Mechanical impact dispersion

Methods of mechanical impact dispersion and liquid spurt impact dispersion... 

Crust formation thus is attributed to the disaggregation of the uppermost soil layer, initiated by the mechanical impact of the rain drops, and the subsequent dispersion of the clay fraction facilitated by the high ESR of the soil and by the low electrolyte content of rain water (Shainberg, 1990). Upon drying, the dispersed clay is responsible for the formation of the hard crust and decreases in infiltration rate. 

Unlike simple mixtures of polystyrene and polybutadiene such blends can be thermoplastically processed without phase separation ( splicing ) Furthermore, they can to a certain extent withstand mechanical impact without disintegration. This is because the above-mentioned graft polymers function also as compatibilizer at the borderline of the hard phase and the rubber-elastic dispersed phase (already at concentrations below 3%). 

In industrial and laboratory settings the subdivision process more commonly involves the comminution of large particles or aggregates into smaller sizes, either dry with subsequent dispersion (size reduction to the order of a few pm) or directly in a slurry (size reduction to as small as a few tenths of pm). Examples of comminution machines include agitator ball mills, colloid mills, cutting mills, disk mills, homogenizers, jet mills, mechanical impact mills, ring-roller mills, and roll crushers. 

Johansson and co-workers (7, 8, 9) have shown that heat transfer from a compressed spherical bubble does not increase the temperature of its liquid surface sufficiently to account for the impact sensitivity of liquid explosives the high sensitivity of nitroglycerin is postulated as arising from the fact that small droplets are readily formed by the impact and ignited by the compressed air. Bolkhovitinov (1) postulated crystallization of the liquid under the impact pressure, with the phase transition causing the temperature increase which causes explosions. Bowden (3) favors the adiabatic compression of gas bubbles combined with the dispersion of the explosive into fine particles as the mechanism for initiation by mechanical impact. 

Dispersibility of powders in the airflow is defined by the balance of forces generated by the mechanical stresses within the dispersion device and the interparticulate forces required to separate the primary particles simultaneously (24). The mechanism of dispersion is very complex and may involve dispersion by acceleration and by shear flow, as well as by impaction or other mechanical forces. 

The main difference between the continuous method and the mechanical impact or the high-speed water impact method is that the former is a continuous production process (Fig. 4.25(c)). In the continuous process, the three-phase electric furnace is used, which allows the liquid to melt continuously. Then, the liquid melt is dispersed into the ball under a certain disturbance. The ZA-fQ spherical catalyst produced by this method has been used in China. 

Of these two mechanisms, namely dispersion and debonding, by which dispersants improve impact resistance, the relative importance of each is not known because both effects occur simultaneously, and the effects cannot be separated. 

Mechanical Properties. Properties of typical grades of PBT, either as unfiUed neat resin, glass-fiber fiUed, and FR-grades, are set out in Table 8. This table also includes impact-modified grades which incorporate dispersions of elastomeric particles inside the semicrystalHne polyester matrix. These dispersions act as effective toughening agents which greatly improve impact properties. The mechanisms are not fiiUy understood in all cases. The subject has been discussed in detail (171) and the particular case of impact-modified polyesters such as PBT has also been discussed (172,173). 

With respect to good adhesion, reduced interfacial tension, fine distribution of TLCP phase, and the use of a compatibilizer can be very effective for this purpose. Remarkably improved mechanical properties (good impact properties as well as tensile properties) can be obtained with optimum amounts of the compatibilizer. Excess amounts of the compatibilizer causes the emulsifying effect to coalesce the dispersed TLCP... 

The aryl C—O—C linkage has a lower rotation barrier, lower excluded volume, and decreased van der Waals interaction forces compared to the C—C bond. Therefore, the backbone containing C—O—C linkage is highly flexible. In addition, the low barrier to rotation about the aromatic ether bond provides a mechanism for energy dispersion which is believed to be the principal reason for the toughness or impact resistance observed for these materials.15 17... 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

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