Latex range

The particle size of typical natural mbber latex ranges from slightly higher than 1 )Tm to as small as 20 nm, and can be destabilized by mechanical or chemical action. Machinery used to stir or maintain latex circulation should be designed to minimize fluid shear, particularly where that may be locally intensified, eg, at the junction of blade with shaft. 

Latex mbber foams are generally prepared in slab or molded forms in the density range 64—128 kg/m (4—8 lbs/fT). Synthetic SBR latexes have replaced natural mbber latexes as the largest volume raw material for latex foam mbber. Other elastomers used in significant quantities are polychloroprene, nitrile mbbers, and synthetic i j -polyisoprene (115). 

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described eadier, it can be operated as a forced-vibration instmment. It is fully computerized and automatically determines G, and tan 5 as a function of temperature at low frequencies (10 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstmctures of polymer blends (285) and latex films (286). 

Polymerization. Emulsion polymerization is used, but the latex is too unstable for use and all the latex is coagulated to dry mbber. The molecular weight range is 100,000—200,000 with a Mooney viscosity of 50—70. 

The Stokes-Einstein equation has already been presented. It was noted that its vahdity was restricted to large solutes, such as spherical macromolecules and particles in a continuum solvent. The equation has also been found to predict accurately the diffusion coefficient of spherical latex particles and globular proteins. Corrections to Stokes-Einstein for molecules approximating spheroids is given by Tanford. Since solute-solute interactions are ignored in this theory, it applies in the dilute range only. 

Most often NR adhesives are supplied either as a solvent dispersion or as a latex for coating onto surfaces. Viscosity can range from very low viscosity solutions for... 

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