Rheology shear sensitivity

A general scheme for the development of an industrial process for alkaloid production is depicted in Pig. 1. On the basis of both fundamental research and feasibility studies the decision can be made whether an industrial production process is achievable. For the design of the process (production volume, process type, bioreactor size and type) detailed knowledge of both the kinetics of growth and product formation and physical properties (rheology, shear sensitivity) is essential. 

G.H. Meeten and J.D. Sherwood, Vane Technique for Shear-sensitive and Wall-slipping Fluids, Theoretical and Applied Rheology, P. Moldenaers and R. Kennings (eds.), Elsevier Science B.V., 1992, pp. 935-937. 

Shear-Sensitive Systems. In addition to hydrodynamic effects and simple viscous behavior, the act of pigmentation creates a certain amount of complex behavior (13). If the particles are fine. Brownian movement (14-17) and rotational diffusion (14. 18. 19) are among the phenomena that cause dispersed systems to display complex rheology. The role of van der Waals forces in inducing flocculation (20) and the countervailing role of two electroviscous effects (17. 21. 22) in imparting stability, particularly in aqueous systems, have been noted. Steric repulsions appear to be the responsible factor in nonaqueous systems (23. 24). The adsorbed layer can be quite large (25-28). as detected by diffusion and density measurements of filled systems or by viscometry and normal stress differences (29). 

In spite of the complexity of the situation, there have been attempts to create theories of rheological behavior of PLCs. Wissbrun [79] represents a PLC material as a space-filling system of domains. At rest, the minimum energy arrangement is achieved when the directors in the planes of contact are parallel. Under shear, the domains slide over each other. The model predicts shear sensitiveness, a phenomenon observed experimentally the curves of viscosity as a function of the shear rate are horizontal for low shear rates and then go down. In fact, for instance the results for PCarb - - PET/ 0.6PHB blends—if we employ such coordinates rather than those in Fig. 41.12—exhibit shear sensitiveness [76]. 

The rheological and thermal conductivity properties of the polymer matrix determine the heat necessary to melt the material. Relatively shear-sensitive materials become less viscous as they pass through the nozzle. For example, nylons form low viscous fluids when melted while polyethylene can undergo considerable mechanical working, producing heat necessary for plastica-tion. 

In Chapter 7 the combination of nanocomposites with metal hydroxide flame retardants has generally been discussed. Since the use of metal hydroxide usually requires very high concentrations within the polymer matrix (often higher than 50% w/w), to achieve desired levels of flame retardancy as noted above regarding the work of Beyer, - the influence on rheology and hence processability can be significant. Hornsby and Roflion have discussed this issue and they report that compounded polymer melt viscosities and shear sensitivities, for example. 

Typically this technique includes the preparation of the base material that involves the blending of film-forming excipients and therefore the API mixed along in a very appropriate solvent or solvent system. The choice of solvent basically depends on the API to be incorporated into the film/strip. The physicochemical properties of the API like heat sensitivity, shear sensitivity, the polymorphic mode of the API utilized, compatibihty of the API with solvent and different strip excipients are to be critically studied. The several components during this are liquid rheology, desired mass to be forged and content uniformity. Solvents used for the preparation of solution or suspension ought to ideally be elite ones from the ICH 3 solvent list [2]. 

Melt rheology offers a spectrum of information about the polymer (or blend), its thermal stability, shear sensitivity, the mechanism of degradation (e.g., chain scission vs. branching and crosslinking), processability, etc. The preferred method of testing is dynamic between cone-and-plate or parallel plates. ... 

The rheology of many of the systems displayed gel-like viscoelastic features, especially for the long-range attractive interaction potentials, which manifested a non-zero plateau in the shear stress relaxation function, C/t), the so-called equilibrium modulus, which has been considered to be a useful indicator of the presence of a gel. The infinite frequency shear rigidity modulus, was extremely sensitive to the form of the potential. Despite being the most short-... 

Surface shear rheology at the oil-water interface is a sensitive probe of protein-polysaccharide interactions. In particular, there is considerable experimental evidence for a general increase in surface shear viscosity of protein adsorbed layers as a result of interfacial complexation with polysaccharides (Dickinson et al., 1998 Dickinson and Euston, 1991 Dickinson and Galazka, 1992 Semenova et al., 1999a Jourdain et al., 2009). One such example is the case of asi-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = - 334 x 10 cm /mol) the interfacial viscosity after 24 hours was found to be five times larger in the presence of pectin (i.e., values of 820 80 and 160 20 mN m 1 with and without pectin, respectively) (Semenova et al., 1999a). 

Protein-polysaccharide complexation affects the surface viscoelastic properties of the protein interfacial layer. Surface shear rheology is especially sensitive to the strength of the interfacial protein-polysaccharide interactions. Experimental data on BSA+ dextran sulfate (Dickinson and Galazka, 1992), asi-casein + high-methoxy pectin (Dickinson et al., 1998), p-lactoglobulin + low-methoxy pectin (Ganzevles et al., 2006), and p-lactoglobulin + acacia gum (Schmitt et al., 2005) have all demon-... 

---