The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
G Titomanlio - One of the best experts on this subject based on the ideXlab platform.
-
nucleation and Crystallization Kinetics of poly lactic acid
Thermochimica Acta, 2011Co-Authors: Felice De Santis, Roberto Pantani, G TitomanlioAbstract:A commercial grade PLA was characterized using differential scanning calorimetry under both isothermal and non-isothermal conditions, and the experimental data were analyzed evaluating the Crystallization Kinetics constants for melt and cold isothermal Crystallization at some temperatures. Furthermore, a peculiar experimental protocol was adopted, varying each time the minimum cooling temperature before the isothermal step, performed monitoring nucleation and growth rate in an adequate range of temperatures. Morphological characterizations were modeled using the classical Lauritzen–Hoffman theory, which assumes that the free energy barrier associated with nucleation has an energetic origin, estimating the dependence on temperature using physical parameters derived from the linear Hoffman–Weeks plot. Crystallization Kinetics was evaluated using the Avrami model, through nucleation and growth rate, describing both the melt and cold Crystallization experimental results. Detailed comprehensive description of the Crystallization Kinetics of PLA is provided, predicting the final crystallinity and the morphology with tailored thermal history.
-
Crystallization Kinetics of virgin and processed poly lactic acid
Polymer Degradation and Stability, 2010Co-Authors: Roberto Pantani, Felice De Santis, Andrea Sorrentino, F De Maio, G TitomanlioAbstract:Abstract Poly(lactic acid) (PLA) is an emerging material mainly because it can be synthesized from renewable resources and is thus environmentally and ecologically safe. The mechanical properties, above all the thermal resistance of PLA are determined by the crystalline content: the heat deflection temperature of crystalline PLA can reach 100 °C, whereas amorphous PLA loses mechanical properties at temperatures slightly higher than 60 °C. However, PLA has a low Crystallization rate, so that after processing it remains mostly amorphous. This characteristic heavily limits the use of PLA for commercial applications. Many studies have been recently published on the Crystallization Kinetics of PLA. The effect of processing on this feature is however often neglected. In this work, the significance of processing on the Crystallization Kinetics of a commercial PLA was investigated. Two processing methods were explored: extrusion and injection moulding. The obtained materials, and the starting pellets of virgin polymer, were analyzed by calorimetry in order to obtain the Crystallization Kinetics. Two protocols were adopted to determine the Crystallization rates during cooling from the melt or heating from the solid. The parameters of a kinetic equation were determined for all the materials and protocols adopted and it was thus possible to describe the evolution of crystallinity during heating and during cooling.
Jiří Málek - One of the best experts on this subject based on the ideXlab platform.
-
Non-isothermal Crystallization Kinetics of GeTe_4 infrared glass
Journal of Thermal Analysis and Calorimetry, 2016Co-Authors: Roman Svoboda, Daniela Brandová, Jiří MálekAbstract:Non-isothermal Crystallization Kinetics of the GeTe_4 chalcogenide glass was studied in dependence on particle size. Complexity of the obtained DSC data was treated by means of the Fraser–Suzuki deconvolution, and the particular Crystallization sub-processes were identified and described in terms of the JMA(2) and AC kinetic models. Bulk as-prepared GeTe_4 samples, on the other hand, exhibited simple zero-order (F0) Crystallization Kinetics. The marked difference between the powder and bulk Crystallization mechanisms was explained based on the mechanically induced defects and heterogeneities, which surrogate/accelerate the primary nucleation process. This concept also accounts for the remarkable stability of the studied telluride glass. Precipitation of Te followed by second-stage GeTe crystal growth was confirmed by XRD for all of the applied experimental conditions. The dominant influence of the nucleation process on the consequent Crystallization Kinetics is thereby implicated. Infrared microscopy was used to confirm the existence of the particular Crystallization mechanism.
-
Crystallization Kinetics of a-Se, part 4: thin films
Philosophical Magazine, 2014Co-Authors: Roman Svoboda, Jan Gutwirth, Jiří MálekAbstract:Differential scanning calorimetry was used to study the Crystallization behaviour of selenium thin films in dependence on film thickness and deposition rate. In the current work, which is the fourth in a sequence of articles dealing with Crystallization Kinetics of a-Se, the non-isothermal Crystallization Kinetics was described in terms of the Johnson-Mehl-Avrami nucleation-growth model. Two-dimensional crystallite growth, consistent with the idea of sterically restricted Crystallization in a thin layer, was confirmed for all data. It was found that neither the film thickness (tested within the 100–2350 nm range) nor the deposition rate appears to have any significant influence on the Crystallization Kinetics. However, the higher amount of intrinsic defects possibly produced by a higher deposition rate seems to accelerate the Crystallization, shifting it towards lower temperatures. Very good correlation between the results obtained for thin films and those for fine powders was found. Based on the obtained...
-
Crystallization Kinetics of amorphous Se
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Roman Svoboda, Jiří MálekAbstract: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 by Thermal Analysis
Journal of Thermal Analysis and Calorimetry, 1999Co-Authors: Jiří MálekAbstract:Thermal Analysis techniques are widely used to study the Crystallization Kinetics in amorphous solids. Such experimental data are frequently interpreted in terms of the Johnson-Mehl-Avrami (JMA) nucleation-growth model. This paper discusses the limits of such approach. A simple method is proposed to verify the applicability of the JMA model as well as the basic assumptions in kinetic analysis. It is shown that the autocatalytic model includes the JMA model and it is a plausible description of the Crystallization Kinetics. The main advantage of the autocatalytic model is the possibility to describe quantitatively the Kinetics of complex Crystallization processes. The experimental data for Crystallization of a chalcogenide glass analyzed in this paper clearly demonstrate rather complex nature of these processes. As a consequence it is very difficult to explore real kinetic mechanism of the Crystallization process unless some complementary studies are made.
-
Crystallization Kinetics of amorphous RuO21
Thermochimica Acta, 1996Co-Authors: Jiří Málek, Akio Watanabe, T. MitsuhashiAbstract:The Crystallization Kinetics of nanocrystalline t-RuO 2 in amorphous ruthenium oxide was studied by differential scanning calorimetry (DSC). It is shown that this process cannot be described by the Johnson Mehl-Avrami model and that the two-parameter empirical Sestak-Berggren equation gives a more quantitative description. The reliability of kinetic parameters calculated from nonisothermal DSC data is tested by comparing calculated and experimental isothermal data. It is shown that a very good prediction of isothermal behavior can be obtained.
Roberto Pantani - One of the best experts on this subject based on the ideXlab platform.
-
Effect of molding conditions on Crystallization Kinetics and mechanical properties of poly(lactic acid)
Polymer Engineering and Science, 2016Co-Authors: Felice De Santis, Valentina Volpe, Roberto PantaniAbstract:Although Poly(lactic acid) (PLA) possesses many desirable properties, above all biodegradability, its heat deflection temperature is too low for many desirable applications. Similarly, to any other polymers, also for PLA the physical and mechanical properties in the solid state depend on the morphology and crystallinity degree, which in their turn are determined by the thermomechanical history experienced during solidification. A large crystallinity degree is highly desirable to increase the heat resistance of PLA but is rather difficult to reach during injection molding due to the very slow Crystallization Kinetics of this material. In this work, the Crystallization Kinetics of an injection molded PLA grade was assessed in function of the thermal history by using calorimetric analysis. The cold Crystallization Kinetics (starting from the amorphous glassy sample) turned out to be faster than melt Crystallization Kinetics. Following the indications gained from Crystallization Kinetics, some samples were injection molded imposing different thermal histories. The effect of molding conditions on crystallinity was determined. This finding was adopted to develop a post-molding stage which allows obtaining crystalline samples in times much shorter (of a factor about two) with respect to samples injection molded in a hot mold kept at temperatures close to the maximum Crystallization rate. POLYM. ENG. SCI., 57:306–311, 2017. © 2016 Society of Plastics Engineers
-
nucleation and Crystallization Kinetics of poly lactic acid
Thermochimica Acta, 2011Co-Authors: Felice De Santis, Roberto Pantani, G TitomanlioAbstract:A commercial grade PLA was characterized using differential scanning calorimetry under both isothermal and non-isothermal conditions, and the experimental data were analyzed evaluating the Crystallization Kinetics constants for melt and cold isothermal Crystallization at some temperatures. Furthermore, a peculiar experimental protocol was adopted, varying each time the minimum cooling temperature before the isothermal step, performed monitoring nucleation and growth rate in an adequate range of temperatures. Morphological characterizations were modeled using the classical Lauritzen–Hoffman theory, which assumes that the free energy barrier associated with nucleation has an energetic origin, estimating the dependence on temperature using physical parameters derived from the linear Hoffman–Weeks plot. Crystallization Kinetics was evaluated using the Avrami model, through nucleation and growth rate, describing both the melt and cold Crystallization experimental results. Detailed comprehensive description of the Crystallization Kinetics of PLA is provided, predicting the final crystallinity and the morphology with tailored thermal history.
-
Crystallization Kinetics of virgin and processed poly lactic acid
Polymer Degradation and Stability, 2010Co-Authors: Roberto Pantani, Felice De Santis, Andrea Sorrentino, F De Maio, G TitomanlioAbstract:Abstract Poly(lactic acid) (PLA) is an emerging material mainly because it can be synthesized from renewable resources and is thus environmentally and ecologically safe. The mechanical properties, above all the thermal resistance of PLA are determined by the crystalline content: the heat deflection temperature of crystalline PLA can reach 100 °C, whereas amorphous PLA loses mechanical properties at temperatures slightly higher than 60 °C. However, PLA has a low Crystallization rate, so that after processing it remains mostly amorphous. This characteristic heavily limits the use of PLA for commercial applications. Many studies have been recently published on the Crystallization Kinetics of PLA. The effect of processing on this feature is however often neglected. In this work, the significance of processing on the Crystallization Kinetics of a commercial PLA was investigated. Two processing methods were explored: extrusion and injection moulding. The obtained materials, and the starting pellets of virgin polymer, were analyzed by calorimetry in order to obtain the Crystallization Kinetics. Two protocols were adopted to determine the Crystallization rates during cooling from the melt or heating from the solid. The parameters of a kinetic equation were determined for all the materials and protocols adopted and it was thus possible to describe the evolution of crystallinity during heating and during cooling.
Felice De Santis - One of the best experts on this subject based on the ideXlab platform.
-
Effect of molding conditions on Crystallization Kinetics and mechanical properties of poly(lactic acid)
Polymer Engineering and Science, 2016Co-Authors: Felice De Santis, Valentina Volpe, Roberto PantaniAbstract:Although Poly(lactic acid) (PLA) possesses many desirable properties, above all biodegradability, its heat deflection temperature is too low for many desirable applications. Similarly, to any other polymers, also for PLA the physical and mechanical properties in the solid state depend on the morphology and crystallinity degree, which in their turn are determined by the thermomechanical history experienced during solidification. A large crystallinity degree is highly desirable to increase the heat resistance of PLA but is rather difficult to reach during injection molding due to the very slow Crystallization Kinetics of this material. In this work, the Crystallization Kinetics of an injection molded PLA grade was assessed in function of the thermal history by using calorimetric analysis. The cold Crystallization Kinetics (starting from the amorphous glassy sample) turned out to be faster than melt Crystallization Kinetics. Following the indications gained from Crystallization Kinetics, some samples were injection molded imposing different thermal histories. The effect of molding conditions on crystallinity was determined. This finding was adopted to develop a post-molding stage which allows obtaining crystalline samples in times much shorter (of a factor about two) with respect to samples injection molded in a hot mold kept at temperatures close to the maximum Crystallization rate. POLYM. ENG. SCI., 57:306–311, 2017. © 2016 Society of Plastics Engineers
-
nucleation and Crystallization Kinetics of poly lactic acid
Thermochimica Acta, 2011Co-Authors: Felice De Santis, Roberto Pantani, G TitomanlioAbstract:A commercial grade PLA was characterized using differential scanning calorimetry under both isothermal and non-isothermal conditions, and the experimental data were analyzed evaluating the Crystallization Kinetics constants for melt and cold isothermal Crystallization at some temperatures. Furthermore, a peculiar experimental protocol was adopted, varying each time the minimum cooling temperature before the isothermal step, performed monitoring nucleation and growth rate in an adequate range of temperatures. Morphological characterizations were modeled using the classical Lauritzen–Hoffman theory, which assumes that the free energy barrier associated with nucleation has an energetic origin, estimating the dependence on temperature using physical parameters derived from the linear Hoffman–Weeks plot. Crystallization Kinetics was evaluated using the Avrami model, through nucleation and growth rate, describing both the melt and cold Crystallization experimental results. Detailed comprehensive description of the Crystallization Kinetics of PLA is provided, predicting the final crystallinity and the morphology with tailored thermal history.
-
Crystallization Kinetics of virgin and processed poly lactic acid
Polymer Degradation and Stability, 2010Co-Authors: Roberto Pantani, Felice De Santis, Andrea Sorrentino, F De Maio, G TitomanlioAbstract:Abstract Poly(lactic acid) (PLA) is an emerging material mainly because it can be synthesized from renewable resources and is thus environmentally and ecologically safe. The mechanical properties, above all the thermal resistance of PLA are determined by the crystalline content: the heat deflection temperature of crystalline PLA can reach 100 °C, whereas amorphous PLA loses mechanical properties at temperatures slightly higher than 60 °C. However, PLA has a low Crystallization rate, so that after processing it remains mostly amorphous. This characteristic heavily limits the use of PLA for commercial applications. Many studies have been recently published on the Crystallization Kinetics of PLA. The effect of processing on this feature is however often neglected. In this work, the significance of processing on the Crystallization Kinetics of a commercial PLA was investigated. Two processing methods were explored: extrusion and injection moulding. The obtained materials, and the starting pellets of virgin polymer, were analyzed by calorimetry in order to obtain the Crystallization Kinetics. Two protocols were adopted to determine the Crystallization rates during cooling from the melt or heating from the solid. The parameters of a kinetic equation were determined for all the materials and protocols adopted and it was thus possible to describe the evolution of crystallinity during heating and during cooling.
-
Improved experimental characterization of Crystallization Kinetics
European Polymer Journal, 2005Co-Authors: Felice De Santis, Gaetano Lamberti, Gerrit W. M. Peters, Valerio BrucatoAbstract:Polymer solidification occurring in many processes, like for instance injection molding, compression molding and extrusion, is a complex phenomenon, strongly influenced by the thermo-mechanical history experienced by the material during processing. From this point of view, characterization of polymer Crystallization in the range of processing conditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal Crystallization Kinetics of two polypropylene resins were investigated using a new method, based on fast cooling of thin samples with air/water sprays and optical detection of the Crystallization phenomenon. The range of cooling rates attained in this experimental study is considerably larger than that achieved by traditional methods. Quiescent Crystallization Kinetics of the resins is also investigated by the means of DSC, operated under isothermal conditions with a limited degree of under-cooling and for constant cooling rates up to about 1 K s � 1 . The results demonstrate the impor
Roman Svoboda - One of the best experts on this subject based on the ideXlab platform.
-
Non-isothermal Crystallization Kinetics of GeTe_4 infrared glass
Journal of Thermal Analysis and Calorimetry, 2016Co-Authors: Roman Svoboda, Daniela Brandová, Jiří MálekAbstract:Non-isothermal Crystallization Kinetics of the GeTe_4 chalcogenide glass was studied in dependence on particle size. Complexity of the obtained DSC data was treated by means of the Fraser–Suzuki deconvolution, and the particular Crystallization sub-processes were identified and described in terms of the JMA(2) and AC kinetic models. Bulk as-prepared GeTe_4 samples, on the other hand, exhibited simple zero-order (F0) Crystallization Kinetics. The marked difference between the powder and bulk Crystallization mechanisms was explained based on the mechanically induced defects and heterogeneities, which surrogate/accelerate the primary nucleation process. This concept also accounts for the remarkable stability of the studied telluride glass. Precipitation of Te followed by second-stage GeTe crystal growth was confirmed by XRD for all of the applied experimental conditions. The dominant influence of the nucleation process on the consequent Crystallization Kinetics is thereby implicated. Infrared microscopy was used to confirm the existence of the particular Crystallization mechanism.
-
Crystallization Kinetics of a-Se, part 4: thin films
Philosophical Magazine, 2014Co-Authors: Roman Svoboda, Jan Gutwirth, Jiří MálekAbstract:Differential scanning calorimetry was used to study the Crystallization behaviour of selenium thin films in dependence on film thickness and deposition rate. In the current work, which is the fourth in a sequence of articles dealing with Crystallization Kinetics of a-Se, the non-isothermal Crystallization Kinetics was described in terms of the Johnson-Mehl-Avrami nucleation-growth model. Two-dimensional crystallite growth, consistent with the idea of sterically restricted Crystallization in a thin layer, was confirmed for all data. It was found that neither the film thickness (tested within the 100–2350 nm range) nor the deposition rate appears to have any significant influence on the Crystallization Kinetics. However, the higher amount of intrinsic defects possibly produced by a higher deposition rate seems to accelerate the Crystallization, shifting it towards lower temperatures. Very good correlation between the results obtained for thin films and those for fine powders was found. Based on the obtained...
-
Crystallization Kinetics of amorphous Se
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Roman Svoboda, Jiří MálekAbstract: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.