Dynamic Rheological Method Research Articles

Rheological properties of graphene oxide/polyamide 6 composites

AbstractIn this work, graphene oxide (GO)/polyamide 6 (PA6) nanocomposites with different graphene content (0.03–0.5 wt%) were prepared via in situ polymerization of GO and ε‐caprolactam. The linear and nonlinear rheological properties and thixotropy of GO/PA6 nanocomposites are investigated using steady state, dynamic, and transient rheological method with a Haake plate rotary rheometer. Cox/Merz rules and Cross model were used to fit the shear rate sweep and dynamic frequency sweep data, and a wider range(10−2–104 s−1) of flow curve was obtained. The results show the PA6 and GO/PA6 melts are shear thinning fluid without yield stress, and have thixotropy.Highlights Dynamic, steady, and transient rheological tests were performed. Cox/Merz rules and Cross model were used to fit the data. A wider range(10−2–104 s−1) of flow curve was obtained.

Adhesion to solid surfaces of gels of iota–carrageenan alone or in mixture with casein

The adhesiveness of iota–carrageenan gels was evaluated versus their rheological properties such as storage modulus and loss tangent levels and the solid surface in contact (steel or plastics). Different viscoelastic behaviours were obtained by varying iota–carrageenan concentration or temperature. Furthermore, gels were added with casein without changing their rheological properties measured in dynamic mode (small deformation), to study the influence of solid surface tension of gels on adhesiveness. After the determination of rheological parameters of gels with dynamic rheological method, the level of adhesion was measured by a pull off test. The maximum force and the energy of adhesion measured during the separation of the gel from the solid surface were studied. Both were inversely related to the storage modulus of the gel. They increase with decreasing loss tangent (corresponding to an increase of the level of structure of the gel). Moreover, the maximum force measured during separation increases with the solid surface tension (steel or plastic) and the more structured the gel, the higher is the adhesiveness differences between surfaces. When 0.2–0.3% (w/v) of casein are added to gels with high enough storage modulus (>90 Pa), the maximum separation force increases whereas the energy of adhesion is not affected. Casein may facilitate the propagation of the rupture at the interface.

Thermal oxidation of metallocene‐catalyzed poly(ethylene octene) by a rheological method

AbstractThe thermal oxidation of a metallocene‐catalyzed poly(ethylene octene) (POE) melt was studied by a dynamic rheological method. Furthermore, to prove the effect of oxygen on the thermal oxidation of POE, cyclic samples, which consisted of virgin POE in the outer circle and POE with antioxidant inside, were made. The results showed that a thermal‐oxidation‐induced crosslinking reaction occurred in the POE melt at a high temperature. The amount of the antioxidant determined the thermal oxidation of POE when the antioxidant was added, and the diffusion of oxygen controlled the thermal oxidation of POE without the antioxidant. In addition, Fourier transform infrared and gel content characterization confirmed that the crosslinking occurred and that carbonyl groups formed in the reaction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Thermosetting gels with modulated gelation temperature for ophthalmic use: the rheological and gamma scintigraphic studies.

For ophthalmic drug delivery, Pluronic F127 solutions have a phase transition temperature too low for them to be instilled into the eye at room temperature. Refrigerator storage is usually required to make administration easier, whereas the potential irritation of cold to the sensitive ocular tissues may result in poor topical bioavailability. The purpose of this study is to develop a thermosetting gel with a suitable phase transition temperature by combining Pluronic analogs and to examine the influence of incorporating mucoadhesive polysaccharide, sodium hyaluronate (HA-Na), on the ocular retention of the gel. Dynamic rheological method and single photon emission computing tomography (SPECT) technique were used to ex/in vivo evaluate the thermosetting gels, respectively. An optimized formulation containing 21% F127 and 10% F68 increased the phase transition temperature by 9 degrees C as evaluated by elasticity modulus compared to that of individual 21% F127 solution. Rheological behaviors of the Pluronic solutions showed that the combined Pluronic formulation was free flowing liquid below 25 degrees C and converted to a firm gel under the physiological condition. Furthermore, this formulation possessed the highest viscosity both before and after tear dilution at 35 degrees C. Gamma scintigraphic data demonstrated that the clearance of the thermosetting gel labeled with 99mTc-DTPA was significantly delayed with respect to the phosphate buffered solution, and at least a threefold increase of the corneal residence time was achieved. However, no further improvement in the ocular retention was observed when adding HA-Na into the thermosetting gel due to the substantially decreased gel strength.

Gelling Temperature of Gellan Solutions Containing Calcium Ions

ABSTRACTGelling temperatures were measured using a dynamic rheological testing method, a spectrophotometric method and direct visual examination combined with use of a thermocouple. Results from the dynamic testing method were most consistent. Gelling temperatures of gellan solutions increased from 30 to 72°C, as polymer concentrations increased from 0.4 to 2.0% w/v and Ca++ concentrations increased from 2 to 40 mM. A mathematical model was developed based on the van't Hoff equation to relate gelling temperatures to composition and polymer molecular weight. The heat of cross‐linking in Ca‐gellan gels was estimated to be 428.6 kJ/mole, about 1.4 to 2.1 times greater than for gelatin gels.

Gelation and retrogradation of concentrated starch systems: 1 Gelation

Small deformation properties of potato and wheat starch suspensions were studied during heating and cooling at rest by a small amplitude dynamic rheological test method. Starch concentrations used were 10 to 30% w/w. The temperature to which the suspensions were heated varied from 65 to 90°C. During heating the moduli of the starch sytems at first increase and subsequently decrease. On prolonged heating the moduli depend greatly on heating temperature: the higher the temperature, the lower the moduli. Properties of concentrated starch systems during heating are related to swelling of granules, melting of crystallites, separation of amy lose from amylopectin and disentanglement of non-covalent bonds. The differences between the rheological properties of potato and wheat starch suspensions are discussed, and compared with those of chemically cross-linked potato starches. Our hypothesis for the explanation of the observed phenomena is that physical entanglements or chemical cross-links, naturally or artificially present in starch granules, reduce the swelling capacity of the granules and increase the stiffness of the swollen granules; as a consequence, they affect the rheological properties of concentrated starch suspensions.

A dynamic rheological method to study the interaction between starch and lipids

A dynamic rheological method was used to follow transitions occurring during heating and cooling of starch–lipid gels that were prepared separately from the rheological measurement. A decrease in storage modulus (G′) and a simultaneous increase in phase shift (δ) were interpreted as due to a transition of the amylose–lipid complex. During cooling an increase in G′ and a decrease in δ were observed. The temperature of this transition (Tm) was found to depend on the type of starch, chain length of complexing ligand, polar head group of the ligand, and salt concentration for ionic ligands. For a hydroxypropylated potato starch lower Tm values were observed than for the native potato starch. Surfactants with longer hydrocarbon chains gave higher Tm values. The polar head influenced the stability so that it increased in the following order: cationic<anionic<nonionic. For the charged ligands Tm increased with the concentration of NaCl. This was explained as due to a generic electrostatic effect of ions on the helix–coil transformation. Not only the transition of the amylose–lipid complex was affected as described. Also the rheological properties of the starch–lipid gel at room temperature were possible to change depending on the ligand used. By combining the proper starch and surfactant/emulsifier it was thus possible to obtain very strong and elastic gels (i.e., high G′ and low δ values) or very weak and viscous gels (i.e., low G′ and high δ values).

Heat‐induced Gelation of Myofibrillar Proteins and Sausages: Effect of Blood Plasma and Globin

ABSTRACTThe gelation of meat myofibrils and sausages was monitored during heating with and without added blood globin and plasma by the dynamic rheological method. During heating of beef myofibrils (pH 6.5; prot conc 6.0%) the storage modulus (G') reached a minimum at 47.7°C, decreased on further heating, and increased above 53°C. At higher pH (6.9) the G’value was lower and the magnitude of tanδ increased substantially between 37 and 42°C. Addition of blood globin and plasma changed the thermal gelation of myofibrils. During heating of control and protein‐supplemented sausages, we observed two minor peaks in storage modulus in the range 40–55°C and a steep increase at 55–80°C. The storage modulus of low fat sausages, where 25% of meat was replaced by globin or plasma, was greater than that of control sausages.

Heat‐induced Gelation of Minced Rainbow Trout (Salmo gairdneri:) Effect of pH, Sodium Chloride and Setting

ABSTRACTThe structure formation of minced rainbow trout was monitored during heating from 30°C to 85°C by a dynamic rheological method. The maxima of storage modulus (G') were found at 37°C and in the range of 45°C to 60°C. The largest differences in rigidity resulted from seasonal variations. Firmest protein matrix was obtained by using well‐fed fish as raw material, by setting the gels at 35°C and using a pH value around 6.1. Sodium chloride in the range 1–2% had little effect on the final rigidity of the minced rainbow trout gels.

Heat‐Induced Gelation of Individual Whey Proteins A Dynamic Rheological Study

ABSTRACTHeat‐induced gelation of the bovine whey proteins [serum albumin (BSA), β‐lactoglobulin (β‐Lg) and α‐lactalbumin (α‐La)] has been studied individually and in mixture at different conditions by a dynamic rheological method. Values in the shear stiffness modulus (/G*/) appeared on heating at low protein concentration for BSA (∼2%) and at intermediate concentration for β‐Lg (∼ 5%). α‐La did not form a heat‐induced gel of concentrations up to 20% (w/v). The ratio of viscous to elastic properties (loss factor) at maximum possible measuring temperature was below 0.07 for the BSA gels and 0.1–0.3 for the β‐Lg gels. The temperature of gelation was highly dependent on pH. In mixture one protein could not be exchange for another without changing the gelation behavior of the mixture.