Non-isothermal Crystallization Research Articles

Modelling the Melting Kinetics of Polyetheretherketone Depending on Thermal History: Application to Additive Manufacturing

Recent techniques for forming thermoplastics, such as welding, automated fibre placement or additive manufacturing, generate successive rapid heating and cooling cycles that cause the partial melting of crystals during the process. The melting of an interface is essential to guarantee a good molecular diffusion across the welded parts. Nevertheless, no model can correctly predict the melting kinetics and consequently the evolution of the crystalline degree during the layers’ deposition process. The purpose of this paper was to define the melting kinetics depending on the crystallization conditions for polyetheretherketone (PEEK). Firstly, a non-isothermal crystallization model was proposed over a wide range of cooling rates from 0.1 K.s−1 to 150 K.s−1. Experimental results have highlighted a dual-mode behaviour of melting and demonstrated the dependence of melting temperatures on crystallization conditions. Based on these observations, a model was developed to predict the melting behaviour after non-isothermal crystallization. The melting model revealed that after high cooling rates, primary and secondary crystals melt separately at low temperatures, while after slow cooling rates, both structures melt simultaneously at higher temperatures. Finally, the melting model was applied to the FFF thermal cycle to illustrate the influence of process parameters on the melting kinetics during deposition.

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.

Crystallization Behavior of Copolyesters Containing Sulfonates.

The polar sulfonate groups in cationic dyeable polyester (CDP) lead to complex crystallization behavior, affecting CDP production's stability. In this study, cationic dyeable polyesters (CDP) with different sulfonate group contents were prepared via one-step feeding of sodium isophthalic acid-5-sulfonate (SIPA), terephthalic acid (PTA), and ethylene glycol (EG). The non-isothermal crystallization behavior of these copolyesters was analyzed by differential scanning calorimetry (DSC). Results show that the crystallization temperature of the sample shifts to lower values with the increase in SIPA content. The relaxation behavior of the molecular chain is enhanced due to the ionic aggregation effect of sulfonate groups in CDP. Therefore, at low cooling rates (2.5 °C/min and 5 °C/min), some molecular chain segments in CDP are still too late to orderly stack into the lattice, forming metastable crystals, and melting double peaks appear on the melting curve after crystallization. When the cooling rate increases (10-20 °C/min), the limited region of sulfonate aggregation in CDP increases, resulting in more random chain segments, and a cold crystallization peak appears on the melting curve after crystallization. The non-isothermal crystallization behavior of all samples was fitted and analyzed by the Jeziorny equation, Ozawa equation, and Mo equation. The results indicate that the nucleation density and nucleation growth rate of CDP decrease with the increase in SIPA content. Meanwhile, analysis of the Kissinger equation reveals that the activation energy of non-isothermal crystallization decreases gradually with the increase in SIPA content, and the addition of SIPA makes CDP crystallization more difficult.

Crystallization of Polymers with a Reduced Density of Entanglements

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of entanglement. The basic knowledge of polymer crystallization was also presented. Then, it was discussed how polymers crystallize during their disentangling. Non-isothermal and isothermal crystallization experiments using disentangled polymers, and for comparison using entangled polymers, are described in more detail. The influence of disentangling on both nucleation and crystal growth is highlighted. It is also shown how the crystallization of polymers changes when macromolecules re-entangle.

Additive Manufacturing of Composite Polymers: Thermomechanical FEA and Experimental Study.

This study presents a comprehensive approach for simulating the additive manufacturing process of semi-crystalline composite polymers using Fused Deposition Modeling (FDM). By combining thermomechanical Finite Element Analysis (FEA) with experimental validation, our main objective is to comprehend and model the complex behaviors of 50 wt.% carbon fiber-reinforced Polyphenylene Sulfide (CF PPS) during FDM printing. The simulations of the FDM process encompass various theoretical aspects, including heat transfer, orthotropic thermal properties, thermal dissipation mechanisms, polymer crystallization, anisotropic viscoelasticity, and material shrinkage. We utilize Abaqus user subroutines such as UMATHT for thermal orthotropic constitutive behavior, UEPACTIVATIONVOL for progressive activation of elements, and ORIENT for material orientation. Mechanical behavior is characterized using a Maxwell model for viscoelastic materials, incorporating a dual non-isothermal crystallization kinetics model within the UMAT subroutine. Our approach is validated by comparing nodal temperature distributions obtained from both the Abaqus built-in AM Modeler and our user subroutines, showing close agreement and demonstrating the effectiveness of our simulation methods. Experimental verification further confirms the accuracy of our simulation techniques. The mechanical analysis investigates residual stresses and distortions, with particular emphasis on the critical transverse in-plane stress component. This study offers valuable insights into accurately simulating thermomechanical behaviors in additive manufacturing of composite polymers.

Exploring the effect of cooling rate on non-isothermal crystallization of copolymer polypropylene by fast scanning calorimetry

Exploring the effect of cooling rate on non-isothermal crystallization of copolymer polypropylene by fast scanning calorimetry

Concurrent effect of shear flow and CNT presence on crystallization behavior and electrical properties of polypropylene based nanocomposites: A comprehensive structure-property investigation

The loading of nanoparticle in the polymer matrix affects their response to shear flows applied during the fabrication process. With this in mind, in the present study, the concurrent effect of carbon nanotube (CNT) presence and shear application on the rheological and electrical properties as well as on the crystallization behavior of polypropylene (PP) based nanocomposites has been investigated. The results of rheological analyses showed that the solid-like behavior increases in proportion to the CNT content, and a remarkable increase in the solid-like behavior is obtained at a CNT content of 2 wt%. The isothermal crystallization results corroborated that crystallization temperature increases proportionally with the CNT content, however does not change with shearing. The non-isothermal crystallization findings confirmed that crystallization kinetics promotes with increasing CNT content, and this effect becomes more pronounced with shearing. The results of thermal analysis confirmed that the melting temperature decreases slightly, and the crystallinity remains almost unchanged with increasing CNT content up to 2%. However, when the CNT content rose up to 4%, the crystallinity decreased significantly due to confined crystallization. When this nanocomposite was subjected to shearing, the crystallinity increased. The results of electrical conductivity measurement revealed that the conductivity increases with increasing CNT content, while it decreases with shearing and the vulnerability of nanocomposites to shearing decreases with increasing CNT content.

The phase structure, transitions, and non-isothermal crystallization kinetics of Zn2V2O7 glass

The Zn2V2O7 glass was prepared by solid-state reaction using the initial reactant ZnO and V2O5 powder. X-ray diffraction was employed to characterize the phase composition of the as-prepared Zn2V2O7 powder. The crystallization kinetics of Zn2V2O7 glass prepared by solid-state reaction was studied using differential thermal analysis under non-isothermal conditions. It was established that the crystallization process of Zn2V2O7 can be divided into two steps, which is controlled first by a Disc-like with kinetic equation G(α)=[-ln(1-α)]1/3 and then by a Fibril-type growth type with kinetic equation G(α)=[1-(1-α)1/3]1/2 . The apparent activation energy calculated by different methods (Kissinger method, Ozawa method, Tang method, and Starink method) under non-isothermal conditions were similar, varying between 335.6 kJ·mol−1 and 371.6 kJ·mol−1, and the average apparent activation energy was equal to 362.2 kJ·mol−1.

Combinatory effects of nanocarbon- and radiation-induced networks on free-volume heterogeneity, nonisothermal crystallization, and electrorecovery

Electro shape-memory polymers (eSMPs) are highly regarded for their ability to undergo preordained transformations in response to electrical cues, a feature intrinsically linked to the prevailing electrical conduction pathways and macromolecular configurations. Alterations through the introduction of nanoparticles or the implementation of crosslinking techniques can produce synergistic or antagonistic shifts in the free volume and nonisothermal crystallization behavior. To date, such effects have remained largely unexplored. In this study, we developed gamma radiation-processed eSMPs that exhibit superior electrorecovery capabilities (approximately 100% recovery at 7.5 V) intrinsically connected to the specific radiation dose administered. Furthermore, we examined the changes in the free volume, extensional viscosity, rheology, and nonisothermal crystallization of these electroconductive composites. Our findings highlight the necessity of a critical radiation dose for the induction of electroshape recovery, and evidence suggests that the radiation dose substantially reduces the crystallization temperature under nonisothermal conditions while simultaneously broadening the crystallization process, especially at high cooling rates. Analyses of extensional stress further underscored the critical role of radiation dose. Positron annihilation lifetime spectroscopy (PALS) studies revealed that both the NCB and radiation dose contribute to an overall reduction in the free-volume size.

Crystallization manipulation of poly(butylene succinate) via hydrazide-based self-assembled hydrogen-bonding interactions

Self-assembled nucleating agents based on hydrogen bonding interactions have been increasingly used to manipulate the crystallization behavior of polymer materials, yet the specific working mechanism is not well unrevealed. In this study, the hydrazide-based nucleator structure of bis-(mono-methyl succinyl)dihydrazide (MSAD) is randomly incorporated in poly(butylene succinate) (PBS) chains to prepare a series copolymers of PBS-co-MSAD. It is confirmed that the multiple hydrogen-bonding interactions strengthen as the content of the MSAD segment increases, leading to a remarkable elevation of crystallization temperature. Meanwhile, the primary nucleation density of PBS is significantly raised without changing crystal modification. The formation of a pre-ordered network of hydrogen-bonding structures during non-isothermal crystallization is confirmed by rheological measurement and Fourier transform infrared spectroscopy investigation, which immediately induces the crystallization of PBS segments once strong enough. In addition, the melt crystallization mechanism of PBS-co-MSAD with heterogeneous hydrogen-bonding segments is elucidated in detail by combining a self-nucleation protocol.

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).

Biobased Immiscible Polylactic Acid (PLA): Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) Blends: Impact of Rheological and Non-isothermal Crystallization on the Bead Foaming Behavior

AbstractNowadays, bead foams are of great interest due to their high lightweight potential. The processing of such foams strongly depends on the crystallization and rheological behavior of the polymers used. By blending polymers, these properties can be tailored to obtain beaded foams with low density, small cell size and high cell density. As a bio-based polymer, PLA is of great interest due to its renewable carbon source. PLA suffers from its low thermal and rheological properties, which can be compensated by using blends. The correlation between the PLA/PHBV ratio and the rheological as well as the crystallization behavior was investigated. The use of PHBV as a minor phase significantly changes the rheological properties and increases the crystallization behavior of PLA. These findings were applied to the foam extrusion process to obtain low density bead foams. Bead foams with densities below 100 kg/m3, mean cell sizes below 50 µm and cell densities of 1 × 107 cells/cm3 were obtained.

Preparation and crystallization behavior of sensitive thermochromic microencapsulated phase change materials

A novel sensitive thermo-chromic microcapsules with inorganic/organic nanoparticles-embedded composite shell was designed and synthesized, and the thermal properties, thermo-chromic performance, crystallization behavior of ethyl myristate (EM) in confined spaces were studied in this paper. As the reaction proceeded, the aminated silica (NH2-SiO2) nanoparticles modified outer shell in the aqueous phase and isophorone diisocyanate (IPDI) in the oil phase gradually self-assembled at the inner interface, leading to the formation of an inorganic/organic polymers composite shell. The effect of NH2-SiO2 nanoparticles content on the crystallization behavior, microstructure, morphology, and phase-change properties as well as the thermal stability of MPCMs were investigated in detail. Interestingly, the covalent attachment of NH2-SiO2 nanoparticles on the capsules surface offered long-term chemical stability compared to that of conventional physical adsorption. The NH2-SiO2 nanoparticles were found distributed uniformly on the surface of MPCMs, and the onset crystallization temperature of MPCMs increased by 7.3 °C with NH2-SiO2 nanoparticles addition of 15% content, which counteracts the super-cooling phenomenon. Microcapsule temperature change optical microscopy and non-isothermal crystallization kinetics revealed that the crystallization of RS-MPCMs were homogeneous as well. RS-MPCMs have significant potential in green energy applications due to their latent heat storage, thermal stability, thermal conductivity, leakage prevention, and mechanical properties.

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.

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.

Non-isothermal crystallization kinetics for CaO–SrO–B2O3–Al2O3–Bi2O3–SiO2 glass system with Ta2O5 addition

The effect of Ta2O5 at the rates of 1, 2, 3 and 4 % mol on the CaO–SrO–B2O3–Al2O3–Bi2O3–SiO2 glass system was examined by the melt-quenching at 1400 °C. Non-isothermal crystallization kinetics of the compounds were calculated using Differential Scanning Calorimetry (DSC). The kinetics study revealed activation energy values of 109.4 kJ/mol for the T1 composition, 302.14 kJ/mol for the T2 composition, 471.5 kJ/mol for the T3 composition, and 344.7 kJ/mol for the T4 composition, as determined by applying the Kissinger method. According to the average of Avrami parameters, two-dimensional crystal growth was observed in T1 glass and surface crystallization was observed in all other glass. The glass forming ability (GFA) of the glasses was investigated with the values obtained as a result of HSM analysis. In the XRD analysis performed after heat treatment at 850 °C, crystal phase development was observed in the glasses. As a result of the crystallization process, it was observed that wollastonite, strontium aluminum silicate, strontium aluminum oxide and bismuth oxide phases were formed in T1, T2 and T3 glasses.

Crystallization, recrystallization and melting behaviors in supramolecular poly(l-lactic acid) bonded by metal-ligand coordination

The effect of metal-ligand coordination on crystallization and melting behaviors of polymers has not been comprehensively investigated. In this study, a series of supramolecular poly(l-lactic acid)s (SM-PLLAs) were prepared by changing various metal ions, length of polymer chains and stoichiometric ratio of ligands to metal ions (L/M). The complexation of metal ions with ligands in SM-PLLAs was confirmed by the intrinsic viscosity and UV–visible spectroscopy. It was found that crystallization rate and crystallinity of SM-PLLAs were strongly dependent on the chain length of precursor in both non-isothermal and isothermal crystallizations. With chain length of 1.6 kg/mol, crystallization of PLLA was completely suppressed regardless of the metal ions, whereas PLLA with longer chain length of 3.0 kg/mol exhibited strong dependence of the type of metal. During the heating process, melting behaviors can be tuned by the strength of metal-ligand coordination, temperature and the degree of complexation. Unlike PLLA precursor and SM-PLLA coordinated with Cu2+ exhibited multiple melting behaviors, only a single melting peak was appeared in PLLA bonded with Co2+, indicative of suppression of recrystallization during heating. With ratio of ligand to Co2+ increased from 1:1 to 6:1, crystallization and melting behaviors were tuned by the content of free and bounded PLLA chains. As compared to Cu2+, SM-PLLA coordinated with Co2+ exhibited higher complex modulus and viscosity due to the high bond strength, as well as a more stable structure underwent heating and shear, making diffusion of polymer chains and the structural adjustment more difficult. This work may shed light on understanding the intricate interplay of metal-ligand coordination effects on the crystallization and melting behaviors of polymers, which may be helpful with the design and making out the relationship between structure and properties of supramolecular polymers.

Non-isothermal crystallization kinetics behavior of ethylene-methyl acrylate copolymer and ethylene-methyl acrylate copolymer/chloroprene rubber thermoplastic vulcanizate

The non-isothermal crystallization kinetics of the pure ethylene-methyl acrylate copolymer (EMA) and EMA/chloroprene rubber (CR) thermoplastic vulcanizate (TPV) prepared by dynamic vulcanization were extensively investigated using differential scanning calorimetry (DSC). The Avrami method modified by the Jeziorny, the Ozawa and the Mo methods were employed to characterize the non-isothermal crystallization process. The results indicated that the Avrami method modified by the Jeziorny and Mo methods effectively characterized the non-isothermal crystallization behavior of both pure EMA and EMA/CR TPV, while the behavior could not be described by the Ozawa modification method.

Preferential formation of the stereocomplex crystals of poly(L‐lactide) and poly(D‐lactide) blend by epoxidized soybean oil under nonisothermal crystallization

AbstractFormation of stereocomplex crystals (SCs) in enantiomeric poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA) blends is an effective way to improve the heat resistance and mechanical performance of polylactide (PLA) products. However, obtaining PLAs with high stereocomplex content is not straightforward as the homocrystal and SCs occur simultaneously and compete with one another. In this work, various amounts of epoxidized soybean oil (SO) or SO at 3%–20% by weight were added to equal amounts of the stereoisomers (PLLA/PDLA; 50/50). From differential scanning calorimetry, it was found that epoxidized SO increased the crystallization temperature, facilitated the SC crystallization, and suppressed the homecrystal formation, whereas SO did not affect the crystallization behavior for the racemic blends. Moreover, epoxidized SO reduced the glass transition temperature, cold crystallization temperature, and melting temperature of the racemic blends. We examined how epoxidized SO affected the crystallization of PLLA/PDLA at cooling rates from 2 to 20°C/min. We discovered that epoxidized SO still encouraged SC crystallization. The activation energy, calculated from Takhor and Kissinger equations, indicated that adding 5 wt% epoxidized SO effectively promoted the crystallization and facilitated the SC formation of the PLLA/PDLA blend.

Effect of Reprocessing on the Crystallization of Different Polyesters

The changes in crystallization characteristics of four polyesters were investigated during multiple processing. Two of these were petroleum-based materials: poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT), and two were bio-based materials: poly (lactic acid) (PLA) and poly (butylene succinate) (PBS). We found that during non-isothermal crystallization the different type of polyesters shown different behaviour: the PET and PLA materials were more sensitive to the cooling rate than the PBT and PBS. Interestingly, at low cooling rates, the number of reprocessing steps had no significant effect on the crystallinity of PBT and PBS, but reduced it for PET, but increased it for PBT.