Latex-based materials

Latex-based polymer materials can be either nature-made, as natural rubber [Stern, 1967 White, 1995], or synthetically made. The synthetically made latexes are commonly based on recipes of monomer, water, surfactant, and free radical initiator to induce chain polymerization [Lovell and El-Aasser, 1997 Wickson, 1993], However, recipes based on step polymerization are also well known, often resulting in crossUnked films [Walker and Shaffer, 1996], The resulting latex material consists of small particles, usually spherical, of 50-500 nm in diameter, dispersed in water. Alternately, polymers are sometimes emulsified after polymerization (direct emulsification, the product sometimes called artificial latexes) via agitation of a melt in the presence of water and surfactant (emulsifier), and sometimes organic solvent or plasticizer [Piirma, 1989]. 

Latexes have long been used in IPNs and related materials. Some of the material types described in the literature are  

Latex Blends. These are combinations of two or more kinds of latexes, differing in chemical 

Core-Shell Latexes. First a seed latex of polymer 1 is synthesized. Then, a second monomer is added to the system, usually with no added surfactant. Often, a starved polymerization route is employed, i.e., the rate of polymerization equals or exceeds the rate of monomer addition. This reduces the swelling of the seed latex by monomer 2, producing a two-layer latex having a spherical core, and an overlaying shell. Obviously, multiple shells can be added. 

Latex IPNs. A crosslinked seed latex of polymer 1 is synthesized first. Then, monomer 2, plus crosslinker and initiator are added, usually without new surfactant. If the monomer 2 mix is added either all at once or rapidly, then swelling of polymer 1 by monomer 2 is encouraged, with subsequent greater interpenetration. 

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In a broad study to evaluate the composite properties of hetero-geneous-latex-based materials, Dickie et synthesized a series of latex semi-IPNs. A two-staged emulsion polymerization procedure was employed that yielded relatively uniform populations of heterogeneous latex particles (HLP). The glassy component was prepared from methyl methacrylate, and the rubbery component used a mixture comprising 95 mol % butyl acrylate (BA) and 5 mol % 1,3-butylene dimethacrylate (BPMA). Heterogeneous latex particles in which the rubbery component was polymerized first were referred to by Dickie et al as HLPl particles for which the order of polymerization was reversed were referred to as HLP2. 

Sealants, while sharing many similarities with adhesives, tend to be made from different materials and include those based on polysulfides (often for uses in contact with fuel), silicones, polyurethanes, acrylics in both solvent-based and latex-based materials, and sealants based on butyl and fluorocarbon polymers. In addition to adhesive and sealant types, this chapter reviews methods for testing and qualifying these materials. 

Another class of water-based materials that has recently (ca 1997) begun to see use ia masoary water repeUeacy treatmeats is sUicoae elastomer latex (89), which can deHver a water-permeable sUicone mbber film. These latex elastomers are ideal as water repeUents for substrates that contain very large pores, such as concrete block. In addition, the elastomer can bridge minor cracks, and wUl expand and contract with the substrate. 

The most common adhesive system used for bonding continuous fibers and fabrics to rubber is resorcinol-formaldehyde latex (RFL) system. In general, RFL system is a water-based material. Different lattices including nitrile and SBR are used as the latex for the adhesive system. 2-Vinylpyridine-butadiene-styrene is the common latex used in the adhesive recipe. RFL system is widely being used in tires, diaphragms, power transmission belts, hoses, and conveyor belts because of its dynamic properties, adhesion, heat resistance, and the capacity to bond a wide range of fabrics and mbbers. 

Organic polymers are functionalized directly at their surface, with the exception of latex-based anion exchangers (see Section 3.3.1.2), where the totally porous latex particle acts as ion-exchange material. Surface-functionalized, pellicular substrates show a much higher chromatographic efficiency compared to the fully functionalized resins. The organic polymers mentioned above are functionalized in a two-step process ... 

Latex-based anion exchangers are comprised of a surface-sulfonated polystyrene/divi-nylbenzene substrate with particle diameters between 5 pm and 25 pm and fully animated porous polymer beads of high capacity, which are called latex particles. The latter have a much smaller diameter (about 0.1 pm) and are agglomerated to the surface by both electrostatic and van-der-Waals interactions. A scanning electron micrograph of this material is shown in Fig. 3-12. Hence, the stationary phase features three chemically distinct regions ... 

Historically the first anticorrosion techniques to appear were combined films - paper and cardboard-based materials covered with paraffin, microcrystalline wax, synthetic latex or PE. These materials are accessible, cheap, rather strong, wear resistant, and display elasticity, vapor and light-impermeability, moisture resistance, shape stability, susceptibility to color... 

Xu et al. heterocoagulated cationic PMMA latex particles of an estimated 150-200 nm in diameter with various clays, Montmorillonite (GelWhite GP and Cloisite Na+) and (fluoro)hectorites (Laponite RD, RDS, B, S, JS), having plate dimensions between 25 and 600 nm. No details on the stable colloidal armored structures were reported. Mass coagulation was induced in order to obtain a nanocomposite bulk material, which was further analyzed [23]. Chen et al. [24] added Ti02 and SiOi/TiOi nanoparticles with a positive surface charge at a very low pH of 0-2 to both anionic and cationic latexes based on PMMA. A bulk nanocomposite blend was analyzed. 

Uses NBR latex for oil- and petrol-resistant proofings and coatings for fabrics and paper dipped goods binders for nonwoven fabric, brake and clutch linings, gasket materials, etc. for impregnation of nonwoven fabrics (e.g., in prod, of base materials for syn. leathers), and for dipped... 

Latex-based polymer materials can be either nature made, as natural rubber (Stem 1967 White 1995), or synthetically made. The synthetically made latexes are... 

This paper reports on the synthesis, characterisation, and applications of novel flame retardant dibromostyrene-based latexes. They are copolymers of dibromostyrene with butadiene, alkyl acrylates and methacrylates, vinyl acetate, styrene and unsaturated carboxylic acids, which form a wide variety of flame retardant latexes via an emulsion polymerisation technique. Choice of monomer or monomer blend is based upon the final glass transition temperature of the copolymer desired. Other criteria include desired physical properties and chemical resistance. Dibromostyrene-based butadiene and acryUc latexes are shown to possess the desired physical properties for use in coatings, adhesives and sealants, and the bromine content of the latexes has enabled the material to pass six different flammability requirements for the end uses such as textile backcoating, latex-based paint, contact adhesive, latex sealant, nonwoven binder, and carpet backing. 18 refs. 

Seamless coated knit gloves are extremely versatile and have revolutionized the fit and feel of hand protection. Knitted from various base materials such as cotton, synthetic yams (polyester and nylon), and high performance yams (Kevlar and Dyneema ), seamless coated gloves are less labor intensive to produce. Use of various synthetic coatings such as latex, nitrile, foam nitrile, and polyurethane can also enhance grip characteristics and provide improved durability and wear life. 

In order to make technologically performing conductive materials, it is crucial to be able to monitor and optimize each step of the latex-based process to make nanocomposites. In particular, this applies to the first step of the process, and implies the optimization of the CNT individualization process, the minimization of the amount of impurities in the CNT batch, as well as the limitation of the possible damage of the CNT walls [induced by treatment such as purification and sonication]. 

A benchmarking, with regard to the achieved electrical properties in these semi-crystalline materials, is performed against a well-described fully amorphous model system, i.e., latex-based polystyrene nanocomposites also prepared by latex technology, which were extensively reported in previous chapters of this book, as well as elsewhere. 

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