Viscosity monitoring

The rheological behaviour of liquids and semisolids can be described as discussed in sections 7.3.10 and 7.4.4 of Chapter 7. Viscosity monitoring can be used as a quality control procedure, but some very practical rheological tests may be carried out. Some are discussed here. 

Here we describe a novel sensor under development by Bosch, which measures the viscosity, permittivity, temperature, and level of the oil [11]. The sensor housing is designed for insertion at the bottom of the oil pan where the opening in the oil pan is sealed by means of an O-ring. The measured viscosity and permittivity are the primary quantities supporting the oil condition evaluation, the temperature measurement is necessary to compensate the temperature-dependence of the sensor elements and because the measured parameters are temperature-de-pendent itself (especially the viscosity). Monitoring the oil level represents an extra feature, which makes the sensor a suitable replacement for already existing oil level sensors. This kind of sensor will be introduced to the market in 2004. 

PA-6/ABS/SAN-MA copolymer Viscosity monitoring/SEM/ mechanical properties Handge et al. 2012... 

Viscometry for Bulk, Reduced, and Intrinsic Viscosity Monitoring... 

As the polymer molecular weight increases, so does the melt viscosity, and the power to the stirrer drive is monitored so that an end point can be determined for each batch. When the desired melt viscosity is reached, the molten polymer is discharged through a bottom valve, often under positive pressure of the blanketing gas, and extmded as a ribbon or as thick strands which are water-quenched and chopped continuously by a set of mechanical knives. Large amounts of PET are also made by continuous polymerization processes. PBT is made both by batch and continuous polymerization processes (79—81). 

Process Control. The progress of the alkyd reaction is usually monitored by periodical deterrninations of the acid number and the solution viscosity of samples taken from the reactor. The frequency of sampling is commonly every half-hour. Deterrnined values are plotted against time on semi-1 ogarithmic coordinates, as shown in Figure 4. 

Figure 36 is representative of creep and recovery curves for viscoelastic fluids. Such a curve is obtained when a stress is placed on the specimen and the deformation is monitored as a function of time. During the experiment the stress is removed, and the specimen, if it can, is free to recover. The slope of the linear portion of the creep curve gives the shear rate, and the viscosity is the appHed stress divided by the slope. A steep slope indicates a low viscosity, and a gradual slope a high viscosity. The recovery part of Figure 36 shows that the specimen was viscoelastic because relaxation took place and some of the strain was recovered. A purely viscous material would not have shown any recovery, as shown in Figure 16b. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Advancement Process. In the advancement process, sometimes referred to as the fusion method, Hquid epoxy resin (cmde diglycidyl ether of bisphenol A) is chain-extended with bisphenol A in the presence of a catalyst to yield higher polymerized products. The advancement reaction is conducted at elevated temperatures (175—200°C) and is monitored for epoxy value and viscosity specifications. The finished product is isolated by cooling and cmshing or flaking the molten resin or by allowing it to soHdify in containers. 

Operate the column at half of the maximum recommended flow rate, taking special care to monitor the pressure, because the cleaning solution may be of different viscosity than the normal mobile phase. 

The molecular weight of the polymer is a function of the extent of polymerization and could he monitored through the melt viscosity. The final polymer may he directly extruded or transformed to chips, which are stored. 

In considering these benefits, the user should not overlook the constraints in using such fluids. They can be summarized as limited wear and corrosion protection (especially with certain metals), increased leakage due to its low viscosity, limited operating temperature range and the need for additional mixing and in-service monitoring facilities. 

Time-resolved optical absorption spectroscopy experiments have shown that arenesul-fonyl radicals decay with clean second-order kinetics14 the values of 2 k,/a h where s2 is the extinction coefficient at the monitoring wavelength, increased linearly with decreasing viscosity of the solvent, further indicating that reaction 16 is clearly a diffusion-controlled process. 

Striking support of this contention is found in recent data of Castro (16) shown in Figure 14. In this experiment, the polymerization (60-156) has been carried out in a cone-and-plate viscometer (Rheometrics Mechanical Spectrometer) and viscosity of the reaction medium monitored continuously as a function of reaction time. As can be seen, the viscosity appears to become infinite at a reaction time corresponding to about 60% conversion. This suggests network formation, but the chemistry precludes non-linear polymerization. Also observed in the same conversion range is very striking transition of the reaction medium from clear to opaque. 

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