Marco Villalobos - Academia.edu (original) (raw)

Papers by Marco Villalobos

Langmuir, Jul 21, 2017

This work explores cellulose nanocrystal (CNC) thin films (<50 nm) and particle-particle i... more This work explores cellulose nanocrystal (CNC) thin films (<50 nm) and particle-particle interactions by investigating film swelling in aqueous solutions with varying ionic strength (1-100 mM). CNC film hydration was monitored in situ via surface plasmon resonance, and the kinetics of liquid uptake were quantified. The contribution of electrostatic double-layer forces to film swelling was elucidated by using CNCs with different surface charges (anionic sulfate half ester groups, high and low surface charge density, and cationic trimethylammonium groups). Total water uptake in the thin films was found to be independent of ionic strength and surface chemistry, suggesting that in the aggregated state van der Waals forces dominate over double-layer forces to hold the films together. However, the rate of swelling varied significantly. The water uptake followed Fickian behavior, and the measured diffusion constants decreased with the ionic strength gradient between the film and the solution. This work highlights that nanoparticle interactions and dispersion are highly dependent on the state of particle aggregation and that the rate of water uptake in aggregates and thin films can be tailored based on surface chemistry and solution ionic strength.

Current Opinion in Colloid and Interface Science, May 1, 2017

A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable... more A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable and renewable materials in place of those that are derived from petrochemical resources. Although current commercial uses of nanocellulose remain limited, research over the past two decades demonstrates numerous applications including reinforcing agents in polymer and cement composites, coatings, foams, gels, tissue scaffolds, and rheological modifiers, amongst others. Because of the hydrophilic nature of nanocellulose many of the potential uses will likely be in water-based formulations or employ water-based processing methods. Thus understanding the interactions between nanocellulose and water-soluble polymers is critical. Although polyelectrolyte adsorption to cellulose is well understood, adsorption of non-ionic polymers is less clear, with hydrogen bonding often cited as a governing factor. Recent work suggests that in fact hydrogen bonding does not play a significant role in nanocellulose systems, and that nonionic polymer adsorption is largely entropically driven. Herein we review current literature that investigates non-ionic polymer adsorption to cellulose nanocrystals (CNCs) and draw upon previous papermaking research to better understand the mechanisms involved. Additionally we analyze recent work that compares the adsorption of polyethylene glycol (PEG) to CNCs and fumed silica that provides further insight into this phenomenon. Our findings, along with current literature, suggest that hydrogen bonding does not significantly impact polymer adsorption in aqueous media despite reports to the contrary.

Langmuir, Dec 13, 2016

The renewability, biocompatibility and mechanical properties of cellulose nanocrystals (CNCs) hav... more The renewability, biocompatibility and mechanical properties of cellulose nanocrystals (CNCs) have made them an attractive material for numerous composite, biomedical and rheological applications. However, for CNCs to shift from laboratory curiosity to commercial applications, researchers must transition from CNCs extracted at the bench scale to material produced at an industrial scale. There are a number of companies currently producing kilogram to ton per day quantities of sulfuric acid-hydrolyzed CNCs, as well as other nanocelluloses, as described herein. With the recent intensification of industrially produced CNCs, the variety of cellulose sources, hydrolysis methods and purification procedures, characterization of these materials becomes critical. This has further been justified by the past two decades of research which demonstrate that CNC stability and behaviour is highly dependent on surface chemistry, surface charge density and particle size. This work outlines key test methods that should be employed to characterize these properties to ensure a "known" starting material and consistent performance. Of the sulfuric acid-extracted CNCs examined, industrially produced material compared well with laboratory-made CNCs, exhibiting similar charge density, colloidal and thermal stability, crystallinity, morphology and self-assembly behaviour. In addition, it was observed that further purification of CNCs, using Soxhlet extraction in ethanol, had minimal impact on nanoparticle properties and is unlikely to be necessary for many applications. Overall the current standing of industrially produced CNCs is positive suggesting that the evolution to commercial scale applications will not be hindered by CNC production. Composition Percentage C1 C2 C3

Cellulose, Sep 5, 2017

The recent intensification of industrially produced cellulose nanocrystals (CNCs) and cellulose n... more The recent intensification of industrially produced cellulose nanocrystals (CNCs) and cellulose nanofibrils has positioned nanocelluloses as promising materials for many water-based products and applications. However, for nanocelluloses to move beyond solely an academic interest, a thorough understanding of their interaction with water-soluble polymers is needed. In this work, we address a conflicting trend in literature that suggests polyethylene glycol (PEG) adsorbs to CNC surfaces by comparing the adsorption behaviour of PEG with CNCs versus fumed silica. While PEG is known to have strong hydrogen bonding tendencies and holds water tightly, it is sometimes (we believe erroneously) presumed that PEG binds to cellulose through hydrogen bonding in aqueous media. To test this assumption, the adsorption of PEG to CNCs and fumed silica (both in the form of particle films and in aqueous dispersions) was examined using quartz crystal microbalance with dissipation, isothermal titration calorimetry, rheology and dynamic light scattering. For all PEG molecular weights (300-10,000 g/mol) and concentrations (100-10,000 ppm) tested, strong rapid adsorption was found with fumed silica, whereas no adsorption to CNCs was observed. We conclude that unlike silanols, the hydroxyl groups on the surface of CNCs do not readily hydrogen bond with the ether oxygen in the PEG backbone. As such, this work along with previous papermaking literature supports the opinion that PEG does not adsorb to cellulose surfaces.

Nanoscale, 2016

The production of well-dispersed reinforced polymer nanocomposites has been limited due to poor u... more The production of well-dispersed reinforced polymer nanocomposites has been limited due to poor understanding of the interactions between components. Measuring the cohesive particle-particle interactions and the adhesive particlepolymer interactions is challenging due to nanoscale dimensions and poor colloidal stability of nanoparticles in many solvents. We demonstrate a new cohesive interaction measurement method using cellulose nanocrystals (CNCs) as a model system; CNCs have recently gained attention in the composites community due to their mechanical strength and renewable nature. Multi-wavelength surface plasmon resonance spectroscopy (SPR) was used to monitor the swelling of CNC thin films to elucidate the primary forces between CNCs. This was achieved by measuring swelling in situ in water, acetone, methanol, acetonitrile, isopropanol, and ethanol and relating the degree of swelling to solvent properties. Films swelled the most in water where we estimate 1.2-1.6 nm spacings between CNCs (or 4-6 molecular layers of water). Furthermore, a correlation was found between film swelling and the solvent's Hildebrand solubility parameter (R 2 =0.9068). The hydrogen bonding component of the solubility parameters was more closely linked to swelling than the polar or dispersive components. The films remained intact in all solvents, and using DLVO theory we have identified van der Waals forces as the main cohesive interaction between CNCs. The trends observed suggest that solvents (and polymers) alone are not sufficient to overcome CNC-CNC cohesion and that external energy is required to break CNC agglomerates. This work not only demonstrates that SPR can be used as a tool to measure cohesive particle-particle interactions but additionally advances our fundamental understanding of CNC interactions which is necessary for the design of cellulose nanocomposites. 3) Advancing the field of reinforced nanocomposites requires methods to extract and predict these interactions in a variety of systems. Cellulose nanocrystals (CNCs) are an abundant and sustainable rod-shaped nanomaterial that has recently been used in biomedical devices, 4-6 as rheological modifiers, 7,8 emulsion stabilizers 9-12 and many other composite applications. 13-17 Depending on the cellulose source (e.g., wood, cotton, bacteria, algae or tunicate) CNCs range from 100-1000 nm in length and 5-20 nm in cross-section and are commonly extracted through sulfuric acid hydrolysis. 16,18,19 Although, applications span several fields, the potential for CNCs to act as reinforcing agents in polymer matrices is widely discussed. 15 Analytical models and experimental measurements report a longitudinal Young's modulus that ranges from 56-220 GPa and a density of 1.5-1.6 g/cm 3. 15 Currently, the major hurdle limiting CNC reinforced nanocomposites is the hydrophilic nature of the particles. High

John Wiley & Sons, Inc. eBooks, Feb 22, 2013

Industrial & Engineering Chemistry Research, Dec 27, 2017

This work compares solvent cast poly(ethylene oxide) (PEO) nanocomposites reinforced with cellulo... more This work compares solvent cast poly(ethylene oxide) (PEO) nanocomposites reinforced with cellulose nanocrystals (CNCs) and fumed silica. Mechanical properties and crystallization behaviour were investigated over a range of polymer molecular weights (10 000-100 000 g/mol) and particle loadings (1-10 wt.%). Polymer adsorption to CNCs and fumed silica was found to alter PEO undercooling and inhibit crystal nucleation. Atomic force microscopy revealed PEO adsorbs to CNCs in a shish-kebab morphology that is readily incorporated into the crystalline domains of the polymer. Tensile testing and nanoindentation showed that the Young's modulus increased by more than 60% for CNC reinforced nanocomposites, and that the Halpin-Kardos model could effectively describe the mechanical properties. Fumed silica reinforced nanocomposites were fit to the Guth-Gold micromechanical model using effective particle volume fractions. Although only solvent cast nanocomposites were investigated, this work provides new insight into the interactions that control dispersion, crystallization and mechanical reinforcement.

Journal of Applied Polymer Science, Oct 10, 1993

The plasticizing effect of n‐pentane on the rate of bulk free radical polymerization of styrene a... more The plasticizing effect of n‐pentane on the rate of bulk free radical polymerization of styrene and molecular weight distribution development has been modeled on the basis of the free volume theory for both monofunctional and bifunctional initiation. A strong decrease in the reaction rate in the late stages of the polymerization, due to the displacement of the onset of the gel effect, has been observed for both types of initiation. This decrease in the polymerization rate limited the terminal conversion to values well below 100% for mono‐functional initiation. However, in bifunctionally initiated polymerization, terminal conversions close to 100% were obtained in spite of the decrease in reaction rate. Contrary to what was expected, the molecular weight distribution obtained at terminal conversion was almost completely insensitive to these changes in polymerization rate. This phenomenon is explained in terms of limited transfer to monomer reactions when n‐pentane is present in the system. In suspension polymerization, the limiting conversion and plasticizing effects of n‐pentane in monofunctionally initiated systems, caused enhanced coalescence leading to suspension set‐up. In bifunctionally initiated systems this enhanced coalescence was completely overcome by the short duration of the particle growth stage, owing to high polymerization rates, and stable suspensions were achieved. For these systems the particle size distributions obtained were similar to that of suspension polystyrene without n‐pentane. © 1993 John Wiley & Sons, Inc.

The use of submicron-particles to enhance properties of polymeric materials is a widely used prac... more The use of submicron-particles to enhance properties of polymeric materials is a widely used practice in many industries, such as, plastics, coatings, adhesives, elastomers, thermosetting composites, etc. From a general frame of reference, the rheological, mechanical, thermal, optical, and electrical performance of particle-polymer composites is governed by two main physical parameters, namely: the state of particle dispersion in the polymer matrix, and the particle-matrix interfacial strength. In this work, the design of Cabot’s submicron-particles along the axes of primary particle size, fractal dimension, and surface chemistry is described in terms of a simple model for particle-polymer and particle-particle interactions based on surface energy measurements. This model allows predictive mapping of particle-polymer systems in phase diagrams that anticipate the state of particle dispersion and interfacial strength for a large range of particle-polymer systems. Several examples are given on the use of this approach in the design of “self-dispersible” or “self-assembling” particles to tailor the rheological, mechanical, thermal, optical, or electrical performance of particle-polymer nano-composites used in coatings, engineering plastics, elastomers, and structural adhesive applications. The design and use of a micro-fluidic device to validate model predictions is also discussed

The Society of Rubber Science and Technology, Japan, 2016

L'invention porte sur un procede de fabrication d'une resine epoxyde avec une fonctionnal... more L'invention porte sur un procede de fabrication d'une resine epoxyde avec une fonctionnalite amine en continu par une premiere zone de reaction dans laquelle une resine a fonctionnalite epoxyde est fabriquee par addition par ouverture de cycle, une deuxieme zone de reaction dans laquelle la resine est mise a reagir avec une amine pour fabriquer un produit a fonctionnalite epoxyde et une troisieme zone de reaction dans laquelle le produit a fonctionnalite epoxyde est mis a reagir avec une amine pour fabriquer la resine epoxyde avec une fonctionnalite amine. Dans d'autres modes de realisation, un peu d'amine peut etre ajoutee dans la premiere zone de reaction pour produire un produit a fonctionnalite epoxyde, avec elimination de la deuxieme zone de reaction, ou la totalite du reactif amine peut etre ajoutee dans la premiere zone de reaction pour produire un produit a fonctionnalite amine, avec elimination a la fois de la deuxieme zone de reaction et de la troisieme zon...

A thermoplastic composition of high flowability comprising: (a) a host polymer; and (b) a flow mo... more A thermoplastic composition of high flowability comprising: (a) a host polymer; and (b) a flow modifier polymer having an average molecular weight weighted less than 15,000, the modifier polymer at least one monomer of (meth) acrylate and at least one vinyl aromatic monomer comprising wherein said composition is characterized by an energy difference relative (RED) between the flow modifier and the host of less than 2.2, an index of melt flow at least 5 percent higher than the host polymer, Izod impact strength polymer kerf of no more than 40% less than the host polymer, a temperature of heat deformation of not more than 10 ° C less than the host polymer and a Vicat softening temperature of no more than 10 ° C less than the host polymer, and the flow modifier polymer is not a polymer of diene-based graft polymer or another rubber based.

Epoxy-functional, styrene-acrylic polymers with low molecular weight, high functionality (> 4)... more Epoxy-functional, styrene-acrylic polymers with low molecular weight, high functionality (> 4) and tailored polydispersity have been designed, synthesized and commercialized to be used as chain extenders or recycling aids PET and other polyesters. Dramatic increases in molecular weight, mechanical, and rheological properties of virgin, reprocessed, and post-consumer recycled polyesters are achieved without the incidence of gellation. Erema’s VacuremaTM recycling equipment is well-suited to processing the additive, and can improve efficiency over 400% Screw selection is shown to be especially important.

Une composition polymere a utiliser dans une contention plastique comprend un extenseur de chaine... more Une composition polymere a utiliser dans une contention plastique comprend un extenseur de chaine, un agent de modification du comportement aux chocs, et un polymere de condensation, l’extenseur de chaine etant le produit de polymerisation de : (i) un monomere (meth)acrylique a fonction epoxy, et (ii) un monomere styrenique et/ou (meth)acrylique. L’extenseur un chaine a un poids equivalent d’epoxy allant d’environ 180 a environ 2800, une valeur de fonctionnalite epoxy moyenne en nombre (Efn) inferieure a environ 30, une valeur de fonctionnalite epoxy moyenne en poids (Efw) de jusqu’a environ 140, et une valeur du poids moleculaire moyen en nombre (Mn) inferieure a 6000, au moins une partie de l’extenseur de chaine reagit avec au moins une partie du polymere de condensation, pour produire un polymere de condensation a chaine allongee.

Current Opinion in Colloid & Interface Science, 2017

A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable... more A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable and renewable materials in place of those that are derived from petrochemical resources. Although current commercial uses of nanocellulose remain limited, research over the past two decades demonstrates numerous applications including reinforcing agents in polymer and cement composites, coatings, foams, gels, tissue scaffolds, and rheological modifiers, amongst others. Because of the hydrophilic nature of nanocellulose many of the potential uses will likely be in water-based formulations or employ water-based processing methods. Thus understanding the interactions between nanocellulose and water-soluble polymers is critical. Although polyelectrolyte adsorption to cellulose is well understood, adsorption of non-ionic polymers is less clear, with hydrogen bonding often cited as a governing factor. Recent work suggests that in fact hydrogen bonding does not play a significant role in nanocellulose systems, and that nonionic polymer adsorption is largely entropically driven. Herein we review current literature that investigates non-ionic polymer adsorption to cellulose nanocrystals (CNCs) and draw upon previous papermaking research to better understand the mechanisms involved. Additionally we analyze recent work that compares the adsorption of polyethylene glycol (PEG) to CNCs and fumed silica that provides further insight into this phenomenon. Our findings, along with current literature, suggest that hydrogen bonding does not significantly impact polymer adsorption in aqueous media despite reports to the contrary.

Langmuir, Jul 21, 2017

This work explores cellulose nanocrystal (CNC) thin films (<50 nm) and particle-particle i... more This work explores cellulose nanocrystal (CNC) thin films (<50 nm) and particle-particle interactions by investigating film swelling in aqueous solutions with varying ionic strength (1-100 mM). CNC film hydration was monitored in situ via surface plasmon resonance, and the kinetics of liquid uptake were quantified. The contribution of electrostatic double-layer forces to film swelling was elucidated by using CNCs with different surface charges (anionic sulfate half ester groups, high and low surface charge density, and cationic trimethylammonium groups). Total water uptake in the thin films was found to be independent of ionic strength and surface chemistry, suggesting that in the aggregated state van der Waals forces dominate over double-layer forces to hold the films together. However, the rate of swelling varied significantly. The water uptake followed Fickian behavior, and the measured diffusion constants decreased with the ionic strength gradient between the film and the solution. This work highlights that nanoparticle interactions and dispersion are highly dependent on the state of particle aggregation and that the rate of water uptake in aggregates and thin films can be tailored based on surface chemistry and solution ionic strength.

Current Opinion in Colloid and Interface Science, May 1, 2017

A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable... more A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable and renewable materials in place of those that are derived from petrochemical resources. Although current commercial uses of nanocellulose remain limited, research over the past two decades demonstrates numerous applications including reinforcing agents in polymer and cement composites, coatings, foams, gels, tissue scaffolds, and rheological modifiers, amongst others. Because of the hydrophilic nature of nanocellulose many of the potential uses will likely be in water-based formulations or employ water-based processing methods. Thus understanding the interactions between nanocellulose and water-soluble polymers is critical. Although polyelectrolyte adsorption to cellulose is well understood, adsorption of non-ionic polymers is less clear, with hydrogen bonding often cited as a governing factor. Recent work suggests that in fact hydrogen bonding does not play a significant role in nanocellulose systems, and that nonionic polymer adsorption is largely entropically driven. Herein we review current literature that investigates non-ionic polymer adsorption to cellulose nanocrystals (CNCs) and draw upon previous papermaking research to better understand the mechanisms involved. Additionally we analyze recent work that compares the adsorption of polyethylene glycol (PEG) to CNCs and fumed silica that provides further insight into this phenomenon. Our findings, along with current literature, suggest that hydrogen bonding does not significantly impact polymer adsorption in aqueous media despite reports to the contrary.

Langmuir, Dec 13, 2016

The renewability, biocompatibility and mechanical properties of cellulose nanocrystals (CNCs) hav... more The renewability, biocompatibility and mechanical properties of cellulose nanocrystals (CNCs) have made them an attractive material for numerous composite, biomedical and rheological applications. However, for CNCs to shift from laboratory curiosity to commercial applications, researchers must transition from CNCs extracted at the bench scale to material produced at an industrial scale. There are a number of companies currently producing kilogram to ton per day quantities of sulfuric acid-hydrolyzed CNCs, as well as other nanocelluloses, as described herein. With the recent intensification of industrially produced CNCs, the variety of cellulose sources, hydrolysis methods and purification procedures, characterization of these materials becomes critical. This has further been justified by the past two decades of research which demonstrate that CNC stability and behaviour is highly dependent on surface chemistry, surface charge density and particle size. This work outlines key test methods that should be employed to characterize these properties to ensure a "known" starting material and consistent performance. Of the sulfuric acid-extracted CNCs examined, industrially produced material compared well with laboratory-made CNCs, exhibiting similar charge density, colloidal and thermal stability, crystallinity, morphology and self-assembly behaviour. In addition, it was observed that further purification of CNCs, using Soxhlet extraction in ethanol, had minimal impact on nanoparticle properties and is unlikely to be necessary for many applications. Overall the current standing of industrially produced CNCs is positive suggesting that the evolution to commercial scale applications will not be hindered by CNC production. Composition Percentage C1 C2 C3

Cellulose, Sep 5, 2017

The recent intensification of industrially produced cellulose nanocrystals (CNCs) and cellulose n... more The recent intensification of industrially produced cellulose nanocrystals (CNCs) and cellulose nanofibrils has positioned nanocelluloses as promising materials for many water-based products and applications. However, for nanocelluloses to move beyond solely an academic interest, a thorough understanding of their interaction with water-soluble polymers is needed. In this work, we address a conflicting trend in literature that suggests polyethylene glycol (PEG) adsorbs to CNC surfaces by comparing the adsorption behaviour of PEG with CNCs versus fumed silica. While PEG is known to have strong hydrogen bonding tendencies and holds water tightly, it is sometimes (we believe erroneously) presumed that PEG binds to cellulose through hydrogen bonding in aqueous media. To test this assumption, the adsorption of PEG to CNCs and fumed silica (both in the form of particle films and in aqueous dispersions) was examined using quartz crystal microbalance with dissipation, isothermal titration calorimetry, rheology and dynamic light scattering. For all PEG molecular weights (300-10,000 g/mol) and concentrations (100-10,000 ppm) tested, strong rapid adsorption was found with fumed silica, whereas no adsorption to CNCs was observed. We conclude that unlike silanols, the hydroxyl groups on the surface of CNCs do not readily hydrogen bond with the ether oxygen in the PEG backbone. As such, this work along with previous papermaking literature supports the opinion that PEG does not adsorb to cellulose surfaces.

Nanoscale, 2016

The production of well-dispersed reinforced polymer nanocomposites has been limited due to poor u... more The production of well-dispersed reinforced polymer nanocomposites has been limited due to poor understanding of the interactions between components. Measuring the cohesive particle-particle interactions and the adhesive particlepolymer interactions is challenging due to nanoscale dimensions and poor colloidal stability of nanoparticles in many solvents. We demonstrate a new cohesive interaction measurement method using cellulose nanocrystals (CNCs) as a model system; CNCs have recently gained attention in the composites community due to their mechanical strength and renewable nature. Multi-wavelength surface plasmon resonance spectroscopy (SPR) was used to monitor the swelling of CNC thin films to elucidate the primary forces between CNCs. This was achieved by measuring swelling in situ in water, acetone, methanol, acetonitrile, isopropanol, and ethanol and relating the degree of swelling to solvent properties. Films swelled the most in water where we estimate 1.2-1.6 nm spacings between CNCs (or 4-6 molecular layers of water). Furthermore, a correlation was found between film swelling and the solvent's Hildebrand solubility parameter (R 2 =0.9068). The hydrogen bonding component of the solubility parameters was more closely linked to swelling than the polar or dispersive components. The films remained intact in all solvents, and using DLVO theory we have identified van der Waals forces as the main cohesive interaction between CNCs. The trends observed suggest that solvents (and polymers) alone are not sufficient to overcome CNC-CNC cohesion and that external energy is required to break CNC agglomerates. This work not only demonstrates that SPR can be used as a tool to measure cohesive particle-particle interactions but additionally advances our fundamental understanding of CNC interactions which is necessary for the design of cellulose nanocomposites. 3) Advancing the field of reinforced nanocomposites requires methods to extract and predict these interactions in a variety of systems. Cellulose nanocrystals (CNCs) are an abundant and sustainable rod-shaped nanomaterial that has recently been used in biomedical devices, 4-6 as rheological modifiers, 7,8 emulsion stabilizers 9-12 and many other composite applications. 13-17 Depending on the cellulose source (e.g., wood, cotton, bacteria, algae or tunicate) CNCs range from 100-1000 nm in length and 5-20 nm in cross-section and are commonly extracted through sulfuric acid hydrolysis. 16,18,19 Although, applications span several fields, the potential for CNCs to act as reinforcing agents in polymer matrices is widely discussed. 15 Analytical models and experimental measurements report a longitudinal Young's modulus that ranges from 56-220 GPa and a density of 1.5-1.6 g/cm 3. 15 Currently, the major hurdle limiting CNC reinforced nanocomposites is the hydrophilic nature of the particles. High

John Wiley & Sons, Inc. eBooks, Feb 22, 2013

Industrial & Engineering Chemistry Research, Dec 27, 2017

This work compares solvent cast poly(ethylene oxide) (PEO) nanocomposites reinforced with cellulo... more This work compares solvent cast poly(ethylene oxide) (PEO) nanocomposites reinforced with cellulose nanocrystals (CNCs) and fumed silica. Mechanical properties and crystallization behaviour were investigated over a range of polymer molecular weights (10 000-100 000 g/mol) and particle loadings (1-10 wt.%). Polymer adsorption to CNCs and fumed silica was found to alter PEO undercooling and inhibit crystal nucleation. Atomic force microscopy revealed PEO adsorbs to CNCs in a shish-kebab morphology that is readily incorporated into the crystalline domains of the polymer. Tensile testing and nanoindentation showed that the Young's modulus increased by more than 60% for CNC reinforced nanocomposites, and that the Halpin-Kardos model could effectively describe the mechanical properties. Fumed silica reinforced nanocomposites were fit to the Guth-Gold micromechanical model using effective particle volume fractions. Although only solvent cast nanocomposites were investigated, this work provides new insight into the interactions that control dispersion, crystallization and mechanical reinforcement.

Journal of Applied Polymer Science, Oct 10, 1993

The plasticizing effect of n‐pentane on the rate of bulk free radical polymerization of styrene a... more The plasticizing effect of n‐pentane on the rate of bulk free radical polymerization of styrene and molecular weight distribution development has been modeled on the basis of the free volume theory for both monofunctional and bifunctional initiation. A strong decrease in the reaction rate in the late stages of the polymerization, due to the displacement of the onset of the gel effect, has been observed for both types of initiation. This decrease in the polymerization rate limited the terminal conversion to values well below 100% for mono‐functional initiation. However, in bifunctionally initiated polymerization, terminal conversions close to 100% were obtained in spite of the decrease in reaction rate. Contrary to what was expected, the molecular weight distribution obtained at terminal conversion was almost completely insensitive to these changes in polymerization rate. This phenomenon is explained in terms of limited transfer to monomer reactions when n‐pentane is present in the system. In suspension polymerization, the limiting conversion and plasticizing effects of n‐pentane in monofunctionally initiated systems, caused enhanced coalescence leading to suspension set‐up. In bifunctionally initiated systems this enhanced coalescence was completely overcome by the short duration of the particle growth stage, owing to high polymerization rates, and stable suspensions were achieved. For these systems the particle size distributions obtained were similar to that of suspension polystyrene without n‐pentane. © 1993 John Wiley & Sons, Inc.

The use of submicron-particles to enhance properties of polymeric materials is a widely used prac... more The use of submicron-particles to enhance properties of polymeric materials is a widely used practice in many industries, such as, plastics, coatings, adhesives, elastomers, thermosetting composites, etc. From a general frame of reference, the rheological, mechanical, thermal, optical, and electrical performance of particle-polymer composites is governed by two main physical parameters, namely: the state of particle dispersion in the polymer matrix, and the particle-matrix interfacial strength. In this work, the design of Cabot’s submicron-particles along the axes of primary particle size, fractal dimension, and surface chemistry is described in terms of a simple model for particle-polymer and particle-particle interactions based on surface energy measurements. This model allows predictive mapping of particle-polymer systems in phase diagrams that anticipate the state of particle dispersion and interfacial strength for a large range of particle-polymer systems. Several examples are given on the use of this approach in the design of “self-dispersible” or “self-assembling” particles to tailor the rheological, mechanical, thermal, optical, or electrical performance of particle-polymer nano-composites used in coatings, engineering plastics, elastomers, and structural adhesive applications. The design and use of a micro-fluidic device to validate model predictions is also discussed

The Society of Rubber Science and Technology, Japan, 2016

L'invention porte sur un procede de fabrication d'une resine epoxyde avec une fonctionnal... more L'invention porte sur un procede de fabrication d'une resine epoxyde avec une fonctionnalite amine en continu par une premiere zone de reaction dans laquelle une resine a fonctionnalite epoxyde est fabriquee par addition par ouverture de cycle, une deuxieme zone de reaction dans laquelle la resine est mise a reagir avec une amine pour fabriquer un produit a fonctionnalite epoxyde et une troisieme zone de reaction dans laquelle le produit a fonctionnalite epoxyde est mis a reagir avec une amine pour fabriquer la resine epoxyde avec une fonctionnalite amine. Dans d'autres modes de realisation, un peu d'amine peut etre ajoutee dans la premiere zone de reaction pour produire un produit a fonctionnalite epoxyde, avec elimination de la deuxieme zone de reaction, ou la totalite du reactif amine peut etre ajoutee dans la premiere zone de reaction pour produire un produit a fonctionnalite amine, avec elimination a la fois de la deuxieme zone de reaction et de la troisieme zon...

A thermoplastic composition of high flowability comprising: (a) a host polymer; and (b) a flow mo... more A thermoplastic composition of high flowability comprising: (a) a host polymer; and (b) a flow modifier polymer having an average molecular weight weighted less than 15,000, the modifier polymer at least one monomer of (meth) acrylate and at least one vinyl aromatic monomer comprising wherein said composition is characterized by an energy difference relative (RED) between the flow modifier and the host of less than 2.2, an index of melt flow at least 5 percent higher than the host polymer, Izod impact strength polymer kerf of no more than 40% less than the host polymer, a temperature of heat deformation of not more than 10 ° C less than the host polymer and a Vicat softening temperature of no more than 10 ° C less than the host polymer, and the flow modifier polymer is not a polymer of diene-based graft polymer or another rubber based.

Epoxy-functional, styrene-acrylic polymers with low molecular weight, high functionality (> 4)... more Epoxy-functional, styrene-acrylic polymers with low molecular weight, high functionality (> 4) and tailored polydispersity have been designed, synthesized and commercialized to be used as chain extenders or recycling aids PET and other polyesters. Dramatic increases in molecular weight, mechanical, and rheological properties of virgin, reprocessed, and post-consumer recycled polyesters are achieved without the incidence of gellation. Erema’s VacuremaTM recycling equipment is well-suited to processing the additive, and can improve efficiency over 400% Screw selection is shown to be especially important.

Une composition polymere a utiliser dans une contention plastique comprend un extenseur de chaine... more Une composition polymere a utiliser dans une contention plastique comprend un extenseur de chaine, un agent de modification du comportement aux chocs, et un polymere de condensation, l’extenseur de chaine etant le produit de polymerisation de : (i) un monomere (meth)acrylique a fonction epoxy, et (ii) un monomere styrenique et/ou (meth)acrylique. L’extenseur un chaine a un poids equivalent d’epoxy allant d’environ 180 a environ 2800, une valeur de fonctionnalite epoxy moyenne en nombre (Efn) inferieure a environ 30, une valeur de fonctionnalite epoxy moyenne en poids (Efw) de jusqu’a environ 140, et une valeur du poids moleculaire moyen en nombre (Mn) inferieure a 6000, au moins une partie de l’extenseur de chaine reagit avec au moins une partie du polymere de condensation, pour produire un polymere de condensation a chaine allongee.

Current Opinion in Colloid & Interface Science, 2017

A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable... more A piqued interest in nanocellulose has recently arisen due to the growing need to use sustainable and renewable materials in place of those that are derived from petrochemical resources. Although current commercial uses of nanocellulose remain limited, research over the past two decades demonstrates numerous applications including reinforcing agents in polymer and cement composites, coatings, foams, gels, tissue scaffolds, and rheological modifiers, amongst others. Because of the hydrophilic nature of nanocellulose many of the potential uses will likely be in water-based formulations or employ water-based processing methods. Thus understanding the interactions between nanocellulose and water-soluble polymers is critical. Although polyelectrolyte adsorption to cellulose is well understood, adsorption of non-ionic polymers is less clear, with hydrogen bonding often cited as a governing factor. Recent work suggests that in fact hydrogen bonding does not play a significant role in nanocellulose systems, and that nonionic polymer adsorption is largely entropically driven. Herein we review current literature that investigates non-ionic polymer adsorption to cellulose nanocrystals (CNCs) and draw upon previous papermaking research to better understand the mechanisms involved. Additionally we analyze recent work that compares the adsorption of polyethylene glycol (PEG) to CNCs and fumed silica that provides further insight into this phenomenon. Our findings, along with current literature, suggest that hydrogen bonding does not significantly impact polymer adsorption in aqueous media despite reports to the contrary.