Nanocomposite materials from latex and cellulose whiskers

Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.     

Rate of deposition and interaction energy on deposition of polymethyl meth acrylate latex on fibers

Summary In order to study the deposition of polymethyl methacrylate latex on fabrics, viz, polyamide (Nylon 6), polyacrylonitrile (Vonnel), polyester (Tetoron), and cotton as a function of pH, the rates of deposition has been determined by the turbidity measurements, and the relation between the rate of deposition and the interaction energy is mainly considered.The rates of deposition on Vonnel fabric are scarcely influenced by the interaction energy. Those on Tetoron and cotton fabrics decrease with increasing the total interaction energy, but those on cotton fabric increase at the initial stage of deposition at low pH. The rates of deposition on Nylon fabric are interpreted satisfactorily by potentials of fabric and latex particles rather than the interaction energy. It is suggested that the deposition may be influenced by the characteristics of fiber, e.g., surface roughness, heterogeneity of electrostatic potential and absorption of water, in addition to the interaction energy.This paper is Part III in a series on Interfacial electrical studies on the deposition of polymer latexes onto fabrics and the removal of these deposited latexes Part II: H. Tamai, T. Hakozaki, and T. Suzawa, Colloid Polymer Sci.258, 870 (1980).     

Physicomechanical properties of nanocomposites based on cellulose nanofibre and natural rubber latex

Cellulose nanofibres (CNF) with diameter 10–60 nm were isolated from raw banana fibres by steam explosion process. These CNF were used as reinforcing elements in natural rubber (NR) latex along with cross linking agents to prepare nanocomposite films. The effect of CNF loading on the mechanical and dynamic mechanical (DMA) properties of NR/CNF nanocomposite was studied. The morphological, crystallographic and spectroscopic changes were also analyzed. Significant improvement of Young’s modulus and tensile strength was observed as a result of addition of CNF to the rubber matrix especially at higher CNF loading. DMA showed a change in the storage modulus of the rubber matrix upon addition of CNF which proves the reinforcing effect of CNF in the NR latex. A mechanism is suggested for the introduction of the Zn–cellulose complex and its three dimensional network as a result of the reaction between the cellulose and the Zinc metal which is originated during the composite formation.     

Bridging flocculation of PEI-functionalized latex particles using nanocrystalline cellulose

Polystyrene microspheres were functionalized by covalent binding of 250 kDa linear PEI and ethanolamine, acting as a blocking agent, through bioconjugation with EDAC. The functionalized spheres were found to become less susceptible to salt-induced flocculation due to electrosteric stability, caused by the PEI chains at low NaCl concentrations, and at high salt concentration, by steric repulsion by the ethanolamine layer, which in combination with van der Waals attraction results in a shallow energy minimum and the formation of a few unstable aggregates. The latex aggregated in the presence of nanocrystalline cellulose (NCC) with varying efficiencies, depending on the ratio of NCC to latex particles in solution. Polyelectrolyte titration showed that each latex sphere contained about 15 grafted PEI chains. The fastest aggregation was detected when about half of these chains were covered by a single NCC particle.     

Metal-catalyzed release of supported boronic acids for C-C bond formation

The viability of solid-supported boronic acids as reagents for Suzuki couplings and nucleophilic additions to aldehydes and enones was successfully demonstrated. This metal-catalyzed cleavage strategy allows the synthesis of a series of functionalized biphenyl products, benzylic alcohols, and beta-substituted ketones.     

Effect of dextran on the deposition of latex on a glass surface

Adsorption of dextran on hairy latex particles affects the electrophoretic mobility differently, depending on the salt concentration. At a low salt concentration, dextran adsorbs between the hairs, and the expected decrease of mobility with dextran concentration is observed. When the thickness of the dextran layer is greater than the length of the hairs, the anomalous deposition of latex on glass, thought to be caused by the hairs, is eliminated.     

Atomic layer deposition of metal-oxide thin films on cellulose fibers

Abstract

Atomic layer deposition (ALD) is a vapor-phase technique capable of producing inorganic thin films with precise control over the thickness of the film. The ALD method offers high precision in the design of advanced 3D nanostructures. In this article, silica and alumina thin films have been grown over fibers of cellulose by the ALD process. The morphology and the chemical composition of the fabricated thin films are characterized, as well as their thermal durability through elevated temperatures. Moreover, XPS is used to confirm the phases of the alumina nanofilms and to further understand the deposition process on the cellulose microfibers.     

DMA analysis and wood bonding of PVAc latex reinforced with cellulose nanofibrils

Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied. The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites, increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state, but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition (tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1.     

The electrokinetic study on the deposition of polystyrene latex onto Nylon fiber

Theζ-potentials of anionic polystyrene latex particles and Nylon fiber were measured as a function of concentration of NaCl, Na₂SO₄, Na₃PO₄ and CaCl₂, and the deposition of the latex onto Nylon fiber was considered. In the range of ionic strength from 5×10^?4 to 5×10^?2 where the rate of deposition was measured, the increase of electrolyte concentration resulted in the slight increase due to the adsorption of negative ion in the negativeζ-potentials of the latex particles. However, the rate of deposition increased with increasing concentration of electrolyte because of the decrease due to compression of the electrical double layer in the negativeζ-potentials of Nylon fiber. This result was supported by the fact that the maximum repulsive energy between electrical double layers of a latex particle and Nylon fiber decreased, as predicted theoretically, with decreasing ratio of theζ-potential of the fiber to that of the latex particle.     

Multicolor saccharide-sensing chips based on boronic acid-containing thin films showing stepwise release and binding of dyes

A novel saccharide sensor that shows a distinct color change resembling a "traffic signal" was developed. By copolymerizing a boronic acid monomer and an amine monomer on a glass plate, a boronic acid-containing thin film was obtained. After adsorbing anionic blue and yellow dyes, the thin film was immersed in aqueous saccharide solutions containing a cationic red dye. As saccharide concentration increased, the thin film changed its color from green to red via yellow. Origin of the distinct color change was attributed to a stepwise release and binding of dyes.     

Organotrifluoroborate hydrolysis: boronic acid release mechanism and an acid-base paradox in cross-coupling

The hydrolysis of potassium organotrifluoroborate (RBF(3)K) reagents to the corresponding boronic acids (RB(OH)(2)) has been studied in the context of their application in Suzuki-Miyaura coupling. The "slow release" strategy in such SM couplings is only viable if there is an appropriate gearing of the hydrolysis rate of the RBF(3)K reagent with the rate of catalytic turnover. In such cases, the boronic acid RB(OH)(2) does not substantially accumulate, thereby minimizing side reactions such as oxidative homocoupling and protodeboronation. The study reveals that the hydrolysis rates (THF, H(2)O, Cs(2)CO(3), 55 °C) depend on a number of variables, resulting in complex solvolytic profiles with some RBF(3)K reagents. For example, those based on p-F-phenyl, naphthyl, furyl, and benzyl moieties are found to require acid catalysis for efficient hydrolysis. This acid-base paradox assures their slow hydrolysis under basic Suzuki-Miyaura coupling conditions. However, partial phase-splitting of the THF/H(2)O induced by the Cs(2)CO(3), resulting in a lower pH in the bulk medium, causes the reaction vessel shape, material, size, and stirring rate to have a profound impact on the hydrolysis profile. In contrast, reagents bearing, for example, isopropyl, β-styryl, and anisyl moieties undergo efficient "direct" hydrolysis, resulting in fast release of the boronic acid while reagents bearing, for example, alkynyl or nitrophenyl moieties, hydrolyze extremely slowly. Analysis of B-F bond lengths (DFT) in the intermediate difluoroborane, or the Swain-Lupton resonance parameter (?) of the R group in RBF(3)K, allows an a priori evaluation of whether an RBF(3)K reagent will likely engender "fast", "slow", or "very slow" hydrolysis. An exception to this correlation was found with vinyl-BF(3)K, this reagent being sufficiently hydrophilic to partition substantially into the predominantly aqueous minor biphase, where it is rapidly hydrolyzed.     

Peculiarities of the coagulation mechanism of a nanocrystalline cellulose hydrosol and a latex

Dynamic light scattering has been employed to study the coagulation kinetics of colloidal dispersion of nanocrystalline cellulose and SKS-27 ARK synthetic latex under the action of sodium chloride. It has been found that, when a system being coagulated is exposed to a mechanical action, aggregates almost cease to grow at some moment. It has been assumed that the first stage of coagulation is caused by the formation of strong contacts between primary particles and their agglomeration, while the second stage is realized via the interaction of residual hydration layers. It has been shown that, as the density of surfactant adsorption layers on the surface of latex particles is enhanced, the duration of the first stage increases, while the average hydrodynamic particle size decreases.     

Aligned cellulose nanocrystals and directed nanoscale deposition of colloidal spheres

Cellulose nanocrystals are aligned in wrinkled polydimethylsiloxane templates and transferred to polyethyleneimine-coated silica surfaces in a printing process similar to microcontact printing. The highly aligned nanorods were deposited onto the surfaces with a line-to-line distance of 225–600 nm without loss of alignment. It was also possible to repeat the transfer process on the same surface at a 90-degree angle to create a network structure. This demonstrates the versatility of the technique and creates more options for advanced multilayering of materials. To demonstrate that the surface properties of the anionic cellulose nanorods were unaffected by the transfer process and to prove the concept of functionalizing transferred particles, cationic latex particles were electrostatically self-assembled onto the cellulose nanorods. The directed deposition of these particles resulted in excellent site specificity and the highest resolution to date for controlled deposition of colloids on an electrostatically patterned surface.     

Anionic cellulose beads for drug encapsulation and release

Cellulose beads were prepared from water-based solvent and oxidised by modified Anelli’s reaction at 20– $80\,^\circ \hbox {C}$ for 2–48 h (Fig. 1). The maximum amount of anionic groups (AGs) was $1.85\,\hbox {mmol}\,\hbox {g}^{-1}$ . The distribution of AGs was verified by absorption of cationic dyes and imaging with confocal fluorescent microscopy. Structural changes were studied spectroscopically and with electron microscopy. Oxidation of the beads drastically increased the swelling capacity of air-dried beads. Uptake of model drug was more than doubled in never-dried beads. This is due to the changes in pore size distribution, mainly opening and widening of the closed pores and narrow cavities. Release profiles of the drug were studied at physiological pH of 7.4 and showed a controlled release rate independently of the amount of the drug encapsulated and amount of AGs.     

Deposition of nanosized latex particles onto silica and cellulose surfaces studied by optical reflectometry

Deposition of positively charged nanosized latex particles onto planar silica and cellulose substrates was studied in monovalent electrolyte solutions at pH 9.5. The deposition was probed in situ with optical reflectometry in a stagnation point flow cell. The surface coverage can be estimated reliably with island film theory as well as with a homogeneous film model, as confirmed with atomic force microscopy (AFM). The deposition kinetics on the bare surface was of first order with respect to the particle concentration, whereby the deposition rate was close to the value expected for a perfect collector. The efficiency coefficient, which was defined as the ratio of the experimental and theoretical deposition rate constants, was in the range from 0.3 to 0.7. Subsequently, the surface saturated and a limiting maximum coverage was attained (i.e., blocking). These trends were in qualitative agreement with predictions of the random sequential absorption (RSA) model, where electrostatic interactions between the particles were included. It was observed, however, that the substrate strongly influenced the maximum coverage, which was substantially higher for silica than for cellulose. The major conclusion of this work was that the nature of the substrate played an important role in a saturated layer of deposited colloidal particles.     

Controlled release of amoxicillin from bacterial cellulose membranes

Bacterial cellulose (BC), a natural polymer with unique physical and mechanical properties, has several applications in the biomedical field, including drug loading and controlled drug delivery. For this study, a Box-Behnken experimental design was employed as a statistical tool to optimize the release of a model drug, amoxicillin, from BC membranes. Independent variables studied were the concentration of the drug (X₁), the concentration of glycerol (X₂) and the concentration of a permeation enhancer (X₃). From the variables studied, drug concentration had the highest effect on drug release. Among the other independent variables, th linear and quadratic X₂ terms, the linear X₃ term and the interaction term X₂X₃ were found to affect the release of amoxicillin from bacterial cellulose membranes.

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The surface characterization of styrene-acrylamide copolymer latex particles and their deposition onto fibers

The surface characteristics of styrene-acrylamide (St-AAm) copolymer latex particles were investigated and their deposition onto polyamide (Nylon 6), polyester (polyethylene terephthalate) and polyacrylonitrile fibers was studied. Conductometric titrations and viscosity measurements of latex dispersions revealed the presence of a water-soluble polymer layer on the particle surface and the thickness of its polymer layer increased with increasing acrylamide fraction in a latex particle. The deposition rates of St-AAm copolymer latices onto Nylon 6 and polyester fibers increased with increasing acrylamide fraction and decreasing pH at a constant ionic strength. These deposition phenomena onto Nylon 6 and polyester fibers agreed qualitatively with prediction based on the electrokinetic data of the latices and the fibers. However, a participation of attractive interaction due to an increase in acrylamide fraction was also suggested.The deposition rate onto polyacrylonitrile fiber decreased with increasing acrylamide fraction in spite of a decrease in electrostatic repulsive interaction, and it was found that a specific large repulsive interaction acts between polyacrylonitrile fiber and St-AAm copolymer latex particles.This paper is part VIII in a series on Interfacial electrical studies on the deposition of polymer latexes onto fabrics and the removal of these deposited latexes. Part VII: Tamai H, Kimura I,Suaza T Coll Polym Sci 261: 661 (1983)     

Polystyrene latex deposition onto polyethylene film consecutively treated with cationic and anionic polymer

The effects of treating polyethylene (PE) film by consecutive adsorption of poly(diallyldimethylammonium chloride), polyDADMAC, followed by poly(sodium p-styrene sulfonate), PSS, on the deposition rate of aqueous polystyrene latex were investigated with the impinging jet technique. Rapid initial deposition occurred on films treated with polyDADMAC; however, significant blocking occurred. Deposition decreased with the concentration of polyDADMAC used to treat the PE film.

Film treatment with polyDADMAC followed by PSS to give an adsorbed polyelectrolyte complex gave decreased deposition rates. The molecular weight of PSS was not a significant variable in the range 5400–1 200 000. It was concluded that PSS increased the electrostatic repulsion between the PE film and the latex particles.     

Separation of 2-aminobenzoic acid-derivatized glycosaminoglycans and asparagine-linked glycans by capillary electrophoresis.

A capillary electrophoresis method was developed for the analysis of oligosaccharides combined with derivatization with 2-aminobenzoic acid. Glycosaminoglycan delta-disaccharides were effectively resolved on a fused-silica capillary tube using 150 mM borate, pH 8.5, as a running electrolyte solution. This analytical method was applied to the identification of glycosaminoglycan in combination with enzymatic digestion. The separation of N-glycans or glucose-oligomers was performed with a phosphate buffer containing polyethylene glycol or borate as an electrolyte solution. This method is expected to be useful in the determination of oligosaccharide structures in a glycoprotein.     

Cationic release behaviour of antimicrobial cellulose/silver nanocomposites

Silver nanoparticles (NPs) have received great attention, mainly due to their application as antimicrobial agents in diverse products, including textile- and paper-based materials. In this context, straightforward methodologies to monitor their cationic silver release capacity in diverse environments are required due to the rise of manufactured products containing silver NPs. Here, we describe the application of a potentiometric method based on a silver-selective electrode to monitor the kinetics of cationic release from cellulose/silver nanocomposites. We designed a set of experiments to apply this method to nanocomposites with several distinct types of cellulose matrices: vegetable, bacterial and nanofibrillated. The morphological features of the cellulose had a great influence on the distribution of silver NPs within the matrix as well as on the Ag⁺ release profiles. The cationic release profiles were interpreted based on common models, showing that, for the vegetal and bacterial cellulose nanocomposites, the kinetics is pseudo-first order, while for the nanofibrillated cellulose materials a model based on Fick’s power law provided the best fit.