Fikentscher function

The intrinsic viscosity [17] (dl/g or ml/g) is an important physico-chemical constant of polymers estimated by extrapolation to an infinite dilution, that is to a zero concentration of the polymer. (For the Fikentscher function k — Eigenviscositat — see p. 278). If the intrinsic viscosity were in fact a measure of the length of the polymer chain molecules, then it would be expected not to vary as a result of changing the solvent. Dobry [59] has determined the viscosities of 0.04% solutions of nitrocellulose (11.4% N) in different solvents and calculated the intrinsic viscosity by means of extrapolation. The results are collected in Table 43. The changes in the... 

Viscosity determinations at the highest convenient concentration are of practical value, because in most of the applications of nitrocellulose, solutions of these concentrations are used, and there is usually little difference between the concentration in use and that used for the determination. All nitrocellulose solutions that are not very dilute show more or less abnormal viscosity, i.e. the rate of flow is not proportional to the applied stress or pressure. The ease of flow of a solution at one degree of stress cannot then be inferred from a viscosity determined at another. Nevertheless the measured viscosity of a comparatively concentrated solution is in general useful information. This advantage is sacrificed in what is the most rational of all viscosity systems, the German I.G. Method. Measurements are made in dilute solutions and the results are expressed in terms of the Eigenviscositat (k) of Fikentscher and Mark [99] a function which to a large extent is independent of concentration ... 

Costabilizers. In most cases the alkyltin stabilizers are particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyltin mercaptides. Mercaptans are quite effective costabilizers for some of the alkyltin mercaptides, particulady those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyltin mercaptide are currently the most efficient stabilizers for PVC extrusion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roll mill performance of some methyltin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. The test formulation contains 100 parts of PVC (Fikentscher K = 65), 1.2 parts of paraffin wax, 0.6 parts of calcium stearate, and 0.4 parts of methyltin-based stabilizers. 

Several researchers, e.g., Staudinger, Fikentscher, Houwink, Huggins, Hess, and Sakurada, developed a method to determine the influence of polymers with a certain molecular weight in diluted solutions by the use of the intrinsic viscosity [36-40]. And the intrinsic viscosity, which is a concentration limit where no interaction between the molecules in a solvent is given, is described by a power law function. It is only dependent mi the concentration of the polymer Cpoiy and the mean molecular weight M, see (20.24). 

---