Crystallization Kinetic Parameters Research Articles

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.

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y2O3 on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B2O3–10SiO2 glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies Eg calculated by using both Kissinger and Moynihan model decrease from 668 kJ/mol to 573 kJ/mol for Kissinger model, and 682 kJ/mol to 587 kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6 mol%. And the glass crystallization kinetics parameters, crystallization activation energy Ec and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58 kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6 mol% yttrium oxide into 60ZnO–30B2O3–10SiO2 glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B2O3–10SiO2 glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893 K and 993 K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B2O3–10SiO2 glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.

Study of the Non-Isothermal Crystallization Kinetics of Lithium Disilicate Glass Ceramic

The glass ceramic with the crystals of lithium disilicate Li2O · 2SiO2 (LS2) as the main crystal phase is one of the prospective materials in the field of restorative dentistry. In this study, the crystallization kinetics of LS2 glass ceramic obtained from the base glass of the system SiO2–Li2O–Al2O3–K2O–P2O5 were investigated by the non-isothermal method using differential thermal analysis at four different heating rates. The DTA curves showed different exothermic crystallization peaks over the temperature ranges of 645–683 and 807–845°C. The lithium metasilicate, Li2O · SiO2 (LS), and the lithium disilicate, crystallized over these respective temperature ranges, was established by XRD technique. The crystallization kinetic parameters were calculated by the Kissinger plot and Augis-Bennett equations for non-isothermal analysis. The calculated activation energy of crystal growth, EC1= 236 kJ/mol, EC2 = 340 kJ/mol, and the Avrami parameters, n1 = 1.46–1.67, n2 = 2.73–2.91, together with the results from SEM observations, indicated that the crystallization mechanism of LS was substantial surface crystallization while the crystallization mechanism of LS2 was dominant bulk crystallization. The calculated activation energy of glass transition was also determined EV = 516 kJ/mol.

Intermediate crystallization kinetics in Germanium-Tellurides

Germanium-Telluride has been widely studied as a phase-change material due to its fast crystallization speed. The understanding of the crystallization kinetics is important to evaluate the potential applications of the material, but this is limited by the conventional calorimetry with low heating rate and narrow temperature range. We here employed an ultrafast calorimetry method, named flash differential scanning calorimetry, to investigate the crystallization kinetics of GexTe100-x in a wide compositional range (15 ≤ x ≤ 55). By means of the X-ray diffraction, we found the complicated competition between crystalline GeTe and Te (or Ge) phases in these binary alloys. The crystallization kinetics of first crystalline phase were estimated and it was found that, GexTe100-x generally has intermediate crystal growth speed and fragility, which is ascribed to the border between covalent and metallic properties. Component dependences of maximum crystal growth rate (Umax) and fragility were investigated, revealing the component in x = 20.4 has the lowest Umax of 1.22 × 10−3 m s−1 with the smallest fragility of 42.2, and the component in x ≈ 50 possesses the largest Umax of 3.5 m s−1. It confirms that, GeTe is the most suitable phase-change material for information storage and GeTe4 is the best media for information transparency in Ge-Te binary. Moreover, a tri-counter pattern was carried out for obtaining the crystal growth rate directly in studied supercooled GexTe100-x liquids (15 ≤ x ≤ 55). In addition, we first found a peculiar component Ge22Te78 with terrible thermal properties, i.e., phase separation, low crystallization temperature, ultrahigh fragility and anomalous crystallization kinetics. More importantly, together with the crystallization kinetics parameters of other glass formers, it was found a specific relation between reduced glass temperature (Trg) and Umax for which can be benefit to simplify material screenings and performance optimizations.

Crystallization kinetics and morphology of poly(lactic acid) with polysaccharide as nucleating agent

An ever-increasing concern about environmental pollution has spearheaded research into alternative biodegradable polymers. Currently, poly(lactic acid) (PLA) is one of the most notable biodegradable polymers due to its superior properties and low production cost. Nucleating agents have been used to overcome slow PLA crystallization. The present work aims at investigating cashew gum (CG) as nucleating agent in PLA produced by casting process. The effect of the CG (1–10 mass%) on the PLA crystallization process was evaluated by thermal analysis and hot-stage optical microscopy. The relative degree of crystallinity, crystallization kinetic parameters under isothermal conditions, and crystallite morphology of pure PLA and PLACG samples were also investigated. The PLA crystallization rate increased with the CG content at a temperature ranging from 130 °C to 140 °C. An increase in the degree of crystallinity and a reduction in the crystallite size of the PLA were observed in the samples which contained 5 and 10 mass% of CG. Cashew gum proved to be an effective nucleating agent for PLA. Results show that cashew gum can be used as a natural nucleating agent for PLA when faster crystallization rate, better crystallite size control or higher degree of crystallinity are required.

The crystallization of polypropylene/halloysite fibers

The halloysite (HNT) in the form of nanotubes was used as an agent for the improved mechanical, thermo-mechanical as well as surface properties of polypropylene (PP) fibers. The halloysite is the nanoadditive that can affect differently the crystallization of PP in the non-oriented and oriented systems. The structure and mechanical properties of PP and PP/HNT fibers depended on the crystallinity and crystallization kinetics of PP at the fiber preparation. The Avrami method on the determination of isothermal crystallization kinetics parameters as well as an estimation of melting and crystallization temperatures and melting and crystallization enthalpies was used for the study of thermal behavior of polypropylene/halloysite non-oriented and oriented blends and fibers. Morphological structure, mechanical and thermo-mechanical properties of polypropylene/halloysite fibers were observed. An influence on all assessed properties was evaluated from the point of halloysite content in the PP and/or PP fibers. The increased HNT content in the non-oriented PP/HNT blends at the isothermal crystallization increases the rate crystallization (decreased t1/2 and free energy σe, increased K) of PP in comparison with the pure PP. The crystallinity of PP in the oriented PP/HNT fibers is not primarily affected by addition of the HNT content 3 mass% and does not change their mechanical and thermo-mechanical properties. 5 mass% HNT increases the crystallinity of PP in PP/HNT fibers expressing mainly the decrease in tenacity at the break, Young’s modulus and shrinkage.

Non-isothermal crystallization behavior of polyethylene glycol/expanded vermiculite form-stable composite phase change material

In this work, non-isothermal crystallization behavior of polyethylene glycol (PEG)/expanded vermiculite (EVM) form-stable composite phase change material (PEG-EVM) was investigated. The activation energy of non-isothermal crystallization of PEG-EVM (−219.7 kJ/mol) was lower than that of PEG (−375.3 kJ/mol), indicating that the energy barrier of heterogeneous nucleation decreased, demonstrating that the EVM significantly accelerated the nucleation of PEG. However, the crystallization kinetic parameters (half-crystallization time, crystallization rate and required cooling rate for a designated relative crystallinity) revealed that the non-isothermal crystalline growth of PEG in PEG-EVM was constrained because the surface interactions of EVM hindered the migration and diffusion of PEG molecular chains to the surface of nucleus.

Manipulating the structure of medium-chain-length polyhydroxyalkanoate (MCL-PHA) to enhance thermal properties and crystallization kinetics

We investigated the effects of the structure of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) on their thermal properties and crystallization kinetics. The predominantly homopolymeric poly(3-hydroxydecanoate), P(3HD)-98, and the poly(3-hydroxydodecanoate), P(3HDD), exhibited sharp crystallization peaks upon cooling, with the latter exhibiting faster crystallization rates. A chemical modification strategy involving reaction with dicumyl peroxide and triallyl trimesate coagent was implemented to introduce branching and enhance the crystallization kinetics of P(3HD-98). Increases in the exothermic crystallization temperature by 8 °C and in the overall crystallinity of the P(3HD)-98 were observed upon chemical modification. The Avrami crystallization kinetic parameters obtained by fitting the isothermal crystallization data revealed a significant increase in the crystallization rate of the modified P(3HD)-98.

Crystallization Kinetics Of Coconut Oil Based On Gompertz Model

The cooling rate and temperature of crystallization has been proven to be very influential on the rate of crystal formation oil. Oil crystallization kinetics can be measured by monitoring changes in the solid fat content(SFC) of oil during cooling process. In this study, SFC measuredusing pulsed Nuclear Magnetic Resonance (pNMR). Four levels of cooling rates and temperature crystallization studied. Crystallization kinetics parameters were measured by applying the model of Gompertz. Gompertz model used to explain the induction time, the increase in the maximum rate of crystallization and the crystalline polymorphic. Crystallization was done by heating the oil at a temperature of 70°C for 10 minutes prior to rapid cooling to 29°C. Then, rate of cooling from 29°C to the crystallization temperature (critical cooling rate) was set below 2°C/minutes. During the process, the oil was stirred at 15 rpm. Solid fraction was measured periodically since the crystallization temperature was reached until maximum solid fraction was achieved. The results showed that the Gompertzmodel able to quantitatively describe the crystallization kinetics of coconut oil. Lower critical cooling rate reduces the induction time of crystallization but accelerate the maximum increase rate of crystallization. Crystallization temperature has a negative correlation with the induction time and the maximum increase rate of crystallization. In the crystallization of coconut oil, critical cooling rate and crystallization temperature are only influence on the thermodynamics and kinetics of crystallization but not on its polymorphic formation.

Quantitative Design of Seed Load Based on model identification of nucleation and crystal growth stages without transmittance data

How to quantitatively design the loading time and amount of seed is a critical problem in the seeded crystallization process. In this study, correlations for different moment of crystal size distribution (CSD) function were established by subsection induction. By using the established different moment of CSD function, a new algorithm for kinetic model that can estimate the nucleation and growth kinetic parameters was proposed. Compared with kinetic model based on the conventional moments method, the new algorithm has a great significance since the overall heat transfer coefficient U is no longer necessary in the entire calculation. Using experimental data from literature, kinetic parameters of crystallization of KNO3 aqueous solution and xylene solution were estimated by the new algorithm, which are in good accordance with those fitting with moments method. This agreement shows the feasibility of the new algorithm. Finally, since it is difficult to measure transmittance data r of some systems, a criterion K that can identify nucleation and crystal growth stages without transmittance data was established. By means of the K curve of para-xylene (PX) and vitamin C, which is based on kinetic simulation results from the new algorithm and different moment of CSD function established by subsection induction, the single step seed load and two steps seed load were designed, respectively.

Kinetic Analysis of Freeze-Thaw Stability of Mayonnaise.

Kinetic analysis was used to study the destabilization of mayonnaise by focusing on the fat crystals. Mayonnaise prepared from rapeseed oil and soybean oil was stored at temperatures ranging from −20 to −40 °C. The destabilization kinetic parameters were measured by observing oil separation over time. The destabilization rate constant, kd, increased with decreasing temperature. The highest value of kd was 1.28 × 10−3 min−1 at −40 °C for rapeseed oil mayonnaise (RoM) and the lowest was 1.95 × 10−6 min−1 at −20 °C for soybean oil mayonnaise (SoM). At each temperature, the kd value in RoM was higher than that in SoM. However, the order of destabilization, n, followed no specific pattern. The crystallization rate constant, Kc, and Avrami constant, n, were calculated using microscopic images of the fat crystals. The increase in crystallization kinetic parameters with decreasing temperature revealed changes in crystal behavior. Both the destabilization rate constant, kd, and the crystallization rate constant, Kc, depended on the temperature. This temperature dependency behavior showed a correlation between kd and Kc, suggesting that the destabilization rate depended on the rate of growth of fat crystals during the freeze-thawing of mayonnaise.

Crystallization kinetics of PCL and PCL–glass composites for additive manufacturing

The non-isothermal crystallization kinetics of polycaprolactone (PCL) and PCL–glass composites, used in fused filament fabrication (FFF), was investigated. Films of PCL and PCL reinforced with powders of a bioactive glass, from the CaO·P2O5·MgO·SiO2 system, were prepared by solvent casting process. Crystal structure of the samples was examined by X-ray diffraction (XRD), and thermal properties were assessed by differential scanning calorimetry (DSC), at different cooling rates (5, 10, 15 and 20 °C min−1). The DSC curves of non-isothermal crystallization showed a significant dependence of crystallinity (Xc) on the cooling rate. The relevant crystallization kinetic parameters were determined from DSC traces applying a combination of Avrami and Ozawa methods (Mo’s method), Jeziorny method and Friedman method. It was observed that the presence of inorganic particles within the polymeric matrix clearly influenced the composite crystallization. The addition of glass particles allowed a decrease in Xc and accelerated the PCL crystallization rate. The slower cooling rates tested proved to be suitable for the biofabrication of PCL–glass composites by FFF techniques.

The effect of microwave on the crystallization process of magnesium carbonate from aqueous solutions

The effect of microwave on reactive crystallization is investigated with magnesium carbonate as the working substance. In the experiments, magnesium carbonate is precipitated by mixing aqueous magnesium sulfate and sodium carbonate solutions in a MSMPR crystallizer located in a microwave reactor. A population balance model along with crystallization kinetics is formulated to assess the influence of microwave energy input on nucleation, growth, agglomeration and breakage during crystallization process. A general high order moment method of classes (HMMC) framework is applied to solve the model numerically. The results show that crystallization kinetics parameters, including the nucleation rate constant (kn), the growth rate constant (kg), the exponent of growth rate (g) and the collision efficiency (Ψag) change significantly due to mass transfer enhancement in microwave field. Meanwhile, the exponent of nucleation (n) and the breakage rate constant (kbr) remain constant or only change slightly. It is further discovered that the crystal suspension attenuates the microwave effect during crystallization process.

Preparation and crystallization kinetics of polyesteramide based on poly(L-lactic acid)

AbstractUsing the melt polycondensation method, a polyesteramide was prepared based on poly(L-lactic acid) prepolymer and poly(ε-caprolactam) prepolymer and was characterized by Fourier transform infrared spectroscopy and 1H-NMR. Isothermal crystallization behavior at different temperatures and non-isothermal crystallization kinetics at different cooling rates were investigated by differential scanning calorimetry, and non-isothermal crystallization kinetics parameters were obtained using the Mo, Ozawa and Jeziorny methods. It was found that the increased cooling rates led to the broadening of the polyesteramide crystallization peaks and their shift toward lower temperatures. Mo and Jeziorny methods were found to be more suitable than the Ozawa method for the analysis of this system, as shown by the comparison these non-isothermal crystallization analysis methods. In addition, the values of activation energy of non-isothermal crystallization for polyesteramide obtained by the Kissinger and Takhor methods were −155.96 and −149.12 kJ/mol, respectively.

Crystallization kinetics of yttrium aluminate glasses

Yttrium aluminate glasses with eutectic AY-E and near-eutectic composition AY-NE were prepared in the form of glass microspheres. Their basic characterization was carried out by XRD, optical microscopy and SEM. In DSC records of both samples, two exothermic peaks in temperature interval 940–1027 °C were observed. In both samples, YAG phase crystallized in two steps, as determined by HT XRD. DSC experiments conducted in the temperature interval 35–1200 °C at heating rates 2, 4, 6, 8 and 10 °C min−1 were performed, and the kinetic parameters of crystallization were determined with the use of the JMAK model. Crystallization in both samples was controlled by diffusion flow with linear nucleation rate time dependence. One-dimensional growth and formation of needle-like (dendritic) YAG crystals was observed in AY-E glass crystallized at 932 °C corresponding to the first exothermic maximum at the DSC curve. Two-dimensional growth and the presence of plate-like YAG crystals were observed in AY-NE glass crystallized at 996 °C. For the second exothermic effect, plate-like crystals crystallized at higher temperatures (996 and 1020 °C) in both compositions. The results of SEM analysis are in agreement with the results of kinetic calculations in the prepared systems.

The effect of well-dispersed nanoclay on isothermal and non-isothermal crystallization kinetics of PHB/LDPE blends

The crystallization kinetics of PHB/LDPE blends and their nanocomposites containing different LDPE and organoclay loadings was investigated using DSC. Nanoclay localization in the PHB phase was determined by XRD and confirmed by rheological measurements and TEM. The rate and other kinetic parameters for crystallization were investigated using theoretical models, such as Avrami, Liu–Mo and Friedman. The effect of nanoclay on the first stage of crystallization was explored, based on Dubreva’s nucleation activity analysis. The Friedman model results showed that incorporation of either nanoclay or LDPE would increase the PHB activation energy of crystallization through two different mechanisms, namely increasing the viscosity and nuclei migration, respectively. Interestingly, the activation energy of PHB/LDPE nanocomposites was not as high as that of PHB/LDPE binary blends. This finding was also observed in isothermal and non-isothermal kinetics studies and could be explained by nuclei transfer from the PHB phase to the melt phase. According to Avrami exponent values, neither Cloisite 10A nor LDPE changed the nucleation mechanism of PHB. Incoroporation of LDPE successfully reduces rigid amorphous amount.

Effect of plasticizer poly(ethylene glycol) on the crystallization properties of stereocomplex-type poly (lactide acid)

The effects of the plasticizer poly(ethylene glycol) (PEG) on crystallization properties of equimolar poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blends were investigated. Formation of the stereocomplex-type poly(lactide acid) (sc-PLA) crystallites was confirmed by Wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) analyses. Sc-PLA crystallites without any homochiral poly(lactide acid) (hc-PLA) formed, as the result of the incorporation of the plasticizer PEG (more than or equal to 10%(wt)) at a processing temperature (240 °C). Moreover, when the M W of PEG reached 1 000 g · mol–1, the crystallizability of stereocomplex crystallites was the best. Isothermal crystallization kinetics further revealed that PEG could accelerate the crystallization rate of sc-PLA, with the optimum crystallization kinetic parameters being obtained at 10% (wt) PEG. Several crystallization kinetics equations were applied to describe the effect of PEG on the crystallization behavior of sc-PLA. The influence of PEG on the spherocrystal morphologies of sc-PLA was also investigated using polarized optical microscopy.

Thermodynamics and kinetics of calcium oxalate crystallization in the presence of amino acids

Specific features of the crystallization of calcium oxalates (CaC2O4) in the presence of amino acids have been established based on thermodynamic and experimental modeling. Phase formation in the Ca2+–C2O4 2-–H2O–amino acid system in a wide range of variation in the component concentrations and solution pH have been theoretically investigated. The influence of pH on the thermodynamic stability of crystallizing compounds is considered. The effect of amino acids of different structures on the formation of the CaC2O4 solid phase in a prototype of physiological solution is analyzed. The kinetic crystallization parameters (induction period and rate constant) and crystallite growth are determined.

A multivariate linear regression method based on an improved rate equation to determine parameters of nonisothermal crystallization kinetics

An improved rate equation was proposed to investigate nonisothermal crystallization kinetics. The reaction model, activation energy and pre-exponential factor were determined by using the multivariate linear regression method. A particular form of the effective activation energy was derived from the improved rate equation, and experimental data reported in previous studies were used to validate the reliability of the proposed rate equation. Results indicate that the values of effective activation energy obtained from the improved rate equation are similar to those obtained from the isoconversional method. When the improved rate equation is used to fit the crystallization rates under different cooling or heating rates simultaneously, the correlation coefficient is between 0.982 and 0.998, which indicates that the proposed rate equation is capable of describing the variation of the crystallization rates during nonisothermal processes.

Structure and crystallization behavior of 50CuO-xTiO2-(50-x)P2O5 (x = 5–20) glasses

Glass samples with molar compositions of 50CuO-xTiO2-(50-x)P2O5 (x=5, 10, 15, 20) were prepared. The crystalline phases, characteristic thermal temperature as well as crystallization kinetic parameters were investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA) under non-isothermal conditions. The Fourier transformed infrared spectroscopy (FTIR) results show that the glass network depolymerizes with the increase of TiO2. However, TiO2 has an aggregation effect on the glass network. As a result of the depolymerization and aggregation effects, the glass transition temperature first increases and then decreases with TiO2. In the meantime, the glass is easier to crystallize. The XRD measurements indicate that when the content of TiO2 is more than 10mol%, desired CuTi2(PO4)3 phase appears in the heat-treated samples. The crystallization kinetics of the samples was studied using the Kissinger and Augis-Bennett models. It is evidenced that the crystallization activation energy increases with TiO2, while surface and bulk crystallization mechanisms dominate in the sample with 5mol and 10–20mol% TiO2, respectively.