Amino resin microcapsules

Dietrich, K. Herma, H. Nastke, R. Bonatz, E. Teige, W. Amino resin microcapsules, II Preparation and morphology. Acta Polymerica (1989), 40(5), 325-331. 

In most cases, anionic water-soluble polymers such as poly(styrene-maleic anhydride), polyacrylic acid, etc., are apphed. These kinds of emulsifiers can influence the microcapsule preparation, mean particle size, and particle size distribution. By emulsification, an electric double layer generates on the dispersed phase. Then the electrostatic interactions between the protonated amino resin prepolymer and the negatively charged orgaific phase can act as a driving force, which enable the wall material polycondensate on the surface of the oil droplets but not throughout the whole water phase. ... 

Nonionic and small molecular emulsifiers such as poly(vinyl alcohol), polyoxyethylene nonyl phenyl ether, sodium dodecyl benzene sulfonate, and sodium lauryl sulfate can also be employed to make amino resin-type microcapsules. 

In situ polymerization is an acid catalyzed polycondensation process pH value cannot only affect the polycondensation rate, but also the surface activity of the amino resin prepolymer. Low pH process promotes the formation of methylene bridges affecting the amino resin solubility and therefore obtains a rough surface. However, for MF microcapsule making, at pH values below 3.0, the fraction of protonated melamine resin prepolymer is increased, and the MF prepolymer becomes more hydrophilic and consequently loses its encapsulation capacity. ... 

In situ polymerization has been industrialized for several decades. The large-scale amino resin microcapsnles are widely applied for carbonless paper, fabric care, and PCM, etc. Even though free formaldehyde is a big concern for its development, as a conventional and economic process, and especially through which excellent thermally and mechanically stable microcapsules can be made, in situ polymerization continues as one of the leading industry methods of microencapsulation. 

The appeal of DCPD and ENB for self-healing has led to the development of several encapsulation techniques for these monomers. Most prominent techniques consist of forming a shell material around monomer droplets by in situ polymerization of an amino resin melamine-urea-formaldehyde (MUF, Figure 10.2a) [56], urea-formaldehyde (UF, Figure 10.2b) [13-16], or melamine-formaldehyde (MF) [17, 18] walls in an oil-in-water emulsion. Comparison of microcapsules made with different shell wall materials is challenging because... 

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