Viscosity shear effect

The degree of polymerization and, therefore, the viscosity, shearing effects, and viscoelastic properties are controlled by the ratio of monofunctional UPy added to the solution, which end-caps the growing chains. By protecting the UPy end-groups or the monofunctional UPy with the photolabile group o-nitrobenzyl, the ability of UPy to dimerize is prevented. 

Fig. 6. Viscosity—time effects for a thixotropic material (a) shearing and (b) recovery. A nonthixotropic material would give horizontal lines in both cases.

The viscous shear properties at any given shear rate are primarily determined by two factors, the free volume within the molten polymer mass and the amount of entanglement between the molecules. An increase in the former decreases the viscosity whilst an increase in the latter, i.e. the entanglement, increases viscosity. The effects of temperature, pressure, average molecular weight, branching and so on can largely be explained in the these terms. 

Besides the main depolymerization reactions, side reactions should also be considered in the kinetic description of a PET recycling process. This is emphasized by the results obtained from a PET extrusion model [85] shown in Figures 2.19-2.23. The complete set of reactions summarized below in Table 2.10 have been used, but shear effects have not been taken into account. Chain degradation, accompanied by a significant reduction of intrinsic viscosity, occurs even within residence times of a few minutes. Carboxyl end groups, vinyl end groups and acetaldehyde are formed in amounts depending on residence time, temperature and initial moisture content of the PET flakes. 

In Eq. (38) the hydrodynamic velocity is that used to evaluate the momentum of the phase. In viscous flow it is the term used in establishing the shear from a knowledge of the viscosity when effects of cross linking of fluxes (01, 02) are neglected. The hydrodynamic velocity and the diffusional velocity are related by... 

The concentration of lactic acid in the steep has been shown to affect both the yield of starch178 and the quality of the resulting starch.179 Starch yields increased with increasing lactic acid concentration up to —0.5%, and decreased when more than —2% lactic acid was used. Shandera and lackson179 tested starch quality when steeped at 57°C with either 0.2% or 1.5% lactic acid and 0.05% or 0.3% sulfur dioxide. The level of sulfur dioxide had a small effect on starch quality, but the level of lactic acid had a pronounced reduction effect on peak viscosity, shear thinning viscosity, set-back viscosity, pasting viscosity and starch water solubility. 

Due to the plastic s viscosity, a melt shear effect is developed throughout the process. This shear is of prime importance between the calender rolls. The calender forms the web as a continuous extrusion between the rolls (Chapter 1). Unlike when processing just through a conventional extrusion line, the plastic mass cannot be confined when being calendered. Because of the lack of confinement, the shear effect and a broad melt band are essential aspects of calendering. 

The Intrinsic viscosities obtained In the Cannon Ubbelohde viscometer were corrected for shear effects by using the curve shown In Figure 2. This curve was obtained by using a Zlmm-type low shear viscometer (17) to determine the Intrinsic viscosities of four emulsion polymerized polystyrene samples (. The curve was linear over the range of Intrinsic viscosity results for polystyrene samples encountered In this study. 

A particle migration model was proposed by Gadala-Maria and Acrivos to describe experimental shear-induced migration observations. This model allows for a better understanding of the shear effects on particle diffusion for concentrated suspensions. Based on these studies, a conservation equation for the solid phase was established by Phillips, Amstrong, and Brown, which takes into account convective transport, diffusion due to particle-particle interactions, and the variation of viscosity within the suspension, namely ... 

Capillary rheometer ASTM D3835-90 Measure shear effects on viscosity at high rates Given sample conditioning (ASTM D618), given pressures or flow rates, determine viscosity via various corrections Determine dwell time that does not influence results (due to curing)... 

Arheopectic pigmented bleach (alkali metal hypochlorite) hard surface cleaner formulated with bentonite clay is disclosed in U.S. Patent 5,688,435. Examples of time-dependent shear effects determined from constant shear rate measurements at 1, 10, 50, and 100 sec-1 are provided in the patent and shown in Figure 4.2 and Figure 4.3. The viscosity data show evidence of shear thickening as a function of time at constant shear rates of 1 and 10 sec-1 and thixotropy occurs at 50 and 100 sec-1. The formulation is rheopectic at 10 sec-1. Dynamic mechanical data are also contained in the patent and the storage and loss modulus as a function of strain amplitude is shown in Figure 4.4, for one patent example. 

Figure 4.1. Within a single product category such as hair care one finds simple low-viscosity Newtonian fluids, non-Newtonian viscoelastic dispersions with time-dependent shear effects, and transparent highly elastic gels.

Both liquid fabric softeners exhibit time-dependent shear effects as shown in step shear rate measurements at room temperature. Figure 4.27 summarizes the steady shear viscosity as a function of time at shear rates of 0.1,0.5,1, and 5 sec-1. Each shear rate is held for a period of 30 sec. 

The effect of overall molecular weight or the number of blocks on rheological properties for the samples from the second fractionation can be illustrated as a plot of reduced viscosity vs. a function proportional to the principal molecular relaxation time (Figure 2). This function includes the variables of zero shear viscosity, shear rate, y, and absolute temperature, T, in addition to molecular weight, and allows the data to be expressed as a single master curve (10). All but one of the fractions from the copolymer containing 50% polystyrene fall on this... 

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