode. Image reconstruction is performed with iterative TOF image reconstruction together with data corrections for scatter and attenuation. Results — The 3‐D proton dose and isotope distributions are obtained. The reconstructed isotope distribution from PET simulation correlates with the original isotope map generated from proton beam irradiation. Some of the factors affecting the obtained PET images will be addressed. In the future, the simulation can be used to quantitatively correlate to the proton dose. It can also facilitate the design of a PET system that can yield an accurate and efficient reconstruction of the isotope activities and verify the proton dose.

Isothermal crystallization kinetics of anhydrous sodium acetate nucleated poly(ethylene terephthalate)

AbstractStudies on the isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nucleated with anhydrous sodium acetate were carried out. The nucleated agent had succeeded in promoting greater rates of crystallization in PET. A study of the melting behavior of the samples revealed that the nucleating agents promoted formation of thinner lamellae. The equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman Weeks procedure. The nonlinear Hoffman Week's procedure was found to be inapplicable in the current study. The Lauritzen‐Hoffman secondary nucleation theory was applied to determine the nucleation parameter (Kg), fold surface energy (σe), and work of chain folding (q). σe and q decreased on addition of nucleating agent. The approximate and exact form of the Lauritzen Z‐test was used to determine the operating regime. The operating regime was found to be primarily regime II for the range of temperatures studied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

X-ray polarization measurement of the Beamline 4B7 of Beijing synchrotron radiation facility using a PET crystal

An experimental method has been developed to measure the X-ray polarization of the Beamline 4B7 on Beijing Synchrotron Radiation Facility in the X-ray energy range 2100–5600 eV by using a PET crystal diagnostic system and rotating the system around the incident X-ray beam by 90°. The experimental results show that the measured X-ray polarization is more than 0.88 in the photon energy range 2100–3600 eV with maximum of 0.99 at 2707.3 eV, and quickly decreases to about 0.38 at 4719.2 eV with photon energy increasing from 3600 to 4719.2 eV, then it keeps almost constant as the photon energy increases further to 5600 eV.

Plasma treatment‐induced fluorine‐functionalized multi‐walled carbon nanotubes to modify poly(ethylene terephthalate) obtained via in situ polymerization

AbstractThe introduction of carbon nanotubes in a polymer matrix can markedly improve its mechanical properties and electrical conductivity, and much effort has been devoted to achieve homogeneous dispersions of carbon nanotubes in various polymers. Our group previously performed successfully fluorine‐grafted modification on the sidewalls of multi‐walled carbon nanotubes (MWCNTs), using homemade equipment for CF4 plasma irradiation. As a continuation of our previous work, in the present study CF4 plasma‐treated MWCNTs (F‐MWCNTs) were used as a nanofiller with poly(ethylene terephthalate) (PET), which is a practical example of the application of such F‐MWCNTs to prepare polyester/MWCNTs nanocomposites with ideal nanoscale structure and excellent properties. As confirmed from scanning electron microscopy observations, the F‐MWCNTs could easily be homogeneously dispersed in the PET matrix during the in situ polymerization preparation process. It was found that a very low content of F‐MWCNTs dramatically altered the crystallization behavior and mechanical properties of the nanocomposites. For example, a 15 °C increase in crystallization temperature was achieved by adding only 0.01 wt% F‐MWCNTs, implying that the well‐dispersed F‐MWCNTs act as highly effective nucleating agents to initiate PET crystallization at high temperature. Meanwhile, an abnormal phenomenon was found in that the melt point of the nanocomposites is lower than that of the pure PET. The mechanism of the tailoring of the properties of PET resin by incorporation of F‐MWCNTs is discussed, based on structure–property relationships. The good dispersion of the F‐MWCNTs and strong interfacial interaction between matrix and nanofiller are responsible for the improvement in mechanical properties and high nucleating efficiency. The abnormal melting behavior is attributed to the recrystallization transition of PET occurring at the early stage of crystal melting being retarded on incorporation of F‐MWCNTs. Copyright © 2009 Society of Chemical Industry

Thermal properties and morphologies of poly(ethylene terephthalate) in blends with epoxidised natural rubber of 25 and 50 mol.-% of epoxy content

Thermal properties and morphologies for polymer blends of poly(ethylene terephthalate) (PET) and epoxidised natural rubber with 25 mol.-% (ENR-25) and 50 mol.-% (ENR-50) epoxy contents were studied using differential scanning calorimeter (DSC) and polarising optical microscope (POM) respectively. The blends were prepared by precipitation method. Immiscibility of the components is revealed by observation of two glass transition temperatures Tg that correspond to that of the neat constituents. Equilibrium melting points Tom of PET in blends was determined by applying Hoffman–Weeks stepwise annealing procedure. The degree of crystallinity of PET in blends with ENR-25 remains constant, whereas the authors observe an increase in the degree in blends with ENR-50. The rate of crystallisation of PET in blends is characterised by the reciprocal halftime t–10·5. It displays an Arrhenius-like behaviour with respect to temperature and it stays constant at isothermal crystallisation temperature (Tc=constant) as long as PET is in excess. Rate of crystallisation of PET in the blends decreases exponentially as the Tc increases. Dispersed phases of ENR-25 and ENR-50 in the matrix of PET can be observed when the content of PET is in excess.

Nonisothermal Crystallization Behaviors of Flame-Retardant Copolyester/Montmorillonite Nanocomposites

In order to obtain poly(ethylene terephthalate) (PET) engineering plastics with good flame retardancy, heat resistance, and mechanical properties, a novel phosphorus-containing copolyester (PET-co-DDP)/organo-montmorillonite (OMMT 1%) nanocomposite (PET-co-DDP/OMMT) was prepared by in situ intercalating polymerization. Nonisothermal crystallization kinetics and nanoscale morphology of this composite have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Based on the results of the nonisothermal crystallization kinetics, the flame-retardant copolyester PET-co-DDP has a lower crystallization rate than pure PET, while PET-co-DDP/OMMT nanocomposite has a higher crystallization rate than pure PET. Based on the Augis and Bennett method, the activation energies for nonisothermal crystallization of pure PET, PET-co-DDP, and PET-co-DDP/OMMT nanocomposite were evaluated as 101, 138, and 76 kJ mol−1, respectively. All the evidence shows that PET-co-DDP strongly influences the crystallization behavior because of its irregular chain structure, while the addition of nanoscale OMMT to this copolymer can significantly enhance the crystallization rate owing to its remarkable nucleating effect. An understanding of the above crystalline behaviors will be beneficial in preparing PET engineering plastics with good overall comprehensive performance.

Molecular weight dependence of fiber structure development in the laser drawing of poly(ethylene terephthalate) fibers

AbstractThe effect of molecular weight on fiber structure development during the continuous neck‐drawing of the amorphous poly(ethylene terephthalate) (PET) fiber was investigated by fiber temperature measurements and online WAXD analysis. The fiber temperature was also simulated using the energy balance equation. The simulated temperature increased differently with molecular weight immediately after the neck point, while the measured temperature showed no difference. The difference in the simulated temperature was caused by the potential energy increase with increasing molecular weight, which would result in a retardation effect in the initial stage of fiber structure development. Online X‐ray measurements were carried out with a time resolution of 0.5 ± 0.06 ms. A two‐dimensionally ordered mesophase was formed within 1 ms after the neck point and developed into a microfibrillar structure. The time required for the disappearance of the two‐dimensionally ordered structure increased with increasing molecular weight, leading to a retardation effect. No molecular weight dependence was observed in the rate of transformation from the two‐dimensionally ordered structure to the PET crystal. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1653–1665, 2009

Antinucleating action of polystyrene on the isothermal cold crystallization of poly(ethylene terephthalate)

AbstractThe effect of polystyrene (PS) on the kinetics of the cold crystallization of poly(ethylene terephthalate) (PET) was thoroughly investigated. The PET/PS blends were essentially immiscible, as observed by dynamic mechanical thermal analysis, which showed two distinct glass‐transition temperatures, and by scanning electron microscopy. The neat PET and its blends were isothermally cold‐crystallized at various temperatures, and the kinetic parameters were determined with the Avrami approach. PET and its blends presented values of the Avrami exponent close to 2, and the kinetic constant increased with the crystallization temperature increasing. For all the crystallization temperatures studied, the presence of only 1 wt % PS significantly reduced the rate of cold crystallization of PET. A further increase in the PS concentration did not show any significant influence. The blends presented higher values of the activation energy for cold crystallization, which was estimated from Arrhenius plots. The equilibrium melting temperature of neat PET was determined on the basis of the linear Hoffman–Weeks extrapolative method to be ∼ 255°C. This value decreased in the presence of PS, and this suggested limited solubility between PET and PS. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter was obtained, and it was shown to be higher for the neat PET than for the blends. Moreover, a transition of regimes (I → II) was observed in both PET and its blends. From the investigations conducted here, it is clear that PS in small amounts causes a reduction in the rate of PET crystallization, acting as an antinucleating agent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

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

AbstractA 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

Effect of Clay Content and Speed Screw Rotation on the Crystallization and Thermal Behaviors of Recycled PET/Clay Nanocomposites

Nanocomposites of recycled poly(ethylene terephthalate) (rPET) containing 2.5 wt% and 5.0 wt% of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a co-rotating twin-screw type extruder with two organoclay contents were used: 2.5 wt% and 5.0 wt% and were prepared using two different rotation speeds: 150 and 250 rpm. Thermal characterization (analysis) of the nanocomposites was performed using differential scanning calorimetry (DSC) analysis. The results from DSC measurements showed that the addition of organoclay affects recycled PET's crystallization for two screw rotation speeds studies. The nucleating effect of organoclay was investigated. Morphological analysis using Transmission Electron Microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm.