Latex morphology

Characterization Techniques Utilized for the Study of Composite Latex Morphologies... 

The effect of the amount of surfactant SDS, hydrophobe hexadecane, iron oxide magnetic particles, MAA and non-ionic cellulose ether, hydroxyethylcellulose, on the magnetic latex morphology, surface quality and size distribution was studied by Forcada et al. for the encapsulation of magnetic particles by miniemulsion polymerization of St. Optimal conditions were 2-3% of SDS, 9-12% of hexadecane, 10% of iron oxide and 2% of HEC, relative to the total amount of St and iron oxide [177]. 

Latex with hydroxyl functionalised cores of a methyl methacrylate/butyl acrylate/2-hydroxyethyl methacrylate copolymer, and carboxyl functionalised shells of a methyl methacrylate/butyl acrylate/methacrylic acid copolymer was prepared by free radical polymerisation. The latex was crosslinked using a cycloaliphatic diepoxide added by three alternative modes with the monomers during synthesis dissolved in the solvent and added after latex preparation and emulsified separately, then added. The latex film properties, including viscoelasticity, hardness, tensile properties, and water adsorption were evaluated as functions of crosslinker addition mode. Latex morphology was studied by transmission electron and atomic force microscopy. Optimum results were achieved by introducing half the epoxide by two-step emulsion polymerisation, the balance being added to the latex either in solution or as an emulsion. 8 refs. 

Paiphansrri U, Tangborihoonrat P (2005) Pievulcanisation of skim latex morphology and its use in natural rubber based composite material. Colloid Polym Sci 284 251-257... 

Sperry P R 1984 Morphology and mechanism in latex flocculated by volume restriction J. Colloid Interface Sol. 99 97-108... 

Emulsion polymeriza tion of ABS (241) gives a mbber-phase particle morphology which is mostly deterrnined by the mbbet-seed latex. Since the mbber particle size, polydispersity, and cross-linking ate estabhshed before the preparation, the main variables relate to grafting, molecular weight... 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

Research on the modelling, optimization and control of emulsion polymerization (latex) reactors and processes has been expanding rapidly as the chemistry and physics of these systems become better understood, and as the demand for new and improved latex products increases. The objectives are usually to optimize production rates and/or to control product quality variables such as polymer particle size distribution (PSD), particle morphology, copolymer composition, molecular weights (MW s), long chain branching (LCB), crosslinking frequency and gel content. 

Abstract Emulsion homopolymers and copolymers (latexes) are widely used in architectural interior and exterior paints, adhesives, and textile industries. Colloidal stabihzators in the emulsion polymerization strongly affect not only the colloidal properties of latexes but also the fdm and mechanical properties, in general. Additionally, the properties of polymer/copolymer latexes depend on the copolymer composition, polymer morphology, initiator, polymerization medium and colloidal characteristics of copolymer particles. 

P.R. Sperry Morphology and Mechanism in Latex Flocculated by Volume Restriction. J. Colloid Interface Sci. 99, 97 (1984). 

Other polymer materials which can be prepared include latexes, or particle agglomerates, by dispersed phase polymerisation. These can be either hydrophilic or hydrophobic in nature, or may have core-shell morphologies. They can be employed as support materials for a number of catalyst systems. Polymerisation of both phases of the emulsions produces composite materials, which have found use as selective membranes for the separation of mixtures of liquids with similar physical properties. 

This is truly reflected in the morphology of the uncured clay preexfoliated rubber nanocomposite films (NLu NA) prepared by the latex blending method (Fig. 7a). Curing the NR/NA nanocomposites in situ prevulcanization (No>NA) does not alter the arrangements of dispersed clay layers greatly, as seen from the... 

Morphology evolution is thus found to be dependent on the processing technique applied to disperse the nanoparticles. The latex-blended and prevulcanized nanocomposites show predominant exfoliation with some intercalation, especially in uncured and prevulcanized samples. In conventionally cured but latex-blended nanocomposites, realignment of NA particles is visible, with a greater tendency of NA platelets towards agglomeration. In solid state mixing, the dispersion is still poorer. XRD studies also corroborate the above observations. 

Recently, Mitra et al. have prepared chemically crosslinked nanosized gels from different rubber lattices [148,149]. When added in small quantity (2-16 phr), these low moduli deformable gels have been found to influence the mechanical properties of virgin elastomers like NR and SBR considerably. For example, sulfur prevulcanized nanosized SBR latex gels were prepared and characterized using various methods [148]. The morphology of gel-filled NR and SBR systems has been studied... 

While most studies of particle swelling have dealt with emulsion polymers containing high acid levels, we have restricted our attention to latexes containing relatively low incorporated acid (ca.2-3%) to avoid substantial solubilization of the particles. Questions under current consideration are related to the location of incorporated carboxyl groups within the latex particles, the morphology of expanded particles, and the detailed mechanism of expansion. Information of this type is valuable not only from a fundamental standpoint but is essential in the investigation of very practical problems such as the viscosity stability of latex formulations. 

This microscopic difference in the copolymer composition could influence the particle morphology, especially the distribution of the carboxyl groups within the latex particle, which in turn could be expected to influence the alkali-swelling behavior. 

Particle Structure - So far, the discussion of non-uniform emulsion polymers has centered around mechanical properties, interpreted in terms of gradations of sequences between set compositional limits. But latexes are aqueous dispersions, and an exploration of particle morphology is equally interesting and important. For instance, can polymer particles be constructed such that particle sequence compositions are located in a desired region of the particle, and what evidence exists that such particle morphologies have been realized ... 

---