Dynamic Rheological Behavior Research Articles

Modeling of the viscoelastic behavior of collagen gel from dynamic oscillatory shear measurements.

Viscoelastic materials contain a continuous spectrum of relaxation time constants that cannot be measured directly from experiments. To model the viscoelastic behavior, discrete Generalized Maxwell model is usually chosen phenomenologically from direct fitting. In the present study, a theoretical framework was developed to determine the continuous spectrum of relaxation time constants, and then applied to study the dynamic rheological behavior of collagen gel using a parallel plate rheometer. Frequency sweep tests were performed to determine the storage and loss modulus of collagen gel. To obtain the continuous relaxation spectrum, Tikhonov regularization method was employed to solve the Fredholm integral equations. A Finite Element Model (FEM) was created to simulate the rheological measurement with viscous material parameters obtained from both direct fitting and continuous spectrum. Discrete spectrum obtained by direct fitting method is not unique and highly depends on the specified fitting criteria. Continuous spectrum obtained by Tikhonov regularization effectively eliminates the possibility of getting nonunique solutions. The storage and loss modulus calculated from FEM compared well with the experimental results. Continuous relaxation spectrum can be determined based on dynamic rheological shear measurements, and incorporated into FEM to study the behavior of viscoelastic materials.

Role of matching water affinities between oppositely charged headgroups in the rheological properties of aqueous mixed cationic/anionic surfactant systems

Steady and dynamic oscillatory shear rheological behaviors of two aqueous mixed cationic/anionic surfactant systems: the sodium dodecanoate (SL)/hexadecyltrimethylammonium bromide (CTAB)/H2O system and the sodium dodecylsulfonate (AS)/CTAB/H2O system with excess CTAB, were investigated and compared. The role of matching water affinities between oppositely charged headgroups has been explored. Both the headgroups of AS and CTAB are soft, they are matched in water affinities, while the headgroups of SL and CTAB are mismatched in water affinities due to the hard headgroup of SL. At lower temperature, the degree of matching in water affinities between oppositely charged headgroups is a crucial factor influencing the synergism, self-assembly of wormlike micelles and their rheological behaviors: in comparison with the SL/CTAB/H2O system, the AS/CTAB/H2O system shows much stronger synergism in zero-shear viscosity η0, stronger ability of wormlike micelles formation and elongation, much higher scission energy, much longer relaxation time and lower plateau modulus. While the role of matching water affinities is less important at higher temperature.

Chemical foaming extrusion of poly(lactic acid) with chain-extenders: Physical and morphological characterizations

The effects of an epoxide-based chain-extender (CE) on the properties of poly(lactic acid) (PLA) foams obtained by chemical foaming extrusion using 4wt.% of chemical foaming agent (CFA) were studied. PLA/CE blends with different weight ratios of CE were initially processed using a co-rotating twin-screw extruder. PLA/CE foams were then produced using a single-screw extruder. Various PLA/CE foams characterizations, including solution viscosity, thermal properties (DSC, TGA), cellular structure (void fraction, cell size, open cell content), mechanical and dynamic rheological behaviors, were investigated. Results show that the addition of CE enhances the viscosimetric average molecular weight and rheological properties (viscosity and storage modulus) of PLA, but it has no significant effects on the thermal properties of PLA, except the occurring of a cold crystallization. The CE incorporation also led to a decrease in the void fraction of cellular PLA, in the cell size and in the open cell content and to an increase in the cell density. Furthermore, the tensile mechanical properties such as yield stress and elongation at break of cellular materials increased with the addition of CE.

Dynamic rheological behavior of reactively compatibilized polypropylene/polyamide 6 blending melts

ABSTRACTThe dynamic rheological behavior is measured by small amplitude oscillatory shear on rotational rheometer for polypropylene/polyamide 6 (PP/PA6) blends compatibilized by a polypropylene grafted maleic anhydride (PP‐g‐MAH). Scanning electron microscope (SEM) results show that the PP/PP‐g‐MAH/PA6 (=100/6/40wt) is sea‐island structure, the PP/PP‐g‐MAH/PA6 (=100/6/60wt) blend is semi‐cocontinuous. Coarse PA6 zones can be observed when the weight ratio is 100/6/80. At low frequency the complex viscosity, dynamic modulus of the PP/PP‐g‐MAH/PA6 (PP/PP‐g‐MAH = 100/6wt) blends first increase then drop with the increase of PA6 weight content in the range of 0–100, the maximum value arrives at the weight content of 60. The Cole–Cole plots as well as the weighted relaxation spectra of the blends have a main arc and a tail when the weight ratio of PP/PP‐g‐MAH/PA6 is in the range of 100/6/20–100/6/60, but have different shapes when the weight ratio increases to 100/6/80 and 100/6/100. The possible reason is the weight ratio of 100/6/80 and 100/6/100 is close to the phase inversion point. In fitting the storage modulus data at low frequency, Palierne's model with two parameters interfacial tension and interfacial shear modulus is better than Bousmina's model. Palierne's model with only one parameter of interfacial tension can not fit the data well. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42091.

Dynamic rheological behavior of two LDPE/HDPE binary blending melts

The dynamic rheological behaviors are measured by small amplitude oscillatory shear on a rotational rheometer for two low-density polyethylene/high-density polyethylene blends: LDPE 2102TN26/HDPE 5306 and LDPE2102TN26/HDPE8916. The composition dependence of zero shear viscosity as well as characteristic relaxation time of the two blends deviate the log addition rule, indicating the two blends are immiscible. Two emulsion models Palierne’s model and Bousmina’s model are used to fit the storage modulus-frequency data, the results indicate the two blends are immiscible except at the 90/10(LDPE/HDPE) weight ratio.

Phosphorus-containing copolyesters: The effect of ionic group and its analogous phosphorus heterocycles on their flame-retardant and anti-dripping performances

A series of copolyesters containing ionic groups (PETIs-K) were synthesized by melt co-polycondensation using terephthalic acid, ethylene glycol, and potassium salt of bishydroxyethyl ester of 10-hydroxy-10-oxo-10H-phenoxaphosphine-2,8-dicarboxylic acid (DHPPO-K) as monomers. The copolyesters only with analogous phosphorus-containing heterocycles (PETPs) were also synthesized and used as a control. The dynamic rheological behaviors confirmed that the complex viscosity of PETIs-K increased with increasing temperature due to the existence of ionic aggregates, which restricted melt dripping, while PETPs had flow behaviors similar to PET: the complex viscosity decreased with increasing temperature. The ionic groups induced the decomposition of the polymer backbone to form a more stable residue at high temperatures, which made PETIs-K exhibit good flame retardancy even with low phosphorus contents. Cone test showed the peak heat release rate and total smoke production of PETP5 decreased to 34% and 58% of pure PET. Compared with PETP5, these values for PETI5-K were reduced by 31% and 50%, respectively. EDX and ICP-AES results demonstrated that 92% of phosphorus for PETI10-K remained in char residues; however, this value for PETP10 was only 45%. Combined with results of XPS, Raman spectroscopy and Py-GC/MS, it can be proved that the ionization of phosphorus took main effects in condensed phase via promoting carbonization to form stable graphitic char, which avoided the decrease of carbonization due to the competitive effects of phosphorus in gas phase.

Dynamic rheological behavior of rice bran protein (RBP): Effects of concentration and temperature

The viscoelastic properties of rice bran protein (RBP) and the effect of temperature and concentration were investigated using small amplitude dynamic oscillatory shear measurements (SAOS). Linear viscoelastic region determined at 0.5% strain. Storage modulus (G′) was greater than the loss modulus (G″) at all concentrations and increased by raising RBP concentration. Yield stress value was determined by stress sweep and it increased from 0.038 to 1.80 Pa, when concentration increased from 10% to 15%. Frequency sweep showed that RBP solution had a typical fluid-gel behavior at low frequencies and complex viscosity (η*) had linear correlation with frequency. Phase angle was remained relatively low (>10) over the 1–10 Hz frequency range, confirming weak network of RBP. The effect of temperature on rheological traits was investigated during heating (20–90 °C) and cooling (90–20 °C) phases. RBP has a weak network and storage modulus was increased more during cooling phase. These rheological properties of RBP make it as a good candidate to apply with gelling materials in nutraceutical and food industries.

Rheological behavior of a LDPE/PS/SBS blending melt

The dynamic rheological behaviors are measured by small amplitude oscillatory shear on a rotational rheometer for a low-density polyethylene (LDPE)/polystyrene (PS)/styrene–butadiene–styrene (SBS) block copolymer blend with the tool of cole–cole plot. The morphology of the blend is measured by scanning electron microscope (SEM) micrograph, the storage moduli–angular frequency (G′–ω) data are fit by the Palierne model, and the relaxation time spectrum is investigated. The storage modulus and loss modulus of the LDPE/PS/SBS blend at low frequency increase when the weight ratio LDPE/PS increases from 10/90, reaches a maximum of 30/70, and drops thereafter. The cole–cole plots of some blends (10/90/3, 70/30/3, 90/10/3 and 100/0/3) have only one main arc due to compatibilizing effect of the SBS, and those of other blends (0/100/3, 30/70/3 and 50/50/3) have a second arc or a long tail besides the main arc probably due to phase separation. The SEM micrographs of the LDPE/PS/SBS = 10/90/3, 30/70/3, 50/50/3 show sea-island, semi-co-continuous and co-continuous structure, respectively. G′–ω curve of two LDPE/PS/SBS = 30/70/3 and 50/50/3 blends shows a power law, and the power index is much lower than one (0.748 and 0.817), respectively, showing a co-continuous morphology also verified by the SEM micrographs. The experimental data of G′–ω curve of the LDPE/PS/SBS blends are fit by Palierne model, the deviation between the fit line and the experimental data increases gradually as the LDPE/PS weight ratio decreases from 90/10 to 10/90. For the LDPE/PS/SBS blends, the weighted relaxation spectra τH (τ)–τ show a main as well as a second arc or tail; the former corresponding to the relaxation of PS phase and the latter corresponding to that of LDPE phase. Due to the compatibilizing effect of SBS the relaxation time and spectrum strength of LDPE/PS = 50/50 (wt) blends are both increased.

Effect of Na-ionomer on dynamic rheological, dynamic mechanical and creep properties of acrylonitrile styrene acrylate (ASA)/Na+1poly (ethylene-co-methacrylic acid) ionomer blend

A special class of engineered copolymers, called ionomers, comprising both electrically neutral repeating units and a fraction of ionized units was melt blended to weather resistant acrylonitrile/styrene/acrylate (ASA) terpolymer for improved electrical conductivity, heat sealing ability, direct adhesion to several polymers, glass and metals without affecting the aesthetics and colorability of ASA. The similar chemical nature of one of the components of each blended materials viz. acrylate rubber in ASA and acrylic acid of Na-ionomer in addition to the presence of ionic crosslinking within Na-ionomer, polar acrylonitrile group in ASA affects chain dynamics as compared to neat polymers. In this context, dynamic rheological properties, DMA properties, creep behavior and DSC of the newly developed ASA/Na-ionomer blends were analyzed. Based on Na-ionomer content, the blend system either forms “mushroom” or “brush” type conformation and formation of ionic crosslinking in “brush regime” leads to three tiers Caylay tree conformation. The different chain topology resulted into characteristic loss modulous (G″) curve during stress relaxation process. The chain conformation as well as ionic crosslinking and ion–dipole interaction between the blend components also affected DSC endotherm peak and glass transition temperature. The tan δ peak temperature from DMA also revealed the similar observation. The creep compliance of the blends was dependent on Na-ionomer content and with temperature. The Findley model analysis of creep compliance suggested that the creep compliance was depended on Na-ionomer content and ionic crosslinking controlled the creep. The findings can be utilized to design weather resistant smart polymer using suitable filler system. Copyright © 2014 John Wiley & Sons, Ltd.

Melt miscibility of HDPE/UHMWPE, LDPE/UHMWPE, and LLDPE/UHMWPE blends detected by dynamic rheometer

The dynamic rheological behavior of high density polyethylene (HDPE)/ultrahigh molecular weight polyethylene (UHMWPE) blends, low density polyethylene (LDPE)/UHMWPE blends and linear low density polyethylene (LLDPE)/ UHMWPE blends was measured in parallel plate rheometer at 200°C. The analysis of log-additivity rule, Cole-Cole plots and Han curves of the three series blends indicated that the LDPE/UHMWPE blends were miscible in the melt, while the HDPE/UHMWPE blends and LLDPE/UHMWPE blends showed phase separation. The DSC results of LLDPE/UHMWPE blends and HDPE/UHMWPE blends were consistent with the rheological properties, while for the thermal properties of LDPE/UHMWPE blends, results revealed three endothermic peaks, which indicated a liquid-solid phase separation in LDPE/UHMWPE blends.

Preparation, Morphology and Properties of Poly(Trimethylene Terephthalate)/Thermoplastic Polyester Elastomer Blends

Poly(trimethylene terephthalate)(PTT)/thermoplastic polyester elastomer (TPEE) blends were prepared and their miscibility, crystallization and melting behaviors, phase morphology, dynamic mechanical behavior, rheology behavior, spherulites morphology, and mechanical properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), parallel-plate rotational rheometry, polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), universal tensile tester and impact tester, respectively. The results suggested that PTT and TPEE were partially miscible in the amorphous state, the TPEE rich phase was dispersed uniformly in the solid matrix with a size smaller than 2 μm, and the glass transition temperatures of the blends decreased with increasing TPEE content. The TPEE component had a good effect on toughening the PTT without depressing the tensile strength. The blends had improved melt viscosities for processing. When the blends crystallized from the melt state, the onset crystallization temperature decreased, but they had a faster crystallization rate at low temperatures. All the blends’ melts exhibited a predominantly viscous behavior rather than an elastic behavior, but the melt elasticity increased with increasing TPEE content. When the blends crystallized from the melt, the PTT component could form spherulites but their morphology was imperfect with a small size. The blends had larger storage moduli at low temperatures than that of pure PTT.

An Investigation on Compatibilization Threshold in the Interface of Polypropylene/Polylactic Acid Blends Using Rheological Studies

This paper reports on the dynamic rheological behavior of polypropylene/(polylactic acid) (PP/PLA) uncompatibilized blends and those compatibilized with a terpolymer of ethylene, butylacrylate, and glycidylmethacrylate (PTW). The PP-rich (75/25) and PLA-rich (25/75) systems with 0, 2.5, 5, and 7.5 wt% of PTW were examined. We show how the decrease in the domain size of dispersed droplets and the homogeneity of the systems strongly depend on the composition. Morphological studies revealed 100% reduction in the size of PLA domains in the compatibilized PP-rich system containing 5 wt% of PTW. Such rigorous domain size reduction was not observed for the PLA-rich system. The complex moduli of the blends predicted by the Palierne emulsion model were compared with those obtained from the experimentally estimated complex moduli. We found two different behaviors for the 75/25 and 25/75 blend systems. Although the predictions for the 75/25 blend showed some deviations from the experimental data at low-frequency region and fitted well at high-frequency region, the 25/75 blends exhibited an opposite behavior. Furthermore, we found that the compatibilization had no significant effect on the predicted complex moduli of the both systems. J. VINYL ADDIT. TECHNOL., 22:19–28, 2016. © 2014 Society of Plastics Engineers

Viscoelastic properties correlations to morphological and mechanical response of HDPE/UHMWPE blends

Melt-mixed and injection molded binary blends of high density polyethylene (HDPE)/ultra high molecular weight polyethylene (UHMWPE) were evaluated for their structural, thermal, rheological, morphological and mechanical attributes. X-ray diffraction (XRD) study has revealed the absence of any significant changes in the crystalline alignment/morphology of the two polyethylene components. Differential scanning calorimetry (DSC) studies revealed the increase in melting temperature, whereas the properties such as crystallization temperature and percentage crystallinity remained broadly unaffected. Dynamic rheological behavior revealed a transition from liquid like behavior (G′ G″) in the composition range of 20–30 wt% of UHMWPE. Scanning electron microscopy (SEM) of the cryo-fractured surface depicts two phase morphology along with very strong interface. The blending of UHMWPE with HDPE matrix has caused improvement in tensile, impact and flexural properties, whereas strain at break suffered a decrease. The analysis of tensile fractured surface morphology by SEM has proved to be useful in qualitatively understanding the underlying failure mechanisms. Eventually, a viscous-to-elastic transition in the rheological behavior has been observed and found to have a correspondence with structural, mechanical and morphological response in the similar composition window.

A mathematical model of rheological behavior of novel bio-based isocyanate-terminated polyurethane prepolymers

In this paper, the results of rheological study on isocyanate-terminated polyurethane prepolymers, containing modified soybean oil residues incorporated into the chemical structure are described. Isocyanate-terminated prepolymers were synthesized from 4,4′-diphenylmethane diisocyanate and the mixture of hydroxylated soybean oil and commercial polyether. The measurements were performed by using rotary rheometer R/S-CPS+ (Brookfield, USA), while the rheological parameters were calculated by using Rheo3000 program. Based on rheological measurements, the viscosity curves and flow curves for prepolymers in the temperature range from 50 to 70°C were plotted. Prepolymer samples were tested with controlled shear rate (CSR). It was found that a viscosity of bio-based isocyanate-terminated prepolymers decreases with increasing content of hydroxylated soybean oil in the polyol mixture. The rheological data for bio-based polyurethane prepolymers were also mathematically modeled. It was found that the synthesized prepolymers are non-Newtonian fluids that can be described by Ostwald-de Waele and Herschel Bulkley functions as optimal individual models. The conducted investigations showed that the dynamic viscosity and rheological behavior of bioprepolymers samples could depend on the amount of hydroxylated soybean oil used in the polyol mixture.

Rheological behaviors of cellulose in 1-ethyl-3-methylimidazolium chloride/dimethylsulfoxide

Dynamic rheological behaviors of α-cellulose 1-ethyl-3-methylimidazolium chloride ([Emim]Cl)/dimethylsulfoxide (DMSO) solutions were investigated in a large range of cellulose concentrations (0.1–10wt%) at 25°C. The overlap concentration c* and the entanglement concentration ce for cellulose in [Emim]Cl/DMSO were determined to be 0.5wt% and 2.0wt% respectively, and the exponents of the specific viscosity ηsp versus cellulose concentration c were determined as 1.1, 2.1 and 4.7 for dilute, semidilute unentangled and entangled regimes respectively, which were in accordance with the scaling prediction for neutral polymer in θ solvent. Under the same cellulose concentration, the complex viscosity η*, the reptation time τrep and the relaxation time of a segment between entanglements τe all decreased with increasing DMSO content in the solvent, while the number of entanglements of cellulose chains and the molar mass of an entanglement strand Me both remained unchanged.

Effects of two biomass ashes on asphalt binder: Dynamic shear rheological characteristic analysis

In this work, two kinds of biomass ashes (BA), rice husk ash (RHA) and wood sawdust ash (WSA) were used to modify asphalt binder. Fourier Transform Infrared (FT-IR) Spectroscopy was used to characterize the effects of biomass ashes on chemical properties of asphalt binder. Physical properties, such as dynamic rheological behavior, high temperature storage stability and aging properties of the modified asphalt were investigated. Test results indicated that there is no chemical reaction between asphalt binder and BA. The RHA and WSA particle effect during blending with asphalt binder under physical agitation dominated the modification. Compared with WSA, RHA showed better effect in improving physical properties of modified asphalt binder. The storage stability tests indicated that the asphalt binder modified with RHA and WSA is stable when ash content is less than 20%. With the enhancement of the content of RHA and WSA to asphalt binder, viscosity, complex modulus and rutting factor (G*/sinδ) of modified asphalt binders increased rapidly at high temperatures. As a consequence, the deformation resistance of these modified binders at high temperatures was especially improved. RHA and WSA can be considered as asphalt modifiers which were more helpful for the improvement of rutting resistance.

Rheological behavior of cellulose nanocrystal suspension: Influence of concentration and aspect ratio

ABSTRACTThe steady and dynamic rheological behaviors of two cellulose nanocrystal (CNC) suspensions were investigated over a wide range of concentrations. The viscosity, storage and loss modules increased with increasing CNC concentration, and both CNC suspensions showed three regions in a viscosity‐concentration graph. The two critical concentrations depended on the aspect ratio and corresponded to the overlap and gelation concentration. Because of the higher aspect ratio, switchgrass CNC suspension transitioned into a biphasic state and formed a hydrogel at lower concentrations than those of cotton CNC suspensions. Furthermore, the complex viscosities of both CNC suspensions were higher than their steady viscosities; therefore, neither CNC suspension followed the Cox–Merz rule, which may be attributed to the existence of a liquid crystal domain in each suspension. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40525.

UV Aging Performance of Asphalt Containing LDHs

In this paper the effect of Layered double hydroxides (LDHs) on aging properties of asphalts was studied. The thin film oven test TFOT tests and ultraviolet (UV) aging process were used to simulate short-term and long-term aging of asphalts, respectively. After aging, the physical properties and dynamic shear rheological behaviors of LDHs modified asphalts were investigated. The viscosity of LDHs modified asphalts was measured by Brookfield viscometer before and after UV aging. After UV aging, with an increase of LDHs, softening point and viscosity value of modified asphalts decreased, while both of ductility and penetration increased, compared to base asphalts. Temperature sweep tests showed that the complex modulus of LDHs modified asphalts was lower than that of base asphalt, while phase angle was higher. The results showed that LDHs improved the UV aging resistance of the asphalt, and it could prevent asphalt from UV aging.

Gums tuning the rheological properties of modified maize starch pastes: Differences between guar and xanthan

The experimental setup aimed at gaining a more fundamental knowledge on the effects of two frequently used food gums, guar and xanthan, on the rheological properties of modified waxy starch systems. With regard to starch/non-starch hydrocolloid combinations, chemically modified starches receive much less attention than their native counterparts, despite their commercial and scientific value. The use of cross-linked waxy starches allows to treat the combined systems as dispersions of undisrupted, swollen granules, surrounded by the gum solution. This hypothesis was verified by using confocal scanning laser microscopy with fluorescently labeled gums. The average swollen granule sizes were derived by laser light scattering, and the corresponding total volume fraction occupied by the swollen starch (Φ) was calculated. The specific effects of the gums appeared to strongly depend on the starch content. Both gums, which were effectively increased in concentration due to the starch swelling, dominated the dynamic rheological properties and flow behavior at low Φ. At higher Φ, granule interactions governed the rheological properties. Whereas both gums could weaken the granule network, they contributed to the elastic behavior by their own entanglements. Moreover, xanthan gum appeared capable of reducing the granule interactions within flow, which results in lower viscosities at high starch volume fractions and high shear rates.

Thermal, crystallization, and dynamic rheological behavior of wood particle/HDPE composites: Effect of removal of wood cell wall composition

ABSTRACTThis study investigated the effect of removal of wood cell wall composition on thermal, crystallization, and dynamic rheological behavior of the resulting high density polyethylene (HDPE) composites. Four types of wood particle (WP) with different compositions: native wood flour (WF), hemicellulose‐removed wood particle (HR), lignin‐removed wood particle (holocellulose, HC), and both hemicellulose and lignin removed particle (α‐cellulose, αC) were prepared and compounded with HDPE using extruder, both with and without maleated polyethylene (MAPE). Results show that removal of the hemicellulose improved the thermal stability of composites, while removal of the lignin facilitated thermal decomposition. WPs acted as nucleating agents and facilitated the process of crystallization, thereby increasing the crystallization temperature and degree of crystallinity. The crystallization nucleation and growth rate of αC and HR based composites without MAPE decreased, as compared with WF based one. Composite melts with and without MAPE exhibited a decreasing order of storage modulus, loss modulus, and complex viscosity as αC > WF > HR > HC and αC > HR > WF > HC, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40331.