scholarly journals Effect of Organic Modifier and Clay Content on Non-Isothermal Cold Crystallization and Melting Behavior of Polylactide/Organovermiculite Nanocomposites

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 364
Author(s):  
M. Jesús Fernández ◽  
M. Dolores Fernández
Keyword(s):  
Rate Coefficient ◽  
Crystallization Rate ◽  
Clay Content ◽  
Melting Behavior ◽  
Cold Crystallization ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Crystallization And Melting Behavior ◽  
Kinetics Of ◽  
Nucleating Effect

In clay/polymer nanocomposites, the crystallization behavior and kinetics of the polymer can be affected by the presence of clay, its content and the degree of miscibility between the clay and the polymer matrix. The effect of two different organomodified vermiculites on the non-isothermal cold crystallization and melting behavior of polylactide (PLA) was studied by differential scanning calorimetry (DSC). In the presence of vermiculites, the cold crystallization of PLA occurred earlier, particularly for the highest content of the most miscible organovermiculite with PLA. The cold crystallinity of PLA decreased at low heating rates, notably at high organoclay loadings, and increased at high heating rates, especially at low vermiculite contents. According to the crystallization half-time, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP) approaches, the cold crystallization rate of PLA increased by incorporating vermiculites, with the effect being most noteworthy for the vermiculite showing better compatibility. The Mo model was successful in describing the non-isothermal cold crystallization kinetics of the PLA/vermiculite composites. The melting behavior was affected by the heating rate and the type and content of clay. The nucleating effect of the most compatible clay resulted in the less perfect crystallites. The activation energy was evaluated using the Kissinger and Takhor methods.

scholarly journals Nonisothermal Cold Crystallization Kinetics of Poly(lactic acid)/Bacterial Poly(hydroxyoctanoate) (PHO)/Talc

2019 ◽  
Vol 17 (1) ◽  
pp. 1266-1278
Author(s):  
Omaima Alhaddad ◽  
Safaa H. El-Taweel ◽  
Yasser Elbahloul
Keyword(s):  
Thermal Stability ◽  
Lactic Acid ◽  
Crystallization Kinetics ◽  
Crystallization Rate ◽  
Cold Crystallization ◽  
Poly Lactic Acid ◽  
Gravimetric Analysis ◽  
Scanning Calorimetry ◽  
Kinetics Of ◽  
Thermal Stability Of

AbstractThe effects of bacterial poly(hydroxyoctanoate) (PHO) and talc on the nonisothermal cold crystallization behaviours of poly(lactic acid) (PLA) were analysed with differential scanning calorimetry (DSC), and the thermal stability of the samples was observed with thermal gravimetric analysis (TGA). The modified Avrami’s model was used to describe the nonisothermal cold crystallization kinetics of neat PLA and its blends. The activation energies E for nonisothermal cold crystallization were calculated by the isoconversional method of Kissinger-Akahira-Sunose (KAS). The DSC results showed that the PLA/PHO blends were immiscible in the whole studied range, and as the PHO and talc content increased, the crystallization rate of PLA accelerated, and the crystallinity of PLA in the PLA samples increased. The values of the Avrami exponent indicated that the nonisothermal cold crystallization of the neat PLA and its blends exhibited heterogeneous, three-dimensional spherulitic growth. The E values were strongly dependent on PHO and talc. The TGA results showed that the presence of PHO and talc slightly influenced the thermal stability of PLA.

scholarly journals Melting Kinetics of Nascent Poly(tetrafluoroethylene) Powder

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 791
Author(s):  
Fotis Christakopoulos ◽  
Enrico Troisi ◽  
Theo A. Tervoort
Keyword(s):  
Kinetic Model ◽  
Heating Rate ◽  
Melting Temperature ◽  
Melting Behavior ◽  
Slow Heating ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Exponential Factor ◽  
Melting Kinetics ◽  
Kinetics Of

The melting behavior of nascent poly(tetrafluoroethylene) (PTFE) was investigated by way of differential scanning calorimetry (DSC). It is well known that the melting temperature of nascent PTFE is about 344 ∘ C, but reduces to 327 ∘ C for once molten material. In this study, the melting temperature of nascent PTFE crystals was found to strongly depend on heating rate, decreasing considerably for slow heating rates. In addition, during isothermal experiments in the temperature range of 327 ∘ C < T < 344 ∘ C, delayed melting of PTFE was observed, with complete melting only occurring after up to several hours. The melting kinetics of nascent PTFE were analyzed by means of the isoconversional methodology, and an apparent activation energy of melting, dependent on the conversion, was determined. The compensation effect was utilized in order to derive the pre-exponential factor of the kinetic model. The numerical reconstruction of the kinetic model was compared with literature models and an Avrami-Erofeev model was identified as best fit of the experimental data. The predictions of the kinetic model were in good agreement with the observed time-dependent melting of nascent PTFE during isothermal and constant heating-rate experiments.

Studies on the effects of 4,4′-dihydroxyphenyl on crystallization and melting behavior of poly (butylene terephthalate)

2017 ◽  
Vol 37 (8) ◽  
pp. 747-755 ◽  
Author(s):  
Zhiyuan Shen ◽  
Faliang Luo ◽  
Jianghua Du ◽  
Xiaomei Lei ◽  
Lijie Ji
Keyword(s):  
Crystallization Rate ◽  
Melting Behavior ◽  
Avrami Equation ◽  
Wide Angle ◽  
Melt Blending ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Butylene Terephthalate ◽  
X Ray ◽  
Crystallization And Melting Behavior

Abstract The blends of poly (butylene terephthalate) (PBT) and 4,4′-dihydroxyphenyl (DHP) were prepared by melt blending, and the effects of DHP on the crystallization and melting behaviors of PBT were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results showed that crystallization temperature and crystallinity of PBT apparently decreased with the addition of DHP. A remarkably decline in crystallization rate of PBT was achieved, and the blends had higher σe and q values than that of pure PBT as analyzed based on the Avrami equation and Lauritzen-Hoffman equation. The crystal structure of PBT did not change by the addition of DHP, while the spherulite size of PBT decreased.

Effects of additives on the cure kinetics of vinyl ester pultrusion resins

2021 ◽  
pp. 002199832110015
Author(s):  
Alexander Vedernikov ◽  
Yaroslav Nasonov ◽  
Roman Korotkov ◽  
Sergey Gusev ◽  
Iskander Akhatov ◽  
...  
Keyword(s):  
Vinyl Ester ◽  
Mean Squared Error ◽  
Cure Kinetics ◽  
Zinc Stearate ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Different Temperatures ◽  
Predicted Values ◽  
Kinetics Of ◽  
Final Degree

Pultrusion is a highly efficient composite manufacturing process. To accurately describe pultrusion, an appropriate model of resin cure kinetics is required. In this study, we investigated cure kinetics modeling of a vinyl ester pultrusion resin (Atlac 430) in the presence of aluminum hydroxide (Al(OH)3) and zinc stearate (Zn(C18H35O2)2) as processing additives. Herein, four different resin compositions were studied: neat resin composition, composition with Al(OH)3, composition comprising Zn(C18H35O2)2, and composition containing both Al(OH)3 and Zn(C18H35O2)2. To analyze each composition, we performed differential scanning calorimetry at the heating rates of 5, 7.5, and 10 K/min. To characterize the cure kinetics of Atlac 430, 16 kinetic models were tested, and their performances were compared. The model based on the [Formula: see text]th-order autocatalytic reaction demonstrated the best results, with a 4.5% mean squared error (MSE) between the experimental and predicted data. This study proposes a method to reduce the MSE resulting from the simultaneous melting of Zn(C18H35O2)2. We were able to reduce the MSE by approximately 34%. Numerical simulations conducted at different temperatures and pulling speeds demonstrated a significant influence of resin composition on the pultrusion of a flat laminate profile. Simulation results obtained for the 600 mm long die block at different die temperatures (115, 120, 125, and 130 °C) showed that for a resin with a final degree of cure exceeding 95% at the die exit, the maximum difference between the predicted values of pulling speed for a specified set of compositions may exceed 1.7 times.

scholarly journals The Effect of WS2 Nanosheets on the Non-Isothermal Cold- and Melt-Crystallization Kinetics of Poly(l-lactic acid) Nanocomposites

Polymers ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 2214
Author(s):  
Mohammed Naffakh ◽  
Pablo Rica ◽  
Carmen Moya-Lopez ◽  
José Antonio Castro-Osma ◽  
Carlos Alonso-Moreno ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Transition Metal Dichalcogenides ◽  
Crystallization Rate ◽  
Melting Behavior ◽  
Hybrid Nanocomposites ◽  
Melt Crystallization ◽  
Heating Rates ◽  
Solution Blending ◽  
New Perspective ◽  
Ws2 Nanosheets

In the present work, hybrid nanocomposite materials were obtained by a solution blending of poly(l-lactic acid) (PLLA) and layered transition-metal dichalcogenides (TMDCs) based on tungsten disulfide nanosheets (2D-WS2) as a filler, varying its content between 0 and 1 wt%. The non-isothermal cold- and melt-crystallization and melting behavior of PLLA/2D-WS2 were investigated. The overall crystallization rate, final crystallinity, and subsequent melting behavior of PLLA were controlled by both the incorporation of 2D-WS2 and variation of the cooling/heating rates. In particular, the analysis of the cold-crystallization behavior of the PLLA matrix showed that the crystallization rate of PLLA was reduced after nanosheet incorporation. Unexpectedly for polymer nanocomposites, a drastic change from retardation to promotion of crystallization was observed with increasing the nanosheet content, while the melt-crystallization mechanism of PLLA remained unchanged. On the other hand, the double-melting peaks, mainly derived from melting–recrystallization–melting processes upon heating, and their dynamic behavior were coherent with the effect of 2D-WS2 involved in the crystallization of PLLA. Therefore, the results of the present study offer a new perspective for the potential of PLLA/hybrid nanocomposites in targeted applications.

Investigating the relationship between tack and degree of conversion in DGEBA-based epoxy resin cured with dicyandiamide and diuron

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ali Kuliaei ◽  
Iraj Amiri Amraei ◽  
Seyed Rasoul Mousavi
Keyword(s):  
Epoxy Resin ◽  
Reaction Order ◽  
Theoretical Data ◽  
Cure Kinetics ◽  
Diglycidyl Ether ◽  
Degree Of Conversion ◽  
Ozawa Method ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Kinetics Of

Abstract The purpose behind this research was to determine the optimum formulation and investigate the cure kinetics of a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin cured by dicyandiamide and diuron for use in prepregs. First, all formulations were examined by the tensile test, and then, the specimens with higher mechanical properties were further investigated by viscometry and tack tests. The cure kinetics of the best formulation (based on tack test) in nonisothermal mode was investigated using differential scanning calorimetry at different heating rates. Kissinger and Ozawa method was used for determining the kinetic parameters of the curing process. The activation energy obtained by this method was 71.43 kJ/mol. The heating rate had no significant effect on the reaction order and the total reaction order was approximately constant ( m + n ≅ 2.1 $m+n\cong 2.1$ ). By comparing the experimental data and the theoretical data obtained by Kissinger and Ozawa method, a good agreement was seen between them. By increasing the degree of conversion, the viscosity decreased; as the degree of conversion increased, so did the slope of viscosity. The results of the tack test also indicated that the highest tack could be obtained with 25% progress of curing.

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7HPhH6 Glassformer

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1487
Author(s):  
Aleksandra Deptuch ◽  
Małgorzata Jasiurkowska-Delaporte ◽  
Ewa Juszyńska-Gałązka ◽  
Anna Drzewicz ◽  
Wojciech Zając ◽  
...  
Keyword(s):  
Differential Scanning Calorimetry ◽  
Optical Microscopy ◽  
Dielectric Spectroscopy ◽  
Cold Crystallization ◽  
Scanning Calorimetry ◽  
Broadband Dielectric Spectroscopy ◽  
Smectic C ◽  
Dimension Analysis ◽  
Fractal Dimension Analysis ◽  
Kinetics Of

An investigation of the glass transition of the antiferroelectric smectic C*A phase and cold crystallization of (S)-4’-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluoro- butoxy)heptyl-1-oxy]benzoate (denoted as 3F7HPhH6) by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy is presented. The fragility index mf = 72, classifying 3F7HPhH6 as a glassformer with intermediate fragility, was obtained from the temperature dependence of the α-process relaxation time, measured upon cooling. Duplication of the α-process was observed exclusively upon heating, before the onset of cold crystallization, and is connected with the pre-transitional effect. The presence of two crystal phases likely influences the kinetics of cold crystallization; the idea stems from a comparison with previous results for the 3F7HPhF6 and 3F7HPhH7 compounds. Additionally, the presence of the smectic C*α; sub-phase in a narrow temperature range was proved based on the differential scanning calorimetry and broadband dielectric spectroscopy results, as well as the fractal dimension analysis of the textures obtained by polarizing optical microscopy.

scholarly journals Non-Isothermal Sublimation Kinetics of 2,4,6-Trinitrotoluene (TNT) Nanofilms

Molecules ◽  
2019 ◽  
Vol 24 (6) ◽  
pp. 1163 ◽  
Author(s):  
Walid Hikal ◽  
Brandon Weeks
Keyword(s):  
Activation Energy ◽  
Analytical Techniques ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Absorbance Spectroscopy ◽  
Calculated Activation Energy ◽  
Sublimation Kinetics ◽  
Sublimation Rates ◽  
First Time ◽  
Kinetics Of

Non-isothermal sublimation kinetics of low-volatile materials is more favorable over isothermal data when time is a crucial factor to be considered, especially in the subject of detecting explosives. In this article, we report on the in-situ measurements of the sublimation activation energy for 2,4,6-trinitrotoluene (TNT) continuous nanofilms in air using rising-temperature UV-Vis absorbance spectroscopy at different heating rates. The TNT films were prepared by the spin coating deposition technique. For the first time, the most widely used procedure to determine sublimation rates using thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) was followed in this work using UV-Vis absorbance spectroscopy. The sublimation kinetics were analyzed using three well-established calculating techniques. The non-isothermal based activation energy values using the Ozawa, Flynn–Wall, and Kissinger models were 105.9 ± 1.4 kJ mol−1, 102.1 ± 2.7 kJ mol−1, and 105.8 ± 1.6 kJ mol−1, respectively. The calculated activation energy agreed well with our previously reported isothermally-measured value for TNT nanofilms using UV-Vis absorbance spectroscopy. The results show that the well-established non-isothermal analytical techniques can be successfully applied at a nanoscale to determine sublimation kinetics using absorbance spectroscopy.

scholarly journals Hydrogen desorption kinetics of MgH2 synthesized from modified waste magnesium

2014 ◽  
Vol 32 (3) ◽  
pp. 385-390
Author(s):  
Aysel Kantürk Figen ◽  
Bilge Coşkuner ◽  
Sabriye Pişkin
Keyword(s):  
Hydrogen Desorption ◽  
Nitrogen Atmosphere ◽  
Desorption Kinetics ◽  
X Ray Diffraction ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Xrf Scanning ◽  
Isothermal Kinetic ◽  
Kinetics Of

AbstractIn the present study, hydrogen desorption properties of magnesium hydride (MgH2) synthesized from modified waste magnesium chips (WMC) were investigated. MgH2 was synthesized by hydrogenation of modified waste magnesium at 320 °C for 90 min under a pressure of 6 × 106 Pa. The modified waste magnesium was prepared by mixing waste magnesium with tetrahydrofuran (THF) and NaCl additions, applying mechanical milling. Next, it was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques in order to characterize its structural properties. Hydrogen desorption properties were determined by differential scanning calorimetry (DSC) under nitrogen atmosphere at different heating rates (5, 10, and 15 °C/min). Doyle and Kissenger non-isothermal kinetic models were applied to calculate energy (Ea) values, which were found equal to 254.68 kJ/mol and 255.88 kJ/mol, respectively.

scholarly journals The effect of hydroxyapatite nanoparticles on crystallization and thermomechanical properties of PLLA matrix

2017 ◽  
Vol 89 (1) ◽  
pp. 125-140 ◽  
Author(s):  
Ioanna-Georgia I. Athanasoulia ◽  
Maximos N. Christoforidis ◽  
Dimitrios M. Korres ◽  
Petroula A. Tarantili
Keyword(s):  
Crystallization Temperature ◽  
Isothermal Crystallization ◽  
Crystallization Behavior ◽  
Crystallization Kinetic ◽  
Crystallization Rate ◽  
Melting Behavior ◽  
Thermomechanical Properties ◽  
Cold Crystallization ◽  
Crystallization Experiments ◽  
Twin Screw

AbstractIn this study, hydroxyapatite (HA) was incorporated in a poly(L-lactic acid) (PLLA) matrix and the thermal properties and crystallization behavior of the derived composites were investigated. The nanocomposites, containing 0–20 wt% HA, were prepared by melt extrusion employing a twin-screw extruder. XRD experiments verified an increase in the intensity of the characteristic diffraction peak of the α-form crystalline phase of PLLA with increasing HA content. By DSC experiments it was observed that the presence of HA increased the crystallinity during cold crystallization, leading to a shift of cold-crystallization temperature to lower values and to an increase in the melting temperature of the PLLA phase. Isothermal crystallization experiments at 100, 110, 115 and 120°C, revealed a maximum in crystallization kinetic around 100°C after the addition of HA compared to 115°C for pure PLLA. The crystallization rate of PLLA matrix in the nanocomposites decreased with increasing crystallization temperature. By using the Avrami and Lauritzen-Hoffman equations the exponent n was calculated in the range 2–3 and a theoretical approach verified that the HA/PLLA systems belong to Regime II of crystallization behavior. The investigated melting behavior of PLLA was attributed to better organized crystalline structure with increasing isothermal crystallization temperatures and might be related with the longer time necessary for the completion of crystallization.

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