Melt-dispersion process

A tertiary amine such as triethylamine is then added to the isocyanate-terminated prepolymer (containing carboxylic acid groups). The tertiary amine reacts with the pendant carboxylic acid groups, forming a carboxylic acid salt. The presence of this salt, together with adequate stirring, allows the dispersion of the prepolymer in water by the so-called melt dispersion process [57]. 

In the melt-dispersion process (95), an NCO-terminated prepolymer is prepared next from a polyester or polyether diol, a diisocyanate, and a glycol containing a potential ionic group. The NCO/OH is between 1.2 and 1.8. Then, the prepolymer is terminated with urea to form biurets, which are further alkylated to give an ionomer as shown in Fig. 17. The bis-biuret can be considered to be somewhat hydrophilic to be methylolated with formaldehyde. Upon dilution with water, a stable dispersion is formed. 

The results of this experiment indicate that during the melting-dispersion process of a thin film into droplets a part of a substance evaporates. Moreover, we were able to observe a mass loss even at the temperature lower than the equilibrium melting temperature but at which the process of dispersion into droplets occurs. 

Gromov, D.G., Gavrilov, S.A., Redichev, E.N. Ammosov R.M (2007). Kinetics of the melting-dispersion process in copper thin films. Physics of die Solid State, Vol. 49, No 1, p>p.l78-184, ISSN 1063-7834... 

Most elastomers that are used for nylon modification contain a small amount of maleic anhydride (0.3 to 2%). In the melt blending process, these elastomers react with the primary amine end groups in nylon, giving rise to nylon grafted elastomers. These grafts reduce the interfacial tension between the phases and provide steric stabili2ation for the dispersed mbber phase. Typically, thermally stable, saturated mbbers such as EPR, EPDM, and styrene—ethylene/butylene—styrene (SEBS) are used. 

Chokshi, R. J., H. K. Sandhu, R. M. Iyer, N. H. Shah, A. W. Malick, and H. Zia. 2005. Characterization of physico-mechanical properties of indomethacin and polymers to assess their suitability for hot-melt extrusion process as a means to manufacture solid dispersion/soJUflbarm ScB4 2463-2474. 

Blends 3 (a,b,c) Rheologically Robust Matrix and Weak Dispersed Components Since PE 1409 is a low viscosity nearly Newtonian polymer melt, its dispersive behavior is uncomplicated and more Newtonian like. Blend 3a forms a small (3-5-pm) droplet dispersion morphology, and Blend 3b is even finer (1-2 pm), becoming, only below 2% concentration, less subject to flow-induced coalescence. The TSMEE-obtained dispersions are finer than those from the TSMEE, with a variety of kneading elements (126). What is noteworthy about these blends is the early stages of the dispersion process, shown on Fig. 11.44, obtained with Blend 3a using the TSMEE at 180°C and 120 rpm. 

End groups are stabilized by treating the PFA with methanol, ammonia, amines and elemental fluorine that produces CF3 end groups. The polymer is recovered, dried and melt-extruded into cubes for melt fabrications processes. PFA is also available in bead (as polymerized), dispersion and fine powders forms. 

Commercially, it is polymerized by free-radical polymerization mechanism, usually in an aqueous (or nonaqueous) media via addition polymerization of TFE and hexafluoropropylene. The initiator for the polymerization is usually water-soluble peroxide, such as potassium persulfate. Chain transfer agents could be used to control the molecular weight of the resin. In general, the polymerization regime and conditions resemble those used to produce PTFE by emulsion polymerization. For melt fabrication processes, FEP is recovered, dried, and melt-extruded into cubes. It is also available in dispersion form. 

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