Shear dispersion

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-... 

Average temperatures (40-70°C) in combination with high-shear dispersion equipment, of which three-roll mills are a good example, appear to afford the best results in terms of pigment dispersion in wetting systems, such as offset varnish. Fig. 33 shows a curve in which the degree of dispersion reaches a distinct maximum at one particular temperature. 

A vertical helical ribbon blender can be combined with an axial screw of smaller diameter (Fig. 18-25). Such mixers are used in polymerization reactions in which uniform blending is required but in which high-shear dispersion is not a factor. Addition of the inner flight contributes little more turnover in mixing newtonian fluids but significantly shortens the mixing time in nonnewtonian systems and adds negligibly to the impeller power [Coyle etal.. Am. Inst Chem. Eng.J., 15, 903 (1970)]. 

Mixing on the meter (subkilometer) scale is dominated by stirring due to shear dispersion by internal and inertial waves and subsequent diapyc-nal mixing (Young et al., 1982), which gives... 

At = t - ts, travelling with speed Vs. (Here Kxc is the longitudinal diffusivity in the canyon which is typically 2 or 3 times greater than Kc as a result of shear dispersion, e.g. Pasquill and Smith, 1983 [484]). Consequently, the length of the cloud as it reaches the top of the canyon ( x (x / )) is very much greater than the width d of the canyon, i.e. 

Jones, S.W. Young, W.R. Shear dispersion and anomalous diffusion by chaotic advection. J. Fluid Mech. 1994, 280, 149-172. 

U.S. 5075027 (1991) [132] Dixit et al. (Colgate- Palmolive) High shear dispersing to entrain air in-line mixing Stable product... 

Mixer in tank drop diameter 4 to 5000 pm capacity >0.05 L/s for viscosities <10 mPa-s. Colloid mill drop diameter 1 to 8 pm capacity 0.01 to 3 L/s for viscosities <10 mPa s but usually >1000 mPa-s. Homogenizer drop diameter 0.1 to 2 pm capacity 0.03 to 30 L/s for viscosities <10 mPa s but usually <200 mPa-s decrease the drop diameter by increasing the exit pressure. High shear disperser for viscosities 10 to 5 x 10 mPa s. Roller mills for viscosities >10 mPa-s. Motionless mixer drop diameter 100 to 1000 pm (about 0.15 times drop diameter for fluid velocity in a pipe... 

Laminar shear dispersion is required in particular mixing applications where the ultimate size of particles or drops of a dispersed phase is to be reduced by the mixing process/ -. In laminar mixing the shear stresses available for dispersion are usually greater when the viscosity of the mix is high. In mixing processes either or both distribution or dispersion may be required and... 

Provides proper combination of pumping action and shear/ dispersion essential for fast consistent results. 

Coarse particle removal by sieving Dispersion 2 Shearing dispersion method Removal of impurities 2 ... 

A balanced combination of the high-shear dispersive and low-shear distributive screw elements... 

Strong shear-thinning behavior can also be verified for suspensions of non-spherical particles under shear. A typical case is fibers suspension. Non-sheared dispersed fibers may exhibit a disordered array that is hardly disturbed under low shear rates. However, as shear increases, fibers adopt a configuration (as shown in Fig. 27) that minimizes interaaions. thus decteasing viscosity. 

Pigments may be introduced into plastics by a variety of methods. Direct dry colouring, in which the pigment is incorporated into the molten polymer often along with other additives using high-shear dispersing... 

Mixing, as a term, is generally used in three different senses i. It corresponds to the blending of two or more components, i.e. it is a unit operation carried out to unify two or more material streams or charges into one. a. Mixing is the synonym of agitation or stirring, i.e. it is an action carried out e.g. by stirrers or motionless mixers to induce relative displacements of various parts of the treated material by convection, shear, dispersion, random movements, turbulence, etc. 

Aqueous dispersions Emulsion polymerization is used to prepare this type of adhesives, mostly made of acrylics, chloroprene, and polyvinyl acetate. High shear dispersion can also be used in the presence of surfactants to obtain water home formulations, as with polyurethanes, epoxies, silicones, and some elastomers. 

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