Crystallization of Polytetrafluoroethylene in a Wide Range of Cooling Rates: Nucleation and Diffusion in the Presence of Nanosilica Clusters

Polytetrafluoroethylene (PTFE) is a polymer that displays exceptional properties. This synthetic fluoropolymer is also known to crystallize very fast upon cooling. The present work highlights for the first time the influence of nanosilica clusters on PTFE crystallization at fast cooling rates (up to 5000 K·s−1). The silica was synthesized from aqueous silicate solution and the surface modification was performed using TriEthoxyFluoroSilane (TEFS). In order to understand the crystallization behavior of PTFE/silica nanocomposite at a fast cooling rate, the measurements were carried out by Fast Scanning Calorimetry (FSC). The data were consequently combined with the measurements performed by conventional Differential Scanning Calorimetry (DSC). Interestingly, the results displayed variation of the crystallization behavior for the nanocomposite at fast cooling rates compared to slow cooling rates. The differences in crystal morphologies were then observed by Scanning Electron Microscopy (SEM) after slow and fast cooling rates. Finally, the effective activation energies (Eα) obtained from the crystallization under various cooling rates were combined in order to obtain one set of Hoffman-Lauritzen parameters. This procedure allowed us to show that the crystallization of PTFE in the presence of silica is promoted or hampered according to the cooling rates employed.

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Crystallization Behaviour of Polytetrafluoroethylene over very Large Cooling Rate Domains

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.747.201 ◽

2013 ◽

Vol 747 ◽

pp. 201-204

Author(s):

Nicolas Bosq ◽

Nathanaël Guigo ◽

Nicolas Sbirrazzuoli

Keyword(s):

Cooling Rate ◽

Glassy State ◽

Crystalline Polymer ◽

Sem Analysis ◽

Scanning Calorimetry ◽

Theoretical Dependence ◽

Cooling Rates ◽

Fast Scanning Calorimetry ◽

Wide Range ◽

Fast Cooling

Polytetrafluoroethylene (PTFE) is a semi-crystalline polymer that demonstrates a very fast crystallization process on cooling. This study investigates the nonisothermal PTFE ultra-fast crystallization over a wide range of cooling rates via conventional Differential Scanning Calorimetry (DSC), Fast Scanning Calorimetry (FSC) and Ultra-Fast Scanning Calorimetry (UFSC). A new knowledge about crystallization kinetics of PTFE is obtained from the data obtained under very fast cooling rates. The shift of the melting peak to lower temperature shows that the crystals formed under fast cooling rates are slightly less stable than those produced under slower cooling rates. SEM analysis allows to observe these differences in crystal morphologies. According to the results, the crystallization is still present even for the fastest cooling rate employed and in consequences it is impossible to reach a metastable glassy state. The effective activation energy (Eα) displays a variation with the relative extent of crystallization (α) that is characteristic of a transition of PTFE crystallization from regime II to regime III around 312°C. Following the Hoffman-Lauritzen theory the Eα dependency obtained from the crystallizations under the different cooling rates was fitted in order to study the theoretical dependence of the growth rate.

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Influence of Cooling Rates on Phase Transitions of Bent-Core Liquid Crystal 1,3-Phenylene-bis[4-(hexylcarboyloxyl)benzylideneamine]

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.428-429.247 ◽

2010 ◽

Vol 428-429 ◽

pp. 247-250 ◽

Cited By ~ 1

Author(s):

Yuan Ming Huang ◽

Qing Lan Ma ◽

Bao Gai Zhai

Keyword(s):

Differential Scanning Calorimetry ◽

Phase Transitions ◽

Liquid Crystal ◽

Optical Microscopy ◽

Cooling Rate ◽

Scanning Calorimetry ◽

Slow Cooling ◽

Cooling Rates ◽

Polarized Optical Microscopy ◽

Fast Cooling

The influence of cooling rate on the phase transitions of a three-benzene-ring containing bent-core liquid crystal 1,3-phenylene-bis[4-(hexylcarboyloxyl)benzylideneamine] has been investigated by means of differential scanning calorimetry and polarized optical microscopy. Our results show that the cooling rates in the second cooling run pose significant effects on the phase transitions of the bent-core liquid crystal despite the cooling rates in the first cooling run pose little effects on the phase transitions. In the second cooling run, the banana phases survived only when the cooling rates were in the range of 14~15oC/min whereas both slow cooling rates which were less than 13oC/min and fast cooling rates which were higher than 16oC/min made the banana phases disappeared.

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Effect of Cooling Rate on Glass Formation for Some Oxynitride Glasses

Materials Science Forum ◽

10.4028/www.scientific.net/msf.554.25 ◽

2007 ◽

Vol 554 ◽

pp. 25-30 ◽

Cited By ~ 1

Author(s):

Wynette Redington ◽

Murt Redington ◽

Stuart Hampshire

Keyword(s):

Cooling Rate ◽

Glass Formation ◽

Resistance Furnace ◽

Slow Cooling ◽

Cooling Rates ◽

X Ray ◽

Glass Forming ◽

Wide Range ◽

Fast Cooling ◽

Nd Systems

Rapid cooling rates and quenching have traditionally been associated with glass formation. Hampshire et al. [1] investigated oxynitride glasses cooled in a tungsten resistance furnace at approximately 200oC/min and found that fast cooling rates were only important near the limits of the glass-forming region. In the current work on various M-Si-Al-O-N (M=Y, La, Yb, Nd) systems, it was found that even at a relatively slow cooling rate glass formation was still possible for a wide range of compositions. Different cooling rates were investigated to determine the minimum cooling rate at which a glass will form. Quantitative X-ray analysis of melted compositions indicated the relative amounts of amorphous phase and crystalline phase.

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Relationship between the Stereocomplex Crystallization Behavior and Mechanical Properties of PLLA/PDLA Blends

Polymers ◽

10.3390/polym13111851 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1851

Author(s):

Hye-Seon Park ◽

Chang-Kook Hong

Keyword(s):

Mechanical Properties ◽

Lactic Acid ◽

Crystallization Behavior ◽

Mechanical Analysis ◽

X Ray Diffraction ◽

Nucleation Agent ◽

Scanning Calorimetry ◽

Nucleation Sites ◽

Wide Range ◽

Degree Of Crystallization

Poly (l-lactic acid) (PLLA) is a promising biomedical polymer material with a wide range of applications. The diverse enantiomeric forms of PLLA provide great opportunities for thermal and mechanical enhancement through stereocomplex formation. The addition of poly (d-lactic acid) (PDLA) as a nucleation agent and the formation of stereocomplex crystallization (SC) have been proven to be an effective method to improve the crystallization and mechanical properties of the PLLA. In this study, PLLA was blended with different amounts of PDLA through a melt blending process and their properties were calculated. The effect of the PDLA on the crystallization behavior, thermal, and mechanical properties of PLLA were investigated systematically by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized optical microscopy (POM), dynamic mechanical analysis (DMA), and tensile test. Based on our findings, SC formed easily when PDLA content was increased, and acts as nucleation sites. Both SC and homo crystals (HC) were observed in the PLLA/PDLA blends. As the content of PDLA increased, the degree of crystallization increased, and the mechanical strength also increased.

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The effect of cooling rate on crystallization behavior and tensile properties of CF/PEEK composites

Journal of Polymer Engineering ◽

10.1515/polyeng-2020-0356 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Guangming Dai ◽

Lihua Zhan ◽

Chenglong Guan ◽

Minghui Huang

Keyword(s):

Cooling Rate ◽

Crystallization Temperature ◽

Crystallization Behavior ◽

Crystalline Polymer ◽

Scanning Calorimetry ◽

Nonisothermal Crystallization ◽

Cooling Rates ◽

Control Range ◽

Temperature Range ◽

Transverse Tensile

Abstract In this study, the differential scanning calorimetry (DSC) tests were performed to measure the nonisothermal crystallization behavior of carbon fiber reinforced polyether ether ketone (CF/PEEK) composites under different cooling rates. The characteristic parameters of crystallization were obtained, and the nonisothermal crystallization model was established. The crystallization temperature range of the material at different cooling rates was predicted by the model. The unidirectional laminates were fabricated at different cooling rates in the crystallization temperature range. The results showed that the crystallization temperature range shifted to a lower temperature with the increase of cooling rate, the established nonisothermal crystallization model was consistent with the DSC test results. It is feasible to shorten the cooling control range from the whole process to the crystallization range. The crystallinity and transverse tensile strength declined significantly with the increase of the cooling rate in the crystallization temperature range. The research results provided theoretical support for the selection of cooling conditions and temperature control range, which could be applied to the thermoforming process of semi-crystalline polymer matrixed composites to improve the manufacturing efficiency.

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First, Do Not Degrade - an Alternative View on Polymer Laser Sintering

10.26434/chemrxiv.14754216 ◽

2021 ◽

Author(s):

Arkadiusz Antończak ◽

Mateusz Wieczorek ◽

Paulina Dzienny ◽

Bartłomiej Kryszak ◽

Anna Krokos ◽

...

Keyword(s):

Gel Permeation Chromatography ◽

Laser Sintering ◽

Polymer Materials ◽

Alternative View ◽

Scanning Calorimetry ◽

Entire Volume ◽

Beam Laser ◽

Dual Beam ◽

Wide Range ◽

First Time

<p>In the work, for the first time, the method of Dual Beam Laser Sintering of polymers (DBLS) was presented, in which, instead of heating the entire volume of the polymer throughout the entire process, a second, additional laser was used for selective in terms of volume and time heating of the material. The principle of operation and the design of the prototype are presented. Using the developed station, an experiment was carried out for sintering samples from technical polylactide powder as a function of selected process parameters. It confirmed the functionality of the method and proved that the sintering process can be controlled in a fairly wide range for the proposed method. A preliminary comparison of changes in the physicochemical properties of the obtained samples in relation to the samples sintered by standard laser sintering was carried out using Gel Permeation Chromatography, Fourier Transform Infrared Reflectance and Differential Scanning Calorimetry. The experiment showed that the presented method has the potential to limit the thermal degradation of sensitive polymer materials.</p>

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Anomalous Anisotropic Diffusion of Electron Swarms in AC Electric Fields

Australian Journal of Physics ◽

10.1071/ph950925 ◽

1995 ◽

Vol 48 (6) ◽

pp. 925 ◽

Cited By ~ 46

Author(s):

RD White ◽

RE Robson ◽

KF Ness

Keyword(s):

Electric Fields ◽

Diffusion Coefficients ◽

Anisotropic Diffusion ◽

Time Varying ◽

Longitudinal Diffusion ◽

Temporal Behaviour ◽

Ac Electric Fields ◽

Wide Range ◽

First Time ◽

And Diffusion

A time-dependent multi-term solution of the Boltzmann equation is used to calculate the drift and diffusion coefficients of electron swarms in gases under the influence of a time varying electric field. Two model gases are considered and for a.c. electric fields results are presented for a wide range of applied frequencies. Of particular interest is the anomalous temporal behaviour of the longitudinal diffusion coefficient, which is discussed here for the first time.

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Characterization of Residual Strain in Si Ingots Grown by the Seed-Cast Method

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.205-206.94 ◽

2013 ◽

Vol 205-206 ◽

pp. 94-99 ◽

Cited By ~ 3

Author(s):

Karolin Jiptner ◽

Masayuki Fukuzawa ◽

Yoshiji Miyamura ◽

Hirofumi Harada ◽

Koichi Kakimoto ◽

...

Keyword(s):

High Temperature ◽

Temperature Gradient ◽

Residual Strain ◽

Strain Distribution ◽

High Temperature Region ◽

Slow Cooling ◽

Cooling Rates ◽

Cooling Conditions ◽

Fast Cooling

The residual strain distribution in cast-grown mono-like Si ingots is analyzed. The effect of the crucible during solidification and the influence of different cooling rates is described. To clarify in which process steps residual strain accumulates, several Si ingots were grown in a laboratory scale furnace (100mm) using different cooling conditions after completion of the solidification. For the cooling, two different cooling rates were distinguished: fast cooling (12deg/min) and slow cooling (5deg/min). It was found that changes in cooling gradients greatly influence the amount of residual strain. The results show that slow cooling in any temperature range leads to strain reduction. The greatest reduction could be found when the temperature gradient was changed to slow cooling in the high temperature region.

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