Alba González - Academia.edu (original) (raw)

Papers by Alba González

Journal of Applied Polymer Science, 2007

Diffusion coefficients of propylene and ethylene through particles and films of isotactic polypro... more Diffusion coefficients of propylene and ethylene through particles and films of isotactic polypropylene (iPP) as well as through films of atactic, completely amorphous, polypropylene have been measured by gravimetric experiments. iPP particles with relatively similar crystallinities but with different particle size distributions (PSD), and different origins have been used. They exhibited very different diffusion coefficients when the average radius of the PSD was used as the dimensional parameter of the diffusion process. However, films prepared with these particles and having similar crystallinities provided similar diffusion coefficients. The results are consistent with the idea of a multigrain structure in the particles, where the apparent (or experimental) diffusion coefficient is a consequence of the complex system formed by internal and external areas. The diffusion coefficient of the films, taken as the real diffusion magnitude, can be used in the calculation of the true diffusional radius of these multigrain particles. Experimental results of the diffusion coefficients have been reasonably well reproduced with the aid of the Vrentas-Duda free volume model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3871–3878, 2007

Journal of Applied Polymer Science, 2010

Polyurethane (PU) fibers were obtained by electrospinning of waterborne PU dispersions. As disper... more Polyurethane (PU) fibers were obtained by electrospinning of waterborne PU dispersions. As dispersion cannot be electrospun, a water-soluble polymer (poly (ethylene oxide) (PEO)) was dissolved in the PU dispersion and fibers were obtained from electrospinning the resulting mixture. Pure PU fibers were obtained after removing PEO with water extraction. Continuous PU fibers were obtained using a PU/PEO weight ratio higher than 2.5.

Vibrational Spectroscopy, 2006

Infrared spectroscopy has been employed to determine absorptivity coefficients and the self-assoc... more Infrared spectroscopy has been employed to determine absorptivity coefficients and the self-association equilibrium constant of 3,4,5-tris(dodecyloxy)benzoic acid in cyclohexane. The obtained value is consistent with data reported in bibliography for other similar compounds. The equilibrium constant describing ethylpyridine/carbonyl hydrogen bonds has been determined for mixtures of the above-mentioned acid and two ethylpyridine isomers. The effect of steric hindrance is discussed.

Polymer, 2004

This work summarizes the miscibility and transport properties of different polymer blends obtaine... more This work summarizes the miscibility and transport properties of different polymer blends obtained by mixing a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) with copolymers of styrene and vinyl phenol (Sty-co-VPh copolymers). Given that iPHB and pure commodity poly(styrene) (PS) form immiscible blends, PS has been modified by copolymerizing it with vinyl phenol (VPh) units, in an attempt to promote blend miscibility. VPh units have appropriate functional groups that interact with iPHB ester moieties. The potential miscibility was investigated by differential scanning calorimetry (DSC) measuring the glass transition temperatures of blends of different compositions. As an additional test, the interaction parameter between the two components, using the iPHB melting point depression caused by the second component, was also measured. Copolymers containing less than 90% styrene showed miscibility with iPHB.Given the remarkable barrier properties of iPHB to gases and vapours, the study has been completed by measuring transport properties of carbon dioxide through different iPHB/Sty-co-VPh copolymer blends, using gravimetric sorptions in a Cahn electrobalance. A clear difference was observed between the behaviour of rubbery blends and those that exhibit a glassy behaviour at the selected experimental temperature (303 K).

Polymer, 2002

The purpose of this work is to study the CO2 transport properties of isotactic poly(3-hydroxybuty... more The purpose of this work is to study the CO2 transport properties of isotactic poly(3-hydroxybutyrate) (iPHB) blended with a miscible second component, a copolymer of vinylidene chloride (VDC) and acrylonitrile (AN) units. All the investigated blends are rubbery, allowing a reasonable strategy to tough PHB without impairing its original biodegradability. The miscibility required for this purpose was confirmed by differential scanning calorimetry, measuring both the glass transition and melting temperatures of the blends. The melting point depression induced by the copolymer was used to quantify the interactions between the components of the blend. Carbon dioxide transport properties of blends having less than 50% by weight of the copolymer were measured by gravimetric sorption experiments in a Cahn electro balance. The effect of the VDC-co-AN copolymer was to decrease the diffusivity and permeability of the pure iPHB due to its well-known high barrier character.

Polymer, 2003

In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotacti... more In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) and its blends with a copolymer of epichlorohydrin and ethylene oxide (ECH-co-EO) have been studied. Blends were prepared by solution/precipitation. The aim to obtain miscible blends of iPHB with a rubbery second component (such as the ECH-co-EO copolymer) is to have mixtures with glass transition temperatures below room temperature. In these conditions, the iPHB chains not involved in the crystalline regions retain its mobility. This mobility seems to be necessary for the attack of microorganisms and the corresponding biodegradability.Miscibility is the general rule of these mixtures, as shown by the existence of a single glass transition temperature for each blend and by the depression of the iPHB melting point. The interaction energy density stabilising the mixtures, calculated using the Nishi–Wang treatment, was similar to those of other polymer mixtures involving different polyesters and poly(epichlorohydrin) (PECH) and ECH-co-EO copolymers. The so-called binary interaction model has been used in order to simulate the evolution of the interaction energy density with the ECH-co-EO copolymer composition. Previously reported experimental data on blends of iPHB with PECH and poly(ethylene oxide) (PEO) have been used to quantify the required segmental interaction energy densities.In the determination of the CO2 transport properties of the mixtures, only iPHB rich blends containing up to 40% of copolymer were considered. The effect of the ECH-co-EO copolymer is to increase the sorption and the diffusion of the penetrant (and, consequently, the permeability) with respect to the values of the pure iPHB. This is primarily due to the reduction of the global crystallinity of the blends and to the low barrier character of the ECH-co-EO copolymer. Sorption data can be reasonably reproduced using an extension of the Henry's law to ternary systems.

Polymer, 2004

In this work a Fourier transform infrared (FTIR) study of blends of styrene–vinyl phenol copolyme... more In this work a Fourier transform infrared (FTIR) study of blends of styrene–vinyl phenol copolymers (containing different proportions of styrene) with atactic PHB is presented. The equilibrium constant describing phenolic OH/ester carbonyl hydrogen bonds (KA) has been experimentally determined from the quantification of the hydrogen-bonded carbonyl group fraction as a function of temperature, and the effect of functional group accessibility on KA values has been discussed. An average value of KA=41 has been employed to perform a prediction of miscibility maps employing the association model of Painter and Coleman. A fairly good agreement between theoretical predictions and experimental results has been obtained.

Polymer Degradation and Stability, 2005

The thermal degradation behaviour of bacterial poly (3-hydroxybutyrate) has been studied by Pyrol... more The thermal degradation behaviour of bacterial poly (3-hydroxybutyrate) has been studied by Pyrolysis–GC–FTIR using a semi continuous furnace in the temperature range of 200–600 °C. At temperatures lower than 400 °C, 2-butenoic acid and higher degradation products have been obtained. However, at higher temperatures propene and carbon dioxide are the major degradation products. The relative composition of the detected compounds changes as a function of pyrolysis temperature. The application of Hi-Res TGA technique permits the minimum temperature of PHB decomposition to be determined with increased precision.

Journal of Sol-gel Science and Technology, 2010

Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave... more Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave irradiation in the presence of an ammonium catalyst. The effect of the reaction time, the reaction temperature, water and ammonium concentrations on particle size and conversion (measured by light scattering and FTIR respectively) were analyzed using multivariate analysis. The results showed that water and ammonium concentrations are the main factors that control the particle size and the conversion. Both properties increase with water and ammonium concentration. Moreover, comparing with the results obtained using traditional heating, the microwave heating gave rise to higher reaction rate and narrower dispersion of the particle size.

Journal of Applied Polymer Science, 2009

In this work, polymer films of low density polyethylene and ethylene-vinyl acetate copolymers con... more In this work, polymer films of low density polyethylene and ethylene-vinyl acetate copolymers containing two types of antifog additives (nonionic surfactants) were exposed to two simulated horticultural greenhouse environments, reproducing hot and cold climate conditions. The evolution of the antifog effect was visually observed and that of the additive concentration measured using Fourier transform infrared spectroscopy (FTIR). All the films studied showed good antifog properties, but in all cases, the duration of the antifog effect was longer in the hot-climate test. From the FTIR, we can conclude that the additives studied showed a low migration rate and, therefore, when the antifog effect is lost, important quantities of the additive remain in the bulk. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Industrial & Engineering Chemistry Research, 2006

In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in ... more In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in series. First, isotactic polypropylene (i-PP) particles are produced in liquid propylene. These particles are transferred to a gas phase fluidized bed reactor where the elastomeric phase is produced within the isotactic polypropylene. The particulate product obtained in the commercial process is heterogeneous. This heterogeneity may be deleterious for the product performance. In this work, the origins of product heterogeneity were studied combining a detailed characterization of the product sampled from the exit lines of the homopolymerization stage (i-PP particles) and the fluidized bed reactor (hiPP particles) of a commercial unit with a mathematical model of the process. It was found that the experimental results were consistent with equally accessible active sites of uniform activity, the residence time distribution of the catalyst in the different reactors playing the major role in product heterogeneity.

Macromolecules, 2005

An extensive characterization (SEM, AFM, mercury porosimetry, sorption, and 13 C NMR) of the part... more An extensive characterization (SEM, AFM, mercury porosimetry, sorption, and 13 C NMR) of the particle morphology prior (isotactic PP particles) and after the gas phase reaction (hiPP particles) was performed in an attempt to gain some knowledge of the gas phase reaction of the hiPP process. It was found that the majority of the elastomer was finely dispersed in the i-PP matrix, but breaking the i-PP matrix and flowing into its pores. It was also found that the interior of the particles was readily accessible to the monomers because of the existence of a network of pores. The catalyst fragmented into small pieces with about ≈210 atoms of Ti per fragment. The copolymer is richer in ethylene than in propylene although the monomer concentration around the active center is [C 3]/[C2] ) 2.75. This behavior could not be justified on the basis of a faster diffusivity of the ethylene with respect to the propylene and hence must be due to higher activity of the catalyst for ethylene. †

Journal of Materials Science, 2009

Abstract Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materi... more Abstract Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materials that have shown significant application potential in a large number of technological contexts, most of them related with biomedical problems where water-soluble polymer systems are ...

Industrial & Engineering Chemistry Research, 2006

In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in ... more In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in series. First, isotactic polypropylene (i-PP) particles are produced in liquid propylene. These particles are transferred to a gas phase fluidized bed reactor where the elastomeric phase is produced within the isotactic polypropylene. The particulate product obtained in the commercial process is heterogeneous. This heterogeneity may be deleterious for the product performance. In this work, the origins of product heterogeneity were studied combining a detailed characterization of the product sampled from the exit lines of the homopolymerization stage (i-PP particles) and the fluidized bed reactor (hiPP particles) of a commercial unit with a mathematical model of the process. It was found that the experimental results were consistent with equally accessible active sites of uniform activity, the residence time distribution of the catalyst in the different reactors playing the major role in product heterogeneity.

Journal of Applied Polymer Science, 2007

Diffusion coefficients of propylene and ethylene through particles and films of isotactic polypro... more Diffusion coefficients of propylene and ethylene through particles and films of isotactic polypropylene (iPP) as well as through films of atactic, completely amorphous, polypropylene have been measured by gravimetric experiments. iPP particles with relatively similar crystallinities but with different particle size distributions (PSD), and different origins have been used. They exhibited very different diffusion coefficients when the average radius of the PSD was used as the dimensional parameter of the diffusion process. However, films prepared with these particles and having similar crystallinities provided similar diffusion coefficients. The results are consistent with the idea of a multigrain structure in the particles, where the apparent (or experimental) diffusion coefficient is a consequence of the complex system formed by internal and external areas. The diffusion coefficient of the films, taken as the real diffusion magnitude, can be used in the calculation of the true diffusional radius of these multigrain particles. Experimental results of the diffusion coefficients have been reasonably well reproduced with the aid of the Vrentas-Duda free volume model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3871–3878, 2007

Journal of Applied Polymer Science, 2010

Polyurethane (PU) fibers were obtained by electrospinning of waterborne PU dispersions. As disper... more Polyurethane (PU) fibers were obtained by electrospinning of waterborne PU dispersions. As dispersion cannot be electrospun, a water-soluble polymer (poly (ethylene oxide) (PEO)) was dissolved in the PU dispersion and fibers were obtained from electrospinning the resulting mixture. Pure PU fibers were obtained after removing PEO with water extraction. Continuous PU fibers were obtained using a PU/PEO weight ratio higher than 2.5.

Vibrational Spectroscopy, 2006

Infrared spectroscopy has been employed to determine absorptivity coefficients and the self-assoc... more Infrared spectroscopy has been employed to determine absorptivity coefficients and the self-association equilibrium constant of 3,4,5-tris(dodecyloxy)benzoic acid in cyclohexane. The obtained value is consistent with data reported in bibliography for other similar compounds. The equilibrium constant describing ethylpyridine/carbonyl hydrogen bonds has been determined for mixtures of the above-mentioned acid and two ethylpyridine isomers. The effect of steric hindrance is discussed.

Polymer, 2004

This work summarizes the miscibility and transport properties of different polymer blends obtaine... more This work summarizes the miscibility and transport properties of different polymer blends obtained by mixing a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) with copolymers of styrene and vinyl phenol (Sty-co-VPh copolymers). Given that iPHB and pure commodity poly(styrene) (PS) form immiscible blends, PS has been modified by copolymerizing it with vinyl phenol (VPh) units, in an attempt to promote blend miscibility. VPh units have appropriate functional groups that interact with iPHB ester moieties. The potential miscibility was investigated by differential scanning calorimetry (DSC) measuring the glass transition temperatures of blends of different compositions. As an additional test, the interaction parameter between the two components, using the iPHB melting point depression caused by the second component, was also measured. Copolymers containing less than 90% styrene showed miscibility with iPHB.Given the remarkable barrier properties of iPHB to gases and vapours, the study has been completed by measuring transport properties of carbon dioxide through different iPHB/Sty-co-VPh copolymer blends, using gravimetric sorptions in a Cahn electrobalance. A clear difference was observed between the behaviour of rubbery blends and those that exhibit a glassy behaviour at the selected experimental temperature (303 K).

Polymer, 2002

The purpose of this work is to study the CO2 transport properties of isotactic poly(3-hydroxybuty... more The purpose of this work is to study the CO2 transport properties of isotactic poly(3-hydroxybutyrate) (iPHB) blended with a miscible second component, a copolymer of vinylidene chloride (VDC) and acrylonitrile (AN) units. All the investigated blends are rubbery, allowing a reasonable strategy to tough PHB without impairing its original biodegradability. The miscibility required for this purpose was confirmed by differential scanning calorimetry, measuring both the glass transition and melting temperatures of the blends. The melting point depression induced by the copolymer was used to quantify the interactions between the components of the blend. Carbon dioxide transport properties of blends having less than 50% by weight of the copolymer were measured by gravimetric sorption experiments in a Cahn electro balance. The effect of the VDC-co-AN copolymer was to decrease the diffusivity and permeability of the pure iPHB due to its well-known high barrier character.

Polymer, 2003

In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotacti... more In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) and its blends with a copolymer of epichlorohydrin and ethylene oxide (ECH-co-EO) have been studied. Blends were prepared by solution/precipitation. The aim to obtain miscible blends of iPHB with a rubbery second component (such as the ECH-co-EO copolymer) is to have mixtures with glass transition temperatures below room temperature. In these conditions, the iPHB chains not involved in the crystalline regions retain its mobility. This mobility seems to be necessary for the attack of microorganisms and the corresponding biodegradability.Miscibility is the general rule of these mixtures, as shown by the existence of a single glass transition temperature for each blend and by the depression of the iPHB melting point. The interaction energy density stabilising the mixtures, calculated using the Nishi–Wang treatment, was similar to those of other polymer mixtures involving different polyesters and poly(epichlorohydrin) (PECH) and ECH-co-EO copolymers. The so-called binary interaction model has been used in order to simulate the evolution of the interaction energy density with the ECH-co-EO copolymer composition. Previously reported experimental data on blends of iPHB with PECH and poly(ethylene oxide) (PEO) have been used to quantify the required segmental interaction energy densities.In the determination of the CO2 transport properties of the mixtures, only iPHB rich blends containing up to 40% of copolymer were considered. The effect of the ECH-co-EO copolymer is to increase the sorption and the diffusion of the penetrant (and, consequently, the permeability) with respect to the values of the pure iPHB. This is primarily due to the reduction of the global crystallinity of the blends and to the low barrier character of the ECH-co-EO copolymer. Sorption data can be reasonably reproduced using an extension of the Henry's law to ternary systems.

Polymer, 2004

In this work a Fourier transform infrared (FTIR) study of blends of styrene–vinyl phenol copolyme... more In this work a Fourier transform infrared (FTIR) study of blends of styrene–vinyl phenol copolymers (containing different proportions of styrene) with atactic PHB is presented. The equilibrium constant describing phenolic OH/ester carbonyl hydrogen bonds (KA) has been experimentally determined from the quantification of the hydrogen-bonded carbonyl group fraction as a function of temperature, and the effect of functional group accessibility on KA values has been discussed. An average value of KA=41 has been employed to perform a prediction of miscibility maps employing the association model of Painter and Coleman. A fairly good agreement between theoretical predictions and experimental results has been obtained.

Polymer Degradation and Stability, 2005

The thermal degradation behaviour of bacterial poly (3-hydroxybutyrate) has been studied by Pyrol... more The thermal degradation behaviour of bacterial poly (3-hydroxybutyrate) has been studied by Pyrolysis–GC–FTIR using a semi continuous furnace in the temperature range of 200–600 °C. At temperatures lower than 400 °C, 2-butenoic acid and higher degradation products have been obtained. However, at higher temperatures propene and carbon dioxide are the major degradation products. The relative composition of the detected compounds changes as a function of pyrolysis temperature. The application of Hi-Res TGA technique permits the minimum temperature of PHB decomposition to be determined with increased precision.

Journal of Sol-gel Science and Technology, 2010

Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave... more Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave irradiation in the presence of an ammonium catalyst. The effect of the reaction time, the reaction temperature, water and ammonium concentrations on particle size and conversion (measured by light scattering and FTIR respectively) were analyzed using multivariate analysis. The results showed that water and ammonium concentrations are the main factors that control the particle size and the conversion. Both properties increase with water and ammonium concentration. Moreover, comparing with the results obtained using traditional heating, the microwave heating gave rise to higher reaction rate and narrower dispersion of the particle size.

Journal of Applied Polymer Science, 2009

In this work, polymer films of low density polyethylene and ethylene-vinyl acetate copolymers con... more In this work, polymer films of low density polyethylene and ethylene-vinyl acetate copolymers containing two types of antifog additives (nonionic surfactants) were exposed to two simulated horticultural greenhouse environments, reproducing hot and cold climate conditions. The evolution of the antifog effect was visually observed and that of the additive concentration measured using Fourier transform infrared spectroscopy (FTIR). All the films studied showed good antifog properties, but in all cases, the duration of the antifog effect was longer in the hot-climate test. From the FTIR, we can conclude that the additives studied showed a low migration rate and, therefore, when the antifog effect is lost, important quantities of the additive remain in the bulk. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Industrial & Engineering Chemistry Research, 2006

In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in ... more In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in series. First, isotactic polypropylene (i-PP) particles are produced in liquid propylene. These particles are transferred to a gas phase fluidized bed reactor where the elastomeric phase is produced within the isotactic polypropylene. The particulate product obtained in the commercial process is heterogeneous. This heterogeneity may be deleterious for the product performance. In this work, the origins of product heterogeneity were studied combining a detailed characterization of the product sampled from the exit lines of the homopolymerization stage (i-PP particles) and the fluidized bed reactor (hiPP particles) of a commercial unit with a mathematical model of the process. It was found that the experimental results were consistent with equally accessible active sites of uniform activity, the residence time distribution of the catalyst in the different reactors playing the major role in product heterogeneity.

Macromolecules, 2005

An extensive characterization (SEM, AFM, mercury porosimetry, sorption, and 13 C NMR) of the part... more An extensive characterization (SEM, AFM, mercury porosimetry, sorption, and 13 C NMR) of the particle morphology prior (isotactic PP particles) and after the gas phase reaction (hiPP particles) was performed in an attempt to gain some knowledge of the gas phase reaction of the hiPP process. It was found that the majority of the elastomer was finely dispersed in the i-PP matrix, but breaking the i-PP matrix and flowing into its pores. It was also found that the interior of the particles was readily accessible to the monomers because of the existence of a network of pores. The catalyst fragmented into small pieces with about ≈210 atoms of Ti per fragment. The copolymer is richer in ethylene than in propylene although the monomer concentration around the active center is [C 3]/[C2] ) 2.75. This behavior could not be justified on the basis of a faster diffusivity of the ethylene with respect to the propylene and hence must be due to higher activity of the catalyst for ethylene. †

Journal of Materials Science, 2009

Abstract Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materi... more Abstract Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materials that have shown significant application potential in a large number of technological contexts, most of them related with biomedical problems where water-soluble polymer systems are ...

Industrial & Engineering Chemistry Research, 2006

In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in ... more In the Spheripol process (Basell), high impact polypropylene (hiPP) is produced in two stages in series. First, isotactic polypropylene (i-PP) particles are produced in liquid propylene. These particles are transferred to a gas phase fluidized bed reactor where the elastomeric phase is produced within the isotactic polypropylene. The particulate product obtained in the commercial process is heterogeneous. This heterogeneity may be deleterious for the product performance. In this work, the origins of product heterogeneity were studied combining a detailed characterization of the product sampled from the exit lines of the homopolymerization stage (i-PP particles) and the fluidized bed reactor (hiPP particles) of a commercial unit with a mathematical model of the process. It was found that the experimental results were consistent with equally accessible active sites of uniform activity, the residence time distribution of the catalyst in the different reactors playing the major role in product heterogeneity.