Batch viscometer

Unfortunately, an on-line viscometer which can provide instantaneous [n] values at low and high temperatures is not available. Although batch viscometers have been used in the past (1, 13) the use of high speed SEC makes them useless due to the smaTT elution volumes. 

A number of instmments are based on the extmsion principle, including sHt flow and normal capidary flow (Table 6). These instmments are useful when large numbers of quahty control or other melt viscosity test measurements are needed for batches of a single material or similar materials. When melt viscosities of a wide range of materials must be measured, rotational viscometers are preferable. Extmsion rheometers have been appHed to other materials with some success with adhesives and coatings (10,161). 

Batch flow times are generally used in other words, the time required for a fixed amount of sample to flow from a reservoir through a capillary is the datum actually observed. Any features of technique that contribute to longer flow times are usually desirable. Some of the principal capillary viscometers in use are those of Cannon-Fenske, Ubbelohde, Fitzsimmons, and Zeitfuchs. 

Earlier experiments involved the collection of SEC effluent aliquots to measure solution viscosity in batches with the very time consuming Ubbelohde drop-time type viscometers. A continuous capillary type viscometer was first proposed for SEC by Ouano. Basically, as shown in Figure 1, a single capillary tube with a differential pressure transducer was used to monitor the viscosity of SEC effluent at the exit of the SEC column. As liquid continuously flows through the capillary (but not through the pressure transducer), the detected pressure drop (AP) across the capillary provides the measure for the fluid viscosity (h) according to the Poiseuille s viscosity law ... 

Figures 2 and 5 illustrate two different configurations of the viscometer that can be used in batch sanple viscosity determinations.

To obtain a larger range in viscosities determined with a capillary viscometer, polymers from different batches were used to prepare the emulsions. The results obtained with the capillary viscometer are given in Figure 3. The ratio between the viscosities of the two components of the emulsions is about 10. 

Often, such reactions occur at high temperatures, and material may freeze up in a normal process viscometer during runs or between batches. 

LVDV-111+ rheometers were set up with LV-4 spindles attached by SP-7Y Quick Connect Couplings. The Quick Connect couplings allowed the standard spindles to be easily disengaged from the viscometer at the end of the experiment. The resin + curing agent mixture was transferred into poly(ethylene) sample vials. Two separate batches were prepared - batch 1 was transferred into vials 1-3 and tested first. Batch 2 was prepared after the first test set was completed, and this batch was transferred to vials 4-6. Each vial was approximately 64 mm high, approximately 13 mm in diameter, and held approximately 5.5 mL. Each vial was clamped to its rheometer stand so that (a) the vial was essentially vertical and (b) the vial was centered about the immersed spindle. 

Monomer conversion can be adjusted by manipulating the feed rate of initiator or catalyst. If on-line M WD is available, initiator flow rate or reactor temperature can be used to adjust MW [38]. In emulsion polymerization, initiator feed rate can be used to control monomer conversion, while bypassing part of the water and monomer around the first reactor in a train can be used to control PSD [39,40]. Direct control of surfactant feed rate, based on surface tension measurements also can be used. Polymer quality and end-use property control are hampered, as in batch polymerization, by infrequent, off-line measurements. In addition, on-line measurements may be severely delayed due to the constraints of the process flowsheet. For example, even if on-line viscometry (via melt index) is available every 1 to 5 minutes, the viscometer may be situated at the outlet of an extruder downstream of the polymerization reactor. The transportation delay between the reactor where the MW develops, and the viscometer where the MW is measured (or inferred) may be several hours. Thus, even with frequent sampling, the data is old. There are two approaches possible in this case. One is to do open-loop, steady-state control. In this approach, the measurement is compared to the desired output when the system is believed to be at steady state. A manual correction to the process is then made, based on the error. The corrected inputs are maintained until the process reaches a new steady state, at which time the process is repeated. This approach is especially valid if the dominant dynamics of the process are substantially faster than the sampling interval. Another approach is to connect the output to the appropriate process input(s) in a closed-loop scheme. In this case, the loop must be substantially detuned to compensate for the large measurement delay. The addition of a dead time compensator can... 

This can be obtained from a single point measurement, but the used concentration should be specified. The inherent viscosity is especially useful to compare the degree of polymerization of different polymer batches, either as quality control or as a means to find the optimum polymerization conditions. Typical conditions are a temperature of 30 °C, a polymer solution with a solid content of 2 g L and a Cannon Ubbelohde viscometer with a 200 pm capillary [8]. 

The majority of published work on extrusion behaviour deals with compounded stock. Those papers reporting work on raw rubbers have usually been on the use of capillary rheometers to determine extrusion properties at higher shear rates than are possible with Mooney viscometers. Capillary rheometers are, in principle, quite simple to use, and the application of electronic, minicomputer and laser technology has reduced the operation and data analysis to a routine task. There are no standard ASTM or other test procedures, but under a specific set of conditions, once a material is characterized, the data can be used as standard for comparison of all subsequent batches. It is readily possible to characterize a raw rubber by an extrusion experiment to determine the viscosity/shear rate curve, extrudate swell, and stress relaxation.Both Sezna and Karg have shown how the Monsanto Processability Tester (MPT), a modified, computerized extrusion rheometer, can be used in predicting mixing behaviour. The MPT (shown schematically in Fig. 7) is a most versatile instrument. It has a larger than conventional barrel for minimal pressure drop in the barrel, a pressure transducer at the entrance to the orifice, a microprocessor system, and a laser device for... 

Viscometers usually contain small samples, and these must be representative of large batches of material, so care should be taken in obtaining samples. 

Park and Rhee [64] used a learning-based NLMPC to control semibatch copolymerization. The purpose was to linearize a nonlinear model based on previous batch data. In this way, the prediction is a function of the increment of inputs between two consecutive batches. They used an online densitometer to obtain conversion and a viscometer to... 

High shear testing machines such as the Wallace rapid plastimeter, the Monsanto processability tester and extrusion viscometers may better differentiate between natural rubber and polyisoprene, and even between polyisoprenes from different suppliers. None of these machines alone, however, will accurately predict the behaviour of the polymer or batch for all processing operations. Thus Mooney viscosity plus practical experience remain the principal factors in categorising factory processing. 

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