Crossover Modulus Research Articles

Ageing effect on chemo-mechanics of bitumen

Ageing has a significant impact on the chemical and mechanical properties of bituminous materials. In this study, Fourier Transform Infrared (FTIR) spectrometer and Dynamic Shear Rheometer (DSR) tests were utilised to investigate the effect of ageing on the chemical and rheological properties of bitumen. Bitumen films with thickness of 2 mm were exposed to laboratory ageing at various conditions. Specifically, different combinations of ageing time, temperature and pressure were applied on the bitumen samples. The FTIR results were used to quantify the changes in the chemical functional groups and to calculate the combined ageing index (summation of carbonyl and sulfoxide indices) of bitumen. In addition, the DSR test results were analysed to determine the evolution of the black diagrams, crossover frequency and crossover modulus with ageing. A linear relationship was found between the combined ageing index and the distance in the crossover map, providing thus a chemo-mechanics framework to describe bitumen ageing. The results were validated by using data of field aged samples.

Rheological, fatigue and relaxation properties of aged bitumen

ABSTRACT Bitumen ageing has a significant impact on the mechanical performance of asphalt concrete. This study utilises dynamic mechanical tests (frequency sweep, fatigue, and relaxation) to investigate the effect of ageing on the viscoelastic characteristics of bitumen. As ageing progressed, a shift of the Black diagrams curves towards lower phase angles was observed; at the same time the shape of the curves changed to a straight line and the curvature reduced. Interestingly, based on the standard fatigue analysis criteria, ageing appears to have a positive effect on bitumen fatigue life. Consequently, it occurs that studying only the stiffness and fatigue behaviour of bitumen cannot directly characterise ageing-induced degradation. The stress relaxation test was found to be more suitable to characterise ageing of bitumen. Aged bitumen had higher residual stresses and longer relaxation times. Hence, aged bitumen was found to be more susceptible to stress accumulation and thus cracking. A linear relationship was established between the crossover modulus and the stress relaxation ageing indices for the studied bitumen. This relationship suggests that crossover modulus has the potential to be used as a parameter to characterise the bitumen relaxation properties by means of routine tests such as the DSR frequency sweep tests.

On the linking of the rheological properties of asphalt binders exposed to oven aging and PAV aging

ABSTRACT This study proposed a rapid method to predict rheological characteristics of asphalt binders due to oxidative aging based on pressure aging vessel (PAV) as the accelerating aging tool. Six types of asphalt binders were aged at various temperatures for different durations with two aging methods, which were oven aging under standard atmosphere, and PAV aging under a pressure of 2.1MPa. The crossover modulus was determined to characterize the rheological property changes with respect to aging. The oxidation aging kinetics model in terms of crossover modulus under oven aging method was developed, the model parameters showed universal correlations of each other. The aging kinetics model parameters using PAV aging method also obtained. Relationship between the aging kinetics model parameter in oven and PAV aging was established. The activation energy as one of the aging kinetics model parameters in oven aging calculated from PAV data using the relationship, along with the universal correlations of aging kinetics model parameter in oven aging, the crossover modulus predicted rapidly and accurately. Such a rapid method is capable of predicting the aging behavior and rheological properties of asphalt binder subjected to oxidation, and is significantly save a great deal of time and effort in the laboratory.

Predict the rheological properties of aged asphalt binders using a universal kinetic model

In this study, universal models were proposed to predict the aging behaviors of five different asphalt binders, where the rheological properties were emphasized on. The carbonyl content and crossover modulus of binders during oxidative aging process were predicted using the proposed universal kinetic models. The carbonyl content test using the Fourier Transform infrared spectroscopy (FTIR) technique and the frequency sweep test using a Dynamic Shear Rheometer (DSR) were performed to obtain the optimum model parameters. From the testing results, the crossover modulus of binders under oxidative aging effect showed similar growth trend to the carbonyl content that follows the two-reaction kinetics of aging. An approximately linear relation was established between the log crossover frequency and the inverse of log crossover modulus. A sufficient good agreement was achieved between the measured and predicted results of carbonyl content and crossover modulus of asphalt binders at given aging temperature and duration. However, it lost a little prediction accuracy when using the universal model parameters, compared to the specific model parameters. Moreover, based on the calculated crossover modulus and crossover frequency, the complex shear modulus and phase angle were successfully predicted based on the Christensen-Anderson model. The proposed universal model provides an effective approach of predicting the rheological properties of aged asphalt binders.

Evaluation of Chemical and Rheological Aging Indices to Track Oxidative Aging of Asphalt Mixtures

Oxidative age hardening in asphalt binder leads to embrittlement. Embrittled asphalt is prone to fatigue and thermal cracking. Therefore, the ability to predict asphalt binder oxidative age hardening within a pavement throughout its service life could inform improved pavement material selection, design, and maintenance practices. Studying the evolution of oxidative aging requires the use of key properties to track oxidation levels, termed aging index properties (AIPs) here. The objective of this study is to identify suitable rheological and chemical AIPs to track oxidation levels in asphalt materials. A wide range of laboratory and field aged materials were evaluated in this study. A range of chemical AIPs determined by Fourier transform infrared spectroscopy (FTIR) absorbance peaks and areas were evaluated based on their correlation with laboratory aging duration. Rheological AIPs were evaluated based on the strength of their relationship to the chemical changes induced by oxidation. The rheological AIPs evaluated included the dynamic shear modulus, zero shear viscosity, Glover-Rowe parameter, and crossover modulus. The chemical AIP evaluation that most strongly correlated with laboratory aging duration is the carbonyl plus the sulfoxide absorbance peaks. The results indicate that both the dynamic shear modulus and Glover-Rowe parameter constitute rheological AIPs that relate directly to the chemical changes induced by oxidation.

In vitro and ex vivo correlation of drug release from ophthalmic ointments

In vitro drug release testing and ex vivo transcorneal drug permeation can provide valuable information on the performance of the Q1/Q2 equivalent ointments prior to any animal studies. Good correlation between in vitro and ex vivo drug release may be indicative of good in vitro and in vivo correlation. Accordingly, it is important to investigate in vitro as well as ex vivo drug release from Q1/Q2 equivalent ophthalmic ointments and evaluate whether a correlation between these release profiles can be established. Four Q1/Q2 equivalent loteprednol etabonate ointments were prepared using different processing methods and excipient sources. The rheological parameters (crossover modulus and K value) of the four formulations were determined. The in vitro drug release testing of the four ointment formulations were performed using three different apparati (Franz diffusion cells, USP apparatus 2 with enhancer cells and USP apparatus 4 with semisolid adapters). Three models (zero order, logarithmic and the Higuchi model) were used to study the release kinetics of the ointment formulations. The transcorneal (rabbit corneas) permeation studies were performed using spherical joint Franz diffusion cells. The USP apparatus 4 method demonstrated better discriminatory ability compared to the USP apparatus 2 and the Franz diffusion cell methods. The in vitro release profiles of the four Q1/Q2 equivalent ointments with manufacturing differences showed a better fit using the Higuchi model (R2 > 0.98) for all three release testing methods, compared to the other two models. Ex vivo drug release through the rabbit corneas displayed zero order release kinetics. A logarithmic correlation between rheological parameters (crossover and K value) and transcorneal flux were established. In addition, a plot of the in vitro release rate against the ex vivo release flux of the four ointment formulations, yielded a straight line (R2 > 0.98) for all three release methods. Accordingly, the rheological parameters may be useful in predicting in vitro as well as ex vivo release properties.

On the Correlation of Rheology and Morphology of Bimodal Polypropylene Reactor Blends Synthesized by Homogeneous Binary Metallocene/Metallocene Catalysts

ABSTRACTIn this study, morphological and rheological characteristics of bimodal polypropylene reactor blends synthesized by binary catalysts based on I: rac-Me2Si(2-Me-4-PhInd)2ZrCl2 and II: (2-PhInd)2ZrCl2 at different molar ratios were investigated. Gel permeation chromatography, scanning electron microscopy, and rheometry analysis were performed to evaluate the effect of molar ratio of catalyst II, responsible for the formation of elastomeric stereoblock polypropylene with low molecular weight, to catalyst I, responsible for production of high molecular weight isotactic (i) polypropylene, on the molecular weight, molecular weight distribution, morphological characteristics and rheological behavior of the synthesized products. The gel permeation chromatography results indicated that once a hybrid of the two catalysts is used, a broad and bimodal molecular weight distribution would be obtained, and the molar ratio of the catalysts governs the values of molecular weight and molecular weight distribution. 13C NMR results suggest that the different polypropylene tacticity resulting from the two catalysts (stereoblock vs. isotactic) is hardly influenced using a binary system. The effect of molecular weight enhancement and molecular weight distribution broadening was confirmed through the linear rheological data (G′ at lower frequencies, crossover modulus and crossover frequency) due to the impeded molecular motions of chains with high molecular weights which play an important role in the elasticity of chains. The zero shear rate viscosity and relaxation time, determined by fitting the Carreau–Yasuda model, are in great conformity with the experimental data at low-frequency region. Likewise, the miscibility and increased level of heterogeneity of microstructure, which is a result of changing the molar ratios of catalysts II/I, are confirmed through the Cole–Cole and Han plots and were further corroborated through the obtained scanning electron microscopy results.

Self-assembly and rheological behaviors of intermacromolecular complexes consisting of oppositely charged fluorinated guar gums

We synthesized fluorinated cationic/anionic guar gums (FCGG and FAGG) and characterized these species using Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The degree of fluorine substitution of FCGG (0.26%) and FAGG (0.21%) was calculated by elemental analysis. In addition, we explored the self-assembly and rheological behaviors of FCGG-FAGG complexes by viscometry, scanning electron microscopy, light scattering, fluorescence spectroscopy, and rheometry. The maximum viscosity and molecular weights were observed with a FAGG:FCGG mass ratio of 7.0:3.0, denoted by COMP. Moreover, FAGG-FCGG interactions in COMP led to the lowest shape factor and critical associating concentration. Additionally, the relaxation time and crossover modulus of COMP (6.65 s and 0.90 Pa, respectively) were remarkably higher than those of FCGG and FAGG alone. Finally, viscoelastic hysteresis loops emerged for FAGG and COMP. The results suggested that the self-assembly behaviors of FAGG-FCGG were influenced by both ionic and fluorinated groups.

Evaluation of the sensitivity of asphalt concrete modulus to binder oxidation with a multiple length scale study

It is well known that the properties of asphalt concrete mixture are affected by the oxidation of asphalt cement. However, the precise relationship between these two length scales remains largely uncharacterized. In the present study, a multiple length scale evaluation approach is applied to study and quantify the sensitivity of the mechanical properties of asphalt concrete mixture to asphalt cement oxidation. The study involves temperature and frequency sweep experiments on unaged and aged asphalt cement (to establish baseline properties), asphalt mastic (to consider physico-chemical aspects), and Fine Aggregate Matrix (FAM – to consider air voids and aggregate interaction effects). The multiscale approach separates effects of aggregate-binder physico-chemical interactions from those caused by air voids and physical aggregate interactions. Also, all asphalt cements were pre-aged to specific aging levels before preparing respective aged mastics or FAM samples. The methodology adopted for assessment of sensitivity was based on the theory of crossover modulus and second order rate kinetics of asphalt binder oxidation. The results from the analysis indicate that the mechanical properties of mastics are more sensitive to binder oxidation than FAM. Also, mechanical properties of mastics and FAM materials prepared with softer binders are more sensitive to oxidation than those with higher modulus asphalt cements. Finally, it is found that if a laboratory aging procedure is found to match the rheological properties of in-service level of asphalt oxidation at a given level of accuracy, then the expected accuracy in matching the resulting modulus of an asphalt mixture tested after being subjected to that laboratory process will be 1.5–3.6 times higher.

Effect of crumb rubber degradation on components distribution and rheological properties of Terminal Blend rubberized asphalt binder

The degradation of crumb rubber modifier (CRM) was confirmed to affect the rheological properties in the production Terminal Blend (TB) rubberized asphalt binder. However, the quantitative analysis on the components distribution of TB rubberized asphalt binder and correlations to rheological properties were not investigated yet. The present study was to investigate the effect of CRM degradation on components distribution and rheological properties of TB rubberized asphalt binders produced under various curing temperatures and times. The solubility test and the Gel Permeation Chromatography (GPC) test were performed to obtain the distribution of insoluble components, dissolved polymers, apparent asphaltenes and maltenes. Brookfield viscometer and Dynamic Shear Rheometer (DSR) were used to investigate the viscosity properties, rutting resistance and rheological behaviour at wide frequencies. The results indicated that interaction time played a similar role as interaction temperature did in promoting the dissolution of CRM whereas the breaking of backbone of the main chain of rubber was more dependent on interaction temperature. With the gradual degradation of CRM, the workability and storage stability were improved with the sacrifice of rutting resistance. In addition, the enhance effects of CRM on |G∗| values at both lower and higher frequencies and phase angle values at lower frequencies gradually weakened. The evolution of log |G∗| lower asymptote and crossover modulus indicated TB rubberized asphalt binders became softer with the degradation of CRM. The well link between apparent asphaltenes and various rheological parameters indicated that it was the transform of CRM from insoluble components and dissolved polymers to medium size molecules that affected the rheological properties of TB rubberized asphalt binder.

In vitro release testing method development for ophthalmic ointments

It is essential as well as challenging to develop a reliable in vitro release testing method for determining whether differences in release profiles exist between qualitatively and quantitatively equivalent ophthalmic ointment formulations. There is a lack of regulatory guidance on in vitro release testing methods for ophthalmic formulations. Three different in vitro release testing methods 1) USP apparatus 4 with semisolid adapters; 2) USP apparatus 2 with enhancer cells; and 3) Franz diffusion cells were investigated. Qualitatively and quantitatively equivalent ointments were prepared via hot melting and simple mixing methods using four different sources of excipients (i.e. white petrolatum). The ointment formulations were characterized for content uniformity, particle size, and rheological parameters. All the formulations showed adequate content uniformity and similar particle size. The ointments prepared via the hot melting processes showed higher rheological parameters, as did the ointments prepared using ‘white’ petrolatum that exhibited a yellowish color. The three in vitro release testing methods were compared and evaluated for reproducibility, discriminatory capability, and correlation with the rheological parameters. Compared with the compendial methods, the non-compendial method (Franz diffusion cells) showed poorer reproducibility. All three methods possessed the ability to discriminate between the ophthalmic ointments with manufacturing differences. However, the USP apparatus 4 method displayed the largest margin of discrimination between the release profiles of the different ophthalmic ointments. In addition, the in vitro release rate obtained using the USP apparatus 4 method showed the strongest logarithmic linear correlation with the rheological parameters (Power law consistency index (K value) and crossover modulus) compared to the other two methods.

Physicochemical attributes and dissolution testing of ophthalmic ointments

The investigation of semisolid ophthalmic ointments is challenging due to their complex physicochemical properties and the unique anatomy of the human eye. Using Lotemax® as a model ophthalmic ointment, three different manufacturing processes and two excipient sources (Fisher® (OWP) and Fougera® (NWP)) were used to prepare loteprednol etabonate ointments that were qualitatively and quantitatively the same across the manufactured formulations. Physicochemical properties including drug content and uniformity, particle size and distribution, as well as rheological parameters (onset point, crossover modulus, storage modulus and Power law consistency index) were investigated. In addition, USP apparatus 2 with enhancer cells was utilized to study the in vitro drug release characteristics of the ophthalmic ointments. Both manufacturing processes and excipient sources had a significant influence on the physicochemical attributes and the in vitro drug release profiles of the prepared ointments. Ointments prepared via the hot melt processes exhibited higher rheological parameters and lower drug release rates compared to ointments prepared without hot melting. Ointments prepared with OWP demonstrated higher rheological parameters and lower in vitro drug release rates compared to ointments prepared with NWP. A strong correlation between the rheological parameters and in vitro drug release rate was shown using logarithmic linear regression. This correlation may be useful in predicting in vitro drug release from measured physicochemical properties, and identifying the critical quality attributes during the development of ointment formulations.

Comparative Effects of MMT Clay Modified with Two Different Cationic Surfactants on the Thermal and Rheological Properties of Polypropylene Nanocomposites

Polypropylene montmorillonite (MMT) nanocomposites were prepared by melt blending using two different organoclays modified with imidazolium and alkylammonium surfactants. The imidazolium and ammonium modified organoclays were characterized by the FTIR and SEM analysis. The effect of organic clay (MMT) on the physical properties of polypropylene was evaluated, thermal and rheological properties with different filler weight percentage. Differential scanning calorimetric results showed that imidazolium modified clay (IMMT) exhibits low melting temperature compared to the ammonium modified clay (AMMT). The crystallinity analysis showed that crystallization improved in all nanocomposites irrespective of surface modification; the thermogravimetric analysis showed that the imidazolium modified polymer composites are more thermally stable than conventional ammonium modified composites. The Transmission Electron Microscopy (TEM) analyses indicated that the PP-IMMT composites displayed exfoliated morphologies compared with the intercalated structure in PP-AMMT, and the rheological analysis at 180°C showed an enhancement in the viscoelastic properties as the clay concentration increases. The melt viscosity, crossover modulus, and relaxation times were comparable for both the surface modified composites with two different cations. The imidazolium based surfactant was found to be an effective organic modification for MMT to prepare thermally stable PP/MMT nanocomposites.

The influence of molecular weight on high shear rate macroscopic rheological properties of polybutene-1 melts through rubber-processing analyzer

The rheological properties of polybutene-1 with different molecular weight (M w) and polydispersity index (PDI) were studied by means of rubber-processing analyzer (RPA). The studies included strain sweeps, frequency sweeps, temperature sweeps, and stress relaxation tests after a sudden shear displacement. It is observed that the linear viscoelastic regions are basically identical for all the samples with different molecular structure and become smaller slightly with increasing frequency. The melts with larger M w and/or PDI present higher viscoelasticity moduli, melts viscosity, relaxation modulus, and better temperature stability, but lower loss factor and critical shear rate. Furthermore, it is found that crossover frequency decreases with increasing M w and crossover modulus increases with decreasing PDI. In addition, stress relaxation followed by substantial stress growth is observed for the PB-1 melt with larger M w in the stress relaxation measurement.

Synthesis of highly isotactic poly 1-hexene using Fe-doped Mg(OEt)2/TiCl4/ED Ziegler–Natta catalytic system

In this article, polymerization of 1-hexene with FeCl3-doped Mg(OET)2/TiCl4/electron donor (ED) catalytic system is presented. For this purpose, first a number of TiCl4 catalysts supported on Mg(OEt)2 and Fe-doped Mg(OEt)2 supports were prepared with ethylbenzoate or dibutylphthalate as the internal EDs. After successive catalysts synthesis, they were employed in 1-hexene polymerization using cyclohexyl methyl dimethoxysilane as external ED as well as without it. The catalysts activity and molecular weight distribution (MWD) of poly 1-hexenes (PHs) were influenced strongly by both FeCl3 doping and donor presence so that a remarkable increase in the catalyst activity was seen in doped catalysts. Deconvolution of MWD curves revealed that increase in the type of active centers by introducing FeCl3 into the support should be responsible for the broadening of MWD of PHs. 13CNMR analysis indicated that while isotacticity does not change considerably by Fe doping, EDs increase its amount as high as 8–21%. Second, the stereoselective behavior of active Ti species in doped and undoped catalysts was fully explored by molecular modeling using density functional theory (DFT) method. Finally, with the aid of rheological measurements, the processability of polymers were evaluated and then the gel permeation chromatography (GPC) results were approved through the values obtained from model fitting as well as changes in moduli crossover modulus.

Linear viscoelastic behaviors of polybutene-1 melts with various structure parameters

The effects of weight-average molecular (Mw), molecular weight distribution (MWD), and isotacticity on the linear viscoelastic behavior of polybutene-1 melts are studied. It is observed that the linear viscoelastic region becomes slightly narrower with increasing frequency. In frequency sweeps, the transition of the polymer melts flow from Newtonian flow to power-law flow can be observed. The melts with higher Mw and/or broader MWD, as well as higher isotacticity exhibit higher complex viscosity, zero shear viscosity, viscoelasticity moduli, relaxation modulus, broader transition zone, while lower critical shear rate, non-Newtonian index, and the frequency at which elasticity begins to play an important role. The relationship of zero shear viscosity on Mw has been established, which agrees with the classical power law. Furthermore, it is found that the cross-over frequency decreases with increasing Mw and the cross-over modulus increases with narrowing MWD.

Prediction of melt rheological properties from GPC molecular weights

The SCLAIR® solution polymerization platform produces a wide variety of ethylene-α-olefin copolymers and polyethylene homopolymers. Commercial products exhibit density and melt index values ranging from about 0.920 to 0.962 g/cm3 and 0.3–75 g/10 min respectively. Polymer molecular weight distributions can be tailored to meet a broad selection of end-use requirements. In this study, we have used a chemometric analysis approach using The Unscrambler® software to demonstrate statistical correlations between rheological properties and fundamental structural parameters for thirty-three commercial SCLAIR polyethylenes. We demonstrate that molten rheological properties such as melt index, stress exponent, zero-shear viscosity, characteristic relaxation time, cross-over modulus and frequency show good non-linear correlations with molecular weight characteristics of SCLAIR products as determined by gel permeation chromatography (GPC). We also show that, with the use of Partial Least Squares (PLS) regression techniques, most melt rheological properties can be accurately predicted on the basis of GPC data.

Two-step build-up of a thermoreversible polymer network: From early local to late collective dynamics.

We probe the mechanisms at work in the build-up of thermoreversible gel networks, with the help of hybrid gelatin gels containing a controlled density of irreversible, covalent crosslinks (CLs), which we quench below the physical gelation temperature. The detailed analysis of the dependence on covalent crosslink density of both the shear modulus and optical activity evolutions with time after quench enables us to identify two stages of the physical gelation process, separated by a temperature-dependent crossover modulus: (i) an early nucleation regime during which rearrangements of the triple-helix CLs play a negligible role, and (ii) a late, logarithmic aging one, which is preserved, though slowed down, in the presence of irreversible CLs. We show that aging is fully controlled by rearrangements and discuss the implication of our results in terms of the switch from an early, local dynamics to a late, cooperative long-range one.

Prediction of Rheological and Damage Properties of Asphalt Binders that Result from Oxidative Aging

Because the aging of asphalt binders affects nearly all critical aspects of asphalt mixtures, aging is a fundamentally important factor that affects pavement performance. This study developed a methodology to predict the rheological and damage properties of asphalt binders after they were subjected to aging. Three asphalt binders (one neat and two modified) were aged at four temperatures in a standard atmosphere for different periods. An approximately linear relationship between the carbonyl area and the log of the crossover modulus was found, but the relationship was asphalt specific. It was also found that the inverse of the log crossover modulus could be characterized with the Arrhenius kinetics model. The relationship between the log crossover frequency and log crossover modulus was linear at each aging temperature. The crossover modulus and crossover frequency were used in the Christensen–Anderson model to predict the complex modulus and phase angle master curves of the binders. The predicted complex shear modulus and phase angle of the asphalt binders after aging, on the basis of the carbonyl area, matched well with the measured complex shear modulus and phase angle values, except for the phase angle of the modified binders at a high temperature or low frequency. The complex shear modulus was converted to the shear relaxation modulus and was found to correlate well with the shear strength and critical strain energy density, which was reported to be a cracking indicator in a previous study.

Rheological Indexes

An investigation was conducted into several commonly used rheological indexes and their influence on oxidation studies. The evaluation considered the low shear viscosity; the dynamic shear rheometer function, or Glover–Rowe parameter; the dynamic shear crossover modulus (G*c) value; and parameters from the Williams–Landel–Ferry and Kaelble shift functions as the rheological indexes in a comparative oxidation characterization between two example asphalt binders. In general, each respective methodology was found to correlate with increasing levels of oxidation but resulted in differing outcomes with respect to oxidation, which depended on the evaluation methodology used. Although each method presented its own merit and respective limitations, a single preferential method was not readily identified. However, the critical need for reliable and sound rheological measures and data processing procedures was clearly demonstrated. This evaluation supported the need for a clear and logical evaluation of the rheological parameters used to characterize asphalt binders. It has been documented that certain rheological indexes have strong correlations to specific distress types or mechanical behaviors and thus may prove beneficial to a particular analysis. However, evaluations must also acknowledge the limitations of selected techniques. When possible, complete characterization through means of the development of full master curves should be beneficial. With sound rheological data and comprehensive measures, several indexes can be determined and provide a more comprehensive view of the investigated material responses.