Rheological characterization of polysaccharide gels

In this Master’s Thesis work the rheological properties of different polysaccharide gels have been studied. The results of this study are used as a starting point for further investigations of potential applications. In order to understand rheological behavior of studied materials, the commercial hydrocolloids such as sodium carboxymethyl cellulose, xanthan gum and guar gum were used as reference and comparison material for rheological studies. As a part the rheological research the development and implementation of proper measurement methods for studied materials were carried out. In the literature review, short introductions of studied materials and application areas of rheological modifiers are summarized. In addition, basic rheological concepts and key fundamentals are explained. In the experimental part the focus was on the rheological characterization of aqueous suspensions of studied materials. Especially, gel strength and solution stability were investigated. The rheological measurements included both rotational and oscillatory measurements in different conditions, where several chemical and physical properties were measured with Anton Paar MCR302 dynamic rotational rheometer. Studied polysaccharide gels can be clearly defined to be shear thinning and thixotropic materials. They have strong gel forming properties even at low concentrations, which explains the superior thickening behavior for some of the samples. Along with rheological characterization of selected materials the factors behind different phenomena were investigated. To reveal value and potential use of polysaccharide gels the influence of various factors such as concentration, temperature and ionic strength were determined. The measurements showed a clear difference between studied materials under investigated external parameters.

Rheological behavior of blueberry

The physical and physicochemical characteristics of blueberry (Vaccinium myrtillus) fruits produced in Brazil were analyzed. Rheological properties were measured at 5, 25, 45 and 65 °C, on a stress controlled rheometer equipped with grooved a stainless-steel parallel-plate in a shear rate range of 0-300 s-1, with the objective of determining the influence of temperature on the rheological properties. The pseudoplastic behavior with yield stress was well described by the Ostwald-de-Waele (Power Law), Herschel-Bulkley (HB) and Mizhari Berk models. The yield stress and behavior index decreased with the increase in the temperatures for 5, 25, and 45 °C whereas for the temperature of 65 °C the effects were the opposite exhibiting elevated values. The viscosity decreased with an increase in temperature, and the Arrhenius equation described adequately the effect of temperature on the apparent viscosity of the puree, in which the activation energy (Ea) determined at a shear rate of 100 s-1 was 9.36 kJ.mol-1.

Effect of sugar and water contents on non-expanded cassava flour extrudates

The effects of sucrose and water contents on cassava flour processed by extrusion at varied concentrations of sucrose (0-20% w/w) and water (28-42% w/w) were studied by applying response surface methodology. The extrusion of the mixtures was performed in a twin screw extruder fitted to a torque rheometer. The specific mechanical energy (SME) dissipated inside a conical twin-screw extruder was measured. Water absorption index (WAI), water solubility index (WSI) and paste viscosity readings (cold viscosity (CV), peak viscosity (PV), breakdown (BD) and set back (SB)) during a gelatinization-retrogradation cycle measured in a Rapid Visco Analyzer were determined on non-directly extruded products. The results indicated that SME and WSI decreased as a function of water and sucrose contents. WAI and pasting properties were influenced by water content. A non antiplasticizing effect of the sucrose content was observed on pasting properties, suggesting that sucrose did not reduce the availability of water available for gelatinizing cassava flour during the extrusion process. The nature of the optimum point was characterized as a saddle point for WAI, WSI, PV and BD, whereas SME showed a maximum and CV and SB a minimum. The results indicated to be valuable for the production of non-expanded cassava flour extrudates with desirable functional properties for specific end users.

Rheological behavior of corn and soy mix as feed ingredients

Foods behave as non-Newtonian fluids, but little is known about how corn and soybean mix behave under viscometric flow. In order to characterize the rheological behavior of animal feed under viscometric flow, a 70:30 (mass:mass) mixture of ground corn and soybean grains was submitted to a capillary rheometer at 3 different temperatures (80, 120, and 160 °C), different moisture levels (26.5 ± 0.08; 30.4 ± 0.31, and 33.4 ± 0.05%), and 4 shear rates (30.4; 72.9; 304.3, and 728.6/second). Different strain rates and die dimensions were used to obtain the target shear rates. The resulting data were fitted to Power Law, Casson, and Bingham models. Based on experimental data, water content, mass temperature, and the effects of shear rate on the apparent shear viscosity of corn-soy mix were fitted to a single expression (p < 0.001, R² = 0.93): η = 18,769.7 (y)-0.86 e (-9.34 U + 935 T), where y is shear rate, U is sample moisture, and T is sample temperature in Kelvin scale. As expected, such mixture presented a pseudoplastic (shear-thinning) behavior.

Density and rheological parameters of goat milk

The rheological behavior and density of goat milk was studied as a function of solids concentration (10.5 to 50.0%) and temperature (273 to 331 k). Newtonian behavior was observed for values of total solids (TS) between 10.5 and 22.0% and temperatures from 276 to 331 k changing to pseudoplastic behavior without yield stress for TS from 25.0 to 39.4% at the same range of temperature. Goat milk with TS between 44.3 to 50.0% and temperatures of 273 to 296 k showed yield stress in addition to pseudoplastic behavior. At 303 to 331 k the power law model was observed again, without yield stress. The density of goat milk ranged from 991.7 to 1232.4 kg.m-3.

Influence de l’agrégation érythrocytaire sur la migration axiale de microparticules simulant des plaquettes sanguines

Lors du phénomène d’hémostase primaire ou de thrombose vasculaire, les plaquettes sanguines doivent adhérer aux parois afin de remplir leur fonction réparatrice ou pathologique. Pour ce faire, certains facteurs rhéologiques et hémodynamiques tels que l’hématocrite, le taux de cisaillement local et les contraintes de cisaillement pariétal, entrent en jeu afin d’exclure les plaquettes sanguines de l’écoulement principal et de les transporter vers le site endommagé ou enflammé. Cette exclusion pourrait aussi être influencée par l’agrégation de globules rouges qui est un phénomène naturel présent dans tout le système cardiovasculaire selon les conditions d’écoulement. La dérive de ces agrégats de globules rouges vers le centre des vaisseaux provoque la formation de réseaux d’agrégats dont la taille et la complexité varient en fonction de l’hématocrite et des conditions de cisaillement présentes. Il en résulte un écoulement bi-phasique avec un écoulement central composé d’agrégats de globules rouges avoisinés par une région moins dense en particules où l’on peut trouver des globules rouges singuliers, des petits rouleaux de globules rouges et une importante concentration en plaquettes et globules blancs. De ce fait, il est raisonnable de penser que plus la taille des agrégats qui occupent le centre du vaisseau augmente, plus il y aura de plaquettes expulsées vers les parois vasculaires. L'objectif du projet est de quantifier, in vitro, la migration des plaquettes sanguines en fonction du niveau d’agrégation érythrocytaire présent, en faisant varier l’hématocrite, le taux de cisaillement et en promouvant l’agrégation par l’ajout d’agents tels que le dextran à poids moléculaire élevé. Cependant, le comportement non Newtonien du sang dans un écoulement tubulaire peut être vu comme un facteur confondant à cause de son impact sur l’organisation spatiale des agrégats de globules rouges. De ce fait, les études ont été réalisées dans un appareil permettant de moduler, de façon homogène, la taille et la structure de ces agrégats et de quantifier ainsi leur effet sur la migration axiale des plaquettes. Du sang de porc anti coagulé a été ajusté à différents taux d’hématocrite et insérer dans un appareil à écoulement de Couette, à température ambiante. Les plaquettes sanguines, difficilement isolables in vitro sans en activer certains ligands membranaires, ont été remplacées par des fantômes en polystyrène ayant un revêtement de biotine. La quantification de la migration de ces fantômes de plaquettes a été réalisée grâce à l’utilisation de membranes biologiques fixées sur les parois internes de l’entrefer du rhéomètre de Couette. Ces membranes ont un revêtement de streptavidine assurant une très forte affinité d’adhésion avec les microparticules biotynilées. À 40% d’hématocrite, à un cisaillement de 2 s-1, 566 ± 53 microparticules ont été comptées pour un protocole préétabli avec du sang non agrégeant, comparativement à 1077 ± 229 pour du sang normal et 1568 ± 131 pour du sang hyper agrégeant. Les résultats obtenus suggèrent une nette participation de l’agrégation érythrocytaire sur le transport des fantômes de plaquettes puisque l’adhésion de ces derniers à la paroi du rhéomètre de Couette augmente de façon quasi exponentielle selon le niveau d’agrégation présent.

Rheology of Short Nylon -6 Fiber Reinforced Styrene-Butadiene Rubber

The rheological characteristics of short Nylon-6 fiber reinforced styrene butadiene rubber (SBR) were studied using a capillary rheometer. The study was done with respect to the effect of shear rate, fiber concentration, and temperature on shear viscosity and die swell. All the melts showed pseudoplastic nature, which decreased with increasing temperature. Shear viscosity increased in the presence of fibers. Introduction of fiber reduces the temperature sensitivity of the rubber matrix. A reduction in die swell was found in presence of fibers.

Silane Grafting of Polyethylenes

Reactive extrusion is an attractive means of polymer processing since the shaping and reaction take place in a single operation. In this paper we report the silane grafting of polyethylenes in a single screw extruder. The optimum conditions for silane grafting, viz. temperature, shear rate, silane and DCP concentrations, were determined on a torque rheometer and then actual extrusion was performed using these conditions. The study shows that an optimum low level of grafting/ crosslinking can be introduced into polyethylene during its extrusion for better mechanical behavior and=or thermal stability without affecting the processability.

Short Nylon Fibre Reinforced PP: Melt Rheology

Short fiber reinforced thermoplastics have generated much interest these days since fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, creep resistance, and some times impact strength of thermoplastics. If the matrix and reinforcement are both based on polymers the composite are recyclable. The rheological behavior of recyclable composites based on nylon fiber reinforced polypropylene (PP) is reported in this paper. The rheological behavior was evaluated both using a capillary rheometer and a torque rheometer. The study showed that the composite became pseudoplastic with fiber content and hence fiber addition did not affect processing adversely at higher shear rates. The torque rheometer data resembled that obtained from the capillary rheometer. The energy of mixing and activation energy of mixing also did not show much variation from that of PP alone.

Modification of Polyethylenes by Reactive Extrusion

The main aim of the study was to optimise the reactive extrusion conditions in the conventional modification processes of polyethylenes in a single screw extruder.The optimum conditions for peroxide crosslinking of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blend were determined in a torque rheometer. The actual reactive extrusion was performed in a laboratory single screw extruder using the optimum parameters. The influence of the coagent, triaUyl cyanurate (TAC), on the cross linking of low density polyethylene in the presence of peroxide was also investigated. The peroxide crosslinking was found to improve the mechanical properties and the thermal stability of the polyethylenes. The efficiency of crosslinking was found to be improved by the addition of coagent such as TAC.The optimum conditions for silane grafting viz temperature, shear rate, silane and DCP concentrations were determined on a torque rheometer in the case of LDPE, LLDPE and their blend. Silane grafting of LDPE in the presence of peroxide was performed with and without addition of water. Compounding of such mixtures in the melt at high temperatures caused decomposition of the peroxide and grafting of alkoxy silyl groups to the polyethylene chains.The optimum parameters for maleic anhydride modification of LDPE, LLDPE and their blend were determined. The grafting reaction was confinned by FTIR spectroscopy. Modification of polyethylenes with maleic anhydride in the presence of dicumyl peroxide was found to be useful in improving mechanical properties. The improvement was found to be mainly due to the grafting of carboxyl group and formation of crosslinks between the chains. The cross linking initiated improvements indicate extended property profiles and new application fields for polyethylenes.On the whole the study shows that the optimum conditions for modifying polyethylenes can be determined on a torque rheometer and actual modification can be performed in a single screw extruder by employing the optimum parameters for improved mechanical! thermal behaviour without seriously affecting their processing behaviour.

Characterization of Linear Low-Density Polyethylene/ Poly(vinyl alcohol) Blends and Their Biodegradability by Vibrio sp. Isolated from Marine Benthic Environment

Increasing amounts of plastic waste in the environment have become a problem of gigantic proportions. The case of linear low-density polyethylene (LLDPE) is especially significant as it is widely used for packaging and other applications. This synthetic polymer is normally not biodegradable until it is degraded into low molecular mass fragments that can be assimilated by microorganisms. Blends of nonbiodegradable polymers and biodegradable commercial polymers such as poly (vinyl alcohol) (PVA) can facilitate a reduction in the volume of plastic waste when they undergo partial degradation. Further, the remaining fragments stand a greater chance of undergoing biodegradation in a much shorter span of time. In this investigation, LLDPE was blended with different proportions of PVA (5–30%) in a torque rheometer. Mechanical, thermal, and biodegradation studies were carried out on the blends. The biodegradability of LLDPE/PVA blends has been studied in two environments: (1) in a culture medium containing Vibrio sp. and (2) soil environment, both over a period of 15 weeks. Blends exposed to culture medium degraded more than that exposed to soil environment. Changes in various properties of LLDPE/PVA blends before and after degradation were monitored using Fourier transform infrared spectroscopy, a differential scanning calorimeter (DSC) for crystallinity, and scanning electron microscope (SEM) for surface morphology among other things. Percentage crystallinity decreased as the PVA content increased and biodegradation resulted in an increase of crystallinity in LLDPE/PVA blends. The results prove that partial biodegradation of the blends has occurred holding promise for an eventual biodegradable product

Consistently inconsistent: commercially available starch-based Dysphagia products

Individuals with dysphagia may be prescribed thickened fluids to promote a safer and more successful swallow. Starch-based thickening agents are often employed; however, these exhibit great variation in consistency. The aim of this study was to compare viscosity and the rheological profile parameters complex (G*), viscous (G″), and elastic modulus (G′) over a range of physiological shear rates. UK commercially available dysphagia products at “custard” consistency were examined. Commercially available starch-based dysphagia products were prepared according to manufacturers’ instructions; the viscosity and rheological parameters were tested on a CVOR Rheometer. At a measured shear rate of 50 s−1, all products fell within the viscosity limits defined according to the National Dysphagia Diet Task Force guidelines. However, at lower shear rates, large variations in viscosity were observed. Rheological parameters G*, G′, and G″ also demonstrated considerable differences in both overall strength and rheological behavior between different batches of the same product and different product types. The large range in consistency and changes in the overall structure of the starch-based products over a range of physiological shear rates show that patients could be receiving fluids with very different characteristics from that advised. This could have detrimental effects on their ability to swallow.

Effects of composition on fat rheology and crystallisation

The crystallisation behaviour of three fat blends, comprising a commercial shortening, a blend of fats with a very low trans fatty acid content ("low-trans") and a blend including hardened rapeseed oil with a relatively high trans fatty acid content ("high-trans") was studied. Molten fats were lowered to a temperature of 31 degrees C and stirred for 0, 15, 30, 45 and 60 min. Samples were removed and their rheological properties studied, using a controlled stress rheometer, employing a frequency sweep procedure. Effects of the progressive crystallisation at 31 degrees C on the melting profile of fat samples removed from the stirred vessel and solidified at -20 degrees C were also studied by differential scanning calorimetry (DSC). The rheological profiles obtained suggested that all of the fats studied had weak viscoelastic "liquid" structures when melted, but these changed to structures perceived by the rheometer as weak viscoelastic "gels" in the early stages of crystallisation (G' (storage modulus) > G" (loss modulus) over most of the measured frequency range). These subsequently developed into weak viscoelastic semi-solids, showing frequency dependent behaviour on further crystallisation. These changes in behaviour were interpreted as changes from a small number of larger crystals "cross-linking" in a liquid matrix to a larger number of smaller crystals packed with a "slip plane" of liquid oil between them. The rate of crystallisation of the three fats was in the order high trans > low-trans > commercial shortening. Changes in the DSC melting profile due to fractionation of triacylglycerols during the crystallisation at 31 degrees C were evident for all three fats. (c) 2006 Elsevier Ltd. All rights reserved.

Variability of starch-based thickened drinks for patients with dysphagia in the hospital setting

Starch-based thickening agents may be prescribed for patients with dysphagia. Thickened fluids alter variables of the swallow reflex, allowing more time for bolus manipulation without compromising airway closure. This investigation explored the variation in viscosity and physical characteristics of thickened drinks prepared in different media under laboratory conditions and compared the results with those of thickened drinks presented to dysphagic patients in one hospital. The rheological characteristics were tested on a simple plastometer and a Bohlin CVOR rheometer (Malvern Instruments, Worcestershire, UK). Samples prepared to “syrup” consistency both in the laboratory and in the hospitalwere significantly different from each other (P < 0.0001). This was also the case for samples prepared to “custard” consistency. Differences existed not only in viscosity, but drinks prepared in different media produced different rheological matrices. This signifies different viscoelastic behaviors that may effect manipulation in the mouth. From this study, preparation of thickened drinks using starch-based instant thickening powders appears to be a highly variable practice.

Time-resolved in situ X-ray scattering studies of aqueous hydroxypropylcellulose solutions

The evolution of the global orientation parameter for a series of aqueous hydroxypropylcellulose solutions both during and following the cessation of a steady-state shear flow is reported. Time-resolved orientation measurements were made in situ through a novel X-ray rheometer coupled with a two-dimensional electronic X-ray camera, and using an intense X-ray source at the LURE synchrotron. After the cessation of flow, the global orientation decreases from the steady-state orientation level to zero following shear flow at low shear rate or to a small but finite value after flow at a high shear rate. The decrease of orientation with time shows different behaviour, dependent upon the previously applied shear rate.