This work aimed to evaluate the properties of butylene adipate-co-terephthalate (PBAT) degraded a... more This work aimed to evaluate the properties of butylene adipate-co-terephthalate (PBAT) degraded after 1800 days of storage (DPBAT) by preparing blends (films) with crosslinked starch (Cm) through extrusion and thermocompression. Different ratios of DPBAT:Cm (70:30, 60:40, and 50:50 m/m) were prepared. The incorporation of Cm into DPBAT significantly changed the properties of the films by making them stiffer (increasing Young’s modulus by up to 50%) and increasing the thermal resistance of DPBAT. The presence of crosslinked starch in the films made them less hydrophobic (with decreased contact angle and increased moisture content), but these parameters did not vary linearly with changes in the content of crosslinked starch in the blend (DPBAT:Cm). The microscopic images show an inhomogeneous distribution of Cm granules in the DPBAT matrix. Thus, the films prepared with PBAT show a significant decrease in their mechanical parameters and heat resistance after long-term storage. However...
Pineapple is a highly demanded fruit in international markets, thanks to its unique appearance an... more Pineapple is a highly demanded fruit in international markets, thanks to its unique appearance and flavor, high fiber content, vitamins, folic acid, and minerals. It makes the pineapple production and processing market a significant source of income for producing countries, such as Costa Rica. Nowadays, its processing produces a large amount of waste with negative consequences for the environment. However, pineapple waste is an essential source of cellulose, hemicellulose, lignin, and other high-value products like enzymes (bromelain). These by-products can be obtained by pineapple waste biorefinery, generating an additional source of export goods and foreign currency, framing pineapple processing in the concept of the circular economy. This review discusses how incorporating biorefinery in the pineapple production processes can contribute to the post-COVID 19 economy in Costa Rica. Pineapple production in Costa Rica is explored, and the contamination of generated residues is deline...
Some results on the amplitude-dependent dynamical behavior of poly(methyl methacrylate) are prese... more Some results on the amplitude-dependent dynamical behavior of poly(methyl methacrylate) are presented. Both the loss tangent (internal friction) and the storage Young's modulus are strain-amplitude-dependent, when measured between room temperature and approximately 400 K, at a frequency of the order of 50 kHz. The data are interpreted in terms of an hyperbolic sine stress dependence of the strain rate, including an effective stress. The activation volume was found to depend on the temperature, with values much larger than those obtained through the usual mechanical tests (tensile, creep, or stress relaxation).
Facile conversion of pine cones into a high-capacity adsorbent for the removal of methylene blue ... more Facile conversion of pine cones into a high-capacity adsorbent for the removal of methylene blue and tetracycline from water.
We report the investigation of high energy ion beam irradiation on titanium (Ti) substrates at ro... more We report the investigation of high energy ion beam irradiation on titanium (Ti) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beam using two different anode materials, graphite and copper, are characterized using standard surface science diagnostic tools, such as x-ray diffraction, scanning electron microscopy,
ABSTRACT Biocomposites with two different fillers, garlic and wheat bran, were studied. They were... more ABSTRACT Biocomposites with two different fillers, garlic and wheat bran, were studied. They were based on cassava starch and contained glycerol as a plasticizer and potassium sorbate as an antimicrobial agent and were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and infrared spectroscopy (IR). The mechanical performance at room and lower temperatures was also studied.SEM micrographies of fractured surfaces of the wheat bran composite films showed some ruptured particles of fiber while fibrils of garlic on the order of nanometers were observed when garlic composite films were studied.Mechanical tests, at room temperature, showed that the addition of wheat bran led to an increment in the storage modulus (E′) and hardening and a decrease in Tan δ, while the garlic composite showed a diminishing in the E′ and hardening and did not produce significant changes in Tan δ values when compared with systems without fillers (matrix). In the range between −90°C and 20°C, all the materials studied presented two peaks in the Tan δ curve. In the case of the wheat bran composite, both relaxation peaks shifted slightly to higher temperatures, broadened and diminished their intensity when compared with those of the matrix; however garlic composite showed a similar behavior to the matrix.DSC thermograms of aqueous systems showed a slight shift of gelatinization temperature (Tgelatinization) to higher values when the fillers were present. Thermograms of films showed that both, garlic and wheat bran composites, had a lower melting point than the matrix.IR data indicated that interaction between starch and fillers determined an increase in the availability of hydroxyl groups to be involved in a dynamic exchange with water.
A new biodegradable photoresponsive material was developed using poly(lactic acid) (PLA) as the m... more A new biodegradable photoresponsive material was developed using poly(lactic acid) (PLA) as the matrix material and Disperse Orange 3 (DO3) as photoisomerizable azo-dye. It was observed that the addition of multi-walled carbon nanotubes (MWCNTs) leads to a new phenomenon consisting of an enhancement of the optical anisotropy in a wide range of temperatures. In particular, the optical anisotropy increases 100% at room temperature. Moreover, the material containing MWCNTs shows a faster optical response that is evidenced as an increase in the growth rate of optical anisotropy. Spectroscopic data is provided to study the interaction among DO3, MWCNTs and PLA. The enhancement of optical anisotropy obtained with the addition of MWCNTs was related to the glass transition temperature (T g ) of each material. Maximum optical anisotropy was obtained 15 • C below the T g for both materials. Results are interpreted in terms of the interactions among DO3, MWCNTs and PLA and the packing density of the dye into the polymer chains.
The bi-layer system has been well developed for many engineering structural components in the air... more The bi-layer system has been well developed for many engineering structural components in the aircraft, automotive, microelectronics and modern space industries in the last few decades. Consequently, a good determination of its dynamic mechanical properties is important for an appropriate design of its industrial application. These studies are usually performed by a three-point bending test using a dynamic mechanical analyzer (DMA). In this work, we show that the three points bending test on a bi-layer system carried out with the test tool provided in a commercial DMA, for example the dynamic mechanical thermal analyzer (DMTA) Rheometric IV, can lead to erroneous results. Measurements on polymer-hard substrate bi-layer systems around the glass transition temperature of the polymer, T g , give larger changes in elastic modulus and loss tangent than they are. This problem is not observed at temperatures lower than T g . The design of new test tool and specimen geometry for the three points bending test is shown together with its application to the measurement of the dynamic elastic properties of a polyvinyl chloride (PVC)-aluminum bi-layer system.
As already well-known, the outstanding mechanical and electrical properties of carbon nanotubes (... more As already well-known, the outstanding mechanical and electrical properties of carbon nanotubes (CNT) are partially lost when CNT aggregate. The fact that CNT tend to aggregate makes difficult to put them into a host matrix, for example. Until now, achieving stable dispersions of CNT is still a challenge. In the present work, we show that the addition of an azobenzene derivative, Disperse Orange 3 (DO3) to dispersions of multi walled carbon nanotubes (MWCNT) in the organic solvent tetrahydrofuran (THF) efficiently helps debundling MWCNT and makes dispersions stable for days. We report UV-Vis optical absorption experiments that suggest an interaction between MWCNT and DO3 molecules following the behavior qualitatively observed. Dispersions with MWCNT and DO3 in THF were observed qualitatively over time. Successful suspensions (for the higher DO3 concentrations studied) were stable for several days. Also, we prepared polymeric films doped with MWCNT non-covalent functionalized with DO3 in one of the proper DO3/MWCNT weight relation where stable supensions were obtained. In this study we show preliminary results where the optical response of these samples was also measured.
Journal of Polymer Science Part A: Polymer Chemistry, 2011
To be used as templates for nanostructured thermosets, a commercial poly(styrene-b-isoprene-b-sty... more To be used as templates for nanostructured thermosets, a commercial poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer (BCP) was epoxidized by three different epoxidation procedures. An exhaustive analysis of methodologies using metal catalyzed/hydrogen peroxide, dimethyldioxirane (DMDO), and meta-chloroperbenzoic acid (m-CPBA) was performed to obtain reactive BCPs. The DMDO approach was the best strategy to obtain highly epoxidized SIS BCP (85 mol %) without formation of side products. Careful control in BCP epoxidation by metal catalyzed/hydrogen peroxide and m-CPBA approaches led to a maximum epoxidation degree (ED) of approximately 60 mol % without the formation of side products. The ED by metal catalyzed/hydrogen peroxide strategy could be further increased to 69 mol %, but a significant amount of cross-linking, ring opening, and polymer chain scission reactions were detected by spectroscopic and chromatographic techniques. The miscibility of epoxidized BCPs with diglycidyl ether of bisphenol-A epoxy system before and after curing was analyzed to develop nanostructured epoxy thermosets. For ED higher than 69 mol %, BCPs were miscible, while those with lower ED presented macrophase separation. Highly epoxidized BCPs obtained by the DMDO methodology were successfully used to obtain ordered nanodomains inside the epoxy matrix, as determined by atomic force microscopy. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4505-4513, 2011
We have measured the specific heat at constant pressure, Cp, of three different samples of multiw... more We have measured the specific heat at constant pressure, Cp, of three different samples of multiwall carbon nanotubes (MWNT). For all samples, Cp departs from a graphitic behavior at T < 120 K. Cp measurements show a temperature threshold from a linear regime for intermediate temperature to a higher-order power law for low temperatures. Moreover, it was found that this crossover only depends on the internal structure of the individual MWNT and not on the spatial order of the MWNT within a bundle.
The multiwalled carbon nanotubes (MWCNT) filled styrene-butadiene rubber (SBR) composites were pr... more The multiwalled carbon nanotubes (MWCNT) filled styrene-butadiene rubber (SBR) composites were prepared by incorporating MWCNT in a SBR/toluene solution and subsequently evaporating the solvent. These composites have shown a significant improvement in Young's modulus and tensile strength with respect to SBR gum without sacrificing high elongation at break. However, this improvement is less than expected at the higher filler content. Then, the influence of low concentrations of MWCNT on the vulcanization process of the SBR composites was studied by means of rheometer torque curves, swelling measurements, differential scanning calorimeter (DSC) analysis, and Fourier transform infrared (FTIR) spectroscopy. Also, their thermal degradation was studied by thermogravimetric analysis (TGA). It has been noticed that MWCNT affects the cure kinetics of SBR gum matrix reducing all parameters, i.e., the total heat rate and order of the reaction, scorch delay, maximum torque, and crosslink density. This effect increases as MWCNT content does, and it was attributed to the adsorption of the accelerator employed in the vulcanization (N-tert-butyl-benzothiazole-2-sulfenamide) onto the MWCNT surface.
We investigate the electronic properties of multiwalled carbon nanotubes both before and after ac... more We investigate the electronic properties of multiwalled carbon nanotubes both before and after acid treatment with concentrated sulphuric and nitric acids. Magnetic susceptibility measurements were performed using a SQUID magnetometer and show that there is a considerable enhancement in the density of states at the Fermi level. The data shows that the diamagnetic influence from the graphitic nanotubes dominates. We
The thermal diffusivity of several natural and synthetic rubber compounds was measured in the tem... more The thermal diffusivity of several natural and synthetic rubber compounds was measured in the temperature range from 125 to 350 K with an automatic device. In every case, a step change has been found in the thermal diffusivity at the glass transition range. In partially crystalline elastomers, the thermal diffusivity shows a minimum, which agrees very well with the melting temperature of crystallites. Also, new estimations of thermal diffusivity of some elastomeric compounds are given at above and below the glass transition temperature.
The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes ... more The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H 2 þ or N 2 þ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.
The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes ... more The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H 2 þ or N 2 þ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.
... preconcentration, speciation and determination of vanadium by ETAAS Rau´l A. Gil,ab Silvia N.... more ... preconcentration, speciation and determination of vanadium by ETAAS Rau´l A. Gil,ab Silvia N. Goyanes,bc Griselda Polla,d Patricia Smichowski,be Roberto A. Olsinaab and Luis D. Martinez*ab ... Acta, 2006, 152, 215. 12 P. Liang, Y. Liu, L. Guo, J. Zeng and H. Lu, J. Anal. At. ...
The dynamical mechanical properties of epoxy composites filled with different amounts of quartz p... more The dynamical mechanical properties of epoxy composites filled with different amounts of quartz powder were investigated. The loss tangent and the storage Young's modulus were measured at frequencies between 5 and 323 Hz with a tension-compression device, from room temperature up to 460 K. The glass transition temperature and the apparent activation energy increase with filler content. The dynamic modulus also increases with quartz powder percentages. Test frequency and temperature dependence of these results were analyzed within the scope of models presented in the literature for composite materials.
This work aimed to evaluate the properties of butylene adipate-co-terephthalate (PBAT) degraded a... more This work aimed to evaluate the properties of butylene adipate-co-terephthalate (PBAT) degraded after 1800 days of storage (DPBAT) by preparing blends (films) with crosslinked starch (Cm) through extrusion and thermocompression. Different ratios of DPBAT:Cm (70:30, 60:40, and 50:50 m/m) were prepared. The incorporation of Cm into DPBAT significantly changed the properties of the films by making them stiffer (increasing Young’s modulus by up to 50%) and increasing the thermal resistance of DPBAT. The presence of crosslinked starch in the films made them less hydrophobic (with decreased contact angle and increased moisture content), but these parameters did not vary linearly with changes in the content of crosslinked starch in the blend (DPBAT:Cm). The microscopic images show an inhomogeneous distribution of Cm granules in the DPBAT matrix. Thus, the films prepared with PBAT show a significant decrease in their mechanical parameters and heat resistance after long-term storage. However...
Pineapple is a highly demanded fruit in international markets, thanks to its unique appearance an... more Pineapple is a highly demanded fruit in international markets, thanks to its unique appearance and flavor, high fiber content, vitamins, folic acid, and minerals. It makes the pineapple production and processing market a significant source of income for producing countries, such as Costa Rica. Nowadays, its processing produces a large amount of waste with negative consequences for the environment. However, pineapple waste is an essential source of cellulose, hemicellulose, lignin, and other high-value products like enzymes (bromelain). These by-products can be obtained by pineapple waste biorefinery, generating an additional source of export goods and foreign currency, framing pineapple processing in the concept of the circular economy. This review discusses how incorporating biorefinery in the pineapple production processes can contribute to the post-COVID 19 economy in Costa Rica. Pineapple production in Costa Rica is explored, and the contamination of generated residues is deline...
Some results on the amplitude-dependent dynamical behavior of poly(methyl methacrylate) are prese... more Some results on the amplitude-dependent dynamical behavior of poly(methyl methacrylate) are presented. Both the loss tangent (internal friction) and the storage Young's modulus are strain-amplitude-dependent, when measured between room temperature and approximately 400 K, at a frequency of the order of 50 kHz. The data are interpreted in terms of an hyperbolic sine stress dependence of the strain rate, including an effective stress. The activation volume was found to depend on the temperature, with values much larger than those obtained through the usual mechanical tests (tensile, creep, or stress relaxation).
Facile conversion of pine cones into a high-capacity adsorbent for the removal of methylene blue ... more Facile conversion of pine cones into a high-capacity adsorbent for the removal of methylene blue and tetracycline from water.
We report the investigation of high energy ion beam irradiation on titanium (Ti) substrates at ro... more We report the investigation of high energy ion beam irradiation on titanium (Ti) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beam using two different anode materials, graphite and copper, are characterized using standard surface science diagnostic tools, such as x-ray diffraction, scanning electron microscopy,
ABSTRACT Biocomposites with two different fillers, garlic and wheat bran, were studied. They were... more ABSTRACT Biocomposites with two different fillers, garlic and wheat bran, were studied. They were based on cassava starch and contained glycerol as a plasticizer and potassium sorbate as an antimicrobial agent and were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and infrared spectroscopy (IR). The mechanical performance at room and lower temperatures was also studied.SEM micrographies of fractured surfaces of the wheat bran composite films showed some ruptured particles of fiber while fibrils of garlic on the order of nanometers were observed when garlic composite films were studied.Mechanical tests, at room temperature, showed that the addition of wheat bran led to an increment in the storage modulus (E′) and hardening and a decrease in Tan δ, while the garlic composite showed a diminishing in the E′ and hardening and did not produce significant changes in Tan δ values when compared with systems without fillers (matrix). In the range between −90°C and 20°C, all the materials studied presented two peaks in the Tan δ curve. In the case of the wheat bran composite, both relaxation peaks shifted slightly to higher temperatures, broadened and diminished their intensity when compared with those of the matrix; however garlic composite showed a similar behavior to the matrix.DSC thermograms of aqueous systems showed a slight shift of gelatinization temperature (Tgelatinization) to higher values when the fillers were present. Thermograms of films showed that both, garlic and wheat bran composites, had a lower melting point than the matrix.IR data indicated that interaction between starch and fillers determined an increase in the availability of hydroxyl groups to be involved in a dynamic exchange with water.
A new biodegradable photoresponsive material was developed using poly(lactic acid) (PLA) as the m... more A new biodegradable photoresponsive material was developed using poly(lactic acid) (PLA) as the matrix material and Disperse Orange 3 (DO3) as photoisomerizable azo-dye. It was observed that the addition of multi-walled carbon nanotubes (MWCNTs) leads to a new phenomenon consisting of an enhancement of the optical anisotropy in a wide range of temperatures. In particular, the optical anisotropy increases 100% at room temperature. Moreover, the material containing MWCNTs shows a faster optical response that is evidenced as an increase in the growth rate of optical anisotropy. Spectroscopic data is provided to study the interaction among DO3, MWCNTs and PLA. The enhancement of optical anisotropy obtained with the addition of MWCNTs was related to the glass transition temperature (T g ) of each material. Maximum optical anisotropy was obtained 15 • C below the T g for both materials. Results are interpreted in terms of the interactions among DO3, MWCNTs and PLA and the packing density of the dye into the polymer chains.
The bi-layer system has been well developed for many engineering structural components in the air... more The bi-layer system has been well developed for many engineering structural components in the aircraft, automotive, microelectronics and modern space industries in the last few decades. Consequently, a good determination of its dynamic mechanical properties is important for an appropriate design of its industrial application. These studies are usually performed by a three-point bending test using a dynamic mechanical analyzer (DMA). In this work, we show that the three points bending test on a bi-layer system carried out with the test tool provided in a commercial DMA, for example the dynamic mechanical thermal analyzer (DMTA) Rheometric IV, can lead to erroneous results. Measurements on polymer-hard substrate bi-layer systems around the glass transition temperature of the polymer, T g , give larger changes in elastic modulus and loss tangent than they are. This problem is not observed at temperatures lower than T g . The design of new test tool and specimen geometry for the three points bending test is shown together with its application to the measurement of the dynamic elastic properties of a polyvinyl chloride (PVC)-aluminum bi-layer system.
As already well-known, the outstanding mechanical and electrical properties of carbon nanotubes (... more As already well-known, the outstanding mechanical and electrical properties of carbon nanotubes (CNT) are partially lost when CNT aggregate. The fact that CNT tend to aggregate makes difficult to put them into a host matrix, for example. Until now, achieving stable dispersions of CNT is still a challenge. In the present work, we show that the addition of an azobenzene derivative, Disperse Orange 3 (DO3) to dispersions of multi walled carbon nanotubes (MWCNT) in the organic solvent tetrahydrofuran (THF) efficiently helps debundling MWCNT and makes dispersions stable for days. We report UV-Vis optical absorption experiments that suggest an interaction between MWCNT and DO3 molecules following the behavior qualitatively observed. Dispersions with MWCNT and DO3 in THF were observed qualitatively over time. Successful suspensions (for the higher DO3 concentrations studied) were stable for several days. Also, we prepared polymeric films doped with MWCNT non-covalent functionalized with DO3 in one of the proper DO3/MWCNT weight relation where stable supensions were obtained. In this study we show preliminary results where the optical response of these samples was also measured.
Journal of Polymer Science Part A: Polymer Chemistry, 2011
To be used as templates for nanostructured thermosets, a commercial poly(styrene-b-isoprene-b-sty... more To be used as templates for nanostructured thermosets, a commercial poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer (BCP) was epoxidized by three different epoxidation procedures. An exhaustive analysis of methodologies using metal catalyzed/hydrogen peroxide, dimethyldioxirane (DMDO), and meta-chloroperbenzoic acid (m-CPBA) was performed to obtain reactive BCPs. The DMDO approach was the best strategy to obtain highly epoxidized SIS BCP (85 mol %) without formation of side products. Careful control in BCP epoxidation by metal catalyzed/hydrogen peroxide and m-CPBA approaches led to a maximum epoxidation degree (ED) of approximately 60 mol % without the formation of side products. The ED by metal catalyzed/hydrogen peroxide strategy could be further increased to 69 mol %, but a significant amount of cross-linking, ring opening, and polymer chain scission reactions were detected by spectroscopic and chromatographic techniques. The miscibility of epoxidized BCPs with diglycidyl ether of bisphenol-A epoxy system before and after curing was analyzed to develop nanostructured epoxy thermosets. For ED higher than 69 mol %, BCPs were miscible, while those with lower ED presented macrophase separation. Highly epoxidized BCPs obtained by the DMDO methodology were successfully used to obtain ordered nanodomains inside the epoxy matrix, as determined by atomic force microscopy. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4505-4513, 2011
We have measured the specific heat at constant pressure, Cp, of three different samples of multiw... more We have measured the specific heat at constant pressure, Cp, of three different samples of multiwall carbon nanotubes (MWNT). For all samples, Cp departs from a graphitic behavior at T < 120 K. Cp measurements show a temperature threshold from a linear regime for intermediate temperature to a higher-order power law for low temperatures. Moreover, it was found that this crossover only depends on the internal structure of the individual MWNT and not on the spatial order of the MWNT within a bundle.
The multiwalled carbon nanotubes (MWCNT) filled styrene-butadiene rubber (SBR) composites were pr... more The multiwalled carbon nanotubes (MWCNT) filled styrene-butadiene rubber (SBR) composites were prepared by incorporating MWCNT in a SBR/toluene solution and subsequently evaporating the solvent. These composites have shown a significant improvement in Young's modulus and tensile strength with respect to SBR gum without sacrificing high elongation at break. However, this improvement is less than expected at the higher filler content. Then, the influence of low concentrations of MWCNT on the vulcanization process of the SBR composites was studied by means of rheometer torque curves, swelling measurements, differential scanning calorimeter (DSC) analysis, and Fourier transform infrared (FTIR) spectroscopy. Also, their thermal degradation was studied by thermogravimetric analysis (TGA). It has been noticed that MWCNT affects the cure kinetics of SBR gum matrix reducing all parameters, i.e., the total heat rate and order of the reaction, scorch delay, maximum torque, and crosslink density. This effect increases as MWCNT content does, and it was attributed to the adsorption of the accelerator employed in the vulcanization (N-tert-butyl-benzothiazole-2-sulfenamide) onto the MWCNT surface.
We investigate the electronic properties of multiwalled carbon nanotubes both before and after ac... more We investigate the electronic properties of multiwalled carbon nanotubes both before and after acid treatment with concentrated sulphuric and nitric acids. Magnetic susceptibility measurements were performed using a SQUID magnetometer and show that there is a considerable enhancement in the density of states at the Fermi level. The data shows that the diamagnetic influence from the graphitic nanotubes dominates. We
The thermal diffusivity of several natural and synthetic rubber compounds was measured in the tem... more The thermal diffusivity of several natural and synthetic rubber compounds was measured in the temperature range from 125 to 350 K with an automatic device. In every case, a step change has been found in the thermal diffusivity at the glass transition range. In partially crystalline elastomers, the thermal diffusivity shows a minimum, which agrees very well with the melting temperature of crystallites. Also, new estimations of thermal diffusivity of some elastomeric compounds are given at above and below the glass transition temperature.
The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes ... more The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H 2 þ or N 2 þ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.
The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes ... more The effect of O 2 þ , H 2 þ þ O 2 þ , and N 2 þ þ O 2 þ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H 2 þ or N 2 þ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.
... preconcentration, speciation and determination of vanadium by ETAAS Rau´l A. Gil,ab Silvia N.... more ... preconcentration, speciation and determination of vanadium by ETAAS Rau´l A. Gil,ab Silvia N. Goyanes,bc Griselda Polla,d Patricia Smichowski,be Roberto A. Olsinaab and Luis D. Martinez*ab ... Acta, 2006, 152, 215. 12 P. Liang, Y. Liu, L. Guo, J. Zeng and H. Lu, J. Anal. At. ...
The dynamical mechanical properties of epoxy composites filled with different amounts of quartz p... more The dynamical mechanical properties of epoxy composites filled with different amounts of quartz powder were investigated. The loss tangent and the storage Young's modulus were measured at frequencies between 5 and 323 Hz with a tension-compression device, from room temperature up to 460 K. The glass transition temperature and the apparent activation energy increase with filler content. The dynamic modulus also increases with quartz powder percentages. Test frequency and temperature dependence of these results were analyzed within the scope of models presented in the literature for composite materials.
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Papers by Silvia Goyanes