Blend time measurement indicators

It turns out that in low-viscosity blending the acdual result does depend upon the measuring technique used to measure blend time. Two common techniques, wliich do not exhaust the possibilities in reported studies, are to use an acid-base indicator and inject an acid or base into the system that will result in a color change. One can also put a dye into the tank and measure the time for color to arrive at uniformity. Another system is to put in a conductivity probe and injecl a salt or other electrolyte into the system. With any given impeller type at constant power, the circulation time will increase with the D/T ratio of the impeller. Figure 18-18 shows that both circulation time and blend time decrease as D/T increases. The same is true for impeller speed. As impeller speed is increased with any impeller, blend time and circulation time are decreased (Fig. 18-19). 

In the homogenous mixture of Starch and Polyvinyl alcohol (PVA), 30 % of plasticizer was mixed to make Pure blend. Then 10 % cellulose was mixed into above mixture followed by removal of extra water gave Cellulose-Reinforced starch-PVA blends. The different proportions of Fly ash were mixed into mixture of Cellulose-Reinforced starch-PVA blends to get various fly ash inserted Cellulose-Reinforced starch-PVA blends. Solubility, swelling behaviour and water absorption studies of Fly ash blends were measured at different time intervals at relative humidity of 50-55%. The insertion of Cellulose into starch-PVA blend decreases the solubility of blends due to the hydrophobicity of cellulose, but the solubility further increases by insertion of Fly ash into starch-PVA matrix that indicating the mechanical stability enhancement of blends. The water absorption behaviour of fly ash blends increases rapidly upto 150 min and then no change. The optimum concentration of Fly ash into Cellulose-Reinforced starch-PVA blend was 4%. 

The heart of the pilot plant study normally involves varying the speed over two or three steps with a given impeller diameter. The analysis is done on a chart, shown in Fig. 36. The process result is plotted on a log-log curve as a function of the power applied by the impeller. This, of course, implies that a quantitative process result is available, such as a process yield, a mass transfer absorption rate, or some other type of quantitative measure. The slope of the line reveals much information about likely controlling factors. A relatively high slope (0.5-0.8) is most likely caused by a controlling gas-liquid mass transfer step. A slope of 0, is usually caused by a chemical reaction, and a further increase of power is not reflected in the process improvement. Point A indicates where blend time has been satisfied, and further reductions of blend time do not improve the process performance. Intermediate slopes on the order of 0.1-0.4, do not indicate exactly which mechanism is the major one. Possibilities are shear rate factors, blend time requirements, or other types of possibilities. 

The crystallization of the blends cannot be followed adequately with density measurements since both components crystallize separately the density measurements indicate only the change of the overall density with time and its interpretation is difficult. 

A blend containing 10% of PMMA was similarly irradiated at 150 C. The only significant volatile product was methyl methacrylate and the weight loss, corresponding to the amount of the PMMA blended, was complete after 5 hours. Infra-red spectral measurements indicated the complete absence of methacrylate in the residue. At all irradiation times up to 5 hours the methacrylate content of the blend is completely separable from the PP by acetone extraction. Thus, these experiments could provide no positive evidence of reaction of either PMMA radicals or methyl methacrylate monomer with PP radicals, all of which were known to be present in the system. 

Dynamic mechanical properties of all pure components and blends were measured as a function of percent strain and indicated a linear viscoelastic region up to approximately 30-35 percent. Therefore, all rheological experiments were conducted at a strain rate of 20 percent. In cases where thermal degradation occurred (as seen in time sweep), the heating chamber was continuously purged with liquid nitrogen. Frequency sweeps, and in some cases frequency-temperature sweeps, were performed on all pure components and blends. 

Fig. 12.25 Result for the dynamic asymmetric blend PS/PVME at a composition 80 %/20 %. Lower panel solid spheres, dielectric data dashed line, temperature dependence of the relaxation times expected for PVME in the blend solid lines indicate the temperature dependence of the relaxation times for the pure components. Upper panel temperature dependence of the heat capacity measured by DSC (All data were taken from reference Cendoya et al. (1999))...

Cruz et al. [21] estimated crystallinities of samples from DTA data. Figure 45 shows how the crystalline fraction of PCL increased with overall PCL content from zero at about 25 wt % PCL to reach a plateau at about 80 wt %, comparable with that found in bulk PCL. Jonza and Porter obtained similar data [126] PCL crystallisation increased from about 8%, in 50 50 (w/w) blends, to about 60% in blends with 70% PCL. These latter workers also studied PCL crystallisation kinetics and found equilibrium crystallisation was achieved (at 37 °C) in 10 min or less for samples containing 70% or more PCL. Crystallisation times in excess of 40 min were required for samples with less PCL (Fig. 46) [126]. Similar measurements indicated that PC crystallised over the same composition range, i.e. PC... 

When analyzing copolymers or polymer blends in LAC mode, the retention time is indicative of the average chemical composition and the peak width is a measure of the CCD. The retention axis has to be calibrated either by standards with known chemical composition or multiple detector combinations can be employed to measure the local chemical composition. The average chemical composition of a copolymer can be easily described by the moments of the CCD. The average composition, G, the width, dG, and the skew, S, of the CCD can easily be calculated. The value of the skew parameter is zero, if the composition distribution is symmetrical. 

Blend times have been measured in agitated vessels using a variety of techniques conductivity, temperature, or pH (using an indicator for color change, as discussed in Section 4-4 and illustrated on the Visual Mixing CD). The results are presented as a relationship between the dimensionless blend time, which is the product of the measured blend time and the impeller rotational speed, dimensionless geometrical ratios, and in some cases, Reynolds and Froude numbers. 

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