Inverse emulsion process

Inverse emulsion process Inverse soaps Invert molasses Invert sugar... 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

Polymer emulsions can be produced by the direct and the inverse emulsion process. The direct emulsion polymerization can be performed in a batch, semibatch and continuous process. 

There is very little published information on the effect of shear or stirring conditions on the stability of water-in-oil emulsions to inversion. It has been established (Keogh et al., 1988) that water-in-oil emulsions (60g of a 7% sodium caseinate solution dispersed in 40 g milk fat) are stable to inversion only within a narrow range of throughput, refrigerant temperature and agitation rate when processed in a single-unit Votator scraped-surface... 

When the monomer is hydrophilic, emulsion polymerization may proceed through what s called an inverse emulsion process. In this case, the monomer (usually in aqueous solution) is dispersed in an organic solvent using a water-in-oil emulsifier. The initiator may be either water-soluble or oil-soluble. The final product in an inverse emulsion polymerization is a colloidal dispersion of a water-swollen polymer in the organic phase. 

Synthetic polymeric latexes can be produced by processes that are different from the standard emulsion polymerization methods described in this chapter. Two such processes, inverse emulsion polymerization and direct emulsification, are described briefly in order to make this paper more complete. The literature on these processes is less extensive, but interest in such processes has recently increased. 

Over the past decade there has been extensive interest in the kinetics and colloidal behavior of water-in-oil polymerizations. However, these efforts have focused on the elucidation of a general set of phenomena to describe water-in-oil processes, without distinguishing inverse-emulsion and inverse-suspension sub-domains. A confounding factor is certainly the inconsistent nomenclature inverse-suspensions (Ila) are within the inverse-macroemulsion polymerization domain (II), and are often described as inverse-emulsions, where the prefix macro has been omitted for brevity. However, inverse-emulsion (lib) is itself a... 

Heterophase processes should be primarily distinguished based on their emulsion structure (oil-in-water or water-in-oil) and type of stability (kinetic or thermodynamic). This identifies four mutually independent polymerization regimes, each with unique colloidal and chemical behavior. L Macroemulsion, II. Inverse-Macroemulsion, HI. Microemulsion, IV. Inverse-Microemulsion. The macroemulsion and inverse-macroemulsion domains can be further subdivided into Suspension (la), Emulsion (lb), Inverse-suspension (Ha) and Inverse-emulsion (lib) subdomains based on a transition at the critical micelle concentration. 

Investigations of water-in-oil polymerizations employing new monomers or emulsifiers for which kinetic or colloidal characterization is incomplete, require careful nomenclature designation. Under such circumstances a general description such as Water-in-Oil Polymerization or Heterophase Polymerization is recommended until the physical and chemical nature of the polymerizations can be identified. The designations inverse-suspension, inverse-emulsion and inverse-microemulsion should be reserved for processes for which a relatively advanced level of understanding exists. 

Various heterogeneous polymerization reactions of hydrophilic or water-soluble monomers in the presence of either difnnctional or multifunctional cross-linkers have been mostly utilized to prepare weU-defined synthetic nanogels. They include precipitation, inverse (mini)emulsion, and inverse micio ulsion polymerization utilizing an uncontrolled free radical polymerization process. 

A second type of stabiliser based on PSA is prepared by condensing the acid with polyethylene glycol to produce a block copolymer.(17). This polymer is an effective emulsifier for aqueous monomer solutions in hydrocarbons in the inverse emulsion process. 

Dual function filtrodynamics, to both characterize the presence, onset, and evolution of particulates that occur in polymerization processes and protect instrumentation through which diluted polymer reactor solution flows (e.g., as in ACOMP), is currently under development. Challenges include delineating which types of filters work best with given particulate systems (e.g., microgels from natural product solutions, or from microgels occurring in polymerization reactions in emulsions and inverse emulsions, etc.)... 

Dry polymer beads are manufactured using a surfactant-stabilized inverse suspension process similar to the inverse emulsion process described earlier. The final beads are obtained by removing solvent via azeotropic distillation and then centrifugation, followed by drying. The particle size of these dry beads is typically less than 0.3 mm. Polyacrylamide beads have the advantage of faster dissolution times than powders, but are more expensive to produce. 

Yang HW, Pacansky TJ. Inverse emulsion process for preparing hydrophobe-containing polymers. US patent 4918123. 

Heidel [39] prepared polysaccharide-acrylate graft polymeric absorbents using an inverse emulsion process. A combination of a lipophilic and a hydrophilic nonionic surfactant was used as dispersant. The combination of surfactants allowed both the aqueous monomer and the starch to be finely dispersed in the continuous oil phase, without gelatinization of the starch. Higher monomer concentrations in the aqueous phase were also possible, which helped the efficiency of the grafting reaction. Persulfates were used as the initiators. 

Manufacturing processes have been improved by use of on-line computer control and statistical process control leading to more uniform final products. Production methods now include inverse (water-in-oil) suspension polymerization, inverse emulsion polymerization, and continuous aqueous solution polymerization on moving belts. Conventional azo, peroxy, redox, and gamma-ray initiators are used in batch and continuous processes. Recent patents describe processes for preparing transparent and stable microlatexes by inverse microemulsion polymerization. New methods have also been described for reducing residual acrylamide monomer in finished products. 

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