Dispersed melt

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

Lipid microparticles and nanopellets for oral use were first described by Speiser [11]. Nanopellets are prepared by dispersing melted lipids with high-speed mixers or via ultrasound techniques. Lipospheres developed by Domb are also prepared from dispersed lipids by stirring and sonication [12]. These preparations may contain a high degree of microparticles, which thus excludes an intravenous injection. For other routes of application (e.g., peroral administration), these microparticles might not be a serious problem. Furthermore, the dispersions may be contaminated by metal shed. With optimized conditions, however, mean particles sizes of 1(X) to 200 nm are possible [13]. 

L. Zhu, K. A. Nahr, and X. Geng, Modeling of Particle-dispersed Melting Mechanism and Its Application in Corotating Twin Screw Extrusion, J. Polym. Sci. Part B Polym. Phys., 39, 2461-2468 (2001). 

The pioneer in this field was Speiser, who developed nanopellets for peroral administration [7], These nanopellets were produced by dispersing melted lipids with high-speed mixers or with ultrasound. A relatively large amount of microparticles was present in these formulations, which might not be a serious problem for peroral administration, but they exclude an intravenous injection. Lipospheres, produced by high-shear mixing or ultrasound, were developed by Domb and represent similar systems [8-10], They also contain large amounts of microparticles. 

The crystaUization behavior of a dispersed melt-phase, for example discrete melt droplets, in an amorphous matrix can be dramatically affected... 

Figure 1.2 Film formation of polyolefine dispersion, melting as function of time during drying (a) 60°C, (b) 80°C, (c) 100°C, and (d) 120°C.

Characterization of the polymer primary structure is best carried out using solution NMR methods due to the increased spectral specificity of solution NMR methods as compared to solid state NMR methods. Solution NMR methods here includes solutions, gels, dispersions, melts, etc. Any method involving dilution, dispersion, increased temperature, etc. that will introduce sufficient motion into the polymer chain such that the unwanted nuclear spin interactions can be averaged to their trace values (zero for dipolar, isotropic chemical shift for the chemical shift anisotropy, scalar coupling for the indirect dipolar interaction, and zero for quadrupolar), on a sufficiently short time scale. 

The crystallization behavior of a dispersed melt phase, for example, discrete melt droplets, in an amorphous matrix can be dramatically affected compared to that of the bulk polymer. It has been reported by several authors that crystaUizable dispersed droplets can exhibit the phenomenon of fractionated crystallization originating from the primary nucleation of isolated melt particles by species with different nucleating activities (heterogeneities, local chain ordering)... 

PRACTICAL EXAMPLE FOR THE PREPARATION OF A POLYURETHANE DISPERSION (MELT-DISPERSION TECHNIQUE)... 

Molecule Dipole Moment (D) Dipole- Dipole Dispersion Melting Point (X) Boiling Point (°C) at 1 atm... 

In situ coating is less expensive as the dispersant is added during extrusion. The dispersant melts and dissolves in the polymer melt, which acts as a solvent to facilitate the surface treatment. 

Preparation Cast from aqueous dispersion Melt extruded... 

Thin films were obtiincd by melt-pressing at temperatures of 30 K above their melting points and then slowly cooled or quenched in cold water. Thble 5 lists the thermal properties and remanent polarization for nylon-MXDs. Nylon-MXD-13 showed no glass transition temperature, but peaks for both crystallization and melting. The quenched ny-lon-MXD-9 showed no exothermic crystalltzalion. but T, and a dispersed melting peak. 

The crystallization behavior of a dispersed melt phase in an amorphous or semi-crystalline matrix phase has generated a lot of interest in recent years. In polymer blends in which the crystallizable phase is dispersed into tine droplets in the matrix, crystallization upon cooling from the melt can occur in several temperature intervals that are initiated at different undercoolings, often ending up with a crystallization at the homogeneous crystallization temperature T(.,hom- This phenomenon is often called fractionated crystallization [73, 74]. The phenomenon of delayed crystallization was directly related to the... 

Wall slip with concentrated dispersions Melt fracture at r,. lO Pa... 

More recently KuHchikhin [83] has found that dispersed melt phases (droplets) organize themselves during shear flow into a series of parallel linear arrangements. This would seem to be the mechanism by which the filaments of the dispersed phases [71 to 76] of the previous paragraph are formed. 

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