Melt Crystallization Process Research Articles

Temperature and shear rate distributions of gas‐assisted injection molded (GAIM) polypropylene and the application in forecast of cooling time

ABSTRACTAn umbrella handle product of polypropylene molded by gas‐assisted injection molding (GAIM) was studied from both aspects: theoretical modeling and simulation as well as in situ temperature measurement. The simulation was primarily through the use of the commercial software Moldflow (version 6.1) coupled with enthalpy transformation method (ETM) in an attempt to investigate the shear rate and temperature fields during GAIM process. A four‐parameter model (FPM) was used to nonlinearly fit the temperature decays during the GAIM cooling stage on the basis of a three‐parameter model (TPM) raised previously in our group. The FPM showed perfect fitting effect as well as presented fairly acceptable cooling time (tc) prediction in comparison to experimental data, which could better reflect the nature of crystalline polymers during melt crystallization process. The understanding of the shear rate and temperature fields would be of practical importance to the further research on relationship of “processing–structure–property” as well as the optimization of cooling parameters for industrial GAIM operations of crystalline polymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47390.

Synthesis and Formation Mechanism of All-Organic Block Copolymer-Directed Templating of Laser-Induced Crystalline Silicon Nanostructures.

This report describes the generation of three-dimensional (3D) crystalline silicon continuous network nanostructures by coupling all-organic block copolymer self-assembly-directed resin templates with low-temperature silicon chemical vapor deposition and pulsed excimer laser annealing. Organic 3D mesoporous continuous-network resin templates were synthesized from the all-organic self-assembly of an ABC triblock terpolymer and resorcinol-formaldehyde resols. Nanosecond pulsed excimer laser irradiation induced the transient melt transformation of amorphous silicon precursors backfilled in the organic template into complementary 3D mesoporous crystalline silicon nanostructures with high pattern fidelity. Mechanistic studies on laser-induced crystalline silicon nanostructure formation revealed that the resin template was carbonized during transient laser-induced heating on the milli- to nanosecond timescales, thereby imparting enhanced thermal and structural stability to support the silicon melt-crystallization process at temperatures above 1250 °C. Photoablation of the resin material under pulsed excimer laser irradiation was mitigated by depositing an amorphous silicon overlayer on the resin template. This approach represents a potential pathway from organic block copolymer self-assembly to alternative functional hard materials with well-ordered 3D morphologies for potential hybrid photovoltaics, photonic, and energy storage applications.

Isothermal crystallization of poly(glycolic acid) studied by terahertz and infrared spectroscopy and SAXS/WAXD simultaneous measurements

Isothermal crystallization of poly(glycolic acid) (PGA) has been studied using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. Changes in the intermolecular interactions in PGA during the isothermal crystallization were monitored using THz spectroscopy, which is an efficient technique for analyzing the higher-order structure of polymers. In the THz spectra, the temporal difference in the intensity observed in the isothermal crystallization is due to the difference in the vibrational origins of two bands at 192 and 65 cm−1. The band at 192 cm−1 primarily originates from the intramolecular vibrational mode (twisting of the local structure of the PGA molecular chain). Furthermore, the band at 65 cm−1 exists due to the intermolecular vibration mode (C = O···H-C hydrogen bonds between polymer chains). In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks. When a lamellar structure is formed and the molecular chains are oriented, the THz band originating from the intermolecular vibration is observed. It is highly possible that the intermolecular vibration appearing in the THz spectra requires the molecular chains to be oriented. Isothermal crystallization of poly(glycolic acid) (PGA) was carried out using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. The intensity of the absorption peak at 192 cm−1 increased before the increase in intensity of the peak at 65 cm−1 during the isothermal melt-crystallization process at 185 °C. This is due to a difference in the vibrational origins of these two bands. In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks

Investigating the Physical Properties of Poly(L-lactic acid) Modified Using an Aromatics Succinic Dihydrazide Derivative

In order to overcome the defect of slow crystallization rate of Poly(L-lactic acid) (PLLA) during manufacturing, a new organic nucleating agent, N,N'-succinic bis(hydrocinnamic acid) dihydrazide (BHSH), was synthesized to evaluate its influence on the crystallization and other physical properties of PLLA in this work. For this purpose, the non-isothermal crystallization, isothermal crystallization of PLLA modified using BHSH were investigated using differential scanning calorimetry and depolarized-light intensity measurement. Additionally, the melting behavior, thermal stability, and optical property of BHSHnucleated PLLA were further studied. The result of the non-isothermal crystallization behavior indicated that BHSH had a distinct accelerating effect for the melt crystallization process of PLLA and the non-isothermal crystallization peak shifted to the higher temperature and became sharper. Meantime, non-isothermal crystallization result further revealed that both the cooling rate and the final set melting temperature affected the non-isothermal crystallization behavior of PLLA. The addition of BHSH could cause the crystallization halftime of PLLA to become shorter, meaning that PLLA/BHSH samples had a faster overall crystallization rate comparing with the pure PLLA. Upon the addition of 2 wt% BHSH, the crystallization half-time of PLLA/BHSH decreased from 575.7 s to the minimum value 48.6 s at 100°C. Melting behavior after crystallization further confirmed the crystallization promoting effect of BHSH for PLLA, and the double-melting peaks were attributed to the melting-recrystallization. Although that the BHSH could improve the crystallization of PLLA, unfortunately, the presence of BHSH decreased the thermal stability and light transmittance of PLLA.

The effect of N,N’-bis(benzoyl)dodecanedihydrazide on enhancing the crystallizationrate of poly(L-lactic acid)

The effect of N,N’-bis(benzoyl)dodecanedihydrazide (BADH) as a newly-developed organic nucleating agent on the crystallization process of poly(L-lactic acid) (PLLA) was examined in this study. Non-isothermal crystallization results indicated that BADH had excellent acceleration effects on the melt-crystallization of PLLA, and a larger proportion of BADH promoted more powerful crystallization. However, BADH inhibited the crystal growth of PLLA during the cold-crystallization process, and an increase of BADH concentration caused the non-isothermal crystallization peak to shift towards a higher temperature and become much wider. Although increased cooling rates might decrease nuclei density, it was surprising to see that BADH contents of 2 wt % to 3 wt % were able to accelerate the crystallization of PLLA upon fast cooling at 20 °C/min or even higher cooling rates. Besides, the effect of the final melting temperature on the melt-crystallization process of PLLA was not negligible, the relevant results implied that 190 °C was the optimal blending temperature of PLLA and BADH. Isothermal crystallization showed that, in the best case of the PLLA/3% BADH sample, the half-time of crystallization has a minimum value of 22.9 s at 115 °C. The calculation of frontier molecular orbital energies confirmed that the interaction between PLLA and BADH could form more easily during the melting blend than PLLA itself, indicating that the probable nucleating mechanism was chemical nucleation.

Interplay between Crystallization and Glass Transition in Nematic Liquid Crystal 2,7-Bis(4-pentylphenyl)-9,9-diethyl-9 H-fluorene.

This article presents the crystallization behavior and molecular dynamics of the supercooled nematic state of the newly synthesized liquid crystal 2,7-bis(4-pentylphenyl)-9,9-diethyl-9 H-fluorene (5P-EtFLEt-P5) studied by means of broadband dielectric spectroscopy (BDS). 5P-EtFLEt-P5 is a fragile glass-forming system with a high fragility parameter ( mf ≈ 121). The study compares the isothermal melt- and cold-crystallization processes at several selected temperatures Tc in the vicinity of the glass-transition temperature Tg (1.07 Tg ≤ T ≤ 1.17 Tg). Our findings reveal that at low temperatures, the crystallization of the Cr1 phase from the nematic melt state occurs more quickly than the cold crystallization. The dimensionality of the growing crystallites ( n) was found to be slightly higher for the cold- than for the melt-crystallization process, varying from n ∼ 5 to n ∼ 3 with increasing temperature. Our experimental results are discussed in terms of dynamic and thermodynamic properties of the material. The study also uses polarized optical microscopy to investigate the isothermal secondary cold crystallization (the formation of Cr2 from Cr1 upon heating), which is inaccessible by BDS measurements because of its very fast crystallization rates.

High-Temperature Metamorphism, Anataxis and Tectonic Evolution of a Mafic Granulite from the Eastern Himalayan Orogen

The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, metamorphic and anatectic conditions and timescales of meta-mafic rocks in the Greater Himalayan Sequences (GHS) in the east-central Himalaya remain controversial. In this paper, we conduct a study of petrology and geochronology of mafic granulite from the Eastern Himalayan Syntaxis (EHS). The mafic granulite with abundant leucosome bands occurs as layers within felsic granulites and is well deformed. The granulite consists of garnet, plagioclase, amphibole and quartz with minor clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite. The garnet has growth compositional zoning and contains abundant mineral inclusions in its core. Peak metamorphic mineral assemblage of the granulite is garnet, amphibole, plagioclase, quartz, clinopyroxene and rutile, recording a high-pressure (HP) and high-temperature (HT) peak-metamorphism under conditions of 14–15.5 kbar and 780–790 °C in the presence of melt. The reconstructed clockwise P-T path is characterized by an early heating and burial prograde metamorphism, and late isothermal and cooling decompression retrogression. The granulite witnessed a long lasting HT metamorphism, partial melting and melt crystallization process which began at ca. 39 Ma and lasted to ca. 11 Ma. The present study shows that various high-grade rocks of the GHS in the EHS core experienced similar metamorphic conditions and P-T-t paths, indicating that they occurred as a coherent slab during the subduction and exhumation of Indian lithosphere. The significant melts generated during the prograde metamorphism of the GHS rocks not only contributed to the formation of the Himalayan leucogranite, but also resulted in the rheological weakening and ductile flow of the thickened lower crust of the Himalayan Orogen.

Epitaxial Crystallization of Isotactic Poly(methyl methacrylate) from Different States on Highly Oriented Polyethylene Thin Film.

Through fixing the orientation of oriented polyethylene (PE) thin film during melt-recrystallization with the help of a vacuum evaporated thin carbon layer, the isothermal melt- and cold-crystallization of isotactic poly(methyl methacrylate) (iPMMA) on oriented PE substrate was studied. The results show that same parallel chain epitaxy of iPMMA on the oriented PE substrate takes place in both cold- and melt-crystallization processes based on a two-dimensional lattice matching. However, the crystallization kinetics in the two processes is quite different. The induction time of iPMMA during melt-crystallization is significantly longer than during cold-crystallization (11 h vs 2.5 h). This is related to the different nucleation mechanism for cold- and melt-crystallization processes. On the other hand, the crystal growth rate of iPMMA from melt is much higher than from glassy solid state. This is associated with a higher molecular chain mobility of iPMMA in supercooled melt than in the frozen amorphous solid film.

A-type Medina batholith and post-collisional anatexis in the Araçuaí orogen (SE Brazil)

The Medina batholith and its host granitic migmatites record intriguing plutonic processes in the northern Araçuaí orogen (SE Brazil). This orogen shows a long lasting (630–480 Ma) succession of granite production events from the earliest pre-collisional plutons to the latest post-collisional intrusions. The Medina batholith includes granite intrusions ascribed to the post-collisional stage. They show high alkali and halogen contents, low CaO (at SiO2 = 71%: Na2O + K2O = 7 to 9%; CaO = 1.6%), and high FeOt/(FeOt + MgO) ratios (0.78 to 0.92). The Medina granites are metaluminous to weakly peraluminous, with ASI (molecular ratio Al/(Ca-1.67P + Na_K)) values of 1.76 to 2.07, and have high concentrations of high field strength elements (Zr + Nb + Ce + Y > 700 ppm), as well as high Ga/Al ratios. Accordingly, the Medina intrusions are typical ferroan A-type granites. UPb ages from zircon (501 ± 2 Ma) and monazite (497 ± 2 Ma) constrain the emplacement timing of the Medina batholith. Surprisingly, all monazite ages from host rocks also cluster around 500 Ma, despite their nature and distance from the batholith, suggesting that they would have shared a same thermal process. The studied host rocks are granitic migmatites varying from patch metatexite to nebulitic diatexite, comprising paleosome of foliated sillimanite-garnet-biotite metagranite to gneiss, and non-foliated garnet-cordierite neosome poor to free of biotite. A metatexite (R14) located relatively far from the Medina batholith, and a diatexite (M26) found at the batholith contact were sampled for detailed studies. The paleosome of foliated metagranite (R14A) only shows zircon grains with igneous features and Th/U ratio from 1.64 to 0.26. Although the spreading of zircon spots, the main cluster yields a Concordia age at 556 ± 6 Ma, constraining the protolith magmatic crystallization. A minor cluster furnishes a Concordia age at 499 ± 7 Ma, in agreement with the UPb monazite age at 501 ± 2 Ma. Extracted from the same metatexite sample, the non-foliated garnet-cordierite neosome (R14B) shows both igneous and metamorphic zircon domains with Th/U ratios ranging from 1.47 to 0.00. Again, the UPb spots cluster at two distinct Concordia ages (562 ± 3 Ma and 499 ± 3 Ma). The youngest of them, fitting with the monazite age (495 ± 3 Ma), constrains melt crystallization, while the oldest age suggests paleosome inheritance. The nebulitic diatexite (M26) shows monazite (497 ± 2 Ma) and zircon (Th/U = 1.7 to 0.0; Concordia ages at 564 ± 2 Ma and 507 ± 3 Ma) populations similar to the metatexite neosome, also with the youngest ages bracketing the melt crystallization process around 500 Ma. Accordingly, all those ages at around 500 Ma disclose a partial melting episode coeval with the Medina batholith emplacement. Phase equilibrium modeling on a garnet-cordierite neosome furnished P-T conditions of 750–840 °C at 2.4–3.5 kbar for that post-collisional anatexis. Evidence for such a late thermal event are common in the Araçuaí orogen, even far from the post-collisional batholiths. Thus, a possible major heat source can be envisaged, like a mantle plume triggering crustal anatexis and regional fluid circulation during the gravitational collapse of the Araçuaí orogen.

Investigation on the modification of N,N′-adipic bis(benzoic acid) dihydrazide on poly(l-lactic acid)

In this study, poly(l-lactic acid) (PLLA) modified using N,N′-adipic bis(benzoic acid) dihydrazide (BAAD) was fabricated by melt blending technology, and the differential scanning calorimetry, optical depolarizer, and thermogravimetric analysis (TGA) evaluated the effects of BAAD on crystallization behavior, melting behavior, and thermal stability of PLLA. Non-isothermal crystallization behavior indicated that BAAD as a heterogeneous nucleating agent had excellent acceleration effectiveness on the melt crystallization process of PLLA; however, an increase in cooling rate weakened the crystallization promoting effect of BAAD for PLLA, resulting from increasing cooling rate which led to decrease in the nuclei density. Additionally, non-isothermal crystallization results revealed that the effect of the final melting temperatures on the crystallization peak temperature and crystallization enthalpy was negligible. Isothermal crystallization measurement showed that the minimum t1/2 of the primary PLLA appeared at 120 °C, but the PLLA/2%BAAD exhibited the shortest t1/2 of 33.9 s at 95 °C comparing to the primary PLLA and other PLLA/BAAD samples. Through the analysis of the frontier molecular orbital energy and thermal stability of PLLA/BAAD system, it was proposed that the nucleation mechanism of the PLLA/BAAD system was chemical nucleation. Melting behavior of PLLA/BAAD system further confirmed the crystallization accelerating effect of BAAD for PLLA, as well as that the melting behavior of a given sample after non-isothermal crystallization was almost not dependent upon the heating rates, but the melting peak after isothermal crystallization shifted toward the higher temperature with the increase in crystallization time. Finally, the results of TGA measurements indicated that BAAD could not change the thermal decomposition profile of PLLA, but the concentration of BAAD could affect the onset decomposition temperature of PLLA.

Optimum operating conditions for manufacturing ibuprofen tablets coated with polyethylene glycol by melt crystallization process

The aim of this work is to apply the melt crystallization technology to manufacture ibuprofen tablets coated with polyethylene glycol in a single step. This technology, based on a pastillation process, allows in situ separation between two components (active ingredient and coating material). The design and application of this technique depend on the thermo-physical properties of the substances used, as well as on the existence of a eutectic point in the phase diagram. To evaluate the prerequisite conditions, first, DSC curves, allowing the construction of the phase diagram of the binary system, were investigated and the eutectic point was determined (30 mass% ibuprofen, 52 °C). Then, the stability of the selected mixture (10:90 mass% of ibuprofen, PEG6000) was studied by thermogravimetric analysis. Finally, the coating quality was investigated under different operating conditions including viscosity, cooling plate temperature, the power of ultrasound and seeding. This parametric study showed that seeding with PEG6000 is necessary to obtain a hemispherical pastille shape, a suitable separation and a pure and thick coating layer. In addition to the optimization of operating conditions of the in situ coating process, it was possible to determine the optimum viscosity and the cooling plate temperature (271.77 m Pa s, 25 °C) to obtain a uniform and crystalline coating. During the deposition of molten drops on the cooled surface, the progression of crystal growth was monitored online by optical microscopy. According to the good separation achieved and to the purity and thickness of the microscopic cross-sectional material, the in situ coating process is conceivable for the production of PEG6000-coated ibuprofen tablets.

Enhancing Stereocomplexation Ability of Polylactide by Coalescing from Its Inclusion Complex with Urea.

In this study, polylactide/urea complexes were successfully prepared by the electrospinning method, then the host urea component was removed to obtain a coalesced poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blend. The crystallization behavior of the coalesced PLLA/PDLA blend (c-PLLA/PDLA) was studied by a differential scanning calorimeter (DSC) and Fourier transform infrared (FTIR) spectroscopy. The c-PLLA/PDLA was found to show better crystallization ability than normal PLLA/PDLA blend (r-PLLA/PDLA). More interestingly, the c-PLLA/PDLA effectively and solely crystallized into stereocomplex crystals during the non-isothermal melt-crystallization process, and the reason was attributed to the equally-distributing state of PLLA and PDLA chains in the PLLA/PDLA/urea complex, which led to good interconnection between PLLA and PDLA chains when the urea frameworks were instantly removed.

Melt-crystallization monitoring system for the purification of 10 kg-scale LiCl salt waste

Salt waste treatment process in the pyrochemical process is under development to separate or concentrate fission products from the LiCl salt waste and to minimize waste volume by recycling the purified LiCl salt into the electrochemical process. In particular, the Cs nuclide in the LiCl salt waste is difficult to separate by chemical method, so that melt-crystallization method has been employed and engineering-scale melt-crystallization system capable of 20 kg/batch treatment has been designed and installed at the PyRoprocess Inactive integrated Demonstration (PRIDE) facility. In this study, in order to evaluate scaled-up design of melt-crystallization process, the preliminary crystallization test was conducted with 10 kg LiCl salt waste having surrogate Cs, Sr, and Ba nuclides. In consideration of temperature gradients generated inside the crystallization vessel owing to the scale-up, melt-crystallization monitoring system was developed. Using the monitoring system, we could obtain purified LiCl crystal with uniform distribution of quantity on 6 crystallization plates and high separation efficiency of over 90% at various cooling conditions.

Mathematical modeling of the crystallization process to obtain a fine fraction aluminates

Considered process of melt crystallization of the material in a twin-roll mold. Resolved an important problem of heat conduction through the wall of variable thickness, using the Fourier method and theorem Duhamel. Obtain theoretical dependence of the thickness of a frozen layer on the physical parameters of the melt and technological parameters of the crystallization process.

Physical and Mathematical Foundations Describing Crystallization Process of Melt Cooling on a Moving Wall by Fourier Method and Duhamel Theorem

The process of melt crystallization of the material in a twin-roll mold is considered. An adjoin of heat conduction through variable thickness of wall "rolls wall - hard layer" with a convective heat exchange from two sides problem important for the chemical industry is solved using Fourier method and Duhamel theorem. A theoretical dependence of the thickness of a frozen layer on the physical parameters of the melt and technological parameters of the crystallization process is obtained.

Specific features of motion of molten zones in the field of silicon structural inhomogeneity

The formation and dynamics of molten Al–Si inclusions in silicon at temperatures of 1123–1273 K in the dislocation-density gradient field are investigated. It is established that the molten inclusion moves as a whole in accordance with the melting–crystallization mechanism: dissolution is observed at the front boundary in the region with a higher dislocation concentration and crystallization and on the back surface in the region with a lower one. The migration rates and activation energies are experimentally determined. It is demonstrated that the inclusion migration is limited by the melting–crystallization processes at the interfaces between the melt and matrix.

Solid–liquid equilibrium of dimethyl terephthalate (DMT), dimethyl isophthalate (DMI) and dimethyl phthalate (DMP) in melt crystallization process

The binary solid–liquid equilibrium of Dimethyl Terephthalate (DMT), Dimethyl Isophthalate (DMI) and Dimethyl Phthalate (DMP) was investigated by experiment and differential scanning calorimetry (DSC). The result demonstrated DMT/DMI and DMT/DMP systems are eutectic while DMI/DMP is a solid-solution system. The eutectic temperature of DMT/DMI system is 336.7 K and that of DMT/DMP is 271.1 K. Furthermore, a classical solid–liquid phase equilibrium model was used to fit the experimental data of the eutectic systems of DMT/DMI and DMT/DMP and the theoretical model could describe the eutectic solid–liquid phase diagrams properly.

Enhanced crystallization and mechanical properties of biodegradable poly(ethylene succinate) by octaisobutyl-polyhedral oligomeric silsesquioxanes in their nanocomposites

Two poly(ethylene succinate) (PES) based nanocomposites containing low loadings (0.5 and 1.0wt%) of octaisobutyl-polyhedral oligomeric silsesquioxanes (oib-POSS) were prepared via a solution and casting method. The scanning electron microscopy observation demonstrated the fine dispersion of oib-POSS in the PES matrix. The nonisothermal cold and melt crystallization behaviors, isothermal melt crystallization kinetics, crystalline morphology, crystal structure, and mechanical properties of PES and its nanocomposites were studied. Oib-POSS not only enhanced the nonisothermal cold and melt behaviors but also accelerated the overall isothermal melt crystallization process of PES in the nanocomposites, indicating its nucleating agent effect. Oib-POSS did not modify the crystal structure of PES in the nanocomposites; furthermore, oib-POSS and PES crystallized separately in the nanocomposites. Oib-POSS obviously enhanced the Young's modulus and yield strength while still maintained relatively good ductility of PES in the nanocomposites, suggesting the efficient reinforcing effect of oib-POSS on the mechanical properties of PES.

Control of the weld structure formation under the influence of low-frequency mechanical oscillations on the weld pool melt (review)

Methods of controlling crystallization of the weld pool metal under external mechanical impact have been considered. There is performed an analysis of the factors influencing the process of melt crystallization when low-frequency oscillations are applied. The role of wave acceleration in determining the parameters of the control action is shown. There are presented the relationships between the parameters of low-frequency oscillations and the natural frequency of crystallization of the bath metal, which are necessary for obtaining a fine-grained structure of the weld.

Mathematical modeling of static layer crystallization for propellant grade hydrogen peroxide

Hydrogen peroxide (H2O2) is an important raw material widely used in many fields. In this work a mathematical model of heat conduction with a moving boundary was proposed to study the melt crystallization process of hydrogen peroxide which was carried out outside a cylindrical crystallizer. Considering the effects of the temperature of the cooling fluid on the thermal conductivity of crude crystal, the model is an improvement of Guardani's research and can be solved by analytic iteration method. An experiment was designed to measure the thickness of crystal layer with time under different conditions. A series of analysis, including the effects of different refrigerant temperature on crystal growth rate, the effects of different cooling rates on crystal layer growth rate, the effects of crystallization temperature on heat transfer and the model's application scope were conducted based on the comparison between experimental results and simulation results of the model.