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    Home > Chemicals Industry > Chemical Technology > Polyacrylamide (PAM) Preparation Method-Inverse Emulsion Polymerization (3)

    Polyacrylamide (PAM) Preparation Method-Inverse Emulsion Polymerization (3)

    • Last Update: 2021-10-21
    • Source: Internet
    • Author: User
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    ⑤The oil-water volume ratio increases the water phase volume fraction.
    On the one hand, the amount of emulsifier dissolved in the oil phase decreases, and the emulsifier distributed at the water-oil interface increases; on the other hand, the amount of acrylamide in the system also increases, which leads to emulsification The efficiency is improved, and the minimum amount of emulsifier does not increase in proportion to the volume fraction of the water phase
    .


    As the volume ratio of water to oil increases, the intrinsic viscosity of the copolymer increases first, and then begins to decrease to a certain extent


    ⑥The temperature change of reaction temperature affects the stability of the emulsification system through the following physical quantities: interfacial tension; elasticity and viscosity of the interfacial film; partition coefficient of the emulsifier in the oil and water phases; mutual solubility between liquid phases; and other thermal agitation
    .


    The initiator decomposes into free radicals to overcome its activation energy, and generally generates active charged initiator ions through thermal decomposition


    When the temperature rises, the Brownian motion of the latex particles intensifies, which increases the rate of collision and coalescence between the latex particles, which leads to a decrease in the stability of the emulsion.
    At the same time, when the temperature rises, water on the surface of the latex particles will increase.
    The thinning of the chemical layer will also cause the stability of the emulsion to decrease, especially when the reaction temperature rises to equal to or greater than the cloud point of the emulsifier, the emulsifier loses its stabilizing effect, and demulsification occurs at this time
    .


    At lower temperatures, the initiator decomposition and free radical activity are affected, and the interaction between active groups and monomers is weakened, hindering the growth of the polymerization chain; at higher temperatures, the chain initiation growth rate constant and the chain termination rate constant increase at the same time , The intrinsic viscosity has a downward trend


    Table 3-8 The influence of reaction temperature

    ⑦Stirring speed In the emulsion polymerization process, an important function of stirring is to disperse the monomers into monomer droplets, which is conducive to mass and heat transfer
    .


    Choosing an appropriate stirring speed is conducive to the formation and maintenance of stable latex


    ⑧ The stability of the electrolyte emulsion polymerization system is closely related to the electrolyte content
    .


    Many people believe that polymer emulsions are most afraid of electrolytes.


    The addition of electrolyte will affect the polymerization conversion rate
    .


    When the electrolyte concentration is low, more monomers are dissolved in the water due to the influence of the salt effect, so the polymerization conversion rate and the intrinsic viscosity of the copolymer increase as the concentration increases


    ⑨The chelating agent may contain a small amount of heavy metal ions in the emulsion polymerization reaction system.
    Even if the content of these heavy metal ions is very small, they will inhibit the emulsion polymerization reaction, seriously affecting the normal progress of the polymerization reaction, and also reduce the polymer Quality and prolong reaction time
    .


    In order to reduce the interference of heavy metal ions, it is often necessary to add a small amount of chelating agent to the reaction system


    ⑩Terminator Terminator has two functions: a.
    Macromolecular free radicals can be chain transferred to the terminator to generate small molecular free radicals that have no initiating activity, or they can undergo copolymerization with the terminator to generate a terminal with a terminator The macromolecular free radicals that have no initiation activity, although they cannot further initiate polymerization, they can undergo diradical termination reactions with other active free radical chains to stop the chain growth reaction; b.
    Terminator can be combined with initiator or initiator One or more components in the system undergo a chemical reaction to destroy the initiator, which can stop the polymerization process and avoid changes in polymer properties during subsequent processing and application
    .


    Hydroquinone is the most widely used terminator in the high temperature emulsion polymerization with persulfate as the initiator .


     

     

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