Cold Crystallization Kinetics Research Articles

Effect of Nano Spinel Ferrites Co0.9Cu0.1Fe2O4 on Non-Isothermal Cold Crystallization Behaviours and Kinetics of Its Composites with Polylactic Acid.

Nanoparticles of spinel ferrites with a composition of Co0.9Cu0.1Fe2O4 (AM NPs) were effectively synthesized via a hydrothermal route. The structure of ferrite nanoparticles was characterized with X-ray diffraction, which showed a single cubic spinel phase. Energy-dispersive X-ray (EDX) spectroscopy and field emission-scanning electron microscopy (FE-SEM) were employed to analyse elemental composition and surface morphology, respectively. Moreover, the effects of the Co0.9Cu0.1Fe2O4 on the morphology of [PLA = polylactic acid] nanocomposites were examined through polarized light optical microscopy (POM) and X-ray diffraction (XRD). The thermal behaviours for tested samples were studied through [DSC = differential scanning calorimetry] and [TGA = thermal gravimetric analysis]. A great number of minor PLA spherulites were detected using POM in the presence of the Co0.9Cu0.1Fe2O4 ceramic magnetic nanoparticles (AM), increasing with AM nanoparticle contents. X-ray diffraction (XRD) analysis showed that the presence of nanoparticles led to an increase in the intensity of diffraction peaks. The DSC findings implied that the crystallization behaviours for the efficient PLA as well as its nanocomposites were affected by the addition of AM nanoparticles. They act as efficient nucleating agents because they shift the temperature of crystallization to a lower value. The Avrami models were used to analyse kinetics data. The experimental data were well described using the Avrami method for all samples tested. The addition of AM to the PLA matrix resulted in a decrease in the crystallization half-time t1/2 values, indicating a faster crystallization rate. TGA data showed that the occurrence of AM nanoparticles decreased the thermal stability of PLA.

Stability of Rapidly Crystallizing Sulfonamides Glasses by Fast Scanning Calorimetry: Crystallization Kinetics and Glass-Forming Ability

Production and evaluation of the kinetic stability of the amorphous forms of active pharmaceutical ingredients are among the current challenges of modern pharmaceutical science. In the present work, amorphous forms of several sulfonamides were produced for the first time using Fast Scanning calorimetry. The parameters, characterizing the glass-forming ability of the compounds, i.e. the critical cooling rate of the melt and the kinetic fragility, were determined. The cold crystallization kinetics was studied using both isothermal and non-isothermal approaches. The results of the present study will contribute to the development of approaches for producing amorphous forms of rapidly crystallizing active pharmaceutical ingredients.

Crystallization kinetics in the chiral compound showing the vitrification of the smectic CA* phase for moderate cooling rates

ABSTRACT The crystallization of the 3F5FPhF6 compound from the liquid crystalline antiferroelectric smectic CA* phase is investigated in various conditions using differential scanning calorimetry and polarizing optical microscopy. The kinetics of isothermal melt and cold crystallization is studied on the basis of the Avrami model. The kinetics of non-isothermal cold crystallization is analysed using the Ozawa model and the activation energy is determined by the Augis-Bennett, Friedman’s differential isoconversional and Matusita methods. The border temperature between the diffusion-controlled crystallization and thermodynamically-controlled crystallization is estimated. The high fragility index of 105 is determined from the α-process in the smectic CA* phase by the broadband dielectric spectroscopy. The metastable, conformationally disordered crystal phase, forming only via cold crystallization, is reported.

Vitrification of the smectic CA* phase and kinetics of cold crystallization investigated for a fluorinated compound with a chiral centre based on (S)-(+)-3-octanol.

The formation of glass of the anticlinic high-tilted smectic CA* phase even at low cooling rates (≥2 K min-1) is reported for (S)-4'-(1-ethylhexyloxycarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pentyl-1-oxy]benzoate. The kinetics of crystallization is investigated via differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The temperature region of the largest crystallization rate, the activation energy of cold crystallization and the energy barrier of nucleation are determined. The coupling of the characteristic crystallization time with the α-relaxation time is studied. A high fragility index equal to 139 is obtained for this glassformer. Comparison with a very similar glassforming compound, with the chiral centre based on (S)-(+)-2-octanol instead of (S)-(+)-3-octanol, is presented.

Phase Sequence, Kinetics of Crystallization and Molecular Dynamics of the Chiral Liquid Crystalline Compound Forming a Hexatic Smectic Glass

The vitrification of the antiferroelectric hexatic smectic XA* phase and cold crystallization are reported for (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]benzoate. The kinetics of isothermal cold crystallization and melt crystallization are investigated, revealing that both are controlled mainly by diffusion, as indicated by decrease in the characteristic crystallization time with increasing temperature of crystallization, with an activation energy of 114 kJ/mol. A weak relaxation process is detected in a crystal phase, with an activation energy of 38 kJ/mol, implying the conformationally disordered crystal phase. The estimated fragility parameter of the investigated glass former is equal to 94.5, which indicates rather high fragility.

The effect of mild CO2 treatment on thermal properties of poly(l-lactic acid): An experimental study

The influence of mild CO2 treatment on thermal properties of poly(l-lactic acid) (PLLA) is discussed in this article. A slowly crystallizing PLLA with 4% d-isomer was treated with CO2 at room temperature and moderate pressures (up to 6.0 MPa) for short times, not longer than 20 min. These mild treatments are sufficient to develop ε-form (PLLA/CO2 complex), which evolves to α"-mesophase after desorption of CO2. The amount of mesophase depends on the pressure of CO2 and the sorption times, and significantly affects the thermal properties of PLLA. Although the mesophase melts immediately above the glass transition, it affects subsequent cold crystallization. The influence of CO2 sorption time and pressure on the cold crystallization kinetics of PLLA is quantified here, and it is found that only a few minutes of treatment with low-pressure CO2 is sufficient to enhance the crystallization rate. After longer exposure to CO2, α-crystals also develop, especially under high CO2 pressure, hence proper adjustment of these parameters can allow tuning the structure and thermal properties of PLLA. The results demonstrate the possibility of producing CO2-induced mesophase at room temperature using very short sorption times, thus introducing a fast, green and cost-effective way to tailor the crystallization kinetics of PLLA.

Influence of rGO on the Crystallization Kinetics, Cytoxicity, and Electrical and Mechanical Properties of Poly (L-lactide-co-ε-caprolactone) Scaffolds.

Biodegradable scaffolds of poly (L-lactide-co-ε-caprolactone) (PLCL) and reduced graphene oxide (rGO) were prepared by TIPS (thermally induced phase separation). The nonisothermal cold crystallization kinetics were investigated by differential scanning calorimetry (DSC) with various cooling rates. The experimental values indicate that nonisothermal crystallization improves with cooling rate, but the increasing rGO concentration delays crystallization at higher temperatures. The activation energies were calculated by the Kissinger equation; the values were very similar for PLCL and for its compounds with rGO. The electrical conductivity measurements show that the addition of rGO leads to a rapid transition from insulating to conductive scaffolds with a percolation value of ≈0.4 w/w. Mechanical compression tests show that the addition of rGO improves the mechanical properties of porous substrates. In addition, it is an anisotropic material, especially at compositions of 1% w/w of rGO. All of the samples with different rGO content up to 1% are cytotoxic for C2C12 myoblast cells.

Kinetics of cold crystallization in two liquid crystalline fluorinated homologues exhibiting the vitrified smectic CA* phase

Dielectric relaxation processes in the supercooled antiferroelectric smectic CA* phase and crystallization kinetics of two chiral fluorinated 5HF6 and 6HF6 compounds from the same homologous series are investigated. Fragility parameters are determined from the relaxation time of the α-process, including τHN from the Havriliak-Negami formula and τpeak denoting the position of the absorption peak. The coupling coefficient ξ between the characteristic time of isothermal cold crystallization and relaxation time of the α-process is obtained. Despite similar values of the fragility index, the even 6HF6 homologue undergoes cold crystallization much faster than the odd 5HF6 homologue, with significantly different ξ coefficients. Influence of the relaxation time of the PH process (anti-phase phason) in the smectic CA* phase on the crystallization kinetics is presumed.

Comparing non-isothermal melt and cold crystallization behavior and kinetics of poly(ethylene 2,5-furandicarboxylate-co-ethylene terephthalate) copolyesters

Comparing non-isothermal melt and cold crystallization behavior and kinetics of poly(ethylene 2,5-furandicarboxylate-co-ethylene terephthalate) copolyesters

Cold crystallization kinetics of slag from the joint smelting of oxidized nickel and sulfide copper ores

Cold crystallization kinetics of slag from the joint smelting of oxidized nickel and sulfide copper ores

Crystal-nuclei formation during injection-molding of poly (l-lactic acid)

Injection-molding of rather slow crystallizing poly (l-lactic acid) (PLLA) was analyzed regarding the formation of crystal nuclei at different distances from the skin in a standard test bar. The relative number of nuclei in the various regions of fully amorphous test bars was estimated by evaluation of the kinetics of cold-crystallization, being faster in the skin than in the core region of the component. Simulation of the cooling-rate- and shear-rate-profiles along the cross-section of the molded bar suggests that the different nuclei numbers in skin and core mainly are caused by the higher shear rate in surface-near regions, though being supercritical for shear-induced nuclei formation also in the core. The latter conclusion is derived by comparing both the cold-crystallization kinetics and semicrystalline morphology with those of non-injection molded PLLA. The simulated shear-rate data, after conversion into specific-work-of-flow data, were found significantly exceeding the critical specific work of flow for shear-induced nuclei formation, being around 25 kPa, in all regions of the component. The results of the present study successfully demonstrate that knowledge about the crystallization kinetics of the sheared and quiescent melt of PLLA can be used to predict structure formation in industrial processing.

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer

An investigation of the glass transition of the antiferroelectric smectic CA* phase and cold crystallization of (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluoro- butoxy)heptyl-1-oxy]benzoate (denoted as 3F7FPhH6) by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy is presented. The fragility index mf = 72, classifying 3F7FPhH6 as a glassformer with intermediate fragility, was obtained from the temperature dependence of the α-process relaxation time, measured upon cooling. Duplication of the α-process was observed exclusively upon heating, before the onset of cold crystallization, and is connected with the pre-transitional effect. The presence of two crystal phases likely influences the kinetics of cold crystallization; the idea stems from a comparison with previous results for the 3F7HPhF6 and 3F7HPhH7 compounds. Additionally, the presence of the smectic Cα* sub-phase in a narrow temperature range was proved based on the differential scanning calorimetry and broadband dielectric spectroscopy results, as well as the fractal dimension analysis of the textures obtained by polarizing optical microscopy.

Kinetics of non-isothermal cold-crystallization of carbamazepine in the glassy state studied by DSC

Kinetics of non-isothermal cold-crystallization of quench-cooled carbamazepine (CBZ) was investigated under different heating rates using Differential Scanning Calorimetry. Relevance of Johnson-Mehl-Avrami, Kissinger, Augis-Bennett, Ozawa, Mo and Matusita models to describe the mechanism of nucleation and growth was thoroughly discussed. Some assumptions of Johnson-Mehl-Avrami and Kissinger models were showed to be inadequate when describing kinetics of cold-crystallization of quench-cooled CBZ. Augis-Bennett, Ozawa and Mo models correctly outlined the nucleation and growth mechanism, however they were not able to distinguish between surface and bulk crystallization. Matusita model was the only one which properly described these two mechanisms and consequently was considered as the most versatile one. Quench-cooled CBZ displayed two different crystallization mechanisms for lower and higher heating rates. In the first case, surface crystallization was dominant, whereas in the second case – the bulk one. Activation energy was noticed to be heating rate, temperature and fractional extent of crystallization dependant.

Mechanical and nonisothermal cold crystallization behaviors of injection molded surface‐modified chitin whiskers/poly(l‐lactide) composites

AbstractTo improve the mechanical, crystallization performances of poly(l‐lactide) (PLLA), pristine and surface grafted chitin whiskers (CWs and g‐CWs) were introduced to PLLA via melt blending. Attributed to the good interfacial compatibility between the g‐CWs and PLLA matrix, the tensile, flexural, and impact performances of the g‐CWs/PLLA composites were better than that of the CWs/PLLA composites with the same whiskers content. The whiskers acted as nucleating agents to promote the crystallization of the PLLA matrix on the one hand, and acted as obstacles to restrict the crystals growth on the other hand. The nonisothermal cold crystallization kinetics revealed that the crystallization rate and crystallinity of the PLLA matrix were improved by the addition of the whiskers, but the promotion effect of g‐CWs was more obvious than CWs.

Investigation of crystallization kinetics and its relationship with molecular dynamics for chiral fluorinated glassforming smectogen 3F5HPhH6.

The phase transitions, crystallization kinetics and molecular dynamics of (S)-4'-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pent-1-oxy] benzoate (3F5HPhH6) are investigated by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The vitrification of the antiferroelectric hexatic phase is observed for cooling rates ≥5 K min-1 and the fragility index determined from dielectric data is mf ≈ 90. Two regimes of non-isothermal cold crystallization are distinguished using the Kissinger and Augis-Bennett methods in the heating rate ranges of 1-5 K min-1 (larger activation energy) and 8-20 K min-1 (lower activation energy). The correlation between the time of non-isothermal cold crystallization (using isothermal approximation) and relaxation time of the α-process is determined. The obtained coupling coefficient ξ ≈ 0.7 and temperature dependence of the crystallization rate Z from the Ozawa model imply a mainly diffusion-controlled cold crystallization below 275 K. The Avrami exponents n and Ozawa exponents nO determined for isothermal melt crystallization and non-isothermal cold crystallization, respectively, weigh in favour of two- rather than three-dimensional crystal growth. The transition between crystal phases is observed on heating, with a lower activation energy for 1-3 K min-1 than for 5-20 K min-1 rates.

Thermal properties and cold crystallization kinetics of deep eutectic solvents confined in nanopores.

Herein, the phase behaviors of both bulk and confined deep eutectic solvents in controlled pore glasses were first investigated. Glass transition, cold crystallization and melting behaviors alter significantly in the nanopores due to the size effect and interfacial interactions. Kinetic analysis of the crystallization reveals increased effective activation energies and pre-exponential factors under nanoconfinement.

Kinetics of non-isothermal cold crystallization in the antiferroelectric smectic phase of 3F5BFBiHex as seen by differential scanning calorimetry and broadband dielectric spectroscopy

The non-isothermal cold crystallization process from the antiferroelectric SmC*A phase of 3F5BFBiHex was studied by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) experiments in detail with various heating rates. DSC studies have revealed the complexity of the crystallization process. The use of the dielectric spectroscopy method allowed to describe the behavior of molecular l-process (reorientation molecules around the long axis) and collective (anti-phase phason) relaxation processes during cold crystallization. The amplitude of l-process decreases faster than the intensity of anti-phase phason process. The kinetics of non-isothermal crystallization process was analyzed in terms of Ozawa and Mo models. The use of the Ozawa model allowed to obtain the dimensionality parameter m and the crystallization constant rate Z. The energy barrier obtained using the Kissinger equation is almost the same in both DSC and BDS methods (51 kJ/mol). Energy barriers obtained by means of Augis-Bennett model for DSC data are around 10–20 kJ/mol smaller than those determined based on dielectric data.

Non-isothermal cold crystallization kinetics of cork–polymer biocomposites based on polylactic acid for fused filament fabrication

Cork–polymer composites (CPC) based on polylactic acid (PLA) matrix were prepared for the development of filaments for fused filament fabrication. The non-isothermal cold crystallization behaviours of PLA and CPC were investigated by differential scanning calorimetry. Cold crystallization kinetic behaviours of PLA and CPC with 15 mass/% of cork powder residues at different heating rates (1.25, 2.5, 5 and 7.5 K min−1) were studied. Results showed that cold crystallization temperature (Tcc) of PLA matrix decreased with the addition of cork. Crystallization kinetic behaviour was studied by Avrami and Tobin models. It was shown that cork powder surface acts as a nucleating agent during non-isothermal cold crystallization, by accelerating the crystallization rate and, therefore, by reducing the half-time crystallization (t1/2) values. Polarized optical microscopy and X-ray diffraction were used to evaluate the crystalline structure of PLA and CPC. Kissinger and Friedman methods were employed to determine the crystallization activation energy (Ec).

Effect of Organic Modifier and Clay Content on Non-Isothermal Cold Crystallization and Melting Behavior of Polylactide/Organovermiculite Nanocomposites.

In clay/polymer nanocomposites, the crystallization behavior and kinetics of the polymer can be affected by the presence of clay, its content and the degree of miscibility between the clay and the polymer matrix. The effect of two different organomodified vermiculites on the non-isothermal cold crystallization and melting behavior of polylactide (PLA) was studied by differential scanning calorimetry (DSC). In the presence of vermiculites, the cold crystallization of PLA occurred earlier, particularly for the highest content of the most miscible organovermiculite with PLA. The cold crystallinity of PLA decreased at low heating rates, notably at high organoclay loadings, and increased at high heating rates, especially at low vermiculite contents. According to the crystallization half-time, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP) approaches, the cold crystallization rate of PLA increased by incorporating vermiculites, with the effect being most noteworthy for the vermiculite showing better compatibility. The Mo model was successful in describing the non-isothermal cold crystallization kinetics of the PLA/vermiculite composites. The melting behavior was affected by the heating rate and the type and content of clay. The nucleating effect of the most compatible clay resulted in the less perfect crystallites. The activation energy was evaluated using the Kissinger and Takhor methods.

Nonisothermal Cold Crystallization Kinetics of Poly(lactic acid)/Bacterial Poly(hydroxyoctanoate) (PHO)/Talc

AbstractThe effects of bacterial poly(hydroxyoctanoate) (PHO) and talc on the nonisothermal cold crystallization behaviours of poly(lactic acid) (PLA) were analysed with differential scanning calorimetry (DSC), and the thermal stability of the samples was observed with thermal gravimetric analysis (TGA). The modified Avrami’s model was used to describe the nonisothermal cold crystallization kinetics of neat PLA and its blends. The activation energies E for nonisothermal cold crystallization were calculated by the isoconversional method of Kissinger-Akahira-Sunose (KAS). The DSC results showed that the PLA/PHO blends were immiscible in the whole studied range, and as the PHO and talc content increased, the crystallization rate of PLA accelerated, and the crystallinity of PLA in the PLA samples increased. The values of the Avrami exponent indicated that the nonisothermal cold crystallization of the neat PLA and its blends exhibited heterogeneous, three-dimensional spherulitic growth. The E values were strongly dependent on PHO and talc. The TGA results showed that the presence of PHO and talc slightly influenced the thermal stability of PLA.