Marcio Loos - Academia.edu (original) (raw)

Papers by Marcio Loos

Journal of Nanomaterials, 2012

The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weig... more The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weight and sulfonation level. All sulfonated polyoxadiazoles synthesized through a polycondensation reaction of the hydrazine sulphate salt and a dicarboxylic acid in poly(phosphoric acid) exhibit rigid-ductile behavior with high Young’s modulus (3–4 GPa) and with larger elongations at break (up to 120%). Sulfonated polyoxadiazoles with maximum reproducible tensile strength (190 6.9 MPa) could be synthesized in the frame of time of 4–5 h.

Current Organic Chemistry, 2013

Composites Science and Technology, 2012

The effects of the addition of eight different block copolymers on the dispersion stability of mu... more The effects of the addition of eight different block copolymers on the dispersion stability of multi-walled carbon nanotubes (MWCNTs) are reported. Suspensions of CNTs in different components of an epoxy system have been prepared using a tip sonicator and different amounts of block copolymers. The resistance to sedimentation of MWCNTs in various media was systematically investigated by using a centrifugation technique. Block copolymers that result in dispersions of MWCNTs in epoxy and hardener stable for more than 1 week have been obtained. Dispersions using a single or a combination of two different dispersing agents have been used for the fabrication of MWCNT nanocomposites. The effect of different preparation routes and use of block copolymers on the tensile properties and surface resistivity of the composites have been evaluated. The results obtained have been related with the dispersion stability of the MWCNTs in the epoxy components.

Powder Technology

A method for the dispersion of particle clusters driven by the pressure generated from the volati... more A method for the dispersion of particle clusters driven by the pressure generated from the volatilization of interstitial liquid is described. To demonstrate the method, carbon black agglomerates were heated to induce the rapid evaporation of incorporated water or acetone, which resulted in breakage of the particle cluster. Measurements of the resulting fragment size distribution demonstrate the influence of processing temperature and type of incorporated liquid on the dispersion process.

High Performance Polymers, 2009

The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weig... more The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weight and sulfonation level. All sulfonated polyoxadiazoles synthesized through a polycondensation reaction of the hydrazine sulphate salt and a dicarboxylic acid in poly(phosphoric acid) exhibit rigid-ductile behavior with high Young's modulus (3-4 GPa) and with larger elongations at break (up to 120%). Sulfonated polyoxadiazoles with maximum reproducible tensile strength (190 1 6.9 MPa) could be synthesized in the frame of time of 4-5 h.

Materials Letters, 2009

In the present work, in-situ polymerizations of fluorinated polyoxadiazole through a polycondensa... more In the present work, in-situ polymerizations of fluorinated polyoxadiazole through a polycondensation reaction of A-A (hydrazine sulphate) and B-B (aromatic dicarboxylic acid) monomers with multiwalled carbon nanotubes (MWCNT) in poly(phosphoric acid) were performed in the frame of time 3 to 48 h. The effect of acid treatment in polyphosphoric acid on the CNT structure was analyzed by SEM, TGA and FTIR. Fluorinated polyoxadiazole/MWCNTs soluble in organic solvents with high molecular weights (around 200 000 g/mol) could be synthesized in 3 h. The fluorinated polyoxadiazole/MWCNTs exhibits high thermal stability with degradation temperature at about 460°C.

Journal of Materials Science, 2008

In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites wer... more In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites were fabricated by tip sonication with the aid of a solvent and subsequent casting. Two different curing cycles were used to study the role of the stiffness of the epoxy matrix on the tensile and thermal behavior of the composites. The addition of a small amount of SWCNTs (0.25 wt.%) in rubbery, i.e., soft matrices, greatly increased Young's modulus and tensile strength of the nanocomposites. The results showed that the tensile properties of soft epoxy matrices are much more influenced by the addition of carbon nanotubes than stiffer ones. The significant improvement in tensile properties was attributed to the excellent mechanical properties and structure of SWCNTs, an adequate dispersion of SWCNTs by tip sonication, and a stronger SWCNT/matrix interfacial adhesion in softer epoxy matrices. A slight improvement in the thermal stability of the nanocomposites was also observed.

Journal of Materials Science, 2008

In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites wer... more In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites were fabricated by tip sonication with the aid of a solvent and subsequent casting. Two different curing cycles were used to study the role of the stiffness of the epoxy matrix on the tensile and thermal behavior of the composites. The addition of a small amount of SWCNTs (0.25 wt.%) in rubbery, i.e., soft matrices, greatly increased Young’s modulus and tensile strength of the nanocomposites. The results showed that the tensile properties of soft epoxy matrices are much more influenced by the addition of carbon nanotubes than stiffer ones. The significant improvement in tensile properties was attributed to the excellent mechanical properties and structure of SWCNTs, an adequate dispersion of SWCNTs by tip sonication, and a stronger SWCNT/matrix interfacial adhesion in softer epoxy matrices. A slight improvement in the thermal stability of the nanocomposites was also observed.

Materials Research-ibero-american Journal of Materials, 2008

Carbon nano-tubes/cement composites (CNTCC) have been prepared by adding different weight ratios ... more Carbon nano-tubes/cement composites (CNTCC) have been prepared by adding different weight ratios of carbon nanotubes (CNT) ranging from (0.01 up to 0.05%). Due to the high potential of CNT to improve the properties of materials, so, this study is aimed to evaluate the effect of the chemical and physical properties of CNT on the mechanical behavior of CNTCC. The effect of CNT addition on compressive, indirect tensile strength, hardness and phase compositions of CNTCC were determined. Rotary mixer was used for dry mixing of CNT with different ratios to the cement matrix to ensure homogeneous distribution. Test samples were prepared following the standard technique as 2×2×2 cm cubes for the compression test and as 1×1×5 cm for hardness test, while test samples as cylinders with 5 cm diameter and 1 cm thickness, was for the indirect tensile strength test. Water of consistency was used for preparing the blended pastes. Indirect tensile and compressive strength tests showed valuable enhancement in mechanical properties of CNTCC with increasing CNT loading ratio. The microstructure of the CNTCC was characterized by means of scanning electron microscope (SEM) analysis, while the mineralogy was analyzed by means of a differential scanning calorimeter (DSC). The addition of CNT by about 0.04% enhanced the indirect tensile strength to about 52%, compression strength to about 48% and hardness to about 232.6%. This is due to uniformly dispersion of CNT and the effect of bridging up the cracks in the composite.

Polimeros-ciencia E Tecnologia, 2008

I I I Í I ity of the neat epoxy which makes the dispersion of these finely divided materials very... more I I I Í I ity of the neat epoxy which makes the dispersion of these finely divided materials very challenging.

Composites Science and Technology, 2009

In the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensat... more In the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensation reaction of A-A (hydrazine sulphate) and B-B (aromatic dicarboxylic acid) monomers with carbon nanotubes in poly(phosphoric acid) were performed. The structures of composites were characterized by elemental analysis, Raman and FTIR spectroscopy. The sulfonated polyoxadiazole composites with high molecular weight (in the order of magnitude of 10 5 g/mol) are soluble in organic solvents and can be cast as dense films. They exhibit good mechanical properties (storage modulus up to around 4 GPa at 300°C) and an electrical conductivity in the order of 10 À5 S m À1 . The composites can be used at temperatures as high as 470°C.

2 Abstract Non modified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) na... more 2 Abstract Non modified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability and electrical conductivity are investigated. Tensile strength, elongation at break and tensile energy to break are shown to increase by more than 28, 45 and 73 %, respectively, by incorporating up to 1.0 wt% pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin-Tsai and modified Halpin-Tsai predictions. The storage modulus is found to increase up to 10 % at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57°C in the initial degradation temperature. The addition of 1.0 wt% MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude.

Composites Part B-engineering, 2011

Pristine carbon black was oxidized with poly(phosphoric acid) to produce carboxyl groups. The car... more Pristine carbon black was oxidized with poly(phosphoric acid) to produce carboxyl groups. The carboxyl groups were consecutively treated with hydrazine sulfate to introduce arylcarbonyl and CONHNH 2 groups. The groups on the CB surface were reacted with dicarboxylic acid to anchor the growing of polyoxadiazole chains. The properties of the bulk POD/CB composites were characterized by elemental analysis (EA), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The final composites were processed in films using a solution method aided by the use of a mini-calendar for final high shear mixing. Transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and tensile tests were used to systemically characterize the high performance composite films. The POD composites with high molecular weight (in the order of magnitude of 10 5 g/ mol) were soluble in polar aprotic solvents and stable at temperatures as high as 465°C. The incorporation of the CB enhanced the overall mechanical properties of the composites at low CB content due to the presence of strong interfacial interaction between the polymer matrix and the filler.

Journal of Nanomaterials, 2012

The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weig... more The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weight and sulfonation level. All sulfonated polyoxadiazoles synthesized through a polycondensation reaction of the hydrazine sulphate salt and a dicarboxylic acid in poly(phosphoric acid) exhibit rigid-ductile behavior with high Young’s modulus (3–4 GPa) and with larger elongations at break (up to 120%). Sulfonated polyoxadiazoles with maximum reproducible tensile strength (190 6.9 MPa) could be synthesized in the frame of time of 4–5 h.

Current Organic Chemistry, 2013

Composites Science and Technology, 2012

The effects of the addition of eight different block copolymers on the dispersion stability of mu... more The effects of the addition of eight different block copolymers on the dispersion stability of multi-walled carbon nanotubes (MWCNTs) are reported. Suspensions of CNTs in different components of an epoxy system have been prepared using a tip sonicator and different amounts of block copolymers. The resistance to sedimentation of MWCNTs in various media was systematically investigated by using a centrifugation technique. Block copolymers that result in dispersions of MWCNTs in epoxy and hardener stable for more than 1 week have been obtained. Dispersions using a single or a combination of two different dispersing agents have been used for the fabrication of MWCNT nanocomposites. The effect of different preparation routes and use of block copolymers on the tensile properties and surface resistivity of the composites have been evaluated. The results obtained have been related with the dispersion stability of the MWCNTs in the epoxy components.

Powder Technology

A method for the dispersion of particle clusters driven by the pressure generated from the volati... more A method for the dispersion of particle clusters driven by the pressure generated from the volatilization of interstitial liquid is described. To demonstrate the method, carbon black agglomerates were heated to induce the rapid evaporation of incorporated water or acetone, which resulted in breakage of the particle cluster. Measurements of the resulting fragment size distribution demonstrate the influence of processing temperature and type of incorporated liquid on the dispersion process.

High Performance Polymers, 2009

The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weig... more The tensile properties of sulfonated polyoxadiazoles were studied as a function of molecular weight and sulfonation level. All sulfonated polyoxadiazoles synthesized through a polycondensation reaction of the hydrazine sulphate salt and a dicarboxylic acid in poly(phosphoric acid) exhibit rigid-ductile behavior with high Young's modulus (3-4 GPa) and with larger elongations at break (up to 120%). Sulfonated polyoxadiazoles with maximum reproducible tensile strength (190 1 6.9 MPa) could be synthesized in the frame of time of 4-5 h.

Materials Letters, 2009

In the present work, in-situ polymerizations of fluorinated polyoxadiazole through a polycondensa... more In the present work, in-situ polymerizations of fluorinated polyoxadiazole through a polycondensation reaction of A-A (hydrazine sulphate) and B-B (aromatic dicarboxylic acid) monomers with multiwalled carbon nanotubes (MWCNT) in poly(phosphoric acid) were performed in the frame of time 3 to 48 h. The effect of acid treatment in polyphosphoric acid on the CNT structure was analyzed by SEM, TGA and FTIR. Fluorinated polyoxadiazole/MWCNTs soluble in organic solvents with high molecular weights (around 200 000 g/mol) could be synthesized in 3 h. The fluorinated polyoxadiazole/MWCNTs exhibits high thermal stability with degradation temperature at about 460°C.

Journal of Materials Science, 2008

In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites wer... more In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites were fabricated by tip sonication with the aid of a solvent and subsequent casting. Two different curing cycles were used to study the role of the stiffness of the epoxy matrix on the tensile and thermal behavior of the composites. The addition of a small amount of SWCNTs (0.25 wt.%) in rubbery, i.e., soft matrices, greatly increased Young's modulus and tensile strength of the nanocomposites. The results showed that the tensile properties of soft epoxy matrices are much more influenced by the addition of carbon nanotubes than stiffer ones. The significant improvement in tensile properties was attributed to the excellent mechanical properties and structure of SWCNTs, an adequate dispersion of SWCNTs by tip sonication, and a stronger SWCNT/matrix interfacial adhesion in softer epoxy matrices. A slight improvement in the thermal stability of the nanocomposites was also observed.

Journal of Materials Science, 2008

In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites wer... more In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites were fabricated by tip sonication with the aid of a solvent and subsequent casting. Two different curing cycles were used to study the role of the stiffness of the epoxy matrix on the tensile and thermal behavior of the composites. The addition of a small amount of SWCNTs (0.25 wt.%) in rubbery, i.e., soft matrices, greatly increased Young’s modulus and tensile strength of the nanocomposites. The results showed that the tensile properties of soft epoxy matrices are much more influenced by the addition of carbon nanotubes than stiffer ones. The significant improvement in tensile properties was attributed to the excellent mechanical properties and structure of SWCNTs, an adequate dispersion of SWCNTs by tip sonication, and a stronger SWCNT/matrix interfacial adhesion in softer epoxy matrices. A slight improvement in the thermal stability of the nanocomposites was also observed.

Materials Research-ibero-american Journal of Materials, 2008

Carbon nano-tubes/cement composites (CNTCC) have been prepared by adding different weight ratios ... more Carbon nano-tubes/cement composites (CNTCC) have been prepared by adding different weight ratios of carbon nanotubes (CNT) ranging from (0.01 up to 0.05%). Due to the high potential of CNT to improve the properties of materials, so, this study is aimed to evaluate the effect of the chemical and physical properties of CNT on the mechanical behavior of CNTCC. The effect of CNT addition on compressive, indirect tensile strength, hardness and phase compositions of CNTCC were determined. Rotary mixer was used for dry mixing of CNT with different ratios to the cement matrix to ensure homogeneous distribution. Test samples were prepared following the standard technique as 2×2×2 cm cubes for the compression test and as 1×1×5 cm for hardness test, while test samples as cylinders with 5 cm diameter and 1 cm thickness, was for the indirect tensile strength test. Water of consistency was used for preparing the blended pastes. Indirect tensile and compressive strength tests showed valuable enhancement in mechanical properties of CNTCC with increasing CNT loading ratio. The microstructure of the CNTCC was characterized by means of scanning electron microscope (SEM) analysis, while the mineralogy was analyzed by means of a differential scanning calorimeter (DSC). The addition of CNT by about 0.04% enhanced the indirect tensile strength to about 52%, compression strength to about 48% and hardness to about 232.6%. This is due to uniformly dispersion of CNT and the effect of bridging up the cracks in the composite.

Polimeros-ciencia E Tecnologia, 2008

I I I Í I ity of the neat epoxy which makes the dispersion of these finely divided materials very... more I I I Í I ity of the neat epoxy which makes the dispersion of these finely divided materials very challenging.

Composites Science and Technology, 2009

In the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensat... more In the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensation reaction of A-A (hydrazine sulphate) and B-B (aromatic dicarboxylic acid) monomers with carbon nanotubes in poly(phosphoric acid) were performed. The structures of composites were characterized by elemental analysis, Raman and FTIR spectroscopy. The sulfonated polyoxadiazole composites with high molecular weight (in the order of magnitude of 10 5 g/mol) are soluble in organic solvents and can be cast as dense films. They exhibit good mechanical properties (storage modulus up to around 4 GPa at 300°C) and an electrical conductivity in the order of 10 À5 S m À1 . The composites can be used at temperatures as high as 470°C.

2 Abstract Non modified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) na... more 2 Abstract Non modified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability and electrical conductivity are investigated. Tensile strength, elongation at break and tensile energy to break are shown to increase by more than 28, 45 and 73 %, respectively, by incorporating up to 1.0 wt% pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin-Tsai and modified Halpin-Tsai predictions. The storage modulus is found to increase up to 10 % at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57°C in the initial degradation temperature. The addition of 1.0 wt% MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude.

Composites Part B-engineering, 2011

Pristine carbon black was oxidized with poly(phosphoric acid) to produce carboxyl groups. The car... more Pristine carbon black was oxidized with poly(phosphoric acid) to produce carboxyl groups. The carboxyl groups were consecutively treated with hydrazine sulfate to introduce arylcarbonyl and CONHNH 2 groups. The groups on the CB surface were reacted with dicarboxylic acid to anchor the growing of polyoxadiazole chains. The properties of the bulk POD/CB composites were characterized by elemental analysis (EA), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The final composites were processed in films using a solution method aided by the use of a mini-calendar for final high shear mixing. Transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and tensile tests were used to systemically characterize the high performance composite films. The POD composites with high molecular weight (in the order of magnitude of 10 5 g/ mol) were soluble in polar aprotic solvents and stable at temperatures as high as 465°C. The incorporation of the CB enhanced the overall mechanical properties of the composites at low CB content due to the presence of strong interfacial interaction between the polymer matrix and the filler.