Thermal degradation kinetics of semi-aromatic polyamide containing benzoxazole unit

The kinetics of the thermal degradation of a new semi-aromatic polyamide containing benzoxazole unit (BO6) have been investigated by thermogravimetric analysis (TG). Thermal degradation of BO6 could be accomplished by one step. The corresponding kinetic parameters of the degradation process are determined by using Kissinger and Flynn–Wall–Ozawa methods, respectively. Coats–Redfern method is also used to discuss the probable degradation mechanism of the BO6. The results show that the activation energy obtained from Kissinger method is in good agreement with the value obtained by using Flynn–Wall–Ozawa method. The solid-state degradation mechanism of the BO6 is a decelerated R ₁ type (phase boundary controlled reaction one-dimensional movement).     

Crystallization kinetics of LDPE/Ny6 blends

The crystallization behaviour of low density polyethylene/nylon 6 blends has been investigated as a function of the composition.The melting points of the polymers are almost uninfluenced by the presence of the other homopolymers except for blends with a nylon content of 75–90%.Blends with 10% nylon content do not exhibit the crystallization peak during the cooling step probably because of the low concentration and high viscosity of the low density polyethylene matrix.The crystallinity degree of the polyethylene is independent of the composition, while some variations are shown by the polyamide.Finally the rate of nucleation is strongly affected by the composition, in particular for the nylon phase.

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Zusammenfassung Die Abhängigkeit des Kristallisationsverhaltens von 6 Polyethylen/Nylon-Gemischen geringer Dichte von der Zusammensetzung wurde untersucht. Der Schmelzpunkt eines jeden Polymers ist nahezu unbeeinflußt von der Anwesenheit des anderen Homopolymers ausgenommen die Gemische mit einem Nylongehalt von 75–90%. Die Gemische mit einem Gehalt von 10% Nylon zeigen während des Abkühlungsschrittes keinen Kristallisationspeak, was wahrscheinlich auf die niedrige Konzentration und auf die hohe Viskosität der Polyethylenmatrix mit geringer Dichte zurückzuführen ist. Der Kristallinitätsgrad des Polyethylens ist unabhängig von der Zusammensetzung, während ein Einfluß des Polyamids festzustellen ist. Die Keimbildungsgeschwindigkeit ist stark von der Zusammenstzung abhängig, was besonders für die Nylonphase gilt.

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— 6 . , 75–90% , . 10% , , , . , . , , .

     

Properties of polyamide 6 and thermoplastic polyurethane blends containing modified montmorillonites

In this paper are reported some experimental data related to the influence of preparation regimes and characteristics of exfoliated graphite based sorbents produced by thermal expansion of H₂SO₄-graphite intercalation compounds (H₂SO₄-GICs) on their sorption properties. Investigations involving X-ray diffraction analyses, surface area, bulk density and oil sorption capacity measurements, have been performed. Sorption capacity was discussed as a function of bulk density, total pore volume and surface area. Some empirical correlation between studied characteristics of exfoliated graphite have been found. The differences among the obtained samples, as a consequence of synthesis conditions, were also put in evidence by thermal analysis (TG, DTG and DTA) performed after their exposure to oil sorption.It was found that thermal analysis method could provide information about the exfoliated graphite pore system related to the sorbed oil oxidation rate. The capacity for oil uptake was also discussed in the case of graphite oxide soot.     

Structure and optical properties of transparent polyamide 6 containing lithium bromide

We investigated the effects of lithium bromide (LiBr) on the structure and properties of polyamide 6 (PA6). The strong ion–dipole interactions between lithium cations and the amide groups in PA6 greatly increased the glass transition temperature (T_g) and retarded the crystallization rate of PA6. As a result, compression-molded PA6 blends were highly transparent and had high T_g values. The rheological terminal region was obvious in the blends because the ion–dipole interactions weakened at high temperatures. This indicates that the melt processability was barely affected by LiBr. We also evaluated the optical anisotropy of the polymer to determine its suitability as a functional optical film. We found that hot-stretched blend films had large positive orientation birefringence with significantly weak wavelength dispersion, which can be attributed to the enhanced anisotropic polarizability of PA6. We also found that the stress-optical coefficient in the glassy region decreased with increasing LiBr content. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1513–1520     

The effect of TiO2 on the kinetics of polyamide 6 crystallization

Colloid and Polymer Science - The kinetics of isothermal and nonisothermal crystallization of polyamide-6 (PA6) containing titania was studied by means of DSC. It was found thatTiO 2 causes an...     

Effect of multi-walled carbon nanotubes on non-isothermal crystallization kinetics of polyamide 6

The non-isothermal crystallization behaviors of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites were investigated by differential scanning calorimetry (DSC). Three methods, namely, Avrami, Ozawa and Mo, were carried out to analyze the non-isothermal crystallization data. The results showed that the MWNTs in PA6 acted as effective nucleation agents. However the crystallization rate of composites obtained was lower than that of the neat PA6. It is indicated that the presence of MWNTs influenced the mechanism of nucleation and the growth of PA6 crystallites.     

Crystallization kinetics of amorphous

The active sites of hydrogen-exchanged Y zeolite (HY) and dealuminated (HDY) zeolites are investigated by TPD of carbon monoxide. Only the high temperature TPD spectra of CO (TM»620-690°C) were observed, meaning that CO molecules interact with very strong acid sites. The amounts of CO bonded on these sites are small (less than 1 molecule per unit cell). The strong influence of dealumination on the coverage degree is found. The calculated values for kinetic parameters indicate chemisorption of CO in the investigated systems (Edes»240 kJ mol^-1, A»1011 s^-1).     

Crystallization kinetics, melting behavior, and RAP of novel etheroatom containing naphthyl polyesters

The changes in crystalline phase of poly(butylene naphthalate) (PBN), poly(diethylene naphthalate) (PDEN) and poly(thiodiethylene naphthalate) (PTDEN) upon thermal treatments were evaluated by X-ray diffraction technique. The melting behavior and the crystallization kinetics of the polymers under investigation were investigated by means of differential scanning calorimetry. Multiple endotherms were evidenced in PBN and PTDEN, due to melting and recrystallization processes. By applying the Hoffman?CWeeks?? method, the T _m° of PBN, PDEN, and PTDEN was derived: the introduction of ethero-atoms along PBN polymer chain causes a decrement of T _m° value. The isothermal crystallization kinetics was analyzed according to the Avrami??s treatment: the presence of ether-oxygen or sulphur atoms in the chain deeply reduces the PBN ability of crystallizing. Finally, no interphase was evidenced both in PDEN and PTDEN.     

Two crystal populations with different melting/reorganization kinetics of isothermally crystallized polyamide 6

Differential scanning calorimetry and fast scanning chip calorimetry heating experiments were carried out in a wide range of rates of temperature change from 0.2 to 60,000 K s^?1 for isothermally crystallized polyamide 6. Multiple melting peaks were observed. With increasing heating rate, the highest‐temperature endotherm shifts toward lower temperatures and finally disappears due to suppression of the reorganization. The critical heating rate to suppress reorganization was 15–50 times higher than the critical cooling rate to cause complete vitrification. On heating at rates higher than the critical heating rate to suppress reorganization, there were observed two melting processes of different kinetics. Four possible assignments were considered regarding the two crystal populations. These are (i) crystals grown during primary and secondary crystallization, (ii) crystals grown in the bulk and nucleated at the surface/substrate, (iii) crystals, which are subjected to different local stress originating from heterogeneities in interlamellar regions, and (iv) the crystal/mesophase polymorphism. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2126–2138     

Crystallization kinetics of amorphous Se

Differential scanning calorimetry was used to study crystallization behavior in selenium glass under non-isothermal conditions. The crystallization kinetics were described in terms of the Johnson–Mehl–Avrami nucleation-growth model; activation energies and kinetic parameter m _JMA were determined. The study was performed in dependence with particle size, so that a novel approach to the evaluation of crystallization kinetics—the advanced interpretation of characteristic kinetic functions—could be employed. Extensive discussion of all aspects of a full-scale kinetic study for a complex crystallization process was performed within the framework of the introduced conception. The complexity of the crystallization process was found to be represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centers arising from the sample preparation treatments and a changing amount of volume nuclei originating from the combination of the pre-nucleation period and the actual glass preparation phase. The main objective of the study is to demonstrate the extent of so-far neglected information hidden in the characteristic kinetic functions and introduce a convenient tool for its acquisition.     

Crystallization kinetics of metallic glasses

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe₇₄Ni_3.5Mo₃B₁₆Si_3.5 and Fe₄₁Ni₃₈Mo₃B_18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.     

Crystallization kinetics of syndiotactic polypropylene

Melting-point and spherulite growth rate measurements for a sample of syndiotactic polypropylene (S = 0.716 and η = 0.356) were analyzed for the parameters characterizing crystal formation and growth: T_m = 159 ± 2°C, σ_e = 47 erg cm ^?2, σ = 4.4 erg cm^?2, and q = 5.6 kcal per mole of folds. The q and σ_e values place syndiotactic polypropylene in the group of “unhindered” polymers. Failure of the isotactic-polypropylene spherulite growth rate data to follow current theories of crystal growth precluded a comparison of crystal parameters of the two stereoisomers. At comparable degrees of supercooling, the absolute growth rates for the two forms are of the same order of magnitude and exhibit one or more crossover(s) in relative position.     

Crystallization kinetics and multiple melting phenomena of a flame‐retardant phosphorus containing copolyester

Melt, cold isothermal crystallization kinetics, and multiple melting phenomena are investigated by differential scanning calorimetry (DSC) for a flame‐retardant phosphorus containing copolyester. The crystallization kinetics was investigated by the Avrami equation. The Avrami exponent is about 2.6 for melt crystallization and about 2 for cold crystallization. The crystallization activation energy for melt crystallization and for cold crystallization is −64.7 and 145.5, respectively. Three melting endotherms are found in the DSC scan, and they are explained in terms of secondary crystallization, primary crystallization, and recrystallization during the scan. A strong evidence of a two‐stage crystallization mechanism was also observed in the DSC isothermal experiment and X‐ray diffraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2269–2277, 1999     

Crystallization kinetics of poly(glycolic acid-alt-6-aminohexanoic acid)

The crystallization behavior of a new regular poly(ester amide) constituted by glycolic acid and 6-aminohexanoic acid units under both isothermal and non-isothermal conditions is studied. Differential scanning calorimetry (DSC) is used to monitor bulk crystallization, and subsequently Avrami and Ozawa analyses are applied. A three-dimensional spherulitic growth from heterogeneous nuclei is deduced for isothermal crystallization, whereas higher exponents are obtained for non-isothermal crystallization when an Avrami equation is applied. However, modifications of the Ozawa methodology indicate a crystallization mechanism similar to that of the isothermal process.The maximum crystallization rate is deduced to take place at a temperature close to 91 °C by considering experimental data and theoretical equations with adjusted parameters. The equilibrium melting temperature is determined to be 168 °C by the characteristic Hoffman-Weeks plot. One crystallization regime is detected by using the Lauritzen-Hoffman kinetic theory for isothermal crystallization and also with an isoconversional method applied for non-isothermal crystallization. Activation energy of molecular transport and nucleation constant are close to 1500 cal/mol and 1.81 × 10⁵ K², respectively. Crystal morphology, nucleation, and spherulitic growth rates are also investigated with hot-stage optical microscopy (HSOM).     

Microinjection molding of polyamide 6

Processing polymers by microinjection molding (μIM) generate specific constraints upon the polymer melt such as high shear stress and rapid cooling, leaving a mark upon the microstructure of the micropart. The present work compares the morphology and structure of polyamide 6 samples produced by melt extrusion and μIM. The specimens obtained were analyzed by polarized light microscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. α and γ crystalline forms were formed in polyamide 6 samples prepared by both methods. The γ form was dominant in the skin of the microinjection molded part, with larger contribution for these samples compared with extruded samples. The conditions used in μIM lead to considerable orientation at the skin region, decreasing toward the core, while the extruded samples showed almost no orientation. The overall degree of crystallinity of the microinjection molded part was lower compared with the extruded sample. Copyright © 2014 John Wiley & Sons, Ltd.