Higher Complex Modulus Research Articles

Effect of high pressure treatment on the structural, mechanical and rheological properties of glucomannan gels

The influence of high hydrostatic pressure (HHP) of 100 (C100), 200 (C200), 400 (C400) and 600 MPa (C600) on the structural, physicochemical, and thermo-rheological properties of aqueous glucomannan dispersions (AGD) was studied. Each AGD was prepared with a 5% concentration of deacetylated glucomannan (GM) at pH = 11 for use in the preparation of restructured fish products. The control (0 MPa) AGD (C0) exhibited a partially crystalline GM network with a glass transition temperature (Tg) of ∼75 °C. C0 gels at 25 °C were rigid, with high breaking force (BF), fracture constant (Kf) and complex modulus (G*) and low tanδ values due to the large number of physical junctions produced by complete deacetylation of the GM chains. This structural response was reflected in high water binding capacity (WBC) and colour (L*) and low cooking loss (CL). Specifically, 200 MPa reduced close packing ability in the crystalline regions, evidenced in the lower Tg∼65 °C and resulting in lower gel strength (S), Kf, G* and a higher viscous component (high tanδ), thus reducing the L* value. Conversely, 600 MPa increased the degree of cross-linking in C600, reinforcing the number and extent of crystalline regions, resulting in the broadening of the O–H stretching band in the FT-IR spectrum and producing a thermoset physical network with no glass transition region. Thus, C600 gel was firmer (higher G*) with greater S, and less flexible (lower strain amplitude-γmax). Consequently, depending on the textural properties desired in the final restructured fish product, the most appropriate pressure would be 200 MPa for softer final gels and 600 MPa for firmer and less deformable gels.

Rheological properties of packaging‐waste‐polyethylene‐modified asphalt

Waste‐polyethylene (WPE) in packaging, instead of virgin polymer, was utilized as a modifier of base asphalt, and rheological properties of the modified asphalt were studied. Results show that the modified asphalt possesses better anti‐distortion capacity than the base asphalt, as indicated by the fact that the modified asphalt has higher viscosity and smaller endothermic peak dispersion in the transformation process of asphalt aggregation. Compared with base asphalt, the modified asphalt has higher complex modulus (G*), storage modulus (G′), and dissipation modulus (G″). In addition, the modified asphalt has smaller phase angle (δ), less tangent (tanδ), and lower rut factor (G*/sinδ), reflecting the high‐temperature rut resistance of the asphalt. The improvement of the rheological properties is related to the main features of the modified asphalt, including the swelling, whereas packaging‐waste‐PE absorbs low‐molecular‐weight fractions of asphalt, the displacement restriction of asphalt particles, and the molecular structure and performance of PE molecules. J. VINYL ADDIT. TECHNOL., 21:215–219, 2015. © 2014 Society of Plastics Engineers

Effects of hydrocolloids as texture improver in coriander bread.

An attempt was made to study the effects of hydrocolloids on loaf weight, volume, crumb grain characteristics, crumb moisture, firmness and dough rheological properties on 3.0% coriander leaf supplemented breads. Carrageenan (CA), carboxymethylcellulose (CMC), guar gum (GG) and xanthan gum (XG) were added in the proportions of 0.25, 0.5, 0.75 and 1.0% w/w of 100g wheat flour. Addition of hydrocolloid increased the loaf volume and decreased the average cell area. An inverse relationship was observed between specific volume and average cell area. XG showed uniform change in crumb moisture on storage at all levels of substitution. However highest loss of moisture occurred in bread samples supplemented with GG. Crumb firming kinetics using Avrami's model showed slower firming rates for GG and CMC. High complex modulus (G*) values were observed in breads with 0.75 and 1.0% XG.

Mechanical properties of filler-asphalt mastics

There has been an increasing awareness of the addition of ordinary Portland cement (OPC) rather than limestone filler into asphalt pavements in Taiwan. Filler interpaticle interaction and physicochemical interaction between cement filler particle and asphalt improved engineering properties of asphalt mixtures. Current Superpave parameters of G*/sinδ and G*sinδ were used to link the rheological properties of asphalt binders to the pavement performance of rutting and fatigue. However, the characteristics of asphalt binders were determined in the linear viscoelastic domain by performing frequency sweeps. The asphalt binder film might perform in the non-linear range due to the considerable difference between the stiffness modulus of aggregates and the modulus of binders. In addition, the filler-asphalt interaction might not be reflected by means of the Superpave parameters. Mechanical properties of stiffness, deformation and fatigue for filler-asphalt mastics may be more appropriate in terms of establishing a correlation with asphalt pavement performance. Oscillatory and creep tests using a dynamic shear rheometer (DSR) were performed to quantify the mechanical properties of cement and limestone filler-asphalt mastics at the same levels of filler contents by weight. The test results showed that the higher complex modulus and stiffening effect of the cement filler-asphalt mastics than those of the limestone filler-asphalt mastics within a linear viscoelastic domain. In terms of creep behavior, the addition of cement filler to base bitumen increases the viscosity at a steady state. The longer fatigue lives for the cement filler-asphalt mastics indicated the addition of active filler may provide a better pavement durability.

Effect of activated crumb rubber on the properties of crumb rubber‐modified bitumen

AbstractBitumen modification was made with the activated crumb rubber concentrate and its efficacy was examined in terms of its consistency and rheological properties. It was found that softening point of the activated crumb rubber‐modified bitumen increased while its penetration and elastic recovery decreased compared with the nonactivated crumb rubber system. Based on contact angle results, the activated crumb rubber–bitumen system was found to be more wettable and exhibited better adhesion to the substrate than those of other systems. The shifting of glass transition temperature towards higher temperature and the occurrence of inter‐mix phases in the activated crumb rubber–bitumen system supported its superior temperature resistance. The difference in viscosity obtained between the activated and nonactivated crumb rubber systems is attributed to the high swelling of activated crumb rubber and its soluble fractions in the bitumen as viewed in scanning electron images. High complex modulus and low phase angle of the activated crumb rubber system over the entire range of temperatures indicated its reduced temperature susceptibility and more elasticity. The activated crumb rubber–bitumen system meets the requirements of commercial standard specification. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Influence of alkali and temperature on glucomannan gels at high concentration

The effect of type and concentration of alkali on 5 g/100 mL of glucomannan gels was examined in depth by mechanical and thermo-rheological analysis. Four KGM gels were made from aqueous glucomannan solutions deacetylated with 0.6 mol/L and 1 mol/L of KOH (A0 and A1) and NaOH (B0 and B1), respectively. At 25 °C all physical networks were too tight and dense due to the large number of extended junction zones, as indicated by the high breaking force (BF), complex modulus (G∗) and low strain amplitude (γmax). The influence of alkali concentration was noticeable only in KOH gels, of which A0 was significantly more elastic and time stable than A1 over both short and longer-time scales. 0.6 mol/L KOH was the most suitable alkali, producing the most stable and homogeneous gel, with the highest level of connectivity, the lowest relaxation exponent (n) and the highest gel strength (S).Increasing temperature resulted in loss of elasticity in A0, where γmax, G∗ and S decreased, and the loss factor (tan δ), creep and recovery compliances (J) and n increased. Thus, the networks become less flexible and more unstable at high temperatures, especially between 25 and 50 °C.

Changes in the rheological behavior of the vagina in women with pelvic organ prolapse.

Pelvic organ prolapse is a common condition impacting the quality of life of millions of women worldwide. Although vaginal estrogen is widely used in women with prolapse, little is known regarding estrogen's benefits on the biomechanical properties of vaginal tissue. Here, we aimed to examine the effect of prolapse on the biomechanical properties of the vagina and determine alterations in vaginal mechanics in the presence and absence of hormone therapy (HT). We characterized the viscoelastic properties of vaginal biopsies from age-matched premenopausal women without (n = 12) and with prolapse (n = 8) and postmenopausal women with prolapse on (n = 18) and off HT (n = 9). Utilizing a single-lap shear testing protocol, full-thickness anterior vaginal biopsies were subjected to ±10% shear strain over a range of frequencies (1-90 Hz). This applied energy is either dissipated (viscous) or stored (elastic) as a function of frequency due to compositional or structural differences in the tissue. Prolapsed tissue was more stiff (higher complex modulus) under shear deformation resulting from increases in both elastic (elastic modulus) and viscous (loss modulus) contributions, with non-prolapsed premenopausal women being the least stiff. Postmenopausal women with prolapse currently on HT were the most stiff of all the groups. These data suggest that prolapsed tissue has an increased elastic contribution likely resulting from changes in biochemical constituents, and hormones increase the viscous contribution of prolapsed tissue. Overall, this study design characterized the viscoelastic properties of vaginal biopsies and may be utilized to conduct longitudinal studies to better understand the mechanisms of prolapse development and progression.

Low temperature rheological and mechanistic characteristics of three different types of asphalt binders

This Study investigates the rheological and mechanistic characteristics of unmodified, polymer modified asphalt binder and epoxy asphalt binder at low temperatures. They dynamic shear rheometer (DSR) test and lap shear strength test were conducted to examine the rheological and mechanistic properties of the three types of asphalt binders. The results indicate that the complex modulus and lap shear strength of modified asphalt binder were higher than unmodified asphalt binder. Epoxy asphalt showed the highest complex modulus at lower temperatures. The phase angle of modified asphalt binder was low, and it increased slightly with the increasing temperature. The results of lap shear testing agree with the DSR test results. The lap shear bonds method is a reliable test method for evaluating asphalt performance at low temperatures quickly.

The effect of polypropylene/polyamide 66 blending modification on melt strength and rheologic behaviors of polypropylene

Common linear polypropylene (PP) was modified by blending with polyamide 66 (PA66) under the act of compatibilizer in a twin-screw extruder in an attempt to improve the melt strength (MS) of PP. The MS of pure PP and modified PPs were measured by MS testing unit at three temperature of 190, 210, and 230 °C, and the MS improvement of PP was verified. The MS of the modified PPs increased with increasing the content of PA66. The steady- and dynamic-shear rheological behaviors of pure PP and modified PPs were investigated using a capillary rheometer and a parallel-plate rotating rheometer. The steady-shear rheological analysis results revealed that modified PPs had higher melt shear viscosity, stronger non-Newtonian behaviors, and higher zero shear-rate viscosity. The dynamic-shear rheological analysis showed modified PPs had higher melt complex modulus and smaller phase angle, which indicated that the melt viscosity and melt elasticity of PP were also enhanced. The modified PPs was characterized by DSC. DSC results revealed that the PA66 phase and PP phase of the modified PPs were in state of crystallization. The enhancement of MS, melt viscosity, and melt elasticity of modified PPs could be due to undisaggregated PA66 crystallization phase within the melt of PP blends.

Relations between crystallisation mechanisms and microstructure of milk fat

Using differential scanning calorimetry, synchrotron time resolve X-ray diffraction and pulsed nuclear magnetic resonance, crystallisation mechanisms of milk fat were elucidated. Under the same crystallisation conditions, the microstructure of the milk fat was analysed with confocal laser scanning microscopy and oscillatory rheology. The milk fat was cooled without agitation to 20 °C at two different cooling rates, i.e., 0.1 and 10 °C min −1. Thereafter, the isothermal crystallisation at 20 °C was monitored. Faster cooling resulted in a two-step crystallisation, and a microstructure that comprised smaller and more uniform crystals than was the case with slower cooling. Consequently, the final texture of the faster cooled milk fat was firmer, i.e., higher complex modulus, than that of the slower cooled milk. X-ray diffraction showed that the two-step crystallisation involved a polymorphic transition from α to β′ phase. Furthermore, it was demonstrated that oscillatory rheology is very useful for detecting polymorphic transition during crystallisation of anhydrous milk fat.

Effect of different montmorillonites on rheological properties of bitumen/clay nanocomposites

Different composites of organomodified montmorillonite (OMMT)/bitumen were prepared by melt blending with hexadecyl dimethyl benzyl ammonium modified montmorillonite (HBM) and double octadecyl dimethyl ammonium modified montmorillonite (DOM). The structures of two kinds of montmorillonite modified bitumen were characterized by X-ray diffraction (XRD). The effects of different montmorillonites on the dynamic rheological properties of the modified bitumens were investigated by dynamic shear rheometer (DSR). The XRD results show that DOM modified bitumen forms an intercalated structure, whereas the HBM modified bitumen forms an exfoliated structure. DSR results indicate that OMMT modified bitumens exhibit higher complex modulus, lower phase angle than pristine bitumen, which means that the resistance to rutting at high temperatures of pristine bitumen is improved due to the introduction of OMMT. Compared with DOM modified bitumen, HBM modified bitumen shows better rutting resistance, which is contributed to the formation of exfoliated structure in HBM modified bitumen.

Characterization of low‐molecular‐weight hyaluronic acid‐based hydrogel and differential stem cell responses in the hydrogel microenvironments

Hyaluronic acid is a natural glycosaminoglycan involved in biological processes. Low-molecular-weight hyaluronic acid (10 and 50 kDa)-based hydrogel was synthesized using derivatized hyaluronic acid. Hyaluronic acid was acrylated by two steps: (1) introduction of an amine group using adipic acid dihydrazide, and (2) acrylation by N-acryloxysuccinimide. Injectable hyaluronic acid-based hydrogel was prepared by using acrylated hyaluronic acid and poly(ethylene glycol) tetra-thiols via Michael-type addition reaction. Mechanical properties of the hydrogel were evaluated by varying the molecular weight of acrylated hyaluronic acid (10 and 50 kDa) and the weight percent of hydrogel. Hydrogel based on 50-kDa hyaluronic acid showed the shortest gelation time and the highest complex modulus. Next, human mesenchymal stem cells were cultured in cell-adhesive RGD peptide-immobilized hydrogels together with bone morphogenic protein-2 (BMP-2). Cells cultured in the RGD/BMP-2-incorporated hydrogels showed proliferation rates higher than that of control or RGD-immobilized hydrogels. Real-time RT-PCR showed that the expression of osteoblast marker genes such as CBFalpha1 and alkaline phosphatase was increased in hyaluronic acid-based hydrogel, and the expression level was dependent on the molecular weight of hyaluronic acid, RGD peptide, and BMP-2. This study indicates that low-molecular-weight hyaluronic acid-based hydrogel can be applied to tissue regeneration as differentiation guidance materials of stem cells.

Effect of Moisture on Hydrothermal Modification of Yam Dioscorea hispida Dennst Starch

AbstractStarch from Thai yam Dioscorea hispida Dennst; locally known as kloy kao niaw (KKN), was hydrothermally modified (HM) at moisture contents (MC) between 13 and 30 g water/100 g starch (wb) at 90°C for 10 h. All treatments caused a decrease in swelling power and amylose leaching, and an increase in gelatinization temperature of the starch indicating a strengthened network within the starch granule. However, when setting 7 g starch/100 g (wb) gelatinized starch dispersion to gel and subjecting the samples to dynamic rheological tests, only HM KKN starch modified at 13 g water/100 g starch (wb) gave starch gel with higher complex modulus (G*) when compared to native KKN starch gel over the test frequency range (0.001 to 30 Hz). The X‐ray diffraction pattern revealed that KKN starch granule's crystalline structure changed from B to C‐type when modified at 13 g water/100 g starch (wb) and stayed unchanged when modified at 18 to 30 g water/100 g starch (wb).

Linear Rheological Behavior of Bituminous Paving Materials

The linearity limits of various unmodified and modified bituminous binders, as well as asphalt mixtures incorporating these binders, have been investigated using a dynamic shear rheometer and a purpose-built, dynamic, direct tension-compression, servohy- draulic testing apparatus. Both continuously graded, as well as gap-graded, asphalt mixtures have been tested together with a fines/filler mortar ~mastic!. Cylindrical specimens of these mixtures were subjected to sinusoidal loading at temperatures between 10 and 40°C, first, under stress sweep conditions and, second, under frequency sweep conditions. The results show that there are binder and bulk strain dependent linearity criteria for both binders and asphalt mixtures at high complex modulus values as well, as a high-temperature binder strain dependent linearity criterion for elastomeric modified binders. The linearity bulk strain criterion for the asphalt mixtures was found to be in the order of 100 microstrain with the binder strain criterion for the binders being at least 100 times greater at just over 10,000 microstrain and the polymer network binder strain criterion at 1,000,000 microstrain. In general, the linear viscoelastic rheological characteristics of the asphalt mixtures were similar with differences in the complex modulus and phase angle only being found at intermediate temperatures and frequencies and are attributed to the rheological characteristics of the binders. However, the extra stiffening effect of the aggregate skeleton did increase the elastic response of the asphalt mixtures relative to that of the binders, particularly at high temperatures and low frequencies.

Use of isocyanate production waste in the preparation of improved waterproofing bitumen

AbstractWaste residue generated during the production of toluene diisocyanate was used as a modifier in making improved waterproofing bitumen. The waste particles were surface‐modified with stearic acid. Various bitumen blends based on untreated particles, surface‐treated particles, and a combination of an SBS elastomer and waste particles were prepared. The optimized blends were subjected to evaluate their response against temperature and frequency sweeps. It was observed that improvement of the softening point and reduction in penetration could be correlated with the blend morphology in terms of the compatibility between the waste particles and the bitumen. The increased glass transition temperature and satisfactory phase miscibility in the modified bitumen observed in MDSC and DMA traces supported these findings. The coefficient of linear thermal expansion of the modified bitumen was found to be 1.21 × 10−4/°C. The rheological studies revealed that time‐dependent properties of the modified bitumen were better in terms of its stiffness and elasticity than that of neat bitumen. The applicability of the Williams–Landel–Ferry (WLF) equation confirms the superior temperature‐dependent response of the modified systems over the control. It was noticed that stearate‐treated waste‐modified bitumen gives the best results in terms of a high complex modulus and a low phase angle. The newly formulated bituminous blend based on stearate‐treated waste meets the requirement of existing standard specifications for waterproofing felt. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1365–1377, 2003

LOW DEFORMATION AND WATER HOLDING MEASUREMENTS OF WHOLE AND COMMINUTED MEAT ORIGINATING FROM TWO MUSCLES OF DIFFERENT FIBRE TYPE COMPOSITION

ABSTRACTThe rheological properties and water uptake in the white muscle m. cutaneus trunci and the red muscle m. masseter of Norwegian red cattle were compared. The two muscle systems were examined intact, ground and chopped, at two different salt levels, and unheated as well as heated to 70C. Three different rheological parameters were recorded: the complex modulus, the phase angle and a parameter measuring nonlinear viscoelastic properties (called deformation index). The white muscle had, in general, the highest complex modulus, the highest phase angle and the lowest deformation index. The variation imposed on the data by the pH variation accompanying different fibre types, made direct comparisons between the two muscles difficult. It is suggested that the complex modulus for unheated systems was most sensitive to fibre type differences. The different rheological parameters recorded revealed different sensitivity to the variables investigated. The complex modulus, measured on unheated systems, were insensitive to the degree of comminution while both the phase angle and the deformation index were sensitive to this mechanical treatment. To record different rheological parameters might therefore be useful when establishing nondestructive viscoelastic measurements for on‐line quality control in factories. However, it is felt that such measurements must be supported by other rapid measurements to fully utilize their potential.