Initial viscosity

Dicyandiamide fluidifies various adhesives and glues. In the presence of dicyandiamide, the initial viscosity of the adhesive formulations is lowered and maintained at a lower range for longer periods of time, thus preventing premature gelling and extending the useful life of the adhesive (see Adhesives). 

With typical values of = 6 x 10 N s/m and b = 0.01 s, penetration will be about ten diameters under a driving pressure of 1 N/mm- (ca. 10 atmospheres). With a higher initial viscosity of 6 x 10 N s/m — perhaps as a result of delay in applying the same adhesive — penetration would only be 3.2 diameters. 

The capacity of the ordered film for supporting loads is between that of the static film and that of the dynamic fluid film. The orientation property of the ordered layer gradually becomes weak with the distance apart from the metal surface. The transition occurs as the ordered film appears more important between the two solid surfaces. The thickness of the ordered film is related to the initial viscosity or molecular size of the lubricant, as shown in Fig. 13, so that we can generally write the critical film thickness as follows ... 

Equation (7) indicates that the critical film thickness changes very slowly with an increase in initial viscosity when it is close to 26 nm. 

Endo-pectinases were determined by reduction of viscosity of a 1% (w/v) pectin solution at 30 C and pH 4.2 using an Ostwald viscosimeter as previously described (9). One unit was defined as the amount of enzyme which reduced the initial viscosity of the solution by 50%. 

Reduction in the apparent bulk viscosity due to a change in polymer rheology. It is well known that ultrasound can lead, via degradation, to a reduction in polymer solution viscosity. Although Fairbrother did not investigate whether degradation of the polymer, and subsequent reduction in R.M.M. and hence viscosity had occurred, it seems reasonable to assume that the polymer melt with an initial viscosity of 30000-100000 poise would certainly have resisted cavitation and thus degradation. 

There will be a compromise between the initial viscosity and the ageing behaviour in the choice of the best dispersant. 

The rate of decrease in viscosity, and the value of the lower limit at which the viscosity becomes stable depends on the type of nitrocellulose and on the solvent used. The higher the initial viscosity, the faster viscosity falls. However, the viscosity curves as a function of time never cross one another. 

Ultrasonic waves also bring about a reduction in the viscosity of nitrocellulose. The effect is more marked the higher the initial viscosity, and thus the longer the nitrocellulose chains (Sollner [93] Schmidt and Rommel [94]). For instance, nitrocellulose with a molecular weight of 123,000, estimated by means of Staudinger s viscosity equation, subjected in solution form to the action of ultrasonic waves suffered a degradation to a molecular weight of 70,000-80,000. 

Such a simplified approach nevertheless proved to be practically acceptable in view of the fact that fju may be taken as constant for the plastisol of the same formulation and preparation time. This probably follows from the relatively low initial viscosity as compared to that aquired by the material upon heating. 

The difference in processing behavior between rotors provided with straight blades and those with pitched blades is shown in Figure 6 by an application referring to solvent recovery from a polymer solution of low initial viscosity. The evaporation capacity of a thin-film evaporator equipped with straight blades decreases considerably as soon as the concentrated polymer reaches a viscosity between 1000 and 2000 P. The greatly increased mean film thickness that characterizes this vis-... 

The heat-transfer coefficients are represented as a function of the peripheral speed of the rotor in Figure 11. In the evaluated tests, a polymer solution having an initial viscosity of approximately 300 P was concentrated down to a final product of about 3000 P. The higher peripheral speed produces only a small increase in the amount of heat... 

Sheet and Bulk Molding Compounds. The activity with SMC and and BMC is based on resin technology which was known more than 20 years ago (3). The key concept involves increasing the viscosity of the unsaturated polyester resin. The polyester resin with an initial viscosity of several thousand centipoise is advanced chemically to a viscosity of several million centipoise. 

Inhibition Studies. A number of compounds were employed to study the amino acid residue(s) that are important for cellulase activity. Samples of enzyme (0.1 mL, 500 units) were pre-incubated with 0.1 mL of inhibitor in semimicroviscometers for 8 min at 35°C. CM-cellulose solution (0.8%, w/v), which had been separately equilibrated at 35°C for 20 min was added to the viscometers and initial viscosity losses were measured after 15 min. Inhibitors were replaced by buffer in control experiments. Compounds that are insoluble in buffer, e.g., N-ethylmalei-mide, diisopropyl fluorophosphate, and succinic anhydride, were dissolved in a small volume of 95% ethanol before assay. p-Chloromercuribenzoate (p-CMB) was first dissolved in 0.2M NaOH and the pH adjusted to eight prior to pre-incubation with cellulases. 

Successful solution of these technical problems depends on the initial viscosity of the material in the sprayer, the surface tension of the material, changes in the rheokinetic properties during the process, sprayer design, and jet configuration. 

Figure 9.1 shows a qualitative plot of the viscosity variation produced during the heating of a thermosetting polymer. Initially, viscosity decreases with the increase in temperature, but as cure progresses, an abrupt increase in viscosity is observed. The processability window is the range of T0 values... 

Initial viscosities seem to be dependent on several resin variables within the plastisol. Resin particle size distribution is important to the viscosity in that decreased interparticle void volume by improved packing will decrease plastisol viscosities. The intraparticle void volume within agglo-... 

It is clear that in order to produce a low initial viscosity plastisol with good viscosity stability, the drying conditions need to be optimized for two factors ... 

Optimization of the particle size distribution in order to minimize void volume in the plastisol to get good initial viscosities. 

The mixing and degassing must be completed in sufficient time to allow complete filling of the mold and for any air bubbles to rise to the surface. The hotter the material, the lower the initial viscosity will be. However, the viscosity will increase more rapidly and the material will gel off more quickly. This is shown in Figure 4.5. 

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