Nonisothermal Crystallization Of Poly Research Articles

The Effect of Polyethylene Glycol on the Non-Isothermal Crystallization of Poly(L-lactide) and Poly(D-lactide) Blends.

The formation of polylactide stereocomplex (sc-PLA), involving the blending of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), enhances PLA materials by making them stronger and more heat-resistant. This study investigated the competitive crystallization behavior of homocrystals (HCs) and stereocomplex crystals (SCs) in a 50/50 PLLA/PDLA blend with added polyethylene glycol (PEG). PEG, with molecular weights of 400 g/mol and 35,000 g/mol, was incorporated at concentrations ranging from 5% to 20% by weight. Differential scanning calorimetry (DSC) analysis revealed that PEG increased the crystallization temperature, promoted SC formation, and inhibited HC formation. PEG also acted as a plasticizer, lowering both melting and crystallization temperatures. The second heating DSC curve showed that the pure PLLA/PDLA blend had a 57.1% fraction of SC while adding 5% PEG with a molecular weight of 400 g/mol resulted in complete SC formation. In contrast, PEG with a molecular weight of 35,000 g/mol was less effective, allowing some HC formation. Additionally, PEG consistently promoted SC formation across various cooling rates (2, 5, 10, or 20 °C/min), demonstrating a robust influence under different conditions.

Non-Isothermal Crystallization Kinetics of PBSu/Biochar Composites Studied by Isoconversional and Model Fitting Methods

Non-isothermal crystallization of Poly(butylene succinate) (PBSu)/biochar composites was studied at various constant cooling rates using differential scanning calorimetry. The analysis of the kinetics data revealed that the overall crystallization rate and activation energy of the PBSu polymer were significantly influenced by the addition of biochar. Specifically, the PBSu/5% biochar composite with a higher filler content was more effective as a nucleation agent in the polymer matrix, as indicated by the nucleation activity (ψ) value of 0.45. The activation energy of the PBSu/5% biochar composite was found to be higher than that of the other compositions, while the nucleation activity of the PBSu/biochar composites decreased as the biochar content increased. The Avrami equation, which is commonly used to describe the kinetics of crystallization, was found to be limited in accurately predicting the non-isothermal crystallization behavior of PBSu and PBSu/biochar composites. Although the Nakamura/Hoffman-Lauritzen model performed well overall, it may not have accurately predicted the crystallization rate at the end of the process due to the possibility of secondary crystallization. Finally, the combination of the Šesták-Berggren model with the Hoffman-Lauritzen theory was found to accurately predict the crystallization behavior of the PBSu/biochar composites, indicating a complex crystallization mechanism involving both nucleation and growth. The Kg parameter of neat PBSu was found to be 0.7099 K2, while the melting temperature and glass transition temperature of neat PBSu were found to be 114.91 °C and 35 °C, respectively, very close to the measured values. The Avrami nucleation dimension n was found to 2.65 for PBSu/5% biochar composite indicating that the crystallization process is complex in the composites.

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.

Physical Properties of Biodegradable Poly(L-lactide) Induced by N, N -Bis(Benzoyl) 1, 3-Cyclohexanedicarboxylic Acid Dihydrazide as Crystallinity Additive

This work is aimed at synthesizing an organic compound N, N -bis(benzoyl) 1,3-cyclohexane-dicarboxylic acid dihydrazide (CABH) to focus on its effect on the non-isothermal crystallization of poly(L-lactide) (PLLA), meanwhile the melting behavior, thermal decomposition process and optical property of PLLA/CABH samples in different CABH concentrations were also investigated. It was found that CABH acted as efficient heterogeneous nucleating agent for inducing PLLA�s crystallization through comparative analysis of melt-crystallization process of the virgin PLLA with PLLA/CABH samples, and a high amount of CABH played a much more significant role in promoting PLLA�s crystallization. Additionally, the melt-crystallization processes also showed that both the cooling rate and the final melting temperature affected the crystallization behavior of PLLA, an increase of cooling rate could weaken the crystallization ability of PLLA/CABH samples, and the final melting temperature of 180�C made PLLA/CABH exhibit the best crystallization ability. For the cold-crystallization process, the cold-crystallization peak became flatter and shifted toward the lower temperature with increasing of CABH concentration, but an increase of heating rate could prevent the cold-crystallization peak from moving to low temperature because of the thermal inertia. The melting behaviors of PLLA/CABH depended on the previous crystallization and heating rate in heating, and the difference in melting behavior of PLLA/CABH samples effectively reflected the nucleation role of CABH, as well as the double melting peaks behavior of PLLA/CABH was thought to due to the melting-recrystallization. The introduction of CABH led to a drop in light transmittance, moreover, this negative effect were more obvious with an increase of CABH loading. In contrast, the fluidity of PLLA was significantly enhanced due to the existence of CABH.

Following isothermal and non-isothermal crystallization of poly(3-hexylthiophene) thin films by UV–vis spectroscopy

We investigated non-isothermal and isothermal crystallization of spin-coated poly(3-hexylthiophene) thin films prepared from the melt by in-situ ultraviolet–visible absorption spectroscopy. Analyzing the absorption spectra according to the Franck-Condon principle allowed for a quantitative assessment of the degree of crystallinity as well as the quality of order within crystalline regions of the films. Measured at room temperature, we observed a similar crystallinity for all differently crystallized films. The highest quality of order, however, was found for the P3HT film cooled slowly from the melt. These results were in full agreement with the results obtained by X-ray diffraction and calorimetry measurements. Consistently, in spite of similar crystallinities, atomic force microscopy images did not show a well-defined structure of ordered domains of preferentially aligned lamellae for the films rapidly cooled from the melt. In addition, heating the P3HT films in a specific range of temperature showed no change in crystallinity in spite of a continuous loss of order quality. Our results revealed that crystallinity and crystalline quality could behave differently while processing a semicrystalline polymer.

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.

Preparation and characterization of poly(ethylene 2,5-furandicarboxylate/nanocrystalline cellulose composites via solvent casting

Abstract The effect of nanocrystalline cellulose dispersion on the nonisothermal crystallization of poly(ethylene 2,5-furandicarboxylate) (PEF) has been investigated by means of solvent casting. The cellulose dispersion plays a significant role on the crystallization temperature, thus dispersive equipments of increasing energies were employed to improve the cellulose particles disaggregation. Therefore, ultra-sonic bath, ultra-sonication, and ultra-turrax were used to disperse cellulose nanocrystals in 1,1,1,3,3,3-hexafluoro-2-propanol. Dissolved separately in the same solvent, PEF was then poured into the cellulose suspension before casting. The cellulose whiskers were inspected by transmission electron microscopy. Differential scanning calorimetry was used to measure the crystallization temperature, while scanning electron microscopy visualized the cellulose dispersion at the fracture surface. After investigation on the interaction of cellulose/PEF via Fourier transform infrared spectroscopy, the thermal stability of the blends was measured by means of thermogravimetric analysis.

Effect of surface modification of cellulose nanocrystal on nonisothermal crystallization of poly(β-hydroxybutyrate) composites

Ring-opening polymerization of l-lactide from cellulose nanocrystal (CNC) surface yielded polylactide-grafted CNC (CNC-g-PLA). The structure and chemical composition of the CNC-g-PLA were characterized by FT-IR, 1H NMR, XPS and XRD. The crystallization behavior and lamellar structure of poly(β-hydroxybutyrate) (PHB) in the presence of pristine CNC and CNC-g-PLA were elucidated via DSC and SAXS, and Babinet's reciprocity theory was applied. Crystallization kinetics were further analyzed using Ozawa, Mo and Kissinger models. In the presence of pristine CNC, nucleation of PHB crystals led to an increase in the crystallization temperature (Tc) of PHB; while CNC-g-PLA acted as antinucleation agent, resulting in a remarkable reduction in Tc of PHB. Accordingly, the composite with pristine CNC possessed a higher crystallization rate than neat PHB, while CNC-g-PLA displayed the lowest crystallization rate. However, the lamellar structure of PHB was not affected by the presence of pristine and modified CNCs, and almost identical crystallization activation energies as the neat PHB were observed, indicating that nucleation is dominant during PHB crystallization, instead of crystal growth. This study offers a promising approach of using pristine and modified CNCs to control the crystallization of biodegradable aliphatic polyesters.

Kinetics of isothermal and non-isothermal crystallization of poly(vinylidene fluoride) by fast scanning calorimetry

Crystallization from melt of poly(vinylidene fluoride) was studied by thin film chip calorimetry at cooling rates from 500 to 100,000 Ks−1 and isothermally down to 76 °C. At ca. 70 °C, for cooling rates higher than 2000 Ks−1, there appears a change in crystallization from high temperature α phase to low temperature β phase. The amorphous state is preserved at cooling rate 100,000 Ks−1. Analysis of the crystallization kinetics with Ziabicki model reveals maximum of the steady-state crystallization rate of β phase as 2200 s−1 at 22 °C, and the highest crystallization rate of α phase as 200 s−1 at 70 °C. Approximation of the temperature dependent steady-state crystallization rate with the Turnbull and Fisher nucleation model results in the equilibrium melting temperatures 227 and 173 °C for the α and β phase, respectively, and in the energy barrier for short-distance transport, ED, as 70–80 kJ mol−1 at high supercooling.

The Effect of Polystyrene on the Crystallization of Poly(3-hydroxybutyrate)

Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB.

Effect of Nanoclay on the Nonisothermal Crystallization of Poly(propylene) and its Blend with Poly[(butylene succinate)-co-adipate

The non-isothermal crystallization behaviour and kinetics of neat poly(propylene)(PP), PP/poly[(butylene succinate)-co-adipate] (PP/PBSA) blend and its composite with nanoclay was studied by differential scanning calorimetry at six different cooling rates. Various models, namely the Avrami, the Ozawa and the combined Avrami-Ozawa, were applied to understand the kinetics of the non-isothermal crystallization. All analyses revealed that the rate dependent crystal growth mechanism of neat PP changes after preparation of blend with PBSA and in presence of nanoclay particles in blend composite. Polarized optical microscopy was used to support this conclusion. The activation energy for the non-isothermal crystallization of neat PP, PP/PBSA blend and nanoclay modified PP/PBSA blend composite samples was evaluated by using Kissinger and Augis-Bennett methods. The results showed that the absolute value of the activation energy for the PP matrix crystallization was increased in the case of PP/PBSA blend and this value was dramatically increased in presence of nanoclay. This indicates the slower crystallization kinetics of the PP matrix in presence of nanoclay.

Effect of ZnO nanofillers treated with triethoxy caprylylsilane on the isothermal and non-isothermal crystallization of poly(lactic acid)

The crystallization of PLA-silane surface-treated ZnO nanocomposites was investigated by DSC and compared to that of neat PLA. Several modes of crystallization were considered: isothermal and non-isothermal cold crystallization and also isothermal and non-isothermal melt crystallization. The kinetics of cold crystallization were studied using different methods, namely the Avrami and Ozawa-Flynn-Wall models, to calculate activation energies and kinetic constants. In contrast to what is typically observed when the foreign particles are added in a polymer matrix, the silane surface-treated ZnO delayed the crystallization of PLA and made it more difficult to start. The nucleation activity of the ZnO nanoparticles, ϕ, was calculated and found to be greater than 1 (ϕ = 1.7). This indicated that ZnO played an anti-nucleating role in the crystallization of PLA nanocomposites. This effect has been linked mainly to the interactions between the silane groups onto the surface of nanoparticles and PLA macromolecules. These interactions which reduce the mobility of polymer chains have been evidenced by rheological experiments.

Effect of nucleation mechanism on complex poly(L‐lactide) nonisothermal crystallization process, part 2: Crystallization kinetics analysis

AbstractIn the first part of this article, we reported the crystalline memory effect on the nonisothermal crystallization of poly(L‐lactide). The experiments were carried out by using polymer single crystals growth from dilute solution as standard starting material. In this article (Part II), we have analyzed in detail the effect of the melting condition on the overall crystallization kinetics by applying the Nakamura‐Avrami model to DSC results. The absence or the low concentration of foreign infusible heterogeneous nuclei in our system allowed us to exalt the self‐nuclei role in polymer crystallization, to follow their concentration decrease during the melting process and to find the limiting melting temperature for their disappearance. Below such a temperature, a stable equilibrium number of self‐nuclei was observed, probably deriving from ordered structures, persisting in the melt, and originated from the single crystals thickening process during the polymer dynamic melting in the DSC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (Kg) – the lowest value of Kg was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be −260 kJ/mol for pure PEO, −538 kJ/mol for PEO/lauric acid blend, and −387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and −135,6 kJ/mol, −114,5 kJ/mol, and −92,8 kJ/mol, respectively, for nonisothermal crystallization.

The nucleation effect of modified carbon black on crystallization of poly(lactic acid)

AbstractThe nonisothermal crystallization of poly(lactic acid) (PLA), PLA/carbon black (CB), and PLA/modified carbon black (MCB) composites were investigated using differential scanning calorimetry (DSC) analysis. The rate of crystallization and the spherulitic morphologies of the PLA and PLA/MCB composites during isothermal crystallization were investigated using DSC and observed by means of polarizing optical microscopy (POM), respectively. The results show that either CB or MCB acts as an efficient nucleating agent for PLA. The nucleation activities of CB and MCB were quantitatively determined. It is shown that MCB has higher nucleating activity than CB in PLA. An isoconversional method correlates the temperature dependence of the effective activation energy and was used to evaluate the effective activation energy of PLA and PLA/MCB composites. It is confirmed that MCB advances the nuclei density and promotes the crystallization rate of the PLA matrix significantly. In addition, an interesting phenomenon of the periodic cracks of PLA spherulites observed by using POM is reported. The unbalanced surface stresses arising from growth features and thermal shrinkage may be the two main factors accounting for the formation of target pattern cracks. POLYM. ENG. SCI., 50:1658–1666, 2010. © 2010 Society of Plastics Engineers

Non-isothermal crystallization of poly(ε-caprolactone)-grafted multi-walled carbon nanotubes

Non-isothermal crystallization behavior of poly(ε-caprolactone) (PCL)-grafted multi-walled carbon nanotubes (MWNTs) was studied in order to determine the effects of functionalized MWNTs (f-MWNTs) on its crystallization behavior. Differential scanning calorimeter measurements showed that an introduction of f-MWNTs into the PCL molecules induced heterogeneous nucleation and the crystal growth process was significantly affected. X-ray diffraction showed a decrease in the crystallinity of composites with the addition of f-MWNTs in PCL, likely due to the occurrence of more heterogeneous nucleation induced by f-MWNTs in the samples. The activation energy for crystallization of PCL drastically reduced with the presence of 2 wt.% f-MWNTs in the samples and increased slightly with increasing content of f-MWNTs. A spherulite structure of PCL-grafted MWNTs with MWNTs at the center was developed, clearly indicating the nucleating action of MWNTs in the crystallization process. The experimental data were also analyzed using various kinetic models e.g., Avrami, Tobin, Ozawa, etc.

Nonisothermal Crystallization Behaviors of Poly(butylene terephthalate) Nucleated with Elastomer-Modified Nano-SiO2, a Commercial Nucleating Agent (P250), and Talc

The nonisothermal crystallization of poly(butylene terephthalate) (PBT) nucleated with elastomer-modified nano-SiO2 [SiO2-(E-MA-GMA)], a commercial nucleating agent (P250), and talc were investigated by differential scanning calorimetry (DSC) under different cooling rates. It was observed that P250, talc, and SiO2-(E-MA-GMA) act as heterogeneous nuclei in PBT; PBT-P250 and PBT-NE [PBT/SiO2-(E-MA-GMA)] blends, in particular, take a shorter time to crystallize. The Avrami, Ozawa, and Mo models were used to analyze the nonisothermal crystallization kinetics. The Avrami-Jeziorny model failed to describe the nonisothermal crystallization of PBT samples. The Ozawa analysis showed that P250, talc, and SiO2-(E-MA-GMA) change the nucleation mechanism and crystal growth of PBT. The crystallization activation energies of all the PBT samples were determined by the Kissinger model. The results show that the crystallization activation energy of PBT-P250 was lower than that of the others, and the nucleating efficiency of SiO2-(E-MA-GMA) on PBT was close to that of P250, while better than that of talc.

Non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear conditions

The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s−1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.

Dependence of the Avrami Exponent on Supercooling During Nonisothermal Crystallization of Poly(phenylene sulfide)

The nonisothermal crystallization behavior of poly(phenylene sulfide) (PPS) was studied by means of differential scanning calorimetry (DSC) at various cooling rates. The nonisothermal crystallization data were analyzed by the Ozawa theory. The Avrami exponent n was determined at several constant cooling rates. A notable variable trend of the Avrami exponent with the temperature was found. Within 215–238°C and 243–255°C, the Avrami exponent of PPS increases markedly with the increase of temperature, respectively, while within narrow temperature range from 238°C to 243°C, a sharp decrease of the Avrami exponent can be seen. It has been suggested that the nuclei formation and the geometry of spherulite growth in the nonisothermal crystallization of PPS are strongly affected by the temperature and correlated with the Regime Transition (the regime II→III transition for PPS).

Poly(butylene terephthalate)/clay nanocomposite compatibilized with poly(ethylene‐co‐glycidyl methacrylate). II. Nonisothermal crystallization

AbstractMelting behaviors and nonisothermal crystallization of poly(butylene terephthalate)/poly(ethylene‐co‐glycidyl methacrylate) (PBT/PEGMA), PBT/commercial modified montmorillonite clays (PBT/Clay), and PBT/exfoliated silicates (PBT/PEGMA/Clay) nanocomposites were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter. PEGMA is used as a compatibilizer. For both isothermally and nonisothermally crystallized samples, PEGMA facilitates the recrystallization of PBT during the heating scans, and leads to a less degree of perfection of the crystals. However, the clay hinders the recrystallization growth during heating scans, and increases perfection of the crystals. Nonisothermal crystallization kinetics was described by kinetic models and undercooling was taken into account. The PEGMA would lead to an increase of the blend viscosity, rendering the chains less mobile and lower the crystallizability of PBT in PBT/PEGMA. The well‐dispersed exfoliated silicates in PBT/PEGMA/Clay cause a large number of nuclei to precede crystallization. The fold surface free energy (σe) and activation energy also supported the interpretation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 564–576, 2008