Latex Systems Research Articles

<i>In Situ</i> Preparation of Magnetic P(AOS-St-BA)-Coated CoFe<sub>2</sub>O<sub>4</sub> Composite Microspheres in Soapless Emulsion

Sodium 2-olefinsulfonate (AOS) is used as reactive surfactant to prepare 10 nm around magnetic CoFe2O4 nanoparticles in advance. Magnetic P(St-BA-AOS)-coated CoFe2O4 composite nanoparticles has been synthesized in situ soapless emulsion. The effects of the amount of the initiator, monomer concentration and polymerizing temperature on the convention of monomer are investigated. So the polymerizing conditions are KPS=4.010-3mol/l St=0.75mol/l, mMP=20g/l, T=75 BA=0.15mol/l t=6.0h [AOS]=2% without any surfactant in the latex system. Results of IR and TEM analysis demonstrate that the desired polymer chains has been covalently bonded to the surface of CoFe2O4 nanoparticles, and confirmed that the composite particles have the core-shell structure. Copolymer P(St-BA-AOS) has a good hydrophile ability with functional groups such as -SO3Na and -COO- groups. The saturated magnetization of CoFe2O4/ P(St-BA-AOS) composite could reach 2.10emu/g, and show the characteristics of super-paramagnetism.

Delivering Solvent Based Polymers in Eco‐Friendly Water Based Systems

AbstractProviding solvent‐borne polymer properties in waterborne systems represents a challenge that has been pursued for a long time. This challenge can now be overcome through the use of miniemulsion polymerization, a unique processing approach that can be applied to incorporate a wide range of polymers, many of which have traditionally only been deliverable using organic solvents. This work highlights some of the advantages of using miniemulsion polymer processing for combining acrylic polymers with a wide range of hydrophobic materials including alkyds/uralkyds, rubbers, tackifiers, and optical brighteners. It can be extended to include an assortment of other hydrophobic materials that are soluble in traditional acrylic, vinyl, and/or styrenic monomers. As a result, these traditionally solvent‐borne polymers can now be made available for many different coating applications in an environmentally friendly latex system.

Diffusion of oligomers in latex systems — A route to low volatile organic compound (VOC) coatings

We synthesize specially designed latex polymer systems by an in situ emulsion polymerization process that yields latex particles with both a high molecular weight polymer phase and a low molecular weight oligomer phase. The oligomer functions as a plasticizer by lowering the glass transition temperature (Tg) of the polymer. A polymer system is prepared by blending soft latex and a hard latex where the hard mode consists of a hard, high molecular weight polymer and an oligomer, allowing for facile film formation at ambient conditions. Upon the soft and hard particles coming into contact during the film formation process, the oligomer preferentially diffuses from the hard polymer to the soft polymer, thus recovering the natural Tg of the hard polymer as described in a recent patent application. Oligomer diffusion allows a hard coalesced phase to be incorporated into a latex film without using a coalescing solvent, which would contribute to the volatile organic compound (VOC) content. A well-coalesced hard phase in a latex film contributes to a variety of desirable coatings properties, such as tack, print, block, and scrub resistance properties.

Formation of nanostructured composites with environmentally-dependent electrical properties based on poly(vinylidene fluoride)–polyaniline core–shell latex system

Submicron poly(vinylidene fluoride) (PVDF)/polyaniline (PANI) core–shell latex particles are synthesized and examined as an active component in a simple conductometric chemical sensor. The structure and physical properties of these particles and nanostructured composite PVDF–PANI polymer films built of them are characterized with transmission electron, atomic force, and helium ion microscopy techniques, differential scanning calorimetry, and conductivity measurements. The nanostructured composite films with conductivity of about 4 × 10−4 S/cm suitable for sensor applications are prepared by casting from the core–shell particles dispersions on glass substrates patterned with silver electrodes followed by annealing at 180 °C, i.e. above Tm of the PVDF component. Sensor properties of these films are tested by measuring current–voltage (I–V) characteristics in response to varying concentration of NH3 or HCl vapors. The developed thin film sensor heterostructures with electrically conductive percolation network of PANI as an active component and employing the conductometric detection scheme show high sensitivity to both analytes. However, the polymer material is especially efficient for application to NH3 sensing with the detection limit as low as 100 ppb, and good reproducible recovery behavior upon repeated exposure to NH3 at ambient conditions.

Reducing Accidental Injuries During Surgery

All surgical healthcare professionals and their patients should be aware of exposure to blood from individuals infected with potentially transmissible disease. The site that was most susceptible to sharp injuries was the index finger of the surgeon's hand. It is also important to note that needles cause the vast majority of sharp injuries. During the last two decades, there have been two revolutionary advances in preventing accidental needlestick injuries during surgery that include the development of blunt tapering point needles as well as the double-glove hole indication systems. During the innovative development of blunt taper point needles, a glove manufacturer, Molnlycke, Inc., devised non-latex and latex double-glove hole puncture indication systems that are being used throughout the world. The reliability of these double-glove hole indication systems in detecting holes in the outer glove has been reliably documented by scientific studies that are published in peer-reviewed journals. On the basis of these extensive quantitative studies, the authors recommended that the double-glove hole indication system be used in all operative procedures to prevent the transmission of deadly bloodborne viral infections.

Bark anatomy in Croton draco var. draco (Euphorbiaceae)

Many arboreal forms of the genus Croton (ca. 800 spp.), amply distributed in the Americas, have latex-producing cells in their bark, which is widely used in traditional medicine to treat skin infections and some forms of cancer. Studies validate its ethnomedicinal use-more than 20 pharmaceutically important secondary metabolites have been reported for its latex and bark-but anatomical and ecological studies are scarce. Given this species' ample distribution, laticifer abundance could be affected by the environment. We tested this for genetically similar trees growing in two types of vegetation in Veracruz, Mexico at sites commonly visited by traditional doctors. We describe the bark anatomy of C. draco, focusing on the laticifers, histochemically characterize the bark and the latex extracted from it, and document differences in laticifer abundance in the two environments. We have also identified another cell type (what we call type B) in the secretory latex system and describe it histochemically and microscopically. The location of bark cells that contain essential oils is reported here for the first time. Given the genetic similarity of the trees at both sites, the between-site variation in the number of laticifers in stem and branch bark appears to be an effect of the environment.

Breathable water-resistant linerboard coatings by electrospraying application

Waterproofing of corrugated packaging with wax or polyethylene hinders recyclability and so is incompatible with current socioeconomic goals of sustainability. Therefore, alternative coating technologies are sought. This study describes our feasibility study of electrohydrodynamic spraying (EHS) towards waterproofing corrugated boxes. Water resistance properties of electro-sprayed polymer-solvent solutions and latex systems air dried onto linerboard surface are reported. Optimization of spraying parameters led to observations of applied coating roughening on a nano-to-micron scale that correlated with increased water contact angle of the treated linerboard. An EHS latex formulation, compared to polymer solvent system, has shown better adhesion to linerboard. EHS application of latex produced a surface coating texture of droplets, which minimizes liquid water absorption, forming a nanopore matrix (of 3 – 50 nm diameter pores) that enabled the transmission of water vapor. Linerboard treated by EHS latex was advantageously found to be comparatively transpiring to water vapor at room temperature and refrigeration conditions, which is encouraging for commercial application of the technique.

AN INSIGHT INTO OPHTHALMIC DRUG DELIVERY SYSTEM

Promising management of eye ailments take off effective concentration of drug at the eye for sufficient period of time. Dosage forms are administered directly to eye for localized ophthalmic therapy. Most of the treatments call for the topical administration of ophthalmic active drugs to the tissues around the ocular cavity. Conventional ophthalmic drug delivery systems including eye drops, ophthalmic ointments, are no longer sufficient to encounter eye diseases. This article reviews the constraints with conventional ocular therapy and explores various novel approaches like in-situ gel, ocular films or ocuserts, nanosuspension, collagen shields, latex systems, nanoparticles, liposomes, niosomes, iontophorosis, eye implants, etc to improve the ophthalmic bioavailability of drugs to the anterior chamber of the eye.

Structure–property relationship in aging acrylic latex films

We have used environmental scanning electron microscopy (ESEM) and mechanical testing to study the effect of aging parameters (temperature, T and relative humidity, RH) on the structure–property relationship of aged specimens from two acrylic latex compositions, referred to as ‘standard’ and ‘novel’. It was found that the tensile strength of the novel system increases as a function of aging time, whereas the tensile strength of the standard specimens remains almost unchanged. This was attributed to the formation of salt dendrites in the aged novel samples. It was also found that humidity does not have a significant effect on the microstructures observed. However, it was found that aging at lower temperatures results in decreased rate of dendritic formation, which is suggested to be due to decreased diffusion of the species taking part in the crystallisation process. Further examination of fractured surfaces of the studied latex systems revealed features indicative for a more ductile behaviour of the standard specimens and a more brittle behaviour for the novel latex samples.

Preparation and properties of alkoxysilane/butyl acrylate/methyl methacrylate copolymer latices

AbstractThe incorporation of alkoxysilanes into latex systems is of major interest in the field of colloidal science. Two kinds of vinyl‐containing alkoxysilanes, methacyloxypropyltrimethoxyl silane and vinyltriethoxysilane, were copolymerized with butyl acrylate and methyl methacrylate by seeded emulsion polymerization, and copolymer latices were obtained. The morphologies of the latex particles were characterized with transmission electron microscopy. Dynamic light scattering showed that the particle size increased and the particle size distributions of all the copolymer latex particles were alike with increasing amounts of organosilane. The effects of the organosilane content on the morphology of the particles, the rheology, and the swelling properties were also investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Core-shell and other multiphase latex particles—confirming their morphologies and relating those to synthesis variables

Composite latex particles made from sequential processing steps may have a wide range of morphologies. The particular structure achieved is the result of a number of complex interactions between the chemical and physical aspects of the emulsion polymerization process. The intention is often to produce a core-shell particle structure, but in reality this is often a nontrivial task. In addition, it is challenging to develop confident conclusions about the detailed morphology of such particles, even when the two-component polymers are well phase-separated. This paper reports on an inter-laboratory study of acrylic-styrene copolymer latices in which the two-component polymers were not well phase-separated—a common result when attempting to make core-shell latex particles. Six different organizations each performed a number of analytical measurements to characterize two different latex systems. Their collective results were presented at a workshop in which the group strived to reach consensus on the detailed structures of the particles. Their conclusions were that multiple, complementary analytical results are required to reach a sound decision. While electron microscope results were always judged to be necessary, considered by themselves, it is often found that one can be led to false conclusions, especially for systems that are not well phase-separated. Given the results of this study it is clearly inappropriate to assume that the polymer formed in the second stage of a semibatch latex polymerization process forms a shell, giving rise to a core-shell morphology.

An environmental scanning electron microscopy examination of the film formation mechanism of novel acrylic latex

We have employed environmental scanning electron microscopy (ESEM) to study the film formation mechanisms of two acrylic latex compositions, here defined as standard (carboxymethyl cellulose stabilised) and novel (stabilised with a novel polysaccharide derived from agricultural waste). The ESEM analysis revealed that the microstructure of the standard system consists of individual particles and upon evaporation a continuous film is formed, which is consistent with the current models. However, in the case of the novel system the microstructure consists of individual particles and clusters and during evaporation a discontinuous film is formed with voids present within its structure. Based on the experimental evidence we propose a modification to the film formation mechanism for the novel latex system.

Modification of Latex Systems with Polymeric Complexes of Sorbic Acid

Modification of Latex Systems with Polymeric Complexes of Sorbic Acid

Characterization of conductive multiwall carbon nanotube/polystyrene composites prepared by latex technology

Conductive multiwall carbon nanotube/polystyrene (MWCNT/PS) composites are prepared based on latex technology. MWCNTs are first dispersed in aqueous solution of sodium dodecyl sulfate (SDS) driven by sonication and then mixed with different amounts of PS latex. From these mixtures MWCNT/PS composites were prepared by freeze-drying and compression molding. The dispersion of MWCNTs in aqueous SDS solution and in the PS matrix is monitored by UV–vis, transmission electron microscopy, electron tomography and scanning electron microscopy. When applying adequate preparation conditions, MWCNTs are well dispersed and homogeneously incorporated in the PS matrix. The percolation threshold for conduction is about 1.5 wt% of MWCNTs in the composites, and a maximum conductivity of about 1 S m −1 can be achieved. The approach presented can be adapted to other MWCNT/polymer latex systems.

Molecular dynamics simulation of water diffusion inside an amorphous polyacrylate latex film

AbstractMolecular dynamics simulations were applied to investigate the diffusion behaviors of water molecules at temperatures ranging from 323 to 443 K inside amorphous polyacrylate. The results showed that the simulated diffusion coefficients and activation energies were similar to those of experiments. Moreover, the activation energy of water molecules at high temperatures was higher than that at low temperatures by 3.16 kcal mol−1, which was close to the hydrogen‐bonding energy between water and polyacrylate. An analysis of the experimental desorption curves of water molecules and their activation energies has confirmed that there are two forms of water molecules inside rubbery polyacrylate, namely, free water and bound water. In addition, it has been concluded that bound water molecules move from one polar group of polyacrylate to another, and this is followed by occasional jumps. Simulated information is very helpful in designing new polyacrylate latex systems and optimizing existent polyacrylate systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 884–891, 2007

Viscoelastic and damping characteristics of poly(n‐butyl acrylate)‐poly(n‐butyl methacrylate) semi‐IPN latex films

AbstractThis article reports the synthesis, characterization, and damping characteristics of semi‐interpenetrating (semi‐IPN) latex systems composed of poly n‐butyl acrylate (PBA) core and poly n‐butyl methacrylate (PBMA) shell. The IPN's were prepared by seeded emulsion polymerization using crosslinked PBA seeds with varying crosslinker (m‐diisopropenyl benzene) concentration. The polymer weight ratio in the first and second stage polymerization is maintained at 1:1 in all the cases. The particle size determined by dynamic light scattering shows a decrease in the shell thickness with increasing crosslinker concentration of the seed. The mechanical properties, like Shore A hardness of the films, increased from 18 to 65 when the crosslinker concentration is increased from 0 to 4.8 mol%. The dynamic mechanical studies show that the modulus value of the IPN's is below that of non‐crosslinked films, and the value depends upon the crosslink density of the seed. Mechanical models, such as the Kerner's model and the Takayanagi's model, were used to explain the variation in the dynamic mechanical properties with the degree of seed crosslinking. The study indicates lower bound (rubbery) behavior for the films with lightly crosslinked cores. The study also shows that, at lower crosslinker concentration enhanced phase separation and better damping properties are achieved but at higher cross linker concentration (>2 mol%) greater interpenetration of the shell monomer to the cores takes place and tough films, with reduced damping properties are formed. Copyright © 2007 John Wiley & Sons, Ltd.

WRITING AND PUBLISHING SCIENTIFIC PAPERS USING TEX AND LATEX

There is a common misbelieve that, in a scientific paper, what really matters is the content, not the layout; in reality, people do not read poorly presented papers. On the other hand, everyone agrees that the author(s) should indeed focus on the content and should not waste time on the layout. (La)TeX is based on this idea, that authors should be able to focus on the meaning of what they are writing without being distracted by the visual presentation of the information. In preparing a (La)TeX document, the author specifies the logical structure using concepts such as chapter, section, table, figure, etc., and lets the (La)TeX system worry about the presentation of these structures. It, therefore, encourages the separation of layout from content, while still allowing manual typesetting adjustments where needed. TeX was developed in late 70’s and early 80’s by Donald E. Knuth, a professor of computer science at Stanford University. TeX is a typesetting language that was designed to produce high quality documents. LaTeX (usually pronounced [`leɪ.tɛk] in English) is a document markup language for TeX that was developed in the mid-80’s by Leslie Lamport and has become the dominant method for using TeX. The current version is LaTeX2e. TeX is distributed under a free software license, the LaTeX Project Public License (LPPL) and has a huge community which sustains its development. A number of TeX distributions are available, including TeX Live (multiplatform), MiKTeX (Windows), MacTeX (Mac OS X). MiKTeX (curent stable version is 2.6) is an up-to-date TeX implementation for the Windows operating system. MiKTeX offers a complete set of utilities, macro packages and fonts, e.g., LaTeX, pdfTeX, ConTeXt, just to name a few.

Effects of Fumed Silica on the Viscosity of Acrylic Latex System

Effects of fumed silica on the viscosity of acrylic latex system were studied by recording curves of the shear complex viscosity over shear rate and temperature and by measuring apparent viscosity with a variety of fumed silica concentrations at various steady angular velocities. Results show that the fumed silica obviously affects the shape and value of curves on the amplitude of complex viscosity versus either shear rate or temperature diagrams. Both dynamic and steady shear measurements illustrate a shear thinning phenomena for the acrylic latex filled with fumed silica. Dependence of the apparent viscosity on the fumed silica concentration can be satisfactorily modeled by the Krieger‐Dougherty expression. A fitted parameter that quantitatively describes the sensitivity of the effect of fumed silica on the acrylic latex system increases with angular velocity, but decreases with latex solid content.

Rheological behavior of nanocomposites of natural rubber and carboxylated styrene butadiene rubber latices and their blends

AbstractFlow behavior of latices is industrially important for the manufacturing of various latex goods. Rheology of latices having fillers can assist in the understanding and quantification of the matrix–filler interaction. The impact of layered silicates such as sodium bentonite and sodium fluorohectorite on the rheological behavior of natural rubber, carboxylated styrene butadiene rubber latices, and their blends was analyzed with special reference to shear rate, temperature, and filler loading. The layered silicates‐reinforced latex samples were characterized by X‐ray diffraction technique to analyze the extent of intercalation and exfoliation. In the presence of layered silicates, latex systems exhibited enhancement in viscosity due to the network formation. Because of the breaking of networks at higher temperature, the viscosity of all systems decreased with increase in temperature. Layered silicates‐reinforced latex systems showed pseudoplastic flow behavior and possesses enhanced zero shear viscosity and yield stress. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2355–2362, 2006

Film formation from pigmented latex systems: Mechanical and surface properties of ground calcium carbonate/functionalized poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) latex blend films

AbstractThe mechanical and surface properties of films prepared from model latex/pigment blends were studied using tensile tests, surface gloss measurements, and atomic force microscopy. Functionalized poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) [P(BMA/BA)] and ground calcium carbonate (GCC) were used as latex and extender pigment particles, respectively. The critical pigment volume concentration of this pigment/latex blend system was found to be between 50 and 60 vol % as determined by surface gloss measurement and tensile testing of the blend films. As the pigment volume concentration increased in the blends, the Young's modulus of the films increased. Nielsen's equations were found to fit the experimental data very well. When the surface coverage of carboxyl groups on the latex particles was increased, the yield strength and Young's modulus of the films both increased, indicating better adhesion at the interfaces between the GCC and latex particles. When the carboxyl groups were neutralized during the film formation process, regions with reduced chain mobility were formed. These regions acted as a filler to improve the modulus of the copolymer matrix and the modulus of the resulting films. The carboxyl groups on the latex particle surfaces increased the surface smoothness of the films as determined by surface gloss measurement. When the initial stabilizer coverage of the latex particles was increased, the mechanical strength of the resulting films increased. At the same time, rougher film surfaces also were observed because of the migration of the stabilizer to the surface during film formation. With smaller‐sized latex particles, the pigment/latex blends had higher yield strength and Young's modulus. Higher film formation temperatures strengthen the resulting films and also influence their surface morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4550–4560, 2006