Viscosity solution polymer stage

Some viscosity may be expected to develop during the solution polymer stage of the polymerization. While the extent and duration of the viscosity that can be tolerated is a fimction of the agitation efficiency and heat removal capability of the reactor, the salt concentration is the primary parameter to be adjusted in order to obtain the optimum in-process viscosity. If the salt concentration has been properly adjusted, then at the onset of the precipitation event the viscosity of the system ops markedly and the polymerization is finished as a dispersion. If the salt concentration is too low during the polymerization, the precipitation event and transition to a heterogeneous system never occurs, and effective mixing and heat transfer will eventually be lost. If, on the other hand, the salt concentration is too high, the dispersion will have little thermodynamic stability in the absence of mechanical shear. 

The polymerisation is carried out in a reactor with an agitator and a water vapour jacket in the presence of a catalyst (10-12% alcohol solution of potassium hydroxide) at 20+5 °C. The polymerisation is continued until the product attains a certain viscosity after that, the reactor is loaded with a required amount of dimethyldichlorosilane to break the chain, with an addition of toluene to dilute the varnish. The polymer is treated with dimethyldichlorosilane for 3-5 hours at agitation the end of the stage is monitored by the universal indicator. The varnish is filtered to eliminate mechanical impurities and potassium chloride and sent to repeated toluene distillation, which is continued until the varnish attains the necessary viscosity and polymer content. 

Most coatings are applied as solutions, emulsions, or suspensions of the pigment, and are converted to solid films after application, usually by allowing the solvent to evaporate. Latex, one of the simplest of paint formulations, is simply a dispersion of high molar mass polymer particles in water. In the first stage of solvent evaporation, the rate of evaporation is essentially independent of the presence of the dissolved or dispersed pigment. As the solvent evaporates, the viscosity increases and the free volume decreases, so that the rate of evaporation becomes dependent on how rapidly solvent molecules can diffuse to the surface of the film [782],... 

The type of polymer obtained depends on factors such as the pH and temperature of reaction, the ratio of melamine to formaldehyde, and the type of catalyst employed. For decorative laminates, melamine-formaldehyde is prepared by reacting melamine in stainless steel kettles under reflux, alkaline conditions with 37% to 46% formaldehyde in aqueous solution. The reaction temperatures used vary from 80 to 100°C and are maintained until the condensation has reached the desired end point—that is, reacted sufficiently but still water-soluble. The end point is checked by measurements of viscosity, cure time, and water tolerance. Depending on the type of laminate to be produced, other constituents (surfactants, plasticizers, release and anti-foam agents) normally are added to the base resin before impregnation of the surface papers. It is common practice also at this stage to adjust the pH by adding acid catalysts. 

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