Dynamic Shear Storage Modulus Research Articles

Rheological Properties of Gellan Gels Containing Filler Particles

ABSTRACT: Influences of rigid (glass) and deformable (gellan) particles dispersed in gellan gels were studied to better understand the effect of structure on the rheological properties of model composite foods. Composites with inclusions at 0%, 10%, 20%, and 30% volume fractions (VF) were tested under small deformation oscillatory shear. In gels containing rigid particles, the dynamic shear storage modulus (G′) decreased initially, exhibited a minimum around 20% VF, then increased at 30% VF behavior that was attributed to physical interactions among particles. In gels containing deformable particles, the linear decrease in G′ with increasing VF may be due to particle compliance under stress or to particle separation from the matrix, thereby causing gel weakening.

The Effect of Crystallinity on the Rheological Behavior of Poly(lactide)

The rheological behavior of poly(lactide) samples, with different levels of crystallinity, was investigated. The dynamic shear storage and loss modulus were obtained as a function of temperature at 1 rad/s. From the glassy to the rubbery region, the dynamic shear modulus decreased more than two decades for the initially amorphous poly(lac-tide) (containing 1% of D-lactide) and about one decade for the annealed (semicrystaJ-line) sample. The dynamic shear modulus data showed that the crystallization rate increased with a decrease of D-lactide in poly(lactide) and an increase of talc (a nucleating agent) in the sample. The steady-state and dynamic shear viscosity were measured at 210°C. The results indicated that the Cox-Merz rule can be used to relate the dynamic shear viscosity to the steady-state shear viscosity. A master curve for the amorphous poly(lactide) was obtained, using the time-temperature superposition principle. The result showed that the temperature dependence of the shift factor can be described by the Arrhenius equation below the glass-transition region, and the WLF (Williams-Landel-Ferry) equation above the glass-transition region.

Pultruded fibre-reinforced PMMA/PU IPN composites: processability and mechanical properties

This paper presents a proprietary process developed to manufacture polyurethane (PU)/polymethyl methacrylate (PMMA) interpenetrating polymer networks (IPNs) pultruded composites. The IPNs prepolymer sythesized in this study was prepared from the blends of MMA prepolymer and blocked NCO-terminated PU prepolymer. The processability, mechanical and dynamic mechanical properties of glass fiber rein forced PU/PMMA IPNs composites have been studied. From the investigation of the pot life of resins, the reactivity of ream and fiber wet-out, it was found that the PU/PMMA IPNs show excellent processability for pultrusion. Results show that the tanδ of IPNs composites shifts to the higher temperature with increasing PMMA content, and dynamic shear storage modulus (G') increases with with PMMA content. The flexural strength, flexural modulus and hardness of IPNs composites increase with PMMA Content, however, the impact strength and swelling ratio of IPNa composites decrease with the increasing of PMMA content.

Comparison of the uniaxial tensile modulus and dynamic shear storage modulus of a filled hydroxy-terminated polybutadiene and GAP propellant

The uniaxial tensile moduli for two filled composite solid propellants, one based on a hydroxy-terminated polybutadiene with an ammonium perchlorate oxidizer and the other on a glycidyl azide polymer with a phase-stabilized ammonium nitrate oxidizer, were measured at various temperatures and over a three decade range of strain rates. Dynamic shear moduli were measured at various strains and temperatures over a three decade range of frequencies. Values of the tensile modulus, ET/3 (assuming Poisson's ratio equals 0.5), were compared with the dynamic storage modulus, G′, for each of the dynamic strain levels investigated. The results demonstrate that it is possible to compare 3G′ measured at different dynamic strains and frequencies with the incremental tangent moduli obtained at corresponding uniaxial strains from constant strain rate tests on specimens with a JANNAF geometry. The comparisons are most favourable when the concave-up region of the stress-strain curve extends only up to approximately 2.0% strain. It was observed that G′ obtained at a dynamic shear strain of 2.0% provided the best overall correlation with ET/3 measured over a range of temperatures and strain rates.

Physico-chemical properties and rheological behaviour of Patella caerula paramyosin.

Paramyosin is a muscle protein which is characteristic of all invertebrates but which is not present in vertebrate muscles. Given the functional importance of paramyosin, the purpose of this paper was to study the physico-chemical properties, including the amino acid composition and rheological behaviour, of purified paramyosin and to investigate its mode of interaction with myosin. Paramyosin was purified from the limpet (Patella caerula) by an ethanol precipitation step. It was soluble at ionic strengths below 0.05 M NaCl and its maximum solubility at neutral pH occurred at approximately 0.4 M NaCl. At this high ionic strength, the pH dependence of solubility was such that paramyosin passed quickly into solution when pH exceeded pH 5, the transitional pH value. By using an immunological method, it was shown that interactions between paramyosin and myosin occurred, even in the presence of actin. The molecular assembly of both proteins was probably specified by hydrophobic interactions, as well as by interactions enhanced by divalent cations. The changes in the dynamic shear storage modulus (G') started between 40 degrees C and 50 degrees C, and reached a maximum at about 75 degrees C.

Dynamic rheological studies on salt-soluble proteins from three porcine muscles

The effect of phosphates on the rheological properties of porcine Longissimus dorsi (LD, white), Serratus ventralis (SV, red) and Vastus intermedius (VI, red) muscle salt-soluble proteins (SSP) was examined. Changes in shear stress and viscosity as a function of shear rate of 4 mg/ml SSP suspensions indicated pseudoplastic flow. Viscosity and shear stress values were higher for LD than for SV samples, and 0.25% tripolyphosphate decreased shear stress for both muscle types. SSP suspensions (5–30 mg/ml) gelled during heating from 20 to 74°C and the changes in the dynamic shear storage modulus ( G′) greatly depended on the protein concentration and differed for LD, SV and VI proteins. Addition of 0.25–0.60% pyro- and tripolyphosphate reduced G′, but NaCl at comparable ionic strengths did not show this effect. It was shown that red and white muscle SSP exhibited different rheological properties but responded similarly to phosphate treatments.

Pultruded fiber‐reinforced poly(methyl methacrylate) composites. II. Static and dynamic mechanical properties, environmental effect, and postformability

AbstractThis paper presents a novel process developed to manufacture poly(methyl methacrylate) (PMMA) pultruded composite. The mechanical, thermal, and dynamic mechanical properties, environmental effect, postformability of various fiber (glass, carbon, and Kevlar 49 aramid fiber) reinforced pultruded PMMA composites have been studied. Results show mechanical properties (i.e., tensile strength, specific tensile strength, tensile modulus, and specific flexural strength) and thermal properties (HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest specific tensile strength and HDT, carbon fiber/PMMA composites show the highest tensile strength and tensile modulus, and glass fiber/PMMA composites show the highest specific flexural strength. Pultruded glass‐fiber‐reinforced PMMA composites exhibit good weather resistance. These composite materials can be postformed by thermoforming under pressure, and mechanical properties of postformed products can be improved. The dynamic shear storage and loss modulus (G′, G″) of pultruded glass‐fiber‐reinforced PMMA composites increased with decreasing pulling rate, and their shear storage moduli are higher than those of pultruded Nylon 6 and polyester composites.

Thermorheological studies of food polymer dispersions

Reversible thermal gelation of methylcellulose (MC) was characterized by measuring the dynamic shear storage modulus (G′) as temperature was increased from 20 to 67° C at scanning rates of 1·0, 0·50 and 0·25 C°/min, and then decreased in a similar manner. The thermally induced gelation of 15·0% dispersions of soy or canola protein and meat emulsion systems with and without canola protein were also studied by measuring G′ as temperature was raised from 20 to 90°C and then lowered at a rate of 2·0C°/min. The storage modulus for solutions of MC decreased from 20 to 40°C. From 40–67°C, log G′ decreased in three stages, first slowly with temperature, then suddenly increasing three orders of magnitude between 54 and 62°C, with only small increases above 62°C. When cooled, G′ for the sample decreased in three similar stages, giving almost the mirror image of the gelation behavior. When heated from room temperature, soy and canola protein dispersions exhibited different viscoelastic behavior. G′ for the canola dispersion decreased slightly more than one order of magnitude when heated to 60°C, while the soy dispersion showed only a slight decrease in G′. At 60–90°C, structure formation in the canola dispersion was detected as G′ increased two orders of magnitude. Structure development for the soy dispersion commenced at about 78°C with G′ increasing only 10-fold. Both proteins exhibited similar increased rigidity throughout cooling. The meat emulsion containing canola experienced structural changes on heating and cooling intermediate to that of isolated canola dispersions and all-meat emulsions. The all-meat protein emulsion showed greater rigidity overall and achieved maximum structure development at a lower temperature than the canola-substituted emulsion. Thermorheological scanning provided a convenient method to explore the mechanisms involved in structure formation in these polysaccharide and protein gelling food systems.

Pultruded fiber reinforced thermoplastic poly(methyl methacrylate) composites. Part II: Mechanical and thermal properties

AbstractA novel process has been developed to manufacture poly(methyl methacrylate) (PMMA) pultruded parts. The mechanical and dynamic mechanical properties, environmental effects, postformability of pultruded composites and properties of various fiber (glass, carbon and Kevlar 49 aramid fiber) reinforced PMMA composites have been studied. Results show that the mechanical and thermal properties (i.e. tensile strength, flexural strength and modulus, impact strength and HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest impact strength and HDT, while carbon fiber/PMMA composites show the highest tensile strength, tensile and flexural modulus, and glass fiber/PMMA composites show the highest flexural strength. Experimental tensile strengths of all composites except carbon fiber/PMMA composites follow the rule of mixtures. The deviation of carbon fiber/PMMA composite is due to the fiber breakage during processing. Pultruded glass fiber reinforced PMMA composites exhibit good weather resistance. They can be postformed by thermoforming, and mechanical properties can be improved by postforming. The dynamic shear storage modulus (G′) of pultruded glass fiber reinforced PMMA composites increased with decreasing pulling rate, and G′ was higher than that of pultruded Nylon 6 and polyester composites.

The Dynamic Shear Storage Modulus of Plastic‐Bonded Explosives and its relationship to sensitivity

AbstractThe linear dynamic mechanical properties of plastic‐bonded explosives (PBXs) were measured from −40 °C to +50 °C over the frequency range of 0.1 Hz to 4 Hz with a Rheometrics dynamic mechanical spectrometer. The purpose of the measurements was to develop correlations between the viscoelastic properties of composite high explosive systems and their impact sensitivities. Data from drop‐skid tests using the 45°‐angled target, as performed by the Los Alamos Scientific Laboratory (LASL), were used in the sensitivity measurements. The skid‐test drop height was inversely proportional to the shear storage modulus of the PBXs and the glass transition temperature (measured dynamically) of the PBXs tested.

Head to head polymers IX: The rheological behavior of H‐H and H‐T atactic polystyrenes

AbstractThe rheological behavior of a sample of H‐H polystyrene of Mn of 41,000 and a Mw/Mn of 2 was compared at 160 and 190°C with a sample of H‐T atactic polystyrene of similar molecular weight. The melt viscosity of H‐H polymer (unlike the H‐T polymer) was non‐Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H‐H polystyrene. The flow activation energy (E*) of H‐H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H‐H polymer has a smaller increase of G′ with ω than that of the H‐T polystyrene.

Dynamic Shear Behavior of Commercial Wheat Gluten

The dynamic shear properties of commercial vital wheat gluten subjected to small-deformation oscillatory shear were investigated. Hydrated wheat gluten was found to be Theologically complex and in general required multiple linear regression analyses to adequately account for variation. Dynamic shear storage modulus was extremely sensitive to moisture content. Other parameters were affected to a lesser though significant amount by moisture level. Cycling, or in effect, working caused an increase in the magnitude of both the storage and loss moduli. However, it was found that working did not alter the ratio of loss to storage modulus. It was found that gluten exhibits a proportional increase in viscous response with increased oscillatory frequency. All findings of this work appeared to be compatible with a published theory for the mechanism of the viscoelastic response of wheat gluten.