Douglas W. Bousfield

Formation of calcium carbonate particles by direct contact of Ca(OH)2 powders with supercritical CO2

A novel method to obtain a high conversion of Ca(OH)2 powder to CaCO3 is reported. The method uses supercritical CO2 containing water that is passed over the dry Ca(OH)2 powder. Conversions greater than 98% are obtained. The dominant crystal structure is calcite. The process has the advantages of the conventional solution based process in terms of high conversion and the advantages of a gas–solid based process in that dry, non-agglomerated particles are obtained by simple venting of the solvent.

Production and Characterization of Cellulose Nanofibers from Wood Pulp

Cellulose nanofibers with a size range of 5–100 nm have the potential to be a low cost renewable material that has application in a range of products. However, current chemical methods to produce crystalline nanofibers suffer from low yields and high chemical costs, while mechanical methods require high energy costs. Methods to lower the energy costs of the mechanical methods have not been well documented in the literature. A bleached softwood kraft pulp was processed using a mechanical dispersion mill and a homogenizer to produce cellulose nanofibers. Two different commercial enzymes were used to pretreat the wood fibers before the mechanical treatments. The resulting nanofibers were characterized by light microscopy, atomic force microscopy, and inverse gas chromatography. Results indicate that the dispersion mill does not affect the overall pulp fiber fibrillation, but does help prepare the sample for the homogenizer. Most fibrillation occurs after three passes through the homogenizer. The enzyme pretreatment has little effect on the size of the fibers, but does allow for higher solids to pass through the homogenizer without clogging. The dispersion component of surface energy of the resulting nanofibrils is impacted by the type of enzyme used. The measurement of acid–base properties proved to be challenging using current IGC experimental protocols.

Rheology of cellulose nanofibers suspensions: Boundary driven flow

Cellulose nanofibers (CNFs) are an exciting new renewable material produced from wood fibers. Even at low solids content, CNF-water suspensions have a complex rheology that includes extreme shear-thinning as well as viscoelastic properties and a yield stress similar to other suspensions of nanoscale particles. When characterizing the rheology of CNF suspensions, the measurement method may influence the results due to a water layer expected at the boundary, but it is unclear how the behavior near walls influences the measurement method. Parallel-plate, Couette, and vane geometries were used to compare yielding and flow of CNF suspensions obtained by steady-state shear and oscillatory rheological measurements. Five different techniques were compared as methods to obtain a yield stress. Cone and plate geometries were found to lead to sample ejection at low shear rates: Floc-floc interactions can explain this ejection. The suspensions violated the Cox-Merz rule by a significant amount; this behavior has been explained in the past as weak gel structures that break down in shear, but for this material it seems that the acting mechanism involves the formation of a water-rich layer near the solid boundaries in steady shear, while for oscillatory tests, these layers do not form. For suspensions lower than 3% solids, the yield stress measured by different procedures was within 20% of each other, but for high solids suspensions, differences between the methods could be as large as 100%; the water-rich layer formation likely is the cause of these results. Oscillatory methods are suggested as a method to obtain yield stress values for this type of material. The Couette geometry data were below the power-law lines fitted to the parallel-plate geometry data from steady-shear measurements perhaps again attributable to different water-rich layers that form in these different geometries.

The importance of adsorbed cationic surfactant structure in dictating the subsequent interaction of anionic surfactants and polyelectrolytes with pigment surfaces

Abstract The adsorption dynamics of the cationic surfactant cetyltrimethylammonium bromide (C16TAB) at the TiO2–water interface was investigated using Fourier transform infrared–attenuated total reflection spectroscopy (FTIR–ATR). Specifically, the response of the adsorbed C16TAB to the anionic surfactant sodium dodecyl sulfate (SDS) is used to discern the structure of the adsorbed C16TAB at the hemimicelle concentration (HMC). In this low concentration regime C16TAB is shown to adsorb as isolated clusters with a ‘defective’ bilayer structure. However, these bilayer structures can be effectively transformed into monolayer structures through the interaction with the non-adsorbing polyelectrolyte sodium polyacrylate (NaPA). It is shown that the structure of the adsorbed C16TAB layer, and not the amount of adsorbed surfactant, dictates the subsequent adsorption of anionic species on negatively charged TiO2 particles.

The influence of substrate absorbency on coating surface chemistry

Abstract The composition of the top surface of a coating layer can influence its functional properties or subsequent processing steps. The effect of the substrate absorbency on the coating surface chemistry is reported. Different coating systems containing a kaolin clay pigment, fine or coarse precipitated calcium carbonates, and a common latex binder were examined. The influence of a soluble polymer added into the coating was characterized. The surface chemistry was measured with attenuated total internal reflectance (ATR) and X-ray photoelectron spectroscopy (XPS). Absorbent substrates generate bulky coatings with high voids and low gloss. Rapid dewatering by the absorbent substrate pulls the small particles, like latex binder, away from the top layers causing a low latex concentration at the surface. On non-absorbent substrates, the addition of the soluble polymer generates coating layers with higher void volume, lower gloss, and lower latex concentrations at the coating surface. However, on absorbent substrates, polymer addition causes coatings with lower void volumes and higher gloss. In this case, the rapid dewatering and mobility of particles is reduced by the polymer, which helps to retain the small particles at the surface. As a result, latex concentration at the surface increases with polymer addition on absorbent substrates.

Shear-thinning predictions from particle motion modeling

A Stokesian dynamics model is presented to predict suspension viscosity and microstructure for concentrated suspensions. The influence of electrostatic repulsive forces, London–van der Waals attractive forces, and boundary interactions on the degree of shear-thinning is reported. Three different mechanisms for shear-thinning are described and quantified. The degree of shear-thinning caused by Brownian motion is well predicted by using random and layered structures. Shear-thinning for repulsive forces between particles is caused by the “melting” or breakup of an ordered or semicrystalline configuration as the shear rate increases. For suspensions flocculated into a secondary minimum, shear-thinning is produced by breakup of particle aggregates as the hydrodynamic forces dominate the interparticle forces. At high concentrations, the dispersed and flocculated suspensions can form slip planes that reduce suspension viscosity. Rough walls increase the viscosity predictions by an order of magnitude and cause th...

The leveling of coating defects with shear thinning rheology

A one-dimensional model is proposed to predict the leveling of coating defects or irregularities on a planar surface. Though shear thinning rheology is the focus of this paper, any viscous non-Newtonian rheology can be included in the model. Surface tension, gravity and viscous forces are accounted for in the model. A novel numerical technique is presented to obtain solutions of the model. Results agree with a full two-dimensional solution of the flow field obtained with a spectral element method. A new dimensionless group is identified which indicates the significance of shear-thinning rheology. Defects are made with a notched blade used to coat pigmented liquids on polymer films. The defect shapes are obtained at different times by drying under infrared. The dried surface is characterized with a stylus profilometer. The surface profiles and the final amount of leveling compare well with the model predictions.

Prediction of suspension viscoelasticity through particle motion modeling

Abstract A modified Stokesian dynamics technique is used in an oscillatory shear fleld to obtain the elastic and storage modulus of the suspension of spherical particles in a Newtonian liquid. Electrostatic or steric repulsive forces between suspended particles result in a viscoelastic behavior of a concentrated suspension. The mechanism for energy storage is a particle microstructure phenomenon: the compression of the electrostatic potential by hydrodynamic forces stores energy.

Modeling of rheological properties of coating colors

The rheology of model suspensions has been characterized by standard experiments and predicted from Stokesian dynamics (SD) computer simulations. Suspensions of spherical monodisperse polystyrene latex particles (average diameter 0.45 μm) are prepared in aqueous solutions of carboxymethyl cellulose (CMC) at different concentrations and molecular weights. The rheological measurements are compared with viscosity predictions of a SD model that includes electrostatic and van der Waals forces. A new method is proposed to include boundary roughness in the SD model. The model is able to predict the correct steady shear viscosity as a function of shear rate, CMC concentration, and molecular weight. The degree of shear thinning, given by the slope of the viscosity curves, is well predicted by the model. Good quantitative agreement can be obtained if the model results are shifted along the shear rate axis by a factor of 50. The microstructural mechanisms responsible for the shear thinning are shown and described. N...

Production and Characterization of Laminates of Paper and Cellulose Nanofibrils

A novel laminate system comprising of sheets of paper bound together using cellulose nanofibrils (CNF) is manufactured and characterized. Bonding properties of CNF were first confirmed through a series of peeling tests. Composite laminates were manufactured from sheets of paper bonded together using CNF at two different consistencies, press times, and press temperatures. Mechanical properties of the laminates in tension and bending were characterized and the results were statistically analyzed. Elastic modulus and strength results met or exceeded those of a short glass fiber reinforced polypropylene and various natural fiber-filled polypropylene composites as well as some wood and paper based laminates. Stiffness properties, assuming perfect bonding within the laminates, were successfully estimated through a classical laminated plate theory (CLPT) with only 2-10% variation compared to experimental results. Laminates, together with CNF-peeled surfaces, were observed and qualitatively analyzed by SEM imaging. Physical properties, namely, water absorption and thickness swelling were measured. Swelling was controlled by the addition of a small percentage of a cross-linking additive.