Mechanical and viscoelastic behavior of natural rubber and carboxylated styrene‐butadiene rubber latex blends

The morphology, mechanical and viscoelastic behavior of latex blends of unvulcanized natural rubber (NR) with carboxylated styrene‐butadiene rubber (XSBR) were investigated, with special reference to the effect of the blend ratio, temperature, and frequency. Mechanical properties like tensile strength, modulus, and elongation at break were also studied. As the XSBR content increased, the tensile strength increased up to a 50:50 NR/XSBR ratio and then decreased as a result of the self‐curing nature of XSBR. The dynamic mechanical properties of these latex blends were analyzed for loss tangent, storage modulus, and loss modulus. The entire blend yielded two glass‐transition temperatures, which corresponded to the transitions of individual components, indicating that the system was immiscible. To determine the change in modulus with time, a master curve of 50:50 NR/XSBR blends was plotted. Time–temperature superposition and Cole–Cole analysis were done to understand the phase behavior of the latex blends. The experimental and theoretical values of storage modulus of blends were compared using the Kerner and Halpin–Tsai models. With the help of optical micrographs, attempts were made to correlate the morphology and viscoelastic behavior of these blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2639–2648, 2003     

Modified emulsifier‐free emulsion polymerization of butyl methacrylate with ionic or/and nonionic comonomers

A modified emulsifier‐free emulsion polymerization of butyl methacrylate (BMA) with ionic or/and nonionic comonomers was successfully used to prepare nanosized poly(butyl methacrylate) (PBMA) latices with high polymer contents. After seeding particles were generated in an initial emulsion system, consisting of a portion of BMA, water, ionic comonomer [sodium styrenesulfonate (NaSS)] or nonionic comonomer [2‐hydroxyethyl methacrylate (HEMA)] and potassium persulfate, most of the BMA monomer or the mixture of BMA and HEMA was added dropwise to the polymerizing emulsion over a period of 6–12 h. Stable latices with high PBMA contents up to 27% were obtained. It was found that the latex particle sizes (2R_h) were largely reduced (34 nm) by the continuous addition of monomer(s) compared to those (107 nm) obtained by the batch polymerization method. The effect of comonomer concentration on the particle size, the number of PBMA particles/mL of latex (N_d), and the molar mass (M_w) of copolymer during the polymerization were discussed. The surface compositions of latex particles were analyzed by X‐ray photoelectron spectroscopy, indicating that the surface of latex particles was significantly enriched in NaSS or/and HEMA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3080–3087, 2004     

Acrylic latices stabilized by polymerizable non-ionic surfactant

The final latex particle size is controlled by the concentration of polymerizable non-ionic surfactant NE-40 in the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The particle size decreases with increasing NE-40 concentration and increases with increasing persulphate initiator concentration. The dependence of particle size on the initiator concentration does not follow conventional Smith–Ewart theory, which is attributed to the bridging flocculation process during the particle nucleation period. The differences in the particle nucleation and growth stages and colloidal stability observed in the NE-40 and nonyl phenol-40 mol ethylene oxide adduct (NP-40) stabilized systems can be attributed to the different distribution patterns of surfactant molecules in the particles. Experimental data also indicate that the particle size decreases with increasing electrolyte concentration, or agitation speed. The total scrap, presumably caused by the bridging flocculation process, increases rapidly with increase in the NaCl concentration The amount of large flocs formed during polymerization is generally greater for the run operated at higher agitation speed. As expected, the latex products stabilized by non-ionic surfactants show excellent stability toward added sodium salt.     

Non-ionic polystyrene latices in aqueous media

Colloidally stable non-ionic polystyrene latices were prepared in aqueous media, with a narrow distribution of particle sizes, using a nonyl phenol polyethylene glycol condensate as the surface-active agent, methoxy polyethylene glycol methacrylate as the comonomer-stabiliser and ascorbic acid-hydrogen peroxide as the initiator system. For comparison, a typical charge-stabilised polystyrene latex was also prepared using an anionic surface-active agent and potassium persulphate as the initiator. These latices were characterised using transmission electron microscopy, conductometric titration and microelectrophoresis. The stability of the latices to the addition of electrolyte was examined and also the stability to freeze-thaw conditions. The glass transition temperatures of the latices were also determined.     

Controlled preparation of nanocolorants via a modified miniemulsion polymerization process

Nanocolorants were successfully prepared via a modified miniemulsion polymerization process into which styrene, a polar monomer, crosslinkers, a highly hydrophobic solvent, dyes, and so forth were introduced. The obtained nanocolorants were nanocomposite entities in which a fraction of dye molecules attached to the crosslinked macromolecular chains and more dye molecules formed clustering because of the phase separation between the dye and polymer during the polymerization process and were further embedded in the interior of the crosslinked polymer because of the high hydrophobicity of the dyes. The effects of the polar monomers, the amounts of the dyes dissolved in styrene, and the polymer crosslinking, as well as the effects of the water‐soluble and oil‐soluble initiator, the amount of the surfactant, and the ultrasonic homogenization time, on the preserving fastness of the dyes in the polymeric matrix and the morphology and particle size distribution of the nanocolorants were studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The Effect of Lowering the Surface Free Energy of Water on the Thermodynamic Work of Adhesion

The dispersive and polar force components of surface free energy have been measured for water left in contact with films dried from various emulsion adhesives. The polar component was lowered but the dispersive components were about 28 mJ m^-2 in each case. From these measurements of thermodynamic work of adhesion in the presence of contaminated water have been calculated for adhesive-polystyrene interfaces. An equation has been derived giving the dependence of thermodynamic work of adhesion upon the total surface free energy of water. It shows that the thermodynamic work of adhesion decreases as the surface free energy of water is lowered, but it eventually reaches a minimum and then may increase slightly.     

Investigation of fluorinated polyacrylate latex with core–shell structure

Fluorinated polyacrylate latices with core–shell structure were prepared by semi‐continuous emulsion polymerization, using a mixed emulsifier system composed of a reactive emulsifier and a small amount of anionic emulsifier. The conversion and chemical components of the final latices were studied by gravimetric methods and Fourier‐transform infrared (FTIR) spectrometry, respectively. The structure of the latex particles was determined by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and particle size analysis. The latex films exhibited a low surface energy and high water‐contact angles. The surface analysis from X‐ray photoelectron spectroscopy (XPS) revealed that the fluorinated components preferentially self‐organized at the film–air interface. From XPS depth profiling of the film, it was found that a gradient concentration of fluorine existed in the structure of the latex film from the film–air interface to the film–glass interface. Compared with the core–shell structure with a fluorinated core, the core–shell structure with a fluorinated shell was more effective for modifying the properties of the latex films. Copyright © 2005 Society of Chemical Industry     

Effect of the vulcanization time and storage on the stability and physical properties of sulfur‐prevulcanized natural rubber latex

Prevulcanized natural rubber latex was prepared by the heating of the latex compound at 55°C for different periods of time (2, 4, 6, 8, and 10 h). The changes in the colloidal stability and physical properties were evaluated during the course of prevulcanization. The prevulcanized latex compounds were stored for 300 days, and the properties were monitored at different storage intervals (0, 20, 40, 60, 120, 180, 240, and 300 days). During prevulcanization, the mechanical stability time increased, and the viscosity remained almost constant. The tensile strength increased during storage for a period of 20 days. The degree of crosslinking, modulus, elongation at break, and chloroform number were varied with the time of storage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1804–1811, 2005     

Palladium‐catalyzed electroless plating of gold on latex particle surfaces

Gold can be deposited onto a latex particle surface via the growth of metal islands with the electroless plating method. A new method is proposed for the electroless plating of gold on the surface of poly(styrene‐co‐vinylimidazole) latex particles, which is catalyzed by palladium present on the latex particle surfaces. The palladium ions are anchored to the latex particle surfaces by the formation of a palladium–imidazole complex, and palladium nanoparticles are nucleated by a reductant. These palladium islands act as catalytic sites, so gold is preferentially deposited onto the latex particle surfaces. Transmission electron microscopy, X‐ray photoelectron spectroscopy, and sucrose density gradient column results indicate that the palladium is associated with the imidazole‐functionalized latex particles. Different gold loading levels and reductant types were explored. Latex particles were partially encapsulated by finely dispersed gold nanoparticles less than 2 nm in diameter or by gold islands with sizes ranging from 10 to 100 nm up to a gold loading level of 3.1 mg of Au/m² of latex. However, using higher gold loading levels led to uncontrollable electroless plating of gold because gold reduction in the water phase became very dominant even in the presence of catalytic palladium on the latex particle surface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009