Polyamideamine epichlorohydrin (PAE) resin is a water soluble additive and the most used permanen... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble additive and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1H and 13C NMR was performed and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied b...
Polymer aqueous nanofluids have numerous industrial applications due to their synergic properties... more Polymer aqueous nanofluids have numerous industrial applications due to their synergic properties as a polymer and nanoparticle in the same fluid. The main goal of this work was to prepare stable aqueous nanofluids with improved viscosity in high temperature and salinity conditions. Aminated carbon nanotube (OCNT-TEPA) presented a CAN photoemission peak at 285.5 eV in X-ray photoelectron spectroscopy spectra, which is evidence of a grafting reaction. Fourier transform infrared spectra presented absorption bands attributed to amide and amine bonds. Elemental analyses showed 1.9 and 3.2 mass % N content increases for OCNT-TEPA and OCNT-TEPA-AM, respectively. Samples aged at 70 8C in brine confirmed that the addition of OCNT-TEPA increased the viscosity of nanofluids to 30% at day 90 compared to acrylamide-acrylic acid copolymer fluids. Nanotubes presented only 35% of the aminated functions compared to carbon black (
Dicyandiamide-formaldehyde condensation copolymer was synthesized and used as a wet-end additive ... more Dicyandiamide-formaldehyde condensation copolymer was synthesized and used as a wet-end additive for papermaking. The retention of fibers and fines was used as a performance index. Factors were evaluated governing the performance of the polymer, including polymer dosage, pH and mixing time. The optimum dosage of the polymer was found to be 0.03% under the conditions. Overall, the polymer was effective in improving the drainage, as well as the retention of fibers and fines in papermaking process.
Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet str... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1 H and 13 C NMR was carried out and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied by using CMC as a model compound for cellulosic fibres and PAE-CMC interactions as a model for PAEfibres interactions. Based on results from NMR and FTIR, we clearly showed that PAE react with CMC that is when carboxylic groups are present in great amounts. Consequently, as the number of carboxylic groups present in lignocellulosic fibres is considerably less important and the resulting formed ester bonds are hydrolysable, we postulate that ester bond formation has a negligible impact on the wet strength of PAEbased papers. In the second part of this work, a 100% Eucalyptus pulp suspension was used to prepare PAE-based papers. PAE was added at different dosages (0.4, 0.6 and 1%) into the pulp suspension and its adsorption was indirectly followed by measuring the zeta potential. Results indicate that the adsorption, reconformation and/or penetration phenomena reach an apparent equilibrium at around 10 min. Moreover, we showed that the paper dry strength was not significantly affected by the conductivity level (from 100 to 3000 µS/cm) of the pulp suspension. However, the conductivity has an impact on the wet strength and this effect seems to be enhanced for the highest PAE dosage (1%). We also demonstrated that storing the treated paper under controlled conditions or boosting the PAE cross-linking with a thermal post-treatment does not necessarily lead to the same wet strength. Degrading studies of cross-linked PAE films showed that PAE degradation in a persulfate solution at alkaline medium was more effective. A preliminary study of coated and uncoated industrial PAE-based papers was also performed. For uncoated paper, persulfate treatment was the most efficient. For coated papers, all treatments were inefficient in the used conditions, although a decrease of the wet tensile force of degraded samples was observed. The main responsible of the decrease of persulfate efficiency for coated papers was probably related to side reactions of free radicals with the coating constituents.
Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet str... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1 H and 13 C NMR was carried out and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied by using CMC as a model compound for cellulosic fibres and PAE-CMC interactions as a model for PAEfibres interactions. Based on results from NMR and FTIR, we clearly showed that PAE react with CMC that is when carboxylic groups are present in great amounts. Consequently, as the number of carboxylic groups present in lignocellulosic fibres is considerably less important and the resulting formed ester bonds are hydrolysable, we postulate that ester bond formation has a negligible impact on the wet strength of PAEbased papers. In the second part of this work, a 100% Eucalyptus pulp suspension was used to prepare PAE-based papers. PAE was added at different dosages (0.4, 0.6 and 1%) into the pulp suspension and its adsorption was indirectly followed by measuring the zeta potential. Results indicate that the adsorption, reconformation and/or penetration phenomena reach an apparent equilibrium at around 10 min. Moreover, we showed that the paper dry strength was not significantly affected by the conductivity level (from 100 to 3000 µS/cm) of the pulp suspension. However, the conductivity has an impact on the wet strength and this effect seems to be enhanced for the highest PAE dosage (1%). We also demonstrated that storing the treated paper under controlled conditions or boosting the PAE cross-linking with a thermal post-treatment does not necessarily lead to the same wet strength. Degrading studies of cross-linked PAE films showed that PAE degradation in a persulfate solution at alkaline medium was more effective. A preliminary study of coated and uncoated industrial PAE-based papers was also performed. For uncoated paper, persulfate treatment was the most efficient. For coated papers, all treatments were inefficient in the used conditions, although a decrease of the wet tensile force of degraded samples was observed. The main responsible of the decrease of persulfate efficiency for coated papers was probably related to side reactions of free radicals with the coating constituents.
The hydrogels are advanced materials used in biomedical applications during wound healing, contro... more The hydrogels are advanced materials used in biomedical applications during wound healing, controlled drug release and to prepare scaffolds. In this work are prepared hydrogels of alginate/chitosan (Alg/Ch) semi-interpenetrating polymer networks (semi-IPN’s) and nanocelluloses. The hydrogels after preparation by freeze drying are namely simply as gels. The cellulose nanocrystals (CNC’s) are obtained from acid hydrolysis of bleached Eucalyptus pulps and oxidized cellulose nanocrystals (CNCT’s) prepared by (2,2,6,6-tetramethylpiperidin-1-yl)oxyl radical catalyzed reaction as known as TEMPO reaction. The cellulose nanofibers (NFC’s) are obtained from mechanical shearing of cellulose pulps and oxidized NFC’s by TEMPO-mediated reaction (NFCT’s). The nanocellulose suspension and gels are characterized by FTIR at ATR mode, TGA, XRD, TEM, SEM, X-ray computed microtomography (micro-CT) and DMTA. The addition of CNC’s, NFC’s, CNCT’s or NFCT’s in the microstructure of gels increases their dime...
A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT)... more A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT) was performed. The influence of ultrasonic cavitation and solid/liquid interface was indirectly evaluated by statistical characterization of MWCNT aspect ratio and degree of functionalization. MWCNT aspect ratio was determined through hundreds of electron microscopy images. Degree of functionalization of MWCNT was characterized by elemental analysis and thermogravimetry. Distribution of different oxygen-containing functional groups was assessed by potentiometric titration. MWCNT aqueous dispersions were evaluated by electrophoretic mobility and dynamic light scattering. An acid volume over 90% lower than usually reported in literature guaranteed MWCNTs with significantly larger aspect ratio, higher proportion of carboxylic groups and a more negative zeta potential in aqueous suspension. These results can be related to a more localized ultrasonic cavitation in MWCNTs/acid interface for reduced liquid volumes. This distinguished influence of ultrasonic cavitation may be a valuable contribution to more eco-friendly processes with nanomaterials.
Hydrogels have been studied as promising materials in different biomedical applications such as c... more Hydrogels have been studied as promising materials in different biomedical applications such as cell culture in tissue engineering or in wound healing. In this work, we synthesized different nanocellulose-alginate hydrogels containing cellulose nanocrystals, TEMPO-oxidized cellulose nanocrystals (CNCTs), cellulose nanofibers or TEMPO-oxidized cellulose nanofibers (CNFTs). The hydrogels were freeze-dried and named as gels. The nanocelluloses and the gels were characterized by different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA), while the biological features were characterized by cytotoxicity and cell growth assays. The addition of CNCTs or CNFTs in alginate gels contributed to the formation of porous structure (diameter of pores in the range between 40 and 150 μm). TEMPO-oxidized cellulose nanofibers have...
Please cite this article in press as: Siqueira, E.J., et al., The effects of sodium chloride (NaC... more Please cite this article in press as: Siqueira, E.J., et al., The effects of sodium chloride (NaCl) and residues of cellulosic fibres derived from sodium carboxymethylcellulose (NaCMC) synthesis on thermal and mechanical properties of CMC films. Ind. Crops Prod.
Currently, there is a demand for new engineering materials presenting a combination of strength, ... more Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix. V
ABSTRACT In this work we used a sequence of organic extraction and chemical modification treatmen... more ABSTRACT In this work we used a sequence of organic extraction and chemical modification treatments in order to increase the compatibility between the mat fibrous of the Luffa cylindrica ripe fruit and the vinyl ester resin for composites preparation. As observed from SEM and suggested from XRD analyses, these sequential treatments did not degrade the L. cylindrica fibres preserving their potential use as a reinforcement. The FTIR analyses and the conductometric titrations showed evidences of interactions between the fibres and the dianhydride. A fibre mass ratio of 15% was used for composites preparation decreasing the density of the composites at ca. 45% when compared with the vinylester matrix. The TG analyses showed that the aluminum hydroxide addition in the matrix increases the thermal stability of the composites. The DMA showed that the fibres did not influence the matrix cure kinetics, and a biphasic system was formed during pre-curing under environmental conditions. The tensile and Charpy impact strength tests showed an increase of the strength of the composites when compared with the matrix. The best results were obtained for PMDA treated fibres/vinyl ester matrix composites, which showed an increase of ca. 30% for tensile strength and 250% for impact strength.
Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ... more Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ash (RHA), a reactive filler. CMCs were obtained by pyrolysis at 1000 and 1600°C of green bodies prepared from a mixture of polysiloxane network and RHA at a weight ratio of 4:1, respectively. The RHA and the CMCs were characterized by thermogravimetric analysis (TGA), X-ray diffraction
Wet strength paper repulping is a challenge for paper recycling. This work proposes a novel appro... more Wet strength paper repulping is a challenge for paper recycling. This work proposes a novel approach to study the degradation of PAE-based papers made from bleached kraft pulps. In a first part, cross-linked PAE films, obtained by casting under controlled conditions, were treated by different chemical additives and the film degradation was evaluated as the relative weight difference between dry PAE films before and after the treatment. The selected reagents were sodium hydroxide, sulfuric acid, potassium persulfate and hydrogen peroxide, used alone or in combination. In a second part, the same chemical systems were applied on coated and uncoated PAE-based papers (industrial papers and model papers, i.e. handsheets). The effect of the repulping chemicals was evaluated using an original method by measuring the residual tensile force of wet paper strips after soaking them in aqueous solutions containing the reagents in given experimental conditions. As persulfate is sometimes suspected to induce paper yellowing, handsheets with and without PAE were submitted to the same treatments in order to compare the optical properties. The aqueous solution containing the chemicals before and after the PAE-based handsheet treatment was also analyzed by UV-vis spectrophotometry.
Currently, there is a demand for new engineering materials presenting a combination of strength, ... more Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix.
Polyamideamine epichlorohydrin (PAE) resin is a water soluble additive and the most used permanen... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble additive and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1H and 13C NMR was performed and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied b...
Polymer aqueous nanofluids have numerous industrial applications due to their synergic properties... more Polymer aqueous nanofluids have numerous industrial applications due to their synergic properties as a polymer and nanoparticle in the same fluid. The main goal of this work was to prepare stable aqueous nanofluids with improved viscosity in high temperature and salinity conditions. Aminated carbon nanotube (OCNT-TEPA) presented a CAN photoemission peak at 285.5 eV in X-ray photoelectron spectroscopy spectra, which is evidence of a grafting reaction. Fourier transform infrared spectra presented absorption bands attributed to amide and amine bonds. Elemental analyses showed 1.9 and 3.2 mass % N content increases for OCNT-TEPA and OCNT-TEPA-AM, respectively. Samples aged at 70 8C in brine confirmed that the addition of OCNT-TEPA increased the viscosity of nanofluids to 30% at day 90 compared to acrylamide-acrylic acid copolymer fluids. Nanotubes presented only 35% of the aminated functions compared to carbon black (
Dicyandiamide-formaldehyde condensation copolymer was synthesized and used as a wet-end additive ... more Dicyandiamide-formaldehyde condensation copolymer was synthesized and used as a wet-end additive for papermaking. The retention of fibers and fines was used as a performance index. Factors were evaluated governing the performance of the polymer, including polymer dosage, pH and mixing time. The optimum dosage of the polymer was found to be 0.03% under the conditions. Overall, the polymer was effective in improving the drainage, as well as the retention of fibers and fines in papermaking process.
Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet str... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1 H and 13 C NMR was carried out and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied by using CMC as a model compound for cellulosic fibres and PAE-CMC interactions as a model for PAEfibres interactions. Based on results from NMR and FTIR, we clearly showed that PAE react with CMC that is when carboxylic groups are present in great amounts. Consequently, as the number of carboxylic groups present in lignocellulosic fibres is considerably less important and the resulting formed ester bonds are hydrolysable, we postulate that ester bond formation has a negligible impact on the wet strength of PAEbased papers. In the second part of this work, a 100% Eucalyptus pulp suspension was used to prepare PAE-based papers. PAE was added at different dosages (0.4, 0.6 and 1%) into the pulp suspension and its adsorption was indirectly followed by measuring the zeta potential. Results indicate that the adsorption, reconformation and/or penetration phenomena reach an apparent equilibrium at around 10 min. Moreover, we showed that the paper dry strength was not significantly affected by the conductivity level (from 100 to 3000 µS/cm) of the pulp suspension. However, the conductivity has an impact on the wet strength and this effect seems to be enhanced for the highest PAE dosage (1%). We also demonstrated that storing the treated paper under controlled conditions or boosting the PAE cross-linking with a thermal post-treatment does not necessarily lead to the same wet strength. Degrading studies of cross-linked PAE films showed that PAE degradation in a persulfate solution at alkaline medium was more effective. A preliminary study of coated and uncoated industrial PAE-based papers was also performed. For uncoated paper, persulfate treatment was the most efficient. For coated papers, all treatments were inefficient in the used conditions, although a decrease of the wet tensile force of degraded samples was observed. The main responsible of the decrease of persulfate efficiency for coated papers was probably related to side reactions of free radicals with the coating constituents.
Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet str... more Polyamideamine epichlorohydrin (PAE) resin is a water soluble and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1 H and 13 C NMR was carried out and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied by using CMC as a model compound for cellulosic fibres and PAE-CMC interactions as a model for PAEfibres interactions. Based on results from NMR and FTIR, we clearly showed that PAE react with CMC that is when carboxylic groups are present in great amounts. Consequently, as the number of carboxylic groups present in lignocellulosic fibres is considerably less important and the resulting formed ester bonds are hydrolysable, we postulate that ester bond formation has a negligible impact on the wet strength of PAEbased papers. In the second part of this work, a 100% Eucalyptus pulp suspension was used to prepare PAE-based papers. PAE was added at different dosages (0.4, 0.6 and 1%) into the pulp suspension and its adsorption was indirectly followed by measuring the zeta potential. Results indicate that the adsorption, reconformation and/or penetration phenomena reach an apparent equilibrium at around 10 min. Moreover, we showed that the paper dry strength was not significantly affected by the conductivity level (from 100 to 3000 µS/cm) of the pulp suspension. However, the conductivity has an impact on the wet strength and this effect seems to be enhanced for the highest PAE dosage (1%). We also demonstrated that storing the treated paper under controlled conditions or boosting the PAE cross-linking with a thermal post-treatment does not necessarily lead to the same wet strength. Degrading studies of cross-linked PAE films showed that PAE degradation in a persulfate solution at alkaline medium was more effective. A preliminary study of coated and uncoated industrial PAE-based papers was also performed. For uncoated paper, persulfate treatment was the most efficient. For coated papers, all treatments were inefficient in the used conditions, although a decrease of the wet tensile force of degraded samples was observed. The main responsible of the decrease of persulfate efficiency for coated papers was probably related to side reactions of free radicals with the coating constituents.
The hydrogels are advanced materials used in biomedical applications during wound healing, contro... more The hydrogels are advanced materials used in biomedical applications during wound healing, controlled drug release and to prepare scaffolds. In this work are prepared hydrogels of alginate/chitosan (Alg/Ch) semi-interpenetrating polymer networks (semi-IPN’s) and nanocelluloses. The hydrogels after preparation by freeze drying are namely simply as gels. The cellulose nanocrystals (CNC’s) are obtained from acid hydrolysis of bleached Eucalyptus pulps and oxidized cellulose nanocrystals (CNCT’s) prepared by (2,2,6,6-tetramethylpiperidin-1-yl)oxyl radical catalyzed reaction as known as TEMPO reaction. The cellulose nanofibers (NFC’s) are obtained from mechanical shearing of cellulose pulps and oxidized NFC’s by TEMPO-mediated reaction (NFCT’s). The nanocellulose suspension and gels are characterized by FTIR at ATR mode, TGA, XRD, TEM, SEM, X-ray computed microtomography (micro-CT) and DMTA. The addition of CNC’s, NFC’s, CNCT’s or NFCT’s in the microstructure of gels increases their dime...
A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT)... more A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT) was performed. The influence of ultrasonic cavitation and solid/liquid interface was indirectly evaluated by statistical characterization of MWCNT aspect ratio and degree of functionalization. MWCNT aspect ratio was determined through hundreds of electron microscopy images. Degree of functionalization of MWCNT was characterized by elemental analysis and thermogravimetry. Distribution of different oxygen-containing functional groups was assessed by potentiometric titration. MWCNT aqueous dispersions were evaluated by electrophoretic mobility and dynamic light scattering. An acid volume over 90% lower than usually reported in literature guaranteed MWCNTs with significantly larger aspect ratio, higher proportion of carboxylic groups and a more negative zeta potential in aqueous suspension. These results can be related to a more localized ultrasonic cavitation in MWCNTs/acid interface for reduced liquid volumes. This distinguished influence of ultrasonic cavitation may be a valuable contribution to more eco-friendly processes with nanomaterials.
Hydrogels have been studied as promising materials in different biomedical applications such as c... more Hydrogels have been studied as promising materials in different biomedical applications such as cell culture in tissue engineering or in wound healing. In this work, we synthesized different nanocellulose-alginate hydrogels containing cellulose nanocrystals, TEMPO-oxidized cellulose nanocrystals (CNCTs), cellulose nanofibers or TEMPO-oxidized cellulose nanofibers (CNFTs). The hydrogels were freeze-dried and named as gels. The nanocelluloses and the gels were characterized by different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA), while the biological features were characterized by cytotoxicity and cell growth assays. The addition of CNCTs or CNFTs in alginate gels contributed to the formation of porous structure (diameter of pores in the range between 40 and 150 μm). TEMPO-oxidized cellulose nanofibers have...
Please cite this article in press as: Siqueira, E.J., et al., The effects of sodium chloride (NaC... more Please cite this article in press as: Siqueira, E.J., et al., The effects of sodium chloride (NaCl) and residues of cellulosic fibres derived from sodium carboxymethylcellulose (NaCMC) synthesis on thermal and mechanical properties of CMC films. Ind. Crops Prod.
Currently, there is a demand for new engineering materials presenting a combination of strength, ... more Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix. V
ABSTRACT In this work we used a sequence of organic extraction and chemical modification treatmen... more ABSTRACT In this work we used a sequence of organic extraction and chemical modification treatments in order to increase the compatibility between the mat fibrous of the Luffa cylindrica ripe fruit and the vinyl ester resin for composites preparation. As observed from SEM and suggested from XRD analyses, these sequential treatments did not degrade the L. cylindrica fibres preserving their potential use as a reinforcement. The FTIR analyses and the conductometric titrations showed evidences of interactions between the fibres and the dianhydride. A fibre mass ratio of 15% was used for composites preparation decreasing the density of the composites at ca. 45% when compared with the vinylester matrix. The TG analyses showed that the aluminum hydroxide addition in the matrix increases the thermal stability of the composites. The DMA showed that the fibres did not influence the matrix cure kinetics, and a biphasic system was formed during pre-curing under environmental conditions. The tensile and Charpy impact strength tests showed an increase of the strength of the composites when compared with the matrix. The best results were obtained for PMDA treated fibres/vinyl ester matrix composites, which showed an increase of ca. 30% for tensile strength and 250% for impact strength.
Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ... more Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ash (RHA), a reactive filler. CMCs were obtained by pyrolysis at 1000 and 1600°C of green bodies prepared from a mixture of polysiloxane network and RHA at a weight ratio of 4:1, respectively. The RHA and the CMCs were characterized by thermogravimetric analysis (TGA), X-ray diffraction
Wet strength paper repulping is a challenge for paper recycling. This work proposes a novel appro... more Wet strength paper repulping is a challenge for paper recycling. This work proposes a novel approach to study the degradation of PAE-based papers made from bleached kraft pulps. In a first part, cross-linked PAE films, obtained by casting under controlled conditions, were treated by different chemical additives and the film degradation was evaluated as the relative weight difference between dry PAE films before and after the treatment. The selected reagents were sodium hydroxide, sulfuric acid, potassium persulfate and hydrogen peroxide, used alone or in combination. In a second part, the same chemical systems were applied on coated and uncoated PAE-based papers (industrial papers and model papers, i.e. handsheets). The effect of the repulping chemicals was evaluated using an original method by measuring the residual tensile force of wet paper strips after soaking them in aqueous solutions containing the reagents in given experimental conditions. As persulfate is sometimes suspected to induce paper yellowing, handsheets with and without PAE were submitted to the same treatments in order to compare the optical properties. The aqueous solution containing the chemicals before and after the PAE-based handsheet treatment was also analyzed by UV-vis spectrophotometry.
Currently, there is a demand for new engineering materials presenting a combination of strength, ... more Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix.
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