Activation Energy Of Non-isothermal Crystallization Research Articles

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.

Analysis of the Non-isothermal Crystallization Kinetics of the Polyamide 6/M-lignin Composites

In this study, investigations of the non-isothermal crystallization kinetics of polyamide 6 (PA6) and PA6/m-lignin composites were conducted by differential scanning calorimetry (DSC). The crystallization kinetics of the PA6, including crystallization temperature and rate, were characterized by monitoring the heat flow during cooling. The study found that the crystallization temperature shifted to lower temperatures and the crystallization kinetics slowed down with increasing lignin. Besides, the Avrami equation modified by Jeziorny and Mo’s method were used to study the non-isothermal crystallization kinetics of the neat PA6 and PA6 composites. The curve fit resulting from the modified Avrami equation was not convincing. However, Mo’s method did successfully characterize the overall non-isothermal crystallization kinetics for neat PA6 and the PA6 composites. In addition, the activation energies of the non-isothermal crystallization were calculated by the Kissinger method. It was found that the PA6 composite crystallization rate increased when adding less than 10% lignin. However, the more the content of m-lignin, the slower the crystallization rate. The same conclusion was reached based on the fitting results of the non-isothermal crystallization activation energies.

Nonisothermal crystallization of poly(L‐lactic acid) promoted by polyols

AbstractThe inherent weak crystallization capacity has an impact on the processability and serviceability of poly(lactic acid) (PLA) and limits its application. D‐mannitol (DM) and xylitol (Xy), acting as a nucleation accelerant, were melt‐blended with poly(L‐lactic acid) (PLLA) and the nonisothermal crystallization behavior was investigated. At 1% dosage, the crystallization temperatures of polyol‐modified PLLAs are 10–15°C higher than those of neat PLLA in the cooling rate range of 5–20°C. The theoretical half‐time of crystallization (t1/2) of the Jeziorny model remains constant over the cooling rate range of 10–20°C min−1, in contrast to the greatly reduced t1/2 reported for heterogeneous nucleating agents. Xy is more effective than DM in promoting crystallization. It increases the crystallinity of PLLA to ~40% within the 1%–5% dosage; and the activation energy of nonisothermal crystallization calculated by the Friendman method follows the order of magnitude: neat PLLA ˃ PLLA/DM ˃ PLLA/Xy. Polyols promote the crystallization of PLLA by a mechanism different from heterogeneous nucleation, providing an efficient and biosafety approach to improve the performance of PLA.

Molecular dynamics simulation and non-isothermal crystallization kinetics of polyamide 4 and different bio-based polyamide blends.

The effects of the structural units and blending ratio on the crystallization behavior of blends of polyamide 4 (PA4) with polyamide 56 (PA56) and polyamide 11 (PA11) were studied using molecular dynamics simulations and non-isothermal crystallization kinetics. The simulation results show that the crystallinity of PA4/PA56 blends (B4/56) with a PA56 content of 30-50% was 3.5-10.8% lower than that of B4/56 with a PA56 content of 20%, and the crystallinity of PA4/PA11 blends (B4/11) decreased by 9.5% as PA11 content increased from 20% to 50%. The experimental results show that both B4/56 and B4/11 form PA4- and PA56-rich (PA11-rich) phases through crystallization-induced phase separation. The interplanar spacing of the PA4-rich phase of B4/56 changed relative to that of PA4, indicating that some PA56 entered the PA4-rich phase unit cell. As the PA56 content increased from 20% to 50%, the crystallinity of B4/56 decreased by 11.2%, and the crystallization-induced phase separation grew distinct. The B4/56 with a higher PA4 content crystallized more easily. As the PA11 content increased from 20% to 50%, the crystallinity of B4/11 decreased by 12.5%, and PA11 barely participated in the crystallization of the PA4-rich phase. The blending ratio had no significant effect on the crystallization rate and crystal-growth degree of B4/11, and the non-isothermal crystallization activation energy of B4/11 was significantly higher than that of B4/56, indicating that the crystallization ability of the B4/11 blend system is worse. This study provides a theoretical basis for the design and performance regulation of PA4-based polyamide blends.

High-Performance Optical PET Analysis via Non-Isothermal Crystallization Kinetics.

The optical properties of PET have always been a problem that related research has been trying to break through. In the previous work, we modified PET by adding PSLDH (phosphate antioxidant) to obtain a PET film with excellent optical properties. Through non-isothermal crystallization kinetic analysis of modified PET, we hope to verify the conclusion of optical properties by the effect of PSLDH addition on the crystallization properties of PET. PET and PSLDH modified PET were tested by DSC at different cooling rates. The non-isothermal crystallization kinetic process was calculated and analyzed by Jeziorny and Mo methods and the non-isothermal crystallization activation energy was analyzed by Kissinger and Friedman methods by analyzing the DSC curves. The results show that the addition of PSLDH at 0.05 wt% can make the crystallization of PET smaller and slower, which is the same as the case required for excellent optical properties. At the same time, the results can also guide the processing of the optical PET film.

Synthesis, Characterization and Non-Isothermal Crystallization Kinetics of a New Family of Poly (Ether-Block-Amide)s Based on Nylon 10T/10I.

A series of novel thermoplastic elastomers based on (poly(decamethylene terephthalamide/decamethylene isophthalamide), PA10T/10I) and poly(ethylene glycol) (PEG) were synthesized via a facile one-pot, efficient and pollution-free method. The thermal analysis demonstrates that the melting points of the resultant elastomers were in the range of 217.1–233.9 °C, and their initial decomposition temperatures were in the range of 385.3–387.5 °C. That is higher than most commercial polyamide-based thermoplastic elastomers. The tensile strength of the resultant elastomers ranges from 21.9 to 41.1 MPa. According to the high-temperature bending test results, the resultant samples still maintain considerably better mechanical properties than commercial products such as Pebax® 5533 (Arkema, Paris, France), and these novel thermoplastic elastomers could potentially be applied in high-temperature scenes. The non-isothermal crystallization kinetics of the resultant elastomers and PA10T/10I was investigated by means of Jeziorny and Mo’s methods. Both of them could successfully describe the crystallization behavior of the resultant elastomers. Additionally, the activation energy of non-isothermal crystallization was calculated by the Kissinger method and the Friedman equation. The results indicate that the crystallization rates follow the order of TPAE-2000 > TPAE-1500 > PA10T/10I > TPAE-1000. From the crystallization analysis, the crystallization kinetics and activation energies are deeply affected by the molecular weight of hard segment.

Isothermal and Non-Isothermal Crystallization Kinetics of PVDF and PVDF/PMMA Blends

Background: poly(vinylidene fluoride) PVDF and PVDF/PMMA blends have been investigated with a focus on the crystal structure, immiscibility and mechanical properties. However, few reports were found on the crystallization behaviors of PVDF and PVDF/PMMA blends, especially on crystallization kinetics. The article is to report the research on isothermal and nonisothermal crystallization kinetics for PVDF and PVDF/PMMA blends using differential scanning calorimetry (DSC). Results: Besides crystallization temperature and isothermal crystallization activation energy, the Avrami equation exponent of PVDF in blends decreased compared with pure PVDF. The nonisothermal crystallization kinetics of PVDF and PVDF/PMMA (70:30) blends were investigated by Ozawa equation, Jeziorny method and crystallization rate constant (CRC) in detail. The nonisothermal crystallization energy of pure PVDF and its blends were determined by the Kissinger and Vyazovkin’s method. Conclusion: The nucleation and growth mechanism of PVDF in blends changed compared with pure PVDF. The Ozawa equation is not applicable in nonisothermal crystallization kinetics of PVDF and PVDF/PMMA blends. The decreasing of crystallization ability of PVDF in blends were found and confirmed by CRC and the decline of crystallization rate constant in Jeziorny method. Such is opposite to the results of Kissinger’s and Vyazovkin’s method, chances are that these two methods were not used to calculate the nonisothermal crystallization activation energy where the nucleation process was influenced.

Non-isothermal crystallization kinetics of paraffin wax as a phase changing energy storage material

Paraffin waxes are becoming increasingly attractive especially on thermal energy storage field. The crystallization process, considered as a major thermal discharging approach, has a significant impact on the thermal performances of paraffin wax. This study aims to comprehend the mechanism of paraffin wax crystallization under non-isothermal conditions by means of Differential Scanning Calorimetry (DSC). Jeziorny and Mo models were applied to reveal the morphology of paraffin wax crystals. Moreover, the non-isothermal crystallization activation energy was calculated through Kissinger and Friedman methods, respectively. Investigations show that the used kinetics models gratifyingly fitted the experimental data, providing crystallization kinetic parameters such as crystallization rate, half-life time (t1/2) as well as the required cooling rate for a designated relative crystallinity. Furthermore, it was found that the average Avrami exponent value is close to 2 which indicates that the crystals are one-dimensional with needle-like morphologies.

Effect of thermal aging on crystallization behaviors and dynamic mechanical properties of glass fiber reinforced polyphenylene sulfide (PPS/GF) composites

In this study, the main purpose is to systematically evaluate isothermal and non-isothermal crystallization behavior of short glass fiber-reinforced polyphenylene sulfide polymer composites (PPS/GF) by a wide range of commonly applied models and also to preciously discuss the crystallization evolution and dynamic mechanical properties together with the consideration of thermal aging effects. Some interesting progress concerning this study can be concluded as follows: the Avrami model was used to examine the isothermal crystallization behavior of PPS/GF and the Avrami plot results exhibit that the isothermal crystallization contains primary and second crystallization process. In terms of non-isothermal crystallization, the Jeriorny model and Mo model could describe the mechanism of nucleation and crystal growth of PPS/GF material under study. Also, the activation energy of non-isothermal crystallization is calculated (−58.78 kJ/mol) by Kissinger method. Another important aspect is that thermal aging has an obvious effect on crystallization behaviors of PPS under study. The degree of crystallinity increases from 44% (virgin sample) to 56% after 96 h of aging at 200 °C. After a long period of oxidation up to 1080 h at 200 °C, the crystallinity degree decreases to 36.6% due to thermo-oxidation effect. DMA results imply that thermal aging may lead to more crosslinking reactions and result into more restriction of molecule mobility in PPS composite materials.

Nonisothermal crystallization of poly(l-lactide) in poly(l-lactide)/olive stone flour composites

Nonisothermal crystallization of poly(l-lactide) in poly(l-lactide)/olive stone flour (PLLA/OSF) composites was studied applying differential scanning calorimetry (DSC). The analysis was carried out during cooling of the melt at different and constant rates. The kinetic parameters of the crystallization were determined by the Avrami, Ozawa and Mo methods. The Avrami analysis revealed the existence of two mechanisms of nonisothermal crystallization in all samples. The Ozawa and Mo methods failed to successfully describe the crystallization behaviour of PLLA with or without OSF. The effective activation energy of nonisothermal crystallization was estimated with the Friedman method. The kinetic analysis using the Friedman method showed the complexity of the crystallization process. The results of structural investigation shown that OSF has a low influence on the interplanetary distance of PLLA crystal phase. The crystallite size of PLLA decreases with increasing cooling rates and the conditions for the growth of the lamellar structure is more suitable at the lower cooling rate.

Non-isothermal crystallization kinetics of hybrid carbon nanotube - silica/ polyvinyl alcohol Nanocomposites

In this paper, a new nanocomposite based on polyvinyl alcohol (PVA) / hybrid carbon nanotube (CNT) - silica (SiO2) with different amounts (1 and 5 wt%) of hybrid nanostructures are successfully prepared by solution-casting method. The crystallization kinetics of PVA and its nanocomposites under non-isothermal conditions are evaluated by differential scanning calorimetry (DSC). Jeziorny, Ozawa and Mo models are used to determine the PVA and PVA/CNT-SiO2 crystallization kinetics parameters. It was found that the Ozawa method is not suitable for the description of the non-isothermal crystallization behavior of PVA and its nanocomposites, while the Jeziorny and Mo models fitted the experimental data very well. Furthermore, Jeziorny analysis indicated that the crystallization process of PVA and PVA/CNT-SiO2 nanocomposites involve two main stages, the primary and secondary crystallization process. Additionally, the activation energy of non-isothermal crystallization is also estimated by using Friedman method, Kissinger method and isoconversional method modified by Vyazovkin, respectively. The latter method is more appropriate to calculate the non-isothermal crystallization activation energy of both PVA and PVA/CNT-SiO2 nanocomposites. The Hoffman-Lauritzen parameters (U* and Kg) were also determined. Based on the findings of Zc values in Jeziorny model, F(T) values in Mo model, crystallization activation energy and the Hoffman-Lauritzen parameters, it was concluded that hybrid carbon nanotube - silica nanostructures promoted PVA non-isothermal crystallization process.

Self-limited growth of nanocrystals in phosphosilicate melts during cooling

In this Letter, we demonstrate that the spontaneous nanophase-separation can greatly enhance the heterogeneous nucleation in the investigated phosphosilicate melts. The two separated phases are found to be the phosphate-rich phase as the floppy domain and the silicate-rich phases as rigid phase. We found that sodium phosphate nanocrystals form in the phosphate-rich phase during melt cooling. The growth of these nanocrystals are self-limited, i.e., limited by the surrounding silicate-rich phase with higher viscosity, and hence lower ionic diffusion compared to the phosphate-rich phase. Our results show that the substitution of B2O3 or Al2O3 for partial Na2O enhances the spontaneous nucleation, although the viscosity of silicate-rich matrix phase is increased by such substitution. This implies that the compositional substitution enhances nanophase separation and thereby lowers the activation energy for non-isothermal crystallization. This work indicates that nanophase separation is crucial for fabrication of transparent glass-ceramics from phosphosilicate melts.

Graphene Nanoplatelet-Reinforced Poly(vinylidene fluoride)/High Density Polyethylene Blend-Based Nanocomposites with Enhanced Thermal and Electrical Properties.

In this study, a graphene nanoplatelet (GNP) was used as a reinforcing filler to prepare poly(vinylidene fluoride) (PVDF)/high density polyethylene (HDPE) blend-based nanocomposites through a melt mixing method. Scanning electron microscopy confirmed that the GNP was mainly distributed within the PVDF matrix phase. X-ray diffraction analysis showed that PVDF and HDPE retained their crystal structure in the blend and composites. Thermogravimetric analysis showed that the addition of GNP enhanced the thermal stability of the blend, which was more evident in a nitrogen environment than in an air environment. Differential scanning calorimetry results showed that GNP facilitated the nucleation of PVDF and HDPE in the composites upon crystallization. The activation energy for non-isothermal crystallization of PVDF increased with increasing GNP loading in the composites. The Avrami n values ranged from 1.9–3.8 for isothermal crystallization of PVDF in different samples. The Young’s and flexural moduli of the blend improved by more than 20% at 2 phr GNP loading in the composites. The measured rheological properties confirmed the formation of a pseudo-network structure of GNP-PVDF in the composites. The electrical resistivity of the blend reduced by three orders at a 3-phr GNP loading. The PVDF/HDPE blend and composites showed interesting application prospects for electromechanical devices and capacitors.

Improvement of Transparencies and Mechanical Properties of Poly(cyclohexylene dimethylene cyclohexanedicarboxylate) Parts Using a Compounding Nucleating Agent to Control Crystallization.

Poly(cyclohexylene dimethylene cyclohexanedicarboxylate) (PCCE) is a kind of copolyester polymer with excellent toughness and outstanding flexibility. However, the opacity caused by crystallization limits the widespread application of PCCE in products that have transparency requirements. The effects of 1,3:2,4-Di-p-methylbenzylidene sorbitol (MDBS) on the crystallization behavior, transparency, and mechanical properties of a PCCE melt were investigated via differential scanning calorimetry (DSC), spectrophotometry, and tensile testing. The results suggest that the transparency and mechanical properties of PCCE drastically improve and that its crystallization behaviors are obviously influenced by the addition of MDBS. PCCE with 0.6 wt% MDBS was then selected as a representative sample, and its thermal behavior and crystal morphology were further investigated by DSC, hot-staged polarizing microscopy (HSPLM), and scanning electron microscopy (SEM). The quantitative results suggest that, compared to neat PCCE resin, PCCE/MDBS has a lower isothermal and nonisothermal crystallization activation energy, which indicates a rapid crystallization process. The results also show that, compared to the pure PCCE melt, the PCCE/MDBS melt experiences a greater increase in the number of crystals and a greater decrease in the crystal size during cooling. The acceleration of the crystallization process and reduction in crystal size can be both attributed to the nucleation effect of the MDBS. In conclusion, because the addition of the nucleating agent improves the transparency and tensile properties of PCCE by adjusting and controlling its thermal and crystallization behaviors, the proposed technique of using a compounding nucleating agent to control crystallization is therefore suitable for PCCE.

Nucleating and retarding effects of nanohydroxyapatite on the crystallization of poly(butylene terephthalate-co-alkylene dicarboxylate)s with different lengths

New biodegradable and biocompatible composites are continuously developed for biomedical applications (e.g., from drug delivery devices to tissue engineering scaffolds). Properties of such systems may depend on their morphology and structure, which are attained after their processing, and therefore, the study of the crystallization kinetics has a particular relevance. The crystallization kinetics of hydroxyapatite-filled poly(butylene terephthalate-co-alkylene dicarboxylate)s has been studied under non-isothermal conditions, using a wide range of cooling rates and different kinetic models. Based on our results, nanohydroxyapatite (nHAp) particles were found to effectively act as additional nucleation sites for poly(butylene terephthalate-co-succinate) (PBST), giving rise to an increased crystallization rate with respect to pure PBST. However, the overall growth rate of HAp nanocomposites decreased compared to the corresponding homopolymers with longer aliphatic dicarboxylic acids (i.e., adipic and sebacic acid derivatives). In order to clarify this point, the activation energy for non-isothermal crystallization was evaluated using the Friedman method and significant differences were observed, suggesting a disturbing effect of nanoparticles on the motion of molecular chains that hindered their capability to reach the growing crystallization front. Isoconversional methods provided a good understanding of the kinetics of the crystallization process and significant information regarding the activation energy, relative crystallinity, and global and local Avrami exponents.

Non-isothermal crystallization of copper-containing composite based on polymer alloy of poly(ethylene oxide) and polyethylene

Non-isothermal crystallization behavior of copper/poly(ethylene oxide)/low density polyethylene (Cu/PEO/LDPE) composite was investigated by using differential scanning calorimetry, and the feasibility of various models for determination the non-isothermal crystallization kinetics and activation energy of its LDPE matrix were evaluated in this work. The results show that the crystallization of its LDPE matrix was retarded by the addition of PEO with a higher molecular weight and accelerated by cooling with a larger cooling rate. The results also show that the crystallization kinetics of the LDPE matrix was not affected by the PEO molecular weights, but the crystallization activation energy of the LDPE matrix was affected and increases with the increase of PEO molecular weight. Additionally, Avrami-Ozawa equation is desirable to determinate the non-isothermal crystallization kinetics of their LDPE matrix, and isoconversional method modified by Vyazovkin is more suitable to calculate the non-isothermal crystallization activation energy of their LDPE matrix.

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.

Thermal properties, phase morphology and stability of biodegradable PLA/PBSL/HAp composites

Blends/composites of poly(lactic acid) (PLA) with poly(butylene succinate-co-lactate) (PBSL) and hydroxyapatite (HAp) were successfully prepared by a conventional melt-mixing process. The thermal properties, phase morphology, crystal structure, and in vitro hydro-degradability of the prepared samples were characterized and compared. Thermogravimetric analysis confirmed that adding HAp increased the thermal stability of PLA/PBSL blends in both air and nitrogen environments. The activation energy for PLA thermal degradation increased with increasing HAp content in the samples. Scanning electron microscopy results showed that HAp was uniformly distributed within the composites. HAp also played a compatibilizer role for the PLA/PBSL blends, leading to evidently reduced size of dispersed PBSL domains. The Avrami crystallization analysis revealed that the n values of PLA in different samples ranged within 2.1–3.9, and the presence of HAp caused athermal nucleation process of PLA crystallization. The activation energy for non-isothermal crystallization of PLA decreased from 136 kJ/mol in neat state to 86 kJ/mol in PLA(70)/PBSL(30)/HAp(20 phr) composite. Melting behavior study revealed that the presence of HAp increased the original crystals stability of PLA in the composites. X-ray diffraction results confirmed that the crystal structures of PLA and PBSL remained in the blends and composites. Finally, in vitro hydrolytic degradation tests showed that the HAp addition facilitated the degradation of the prepared samples.

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.

Morphology and non-isothermal crystallization of dynamically vulcanized PP/EPDM blends in situ compatibilized via magnesium dimethacrylate

Polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends in situ compatibilized by magnesium dimethacrylate (MDMA) were fabricated via peroxide-induced dynamic vulcanization. Scanning electron microscope observation indicated that the size of cross-linked EPDM particles decreased with incorporation of MDMA. Polarizing Optical Microscope (POM) analysis suggested that the spherulite size of PP phase decreased sharply with incorporation of MDMA during dynamic vulcanization. The Pseudo-Avrami, Ozawa and Mo's models were applied to analyze the non-isothermal crystallization kinetics of the composites. The analyzed data indicated that the crosslinked EPDM particles and homopolymerized MDMA acted as heterogeneous nucleating agents, which enhanced the crystallizability and decreased the spherulite size of the PP phase. In addition, the non-isothermal crystallization activation energy (ΔE) was calculated through the Kissinger and Friedman methods, and the ΔE value was found increase with incorporation of MDMA.