ABSTRACT We analyze the pore structure changes during the fabrication of polypropylene-based micr... more ABSTRACT We analyze the pore structure changes during the fabrication of polypropylene-based microporous membranes via the stretching method. The membranes were prepared via melt extrusion followed by annealing and stretching at room temperature and at an elevated temperature (cold and hot stretching steps, respectively). Understanding the pore formation mechanisms is important for effective control of the membrane performance. Hence, the pore structure along the membrane surface and across the thickness, which determined the size, number, and interconnectivity of the pores, was analyzed to quantify the effect of stretching on the membrane performance. The cold stretching step was found to be the important one for promoting interconnection between the pores. Furthermore, it was shown that applying a low strain rate improved the permeability of the membranes. Finally, no maximum was observed in the permeability by increasing the stretch ratio during the hot stretching step.
A double helical-ribbon impeller (HRI) bioreactor with a 11-L working volume was developed to gro... more A double helical-ribbon impeller (HRI) bioreactor with a 11-L working volume was developed to grow high-density Catharanthus roseus cell suspensions. The rheological behavior of this suspension was found to be shear-thinning for concentrations higher than 12 to 15 g DW . L(-1). A granulated agar suspension of similar rheological properties was used as a model fluid for these suspensions. Mixing studies revealed that surface baffling and bottom profiling of the bioreactor and impeller speeds of 60 to 150 rpm ensured uniform mixing of suspensions. The HRI power requirement was found to increase significantly for agar suspensions higher than 13 g DW . L(-1), in conjunction with the effective viscosity increase. Oxygen transfer studies showed high apparent surface oxygen transfer coefficients (k(L)a approximately 4 to 45 h(-1)) from agar suspensions of 30 g DW . L(-1) to water and for mixing speeds ranging from 120 to 150 rpm. These high surface k(I)a values were ascribed to the flow pattern of this bioreactor configuration combined with surface bubble generation and entrainment in the liquid phase caused by the presence of the surface baffles. High-density C. roseus cell suspension cultures were successfully grown in this bioreactor without gas sparging. Up to 70% oxygen enrichment of the head space was required to ensure sufficient oxygen supply to the cultures so that dissolved oxygen concentration would remain above the critical level (> or =10% air saturation). The best mixing speed was 120 rpm. These cultures grew at the same rate ( approximately 0.4 d(-1)) and attained the same high biomass concentrations ( approximately 25 to 27 g DW . L(-1), 450 to 500 g filtered wet biomass . L(-1), and 92% to 100% settled wet biomass volume) as shake flask cultures. The scale-up potential of this bioreactor configuration is discussed.
Page 1. Page 1 EFFECT OF FLOW HISTORY ON THE RHEOLOGY OF MWNT-EPOXY SUSPENSIONS Fatemeh Khalkhal ... more Page 1. Page 1 EFFECT OF FLOW HISTORY ON THE RHEOLOGY OF MWNT-EPOXY SUSPENSIONS Fatemeh Khalkhal and Pierre J. Carreau ... Strain sweep measurements were performed at 0.1 (rad/s) and 10 (rad/s). The results are shown in Fig. 2a. ...
Electrosterically stabilized nanocrystals of cellulose (ENCCs) have emerged recently as new cellu... more Electrosterically stabilized nanocrystals of cellulose (ENCCs) have emerged recently as new cellulose nanoparticles among common nanocrystals of cellulose (NCCs) and cellulose nanofibers. ENCC has a special structure being composed of a crystal with protruded amorphous chains at each endcaps bearing carboxyl groups. Here, we studied the intrinsic viscosity of aqueous suspensions of ENCCs as a function of pH and ionic strength. Low pH or high ionic strength reduced the ENCCs to rigid rod-like particles while a polyelectrolyte-like behavior was observed for suspensions of ENCCs around pH 7 and at low ionic strength. The pH had a great effect on charges due to both deprotonation of carboxyl groups and counter-ion effect, while the ionic strength only affected the surface charges of the particles. The zeta potential of ENCC suspensions was measured as a function of pH and ionic strength to establish a link between particle charges and the intrinsic viscosity. Finally, the Fedors model w...
A nionic ring-opening polymerization of ε-caprolactam leads to the formation of polyamide 6 (PA6)... more A nionic ring-opening polymerization of ε-caprolactam leads to the formation of polyamide 6 (PA6). This reaction takes place at a significantly faster reaction rate and gives a narrower molecular weight distribution than the other techniques. Due to this advantage, anionic polymerization of ε-caprolactam towards PA6 in melt blending was investigated in this work. PA6 was prepared in an internal mixer via melt polymerization of ε-caprolactam as a monomer with sodium caprolactam as its catalyst and hexamethylene diisocyanate as an activator. The effects of various concentrations of catalyst and activator on the initiation time of the reaction and on the residual monomer were determined. The residual monomer was collected using a solvent extraction method and determined by GC-mass technique. The physical and mechanical properties of the PA6 prepared via melt blending and of a commercial PA6 prepared were determined by differential scanning calorimetry (DSC), thermal gravimetric analysi...
ABSTRACT In this work, the rheological, mechanical and morphological properties of flax fiber pol... more ABSTRACT In this work, the rheological, mechanical and morphological properties of flax fiber polypropylene composites were investigated. The effect of incorporating a polypropylene grafted acrylic acid or a polypropylene grafted maleic anhydride on these properties has been studied as well. According to scanning electron microscopic observations and tensile tests, the addition of a compatibilizer improved the interfacial adhesion between the flax fibers and the polymer matrix. The tensile modulus of composite containing 30 wt% flax fibers was improved by 200 % and the tensile strength improved by 60 % in comparison with the neat PP. Plasticizing effect of the compatibilizers as a result of their lower melt flow index was also shown to decrease the rheological properties of the composites, even though the effect was not pronounced on the mechanical properties.
ABSTRACT We analyze the pore structure changes during the fabrication of polypropylene-based micr... more ABSTRACT We analyze the pore structure changes during the fabrication of polypropylene-based microporous membranes via the stretching method. The membranes were prepared via melt extrusion followed by annealing and stretching at room temperature and at an elevated temperature (cold and hot stretching steps, respectively). Understanding the pore formation mechanisms is important for effective control of the membrane performance. Hence, the pore structure along the membrane surface and across the thickness, which determined the size, number, and interconnectivity of the pores, was analyzed to quantify the effect of stretching on the membrane performance. The cold stretching step was found to be the important one for promoting interconnection between the pores. Furthermore, it was shown that applying a low strain rate improved the permeability of the membranes. Finally, no maximum was observed in the permeability by increasing the stretch ratio during the hot stretching step.
A double helical-ribbon impeller (HRI) bioreactor with a 11-L working volume was developed to gro... more A double helical-ribbon impeller (HRI) bioreactor with a 11-L working volume was developed to grow high-density Catharanthus roseus cell suspensions. The rheological behavior of this suspension was found to be shear-thinning for concentrations higher than 12 to 15 g DW . L(-1). A granulated agar suspension of similar rheological properties was used as a model fluid for these suspensions. Mixing studies revealed that surface baffling and bottom profiling of the bioreactor and impeller speeds of 60 to 150 rpm ensured uniform mixing of suspensions. The HRI power requirement was found to increase significantly for agar suspensions higher than 13 g DW . L(-1), in conjunction with the effective viscosity increase. Oxygen transfer studies showed high apparent surface oxygen transfer coefficients (k(L)a approximately 4 to 45 h(-1)) from agar suspensions of 30 g DW . L(-1) to water and for mixing speeds ranging from 120 to 150 rpm. These high surface k(I)a values were ascribed to the flow pattern of this bioreactor configuration combined with surface bubble generation and entrainment in the liquid phase caused by the presence of the surface baffles. High-density C. roseus cell suspension cultures were successfully grown in this bioreactor without gas sparging. Up to 70% oxygen enrichment of the head space was required to ensure sufficient oxygen supply to the cultures so that dissolved oxygen concentration would remain above the critical level (> or =10% air saturation). The best mixing speed was 120 rpm. These cultures grew at the same rate ( approximately 0.4 d(-1)) and attained the same high biomass concentrations ( approximately 25 to 27 g DW . L(-1), 450 to 500 g filtered wet biomass . L(-1), and 92% to 100% settled wet biomass volume) as shake flask cultures. The scale-up potential of this bioreactor configuration is discussed.
Page 1. Page 1 EFFECT OF FLOW HISTORY ON THE RHEOLOGY OF MWNT-EPOXY SUSPENSIONS Fatemeh Khalkhal ... more Page 1. Page 1 EFFECT OF FLOW HISTORY ON THE RHEOLOGY OF MWNT-EPOXY SUSPENSIONS Fatemeh Khalkhal and Pierre J. Carreau ... Strain sweep measurements were performed at 0.1 (rad/s) and 10 (rad/s). The results are shown in Fig. 2a. ...
Electrosterically stabilized nanocrystals of cellulose (ENCCs) have emerged recently as new cellu... more Electrosterically stabilized nanocrystals of cellulose (ENCCs) have emerged recently as new cellulose nanoparticles among common nanocrystals of cellulose (NCCs) and cellulose nanofibers. ENCC has a special structure being composed of a crystal with protruded amorphous chains at each endcaps bearing carboxyl groups. Here, we studied the intrinsic viscosity of aqueous suspensions of ENCCs as a function of pH and ionic strength. Low pH or high ionic strength reduced the ENCCs to rigid rod-like particles while a polyelectrolyte-like behavior was observed for suspensions of ENCCs around pH 7 and at low ionic strength. The pH had a great effect on charges due to both deprotonation of carboxyl groups and counter-ion effect, while the ionic strength only affected the surface charges of the particles. The zeta potential of ENCC suspensions was measured as a function of pH and ionic strength to establish a link between particle charges and the intrinsic viscosity. Finally, the Fedors model w...
A nionic ring-opening polymerization of ε-caprolactam leads to the formation of polyamide 6 (PA6)... more A nionic ring-opening polymerization of ε-caprolactam leads to the formation of polyamide 6 (PA6). This reaction takes place at a significantly faster reaction rate and gives a narrower molecular weight distribution than the other techniques. Due to this advantage, anionic polymerization of ε-caprolactam towards PA6 in melt blending was investigated in this work. PA6 was prepared in an internal mixer via melt polymerization of ε-caprolactam as a monomer with sodium caprolactam as its catalyst and hexamethylene diisocyanate as an activator. The effects of various concentrations of catalyst and activator on the initiation time of the reaction and on the residual monomer were determined. The residual monomer was collected using a solvent extraction method and determined by GC-mass technique. The physical and mechanical properties of the PA6 prepared via melt blending and of a commercial PA6 prepared were determined by differential scanning calorimetry (DSC), thermal gravimetric analysi...
ABSTRACT In this work, the rheological, mechanical and morphological properties of flax fiber pol... more ABSTRACT In this work, the rheological, mechanical and morphological properties of flax fiber polypropylene composites were investigated. The effect of incorporating a polypropylene grafted acrylic acid or a polypropylene grafted maleic anhydride on these properties has been studied as well. According to scanning electron microscopic observations and tensile tests, the addition of a compatibilizer improved the interfacial adhesion between the flax fibers and the polymer matrix. The tensile modulus of composite containing 30 wt% flax fibers was improved by 200 % and the tensile strength improved by 60 % in comparison with the neat PP. Plasticizing effect of the compatibilizers as a result of their lower melt flow index was also shown to decrease the rheological properties of the composites, even though the effect was not pronounced on the mechanical properties.
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Papers by Pierre Carreau