Isothermal Crystallization Process Research Articles

Relaxation dynamics and crystallization study of glass-forming chiral-nematic liquid crystal S,S-2,7-bis(4-pentylphenyl)-9,9-dimethylbutyl 9H-fluorene (5P-Am*FLAm*-P5)

.The chiral nematic S,S-2,7-bis(4-pentylphenyl)-9,9-dimethylbutyl9H-fluorene (5P-Am*FLAm*-P5) liquid crystal shows a complex phase diagram strongly dependent on thermal treatment as identified by Polarizing Optical Microscopy (POM) and differential scanning calorimeter (DSC). The molecular dynamics in various thermodynamics states was studied by means of broadband dielectric spectroscopy (BDS). The vitrification of a chiral nematic phase (N*) is manifested by a Vogel-Fulcher-Tammann (VFT)-type temperature dependence of structural relaxation time (tau_{alpha}). Three dielectric relaxation processes exhibiting Arrhenius-like thermal activation were found in conformationally disordered (condis) Cr1 and Cr2 structures. The isothermal cold crystallization process of Cr2 occurs in the metastable N* phase; however, in the non-isothermal experiments, the Cr2 phase is formed in the isotropic phase obtained on heating the metastable N* phase. The findings for the isothermal process were compared with those regarding non-isothermal crystallization.Graphical abstract

Beeswax and carnauba wax modulate the crystallization behavior of palm kernel stearin

There is limited literature on the modulation of fat crystallization by natural waxes, which are underutilized and cost-effective food industry resources. In this study, the effects of two natural waxes (beeswax (BW) and carnauba wax (CW)) on the crystallization behavior of palm kernel stearin (PKS85) were systematically investigated by using differential scanning calorimetry (DSC), pulsed nuclear magnetic resonance (p-NMR), X-ray diffraction (XRD) and polarized light microscope (PLM). CW addition significantly promoted the isothermal crystallization process of PKS85, especially at 20 °C, while BW had no obvious effect on the crystallization rate. BW and CW addition changed the crystal growth mode at 20 °C. BW and CW could participate in the crystallization of TAGs in PKS85, induce the formation of a new hydrocarbon chain distances of 3.70 and 4.15 Å and decrease the lamellar distance (d(001)) and domain size (ξ) of the single crystallites, leading to a different morphology of fat crystals. Our findings indicated that BW and CW could modulate the fat crystal structure and possibly engineer the functional properties of fats and fat-structured materials, which also provided new application of natural waxes in the food industry.

Temperature- and pressure-induced phase transitions of choline chloride-urea deep eutectic solvent

FT-IR spectroscopy has been used to decipher structural rearrangements in a choline chloride-urea (ChCl-Urea) deep eutectic solvent, as a function of temperature (−60–20 °C) at atmospheric pressure and as a function of pressure (0.1 MPa to 5.2 GPa) at room temperature. Under atmospheric pressure, the ChCl-Urea deep eutectic solvent (DES) underwent glass-to-crystal and crystal-to-liquid phase transitions during the heating process. However, at room temperature, with pressure increasing, the ChCl-Urea DES experienced liquid-liquid and liquid-crystal phase transitions at approximately 1.6 and 2.6 GPa. In addition, the partial breakage of intermolecular hydrogen bonds between ChCl and urea was observed during the isothermal crystallization process; however, intermolecular hydrogen bonding between two urea molecules was enhanced during the pressure-induced crystallization process. Consequently, urea could act as a “spacer” in the regular ChCl packing of ChCl-Urea DES cocrystals, and could regulate the intermolecular hydrogen bondings according to the competition among the complexed cations and anions in different crystallization environments.

Response to comment on “The irrelevance of phantom nuclei in crystallization kinetics: An integral equation approach”

In a recent article I have concluded that phantom nuclei are irrelevant for an isothermal crystallization process that consists of nucleation and spherical growth, and for the type of growth rates considered in my study. I illustrated phantom irrelevance by comparing two solutions of the crystallization formulation I introduced: the first one is a constant nucleation rate model, which can be represented by the Avrami equation and does not excludes phantoms; the second is a solution with a varying nucleation rate that is proportional to the fraction of untransformed material. I maintain that this latter case excludes phantoms. In a Comment on my article by Tomellini and Fanfoni it is claimed that my comparison is invalid. Their main argument is that a varying nucleation rate solution does not exclude phantoms. To refute this claim, I present arguments supporting my assertion that a phantom-excluding model can be obtained by introducing a nucleation rate proportional to the fraction of untransformed phase.

Study of crystallization behavior and kinetics of magnetic FeCoCrNiZr high entropy amorphous alloy

A new magnetic Fe36Co22Cr17Ni15Zr10 high entropy amorphous alloy has been prepared and its crystallization behavior and kinetics been studied. The results show that, under non-isothermal conditions, the crystallization activation energy Ex was calculated by the Kissinger equation, which yield 373 kJmol−1. Relation plot of Ex vs crystallization volume fraction(x) manifests the non-isothermal crystallization process is from difficult to easy. On the other hand, base on Arrhenius relation, the crystallization activation energy Ec under isothermal conditions was calculated to be 370 kJmol−1. Relation plot of Ec vs x manifests the isothermal crystallization process is from easy to difficult. The isothermal kinetics was modeled by Johnson-Mehl-Avrami(JMA) equation, as the isothermal annealing temperature increases, the nucleus growth mechanism from diffusion-controlled 3-D growth convert into interface-controlled 3-D growth. Though proper heat treatment, the saturation magnetization Ms of this alloy can reach up to 106.8A∙m2∙kg−1, it will become promising functional materials in the future.

Investigation of crystallization behavior of asymmetric PLLA/PDLA blend using Raman Imaging measurement

In the present study, isothermal crystallization of asymmetric PLLA/PDLA blend (4/1) at around 100 °C was investigated by in-situ time-resolved FTIR and Raman Imaging measurement. FTIR result indicated that crystallization of homo-crystal (HC) was retarded due to the formation of large amount of stereocomplex (SC) in the isothermal process. A unique spherulite morphology was observed through polarized optical microscopy (POM) and the distribution of SC and HC in and out of the big spherulite was revealed under the assistance of Raman imaging measurement. These results demonstrated that the SC crystal dispersed homogeneously both in the amorphous and spherulite region. However, the HC mainly located in the big spherulite area. A possible isothermal crystallization process for the asymmetric PLLA/PDLA blend was proposed.

The Influence of DMDBS on Crystallization Behavior and Crystalline Morphology of Weakly-Phase-Separated Olefin Block Copolymer.

Olefin block copolymer (OBC), with its low hard segments, can form unique space-filling spherulites other than confined-crystallization morphologies, mainly due to its weak phase-separation. In this work, 1,3;2,4-Bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), a well-known nucleating agent, was used to tailor the crystallization behavior and crystalline morphology of OBC. It was found that DMDBS can precipitate within an OBC matrix and self-assemble into crystalline fibrils when cooling from the melt. A non-isothermal crystallization process exhibited an increased crystallization rate and strong composition dependence. During the isothermal crystallization process, DMDBS showed a more obvious nucleating efficiency at a higher crystallization temperature. OBC showed typical spherulites when DMDBS was added. Moreover, a low addition of DMDBS significantly decreased the crystal size, while a large addition of DMDBS induced aggregates, due to the limited miscibility of DMDBS with OBC. The efficient nucleating effect of DMDBS on OBC led to an increased optical transparency for OBC/DMDBS composites.

Dynamical behaviors of polylactide crystallization

In this paper, we presented a detailed investigation on the dielectric relaxation behavior of amorphous PLLA, and analyzed the evolution of segmental relaxation dynamic during the isothermal cold- and melt-crystallization process of PLLA at different temperatures. The amorphous PLLA exhibits a segmental relaxation process and a dielectric normal relaxation process at the temperature from the glass transition temperature to the melting point of PLLA. For both melt- and cold-crystallized PLLA, it was found that the relaxation strength of the segmental relaxation process increases with temperature. A significant increase of α breadth and decrement of intensity with increasing crystallization temperature could be detected. The obtained results indicate the segmental dynamics of PLLA were not determined by crystallinity but by the degree of supercooling. The change trends of segmental evolution during the cold isothermal crystallization process are different from that during the melt isothermal crystallization process. The maximum loss frequency of segmental relaxation process of PLLA shifts to the lower frequency range continually during the cold crystallization, but it keeps almost unchanged during the melt crystallization process.

Crystallization Kinetics and Multiple Melting Behavior of Biodegradable Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Abstract The crystallization and melting behavior of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with 11 % 4HB content was investigated by differential scanning calorimetry (DSC), small and wide angle X-ray scattering (SAXS and WAXS). The Avrami analysis was performed to obtain the kinetic parameters of crystallization. The results showed that the Avrami equation was suitable for describing the isothermal and nonisothermal crystallization processes of P(3HB-co-4HB). Based on the values of the equilibrium melting temperature and the half-time of crystallization, its nucleation constant of crystal growth kinetics was obtained by using the Lauritzen-Hoffman model, which was found to be 1.92 × 105 K2, lower than that for pure PHB. During the subsequent heating process, quite different multiple melting behaviors were observed for P(3HB-co-4HB) crystallized isothermally or nonisothermally. The origins of the multiple melting behaviors were discussed based on either the presence of dual lamellar thicknesses or the melt-recrystallization mechanism. In general, the crystallization and melting behaviors were elucidated by this work.

Enthalpy of formation and disordering temperature of transient monotropic liquid crystals of poly(butylene 2,6-naphthalate)

Melt-crystallization of poly(butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages via intermediate formation of a smectic liquid crystalline phase (LC-phase). The transient LC-phase has been isolated by interruption of the isothermal crystallization process at 140 °C at sub-second timescale, and then its disordering was analyzed on heating at a rate of 2000 K/s, which suppresses the transition into α-crystals. The disordering temperature of the LC-mesophase is slightly lower than 200 °C, and as such 20–30 K lower than the melting temperature of α-crystals formed from the LC-phase at 140 °C. Analysis of the bulk enthalpy of formation of the LC-phase revealed that it covers only 20–25% of the total bulk enthalpy of crystallization, which is considered further proof of its smectic nature.

Cationic Cyclopentadienyliron Complex as a Novel and Successful Nucleating Agent on the Crystallization Behavior of the Biodegradable PHB Polymer.

Cationic cyclopentadienyliron (CpFe+) is one of the most fruitful organometallic moieties that has been utilized to mediate the facile synthesis of a massive number of macromolecules. However, the ability of this compound to function as a nucleating agent to improve other macromolecule properties has not been explored. This report scrutinizes the influence of the cationic complex as a novel nucleating agent on the spherulitic morphology, crystal structure, and isothermal and non-isothermal crystallization behavior of the Poly(3-hydroxybutyrate) (PHB) bacterial origin. The incorporation of the CpFe+ into the PHB materials caused a significant increase in its spherulitic numbers with a remarkable reduction in the spherulitic sizes. Unlike other nucleating agents, the SEM imageries exhibited a good dispersion without forming agglomerates of the CpFe+ moieties in the PHB matrix. Moreover, according to the FTIR analysis, the cationic organoiron complex has a strong interaction with the PHB polymeric chains via the coordination with its ester carbonyl. Yet, the XRD results revealed that this incorporation had no significant effect on the PHB crystalline structure. Though the CpFe+ had no effect on the polymer’s crystal structure, it accelerated outstandingly the melt crystallization of the PHB. Meanwhile, the crystallization half-times (t0.5) of the PHB decreased dramatically with the addition of the CpFe+. The isothermal and non-isothermal crystallization processes were successfully described using the Avrami model and a modified Avrami model, as well as a combination of the Avrami and Ozawa methods. Finally, the effective activation energy of the PHB/CpFe+ nanocomposites was much lower than those of their pure counterparts, which supported the heterogeneous nucleation mechanism with the organometallic moieties, indicating that the CpFe+ is a superior nucleating agent for this class of polymer.

Isothermal Crystallization Kinetics of Nylon 10T and Nylon 10T/1010 Copolymers: Effect of Sebacic Acid as a Third Comonomer

Nylon 10T and nylon 10T/1010 samples were synthesized by direct melt polymerization. The isothermal crystallization kinetics of nylon 10T and nylon 10T/1010 was investigated by means of differential scanning calorimetry (DSC). The crystallization kinetics under isothermal condition has been analyzed by the Avrami equation. It was found that the Avrami equation was well-suited to describe the isothermal crystallization kinetics, combined with the results of the Turnbull-Fisher equation. The values of T 0 and Kg were obtained by Hoffman-Weeks and Lauritzen-Hoffman equations, respectively. The activation energies for isothermal crystallization of nylon 10T and nylon 10T/1010 were determined using the Arrhenius equation and found to be -123.24 and -81.86 kJ·mol-1, respectively, which reveals that the crystallization ability of nylon 10T/1010 was lower than that of nylon 10T during the isothermal crystallization process. The crystal morphology was observed by means of polarized optical microscopy (POM) and X-ray diffraction (XRD). It was found that the addition of sebacic acid comonomer did not change the crystal form of nylon 10T, but significantly increased the number and decreased the size of spherulites.

Crystallization Behavior of Polyvinyl Alcohol with 1,2-Diol Side-Chains

Abstract The crystallization behavior of a newly developed polyvinyl alcohol with 1,2-diol side-chains (DPVA) was investigated for different 1,2-diol side-chain, magnesium acetate, and sodium acetate contents. Crystallization by stepwise cooling, isothermal and non-isothermal crystallization (the actual cooling process in melt molding) experiments were conducted. Upon crystallization analysis by stepwise cooling, the end surface energy of DPVA increased as the 1,2-diol side-chain content was increased. The isothermal crystallization process exhibited longer half crystallization times at high 1,2-diol side-chain and magnesium acetate contents. Upon Kissinger analysis of the non-isothermal crystallization results, the effect of the acetate salts was found to be smaller than that for isothermal crystallization, while the smaller number of repeating units in the lamellar structure, reflecting a higher side-chain 1,2-diol content, resulted in a smaller activation energy for DPVA crystallization. In addition, analyses by the Ozawa method and the Kissinger Plot suggested possible changes in the mode and dimension of the crystal growth of DPVA.

Study on electron beam cross‐linked ethylene‐tetrafluoroethylene copolymer‐insulated cables for aerospace applications: Mechanical performance, crystallization kinetics, and fluoride precipitation

The cross‐linking effects of cross‐linked ethylene‐tetrafluoroethylene copolymer (XETFE)‐insulated cables at different electron beam radiation doses were analyzed in this paper. Evaluation of the mechanical performance of the cables revealed that the highest tensile and breaking elongation was achieved at a radiation dose of 8 × 104 Gy and that XETFE had a good resistance to extreme electron beam irradiation. This is attributed to the cross‐linking effects induced by electron beam irradiation, and this takes full advantage of the strength of molecular chain crosslink to each other. The crystallization kinetics of XETFE at different electron beam radiation doses were studied in detail in terms of the non‐isothermal and isothermal crystallization processes. The results indicated that the crystallinity of the XETFE domain increased with an increase in the radiation dose as a result of heterogeneous nucleation. Moreover, the highest ΔEa was obtained, indicating that XETFE absorbed some energy at a radiation dose of 8 × 104 Gy. These kinetic parameters had help in carrying out a comprehensive evaluation of the performance of XETFE‐insulated cables for aerospace applications. Moreover, the fluoride precipitation observed in this study indicated that upon electron beam irradiation, XETFE could internally produce hydrogen fluoride, which is corrosive to metals. Thus, optimizing the radiation dose was necessary to achieve the desired performance. We could believe that the improvement for properties of electron beam XETFE insulation cables would expand their range of applications in the aerospace field.

Effect of WS₂ Inorganic Nanotubes on Isothermal Crystallization Behavior and Kinetics of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate).

Nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and tungsten disulfide inorganic nanotubes (INT-WS2) were prepared by blending in solution, and the effects of INT-WS2 on the isothermal crystallization behavior and kinetics of PHBV were investigated for the first time. The isothermal crystallization process was studied in detail using various techniques, with emphasis on the role of INT-WS2 concentration. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) showed that, in the nucleation-controlled regime, crystallization rates of PHBV in the nanocomposites are influenced by the INT-WS2 loading. Our results demonstrated that low loadings of INT-WS2 (0.1–1.0 wt %) increased the crystallization rates of PHBV, reducing the fold surface free energy by up to 24%. This is ascribed to the high nucleation efficiency of INT-WS2 on the crystallization of PHBV. These observations facilitate a deeper understanding of the structure-property relationships in PHBV biopolymer nanocomposites and are useful for their practical applications.

Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics.

In this study, the isothermal crystallization process of poly(l-lactide) (PLLA) has been investigated using in situ XRD, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Linear and nonlinear extrapolation methods have been deployed to estimate the equilibrium melting temperature (), which is used for analyzing the supercooling dependence of the PLLA spherulitic growth rate (G). A double-melting behavior observed for PLLA under crystallization Tc < 120 °C has been attributed to the formation of both α′ and α crystals. The values of both α′ and α crystals have been evaluated using the linear method (172.8 °C) and nonlinear method (196.4 °C), with the nonlinear estimate being 23.6 °C higher. A discontinuity in the temperature dependence of spherulite growth rate is observed around 128.3 °C. Regime II–III transition is found to occur at 128.3 °C when = 196.4 °C as estimated by the nonlinear extrapolation method.

Initial lamellar thickness dependency of recrystallization behavior of poly(4‐methyl‐1‐pentene)

ABSTRACTThe isothermal crystallization and subsequent melting process in semicrystalline poly(4‐methyl‐1‐pentene) were investigated via temperature‐dependent small‐ and wide‐angle X‐ray scattering and Flash DSC techniques. In a phase diagram of inversed crystalline lamellar thickness and temperature, the crystallization and melting lines can be described by two linear dependencies of different slopes and different limiting temperatures at infinite lamellar thickness. Upon subsequent heating, recrystallization lines with different slopes were observed for samples with different lamellar thickness, indicating changes in surface free energy difference between stabilized crystallites and mesomorphic phase. The surface free energy of native crystallites with extended‐chain conformation decreased with increasing lamellar thickness due to a more ordered surface region and less chain ends which changes cooperatively with mesomorphic phase. The surface free energy of stabilized crystallites remained unchanged for all lamellar thickness. Therefore, the recrystallization lines with different slopes are consequences of changes in surface free energy of mesomorphic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 219–224

Influence of graphene nanosheets on stereocomplex crystallization behaviors of star‐shaped poly (D(L)‐lactide) stereoblock copolymer

The nanocompsites of star‐shaped poly(D‐lactide)‐co‐poly(L‐lactide) stereoblock copolymers (s‐PDLA‐PLLA) with two‐dimensional graphene nanosheets (GNSs) were prepared by solution mixing method. Crystallization behaviors were investigated using differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction. The results of isothermal crystallization behaviors of the nanocompsites clearly indicated that the GNS could remarkably accelerate the overall crystallization rate of s‐PDLA‐PLLA copolymer. Unique stereocomplex crystallites with melting temperature about 207.0°C formed in isothermal crystallization for all samples. The crystallization temperatures of s‐PDLA‐PLLAs shifted to higher temperatures, and the crystallization peak shapes became sharper with increasing GNS contents. The maximum crystallization temperature of the sample with 3 wt% GNS was about 128.2°C, ie, 15°C higher than pure s‐PDLA‐PLLA. At isothermal crystallization processes, the halftime of crystallization (t0.5) of the sample with 3 wt% GNS decreased to 6.4 minutes from 12.9 minutes of pure s‐PDLA‐PLLA at 160°C.The Avrami exponent n values for the nanocomposites samples were 2.6 to 3.0 indicating the crystallization mechanism with three‐dimensional heterogeneous nucleation and spherulites growth. The morphology and average diameter of spherulites of s‐PDLA‐PLLA with various GNS contents were observed in isothermal crystallization processes by polarized optical microscopy. Spherulite growth rates of samples were evaluated by using combined isothermal and nonisothermal procedures and analyzed by the secondary nucleation theory. The results evidenced that the GNS has acceleration effects on the crystallization of s‐PDLA‐PLLA with good nucleation ability in the s‐PDLA‐PLLA material.

Entropy generation minimization for isothermal crystallization processes with a generalized mass diffusion law

Entropy generation minimization for a class of isothermal crystallization processes with a generalized mass diffusion law is investigated in this paper. For the given total mass of crystals, the optimality condition corresponding to the MEG (Minimum Entropy Generation) of the process is obtained firstly, and special cases for both the linear [g∝Δ(μ)] and the diffusive [g∝Δ(c)] mass diffusion laws are further derived. The optimization results are also compared with the two different mass diffusion strategies of CKCC (Constant Key Component Concentration) and CMDF (Constant Mass Diffusion Flux) operations. The results indicate that for the case with the linear law, the entropy generation rate for the MEG of the process keeps constant, and the total entropy generations for the strategies of CKCC and CMDF operations are equal to each other; while for the case with the diffusive law, the entropy generation rate for the MEG of the process decreases with the time, and the strategy of CMDF is superior to that of CKCC. The results can provide important guidelines for optimal design and operation of the crystallization processes in engineering.

Influences of the chemical defects on the crystal thickness and their melting of isothermally crystallized isotactic polypropylene

Ziegler-Natta and Metallocene Catalysis isotactic polypropylene with different chemical defects were isothermally crystallized at various crystallization temperatures. The crystal thickness and their corresponding melting behavior were studied using small angle X-ray scattering, atomic force microscopy, optical microscopy, and differential scanning calorimetry. The equilibrium melt temperature of the samples was calculated from the Hofmann-Weeks extrapolation for the supercooling. Two lamellar populations were distinctly observed in all cases during the crystallization process. Relatively thicker and stable lamellar crystals which melt at higher temperatures were observed with lowering the supercooling and found catalysis dependence in these crystals. During melting, no significant recrystallization of the samples has been detected for higher crystallization temperature where recrystallization processes enhance the lamellae thickness. The melting of the crystals has found strong dependence with the crystallization temperatures, the catalysis process and the nature of the defects present in the isotactic polypropylene. The increase of the crystal lamellae thickness and their melting temperature might be presumably related with the chain folding mechanism as well as the stability of the crystals formed during the isothermal crystallization process. A combined plot of SAXS and DSC results is demonstrated for the equilibrium melting temperature followed by critical analysis of the results.