Study of the rheology of aqueous radiation curable polyurethane dispersions modified with associative thickeners

The chemistry of radiation curable polyurethane dispersions is outlined with an emphasis on the microstructure of the aqueous polymer dispersion and the possible interactions with associative thickeners. The steady-shear flow was studied for two model dispersions prepared from the same unsaturated polyurethane but showing significantly different particle size distributions. A hydrophobically modified ethoxylated urethane (HEUR) associative thickener with a linear structure was incorporated at different amounts to the dispersions with varying particle volume fractions. The steady-state viscosity at 25 and 10 °C was always reached quickly after instant flow rate changes so that no significant thixotropic effects were reported within the experimental timescale. Without thickener, the flow curves of the two model dispersions exhibited a Newtonian behavior except at the highest volume fractions where shear thinning became apparent. The maximum packing values determined from the Krieger–Dougherty relationship were essentially the same for the two systems. In the presence of thickener, the flow curves were characterized by a Newtonian plateau followed by a marked shear thinning region even at low particle volume fractions. This behavior typically suggests the formation of a physical network between polyurethane particles and thickener molecules partly adsorbed onto the polymer surface. The zero-shear viscosity of the two dispersions was compared with respect to: (i) particle volume fraction and (ii) particle surface area at different HEUR concentrations. At a given volume fraction, the particle size affects the viscosity of thickened models. As a corollary, a relationship is found between the particles size and the level of thickener required to reach a target viscosity. This study offers practically relevant data in terms of application conditions and provides a better insight into the thickening protocol.     

The engineering rheology of liquid explosives as highly concentrated emulsions

Rheological properties of liquid explosives are summarized and discussed in this paper. Liquid explosives are highly concentrated emulsions by their physical nature. During the internal phase, it is an aqueous supersaturated solution of mainly ammonium nitrate which is a useful component of a multi-component system, and at the continuous phase it is a solution of emulsifier in hydrocarbon oils. Liquid explosives demonstrate a complex set of properties characteristic for highly concentrated emulsions, such as visco-plasticity, existence of the yield stress, thixotropy (or time-dependent behavior), non-Newtonian flow at stresses exceeding the yield stress. Rheological properties depend on the concentration of internal phase, size of droplets, and the nature of the used surfactant. Stability of these materials is determined mainly by the tendency of an aqueous solution to crystallization at prolonged storage, though shearing does not influence on phase separation. Wall slip is absent in flow of liquid emulsions through tubes. Therefore, it allows us to make reliable predictions on the output vs. pressure dependence for real technological practice.     

Dynamics and rheology of entangled linear polymers

In order to describe the dynamics of the linear polymer in monodisperse melts, we present the so-called reaction-diffusion type equation that contains contributions from reptation and contour-length fluctuation based on the tube model. The relaxation function calculated from this equation is in good agreement with the experimental results of the dielectric relaxation function and also gives the stress relaxation function in binary blends by use of semi-empirical scheme called double reptation. We add advection term to this equation in order to predict the nonlinear rheological properties of steady shear. The calculated shear stress and the first normal stress difference at steady state agree well with the measurements.     

Proton saturation and rheological properties of smectite dispersions

Proton-saturated dispersions of the <2-μm fractions of five smectites were prepared. Potentiometric titration data of freshly saturated and autotransformed samples were analysed by calculating proton affinity distribution curves to distinguish different proton interacting sites. Sites with pK values of 2.8 and 11.3 were assigned to protons exchanged for sodium ions and deprotonisation of silanol groups, respectively. Hydrated aluminum ions in freshly proton-saturated dispersions were characterized by pK6. This group of weakly acidic centers also included oligomeric hydroxoaluminum cations because the amount of these sites increased during autotransformation and was accompanied by a shift to pK5.5. The freshly prepared proton-saturated dispersions showed low pH values (2.6), and the particles interacted by edge(+)/face(−) contacts. This increased the viscosity in comparison to the sodium forms at pH7, and, depending on the smectite, yield values between 10 and 400 mPa were observed. Autotransformation removed all sites with pK2.8, reduced the viscosity, the yield value (mostly <10 mPa), and the flow behaviour approached that of the sodium smectite dispersions at pH7. The cause is enrichment of aluminum and/or oligomeric hydroxoaluminum cations in the solution and Stern layer, which leads to fragmentation of the networks into smaller stacks of more densely packed particles.     

Ammonium phosphate slurry rheology and particle properties—The influence of Fe(III) and Al(III) impurities, solid concentration and degree of neutralization

Ammonium phosphate slurries are produced from impure phosphoric acid that contains Fe(III), Al(III) and Mg(II) ions. The insolubility of these metal ions and the onset of solid formation determined as a function of pH or mole ratio (MR) of ammonia to phosphoric acid were consistent with the trend for the pH of formation of the first hydrolysis product that decreases in the following order: Fe(III)<Al(III)<Mg(II). The hydrolysis products of Fe(III) formed at pH>2.0 or MR>0.5 initiate ammonium phosphate crystallization, reduce the size of particles formed and generate attractive interparticle forces. Similarly, the Al(III) hydrolysis products formed later at pH>2.6 MR>0.7), will also initiate further crystallization, adsorb on particles and produce attractive forces. The attractive forces and the high number concentration of particle—particle interactions are responsible for the increased viscosity and non-Newtonian flow behavior displayed at increasing Fe(III) and Al(III) concentration. Mg(II) ions are not hydrolyzed at MR<1.0 so its effect on rheology is negligible and its effect at MR<1.0 is also small as its concentration is much smaller than that of Fe(III) and Al(III) ions. The change in slurry viscosity with the degree of neutralization is also explained in terms of particle size distribution, solubility and solids concentration variations.     

Crystal morphology of organic pigments and rheology of dispersions in ink and paint media

The purpose of this work is to establish relationships between physico-chemical character of pigments and rheological behaviour of dispersions under steady shear conditions. It has been found that the approximately cube-shaped crystals of CI Pigment Yellow 13-type pigments disperse substantially as individual crystals in (highly viscous) lithographic ink media; strength of structure and plastic viscosity relate simply to number concentration of crystals and area of the pigment/medium interface, respectively. Interpretation of data for dispersions of Red 57.1 pigments in similar media is complicated by persistent face-to-face aggregation of their rectangular plate-shaped crystals. In dispersions of metal-free monoazo pigments (Yellows 1 and 74, Reds 3 and 112) in decorative paint media (relatively low viscosity) strength of structure shows a markedly increased dependence on pigment concentration above a critical concentration. This concentration is different for each pigment and is determined primarily by crystal shape, the less cube-shaped the crystals the lower the critical concentration. Plastic viscosity is dependent upon area of the pigment/medium interface and thickness of adsorbed layer of paint medium.     

Use of novel polyetheralkanolamine comb polymers as pigment dispersants for aqueous coating systems

The adsorption of a series of polyetheralkanolamine comb polymers characterized by a different length of the hydrophilic tail has been investigated at the carbon black/water interface by measuring adsorption isotherm, contact angle, wetting rate, zeta potential, and particle size distribution. Zeta potential measurements and adsorption layer thickness results suggest that polyetheralkanolamines with high ethylene oxide (EO) content provide only steric stabilization and they adsorb at the interface with the ethylene oxide chains in a coil conformation. The thickness of the adsorbed layer increases with increasing EO units; however, the surface tension and interfacial tension decrease with increasing EO content. Adsorption isotherms show that most of the added polyetheralkanolamine adsorbs onto the carbon black and only a small amount stays in the water phase. When treated with a polyetheralkanolamine, carbon black dispersions show uniform (unimodal) and narrow particle size distribution with very small median sizes of about 0.10 μm. The pigment concentrates containing the polyetheralkanolamine show excellent color compatibility in various decorative commercial white paints containing a wide range of resins and exhibit low viscosity with nearly Newtonian flow behavior. Presented at the 2006 FutureCoat! Conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

The numerical simulation of some contraction flows of highly elastic liquids and their impact on the relevance of the Couette correction in extensional rheology

Existing experimental data on planar and axisymmetric contraction flows of constant-viscosity and shear-thinning elastic liquids have presented rheologists with some provocative challenges, some of which we hope to discuss in this paper by carrying out numerical simulations for various constitutive models. Amongst the questions we hope to address are the following:

1.

Why do existing numerical simulations for the Oldroyd B model fail to predict the significant increases observed in the Couette correction for Boger fluids?

2.

What are the roles of ‘normal stress differences’ and ‘extensional viscosity’ in determining the Couette correction?

3.

What is the future for contraction-flow experiments in providing a measure of ‘resistance to stretch’?

In order to make headway, we shall concentrate on the axisymmetric contraction-expansion 4:1:4 geometry with rounded corners, which from a numerical standpoint is easier to handle than the more popular 4:1 contraction geometry with sharp corners. (There is sufficient evidence in the experimental literature to indicate that the contraction-expansion geometry shows many of the features found in the 4:1 contraction geometry.)     

Studies on equilibrium swelling,dye adsorption,and dynamic shear rheology of polymer systems based on chitosan-poly(vinyl alcohol) and montmorillonite

Chitosan-poly(vinyl alcohol)/clay membranes were prepared by physical blending. These hybrid systems were characterized through infrared spectroscopy, microscopy, swelling, and oscillatory rheology. Adsorption of a commercial reactive dye by these membranes was further studied. Results showed that more stable blend membranes were formed due to the strong interaction in the polymers. These membranes showed substantial percent swelling in water and shrinking in saline solution. Adsorption analysis showed the ability of the blends to fix organic dyes, and to be used in liquid waste processing. In dynamic rheology, it was observed that all measured viscoelastic properties were influenced by polymer composition and clay content. For all samples, results show a typical behavior of an entangled system in the case of low concentrated macromolecular viscoelastic fluids. The dynamic moduli exhibited higher values for blends, compared with values of the pure polymers, which is an indication of good stability and tendency of gel formation.     

Synthesis and Evaluation of Bis-quaternary-Based Surfactants as Additives for Water-Based Mud

Two series of cationic gemini surfactants, alkanediyl-α,ω-bis[N,N-dimethyl alkyl (octyl or dodecyl)ammonium] dibromide (R-s-R; s = 6, 10, 12 and R = 8 and 12) were prepared and evaluated as additives for water-based mud. The chemical structures of the prepared surfactants were confirmed using FTIR and mass spectroscopy. Surface activity of these compounds has been studied and their surface properties including surface tension, emulsification power, critical micelle concentration, effectiveness, maximum surface excess and minimum surface area were determined. The results showed that the prepared compounds have significant surface activity, especially those of longer hydrophobic chain length. The prepared cationic gemini surfactants were evaluated as viscosifiers and filter loss additives for water-based mud formulated from local Na-montmorillonite clay. XRD analysis was carried out to the Na-montmorillonite clay to determine the interaction of the surfactants with inter layers of the clay structure. Rheological properties, gel strength, thixotropy, filtration properties and the effect of temperature on rheological properties of the water-based mud were studied. The results indicated that the gemini surfactants have a positive effect on the rheological and filtration properties of the Na-montmorillonite clay according to American Petroleum Institute specifications.     

Rheology,structure, and sintering of zirconia suspensions with pyrogallol-poly(ethylene glycol) as polymeric surfactant

Yttria-stabilized zirconia (YSZ) nanoparticles have been dispersed in water with pyrogallol-poly(ethylene glycol) polymer (i.e., Gallol-PEG) as surfactant. Fluid YSZ suspensions with an apparent viscosity  < 10² Pa s at a shear rate of 10² s^?1 have been prepared with a solids concentration of 45 vol.% for the 90-nm YSZ nanoparticles. Theoretical calculation of interparticle potentials indicates that the adsorbed polymer renders steric hindrance critical to the suspension stabilization. The concentrated YSZ suspensions exhibit shear-thinning flow over a broad shear-rate range, resulted from the weak attractive minimum (～2.7 k_BT) found between the neighbouring particles in close proximity. The Gallol-PEG concentration influences not only the suspension rheology but also the particle-packing structure and sintered density of the slip-casted YSZ compacts. The YSZ suspensions with an optimal Gallol-PEG concentration of 2 wt.% exhibit a low pore volume in the green state, facilitating hence densification (> 99% theoretical) upon subjected to sintering.     

Ionizable interpenetrating polymer networks of carboxymethyl cellulose and polyacrylic acid: Evaluation of water uptake

A semi interpenetrating polymer network (IPN) of carboxymethyl cellulose (CMC) and crosslinked polyacrylic acid (PAA) has been prepared and its water‐sorption capacity has been evaluated as a function of chemical architecture of the IPN, pH, and temperature of the swelling medium. The water uptake potential of the IPNs has also been investigated in inorganic salt containing aqueous solutions and simulated biological fluids. The IPN was characterized by IR spectral analysis, and the network parameters such as average molecular weight between crosslinks (M_c), crosslink density (q), and number of elastically effective chains (V_e) have been evaluated by water‐sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2054–2065, 2004     

Formation and characteristics of cationic-polymer/bentonite complexes as adsorbents for dyes

The adsorption of cationic polymer, i.e., epicholorohydrin-dimethylamine polyamine (EPI-DMA), on bentonite particles was investigated under various conditions of bulk polymer concentration, pH, inorganic salts, and temperature. The resulting high adsorption rate and alkaline solution (pH = 7–11) effect indicated a strong electrostatic interaction between the clay particles and EPI-DMA molecules. Addition of salt can also influence the adsorption of EPI-DMA onto bentonite by affecting the clay particle sizes, the polymer zeta potential and etc. The Freundlich and Langmuir isotherm models were employed and fit the experimental data well in the low EPI-DMA concentration range 0.5–5.0 mg L^− 1. The enthalpy implied by the temperature dependence of adsorption of EPI-DMA on bentonite is 7.93 kJ mol^− 1, suggesting that neither coordination exchange nor chemical bond forces exit in this system. In addition, at high temperatures, larger amounts of EPI-DMA were adsorbed by bentonite, which indicated that increased entropy in the dissolved EPI-DMA molecules contributes to adsorption. The X-ray diffraction (XRD) analysis showed that besides the EPI-DMA molecules intercalated between the layers of bentonite, excess polymer molecules were adsorbed onto polymer loops protruding from the surface of the complex. The TGA and corresponding DSC plots demonstrated that the EPI-DMA polymer had intercalated into the clay layers and thus the EPI-DMA/bentonite was more hydrophobic than natural bentonite. With the addition of EPI-DMA polymer, the negatively charged clay particles increased to a net positive charge and the capacity for dye removal also went up with increasing polymer contents in EPI-DMA/bentonite complexes.     

Sorption and desorption of water vapour by membranes of the polyelectrolyte complex of chitosan and carboxymethyl cellulose

Sorption of water vapour by chitosan/carboxymethyl cellulose polyelectrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake (W) on time was observed for W values lower than 0.5 g of water per gram of membrane. For higher values of W diffusion becomes controlled by the relaxation of the chains, and second-order kinetics is observed. An equation that satisfactorily reproduces this behaviour is proposed. Desorption experiments were carried out at different temperatures and the W versus time curves obtained exhibited the same general pattern and were also adjusted by this equation. The approximate average diffusion coefficients were evaluated at each temperature and the apparent activation energy for the diffusion process is reported.     

Preparation and release kinetics of carboxymethyl chitosan/cellulose acetate microspheres as drug delivery system

Carboxymethyl chitosan, a water soluble chitosan derivative, was prepared from chitosan using monochloroacetic acid. Carboxymethyl chitosan/cellulose acetate microspheres (CCM) were prepared using the method of W/O/W and emulsification solvent evaporation as drug delivery system. The CCMs prepared were spherical, free‐flowing, and nonaggregated with the smooth appearance and many small pores on the surface. All CCMs prepared had sustained release efficiency for acetaminophen and the optimal formulation was that carboxymethyl chitosan of 2.0% and 1360 KD. In addition, the release rate of drug from CCMs in dilute hydrochloric acid was much slower than that in phosphate buffer saline (pH 6.8) during 24 h. It is illustrated that the drug loaded in CCMs released slower in simulated gastric fluid than that in simulated intestinal fluid. Furthermore, the drug release data showed better fitness with the first order model which indicated that the drug release from CCMs was depended on the drug concentration in the polymeric networks. And the release of drug from CCMs indicated diffusion‐controlled drug release based on Fickian diffusion and accompanied with anomalous transport (i.e., non‐Fickian diffusion) according to the values obtained from Higuchi model and Peppas models. So it was shown that the CCMs might be an ideal sustained release system for acid‐labile drugs both for the solubility of carboxymethyl chitosan and the release media. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42152.     

Radiation-induced grafting of acrylamide and methacrylic acid individually onto carboxymethyl cellulose for removal of hazardous water pollutants

Carboxymethyl cellulose hydrogels were synthesized by grafting of acrylamide (AAm) and methacrylic acid (MAAc) individually with different concentrations onto carboxymethyl cellulose (CMC) using direct radiation grafting technique. It was found that for both Poly(CMC/AAm) and Poly(CMC/MAAc), the grafting yield and grafting ratio increase with the increasing monomer concentration. Also, it is noted that both grafting ratio and grafting yield of Poly(CMC/AAm) are higher than that of Poly(CMC/MAAc). The effect of different monomer concentrations on gel (%) and swelling behavior was studied. It is found that the increasing monomer concentration increases gel (%). For Poly(CMC/AAm) hydrogels, the swelling behavior decreases with increasing AAm concentration due to high crosslinking hydrogel formation, while as MAAc content increases, swelling behavior increases up to Poly(CMC/MAAc) 1:25 wt%. Swelling kinetics and diffusion mechanism indicate that the water penetration obeys non-Fickian transport mechanism. The structures and properties of the original CMC and the prepared Poly(CMC/MAAc) and Poly(CMC/AAm) were characterized using different analytical tools such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). This study provides a solution to the discharge of different pollutants from wastewater. The adsorption capacity of Poly(CMC/MAAc) and Poly(CMC/AAm) hydrogels toward heavy metals, Cu⁺² and Co⁺², dyes such as acid blue dye and methyl green, and organic contaminants such as 4-chlorophenol and 2,4-Dichlorophenoxy acetic acid has been investigated.     

Stability and rheological study of sodium carboxymethyl cellulose and alginate suspensions as binders for lithium ion batteries

Currently, the most widely used binder in batteries is polyvinylidene fluoride with N‐methyl‐2‐pyrrolidone used as a solvent. This solvent is flammable and toxic. Here, we focus on the suitability of using water‐soluble sodium alginate (Na‐alginate) and sodium carboxymethyl cellulose (Na‐CMC) as alternative biobased binder materials for the anodes of lithium ion batteries. It reduces the environmental impact of current manufacturing processes. However, control of the rheological characteristics of the binder whilst containing active and conductive additives is key for optimized processing. Here, we perform stability and rheological measurements of Na‐alginate and Na‐CMC solutions containing varying amounts of graphite and carbon black used as active and conductive materials, respectively. Compared with the benchmark Na‐CMC, the degree of flocculation shows that for the same concentration of binder in water, Na‐alginate suspensions are more stable. The rheology measurements show that Na‐alginate slurries have a higher viscosity than Na‐CMC at a shear rate of 50 s^?1 with that for a 1.5% of Na‐alginate binder being 1.26 Pa s while for Na‐CMC it was for 0.20 Pa s. The loss factor was lower for Na‐Alginate, between 2 and 3 against between 2.9 and 3.3 for Na‐CMC, showing a more developed network structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46217.     

The effect of water‐soluble polymers on rheology of microfibrillar cellulose suspension and dynamic mechanical properties of paper sheet

Rheological properties of fiber/polymer suspensions and dynamic mechanical analysis (DMA) of paper sheets containing the same polymers were measured. Correlations between viscoelastic properties of suspensions and strength of paper sheet are presented. Rheological properties of suspensions of microfibrillar cellulose (MFC) and a set of water soluble polymers were measured. Rheological properties of these complex fluids vary considerably depending on the added polymer. A suspension of fiber and carboxymethyl cellulose (CMC) exhibits a viscosity higher than the sum of the viscosity of the individual components in the suspension. In contrast, when cationic starch (CS) is used together with the fiber, the yielding behavior rather than the viscosity is characteristic of the suspension. Dynamic mechanical properties of paper sheets containing CMC or CS as additives were studied at different humidity levels. Different yielding behavior observed in oscillatory rheology can be correlated with straining behavior in dynamic mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Alginate and carboxymethyl cellulose in monolayer and bilayer films as wound dressings: Effect of the polymer ratio

In this study, we investigated different proportions of alginate and carboxymethyl cellulose (CMC) biopolymers in the formulation of films to act as wound dressings. With the casting method, monolayer and bilayer (BL) films were produced with alginate/CMC proportions (weight percentages) of 0:100 (0A), 25:75 (25A), 50:50 (50A), 75:25 (75A), and 100:0 (100A). Thin, homogeneous, and continuous films were obtained with glycerol and crosslinking with CaCl₂. The fluid uptake, film stability, and morphological, mechanical, thermal, and barrier properties were evaluated. A general tendency of the film characteristics was visualized: 50A had intermediary characteristics from both polymers; although the liquid behavior characteristics were improved with increasing CMC content, the mechanical properties worsened. When compared to the monolayer film (50A), the BL film 50A–BL demonstrated a better water vapor transmission rate. In this study, we demonstrated the necessity of varying the polymer concentrations to assist in the production of wound dressings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46941.