Cone-plate Rheometry Research Articles

Upgrading and Enhancement of Recycled Polyethylene Terephthalate with Chain Extenders: In-Depth Material Characterization.

Chemical chain extenders (CEs) can be used to restore the properties of recycled low-molecular-weight polyethylene terephthalate (PET). The aim of this work is to investigate the influence of the type and concentration of the CEs Joncryl and pyromellitic dianhydride (PMDA) on the viscosity and other rheological properties with a unique combination of different methods based on industrial samples originating from recycled PET bottles and trays. The resulting chain-extended thermoplastics were characterized by a combination of differential scanning calorimetry, viscometry, cone plate rheometry, pyrolysis-gas chromatography-mass spectroscopy, optical photothermal infrared spectroscopy, 13C solid-state- and 1H NMR liquid spectroscopy, and size exclusion chromatography. For a recycled PET mixture containing bottle and tray materials, our investigations have shown that a significantly better effect for chain elongation can be achieved with Joncryl compared to PMDA. This can presumably be attributed to water molecules formed during the use of PMDA, which accelerate the degradation of PET. The storage modulus values are therefore significantly higher for the samples with Joncryl compared to PMDA. The results of this study show that chain extension with Joncryl proceeds better compared to the reaction with PMDA.

Effect of Dehydration on the Rheological Measurement of Surimi Paste in Cone-Plate Rheometry: Heat and Mass Transfer Simulation

Moisture transfer characteristics of Alaska pollock (AP) surimi were investigated at various temperatures. The effective moisture diffusivity increased from 5.50 × 10−11 to 2.07 × 10−9 m2/s as the temperature increased from 30 °C to 90 °C. In order to investigate the mass and heat transfer characteristics of AP surimi, the simulation model was developed and evaluated by root-mean-square error (RMSE) (<2.95%). Rheological properties of AP surimi were investigated at different heating rates (1 °C/min, 5 °C/min, 10 °C/min, 20 °C/min and 30 °C/min). As heating rate increased to 20 °C/min and 30 °C/min, elastic modulus (G’) significantly diminished. The diminished G’ could be explained by impaired gel during temperature sweep supported by the predicted temperature distribution in the simulation model. Changes in moisture content of AP surimi during temperature sweep were also measured and predicted by the simulation model. The results showed the decreased amount of moisture content significantly increased as heating rate increased.

Degradation in cone-plate rheometry.

We analyze quantitatively the oxidative degradation of a sample in a cone-plate rheometer, as oxygen diffuses inward, radially, from the free boundary. We examine rheometer error mitigation by means of nitrogen blanketing, and also, of cone-plate partitioning. We arrive at exact analytical expressions for the oxygen concentration, and thus, for the degradation rate. We then integrate this rate over time to get the amount of oxygen reacted as a function of radial position and time in the degrading sample. To illustrate the usefulness of our analytical expressions, we provide two worked examples investigating the effect of nitrogen blanketing and cone-plate partitioning. We find that, though nitrogen blanketing always produces less degradation, its benefits are limited for short times. Additionally, cone-plate partitioning provides a simpler solution and allows samples to be run for longer times without degradation compromising measurement, even in samples initially saturated with oxygen. We close by considering the effect of antioxidants.

Effect of the Flow Shutdown Temperature on the Gelation of Slurry Flows in a Waxy Oil Pipeline

When uninsulated pipelines are used to transport crude oils with high wax content (greater than 2 wt %) in cold environments, the pipelines may become plugged with wax gels when a flow shutdown occurs. The local value of the oil temperature in a pipeline decreases monotonically with axial distance from the well head and, in some pipelines, may decrease significantly below the wax appearance temperature (WAT), in which case the local wax gel forms from a wax slurry precursor state. For a model waxy oil, we show that the restart pressure of a gelled laboratory pipeline at fixed restart temperature decreases with a decrease in the temperature of the slurry flow at the time of flow shutdown. Approximately 90% of this decrease occurs for a flow shutdown temperature only five degrees below the WAT. These laboratory results imply that the strength of the wax gel that forms during the shutdown of an uninsulated pipeline in the field decreases with axial distance from the well head. The dependence of the laboratory flow loop restart pressure on the flow shutdown temperature is qualitatively similar to the dependence of the wax gel yield stress value on the preshear temperature, as measured by cone–plate rheometry.

Foaming and rheological properties of the liquid phase extracted from wheat flour dough

Dough liquor (DL) is considered as a good model of bread dough liquid phase which plays an important role in alveolar structure creation. In this work, DL was extracted from dough pieces of various contents (g for 100 g flour) of water (55–70), sugar (0–15), rapeseed oil (0–10) and bran (0–20). The extraction yield of DL was 5.0 ± 2.4% and its dry matter content varied between 10.8 and 27.2% of total DL mass. Its composition has been determined in terms of lipids content (≤0.08 mg/mL), polysaccharides, mostly arabinoxylans (0.9–4.7 mg/mL), arabinogalactan-proteins (AGP) and soluble proteins (20.7–38.0 mg/mL). The rheological properties (bulk and surface) of fresh DL, and foaming properties of diluted DL (1/10), were determined using cone-plate rheometry, pendant drop method and Foamscan device, respectively. DL behaved like a macromolecular solution, displaying a slight shear-thinning behavior with an apparent viscosity varying between 0.03 and 0.6 Pa sn, at shear rate 10 s−1. Its surface tension varied between 35 and 45 mN/m. Its adsorption kinetics, governed by protein diffusion to the interface, followed two regimes, the first one depending on sugar content, and the second one on AGP content. Drainage and foam stability kinetics were influenced by neutral sugars, probably through the impact of glucose and mannose on DL viscosity. The understanding of the mechanisms of fermented dough stability could be improved by taking the results of DL surface tension into account.

Wall slip and flow of concentrated hard-sphere colloidal suspensions

We present a comprehensive study of the slip and flow of concentrated colloidal suspensions using cone-plate rheometry and simultaneous confocal imaging. In the colloidal glass regime, for smooth, nonstick walls, the solid nature of the suspension causes a transition in the rheology from Herschel–Bulkley (HB) bulk flow behavior at large stress to a Bingham-like slip behavior at low stress, which is suppressed for sufficient colloid-wall attraction or colloid-scale wall roughness. Visualization shows how the slip-shear transition depends on gap size and the boundary conditions at both walls and that partial slip persist well above the yield stress. A phenomenological model, incorporating the Bingham slip law and HB bulk flow, fully accounts for the behavior. Microscopically, the Bingham law is related to a thin (subcolloidal) lubrication layer at the wall, giving rise to a characteristic dependence of slip parameters on particle size and concentration. We relate this to the suspension’s osmotic pressure and yield stress and also analyze the influence of van der Waals interaction. For the largest concentrations, we observe nonuniform flow around the yield stress, in line with recent work on bulk shear banding of concentrated pastes. We also describe residual slip in concentrated liquid suspensions, where the vanishing yield stress causes coexistence of (weak) slip and bulk shear flow for all measured rates.

Slip and Flow of Hard-Sphere Colloidal Glasses

We study the flow of concentrated hard-sphere colloidal suspensions along smooth, nonstick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the "solid" microstructure during full slip and the local nature of the "slip to shear" transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.

Dissolution and forming of cellulose with ionic liquids

The dissolution of cellulose in different ionic liquids will be described as a very recent subject for a direct dissolving process, which was used to prepare regenerated cellulose fibres. The preparation of the dopes was arranged starting from slurry of cellulose in the aqueous ionic liquid by removing the water at elevated temperature, vacuum and high shearing rates. As ionic liquids, the 1-N-Butyl-3-methylimidazolium chloride, the 1-Ethyl-3-methylimidazolium chloride, the 1-N-Butyl-2,3-dimethylimidazolium chloride, the 1-N-Butyl-3-methylimidazolium acetate and the 1-Ethyl-3-methylimidazolium acetate were investigated. The cellulose solutions in ionic liquids were characterised by means of light microscopy, cone-plate rheometry and particle analysis. In addition these results were compared with cellulose solutions in N-methyl-morpholine-N-oxide monohydrate. Finally the cellulose dopes were shaped by a dry-wet spinning process to manufacture cellulose fibres. The properties of the resulted fibre had been determined and will be discussed.

Thermal behavior and rheological properties of PANI-DBSA/PAN blends

Conducting blends of polyacrylonitrile (PAN) copolymer and dodecylbenzene sulfonic acid doped polyaniline (PANI-DBSA) were prepared by solution blending of the two components. By means of various characterization methods including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and cone-plate rheometry, the effects of PANI-DBSA content on the thermal behavior, morphological and rheological properties of the blends were investigated. A single and composition-dependent Tg was found for each of all blends and the thermal stability of PANI-DBSA/PAN was superior to that of both pure Co-PAN and PANIDBSA. Rheological results show that the apparent viscosity of blend solution decreased at low PANIDBSA content (2.5 wt%) while increased at high PANI-DBSA content (7.5wt%–10 wt%). Moreover, the shear-thinning appeared more distinctly with the incorporation of PANI-DBSA into the blend solutions especially at a high shear rate.

Evaporation Blocker for Cone-Plate Rheometry of Volatile Samples

Abstract We report on the design and implementation of an evaporation blocker for cone-plate and plate-plate geometries. In addition to minimizing sample evaporation by trapping the saturated vapor inside a sample chamber, an important feature of the evaporation blocker is the suppression of solvent transport through condensation. Validation tests with DI-water, hydrogels, and colloidal suspensions demonstrate that the new accessory reduces solvent evaporation significantly more than commercially available environmental control chambers. Experiments were also performed to show that the evaporation blocker enables a variety of experiments on thermoresponsive complex fluids that were previously impossible, and provide new insight into the molecular organization of these materials. The evaporation blocker was specifically designed for an Anton Paar MCR rheometer, but the fundamental principles are widely applicable.

Evaluation and identification of degradative processes in post-consumer recycled high-density polyethylene

We have studied the degradation resulting from reprocessing of post-consumer HDPE in order to verify its re-stabilization needs. Cone-plate rheometry was used to provide information about the molar mass and the molar mass distribution after reprocessing and stabilizing the material. Infrared spectroscopy (FTIR), oxidation induction time (OIT), melt flow index (MFI) and cone-plate rheometry measurements were performed. Also, atomic absorption spectrophotometry tests were carried out to verify which catalytic residue was present in the recycled HDPE so as to correlate it to the degradation processes taking place in the polymer. The results showed that in this case the post-consumer HDPE displayed cross-linking when reprocessed, indicating the need for re-stabilization. They also showed that the use of 0.2% antioxidant was efficient in blocking these processes, and that the cone-plate rheometry technique was powerful in assessing degradative processes.

Non-Newtonian viscous flow in soda-lime-silica glass at forming and annealing temperatures

Viscous flow was measured at high shear rates by fiber elongation and cone-plate rheometry. Non-Newtonian viscosity data were taken from 10 6 to 10 14 P between 533 and 810°C on 2 soda-line-silica glasses of similar composition. The results show that the viscosity shear thinning effect can be scaled to a universally applicable behavior by assuming that the glass has a temperature-dependent limiting strength which decreases with the viscosity. This weakening of the structure with increasing temperature results in the appearance of shear thinning effects at lower strain rates than predictedby relaxation time scaling alone.