Viscous latexes

This is dipping without the assistance of ancillary aids such as coacervants. Thin deposits are formed by viscous latex wetting the former. Single dips are prone to defects such as pinholes, whereas multi-dipping can build up thicknesses of 0.005 to 0.010 inches (127 to 254 ycm) and prevent the occurrence of pinholes the deposit is allowed to partially, or totally dry between dips. Condoms are an example of a product produced by simple dipping. 

The polymer is a water-soluble viscous liquid which has found application in the adhesive and rubber industries. One particular use has been a heat sensitiser used in the manufacture of rubber latex dipped goods. 

Cellulose is also commercially modified by acetylation to produce a material suitable for X-ray and cine film. Commercially cellulose ethers are also prepared, such as methylcellulose. This material is water-soluble and gives a highly viscous solution at very low concentrations. Hence it is widely used as a thickener in latex paints and adhesives, in cosmetics and for coating pharmaceutical tablets. 

The typical viscous behavior for many non-Newtonian fluids (e.g., polymeric fluids, flocculated suspensions, colloids, foams, gels) is illustrated by the curves labeled structural in Figs. 3-5 and 3-6. These fluids exhibit Newtonian behavior at very low and very high shear rates, with shear thinning or pseudoplastic behavior at intermediate shear rates. In some materials this can be attributed to a reversible structure or network that forms in the rest or equilibrium state. When the material is sheared, the structure breaks down, resulting in a shear-dependent (shear thinning) behavior. Some real examples of this type of behavior are shown in Fig. 3-7. These show that structural viscosity behavior is exhibited by fluids as diverse as polymer solutions, blood, latex emulsions, and mud (sediment). Equations (i.e., models) that represent this type of behavior are described below. 

Albert Einstein derived a simple equation for the viscosity of a solution of spherical particles, and from this result it is obvious that if we could make the polymer in small colloidal-sized balls, then the solution would be much less viscous. Also, if we could use surfactants to stabilize (e.g. by charging) the polymer particles in water, then there would be no need for organic solvents. Both these conditions are neatly obtained in the emulsion polymerization process, which is schematically explained in Figure 5.3. A polymer latex is produced by this process and can contain up to 50% polymer in the form of 0.1-0.5 im size spherical particles in water. A typical starting composition is ... 

Other latexes which have been produced by this method include poly(butyl methacrylate), poly(butyl acrylate) and poly(styrene/DVB) [161]. Additionally, polymer blends were produced by mixing, under high shear, HIPEs of partially polymerised monomer, followed by completion of polymerisation. The conversion prior to blending had to be less than 5%, to allow efficient mixing of the highly viscous emulsions. The materials thus produced resembled agglomerates of latex particles, due to copolymerisation at the points of contact of partially polymerised droplets. 

The range of monomers which are available to prepare latexes from HIPEs is limited to those which are sufficiently hydrophobic to form stable o/w concentrated emulsions. However, Ruckenstein and coworker [174] have shown that this range can be extended by prepolymerising the monomer, in bulk, to low conversion, then using the resulting viscous liquid to form the HIPE. By this method, PMMA latexes could be formed whereas attempts to emulsify MMA monomer in aqueous solution resulted in phase separation. 

Some fluids are called shear thinning. Common household examples include mayonnaise and latex paint. As they sit in a jar or can, these materials are quite viscous, almost gel-like. However, the harder we stir them, the lower their viscosities become (up to a point). Latex paint sticks to a brush or roller, but flows easily when we apply the brush or roller to a surface. Once... 

Scleroglucan Sclerolium glucanicum Highly viscous and pseudoplastic, drilling muds, latex points... 

Gutta-percha (with or without the hyphen) is the hardened latex from a number of different trees found in Borneo, Sri Lanka, and Malaya. The name comes from the Malayan words for juice (gutta) and tree (percha). This viscous plant sap hardens quickly and, after vulcanization, looks and behaves like hard rubber. The term gutta percha has also been used to describe unvulcanized hard rubber, regardless of its origin. 

The polymer is formed as low-viscosity latex rather than as the solid or viscous solution as in bulk and solution polymerization. 

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