Non-isothermal Crystallization Kinetics Of Poly Research Articles

Manipulation of non-isothermal crystallization kinetics of poly(lactic acid) composite film by a novel nucleating agent

As a type of renewable and biodegradable polymer, poly(lactic acid) (PLA) has been widely used in various fields. However, its weak crystallization ability deteriorates the properties of the final product. In this work, a novel nucleating agent (MWCNTs@CeO2), multi-walled carbon nanotubes (MWCNTs) decorated with ceria (CeO2), was synthesized using the hydrothermal method and subsequently used to manipulate the non-isothermal crystallization kinetics and nucleation behavior of PLA. The results show that MWCNTs@CeO2 can act as an effective nucleating agent to accelerate the crystallization rate of PLA by reducing the half-crystallization time. In non-isothermal crystallization kinetics, the Avrami equation modified by Jeziorny cannot accurately describe the non-isothermal crystallization behavior of PLA and PLA/MWCNTs@CeO2 composite films, whereas the Mo method can. Furthermore, it is found that the addition of MWCNTs@CeO2 does not change the crystal structure of PLA, but increases the nucleation and growth rate of PLA, thereby promoting its crystallization.

Non-Isothermal Crystallization Kinetics of Poly (ɛ-Caprolactone) (PCL) and MgO Incorporated PCL Nanofibers.

The study delves into the kinetics of non-isothermal crystallization of Poly (ɛ-caprolactone) (PCL) and MgO-incorporated PCL nanofibers with varying cooling rates. Differential Scanning Calorimetry (DSC-3) was used to acquire crystallization information and investigate the kinetics behavior of the two types of nanofibers under different cooling rates ranging from 0.5-5 K/min. The results show that the crystallization rate decreases at higher crystallization temperatures. Furthermore, the parameters of non-isothermal crystallization kinetics were investigated via several mathematical models, including Jeziorny and Mo's models. Mo's approach was suitable to describe the nanofibers' overall non-isothermal crystallization process. In addition, the Kissinger and Friedman methods were used to calculate the activation energy of bulk-PCL, PCL, and MgO-PCL nanofibers. The result showed that the activation energy of bulk-PCL was comparatively lower than that of nanofibers. The investigation of the kinetics of crystallization plays a crucial role in optimizing manufacturing processes and enhancing the overall performance of nanofibers.

Non-isothermal crystallization kinetics of poly(propylene)-based graphene nanocomposites for injection moulding

Non-isothermal crystallization kinetics of poly(propylene)-based graphene nanocomposites for injection moulding

Non-Isothermal Crystallization Kinetics of Polyvinylidene Fluoride (PVDF)/Microcrystalline Graphite (MCG) Composites

The Avrami equation modified by Jeziorny, the Ozawa model and the Mo equation combining the Avrami and Ozawa theories were employed to describe the non-isothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF), and PVDF/microcrystalline graphite (MCG) composites. It was found that the Ozawa model failed to describe the non-isothermal crystallization process for PVDF and its composites, while Mo’s theory provided good fitting for neat PVDF but did not describe the non-isothermal crystallization well for the PVDF/MCG composites. The addition of MCG promoted the crystallization rate of PVDF, which indicates that MCG acted as a nucleating agent. The absolute values of the effective activation energy of the PVDF/MCG composites calculated by the Kissinger equation, were higher than that of neat PVDF, confirming that MCG acted as a nucleating agent and promoted the crystallization rate of PVDF.

Approach to nonisothermal crystallization kinetics of poly(4‐methyl‐1‐pentene) melt: Effect of gamma‐ray

AbstractUnderstanding the effect of gamma‐ray irradiation on the nonisothermal crystallization of polymer during cooling is of practical importance for the applications and manufacturing of crystallized polymer. In this work, we expose poly(4‐methyl‐1‐pentene) (PMP) to gamma‐ray with different irradiation doses and study the crystallization of the gamma‐ray irradiated PMPs. All the PMPs exhibit a doublet peak in the differential scanning calorimeter thermograms for the cooling rates in a range of 2.5–20°C/min. We use linear superposition of two inverse Gaussian functions to decompose the doublet peak into two individual peaks and analyze the crystallization kinetics of the crystallization processes associated with individual peaks. The Avrami exponent decreases with the decrease of the crystallization temperature and is in a range of 0.96–2.43 for the crystallization near the melting point and a range of 0.72–1.68 for the crystallization away the melting temperature. The activation energy for the crystallization near the melting temperature decreases with the increase of the irradiation dose. For the crystallization away from the melting temperature, the activation energy for the PMPs without gamma‐ray irradiation is smallest.

Non-Isothermal Crystallization Kinetics of Poly(4-Hydroxybutyrate) Biopolymer.

The non-isothermal crystallization of the biodegradable poly(4-hydroxybutyrate) (P4HB) has been studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). In the first case, Avrami, Ozawa, Mo, Cazé, and Friedman methodologies were applied. The isoconversional approach developed by Vyazovkin allowed also the determination of a secondary nucleation parameter of 2.10 × 105 K2 and estimating a temperature close to 10 °C for the maximum crystal growth rate. Similar values (i.e., 2.22 × 105 K2 and 9 °C) were evaluated from non-isothermal Avrami parameters. All experimental data corresponded to a limited region where the polymer crystallized according to a single regime. Negative and ringed spherulites were always obtained from the non-isothermal crystallization of P4HB from the melt. The texture of spherulites was dependent on the crystallization temperature, and specifically, the interring spacing decreased with the decrease of the crystallization temperature (Tc). Synchrotron data indicated that the thickness of the constitutive lamellae varied with the cooling rate, being deduced as a lamellar insertion mechanism that became more relevant when the cooling rate increased. POM non-isothermal measurements were also consistent with a single crystallization regime and provided direct measurements of the crystallization growth rate (G). Analysis of the POM data gave a secondary nucleation constant and a bell-shaped G-Tc dependence that was in relative agreement with DSC analysis. All non-isothermal data were finally compared with information derived from previous isothermal analyses.

Non-isothermal crystallization kinetics of poly(3-hydroxybutyrate)/EVA 80 blends enhanced by NH4Cl as a nucleating agent

The crystallization kinetics of poly(3-hydroxybutyrate) (PHB), PHB/NH4Cl composites, PHB/ethylene-vinyl acetate (EVA 80) blends and PHB/EVA 80/1 mass% NH4Cl blends were studied under non-isothermal conditions. The modified Avrami equation and the MO approach were found to successfully describe the non-isothermal crystallization process. It was found that the inverse half time of crystallization and the values of Avrami rate constant, K, of PHB increased with decreasing EVA 80 content, increasing cooling rate and the addition of NH4Cl. Moreover, the crystallization mechanism remains unchanged in spite of the EVA 80 content and the presence of NH4Cl. Furthermore, the effective energy barrier of the non-isothermal crystallization process, EX(t), was evaluated with the isoconversional methods of Friedman. The EX(t) values of PHB/NH4Cl composites are much lower than those of pure PHB. Moreover, EX(t) values of PHB in PHB/EVA 80/1 mass% NH4Cl increase with increasing EVA content. A large number of small PHB spherulites were observed by polarized optical microscopy in the presence of NH4Cl.

Nanocomposites based on chain extended poly(l-lactic acid)/carboxylated carbon nanotubes: Crystallization kinetics and lamellar morphology

Isothermal and nonisothermal crystallization kinetics of poly(l-lactide) and its nanocomposites with different multiwalled carbon nanotubes (i.e., pristine and functionalized) were investigated. The effects of chain extension and nanofiller content on the crystallization kinetics were also explored. The Avrami analysis was applied as a useful tool for the study of isothermal crystallization kinetics, which was also supported by optical microscopy observations. In addition, in nonisothermal crystallization process, the Avrami and Mo methodologies were used to study the crystallization kinetics as well as the evaluation of activation energy from isoconversional methods. The activation energy was always negative for the process driven by the secondary nucleation. Great differences were found between the studied samples, but activation energy values indicated a favored crystallization (i.e., less negative energies) when functionalized multiwalled carbon nanotubes were added at a concentration of 0.2 wt%. Cold crystallization was also influenced by the multiwalled carbon nanotube content due to the nucleating effect and the existence of geometrical constrictions that limited the size of crystalline domains. Small-angle X-ray scattering studies showed that the size of crystal lamellae after cold crystallization could vary by a magnitude of 3 nm depending on the way as the sample was previously cooled (i.e., by the presence of incipient crystalline domains).

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/epoxidized ethylene propylene diene rubber/glass fiber composites

Nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/glass fiber (GF) and PBT/epoxidized ethylene propylene diene rubber (eEPDM)/GF composites were investigated by differential scanning calorimetry (DSC) at a cooling rates of 2.5, 5, 10, and 20 °C/min, respectively. Morphologies of samples were observed with scanning electron microscopy and polarized optical microscopy. The specimens were prepared by melt blending. Analyses of the melt crystallization data by various macrokinetic models such as Jeziorny‐modified Avrami, Liu–Mo models, and Lauritzen–Hoffman equation revealed that GF accelerated the crystallization rate of PBT; furthermore, the eEPDM had two functions: on the one hand, eEPDM promoted PBT to form nuclei; on the other hand, eEPDM hindered the diffusion of polymer chains, but the nucleation effect exceeded the diffusion effect, thus, the eEPDM could increase the crystallization rate of PBT in PBT/eEPDM/GF. These results were further supported by the effective activation energy calculated by isoconversional method of Friedman. POLYM. ENG. SCI., 59:330–343, 2019. © 2018 Society of Plastics Engineers

Non-isothermal crystallization kinetics of Poly(Butylene succinate) (PBS) nanocomposites with different modified carbon nanotubes

In this study, the effect of surface modification (acid treatment and chemical modification) of multi-walled carbon nanotubes (MWCNT) on the non-isothermal crystallization kinetics of poly (butylene succinate) (PBS) was studied. The chemical modifications of MWCNTs were conducted by using alcohols having different molecular weights. A twin screw microcompounder was used to prepare the MWCNT based nanocomposites. The filler content was 0.50% and 1% by weight. Fourier transform infrared spectroscopy (FTIR) was used to analyze changes in the surface chemical bonding and structure of the MWCNT's before and after surface modification processes. Transmission electron microscopy (TEM) was used to evaluate the morphological structures on the surfaces of the functionalized MWCNTs. The dispersions of surface modified and unmodified MWCNTs in PBS matrix and different solvents were characterized by scanning electron microscope (SEM) and polarized optical microscopy (POM), respectively. Different kinetic approaches such as Avrami, Ozawa and combined Avrami and Ozawa were studied to examine the non-isothermal crystallization kinetics of PBS and its nanocomposites. The nucleation activity of MWCNT nanoparticles was investigated in terms of Dobreva and Gutzow models. Activation energies for crystallization of PBS and its nanocomposites were evaluated by Friedman model. Besides, POM equipped with a hot-stage was used to examine the morphology during the crystal growth. FTIR and TEM analysis showed that surface modification of MWCNTs successfully accomplished. It was obtained that chemically modified MWCNT nanoparticles were well dispersed in both organic solvent and PBS matrix. Kinetic analysis revealed that crystallization rate of PBS increased especially in the presence of pristine MWCNT and chemically modified MWCNT nanoparticles. Moreover, crystallization rate of PBS increased as the length of the alkyl chains grafted onto the surface of MWCNT increased after chemical modification with alcohols. Pristine MWCNT exhibited the highest nucleation activity for PBS. POM analysis showed that nucleation density was higher in the presence of both pristine and chemically modified MWCNT filled PBS nanocomposites.

Isothermal and non-isothermal crystallization kinetics of poly(butylene succinate) with nanoprecipitated calcium carbonate as nucleating agent

Poly(butylene succinate) (PBS) nanocomposites filled with nanoprecipitated calcium carbonate (NPCC) were prepared via melt blending. The hybrid materials were crystallized under isothermal and non-isothermal conditions in order to understand the influence of NPCC on the crystallization behavior of PBS matrix. For both of these conditions, the nucleating effect induced by the addition of NPCC was clearly shown by differential scanning calorimetry (DSC) additionally to an increase of crystallinity. The analysis of isothermal crystallization by Avrami theory allowed to notice a variation of the crystallization mechanism in the presence of the filler and the apparition of secondary stage crystallization. The nanocomposites exhibited higher nucleation activity than the neat PBS and a faster crystallization process as indicated by the values of the half-time of crystallization. Ozawa and Mo theory applied on DSC data highlighted the variations of PBS crystallization behavior in the presence of NPCC. Finally, the crystallization ability of each material was evaluated via the theories of Takhor and Augis–Bennett. The crystallization activation energy showed a promotion of polymer chain diffusion that was correlated with the simultaneous apparition of secondary crystallization stage.

Preparation, performance and non-isothermal crystallization kinetics of poly(lactic acid)/amidated humic acid composites

Amidated humic acid (AHA) was prepared by amidation of humic acid (HA) and its structure was verified by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Then poly(lactic acid)/amidated humic acid composites (PLA/AHA) were prepared using AHA as the nucleating agent. The mechanical properties, thermal stability, and crystallization behavior of the PLA/AHA composites were investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheological analysis. The mechanical properties and thermogravimetric analysis showed that the tensile properties, impact resistance, and thermal stability of the PLA/AHA composites were improved. The cross-sectional morphology of the fractured surface showed that the addition of the nucleating agent significantly changed the crystallinity of PLA. The DSC results showed that the crystallinity of PLA/AHA composites increased from 4.19 to 35.36% after introduction of the nucleating agent. The POM of PLA/AHA composites demonstrated that AHA increased the crystallization rate of PLA. The maximum torque of PLA/AHA composites was 75.0% higher than that of PLA and the apparent viscosity was increased by 172.5%. This proved that the AHA changed the crystalline lattice structure and stiffness of PLA matrix. Non-isothermal crystallization kinetics showed that HA provided a large number of heterogeneous nucleation sites and improved the crystallization rate of PLA.

Influence of graphene on the non-isothermal crystallization kinetics of poly(vinyl alcohol)/starch composite

Non-isothermal crystallization behavior of poly(vinyl alcohol)/starch and poly(vinyl alcohol)/starch/graphene nanocomposites was studied using differential scanning calorimetry (DSC). Ozawa and Mo models were used to analyze the non-isothermal kinetics. The differential Friedman method was used to evaluate the effective activation energy (E A ) of the nanocomposites. The data fits the Mo Model well in the investigated temperature range. Graphene nucleates the crystallization of the composites by increasing the crystallization onset temperature along with the lowering of E A . However, significant changes in the crystallization half-time were not observed, suggesting that the effect of graphene is more prominent at the nucleation stage.

Effect of Organoclay Platelets on Crystallization of PTT/POE-g-MA Blends: Non-isothermal Melt Crystallization Kinetics

1The non-isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT)/maleic anhydride grafted poly (ethylene-octene) (POE-g-MA) blends with different amounts of an organoclay were investigated. The Avrami and a method proposed by Mo were used to analyze the non-isothermal crystallization process of PTT/POE-g-MA blends with various amounts of the organoclay. The Avrami analysis results showed that adding organoclay into blend caused significant heterogeneous nucleation and changed the crystallization nucleation and growth of PTT. According to the Mo analysis results, the crystallization rate of PTT/POE-g-MA blends with organoclay was faster than that of PTT/POE-g-MA blends without organoclay.

Effect of polyethylene glycol-grafted graphene on the non-isothermal crystallization kinetics of poly(ethylene oxide) and poly(ethylene oxide):lithium perchlorate electrolyte systems

Graphene nanoplatelets were chemically modified by polyethylene glycol (PEG), via an amidation reaction. Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray analysis (EDX) and thermo-gravimetric analysis (TGA) revealed the successful accomplishment of reaction. Functionalized graphene (FGnP) were incorporated into poly(ethylene oxide) (PEO) and solid polymer electrolytes (SPE) based on PEO and lithium perchlorate salt (LiClO4). The non-isothermal crystallization kinetics of samples were studied using differential scanning calorimetry (DSC). Modified Avrami and combined Avrami-Ozawa equations were used to analyze the non-isothermal crystallization. The Avrami exponent values showed that FGnP did not change the nucleation mechanism and crystal growth in neither PEO nor PEO:LiClO4. However, the half-time of crystallization increased by addition of FGnP in both PEO and PEO:LiClO4 systems. A more considerable effect of FGnP on the crystallization behavior of SPE/FGnP electrolytes was found in comparison to PEO/FGnP nanocomposites, which can be related to the FGnP induced dissociation of lithium salt.

A novel approach to study the isothermal and non-isothermal crystallization kinetics of Poly(Ethylene Terephthalate) by Raman spectroscopy

This paper focuses on the study of the crystallization kinetics of an initially quasi-amorphous Poly(Ethylene Terephthalate) (PET) during controlled heating treatments using Raman Spectroscopy. Characteristic vibrational bands of both crystalline and amorphous phases are then investigated in terms of wavenumber values, full widths at half maximum and integrated intensities variations which led to the establishment of a more accurate crystallinity ratio criterion than the one obtained by standard differential scanning calorimetry (DSC) analysis too much dependent on the low polymer thermal conductivity. Applying this last criterion, isothermal and non-isothermal crystallization kinetics were investigated following the Avrami’s and Ozawa’s theories in order to identify the germination and growth modes of the triclinic crystals of PET as a function of thermal treatment. Moreover, all the specific microstructural transitions such as cold crystallization, crystallization from the melt, melting and glass transition are detected and characterized. Similar thermal behaviors were obtained from Raman results and conventional differential scanning calorimetry measurements.

Model-free non-isothermal crystallization kinetics of poly(3-hydoxybutyrate) filled with carbon black

Non-isothermal crystallization kinetics of poly(3-hydoxybutyrate) (PHB) filled with different amounts of carbon black (CB) was investigated by differential scanning calorimetry for both, the cold and melt crystallization process. The Friedman method was applied to describe the crystallization kinetics and to determine the conversion dependent apparent activation energies. It was found that carbon black acts as a nucleating agent, reducing the apparent activation energy for the crystallization onset significantly, and thus greatly facilitating the phase transformation. Considering PHB-CB compounds with CB content ≥5%, the kinetic data can only be interpreted assuming a complex multi-step crystallization mechanism, where the exact role of CB is unclear.

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.

Non-isothermal cold crystallization kinetics of poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG) copolyesters with different compositions

In this work, the non-isothermal crystallization kinetics of poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG) random copolyesters with different compositions was first investigated from the glassy state. Regardless of the composition, the value of the Avrami exponent determined from Jeziorny theory was 2.1–2.4, depending on the heating rate, whereas the value of α (the ratio of the Avrami exponent to the Ozawa exponent) obtained from Mo's method was 1.3–1.6, depending on the relative crystallinity. These results indicated that the nucleation and growth mechanism of the PETG copolyesters were apparently identical to those of the poly(ethylene terephthalate) (PET) homopolymer. However, the cold crystallization rate was accelerated by increasing the heating rate, but retarded by incorporating the 1,4-cyclohexanedimethanol (CHDM) unit into the polymer backbone. Based on the crystallization rate coefficient (CRC) and the crystallization rate parameter (CRP) approaches, the cold crystallization rate was in the following order: PET > PETG(30/70) > PETG(85/15) > PETG(50/50) > PETG(70/30).

Nonisothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) and calcium carbonate nanocomposites

Nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/nano calcium carbonate (CaCO3) composites were investigated by differential scanning calorimetry and polarized optical microscopy. PBT/nano CaCO3 composites containing different wt.% of nano CaCO3 were prepared by melt blending. Analysis of the melt crystallization data by various macrokinetic models like modified Avarami and Liu and Mo models revealed the dependence of crystallization rate on nano CaCO3 content. Nano CaCO3 addition upto 5wt.% greatly accelerated the crystallization rate. However, higher loadings of the filler retarded the crystallization rate. These results were further supported by the effective activation energy calculations by isoconversional method of Friedman. Polarized optical microscopy showed a decrease in spherulites size with increase in filler content. The study showed that small amount of nano CaCO3 acts as additional nucleating agent and is effective in accelerating the crystallization rate whereas higher loadings increase the nucleation density but restrict the mobility of polymer chains and retard the growth process.