On-line Viscometer Research Articles

Effect of Temperature on Ultrasonic Degradation of Sodium Poly(Styrene Sulfonate): Analysis of Online Viscometric Data with Theoretical Models and Machine Learning Approaches

The effect of temperature (15, 20, 25, 30, and 35 °C) on the ultrasonic degradation of sodium poly(styrene sulfonate) polyelectrolyte (5.10−3 g/ml) in aqueous NaCl solutions (2.75 m) was investigated. Using the thousands of data obtained by an online viscometer monitoring technique, the degradation kinetics, and the effect of temperature on this process were analyzed in detail with 12 theoretical models reported in the literature. The Giz, OHM, and Tang-Goto models were found to give good results, and these models were selected to evaluate the effect of temperature on the ultrasonic polymer degradation. The degradation constant and the limiting molecular weight at which no polymer chain scission occurs were found to decrease with increasing temperature for all models. Furthermore, modeling was performed using popular machine learning algorithms, such as Multilayer Perceptron, Adaptive Neuro-Fuzzy Inference System, Long Short-Term Memory, Gradient Boosting Regression, Light Gradient Boosting Machine, eXtreme Gradient Boosting Regressor, CatBoost, and Random Forest. The best results were obtained with the Long Short-Term Memory, a deep learning approach. In addition, optimization techniques, such as Particle Swarm Optimization, Genetic Algorithm, Artificial Bee Colony, Clustering, and Global Optimization Method based on a parabolic approach, were used to determine the optimum molecular weight evolution and degradation temperature.

Characterizing Styrene Monomer and Oligomers by SEC/MALS/VISC/DRI

Worldwide polystyrene (PS) production in 2020 was approximately 27 million metric tons, distributed among many nations, making it one of the most heavily imported and exported chemicals. Commercially produced PS usually possesses a broad molar mass distribution, often with a substantial oligomeric component. The latter can significantly affect processing and end-use, in addition to having potentially hazardous health effects and to impacting the polymer’s export classification by regulatory agencies. Quantitation of the oligomeric region of polymers by size-exclusion chromatography with concentration-sensitive and/or static light scattering detection is complicated by the non-constancy of the specific refractive index increment (∂n/∂c) in this region, which affects the calculated amount (mass fraction) of oligomer in a polymer, molar mass averages, and related conclusions regarding macromolecular properties. Here, a multi-detector SEC approach including differential refractometry, multi-angle static light scattering, and differential viscometry has been applied to determining the ∂n/∂c of n-butyl terminated styrene oligomers at each degree of polymerization from monomer to hexamer, and also of a hexadecamer. Large changes in this parameter from one degree of polymerization to the next are observed, including but not restricted to the fact that the ∂n/∂c of the monomer is less than half that of PS polymer at identical experimental conditions. As part of this study, the individual effects of injection volume, flow rate, and temperature on chromatographic resolution were examined. Incorporation of the on-line viscometer allowed for accurate determination of the intrinsic viscosity and viscometric radius of the monomer and oligomers.

High temperature-size exclusion chromatography with triple detection to assess the molecular architecture of low-density polyethylene: Insight into branching and processability correlations.

In this study, three commercially available low-density polyethylene (LDPE) polymers produced via a tubular reactor process, with varying melt flow rates at 190°C/2.16kg (4.0, 1.9, and 0.75g/10min), have been selected and subjected to high temperature-size exclusion chromatography (SEC) analysis coupled with an infrared-5 (IR-5), viscometer (VISCO), and multiangle laser light-scattering detectors. The molecular weight (MW), MW distribution, short-chain branching (SCB), and long-chain branching parameters were investigated. It was found that MW obtained by the universal technique (∼1.57-1.7 times) and multiangle laser light-scattering detection technique is (∼1.43-1.55 times) higher than that of the conventional calibration technique, which could be attributed to structural complexity associated with LDPEs which is not clearly understood by conventional SEC mode alone. The bulk SCB per 1000 total carbon atoms estimated by IR-5 detection was found to range from 16.50 to 17.80. On the other hand, long chain branching frequency per 1000 total carbon atoms obtained by online VISCO and multiangle laser light-scattering detection ranged from 0.46 to 0.54 and 0.65 to 0.94, respectively. Further, the significance of long chain branching parameters on the polymer processing behavior was studied in correlation with rheological property (Die swell ratio).

Synthesis and molecular structure of highly compact star-like poly(methyl methacrylate) and poly(butyl methacrylate)

Poly(methyl methacrylate) and poly(n-butyl methacrylate) highly dense star-like polymers with a varied number and length of arms were prepared by the arm-first group transfer polymerization. The work is focused on the detailed characterization of the molecular structure and dilute solution properties of star-like polymers. The refractive index increment of the star-like polymers was compared with that of corresponding linear homopolymers. The prepared polymers were characterized by size exclusion chromatography coupled with a multi-angle light scattering detector and an online viscometer. Except for the commonly used molar mass, root mean square radius, and intrinsic viscosity, the obtained data also allowed the determination of the distribution of the arms per molecule, the calculation of the average number of arms per molecule, and the determination of the molar mass dependency of the draining factor. The relation between the number of arms per molecule and molar mass was estimated using various theoretical equations and compared with the true values obtained by the division of the slice molar mass by the molar mass of arms.

On-line ascertain the processing fluidity of concentrated poly(vinyl alcohol) aqueous solutions

Understanding the viscous fluid behavior of concentrated aqueous solution of poly (vinyl alcohol) (PVA), wherein macromolecular coils severely overlap and/or entangle each other, is of significance to the process design of PVA solution fabrication. However, exploiting the fluidity of PVA solutions under severe conditions of simultaneously high operational temperature (Top), high concentration (CPVA) and large polymerization degree (PD) has been less involved in the past studies irrespective of practical importance. Herein, we utilize a self-made hydrothermal kettle with a built-in online viscometer to systematically trace the changes of apparent viscosity (ηap) of PVA aqueous solutions arising from the variables of Top (up to 160 °C), CPVA (high as 28%) and PD (largest at 3000). Applying Andrade's equation, the activation free energy of viscous flow (Eη) is deduced from ln ηap ∝ 1/Top. It shows that all the values of Eη approximate to 37 (±3) kJ·mol−1 although both CPVA and PD increased progressively, indicating that these two factors will not affect the Top sensitivity of ηap. Meanwhile, the contour plots of ηap in CPVA-Top space are established for various PVAs with different PDs, to manifest the development trend of fluidity upon multiple external-fields coupling. Clarifying the synergic effect of CPVA-Top-PD on ηap may offer guidance for the preparation of PVA films by determing appropriate solution processing variables. The results of our study are of help to the PVA fabrications such as spinning fiber and casting film, in which precise control of flowability of concentrated solution is crucial.

Effects of waxes on hydrate behaviors in water-in-oil emulsions containing asphaltenes

In this study, the effects of waxes on carbon dioxide hydrate formation and dissociation in asphaltene-containing emulsions were systematically investigated using a high-pressure stirred autoclave equipped with an on-line viscometer. The results showed that the presence of waxes strengthened the inhibiting effect of asphaltenes on hydrate formation. Specifically, the induction time increased and the amount of formed hydrates decreased with increasing wax content in water-in-oil emulsion containing asphaltenes. The results indicated that waxes increased the viscosity of emulsions. It was observed that wax crystals dispersed in the bulk phase and got adsorbed at water–oil interface through the synergistic effect with asphaltenes. Furthermore, waxes inhibited the dissociation of hydrates in these emulsions. Both the gas emission rate and the average rate of hydrate dissociation decreased with an increase in wax content. The possible mechanisms were proposed to illustrate the effects of waxes on hydrate formation and dissociation in asphaltene-containing water-in-oil emulsions.

Entropic-Based Separation of Diastereomers: Size-Exclusion Chromatography with Online Viscometry and Refractometry Detection for Analysis of Blends of Mannose and Galactose Methyl-\u03b1-pyranosides at \u201cIdeal\u201d Size-Exclusion Conditions

The separation of carbohydrate diastereomers by an ideal size-exclusion mechanism, i.e., in the absence of enthalpic contributions to the separation, can be considered one of the grand challenges in chromatography: Can a difference in the location of a single axial hydroxy group on a pyranose ring (e.g., the axial OH being located on carbon 2 versus on carbon 4 of the ring) sufficiently affect the solution conformational entropy of a monosaccharide in a manner which allows for members of a diastereomeric pair to be separated from each other by size-exclusion chromatography (SEC)? Previous attempts at answering this question, for aqueous solutions, have been thwarted by the mutarotation of sugars in water. Here, the matter is addressed by employing the non-mutarotating methyl-α-pyranosides of d-mannose and d-galactose. We show for the first time, using SEC columns, the entropically driven separation of members of this diastereomeric pair, at a resolution of 1.2–1.3 and with only a 0.4–1% change in solute distribution coefficient over a 25 °C range, thereby demonstrating the ideality of the separation. It is also shown how the newest generation of online viscometer allows for improved sensitivity, thereby extending the range of this so-called molar-mass-sensitive detector into the monomeric regime. Detector multidimensionality is showcased via the synergism of online viscometry and refractometry, which combine to measure the intrinsic viscosity and viscometric radius of the sugars continually across the elution profiles of each diastereomer, methyl-α-d-mannopyranoside and methyl-α-d-galactopyranoside.

Modeling and Simulation of Vibrating Online Viscometer System

Aiming at the present situation of the difficulties in the analysis and research of the vibration type on-line viscometer system, the structural characteristics and mathematical model of the vibrating online viscometer are analyzed and studied. Based on this, the closed-loop control principle is further elaborated. At the same time, the simulation model of the vibrating online viscometer system was built by closed-loop control technology. The MATLAB simulation results verify the accuracy of the closed-loop control and the effectiveness of the simulation model, which provides a theoretical basis and guiding ideas for the system design and debugging of the vibrating online viscometer.

Effect of wax on hydrate formation in water-in-oil emulsions

Gas hydrates are non-stoichiometric crystalline compounds that can block pipelines, representing a significant threat to subsea flow assurance. In addition, wax precipitation is also a common issue in subsea pipelines. Since the multiphase flow is transported under low temperature and high-pressure conditions, formation of gas hydrates and wax precipitation may occur simultaneously, potentially posing greater challenges to subsea pipelines. The presence of wax complicates the hydrate formation issue. In this work, the influence of wax on hydrate formation was experimentally investigated in a high-pressure autoclave equipped with an online viscometer. Since natural surfactants are common in crude oil, Span 80 was used to simulate the presence of natural surfactants, and the effect of this compound on hydrate formation was considered. The presence of wax or Span 80 was observed to increase the difficulty of the hydrate formation at similar temperatures. The wax shell structure was found to grow at the water/oil interface based on the microscopic observation. Wax was also found to increase the hydrate induction time significantly. By associating the microscopic observation, a possible mechanism based on the mass transfer resistance was proposed to clarify the influence of wax on hydrate nucleation. Moreover, in the absence of Span 80, the amount of hydrate formed was observed to increase with the amount of wax in the emulsions.

Comprehensive branching analysis of star-shaped polystyrenes using a liquid chromatography-based approach.

The comprehensive branching analysis of complex polymers is still a challenge in advanced polymer analysis. Average branching information (average number and length of branches) can be obtained by spectroscopic methods, mainly NMR spectroscopy. The determination of the branching distribution, i.e., the concentration of macromolecules with a given number of branches, however, requires fractionation. Typically, size exclusion chromatography is used that separates the complex mixture with regard to molecular size in solution and not strictly with regard to the number of branches. In the present approach, model star-shaped polystyrenes were synthesized with a pre-determined architecture to give theoretical three-arm, four-arm, and six-arm structures. The branched samples were compared with a linear analogue of comparable molar mass known not to contain branching. Triple detector size exclusion chromatography with refractive index, multiangle light scattering, and online viscometer detection was used to determine absolute molar masses, radii of gyration, and branching distributions of the star-shaped polymers. 1H-NMR was used to calculate the average functionality and a reasonable agreement between the results of the two methods was obtained. Thermal gradient interaction chromatography and solvent gradient interaction chromatography were employed to separate the complex reaction products according to chemical composition (number of branches) and to resolve by-products. The separation capabilities of the two chromatographic techniques were compared and evaluated. Comprehensive two-dimensional liquid chromatography was used to separate the polydisperse star-shaped polystyrenes with regard to both branching and molar mass. Graphical abstract.

Molar mass distribution by size exclusion chromatography: Comparison of multi‐angle light scattering and universal calibration

ABSTRACTSeries of polymers of various molar mass, chemical composition, and molecular architecture was analyzed by size exclusion chromatography (SEC) coupled with a multi‐angle light scattering (MALS) photometer and an online viscometer. The molar mass averages were determined from the signal of MALS or calculated from the intrinsic viscosity and universal calibration. The comparison of the obtained results showed significant differences between the two methods. The MALS detection was shown to be more accurate for the determination of the weight‐average molar mass and less vulnerable to the spreading of polymer peak by band broadening. The universal calibration can yield more accurate estimation of the number‐average molar mass of branched polymers. It is also significantly more accurate for the characterization of fluorescent polymers than MALS with a regular laser of 660 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47561.

Induction Time of Hydrate Formation in Water-in-Oil Emulsions

Blockage of pipelines due to hydrate formation is a major problem for subsea flow assurance. Induction time for hydrate formation from the multiphase system within a pipeline is a critical parameter to determine whether hydrates may form at a given time. In this work, the induction time for hydrate formation in water-in-oil emulsions was investigated under different conditions. For this purpose, an autoclave with an online viscometer was designed and built. Based on the viscosity variation observed in the experiments during hydrate formation, a new avenue for defining induction time is proposed, which should be more convenient for determining the hydrate formation time in some pipelines. As hydrate formation in emulsions is more complicated than in pure water, the effects of several factors were considered in this study, including water cut of the emulsions, shear rate, driving force, and memory effect. Additionally, wax precipitation is also a common problem in subsea pipelines and can impact flow assura...

Detection Orthogonality in Macromolecular Separations: Role of the On-Line Viscometer in Characterizing Polymers at Conditions of “Spectroscopic Invisibility”

Much has been written over the last two decades about the advantages of separation orthogonality for the characterization of complex polymers and blends, and of the additive and synergistic benefits of combining various physical and chemical detection methods in the determination of molar mass, chemical heterogeneity, dilute solution conformation, etc. Less attention has been paid to the complementarity of detection methods that are truly orthogonal to each other with respect to a given property. A common, yet particularly different type of macromolecular liquid chromatography detector is the on-line viscometer, as its measurement principle is based on hydrodynamic transport properties, thus separating it from the large variety of spectroscopically based detectors. Here, we explore how the on-line viscometer can provide insights into the size-exclusion chromatographic analysis of individual homopolymer samples and of blends, even in cases where no response is observed with commonly employed detectors such as on-line refractometry and static and quasi-elastic light scattering, i.e., when analyses are conducted at conditions of “spectroscopic invisibility”.

In‐line analysis of the influence of monomeric and oligomeric hindered amine on the hydrolysis of polycarbonate in a PC/ABS blend

AbstractThe polycarbonate/polyacrylonitrile butadiene styrene (PC/ABS) blends lose mechanical properties when exposed to outdoor conditions. This is due to the ultraviolet (UV) induced photo‐oxidation of the PC phase and the polybutadiene portion of the ABS. It is known that ABS can be stabilised against terrestrial light by the use of hindered amine in combination with a UV absorber. However, such hindered amine cannot be used when PC is present in a multi component polymer blend. The hydrolysis of PC is accelerated when a small amount of hindered amine light stabilisers (HALS) is incorporated in the resin and is exposed to elevated temperature. In this article the effect of monomeric and oligomeric hindered amine on the hydrolysis of PC during the compounding of PC/ABS blend in a twin screw extruder at 240°C is observed by means of in‐line UV‐vis spectroscopy. Tinuvin 765 was used as monomeric hindered amine and Tinuvin 622 as oligomeric hindered amine. The molecular weight of the compounded sample was determined by gel permeation chromatography (GPC) and the rheological properties were observed using an online viscometer. It was found that the extent of hydrolysis induced by the oligomeric hindered amine is less compared to monomeric amine. It was also observed that polymeric hindered amine imparts better dispersion of the ABS phase into the polymer blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Solution Properties of Poly(Methyl Methacrylate) in Dimethylsulfoxide

The solution properties of polymethylmethacrylate in dimethylsulfoxide were studied using multi-angle light scattering and an online viscometer coupled to size exclusion chromatography. The data demonstrate that DMSO is a suitable eluent for the determination of the molecular weight of PMMA by SEC. The Mark-Houwink coefficients K and α were determined as a function of temperature. At 35°C, DMSO is a theta solvent for PMMA, and it becomes a good solvent as the temperature increases. The unperturbed dimension Kθ was calculated using three different procedures. The data do not show evidence of a conformational transition controlled by the temperature such as the one reported in benzene and confirm the existence of a general relationship between the ratio K/Kθ and α. In the case of PMMA, the comparison of the dipole moment of the side group to that of the solvent can be used to predict the existence of a conformational transition.

CONTROL OF A CONTINUOUS POLYMERIZATION REACTOR BY WIENER INPUT/OUTPUT DATA-BASED PREDICTIVE CONTROLLER WITH DIRECT INVERSE IDENTIFICATION

ABSTRACT This article reports an experimental study for the identification and predictive control of a continuous methyl methacrylate (MMA) solution polymerization reactor. The Wiener model was introduced to identify the polymerization reactor in a more efficient manner than the conventional methods of Wiener model identification. In particular, the method of subspace identification was employed and the inverse of the nonlinear part was directly identified. The input variables in this work were the jacket inlet temperature and the feed flow rate, while the monomer conversion and the weight average molecular weight were selected as the output variables. On the basis of the identified model a Wiener-type input/output data-based predictive controller was designed and applied to the property control of polymer product in the continuous MMA polymerization reactor by conducting an on-line digital control experiment with online densitometer and viscometer. Despite the complex and nonlinear characteristics of the polymerization reactor, the proposed controller was found to perform satisfactorily for property control in the multiple-input multiple-output system with input constraints for both set-point tracking and disturbance rejection. This was also confirmed by simulation results.

Hexafluoroisopropanol as size exclusion chromatography mobile phase for polyamide 6.

The present study deals with the use of hexafluoroisopropanol (HFIP) as size exclusion chromatography (SEC) mobile phase for polyamide 6 (PA6). Contradictory conclusions relating to the use of HFIP as SEC mobile phase for polyamides are found in the literature. By using a multi-detector SEC apparatus equipped with on-line viscometer and multi-angle light scattering we have studied the chromatographic artifacts and the validity of the universal calibration (UC) in HFIP for different PA6 samples (hydrolytic and anionic, monofunctional or bifunctional activator). Appropriate SEC columns and optimized experimental conditions allow most of the chromatographic artifacts to be avoided, even in neat HFIP. The use of a salt in the mobile phase, namely 0.01 M tetraethylammonium nitrate (TEAN), slightly increases the elution volume for both PA6 and PMMA polymers. Under the right conditions, the UC substantially holds for PA6. The validity of the UC is not linked to the presence of TEAN in the mobile phase. With some PA6 samples, namely those anionically synthesized using a bifunctional activator, aggregation becomes a problem and the molar mass in neat HFIP is overestimated. Addition of TEAN prevents any aggregation of the above anionically synthesized PA6. In contrast, the use of a different salt, namely potassium trifluoroacetate, increases the extent of aggregation.

Investigation of the effects of chrome ball charge on slurry rheology and milling performance

Ten surveys of the ball milling circuit at the Mt Isa Mines (MIM) Copper Concentrator were conducted aiming to identify any changes in slurry rheology caused by the use of chrome balls charge, and the associated effect on grinding performance. Slurry rheology was measured using an on-line viscometer. The data were mass balanced and analysed with statistical tools. Comparison of the rheogram demonstrated that slurry density and fines content affected slurry rheology significantly, while the effect of the chrome ball charge being negligible. Statistical analysis showed the effects of mill throughput and cyclone efficiency on the Grinding Index (a term describing the overall breakage). There was no difference in the Grinding Index between using the chrome ball charge and the ordinary steel ball charge.

MOLECULAR WEIGHT DISTRIBUTION OF POLYAMIDES BY GPC-VISCOMETRY. A COMPARISON BETWEEN HIGH TEMPERATURE AND LOW TEMPERATURE ELUANTS

Synthetic polyamides (PA) owe many outstanding properties to their semicristalline morphology and to the intermolecular hydrogen bonding of the amide groups. Although the strength of the Van der Waals network confers an exceptional solvent resistance to this class of polymers, it may lead to serious difficulties in their solution characterization, such as the determination of molecular weight distribution (MWD). Over the years, a large number of dissolution schemes have been developed for the GPC characterization of PA. A recent IUPAC round-robin test on the GPC of aliphatic PAs nevertheless showed large variations in the experimental data not only between laboratories employing different methods, but also between laboratories adopting similar protocols. The purpose of the present investigation is to understand the origins of these disparities by comparing GPC-Viscometry data obtained with some frequently used eluant systems: a. benzyl alcohol at high temperature; b. hexafluoro-isopropanol, pure or mixed with dichloromethane, at low temperature; c. common GPC solvents (THF, CH2Cl2,) after N-trifluoracetylation of the PA. Apart from pure HFIP, all the methods tested show consistent MW results when measured in the same laboratory. Viscometry data reveal, however, that the expected linear viscosity law is obeyed only in benzyl alcohol. With the other eluants, significant departure from the Mark-Houwink relation denotes presence of non-size exclusion effects, rendering data evaluation imprecise with the Universal Calibration. The problems are particularly acute for polyamides with short methylene sequences which can only be dissolved in mixtures containing a high concentration of HFIP. To improve accuracy, it is proposed that GPC calibration for this class of polymer be performed with absolute detection (on-line viscometer, light scattering) or with a broad MWD standard of identical chemical composition to the analyzed sample.

Synthesis and solution properties of star-shaped poly(tert-butyl acrylate)

A series of star polymers consisting of poly(tert-butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of arms is reached the intrinsic viscosity even decreases with molecular weight. Computer simulations for star polymers were carried out where the radius of gyration was calculated as a function of the number of arms. The results are in good agreement with the experimental data.