Molecular viscosity, factors affecting

This work describes the design, operation and application of the continuous GPC viscosity detector for the characterization of the molecular weight distribution of polymers. Details of the design and factors affecting the precision and accuracy of results are discussed along with selected examples of polymers with narrow and broad molecular weight distribution. 

Since the results of zone refining depend on the interaction of momentum, heat and mass transfer in the system, all the basic factors affecting these three processes, both molecular and convective, have to be taken into consideration. These basic factors are concentration W, Density f, viscosity /i, heat capacity Cp, temperature den-sification coefficient, thermal conductivity k, molecular dif-fusivity D, zone diameter d, zone length L, zone travel speed u, temperature difference in zone A T and acceleration g. The concentration W may affect, JJi, Cp,, k, and D as well as the properties of the P.S.Z. (mushy region). Aside from the concentration W, all... 

The choice of shear stability level is also a major factor affecting the CCS viscosity, and therefore choice of base stock. Since shear stable, lower molecular weight, VI improvers are inherently poorer thickeners, high use levels are required with a necessary compensating reduction in base stock viscosity. 

The molecular weight of a polymer is the most important factor affecting rheology. For most polymers the zero-shear viscosity is approximately proportional to the weight-average molecular weight (M ) below a critical value (M ) and depends on M to a power equal to 3.5 at molecular weights above M ... 

Because a latex polymer is insoluble in water, the factors affecting the viscosity of latexes differ significantly from polymers dissolved in solvents. Since the aqueous continuous phase interacts with the polymer only at the surface of the latex particle, the molecular stracture of the polymer does not have the effect that it would if the polymer were dissolved in the liquid. The molar mass and polymer backbone flexibility, in particular, have no direct effect on the viscosity of the latex. The principal latex parameter that influences latex viscosity is of course... 

Viscosity is affected by the discussed additives in different ways. Figure 10.36 shows a marginal decrease in viscosity with concentration. Addition of ultrahigh molecular weight silicone additive, which is used as a mold release, decreases viscosity of polyethylene melt and thus lowers energy input in extrusion (Figure 10.37). Addition of 0.2 wt% of silicone additive reduced Brabender torque by 40%, elongational viscosity by a factor of four, and increased spiral mold flow by 30%. ... 

Polyethylene crystallizes from the molten state or solution when prevailing conditions make the crystalline state more stable than the disordered one. The processes by which polyethylene crystallizes reflect the properties of the disordered state from which the ordered phase condenses. Thus, for instance, levels of chain entanglement, molecular dimensions, and viscosity all play important roles. The factors affecting the structure of the disordered state are both intrinsic to the molecules and extrinsic to the surrounding conditions. The principal molecular factors are the molecular weight, molecular weight distribution, and concentration, type, and distribution of branches. External factors include temperature, pressure, shear, concentration of solution, and polymer-solvent interactions. 

Molecular weight distribution (MWD) is an important factor affecting the rheological behavior of a polymer solution. The effects of MWD on polymer blend and melt were studied previously by many groups. Struglinski el al [1] analyzed the linear viscoelastic properties of the binary polydispersed entangled polymers. They concluded that the behavior of the binary mixture depends both on the relaxation time and weight fraction of the individual component. The zero shear viscosity pA of the mixture is dominated by the... 

Rheology of LLDPE. AH LLDPE processiag technologies iavolve resia melting viscosities of typical LLDPE melts are between 5000 and 70, 000 Pa-s (50,000—700,000 P). The main factor that affects melt viscosity is the resia molecular weight the other factor is temperature. Its effect is described by the Arrhenius equation with an activation energy of 29—32 kj/mol (7—7.5 kcal/mol) (58). 

Having thus seen that enviromental factors determine viscosity largely by their effect on free volume let us now consider the influence of molecular factors which affect viscosity largely by entanglement effects. 

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