We have performed dielectric spectroscopy and thermally stimulated-depolarization-current experim... more We have performed dielectric spectroscopy and thermally stimulated-depolarization-current experiments to study the molecular dynamics of the twist-bend nematic phase close to the glass transition of two members of the 1 ,7-bis(4-cyanobiphenyl-4-yl)alkane homologous series (CBnCB): the liquid crystal (LC) dimers CB9CB and CB7CB, as well as a binary mixture of both. By doping CB9CB with a small quantity of CB7CB, the crystallization is inhibited when cooling the sample down, while the bulk properties of CB9CB are retained and we can investigate the supercooled behavior close to the glass transition. The study reveals that the inter-and intramolecular interactions of the mixture are similar to those of pure CB9CB and confirms that there is a single glass transition in symmetric LC dimers.
This website provides a complementary tool for the laboratory of the Physics II course in the Che... more This website provides a complementary tool for the laboratory of the Physics II course in the Chemical Engineering undergraduate studies. There is a collection of images of all the instrumentation and experimental setups used in the laboratory workshops, and the guide to the realisation of all the experiments that have to be carried out in this laboratory. There is a main page from where the pages corresponding to each experiment can be reached. In the pages corresponding to the experiments, there are links to an instrumentation section, an experimental setups section, both with the corresponding images, to a html version of the guide with links to the images, and pdf versions of this guide and of the record sheet that has to be filled at the laboratory. Instruccions del recurs: Un cop descarregats els fitxers al vostre ordinador, descomprimir-los a la carpeta on trieu. Després feu doble click sobre l’arxiu “index.htm” per executar el programa.
The recycling and disposal of disused tires is a topic of great concern to today’s companies, res... more The recycling and disposal of disused tires is a topic of great concern to today’s companies, researchers, and society in general. In this sense, our research aims to recycle end-of-life tires (GTRs) through the separation of the fraction of vulcanized rubber from the other compounds in order to later grind this fraction and separate it into lower particle sizes. Finally, we aim to incorporate these GTR particles as a filler of an ethylene-polyethylene-diene monomer (EPDM). The obtained composites with EPDM and GTR are tested (5%, 10%, 20%) comparing these values with neat EPDM as a control sample. Thermal tests such as differential calorimetry (DSC) and thermogravimetric analysis (TGA) as well as dielectric tests (DEA) are performed in order to characterize these materials and check their viability as dielectric or semiconductor, for industrial use. It is checked how the presence of GTR increases functional properties such as conductivity/permittivity. The influence of temperature ...
RESUM L'Espai Europeu d'Educació Superior (EEES) és l'àmbit on s'estan començant a moure els nost... more RESUM L'Espai Europeu d'Educació Superior (EEES) és l'àmbit on s'estan començant a moure els nostres estudiants i és també el marc en el que es produirà el futur desenvolupament de l'oferta universitària de graus i màsters de la UPC. La transició dels nostres estudiants, des del model educatiu aplicat al Batxillerat al model educatiu a la Universitat, i més concretament a la Fase Selectiva de la UPC, ha estat sempre un problema difícil d'enfocar ja que el conjunt de variables que intervenen és elevat, la seva formulació és complexa i els resultats d'una no-adaptació de l'estudiant a la Universitat, suposen la desvinculació d'aquell, un cop s'han esmerçat un conjunt de recursos important. En aquesta presentació es volen dur a terme un conjunt de reflexions obertes en relació a aquella transició Batxillerat-Universitat, a la vista del que l'oportunitat de l'EEES pot significar, tenint present la experiència acumulada a l'Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa (ETSEIAT) quant a les diferents accions preses a la seva Fase Selectiva (FS).
It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at... more It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at temperatures above the glass transition are strongly influenced by space charge. We have studied space charge relaxation in two commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this technique. The electric modulus formalism has been used to interpret their conductive properties. In both grades of polyetherimide, asymmetric Argand plots are observed, which are related to a sublinear power-law dependency (ω n with n < 1) in the real part of the conductivity. This behaviour is attributed to correlated ion hopping. The imaginary part of the electric modulus exhibits a peak in the low frequency range associated to conduction. Modelling of this peak allows us to obtain the dependence, among other parameters, of the conductivity (σ 0), the fractional exponent (n) and the crossover frequency (ω p) on the temperature. The α relaxation, that appears at higher frequencies, has also to be modelled since it overlaps the conductivity relaxation. The study of the parameters in terms of the temperature allows us to identify the ones that are thermally activated. The difference between the conductivity relaxation time and the Maxwell relaxation time indicates the presence of deep traps. The coupling model points out that the correlation of the ionic motion diminishes with temperature, probably due to increasing disorder due to thermal agitation.
The influence of foaming a semi-crystalline polymer reinforced with different concentrations of c... more The influence of foaming a semi-crystalline polymer reinforced with different concentrations of carbon nanofibres (0–20 wt.%) on the formation of an electrically conductive network was studied at room temperature using an impedance analyzer over a wide interval of frequencies (from 10−2 to 106 Hz). Composites were prepared by melt-compounding using a twin-screw extruder, and later chemically foamed. Although composite materials displayed lower conductivities than expected, assuming a percolative behavior, foaming promoted a tunnel-like conduction at lower CNF concentrations than in the solids. At higher CNF concentrations, no great improvements were achieved as tunneling conduction decreased with increasing local crystallinity. Foams showed electrical conduction characteristics typical of a conductive random-distributed fibre-like system, while the behavior of the solids was closer to a system of spherical particles, related to CNF aggregation. The anisotropic cellular structure of the 20 wt.% CNF composite foamed by a physical foaming process disrupted the preferential in-plane CNF orientation attained during solid preparation, with these foams showing higher through-plane conductivity and more isotropic electrical properties than the chemically-foamed ones. It has been demonstrated that foaming PP–CNF composites resulted in the formation of a conductive network at lower CNF concentrations than in the solids, with foams showing the potential for use in conductive high-performance lightweight composite systems.Closed-cell carbon nanofibre-reinforced polypropylene (CNF–PP) foams (bulk density 300 kg m−3) were produced and studied regarding their broad-band electrical conduction behaviour, with the main objective of producing lightweight rigid PP-based materials for electrical applications.► PP–CNF foams display higher conductivity than the solid composites. ► Foaming causes higher CNF dispersion and reduces interfibre distance. ► Tunnel conduction model fits well to experimental values of electrical conductivity. ► Through- and in-plane conductivities are affected by the foam cellular structure. ► Within certain limits a master curve was constructed for the foamed composites.
Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) h... more Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) have been used to study the e †ect of physical ageing in polyetherimide (PEI : ULTEM Ageing temperatures between 48 1000}).
In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton... more In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton HN to corona charging and measured its surface potential decay with an electrostatic voltmeter. We propose a two terms mobility to explain the experimental data: a non-dispersive contribution based on Toomer and Lewis model added to a dispersive process, which is associated with the disordered structure of the material. The non-dispersive model alone did not fit well to the data for short times, but our assumption makes the theoretical expression fit successfully to the experimental data. Some important parameters related to the charge transport properties of the material are determined and discussed.
The windowing polarization technique is an electret formation method which has been widely used t... more The windowing polarization technique is an electret formation method which has been widely used to study the structure of polar relaxations in polymers. In this paper we have studied the effect of some polarization parameters to extend the applicability of this method to the explanation of space charge relaxation in poly(methyl methacrylate).
Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) h... more Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) have been used to study the e †ect of physical ageing in polyetherimide (PEI : ULTEM Ageing temperatures between 48 1000}).
A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethy... more A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN), has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic electric analysis (DEA). As received, PEN (partially crystalline) shows, in the temperature range from −150 to 200°C, four relaxations located, in increasing temperature order, around −70°C (β), 60°C (β∗), 130°C (α) and 170°C (ρ). Amorphous PEN has been crystallized thermally heating up to different temperatures between 170 and 200°C. The DSC measurements of these samples show a small endothermic premelting peak, once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the presence of this endothermic peak, the ρ relaxation passes through a maximum and presents a sharp decrease as it is further thermally treated. The α-relaxation, detected by dynamic mechanical as well as dielectric (ac) measurements, shifts to higher temperatures and broadens as the crystallinity degree increases. The kinetic parameters of the observed relaxations have been determined fitting experimental data to standard models.
In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton... more In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton HN to corona charging and measured its surface potential decay with an electrostatic voltmeter. We propose a two terms mobility to explain the experimental data: a non-dispersive contribution based on Toomer and Lewis model added to a dispersive process, which is associated with the disordered structure of the material. The non-dispersive model alone did not fit well to the data for short times, but our assumption makes the theoretical expression fit successfully to the experimental data. Some important parameters related to the charge transport properties of the material are determined and discussed.
Using thermally stimulated depolarization currents of PET-a electrets formed by the windowing pol... more Using thermally stimulated depolarization currents of PET-a electrets formed by the windowing polarization technique, the effect of the storage time previous to depolarization on the free charge relaxation, ρ, has been studied. It was noted that the temperature at which the relaxation maximum appears increases with the storage time, whereas the intensity of the maximum decreases. This behaviour depends on both the polarization temperature and the polarizing field. It was also observed that there is a polarization temperature, the optimal polarization temperature, for which the relaxation maximum temperature does not depend on the polarizing field.
The windowing polarization technique is an electret formation method which has been widely used t... more The windowing polarization technique is an electret formation method which has been widely used to study the structure of polar relaxations in polymers. In this paper we have studied the effect of some polarization parameters to extend the applicability of this method to the explanation of space charge relaxation in poly(methyl methacrylate).
Dynamic electrical analysis shows that conductivity conditions the electrical properties of a pol... more Dynamic electrical analysis shows that conductivity conditions the electrical properties of a polymer at high temperatures and low frequencies. In this paper we show the possibilities of the electric modulus formalism to study the properties of carrier transport and space charge relaxation processes in polymethyl methacrylate. Asymmetric Argand's plots are observed in the temperature range between 150 and 210 °C. This asymmetry is related to power-law dependencies in the real part of the conductivity, of the form ωn with n<1, as a result of correlated ion hopping. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with these conductive processes. In the case of the relaxation time related to conductive processes, it has been observed that Maxwell time is higher than the characteristic time associated with the crossover frequency which determines the transition from dc to ac regime. This fact is explained by the presence of deep traps. Finally, a maximum in the value of n is observed between 180 and 190 °C which may be related to coupling between charge transport and chain segment motions.
A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethy... more A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN), has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic electric analysis (DEA). As received, PEN (partially crystalline) shows, in the temperature range from −150 to 200°C, four relaxations located, in increasing temperature order, around −70°C (β), 60°C (β∗), 130°C (α) and 170°C (ρ). Amorphous PEN has been crystallized thermally heating up to different temperatures between 170 and 200°C. The DSC measurements of these samples show a small endothermic premelting peak, once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the presence of this endothermic peak, the ρ relaxation passes through a maximum and presents a sharp decrease as it is further thermally treated. The α-relaxation, detected by dynamic mechanical as well as dielectric (ac) measurements, shifts to higher temperatures and broadens as the crystallinity degree increases. The kinetic parameters of the observed relaxations have been determined fitting experimental data to standard models.
Abstract Relaxations in poly (etherimide) PEI Ultem 1000 have been analysed by differential scann... more Abstract Relaxations in poly (etherimide) PEI Ultem 1000 have been analysed by differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) ...
We have performed dielectric spectroscopy and thermally stimulated-depolarization-current experim... more We have performed dielectric spectroscopy and thermally stimulated-depolarization-current experiments to study the molecular dynamics of the twist-bend nematic phase close to the glass transition of two members of the 1 ,7-bis(4-cyanobiphenyl-4-yl)alkane homologous series (CBnCB): the liquid crystal (LC) dimers CB9CB and CB7CB, as well as a binary mixture of both. By doping CB9CB with a small quantity of CB7CB, the crystallization is inhibited when cooling the sample down, while the bulk properties of CB9CB are retained and we can investigate the supercooled behavior close to the glass transition. The study reveals that the inter-and intramolecular interactions of the mixture are similar to those of pure CB9CB and confirms that there is a single glass transition in symmetric LC dimers.
This website provides a complementary tool for the laboratory of the Physics II course in the Che... more This website provides a complementary tool for the laboratory of the Physics II course in the Chemical Engineering undergraduate studies. There is a collection of images of all the instrumentation and experimental setups used in the laboratory workshops, and the guide to the realisation of all the experiments that have to be carried out in this laboratory. There is a main page from where the pages corresponding to each experiment can be reached. In the pages corresponding to the experiments, there are links to an instrumentation section, an experimental setups section, both with the corresponding images, to a html version of the guide with links to the images, and pdf versions of this guide and of the record sheet that has to be filled at the laboratory. Instruccions del recurs: Un cop descarregats els fitxers al vostre ordinador, descomprimir-los a la carpeta on trieu. Després feu doble click sobre l’arxiu “index.htm” per executar el programa.
The recycling and disposal of disused tires is a topic of great concern to today’s companies, res... more The recycling and disposal of disused tires is a topic of great concern to today’s companies, researchers, and society in general. In this sense, our research aims to recycle end-of-life tires (GTRs) through the separation of the fraction of vulcanized rubber from the other compounds in order to later grind this fraction and separate it into lower particle sizes. Finally, we aim to incorporate these GTR particles as a filler of an ethylene-polyethylene-diene monomer (EPDM). The obtained composites with EPDM and GTR are tested (5%, 10%, 20%) comparing these values with neat EPDM as a control sample. Thermal tests such as differential calorimetry (DSC) and thermogravimetric analysis (TGA) as well as dielectric tests (DEA) are performed in order to characterize these materials and check their viability as dielectric or semiconductor, for industrial use. It is checked how the presence of GTR increases functional properties such as conductivity/permittivity. The influence of temperature ...
RESUM L'Espai Europeu d'Educació Superior (EEES) és l'àmbit on s'estan començant a moure els nost... more RESUM L'Espai Europeu d'Educació Superior (EEES) és l'àmbit on s'estan començant a moure els nostres estudiants i és també el marc en el que es produirà el futur desenvolupament de l'oferta universitària de graus i màsters de la UPC. La transició dels nostres estudiants, des del model educatiu aplicat al Batxillerat al model educatiu a la Universitat, i més concretament a la Fase Selectiva de la UPC, ha estat sempre un problema difícil d'enfocar ja que el conjunt de variables que intervenen és elevat, la seva formulació és complexa i els resultats d'una no-adaptació de l'estudiant a la Universitat, suposen la desvinculació d'aquell, un cop s'han esmerçat un conjunt de recursos important. En aquesta presentació es volen dur a terme un conjunt de reflexions obertes en relació a aquella transició Batxillerat-Universitat, a la vista del que l'oportunitat de l'EEES pot significar, tenint present la experiència acumulada a l'Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa (ETSEIAT) quant a les diferents accions preses a la seva Fase Selectiva (FS).
It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at... more It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at temperatures above the glass transition are strongly influenced by space charge. We have studied space charge relaxation in two commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this technique. The electric modulus formalism has been used to interpret their conductive properties. In both grades of polyetherimide, asymmetric Argand plots are observed, which are related to a sublinear power-law dependency (ω n with n < 1) in the real part of the conductivity. This behaviour is attributed to correlated ion hopping. The imaginary part of the electric modulus exhibits a peak in the low frequency range associated to conduction. Modelling of this peak allows us to obtain the dependence, among other parameters, of the conductivity (σ 0), the fractional exponent (n) and the crossover frequency (ω p) on the temperature. The α relaxation, that appears at higher frequencies, has also to be modelled since it overlaps the conductivity relaxation. The study of the parameters in terms of the temperature allows us to identify the ones that are thermally activated. The difference between the conductivity relaxation time and the Maxwell relaxation time indicates the presence of deep traps. The coupling model points out that the correlation of the ionic motion diminishes with temperature, probably due to increasing disorder due to thermal agitation.
The influence of foaming a semi-crystalline polymer reinforced with different concentrations of c... more The influence of foaming a semi-crystalline polymer reinforced with different concentrations of carbon nanofibres (0–20 wt.%) on the formation of an electrically conductive network was studied at room temperature using an impedance analyzer over a wide interval of frequencies (from 10−2 to 106 Hz). Composites were prepared by melt-compounding using a twin-screw extruder, and later chemically foamed. Although composite materials displayed lower conductivities than expected, assuming a percolative behavior, foaming promoted a tunnel-like conduction at lower CNF concentrations than in the solids. At higher CNF concentrations, no great improvements were achieved as tunneling conduction decreased with increasing local crystallinity. Foams showed electrical conduction characteristics typical of a conductive random-distributed fibre-like system, while the behavior of the solids was closer to a system of spherical particles, related to CNF aggregation. The anisotropic cellular structure of the 20 wt.% CNF composite foamed by a physical foaming process disrupted the preferential in-plane CNF orientation attained during solid preparation, with these foams showing higher through-plane conductivity and more isotropic electrical properties than the chemically-foamed ones. It has been demonstrated that foaming PP–CNF composites resulted in the formation of a conductive network at lower CNF concentrations than in the solids, with foams showing the potential for use in conductive high-performance lightweight composite systems.Closed-cell carbon nanofibre-reinforced polypropylene (CNF–PP) foams (bulk density 300 kg m−3) were produced and studied regarding their broad-band electrical conduction behaviour, with the main objective of producing lightweight rigid PP-based materials for electrical applications.► PP–CNF foams display higher conductivity than the solid composites. ► Foaming causes higher CNF dispersion and reduces interfibre distance. ► Tunnel conduction model fits well to experimental values of electrical conductivity. ► Through- and in-plane conductivities are affected by the foam cellular structure. ► Within certain limits a master curve was constructed for the foamed composites.
Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) h... more Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) have been used to study the e †ect of physical ageing in polyetherimide (PEI : ULTEM Ageing temperatures between 48 1000}).
In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton... more In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton HN to corona charging and measured its surface potential decay with an electrostatic voltmeter. We propose a two terms mobility to explain the experimental data: a non-dispersive contribution based on Toomer and Lewis model added to a dispersive process, which is associated with the disordered structure of the material. The non-dispersive model alone did not fit well to the data for short times, but our assumption makes the theoretical expression fit successfully to the experimental data. Some important parameters related to the charge transport properties of the material are determined and discussed.
The windowing polarization technique is an electret formation method which has been widely used t... more The windowing polarization technique is an electret formation method which has been widely used to study the structure of polar relaxations in polymers. In this paper we have studied the effect of some polarization parameters to extend the applicability of this method to the explanation of space charge relaxation in poly(methyl methacrylate).
Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) h... more Thermally stimulated depolarization currents (TSDC) and di †erential scanning calorimetry (DSC) have been used to study the e †ect of physical ageing in polyetherimide (PEI : ULTEM Ageing temperatures between 48 1000}).
A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethy... more A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN), has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic electric analysis (DEA). As received, PEN (partially crystalline) shows, in the temperature range from −150 to 200°C, four relaxations located, in increasing temperature order, around −70°C (β), 60°C (β∗), 130°C (α) and 170°C (ρ). Amorphous PEN has been crystallized thermally heating up to different temperatures between 170 and 200°C. The DSC measurements of these samples show a small endothermic premelting peak, once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the presence of this endothermic peak, the ρ relaxation passes through a maximum and presents a sharp decrease as it is further thermally treated. The α-relaxation, detected by dynamic mechanical as well as dielectric (ac) measurements, shifts to higher temperatures and broadens as the crystallinity degree increases. The kinetic parameters of the observed relaxations have been determined fitting experimental data to standard models.
In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton... more In order to study charge trapping and transport in polyimide, we have submitted samples of Kapton HN to corona charging and measured its surface potential decay with an electrostatic voltmeter. We propose a two terms mobility to explain the experimental data: a non-dispersive contribution based on Toomer and Lewis model added to a dispersive process, which is associated with the disordered structure of the material. The non-dispersive model alone did not fit well to the data for short times, but our assumption makes the theoretical expression fit successfully to the experimental data. Some important parameters related to the charge transport properties of the material are determined and discussed.
Using thermally stimulated depolarization currents of PET-a electrets formed by the windowing pol... more Using thermally stimulated depolarization currents of PET-a electrets formed by the windowing polarization technique, the effect of the storage time previous to depolarization on the free charge relaxation, ρ, has been studied. It was noted that the temperature at which the relaxation maximum appears increases with the storage time, whereas the intensity of the maximum decreases. This behaviour depends on both the polarization temperature and the polarizing field. It was also observed that there is a polarization temperature, the optimal polarization temperature, for which the relaxation maximum temperature does not depend on the polarizing field.
The windowing polarization technique is an electret formation method which has been widely used t... more The windowing polarization technique is an electret formation method which has been widely used to study the structure of polar relaxations in polymers. In this paper we have studied the effect of some polarization parameters to extend the applicability of this method to the explanation of space charge relaxation in poly(methyl methacrylate).
Dynamic electrical analysis shows that conductivity conditions the electrical properties of a pol... more Dynamic electrical analysis shows that conductivity conditions the electrical properties of a polymer at high temperatures and low frequencies. In this paper we show the possibilities of the electric modulus formalism to study the properties of carrier transport and space charge relaxation processes in polymethyl methacrylate. Asymmetric Argand's plots are observed in the temperature range between 150 and 210 °C. This asymmetry is related to power-law dependencies in the real part of the conductivity, of the form ωn with n<1, as a result of correlated ion hopping. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with these conductive processes. In the case of the relaxation time related to conductive processes, it has been observed that Maxwell time is higher than the characteristic time associated with the crossover frequency which determines the transition from dc to ac regime. This fact is explained by the presence of deep traps. Finally, a maximum in the value of n is observed between 180 and 190 °C which may be related to coupling between charge transport and chain segment motions.
A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethy... more A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN), has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic electric analysis (DEA). As received, PEN (partially crystalline) shows, in the temperature range from −150 to 200°C, four relaxations located, in increasing temperature order, around −70°C (β), 60°C (β∗), 130°C (α) and 170°C (ρ). Amorphous PEN has been crystallized thermally heating up to different temperatures between 170 and 200°C. The DSC measurements of these samples show a small endothermic premelting peak, once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the presence of this endothermic peak, the ρ relaxation passes through a maximum and presents a sharp decrease as it is further thermally treated. The α-relaxation, detected by dynamic mechanical as well as dielectric (ac) measurements, shifts to higher temperatures and broadens as the crystallinity degree increases. The kinetic parameters of the observed relaxations have been determined fitting experimental data to standard models.
Abstract Relaxations in poly (etherimide) PEI Ultem 1000 have been analysed by differential scann... more Abstract Relaxations in poly (etherimide) PEI Ultem 1000 have been analysed by differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) ...
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Papers by Miguel Mudarra