Online viscosity determination

Table 5 shows the given (determined by LALLS) and intrinsic viscosities determined from an online viscometer (Viscotek Model 110) and the measured determined by different calibration techniques for six samples. The deviations [(measured -given )/(given )] x 100 between... 

A complementary use of polymer viscometry is the indirect evaluation of the MWD of a polymer from dynamic viscosity measurements [28-30]. The methods used to correlate the MWD of polymers to rheological data are based on the previous determination of the polymer relaxation spectrum from linear oscillatory shear experiments [31, 32]. MWDs obtained from viscometric data analysis can help in the determination of the MWD curve from online measurements, or in cases where this curve cannot be easily determined from size exclusion chromatography (SEC) [30, 31]. 

As the system is aqueous based, it is routinely used for the analysis of nonvolatile analytes with no need for derivatization of sample to maintain analyte solubility. A typical LC system experiences lower diffusion rates than GC because the mobile phase has a higher viscosity and density. LC can be coupled online to sensitive electrochemical and fluorescence detection units. This is an important consideration for the analysis of EDCs present at low concentrations in environmental matrices. Both UV and EC detection were applied to the determination of estrogenic compounds in water samples using LC. 

Figure 2 The molar mass distributions of two hydroxypropyl-methyl cellulose (HPMC) batches (Metolose 60 SH 10 OOOcps, Shin-Etsu, Tokyo, Japan) determined with SEC connected online to multi-angle scattering (MALS) and refractometric (Rl) detectors. The broad distributions contain HPMC chains ranging from a few thousands up to several millions in molar mass. Despite the fact that the two batches belong to the same viscosity grade, significant differences are seen in the molar mass distributions. This emphasizes the importance of proper characterization of the complete molar mass distribution instead of only estimations via viscosity averages. (Reproduced with permission from Bengt Wittgren, Analytical Development, Astra Hassle/AstraZeneca, Moindal, R D Mbindal.)...

Online viscometers (single, dual, or four capillary type viscometers with a symmetrical or asymmetrical bridge) These measure the pressure difference between a sample path and a reference path filled with pure solvent. Viscometers are used to measure specific and intrinsic viscosity, molar masses based on Benoit s universal calibration approach [6] and Mark-Houwink coefficients. Mass spectrometry (MS) detectors (see Chapter 10) Different MS methods have been used in macromolec-ular analysis. They are used to determine absolute molar masses for homo- and copolymers and to detect polymer structures. Matrix-assisted laser desorption ionizationtime of flight (MALDI-ToF) and electrospray ionization (ESI) are the most common instruments used in combination with SEC (Section 9.4.2.4). A recent application summary is available [12]. 

FIGURE 12.7 Automatic Continuous Online Monitoring of Polymerization Reactions detectors response (LS90 ° and viscosity) to the different components of the diluted, phase inverted polyacrylamide emulsion (top) determination of dissolution time, from RI data for polyacrylamide in emulsion and in dry form. Reprinted (adapted) with permission from Alb AM, Farinato F, Calbick J, Reed WF. Online monitoring of polymerization reactions in inverse emulsions. Langmuir 2006 22 831-840. 2006 American Chemical Society. 

Whereas the online determination of M, conversion, and rednced viscosity was of primary concern, the study of the time dependent light scattering signatures, lit), from different reactions was of interest since they exhibit features characteristic of the type of reaction taking place. 

Extensive work has been done to build models around standard process data as well as other types of online data such as online melt flow index, bulk viscosity, and so on the primary goal of these is to attempt to infer polymer properties to enable better process control [22-26]. Generally, much of the model building work is done off-line to determine optimal operating poUdes and optimal process variable trajectories that define end-product quality and reaction yield. Several types of advanced software have also been developed toward this goal [27,28]. There is more discussion of process control theory and application in other chapters of this book, especially Chapters 16-18. 

Additionally, online monitoring methods have been developed to adapt off-line characterization methods into in situ (i.e., in-reactor) probes for determination of kinetics and monomer conversion with optical methods such as mass spectroscopy (MS), ESR, FTIR, near IR, and Raman spectroscopy. However, frequently, due to high turbidity and viscosity of the polymer reaction milieu, the optical surfaces are easily fouled, leading to frequent sensor failure. Furthermore, data acquired with these probes are model dependent the empirical and inferential calibration schemes used can be expensive and time consuming to develop and can drift and become unreliable as reactor conditions change and as sensors become fouled. Another limiting feature of these methods is that they usually measure only one characteristic of the reaction, such as monomer conversion and are not directly sensitive to polymer molecular mass and intrinsic viscosity. More detailed discussion of these techniques can be found in Chapters 6-10 of this book. 

Product quality is usually determined and certified off-line in a quality control laboratory to ensure that specified properties of a production batch fall within the established range. Specifications related to molecular weight, charge density, composition, particle size, viscosity, rate of dissolution, solution viscosity, and residual monomer are common. Production batches that do not meet the specifications either require further processing, rework, or disposal and reduce production efficiency. As online analytical methods are employed, first pass yields (the proportion of production that meets specifications the first time) usually increase. 

Alternative ways to obtain absolute data from SEC include the use of viscometry detectors that allow the intrinsic viscosity to be measured online. Also, light scattering may be used to determine absolute molar masses as a function of the elution volume. Finally, SEC may be calibrated using mass spectrometry (MS). For some polar polymers, online SEC - electrospray-ionization - MS has been demonstrated. More commonly. 

U-tube density cell (ASTM D-4052 method), viscosity by a Stabinger viscosity cell (ASTM D-7042 method), and boiling point distribution by ASTM D-86 method. The gas product was analyzed by online gas chromatograph. Physical properties of the catalyst such as bulk density and total pore volume using the Brunauer-Emmett-Teller (B.E.T.) technique were determined by ASTM C-29 and ASTM-4222 methods, respectively. 

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