Crystallization Rate Research Articles

Non-isothermal crystallization and thermal degradation studies on nylons 7,10 and 10,7 as isomeric odd-even and even-odd polyamides

Aliphatic polyamides (nylons) show a remarkable variability in terms of crystallographic structures, polymorphic transitions and crystal morphology despite all polymers of this family have a simple constitution that is based on amide groups and polymethylene segments. Nylons derived from diamines and dicarboxylic acids having different parity (e.g., even or odd) have peculiar characteristics due to the difficulty of establishing an optimal hydrogen-bonding geometry when molecular chains adopt a typical all trans conformation. In this work, two isomeric odd-even (nylon 7,10) and even-odd (nylon 10,7) polyamides with the same methylene/amide ratio have been studied. Specifically, crystallization kinetics have been evaluated from calorimetric data, while thermal degradation mechanisms from thermogravimetric analysis. Classical methods (e.g., Avrami) together with isoconversional analyses have been considered for crystallization studies, being found significant differences between both nylons in terms of nucleation and activation energies. The isoconversional analyses of the non-isothermal crystallization allowed to determine the temperature dependence of both the crystal growth and the overall crystallization rate that points out the slower crystallization process of nylon 10,7. Isoconversional methods (integral and differential) were applied to evaluate thermal degradation. The mechanism was similar for both nylons (e.g., A3/2 and A1.8 for nylons 7,10 and 10,7, respectively), although a remarkable difference was determined for the corresponding activation energies (175 and 210 kJ/mol for nylons 7,10 and 10,7, respectively).

Controlling Crystal Morphology of Anisotropic Zeolites with Elemental Composition.

The morphology of zeolite crystals strongly affects their textural, catalytic, and mechanical attributes. However, controlling zeolite crystal morphology without using modifiers or structure-directing agents remains a challenging task because of our limited understanding of the relationships between zeolite crystal shape, crystallization mechanism, and composition of the starting synthesis mixture. In this study, we aimed at developing a general method for controlling the morphology of zeolites by assessing the impact of the Si/T molar ratio of the synthesis gel on the growth rate of zeolite crystals in various crystallographic directions and on the final crystal morphology of the UTL germanosilicate with a 2D system of intersecting 14- and 12-ring pores. Our results showed that flat UTL crystals progressively thicken with the Si/Ge molar ratio, demonstrating that Ge concentration controls the relative rate of crystal growth in the perpendicular direction to the pore system. The morphology of other zeolites and zeotypes with an anisotropic structure, including AFI (12R), IFR (12R), MWW (10-10R), and IWW (12-10-8R), can also be predicted based on their Si/T ratio, suggesting a systematic pattern across zeolite structures and in a wide range of zeolite framework elements. Combined, these findings introduce a facile and cost-efficient method for directly controlling crystal morphology of zeolites with anisotropic structures with a high potential for scale-up while providing further insights into the role of elemental composition in zeolite crystal growth.

Alkali-treated and silanated luffa fiber reinforced poly(butylene succinate) composites: A study of mechanical and water absorption characterization

As a degradable polymer material, polybutylene succinate (PBS) has the disadvantages of high cost, slow crystallization rate, and low strength modulus. Reinforcing modification with plant fibers is a popular method. A unique three-dimensional network structure was found in luffa fiber (LF). Compared to other plant fibers, this fiber has excellent mechanical strength due to its unique three-dimensional structure. Its structure allows it to maintain the integrity of the reinforcement phase in the polymer aggregate, overcoming the dispersion and defects of short fiber reinforcement. Herein, the LF was treated with alkali treatment and silanated with three coupling agents and pre-impregnation methods to improve interfacial properties with the PBS matrix. Then it was laminated with polybutylene succinate to prepare a PBS/LF composite board with three layers of LF. The performance of the composite material using the KH550 coupling agent was improved the most. The tensile strength and modulus of the material were increased by 24.9% and 82.9%, respectively, the flexural strength and modulus were increased by 21.7% and 18.5%, and the impact strength was increased by 12.5%. The water absorption weight gain rate is also the lowest, about 3.5%. For the LF-reinforced PBS, the preparation method is simple, and the reinforcement effect is better, that the cost was effectively reduced, and the application field of the PBS green material was expanded. A new possibility for the development of green degradable polymer composites was provided.

Improving Active Ti Contents in TS-1 by Controlling the Alkalinity and Crystallization Rate

Improving Active Ti Contents in TS-1 by Controlling the Alkalinity and Crystallization Rate

Isothermal and nonisothermal crystallization kinetics of modified hydroxyapatite-enhanced poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) is a biodegradable material, and efforts have been devoted to enhancing its mechanical properties and biocompatibility for biomedical applications. However, there is a lack of research confirming the influence of nucleating agents on its crystallization behavior. In this study, the isothermal crystallization process was described using the Avrami model. The non-isothermal crystallization process was investigated using the Avrami-Jeziorny and Mo models. The effects of different calcium hydroxyapatite (CA-HA) contents on the nucleation activity, crystallization activation energy, and equilibrium melting point of P34HB/CA-HA composites were compared. The impact of CA-HA on the crystallization rate, nucleation rate, and crystal growth rate of the polymer matrix was discussed. The results indicate that with an increase in CA-HA content, the crystallization rate initially decreases and then increases. The minimum crystallization rate is observed at a CA-HA content of 9 wt%. Moreover, as the CA-HA content increases, nucleation activity is enhanced, suggesting that CA-HA acts as a nucleating agent, facilitating the nucleation process. When the CA-HA content exceeds 9 wt%, the increase in crystallization rate may be attributed to the further enlargement of molecular clusters formed by CA-HA, leading to a reduced dispersion of CA-HA in the polymer matrix. Furthermore, when the CA-HA content surpasses 9%, a significant decrease in crystallization activation energy is observed, indicating a reduction in the mobility of polymer chain segments.

Scalable manufacturing of an amide-based nucleating agent for transparency and high heat resistance of polylactic acid

The prevalent use of disposable plastic tableware presents notable environmental and health risks. An alternative, polylactic acid (PLA), often does not meet usage requirements due to its low crystallization rate. This research introduces an amide-based nucleating agent, BRE-T-100, developed through a straightforward method to enhance the heat resistance and crystallization rate of PLA. This study systematically investigates the impact of BRE-T-100 and other nucleating agents on the properties of PLA composites. The incorporation of 0.8 % BRE-T-100 increases the crystallization temperature of PLA from 109.6 °C to 131.9 °C. Further, the total crystallization time of PLA composites at 120 °C is reduced to <60 s, while maintaining good transparency. BRE-T-100 exhibits superior comprehensive properties compared to talcum, TMC-200, and TMC-300 and is nearly on par with LAK-301. Its application as a nucleating agent in PLA-based disposable tableware shows promise.

PET mechanical recycling. A new principle for chain extender introduction

The introduction of chain extenders into the melt of recycled PET (rPET) is traditionally performed at the activation temperature of the extension reaction. The disadvantage of this approach is the low dispersion of chain extender particles, which does not contribute to the full extension reaction. As a result, some rPET chains do not react with the chain extenders, and unreacted chain extenders lead to a decrease in the crystallinity or crystallization rate of rPET, an increase in its degradation rate, and also present deleterious low molecular weight migrating compounds. Herein, a new principle of chain extenders introduction based on a two-stage scheme is considered for the first time, which includes a preliminary stage of mixing chain extenders in an rPET melt at a temperature below the activation temperature of the extension reaction and a stage of PET chain extension at the activation temperature of the extension reaction. It has been shown that rPET modified in this way has higher melt viscosity, strength and ductility compared to rPET modified in the traditional way. The reaction time is reduced by 10–20% depending on the type and concentration of chain extenders used. The differences in the structures formed are demonstrated by NMR, FTIR, DSC, WAXS and rheological test methods. The economic and environmental implications associated with the introduction of a new principle are discussed.

Modulating fat crystallization behavior in ice cream with mono- and diglycerides: Influence on microstructure and shrinkage

Ice cream commonly experiences volume shrinkage, especially during storage and transportation with temperature fluctuations. The 3D semi-crystalline fat network supports the spatial structure of ice cream, preventing the coarsening of elements like foams and ice crystals during temperature fluctuations, ultimately reducing volume shrinkage. This study investigates the impact of fat crystallization behavior on the formation of the fat network, examining the correlation between ice cream shrinkage and fat crystallization induced by mono- and diglycerides. Techniques include differential scanning calorimetry, polarization microscopy, contact angle measurement and oscillatory thermorheometry. Shape retention is assessed through melting and freeze-thaw tests, and ice cream microstructure is observed using microscopy. Results shown mono- and diglycerides significantly impacted fat crystal wettability and emulsified fat crystallization kinetics, altering the ice cream microstructure, and contributing to heat shock-induced shrinkage. Saturated monoglyceride formed a two-dimensional crystalline layer at fat globule interface, causing fat network absence and significant shrinkage. Slightly unsaturated monoglycerides increased nucleation dimensions (n from 2.22 to 2.71), forming large fat aggregates (around 39 μm), supporting a rigid network, and reducing the shrinkage rate (from 36% to 23%). Highly unsaturated monoglycerides increased crystal growth rate (kz from 0.72 to 0.84), elevating solid fat content, and creating protrusions that damaged air bubbles, leading to a 45% shrinkage rate. Additionally, saturated emulsifiers with diglycerides reduced crystal growth rates, increased fat crystal nucleation dimensions, and hydrophobicity (kz from 0.72 to 0.63 and n from 2.22 to 3.12), forming smaller fat aggregates (around 7 μm) and minimizing shrinkage to 6%.

From salt water to bioceramics: Mimic nature through pressure-controlled hydration and crystallization.

Modern synthetic technology generally invokes high temperatures to control the hydration level of ceramics, but even the state-of-the-art technology can still only control the overall hydration content. Magically, natural organisms can produce bioceramics with tailorable hydration profiles and crystallization traits solely from amorphous precursors under physiological conditions. To mimic the biomineralization tactic, here, we report pressure-controlled hydration and crystallization in fabricated ceramics, solely from the amorphous precursors of purely inorganic gels (PIGs) synthesized from biocompatible aqueous solutions with most common ions in organisms (Ca2+, Mg2+, CO32-, and PO43-). Transparent ceramic tablets are directly produced by compressing the PIGs under mild pressure, while the pressure regulates the hydration characteristics and the subsequent crystallization behaviors of the synthesized ceramics. Among the various hydration species, the moderately bound and ordered water appears to be a key in regulating the crystallization rate. This nature-inspired study offers deeper insights into the magic behind biomineralization.

Non‐isothermal crystallization kinetic of recycled PET and its blends with PBT modified with epoxy‐based multifunctional chain extender

AbstractA fundamental understanding of crystallization behavior is essential for the processing of both virgin and recycled polymers. This research delves into the crystallization characteristics and non‐isothermal crystallization kinetics of recycled polyethylene terephthalate (rPET) and its blends with poly butylene terephthalate (PBT), which have been modified using epoxy‐based multifunctional chain extenders (CE). The preparation of rPET/PBT blends involved a twin‐screw extruder, with varying weight ratios and different CE concentrations. Differential scanning calorimetry was employed to perform crystallization analysis on the samples. The results underscore the profound impact of blend composition on the thermal characteristics of the system, with CE exerting only a marginal influence. The glass transition temperatures (Tg) of the two polymers were measured at 49 and 79°C. During blending, the Tg values demonstrated variations relative to the proportions but did not adhere to the Fox equation. Furthermore, PBT was found to enhance the crystallization tendencies of rPET, resulting in an increase in relative crystallinity from 11% to 36%. Notably, the crystallization rate of PBT at 0.40 min−1 exceeded that of rPET at 0.36 min−1. PBT minimally affected the crystallization rate constant of rPET‐dominant blends, while rPET significantly reduced the crystallization rate in PBT‐dominant blends.

Influence of Nucleation on Relaxation, Molecular Cooperativity, and Physical Stability of Celecoxib Glass.

Although nucleation is considered the first step in the crystallization of glass materials, the structure and properties of the nuclei are not understood well. Influence of nucleation on the structure and dynamics of celecoxib glass was evaluated in this study. The nuclei for Form III were induced by annealing the glass at freezing temperature, and their impact on the relaxation behavior was investigated using thermal analysis and broadband dielectric spectroscopy to find accelerated α relaxation and suppressed β relaxation. In addition, observed after nucleation was a decrease in cooperativity of the molecular motion, presumably because of the appearance of void spaces in the glass structure. During long-term isothermal crystallization studies, crystal growth to Form III was accelerated in the presence of the nuclei, whereas this effect was less remarkable when a different crystal form dominated the crystallization behavior. These observations should provide more detailed insights into the nucleation mechanism and impact of nucleation on molecular dynamics including physical stability of pharmaceutical glasses. In addition, discussed is the remarkable acceleration of the crystallization rate of the celecoxib glass just below its Tg, which could be understood by diffusionless crystal growth.

The Effect of Powder Re-Use on the Coalescence Behaviour and Isothermal Crystallisation Kinetics of Polyamide 12 within Powder Bed Fusion.

Polymer powder bed fusion (PBF) is becoming increasingly popular for the fabrication of lightweight, high-performance parts, particularly for medical and aerospace applications. This study investigates the effect of powder re-use and material aging on the coalescence behaviour, melt flowability, and isothermal crystallisation kinetics of polyamide-12 (PA-12) powder. With increased powder re-use, a progressive reduction in melt flowability and material coalescence is observed; at 200 °C, the particle consolidation time increases from 15 s in virgin powder to 180 s in powder recovered from build 6. The observed changes in the behaviour of PA-12 were attributed to polycondensation and cross-linking; these aging phenomena also create structural defects, which hinder the rate and extent of primary crystallisation. At an isothermal crystallisation temperature of 165 °C, the crystallisation half-time increased from 12.78 min in virgin powder to 23.95 min in powder re-used across six build cycles. As a result, the commonly used Avrami model was found to be unsuitable for modelling the crystallisation behaviour of aged PA-12 powder, with the co-efficient of determination (R2) reducing from >0.995 for virgin powder to as low as 0.795 for re-used powder. On the other hand, an alternative method, the Hay model, is able to successfully track full phase transformation within re-used powder (R2 > 0.99). These results highlight the importance of selecting the most appropriate model for analysing the crystallisation kinetics of PA-12 powder re-used across multiple build cycles. This understanding is crucial for obtaining the strong mechanical properties and dimensional precision required for the fabrication of functional, end-use parts within PBF.

Trace polymer coated clarithromycin spherulites: Formation mechanism, improvement in pharmaceutical properties and development of high-drug-loading direct compression tablets

Clarithromycin (CLA) is a high dose antibiotic drug exhibiting poor flowability and tabletability, making the tablet development challenging. This study aims to develop spherulitic CLA by introducing trace amount of polymer in crystallization solution. Its formation mechanism, physicochemical properties and potential for the direct compression (DC) tablets development were also investigated. Morphological analyses and the in situ observation on crystallization process revealed that the CLA spherulites are formed by fractal branching growth from both sides of the threadlike precursor fibers. 1H NMR analysis and nucleation time monitoring indicated that the existence of hydroxypropyl cellulose in solution slowed down the crystal nucleation and growth rate by forming hydrogen bonding interactions with CLA molecules, making the system maintain high supersaturation, providing high driving forces for CLA spherulitic growth. In comparison to commercial CLA, the CLA spherulites exhibit profoundly improved flowability, tabletability and dissolution behaviors. XPS, contact angle and Raman mapping analysis confirmed the presence of a thin HPC layer on the surfaces and interior of CLA spherulitic particles, resulting in increasing powder plasticity, interparticulate bonding strength and powder wettability, thus better tabletability and dissolution performances. The improved flowability and tabletability of CLA spherulites also enabled the successful development of DC tablet formulation with a high CLA loading (82.8 wt%) and similar dissolution profiles to reference listed drug. This study provides a novel solid form of CLA with superior manufacturability for further development.

Boosting CsSnI3‐based near‐infrared perovskite light‐emitting diodes performance via solvent coordination engineering

AbstractDue to their unique photoelectric properties, nontoxic tin‐based perovskites are emerging candidates for efficient near‐infrared LEDs. However, the facile oxidation of Sn2+ and the rapid crystallization rate of tin‐based perovskites result in suboptimal film quality, leading to inferior efficiencies of tin‐based perovskite light‐emitting diodes (Pero‐LEDs). In this study, we investigate the influence of commonly used solvents on the quality of the CsSnI3 films. Remarkably, DMSO exhibits a stronger interaction with SnI2, forming a stable intermediate phase of SnI2·3DMSO. This intermediate effectively inhibits the oxidation of Sn2+ and slows down the crystallization rate, bringing in lower defect state density and higher photoluminescence quantum yield of the prepared perovskite films. Consequently, the corresponding Pero‐LEDs achieve a maximum external quantum efficiency (EQE) of 5.6%, among the most efficient near‐infrared Pero‐LEDs. In addition, the device processes ultra‐low efficiency roll‐off and high reproducibility. Our research underscores the crucial role of solvent‐perovskite coordination in determining film quality. These findings offer valuable guidance for screening solvents to prepare highly efficient and stable tin‐based perovskites.

Effects of Assisting Solvents on Purification Efficiency in the Layer Melt Crystallization of Glycerol.

The efficiency of layer melt crystallization for the selective separation of glycerol from a glycerol-diethylene glycol mixture containing 4 wt % of diethylene glycol was evaluated using solvent-free and solvent-aided approaches. The effect of 1-butanol and the binary solvent of 1-butanol and acetone with a total molar composition of 25 mol % on the crystal growth kinetics and the purity of the final product was studied at different undercooling degrees and crystallization yields. The melting point temperature of the mixtures was predicted by using the modified UNIFAC Dortmund model. The addition of both a single and binary solvents significantly increased the crystal growth rate and purity of the final product compared to crystallization from the solvent-free mixture. Additionally, higher crystal growth rates and product purity were observed in the binary solvent system compared to those in the single solvent system at the same degree of undercooling. The second stage of solvent-aided crystallization resulted in glycerol with a purity above 99.5 wt %, depending on the type of solvent used and the rate of crystal growth.

Medium-range structural order in amorphous Ge2Sb2Te5 phase change material

The crystallization rate is an important factor for the application of phase change materials as memory devices, which, thus, motivates a strong interest in the underlying crystallization processes. We analyzed the crystallization kinetics of as-deposited amorphous Ge2Sb2Te5 by differential scanning calorimetry, revealing that the thermal treatment below the crystallization onset temperature effectively enhances the crystallization rate compared to the as-deposited samples. Variable resolution fluctuation electron microscopy was carried out to characterize the corresponding amorphous structure of the as-deposited films and the differently annealed states regarding their medium-range order (MRO). As a result, relatively large MRO correlation lengths in the range of 3–4 nm were observed, whereas the MRO volume fraction doubled after longer annealing treatments, demonstrating the importance of MRO and MRO tuning for optimizing the properties of amorphous phase change materials. The increased volume fraction of the MRO seems to also favor an increased nanoindentation hardness.

Enhancing fluorescence properties in transparent glass ceramics via optimized Gd2O3/Ga2O3 ratios and crystallization conditions

In this study, Gd2O3–Ga2O3-GeO2-Nd2O3 glasses and glass ceramics were synthesized, and their structural, thermal, and crystallization characteristics were analyzed. Our findings indicate that substituting Gd2O3 for Ga2O3 positively influences the enhancement of bridge oxygen content and network structure stability. Heat treatments at different temperatures showed no significant impact on the crystal phase type but did alter the crystallization rate. Optimal conditions were identified: a Gd2O3/Ga2O3 ratio of 0.6 facilitated the production of transparent glass ceramics containing a single-phase GdGaGe2O7 nano-crystal. Notably, the glass ceramic nucleated at 780 °C for 24 h and crystallized at 840 °C for 5 min exhibited superior performance. Despite a 6% reduction in transmission rate, the emission intensity at 1060 nm increased by 1.5 times. This material holds promise for various applications in solid-state lasers operating within the 1.06 μm region.

Preparation and Properties of Polyvinyl Alcohol (PVA) Composite Films by Incorporation of Octadecylamine Polyoxyethylene Ether Modified Carbon Black Particles as Filler

In our research described here, a strong acid oxidizing agent was selected to modify the surface of carbon black (CB) to obtain oxidized carbon black (OCB) particles. These OCB particles were then subjected to an ionic bonding reaction with alkaline amine groups present on the surface of octadecylamine polyoxyethylene ether (AC1830) in the form of a paste, resulting in the production of polyether amine-modified oxidized carbon black particles (A-CB). FTIR confirmed the successful production of the A-CB particles. The PVA composite films were prepared using the casting method with varying amounts of A-CB as filler and PVA as the matrix. The films were then analyzed using tensile, scanning electron microscopy, dynamic thermo-mechanical analysis, DSC, and water absorption testing. The results showed that the tensile strength was highest at 3% A-CB, reaching 154.85 MPa. A-CB was well dispersed in PVA at low contents (1% and 3%). The loss modulus, energy storage modulus, crystallinity, and crystallization rate of the A-CB/PVA films improved compared to PVA films. Additionally, the issue of excessive water absorption in A-CB/PVA has been improved.

The Influence of Thermal Parameters on the Self-Nucleation Behavior of Polyphenylene Sulfide (PPS) during Secondary Thermoforming.

During the secondary thermoforming of carbon fiber-reinforced polyphenylene sulfide (CF/PPS) composites, a vital material for the aerospace field, varied thermal parameters profoundly influence the crystallization behavior of the PPS matrix. Notably, PPS exhibits a distinctive self-nucleation (SN) behavior during repeated thermal cycles. This behavior not only affects its crystallization but also impacts the processing and mechanical properties of PPS and CF/PPS composites. In this article, the effects of various parameters on the SN and non-isothermal crystallization behavior of PPS during two thermal cycles were systematically investigated by differential scanning calorimetry. It was found that the SN behavior was not affected by the cooling rate in the second thermal cycle. Furthermore, the lamellar annealing resulting from the heating process in both thermal cycles affected the temperature range for forming the special SN domain, because of the refined lamellar structure, and expelled various defects. Finally, this study indicated that to control the strong melt memory effect in the first thermal cycle, both the heating rate and processing melt temperature need to be controlled simultaneously. This work reveals that through collaborative control of these parameters, the crystalline morphology, crystallization temperature and crystallization rate in two thermal cycles are controlled. Furthermore, it presents a new perspective for controlling the crystallization behavior of the thermoplastic composite matrix during the secondary thermoforming process.

Flux creep regimes and vortex phase diagram in β-FeSe single crystals

We analyze the relationship between critical current densities (JC) and flux creep rates (S) in β-FeSe single crystals. This analysis was based on magnetization measurements. Additionally, we establish correlations with the recently reported magnetic field-induced geometrical deformation of the vortex lattice, transitioning from hexagonal to square shape due to a rhombic distortion [A. V. Putilov et al. Phys. Rev 99 (2019) 144514]. The results show that the magnetic field dependence of Jc displays distinct regimes, which is reflected by changes in S. The vortex dynamics is analyzed within the framework of the collective creep theory. S is characterized by low pinning energies and glassy exponents according to the expectation for small-bundles at low temperatures and magnetic fields where a hexagonal vortex lattice was reported. Conversely, we observe a systematic increase in S, resembling a shift from small to large vortex bundles, at magnetic fields corresponding to the rhombic distortion. Last, the relaxation rates exhibit significant values for magnetic fields where a square vortex lattice is expected, suggesting a potential crossover from elastic to plastic creep. Our findings highlight a direct relationship between vortex lattice deformations and a decrease in vortex pinning related to vortex-defect interactions.