Loss Modulus (loss + modulus)

Distribution by Scientific Domains

Selected Abstracts

The effect of high pressure treatment on rheological characteristics and colour of mango pulp

Jasim Ahmed
Summary The effect of high-pressure (HP) treatment (100,400 MPa for 15 or 30 min at 20 C) on the rheological characteristics and colour of fresh and canned mango pulps was evaluated. Differences were observed in the rheological behaviour of fresh and canned mango pulps treated with HP. Shear stress,shear rate data of pulps were well described by the Herschel,Bulkley model. The consistency index (K) of fresh pulp increased with pressure level from 100 to 200 MPa while a steady decrease was noticed for canned pulp. For fresh pulp the flow behaviour index decreased with pressure treatment whereas an increasing trend was observed with canned pulp. Storage and loss moduli of treated fresh pulp with HP increased linearly with angular frequency up to 200 MPa for a treatment time of 30 min while a steady decreasing trend was found for processed pulp. No significant variation in colour was observed during pressure treatment. [source]

Rheological behavior and mechanical properties of high-density polyethylene blends with different molecular weights

Lu Bai
Abstract The dynamic rheological and mechanical properties of the binary blends of two conventional high-density polyethylenes [HDPEs; low molecular weight (LMW) and high molecular weight (HMW)] with distinct different weight-average molecular weights were studied. The rheological results show that the rheological behavior of the blends departed from classical linear viscoelastic theory because of the polydispersity of the HDPEs that we used. Plots of the logarithm of the zero shear viscosity fitted by the Cross model versus the blend composition, Cole,Cole plots, Han curves, and master curves of the storage and loss moduli indicated the LMW/HMW blends of different compositions were miscible in the melt state. The tensile yield strength of the blends generally followed the linear additivity rule, whereas the elongation at break and impact strength were lower than those predicted by linear additivity; this suggested the incompatibility of the blends in solid state. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Influence of powder particle size distribution on complex viscosity and other properties of acrylic bone cement for vertebroplasty and kyphoplasty,

Lidia Hernndez
Abstract For use in vertebroplasty and kyphoplasty, an acrylic bone cement should possess many characteristics, such as high radiopacity, low and constant viscosity during its application, low value of the maximum temperature reached during the polymerization process (Tmax), a setting time (tset) that is neither too low nor too high, and high compressive strength. The objective of this study was to investigate the influence of the powder particle distribution on various properties of one acrylic bone cement; namely, residual monomer content, Tmax, tset, complex viscosity, storage and loss moduli, injectability, and quasi-static compressive strength and modulus. It was found that the formulations that possessed the most suitable complex viscosity-versus-mixing time characteristics are those in which the ratio of the large poly(methyl methacrylate) beads (of mean diameter 118.4 ,m) to the small ones (of mean diameter 69.7 ,m) was at least 90% w/w. For these formulations, the values of the other properties determined were acceptable. 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring-opening polymerization of glycolide

Estelle Gautier
Abstract Ring-opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1-dodecanol and 1,4-butanediol and tin(II) 2-ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well-defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (Tg,) of 44.8 C was thus calculated. From rheological data, the critical molar mass for entanglement, Mc, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency , = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200,230 C. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440,1449, 2009 [source]

Dispersion of multiwalled carbon nanotubes in thermoplastic elastomer gels: Morphological, rheological, and electrical properties

Marissa A. Paglicawan
An investigation was reported here with an aim to prepare nanocomposite thermoplastic elastomer gels by dissolving polystyrene- b -poly(ethylene/butylene)- b -polystyrene (SEBS) triblock copolymer in selective hydrocarbon oils with the presence of multiwalled carbon nanotubes (MWCNTs). The properties related to morphology, viscoelasticity, electrical and mechanical properties, and thermal stability were explored and discussed. Dynamic rheological measurements of the resultant nanocomposite thermoplastic elastomer gels (NCTPEGs) confirmed that addition of MWCNTs affects the linear viscoelastic properties in which dynamic storage and loss moduli increase to some extent. At a temperature between 30C and 40C below the gel point the NCTPEGs have dynamic storage modulus greater than loss modulus (G, and G,), thereby indicating that at room temperature a physical network is still present despite the addition of MWCNTs. The morphological properties revealed that MWCNTs were dispersed and exfoliated within the swollen TPE. The incorporation of small quantity of MWCNTs improved the thermal stability and mechanical properties of NCTPEGs. POLYM. COMPOS., 2010. 2009 Society of Plastics Engineers [source]

A new linear viscoelastic model for emulsions and suspensions

Rajinder Pal
A new modified form of the Palierne model is proposed to describe the linear viscoelastic behavior of concentrated emulsions and suspensions. The proposed model takes into consideration the crowding effect and packing limit of particles. The model is verified using two sets of experimental data on the storage and loss moduli of emulsions and suspensions. POLYM. ENG. SCI., 2008. 2008 Society of Plastics Engineers [source]

Solid-state linear viscoelastic properties of intercalated poly(L -lactide)/organo-modified montmorillonite hybrids

Pham Hoai Nam
Abstract Hybrids of poly(L -lactide)/organophilic clay (PLACHs) have been prepared by a melt-compounding process using poly(L -lactide) (PLLA) and different contents of surface-treated montmorillonite modified with a dimethyl dioctadecyl ammonium salt. The dispersion structures of clay particles in PLACHs were investigated using wide-angle X-ray diffraction and transmission electron microscopy. The solid-state linear viscoelastic properties for these PLACHs were examined as functions of temperature and frequency. The incorporation of organo-modified silicate into PLLA matrix enhanced significantly both storage moduli (E,) and loss moduli (E,). The strong enhancement observed in dynamic moduli of PLACHs could be attributed to uniformly dispersed state of the clay particles with high aspect ratio (= length/thickness of clay) and the intercalation of the PLLA chains between silicate layers. Copyright 2006 Society of Chemical Industry [source]

Viscoelastic properties of branched polyacrylate melts

Nasir M Ahmad
Abstract The viscoelastic properties of poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate) melts have been studied using samples that varied in both molar mass and the mol% branched repeat units, these properties having been previously determined by gel permeation chromatography and 13C NMR spectroscopy, respectively. Poly(n-butyl acrylate) was studied most extensively using seven samples; one sample of poly(n-butyl acrylate), two samples of poly(ethyl acrylate) and one sample of poly(methyl acrylate) were used to study the effect of side-group size. Storage and loss moduli were measured over a range of frequency (1,,10,3 to 1,,102,rad,s,1) at temperatures from Tg,+,20,C to Tg,+,155,C and then shifted to form master curves at Tg,+,74,C through use of standard superposition procedures. The plateau regions were not distinct due to the broad molar mass distributions of the polyacrylates. Hence, the upper and lower limits of shear storage modulus from the nominal ,plateau' region of the curves for the seven poly(n-butyl acrylate) samples were used to calculate the chain molar mass between entanglements, Me, which gave the range 13.0,kg,mol,1,<,Me,<,65.0,kg,mol,1. The Graessley,Edwards dimensionless interaction density and dimensionless contour length concentration were calculated for poly(n-butyl acrylate) using the mean value of plateau modulus (1.2,,105,Pa) and three different methods for estimation of the Kuhn length; the data fitted closely to the Graessley,Edwards universal plot. The Williams,Landel,Ferry C1 and C2 parameters were determined for each of the polyacrylates; the data for the poly(n-butyl acrylate) samples indicate an overall reduction in C1 and C2 as the degree of branching increases. Although the values of C1 and C2 were different for poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate), there is no trend for variation with structure. Thus the viscoelastic properties of the polyacrylate melts are similar to those for other polymer melts and, for the samples investigated, the effect of molar mass appears to dominate the effect of branching. 2001 Society of Chemical Industry [source]

Amplitude- and temperature effects of filler-reinforced rubber: Experiments and Modelling

Martin Rendek
Rubber,like materials exhibit special mechanical properties in a wide range of technical applications. To achieve a desired behaviour of the end product, the materials are reinforced with active fillers like carbon black. In the focus of this paper are selected cyclic,monofrequent experiments with constant strain amplitudes. Special attention will be focused to the excitation with small dynamic amplitudes. The amplitude dependence of the storage and loss moduli is known as the Payne,effect. We study the amplitude, and temperature dependence of storage and loss modulus as well as dissipation effects. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Rheological behavior of crystallizing palm oil

Veerle De Graef
Abstract The static isothermal crystallization of palm oil was studied by oscillatory rheology. The phase angle, complex modulus, storage modulus and loss modulus were followed as a function of the crystallization time. Various crystallization temperatures were applied, and the results obtained by oscillatory rheology were compared with crystallization data obtained by more classical techniques like differential scanning calorimetry (DSC) and pulsed nuclear magnetic resonance (pNMR). It was shown that oscillatory rheology is a valuable complementary method to DSC and pNMR to evaluate primary crystallization. Like DSC and pNMR, oscillatory rheology is capable of differentiating whether crystallization occurs in a two-stage or a single-stage process. In addition, oscillatory measurements also allow the evaluation of aggregation, network formation and post-hardening events like sintering and thus provide information on the crystal network and the final macroscopic properties of the crystallized sample. [source]

Changes in functional properties of shark (Isurus oxyrinchus) cartilage gelatin produced by different drying methods

Ki-Seok Kwak
Summary Fish gelatins extracted from shark (Isurus oxyrinchus) cartilage were dried by three different methods: freeze drying, hot-air drying and spray drying; and their functional properties were investigated. Freeze-dried gelatin was found to have the strongest gel strength, while gelatins made at high temperatures formed weaker gels. The 135-kPa gel strength of freeze-dried gelatin was relatively high. While foam formation ability of the freeze-dried gelatin was the highest, its foam stability was the lowest. In addition, spray-dried gelatin had the best emulsion capacities. Dynamic viscoelastic properties of shark cartilage gelatins prepared by these drying methods were closely correlated with their gel strength. Elasticity modulus (G'; Pa) and loss modulus (G"; Pa) of the freeze-dried gelatin had higher values than those prepared by hot-air drying and spray drying; viscoelastic properties of the freeze-dried gelatin were maintained longer than those of other drying methods. [source]

Starch-lipid composites in plain set yogurt

Mukti Singh
Summary Starch-lipid composites (SLC) were used to replace milk solids in yogurt mixes. The effects of the SLC on the yogurt fermentations and rheology were studied. The rate of fermentation was evaluated by the change of pH during the fermentation of yogurt. The syneresis of yogurt was observed over 3 weeks of storage. Small amplitude oscillatory shear flow measurements of the storage modulus, the loss modulus, and the loss tangent were obtained using a vane geometry. Yogurt mixes with milk solids partially replaced by SLC fermented at a similar rate than as with no milk solids replaced. Initial viscosity was higher for yogurt mixes with higher levels of SLC. The higher initial viscosity did not affect the gel structure. The addition of SLC above a level of 3% strengthened the gel and resulted in no syneresis for yogurt samples stored for 3 weeks at 4 C. [source]

Polymer characterization by ultrasonic wave propagation

Francesca Lionetto
Abstract The propagation of low-intensity ultrasound in polymers, acting as a high-frequency dynamic mechanical deformation, can be successfully used to monitor changes in the modulus of polymers associated with glass transition, crystallization, cross-linking, and other chemical and physical phenomena related to changes in the viscoelastic behavior, such as gelation phenomena. The velocity of sound is related to the polymer storage modulus and density, whereas the absorption of ultrasonic waves is related to the energy dissipation in the material and, therefore, to the loss modulus. Accordingly, ultrasonic measurements have been used by several authors to monitor the evolution of the viscoelastic moduli of polymers as a function of time or temperature and, recently, become a characterization technique of its own right, generally known as ultrasonic dynamic mechanical analysis (UDMA). Often the technique is used in conjunction with rheological methods as a means of providing a better insight into the viscoelastic behavior of polymer systems. As yet UDMA is underutilized primarily because of the low operating temperatures (usually below 100,C) of commercially available ultrasonic transducers, and also due to the requirement of a coupling medium to ensure an efficient energy transfer mechanism between the transducer and the test material. Despite these limitations, this paper shows that the use of ultrasonics is potentially a powerful method for the characterization of polymers, particularly as a tool for online monitoring of events occurring during polymer processing and in the manufacture of polymer matrix composites. The aim of this paper is to review the progress made in recent years, highlighting the potential and reliability of UDMA for monitoring physical transitions in polymers such as glass transition, melting, crystallization, as well as physical changes taking place during curing of thermosetting resins. 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:63,73, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20124 [source]

Structure,properties relations of the drawn poly(ethylene terephthalate) filament sewing thread

Andreja Rudolf
Abstract This article presents research into draw ratio influence on the structure,properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effects of ultraviolet irradiation on the static and dynamic properties of neoprene rubbers

Hsoung-Wei Chou
Abstract Rubbers deteriorate when they are exposed to ultraviolet irradiation for long periods of time. By conducting a series of hardness measurements and simple tension tests, the static properties of neoprene rubbers before and after exposure to various durations of ultraviolet irradiation were first measured. It is found that the Shore A hardness and tensile modulus of neoprene rubbers after exposure to ultraviolet irradiation are increased but their elongation at break, tensile strength, and energy to break are significantly decreased. On the basis of a complex spring model of a vibration system, the dynamic shear properties of neoprene rubbers before and after exposure to different durations of ultraviolet irradiation were then determined from the experimental results of dynamic transmissibility tests. It is also found that the storage modulus, loss modulus, and loss factor of neoprene rubbers are drastically affected by the duration of ultraviolet irradiation they experienced. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Polyamide 6/maleated ethylene,propylene,diene rubber/organoclay composites with or without glycidyl methacrylate as a compatibilizer

Lingyan Zhang
Abstract Polyamide 6 (PA6)/maleated ethylene,propylene,diene rubber (EPDM- g -MA)/organoclay (OMMT) composites were melt-compounded through two blending sequences. Glycidyl methacrylate (GMA) was used as a compatibilizer for the ternary composites. The composite prepared through via the premixing of PA6 with OMMT and then further melt blending with EPDM- g -MA exhibited higher impact strength than the composite prepared through the simultaneous blending of all the components. However, satisfactorily balanced mechanical properties could be achieved by the addition of GMA through a one-step blending sequence. The addition of GMA improved the compatibility between PA6 and EPDM- g -MA, and this was due to the reactions between PA6, EPDM- g -MA, and GMA, as proved by Fourier transform infrared analysis and solubility (Molau) testing. In addition, OMMT acted as a compatibilizer for PA6/EPDM- g -MA blends at low contents, but it weakened the interfacial interactions between PA6 and EPDM- g -MA at high contents. Both OMMT and GMA retarded the crystallization of PA6. The complex viscosity, storage modulus, and loss modulus of the composites were obviously affected by the addition of OMMT and GMA. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Photoinitiating polymerization to prepare biocompatible chitosan hydrogels

Xiaohong Hu
Abstract Chitosan hydrogels were prepared from water soluble chitosan derivatives (chitosan-MA-LA, CML) by photoinitiating polymerization under the existence of Irgacure2959 and the irradiation of UV light. The CML was obtained by amidation of the amine groups of chitosan with lactic acid and methacrylic acid. Gelation time of the hydrogel could be adjusted within a range of 5,50 min, and controlled by factors such as the degree of MA substitution, initiator concentration, existence of oxygen, and salt. The dry hydrogel adsorbed tens to hundred times of water, forming a highly hydrated gel. The swelling ratio was smaller at the higher degree of MA substitution, higher pH, and higher salt concentration. Rheological test showed that the hydrogel is elastomeric in the measuring frequency range, with a storage modulus and loss modulus of 0.8,7 kPa and 10,100 Pa, respectively. In vitro culture of chondrocytes demonstrated that the cells could normally proliferate in the extractant of the hydrogels, showing no cytotoxicity at lower initiator concentration. By contrast, the extractant of the hydrogel made by the redox initiating system, i.e., ammonium persulfate (APS) and N,N,N,,N,-tetramethylethylenediamine (TEMED), showed apparent cytotoxicity. Thus, the chitosan hydrogels initiated by the Irgacure2959 have better comprehensive properties, in particular better biocompatibility, and are more suitable for biomedical applications. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effect of the structure of silane-coupling agent on dynamic mechanical properties of dental resin-nanocomposites

Irini D. Sideridou
Abstract This work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis-GMA/TEGDMA (50/50 wt/wt) matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3-[(1,3(2)-dimethacryloyloxypropyl)-2 (3)-oxycarbonylamido] propyltriethoxy-silane (UDMS), 3-methacryloxypropyl-trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10% by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60% filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E,), loss modulus (E,), tangent delta (tan ,), and glass transition temperature (Tg). Measurements were performed in samples immediately after curing and samples stored in water at 37C for 1, 7, 30, or 120 days. OTMS-composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS-composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS-composite remained constant, while that of the other composites increased after 1 day and then remained constant up to 120 days. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Dynamic mechanical and thermal properties of PE-EPDM based jute fiber composites

Gautam Sarkhel
Abstract The present investigation deals with the mechanical, thermal and viscoelastic properties of ternary composites based on low density polyethylene (LDPE)-ethylene,propylene,diene terpolymer (EPDM) blend and high density polyethylene (HDPE)-EPDM blend reinforced with short jute fibers. For all the untreated and compatibilizer treated composites, the variation of mechanical and viscoelastic properties as a function of fiber loading (10, 20 and 30 wt %) and compatibilizer concentration (1, 2, and 3%) were evaluated. The flexural strength, flexural modulus, impact strength, and hardness increased with increasing both the fiber loading and the compatibilizer dose. The storage modulus (E,) and loss modulus (E,) of the HDPE-EPDM/jute fiber composites were recorded higher compared to those of the LDPE-EPDM/jute fiber composites at all level of fiber loading and compatibilizer doses. The tan, (damping efficiency) spectra showed a strong influence of the fiber loading and compatibilizer dose on the , relaxation process of polymer matrix in the composite. The thermo-oxidative stability was significantly enhanced for treated composites compared to untreated composites. Scanning electron microscopy investigation confirmed that the higher values of mechanical and viscoelastic properties of the treated composites compared to untreated composites is caused by improvement of fiber-matrix adhesion as result of compatibilizer treatment. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effect of silica reinforcement on natural rubber and butadiene rubber vulcanizates by a sol,gel reaction with tetraethoxysilane

Kyong-Hwan Chung
Abstract The effect of silica reinforcement was studied for natural rubber (NR) and butadiene rubber (BR) vulcanizates by a sol,gel reaction with tetraethoxysilane at different temperatures. The formation of silica in the rubber vulcanizates was investigated analytically with Fourier transform infrared spectroscopy and energy-dispersive X-ray analysis. The variations of the mechanical and dynamic properties were measured in the NR and BR vulcanizates with silica filling. The hardness of the rubber vulcanizates increased with silica filling in the rubber matrix. The tensile strength and elongation at break decreased with silica filling in the NR vulcanizates. The moduli at 50, 100, and 300% elongation increased with silica filling in the rubber matrix. The storage modulus of silica-filled rubber vulcanizates became higher than that of pure rubber vulcanizates. The temperature dependence of the loss modulus also increased with silica filling. The temperature dependence of the loss tangent was maintained, regardless of silica filling in the BR vulcanizates. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

Rheological properties of poly(methyl methacrylate)/rigid ladderlike polyphenylsilsesquioxane blends

Guizhi Li
Abstract A series of poly(methyl methacrylate) (PMMA) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared at weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20 by solution casting and then hot-pressing. Their rheological properties have been studied under both dynamic shear and uniaxial elongation conditions. Their rheological properties depend on the compositions. The storage modulus, G,, loss modulus, G,, and dynamic shear viscosity, ,*, of the PMMA/PPSQ 95/5 blend were slightly lower than those of pure PMMA. However, the values of G,, G,, and ,* for the other PMMA/PPSQ blends are higher than those of PMMA. The G, values increase with an increase in PPSQ content from 5% through 15% PPSQ at low frequencies and then drop as the PPSQ content increases to 20%. Uniaxial elongational viscosity (,E) data demonstrate that PMMA/PPSQ blends exhibit slightly weaker (5% PPSQ) and much weaker (10% PPSQ) strain-hardening than PMMA. In contrast, the PMMA/PPSQ 85/15 blend shows strain-softening. Neither strain-hardening nor strain-softening was observed in the 80/20 blend. The special rheological properties for the 95/5 blend is probably due to a decrease in PMMA entanglements brought by the specific PMMA,PPSQ interactions. Rheological properties of PMMA/PPSQ blends with higher PPSQ content (,10%) are mainly affected by formation of hard PPSQ particles. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 352,359, 2007 [source]

Characterization of end-functionalized styrene,butadiene,styrene copolymers and their application in modified asphalt

Qiang Wang
Abstract End amino, carboxylic acid, and hydroxyl functionalized styrene,butadiene,styrene (SBS) triblock copolymers were prepared with 1,5-diazabicyclo[3.1.0]hexane, carbon dioxide, and epoxy ethane as capping agents, respectively. The effects of the end polar groups on the morphology and dynamic mechanical properties were investigated. Transmission electron microscopy images suggested that the group at the end of the polystyrene (PS) segment made the morphology of the PS domains disordered and incompact. Dynamic mechanical results showed that the storage and loss modulus increased after SBS was end-functionalized. End amino and carboxylic acid groups improved the compatibility and storage stability of SBS-modified asphalt. However, the effect of the end-hydroxyl group on the improvement of the storage stability of SBS-modified asphalt was not obvious. The differential scanning calorimetry analysis of SBS-modified asphalt further showed that the compatibility and storage stability of SBS-modified asphalt were improved by the attachment of amino or carboxylic acid groups through the anionic polymerization method. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 8,16, 2007 [source]


ABSTRACT Good spreadability is a highly desirable quality for crystallized honey used in product applications. In this study, we processed Taiwanese liquid litchi honey into crystallized honey by adding a new nuclei material, namely 0.1% (w/w) glucose powder, instead of the traditional 5,10% (w/w) natural nuclei. Rheological properties of the resulting product were determined during heating and cooling utilizing small amplitude oscillatory shear to assess spreadability. As the product was heated, it exhibited decreased consistency and improved fluidity (evidenced by decreasing storage modulus [G,] and loss modulus [G,] values) and three distinct regions within the G,curve ("softening,""crystalline plateau" and "melting"). As the product was cooled from 55 to 0C, moduli were lower than those obtained during heating, and the product did not exhibit the three G,curve regions across the temperature range. Therefore, we observed incomplete reversible crystallization and rheological properties during temperature migration. Flow properties of crystallized honey in the 0,25C temperature range could be successfully predicted using the Herschel,Bulkley model (R2 > 0.97). However, the product approached Newtonian flow behavior as temperatures neared the upper end of this range. Higher viscosity and lower yield stress were observed at temperatures below 15C. The crystallized honey developed for this study exhibited shear-thinning properties desirable in honey products intended to be spread. PRACTICAL APPLICATIONS Crystallized honey is traditionally prepared by introducing 5,10% natural nuclei into liquid honey. Our lab developed a new method that replaces the natural nuclei with glucose powder, which, at 0.1% (w/w), produces a good quality creamed honey that, in commercial production, offers the potential for significant production cost advantages. As crystallized honey is used in commercial/consumer applications as a spread, its dynamic rheology is of both academic and industrial interest. In this study, we discuss the physical properties of the crystallized honey developed using glucose powder to help better identify the factors and variables involved in honey spreadability and thus facilitate the development of better honey products with more desirable spreadability profiles. This study also provides a rheological properties and spreadability database for crystallized honey that reflects the range of temperature changes that can be expected to occur during normal product storage and use. [source]

Characterization of Phase Separation Behavior, Emulsion Stability, Rheology, and Microstructure of Egg White,Polysaccharide Mixtures

E. Alben Erelebi
ABSTRACT:, Phase separation behavior of egg white-pectin/guar gum mixtures was investigated. These systems led to phase separation arisen by either depletion flocculation or thermodynamic incompatibility. The influence of polysaccharides on the emulsifying activity index (EAI), emulsifying stability index (ESI), creaming stability, microstructure, and rheological properties was also studied at different polysaccharide concentrations (0% to 0.5%, [w/v]). Increasing pectin and guar gum concentration from 0.01% to 0.5% significantly improved EAI by 51% and 25%, respectively. The highest ESI and EAI values were obtained in the presence of 0.5% (w/v) pectin/guar gum. Microscopic images showed that emulsions containing polysaccharides had small droplets as compared to that of emulsions without polysaccharides. The addition of polysaccharides improved emulsion stability against creaming. Egg white-stabilized emulsions with and without polysaccharides reflect the pseudoplastic behavior with,n,< 1.0. Polysaccharides, especially at high concentrations, affected the viscoelastic behavior of the emulsions; storage (G,) and loss modulus (G,) crossed-over at lower frequency values as compared to that of emulsions containing no polysaccharide. [source]

Thermal Effects on Fast Skeletal Myosins from Alaska Pollock, White Croaker, and Rabbit in Relation to Gel Formation

H. Fukushima
ABSTRACT Thermodynamic properties in differential scanning calorimetry (DSC) and changes in viscoelasticity upon heating of myosins from white croaker, Alaska pollock, and rabbit fast muscles were investigated in relation to their thermal gel formation abilities. Alaska pollock myosin unfolded in a wide temperature range of 19 to 69C as revealed by DSC, whereas rabbit myosin unfolded in very narrow range of 32 to 56C. Thermal unfolding of white croaker myosin occurred in an intermediate temperature range of 30 to 60C. Viscoelastic properties determined as storage modulus, G,, and loss modulus, G,, reflected differences observed in DSC for the 3 myosins. [source]

Combinatorial development of polymer nanocomposites using transient processing conditions in twin screw extrusion

AICHE JOURNAL, Issue 7 2008
Arun K. Kota
Abstract A new approach is presented for combinatorial development of polymer nanocomposites with compositional gradients (CGs). The CGs were developed using transient processing conditions in twin screw extrusion with small quantities of expensive nanoscale fillers. Convolution of step input with normalized residence volume distributions (RVDs) was used to establish the processing,structure relationship for the CGs. The normalized RVD was established as a process characteristic independent of processing conditions and measured in situ using an optical probe. The CG determined nondestructively using the new combinatorial approach was validated through comparison with more time-consuming and destructive thermogravimetric analysis. The CG could also be established with relatively inexpensive microscale fillers using the normalized RVD obtained with nanoscale fillers, suggesting that transient effects of the mixing process are independent of the size of the filler. Finally, structure,property relationship of combinatorially developed polymer nanocomposites was established by characterizing their dynamic mechanical behavior (storage modulus, G,, and loss modulus, G,). The dynamic mechanical behavior of the combinatorially developed composites correlated well with the batch-processed ones, indicating that the transient mixing conditions in extrusion do not affect the material properties. 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

Acyclovir delivery matrices based on poly(ethylene glycol)/chitosan semi-interpenetrating networks

O. Diez-Sales
Abstract Chitosan matrix systems have been studied as potential vehicles for the prolonged release of acyclovir (ACV). The influence of chitosan concentration (from 0.83% to 1.67%) on viscoelastic properties of formulations with and without glyoxal was analyzed. For chitosan-poly(ethylene glycol) 400 formulations loss modulus (G,) are greater than storage modulus (G,). This corresponds to the characteristic behavior of nonstructured systems. When glyoxal was added to the chitosan-poly(ethylene glycol) 400 formulations, gelled matrix was obtained (i.e., G, is higher than G,), except for the lowest chitosan concentration. ACV release rates for the both types of systems, with and without glyoxal, were also determined. The ACV diffusion coefficient values from matrices are less than for the respective formulation without glyoxal and it was found to depend on the crosslink density within the matrices. Viscoelastic parameters, dynamic moduli (G,, G,), and complex viscosity (,*), were correlated with the ACV diffusion coefficients (D). The complex viscosity (,*) could be used as a parameter of predictive value for the release rate of drugs. 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:1653,1657, 2007 [source]

Application of ultrasonic shear rheometer to characterize rheological properties of high protein concentration solutions at microliter volume

Atul Saluja
Abstract The purpose of this work was to conduct preliminary rheological analysis on high protein concentration solutions by using the technique of ultrasonic shear rheometry at megahertz frequencies. The work was aimed at establishing the viability of the technique for analyzing protein solution rheology as well as obtaining an initial understanding of the effect of solution conditions on solution rheology of a model protein. Bovine serum albumin (BSA) was used for this study, and rheological analysis was conducted at 20 ,L sample volume between pH 2.0 and 9.0 at different ionic strengths at 25C using 5 and 10 MHz quartz crystals. Significant differences in storage modulus among solutions at pH 5.0, 7.0, and 9.0 could only be detected at 10 MHz, and the errors associated with measurements were smaller as compared to those at 5 MHz for all the solutions studied. Solutions at pH 2.0 and 3.0 showed a time-dependent change in solution rheology. For solutions at pH 5.0, 7.0, and 9.0, which did not show time dependence in solution rheology, loss modulus data at lower concentrations correlated well with the dilute solution data in the literature. At higher concentrations, pH 5.0 solutions exhibited a higher loss modulus than pH 7.0 and pH 9.0 solutions. Storage modulus decreased with increasing ionic strength, unlike loss modulus, which did not show any change, except at pI of protein when no effect was observed. The results show the potential of high frequency rheometry for analyzing subtle differences in rheology of pharmaceutically relevant protein solutions at microliter volume. 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1161,1168, 2005 [source]


ABSTRACT Rheological and thermal properties of xanthan produced by Xanthomonas campestris from date by-products (DBP-xanthan) and commercial xanthan were determined. DBP-xanthan gave solutions with lower apparent viscosity than commercial xanthan. However, DBP-xanthan solutions were more stable to temperature changes and ionic strength than commercial xanthan. Gradual increase of storage modulus (G,) as function of frequency was observed for the two polysaccharides. On the other hand, loss modulus (G,) remained constant for DBP-xanthan and an increase was observed for commercial xanthan. Granulometric profile indicates that DPB-xanthan particle size was lower than commercial xanthan. Differential scanning calorimetry showed that the melting temperatures (Tm) and enthalpy (,Hm) of DBP-xanthan were higher than those of commercial xanthan. These properties of DBP-xanthan are quite rare among xanthan described in the literature and give this new gum great potential for use in the field of bioindustries as thickening and stabilizing agents. PRACTICAL APPLICATIONS Xanthan gum from date by-products (DBP-xanthan) was recently produced in our laboratory. No work has been undertaken to study the rheological properties of this polysaccharide to date. Rheological and some physicals properties were compared to those of commercial xanthan. This could promote industrial use of DBPs as low-cost natural source for xanthan gum production. [source]


ABSTRACT The effect of inulin addition on rheology and texture of nonfat yogurt (NFY) was studied by the large (texture analyzer) and small (dynamic oscillatory rheometry) deformation tests. Skim milks (12% solids) were supplemented with three commercial chicory inulins with different chain lengths at 4% level and inoculated with mixed cultures of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. Textural and rheological tests were conducted after an overnight storage at 4C and during a shelf life of 28 days. A good correlation was observed between the two tests. During storage, all inulin-containing yogurts in comparison with the control NFY were characterized by lower values of firmness, apparent viscosity, yield stress, complex viscosity, storage modulus and loss modulus. NFYs supplemented with long-chain inulin demonstrated a rheological behavior closer to that of control full-fat yogurt. PRACTICAL APPLICATIONS The use of inulin and oligofructose in the food industry has grown recently because of their interesting nutritional and technological properties. In the work presented here, three commercial inulin products with different chemical composition and functions were added to yogurt milk, and changes in rheological properties of yogurt were investigated in comparison with nonsupplemented control yogurts. According to the manufacturer's specifications, Raftiline HP and Raftiline GR are suitable for fat replacement because of the presence of long-chain inulins, while Raftilose P95, being rich in mono- and disaccharides, is highly recommended for sugar replacement. The knowledge obtained from this study may be applied for the development of nonfat yogurts to satisfy the nutritional expectations of ever-increasing health conscious consumers and at the same time to match the sensory and textural characteristics of full-fat yogurt. [source]