A. Tejado | TECNALIA Research (original) (raw)
Papers by A. Tejado
Journal of Applied Polymer Science, 2007
Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degre... more Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degrees have been synthesized using three L from different origin (kraft pine L, soda/anthraquinone (AQ) flax L, and sulfonated kraft softwood L). These lignophenolic (LPF) resins have been characterized by means of free P and formaldehyde (F) analysis, viscosity, chemical structure (FTIR), and thermal behavior (DSC). Temperature at which curing reaction begins (DSC), hardening time at several curing temperatures (rheology) and volumetric changes (PVT) have also been determined for the curing process with 10 wt % hexamethylenetetraamine (HMTA). All the results have been compared to those obtained for a commercial novolac. Depending on the L type employed a homogeneous material with lower curing onset temperature and gelation time than reference PF can be obtained even at high P substitution level (45 wt %).
Industrial Crops and Products, 2008
This work proposes the use of a diisocyanate as curing agent for novolac-type lignin-phenol-forma... more This work proposes the use of a diisocyanate as curing agent for novolac-type lignin-phenol-formaldehyde (LPF) resins, instead of typical hexamethylene-tetraamine (HMTA), with the aim of overcoming the loss of reactivity of lignophenolic resins resulting from the introduction of lignin. Curing LPF resins with methylene-diisocyanate (MDI) and HMTA has been investigated through Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and rheological analysis. The analysis of experimental results shows that the proposed curing reaction with MDI gives similar results to those for HMTA-cured systems. However, MDI curing is faster than HMTA one and proceeds easier at lower temperatures.
Industrial & Engineering Chemistry Research, 2008
... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental E... more ... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental Engineering Department, University of the Basque Country, Plaza Europa 1, 20018, Donostia-San Sebastián, Gipuzkoa, Spain. Ind. Eng. Chem. Res. ...
Langmuir, 2017
Cellulose fibers were first functionalized on their surface by silanization with trichloromethyls... more Cellulose fibers were first functionalized on their surface by silanization with trichloromethylsilane in an optimized gas−solid reaction, and the occurrence of the reaction was assessed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Then, the changes in the physicochemical surface properties of the material were thoroughly assessed using inverse gas chromatography (IGC) and X-ray photoelectron spectroscopy as surface specific tools. A very surprising combination of results was obtained: (i) the dispersive component of the surface energy was found to decrease from 42 to 14 mJ m −2 (at 40°C), the latter figure representing one of the lowest values ever reported (by IGC) for cellulose-based materials, and (ii) both Lewis acidic and Lewis basic characters of the fiber surface, as measured by the injection into the IGC columns of 15 different vapor probes, significantly increased with silanization. Moreover, those remarkable changes in the surface properties of the material were obtained at a low degree of silanization (as shown by ATR-FTIR). The present results may have a great impact in what concerns the application of the described type of superhydrophobic cellulose fibers for the production of new biocomposites: an unusual enhanced compatibility both with low-surface-energy polymeric matrices, such as polyolefins, as well as with other types of matrices through Lewis acid−base interactions, can be predicted. 55 compounds are so efficient that they are able to decrease the 56 surface energy of the cellulose to a level wherein a drop of 57 water slides off at tilt angles as low as a few degrees. This new 58 performing limit, known as "superhydrophobicity", is also 59 characterized by water drops forming contact angles larger than 60 150°with the cellulosic surface. In parallel, new methods of 61 application have also been targeted including diverse techniques 62 such as spray-coating, 12 dip-coating, 7,9 chemical vapor deposi-63 tion (CVD), 8,13−16 plasma treatments, 10 atom transfer radical 64 polymerizations, 11 or even designing specific processes, such as 65 that named chromatogenic method. 4 66 Among all of those methods and reactants, CVD of 67 trichloromethylsilane (TCMS) has shown special relevance. 68 TCMS can react not only with OH groups on the surface of the 69 fiber to give ether bridges through a condensation reaction but 70 also with itself, leading to the formation of a polymethylsilses-71 quioxane coating. 7,15 Previously, the Cl atoms are substituted 72 by OH (thus the silane is converted into a silanol) by reaction
Journal of Wood Chemistry and Technology
The surface of a thermomechanical pulp (TMP), containing 26 wt% of lignin, was modified by silani... more The surface of a thermomechanical pulp (TMP), containing 26 wt% of lignin, was modified by silanization with trichloromethylsilane (TCMS) via chemical vapor deposition, and thoroughly analyzed for its physicochemical properties by inverse gas chromatography (attenuated total reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy being used as complementary tools). For a 2-min TCMS-treated TMP, a decrease of the dispersive component of the surface energy from 38 to 14 mJ m −2 (at 40°C), and, at the same time, an increase of the Lewis acidic and Lewis basic characters were found. The surface of this sample, modified in a high extent, was similar to that of a bleached kraft pulp (<0.1 wt% of lignin) subjected to the same silanization process, which is suggested as being due, in both cases, to the formation of a methyl-silica coating on the fiber's surface. The new silanized fibers obtained from cheap TMP can be used for the production of a new generation of biocomposites with a variety of matrices.
Since the last 30 years lignin has been subjected to an intensive investigation due to its unique... more Since the last 30 years lignin has been subjected to an intensive investigation due to its unique structure that makes it useful for many applications, including polymer synthesis, obtaining of value added chemicals or as an additive with interesting properties. In this work a series of 4 black liquors from different origin, including kraft liquor from pine (pinus radiata), soda liquors from flax (linum usitatissimum), this one using anthraquinone as catalyst, and grapevine (Vitis vinifera) vineshoot, and another one from wild tamarind (leucaena leucocephala) extracted by the organosolv Alcell method, have been subjected to chemical treatments in order to isolate different types of lignin. Subsequently, these lignins have been characterized using Fourier transform infrared spectroscopy (FT IR) and H-1-NMR to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD) and thermogravimetric analysis ...
Bioresource Technology, 2008
In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proli... more In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proliferus L.F.) with soda and anthraquinone (AQ) have been used to develop a model using a neural network. The paper presents the development of a model with a neural network to predict the effects that the operational variables of the pulping reactor (temperature, soda concentration, AQ concentration, time and liquid/solid ratio) have on the properties of the paper sheets of the obtained pulp (brightness, traction index, burst index and tear index). Using a factorial experimental design, the results obtained with the neural network model are compared with those obtained from a polynomial model. The neural network model shows a higher prediction precision that the polynomial model.
Chemical Engineering …, 2009
Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellu... more Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellulose, lignin and hemicelluloses obtaining following sustainable criteria. An organosolv pulping process based on ethylene glycol-water mixtures, which allowed an easy recycling of solvents as well as the recovery of generated by-products, was used to induce delignification. Computer simulations using commercial software (Aspen Plus) were made on the whole process in order to design the solvents recovery stages and optimise the operation conditions. Laboratory experiments were carried out with the aim of characterizing raw material, black liquors and released by-products. Considerable high proportion of recycled solvents (91 wt% ethylene glycol and 88 wt% water) was reached with the proposed scheme. This resulted in 70 and 80 wt% reduction of fresh solvent input for ethylene glycol and water respectively, thus reducing the environmental impact of the process. EFB organosolv pulp could be considered an acceptable alternative for producing certain paper qualities with moderate strength requirements while allowing an agricultural residue from a major economic activity (viz. oil palm production) to be exploited.
Industrial Crops and Products, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Industrial & Engineering Chemistry Research, 2008
... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental E... more ... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental Engineering Department, University of the Basque Country, Plaza Europa 1, 20018, Donostia-San Sebastián, Gipuzkoa, Spain. Ind. Eng. Chem. Res. ...
Thermochimica Acta, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Thermochimica Acta, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Journal of Applied Polymer Science, 2006
Phenolic novolac resins have been modified with chestnut tannin for reduction of phenol content i... more Phenolic novolac resins have been modified with chestnut tannin for reduction of phenol content in resins. In this work, rheological and kinetic analysis of curing reactions of these resins with hexamethylenetetramine (hexamine) has been performed. Chemical structure of obtained materials has been analyzed and compared with that of nonmodified resins. Results reveal that cure reactions of resin modified with chestnut tannin are different when compared with nonmodified novolacs not only in the cure kinetics values but also in final chemical structure.
Journal of Applied Polymer Science, 2006
ABSTRACT
Industrial Crops and Products, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Chemical Engineering Journal, 2009
Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellu... more Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellulose, lignin and hemicelluloses obtaining following sustainable criteria. An organosolv pulping process based on ethylene glycol-water mixtures, which allowed an easy recycling of solvents as well as the recovery of generated by-products, was used to induce delignification. Computer simulations using commercial software (Aspen Plus) were made on the whole process in order to design the solvents recovery stages and optimise the operation conditions. Laboratory experiments were carried out with the aim of characterizing raw material, black liquors and released by-products. Considerable high proportion of recycled solvents (91 wt% ethylene glycol and 88 wt% water) was reached with the proposed scheme. This resulted in 70 and 80 wt% reduction of fresh solvent input for ethylene glycol and water respectively, thus reducing the environmental impact of the process. EFB organosolv pulp could be considered an acceptable alternative for producing certain paper qualities with moderate strength requirements while allowing an agricultural residue from a major economic activity (viz. oil palm production) to be exploited.
Bioresource Technology, 2007
During the last decades lignin has been investigated as a promising natural alternative to petroc... more During the last decades lignin has been investigated as a promising natural alternative to petrochemicals in phenol-formaldehyde (PF) resin production, due to their structural similarity. Physico-chemical characterization of three types of lignin, namely kraft pine lignin (L1), soda-anthraquinone flax lignin (L2), and ethanol-water wild tamarind lignin (L3) has been evaluated to determine which one is the most suitable chemical structure for above purpose. Characterization has been performed using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectrometry ( 1 H NMR) to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD), differential scanning calorimetry (DSC) to measure the glass transition temperature and thermogravimetric analysis (TGA) to follow the thermal degradation. Both structural and thermal characteristics suggest that kraft pine lignin (L1) would be a better phenol (P) substitute in the synthesis of lignin-phenol-formaldehyde (LPF) resins, as it presents higher amounts of activated free ring positions, higher MW and higher thermal decomposition temperature.
Bioresource Technology, 2008
In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proli... more In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proliferus L.F.) with soda and anthraquinone (AQ) have been used to develop a model using a neural network. The paper presents the development of a model with a neural network to predict the effects that the operational variables of the pulping reactor (temperature, soda concentration, AQ concentration, time and liquid/solid ratio) have on the properties of the paper sheets of the obtained pulp (brightness, traction index, burst index and tear index). Using a factorial experimental design, the results obtained with the neural network model are compared with those obtained from a polynomial model. The neural network model shows a higher prediction precision that the polynomial model.
Journal of Applied Polymer Science, 2007
Several hexamethylenetetraamine-cured novolac-type lignophenolic resins have been subjected to me... more Several hexamethylenetetraamine-cured novolac-type lignophenolic resins have been subjected to mechanical analysis to check the influence of the addition of different types of lignins (kraft pine lignin, soda/anthraquinone flax lignin, and sulfonated kraft lignin from mixed softwoods) and the influence of different phenol substitution levels. Both flexural and compression tests have been performed to evaluate the influence of the curing temperature and pressure. The results have been compared with those from a commercial novolac system. Flexural tests show that lignin incorporation leads to systems with increased rigidity, whereas up to 82% of the maximum strength can be retained with respect to a commercial phenolic (phenol-formaldehyde) at a 45 wt % substitution degree. Compression analyses show that modified prepolymers are not significantly affected by the presence of lignin at a medium curing pressure (150 bar), but their deformability results considerably increase at high curing pressures (400 or 600 bar).
Journal of Applied Polymer Science, 2007
Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degre... more Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degrees have been synthesized using three L from different origin (kraft pine L, soda/anthraquinone (AQ) flax L, and sulfonated kraft softwood L). These lignophenolic (LPF) resins have been characterized by means of free P and formaldehyde (F) analysis, viscosity, chemical structure (FTIR), and thermal behavior (DSC). Temperature at which curing reaction begins (DSC), hardening time at several curing temperatures (rheology) and volumetric changes (PVT) have also been determined for the curing process with 10 wt % hexamethylenetetraamine (HMTA). All the results have been compared to those obtained for a commercial novolac. Depending on the L type employed a homogeneous material with lower curing onset temperature and gelation time than reference PF can be obtained even at high P substitution level (45 wt %).
Industrial Crops and Products, 2008
This work proposes the use of a diisocyanate as curing agent for novolac-type lignin-phenol-forma... more This work proposes the use of a diisocyanate as curing agent for novolac-type lignin-phenol-formaldehyde (LPF) resins, instead of typical hexamethylene-tetraamine (HMTA), with the aim of overcoming the loss of reactivity of lignophenolic resins resulting from the introduction of lignin. Curing LPF resins with methylene-diisocyanate (MDI) and HMTA has been investigated through Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and rheological analysis. The analysis of experimental results shows that the proposed curing reaction with MDI gives similar results to those for HMTA-cured systems. However, MDI curing is faster than HMTA one and proceeds easier at lower temperatures.
Industrial & Engineering Chemistry Research, 2008
... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental E... more ... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental Engineering Department, University of the Basque Country, Plaza Europa 1, 20018, Donostia-San Sebastián, Gipuzkoa, Spain. Ind. Eng. Chem. Res. ...
Langmuir, 2017
Cellulose fibers were first functionalized on their surface by silanization with trichloromethyls... more Cellulose fibers were first functionalized on their surface by silanization with trichloromethylsilane in an optimized gas−solid reaction, and the occurrence of the reaction was assessed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Then, the changes in the physicochemical surface properties of the material were thoroughly assessed using inverse gas chromatography (IGC) and X-ray photoelectron spectroscopy as surface specific tools. A very surprising combination of results was obtained: (i) the dispersive component of the surface energy was found to decrease from 42 to 14 mJ m −2 (at 40°C), the latter figure representing one of the lowest values ever reported (by IGC) for cellulose-based materials, and (ii) both Lewis acidic and Lewis basic characters of the fiber surface, as measured by the injection into the IGC columns of 15 different vapor probes, significantly increased with silanization. Moreover, those remarkable changes in the surface properties of the material were obtained at a low degree of silanization (as shown by ATR-FTIR). The present results may have a great impact in what concerns the application of the described type of superhydrophobic cellulose fibers for the production of new biocomposites: an unusual enhanced compatibility both with low-surface-energy polymeric matrices, such as polyolefins, as well as with other types of matrices through Lewis acid−base interactions, can be predicted. 55 compounds are so efficient that they are able to decrease the 56 surface energy of the cellulose to a level wherein a drop of 57 water slides off at tilt angles as low as a few degrees. This new 58 performing limit, known as "superhydrophobicity", is also 59 characterized by water drops forming contact angles larger than 60 150°with the cellulosic surface. In parallel, new methods of 61 application have also been targeted including diverse techniques 62 such as spray-coating, 12 dip-coating, 7,9 chemical vapor deposi-63 tion (CVD), 8,13−16 plasma treatments, 10 atom transfer radical 64 polymerizations, 11 or even designing specific processes, such as 65 that named chromatogenic method. 4 66 Among all of those methods and reactants, CVD of 67 trichloromethylsilane (TCMS) has shown special relevance. 68 TCMS can react not only with OH groups on the surface of the 69 fiber to give ether bridges through a condensation reaction but 70 also with itself, leading to the formation of a polymethylsilses-71 quioxane coating. 7,15 Previously, the Cl atoms are substituted 72 by OH (thus the silane is converted into a silanol) by reaction
Journal of Wood Chemistry and Technology
The surface of a thermomechanical pulp (TMP), containing 26 wt% of lignin, was modified by silani... more The surface of a thermomechanical pulp (TMP), containing 26 wt% of lignin, was modified by silanization with trichloromethylsilane (TCMS) via chemical vapor deposition, and thoroughly analyzed for its physicochemical properties by inverse gas chromatography (attenuated total reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy being used as complementary tools). For a 2-min TCMS-treated TMP, a decrease of the dispersive component of the surface energy from 38 to 14 mJ m −2 (at 40°C), and, at the same time, an increase of the Lewis acidic and Lewis basic characters were found. The surface of this sample, modified in a high extent, was similar to that of a bleached kraft pulp (<0.1 wt% of lignin) subjected to the same silanization process, which is suggested as being due, in both cases, to the formation of a methyl-silica coating on the fiber's surface. The new silanized fibers obtained from cheap TMP can be used for the production of a new generation of biocomposites with a variety of matrices.
Since the last 30 years lignin has been subjected to an intensive investigation due to its unique... more Since the last 30 years lignin has been subjected to an intensive investigation due to its unique structure that makes it useful for many applications, including polymer synthesis, obtaining of value added chemicals or as an additive with interesting properties. In this work a series of 4 black liquors from different origin, including kraft liquor from pine (pinus radiata), soda liquors from flax (linum usitatissimum), this one using anthraquinone as catalyst, and grapevine (Vitis vinifera) vineshoot, and another one from wild tamarind (leucaena leucocephala) extracted by the organosolv Alcell method, have been subjected to chemical treatments in order to isolate different types of lignin. Subsequently, these lignins have been characterized using Fourier transform infrared spectroscopy (FT IR) and H-1-NMR to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD) and thermogravimetric analysis ...
Bioresource Technology, 2008
In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proli... more In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proliferus L.F.) with soda and anthraquinone (AQ) have been used to develop a model using a neural network. The paper presents the development of a model with a neural network to predict the effects that the operational variables of the pulping reactor (temperature, soda concentration, AQ concentration, time and liquid/solid ratio) have on the properties of the paper sheets of the obtained pulp (brightness, traction index, burst index and tear index). Using a factorial experimental design, the results obtained with the neural network model are compared with those obtained from a polynomial model. The neural network model shows a higher prediction precision that the polynomial model.
Chemical Engineering …, 2009
Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellu... more Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellulose, lignin and hemicelluloses obtaining following sustainable criteria. An organosolv pulping process based on ethylene glycol-water mixtures, which allowed an easy recycling of solvents as well as the recovery of generated by-products, was used to induce delignification. Computer simulations using commercial software (Aspen Plus) were made on the whole process in order to design the solvents recovery stages and optimise the operation conditions. Laboratory experiments were carried out with the aim of characterizing raw material, black liquors and released by-products. Considerable high proportion of recycled solvents (91 wt% ethylene glycol and 88 wt% water) was reached with the proposed scheme. This resulted in 70 and 80 wt% reduction of fresh solvent input for ethylene glycol and water respectively, thus reducing the environmental impact of the process. EFB organosolv pulp could be considered an acceptable alternative for producing certain paper qualities with moderate strength requirements while allowing an agricultural residue from a major economic activity (viz. oil palm production) to be exploited.
Industrial Crops and Products, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Industrial & Engineering Chemistry Research, 2008
... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental E... more ... María González, Álvaro Tejado, Cristina Peña, and Jalel Labidi*. Chemical and Environmental Engineering Department, University of the Basque Country, Plaza Europa 1, 20018, Donostia-San Sebastián, Gipuzkoa, Spain. Ind. Eng. Chem. Res. ...
Thermochimica Acta, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Thermochimica Acta, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Journal of Applied Polymer Science, 2006
Phenolic novolac resins have been modified with chestnut tannin for reduction of phenol content i... more Phenolic novolac resins have been modified with chestnut tannin for reduction of phenol content in resins. In this work, rheological and kinetic analysis of curing reactions of these resins with hexamethylenetetramine (hexamine) has been performed. Chemical structure of obtained materials has been analyzed and compared with that of nonmodified resins. Results reveal that cure reactions of resin modified with chestnut tannin are different when compared with nonmodified novolacs not only in the cure kinetics values but also in final chemical structure.
Journal of Applied Polymer Science, 2006
ABSTRACT
Industrial Crops and Products, 2008
Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger... more Several phenomenological models (including simple models by Ozawa and Kissinger and the Kissinger-Akahira-Sunose isoconversional method) have been used to compare the cure kinetics of two lignin-based novolac-type phenolic resins with those from a commercial novolac system. When 45 wt% phenol is substituted by a sulfonated kraft lignin, an important reduction in the activation energy is obtained. This behaviour has been attributed to the incorporation of an extra amount of hydroxymethyl groups in the formulation, as they are present in important quantities in the original lignin structure. KAS isoconversional model shows that the rise in viscosity derived from lignin introduction leads to a moderate change in the limiting stage from a kinetic to a diffusion regime, while condensation reactions, which are favoured by the abundance of lignin hydroxymethyl groups, acquire high relevance in LPF-45 system cure. Finally, competition with other mechanisms initiated at high temperature is reported at high conversion grades for all cases.
Chemical Engineering Journal, 2009
Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellu... more Agricultural crop residues (palm oil empty fruit bunches-EFB) were used as raw material for cellulose, lignin and hemicelluloses obtaining following sustainable criteria. An organosolv pulping process based on ethylene glycol-water mixtures, which allowed an easy recycling of solvents as well as the recovery of generated by-products, was used to induce delignification. Computer simulations using commercial software (Aspen Plus) were made on the whole process in order to design the solvents recovery stages and optimise the operation conditions. Laboratory experiments were carried out with the aim of characterizing raw material, black liquors and released by-products. Considerable high proportion of recycled solvents (91 wt% ethylene glycol and 88 wt% water) was reached with the proposed scheme. This resulted in 70 and 80 wt% reduction of fresh solvent input for ethylene glycol and water respectively, thus reducing the environmental impact of the process. EFB organosolv pulp could be considered an acceptable alternative for producing certain paper qualities with moderate strength requirements while allowing an agricultural residue from a major economic activity (viz. oil palm production) to be exploited.
Bioresource Technology, 2007
During the last decades lignin has been investigated as a promising natural alternative to petroc... more During the last decades lignin has been investigated as a promising natural alternative to petrochemicals in phenol-formaldehyde (PF) resin production, due to their structural similarity. Physico-chemical characterization of three types of lignin, namely kraft pine lignin (L1), soda-anthraquinone flax lignin (L2), and ethanol-water wild tamarind lignin (L3) has been evaluated to determine which one is the most suitable chemical structure for above purpose. Characterization has been performed using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectrometry ( 1 H NMR) to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD), differential scanning calorimetry (DSC) to measure the glass transition temperature and thermogravimetric analysis (TGA) to follow the thermal degradation. Both structural and thermal characteristics suggest that kraft pine lignin (L1) would be a better phenol (P) substitute in the synthesis of lignin-phenol-formaldehyde (LPF) resins, as it presents higher amounts of activated free ring positions, higher MW and higher thermal decomposition temperature.
Bioresource Technology, 2008
In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proli... more In this work, published experimental result data of the pulping of tagasaste (Chamaecytisus proliferus L.F.) with soda and anthraquinone (AQ) have been used to develop a model using a neural network. The paper presents the development of a model with a neural network to predict the effects that the operational variables of the pulping reactor (temperature, soda concentration, AQ concentration, time and liquid/solid ratio) have on the properties of the paper sheets of the obtained pulp (brightness, traction index, burst index and tear index). Using a factorial experimental design, the results obtained with the neural network model are compared with those obtained from a polynomial model. The neural network model shows a higher prediction precision that the polynomial model.
Journal of Applied Polymer Science, 2007
Several hexamethylenetetraamine-cured novolac-type lignophenolic resins have been subjected to me... more Several hexamethylenetetraamine-cured novolac-type lignophenolic resins have been subjected to mechanical analysis to check the influence of the addition of different types of lignins (kraft pine lignin, soda/anthraquinone flax lignin, and sulfonated kraft lignin from mixed softwoods) and the influence of different phenol substitution levels. Both flexural and compression tests have been performed to evaluate the influence of the curing temperature and pressure. The results have been compared with those from a commercial novolac system. Flexural tests show that lignin incorporation leads to systems with increased rigidity, whereas up to 82% of the maximum strength can be retained with respect to a commercial phenolic (phenol-formaldehyde) at a 45 wt % substitution degree. Compression analyses show that modified prepolymers are not significantly affected by the presence of lignin at a medium curing pressure (150 bar), but their deformability results considerably increase at high curing pressures (400 or 600 bar).