In the process of emulsion polymerization, an important role of agitation is to disperse the monomer into droplets and to facilitate heat transfer. However, the stirring intensity should not be too high, when the stirring intensity is too high, the number of latex particles will be reduced, the diameter of latex particles will be increased and the polymerization rate will be reduced, and the emulsion will produce gel and even break the milk. Therefore, moderate mixing should be used.
The effect of stirring intensity on the diameter of latex particles: in emulsion polymerization, the larger the stirring speed, the larger the diameter of latex particles and the smaller the number of latex particles. This is because in the stage of emulsion polymerization and dispersion, when the number of revolutions is large, the monomer is dispersed into smaller monomer droplets, and the surface area of the monomer droplets in each 1cm³ water is larger, and the emulsion dose adsorbed on the surface of the monomer droplets is increased. As a result, the number of micelles per 1cm³ water is reduced, the probability of nucleation is reduced, and the number of latex particles Np(1cm³ water) generated is reduced. When the initial monomer amount is constant, the diameter of latex particle will increase.
Effect of stirring intensity on polymerization reaction rate: As mentioned above, when stirring intensity is high, the number of latex particles in water per 1cm³ decreases, and the reaction center decreases, resulting in a low polymerization reaction rate; On the other hand, when the stirring intensity is high, the air mixed into the system increases, and the oxygen in the air is the inhibitor of the free radical reaction, which will also reduce the reaction rate.
The effect of stirring on the stability of the emulsion: excessive mechanical action will reduce the stability of the emulsion, and even gel, demulsification, this is because: ① The stirring action will give the latex particles with kinetic energy, when the kinetic energy of the latex particles exceeds the repulsion or steric hindration between the latex particles, the latex particles will condense and gel. (2) The emulsifier has a certain bonding fastness on the surface of the latex particle. When the stirring intensity increases, the emulsifier on the latex particle will be pulled away instantaneously due to the increased friction between the surface of the latex particle and the water medium, so the coverage of the emulsifier on the surface of the latex particle is reduced, so the stability is decreased. When a large number of bubbles are aroused (mainly from emulsifiers), the impact on stability is greater. ③ The stabilizing effect of non-ionic emulsifiers on the emulsion depends on hydration. When the stirring intensity increases, the friction between the latex particles and water increases, resulting in the thinning of the hydration layer, so the stability decreases.
To sum up, in order to ensure the smooth production process and uniform product quality, the vertical motor reactor should be equipped with a frequency conversion governor. The horizontal motor reactor should determine the appropriate wheel diameter ratio according to the shape of the stirring rod and the stirring efficiency to ensure the best stirring intensity.
