Rheological behavior and mechanical properties of sawdust/polyethylene composites

We have characterized the melt rheological behavior and the solid tensile properties of sawdust/polyethylene composites prepared in an internal mixer. Various concentrations (from 0 to 60 wt %) and three particle sizes have been tested, in presence of a coupling agent (maleic anhydride grafted polyethylene). In the molten state, for each particle size, a mastercurve of the complex viscosity as function of frequency can be plotted, using a shift factor depending on weight fraction. We show that the shift factors can be described by a Krieger‐Dougherty law, leading to a “universal” viscosity law of the Carreau‐Yasuda type. In the solid state, the presence of sawdust increases Young modulus in uniaxial elongation, mainly for small size particles, but reduces dramatically deformation at break and tensile strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

黏弹性流体基纳米流体流变学特性

黏弹性流体基纳米流体（viscoelastic fluid based nanofluid,VFBN）是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10^-3、5×10^-3、1×10^-2三种质量分数的十六烷基三甲基氯化铵/水杨酸钠水溶液为基液,粒子体积分数为0.1%、0.25%、0.5%、1.0%的铜纳米流体的剪切黏度、零剪切黏度以及松弛时间的测量,实验结果表明VFBN有明显的剪切稀变特性,同时纳米粒子的添加增大了基液的零剪切黏度,并导致基液黏弹性增强。以Giesekus本构模型为理论基础,利用实验参数得到了描述VFBN剪切黏度的实验关联式。     

Rheological aspects of microbial hyaluronic acid

The rheological properties of the hyaluronic acid (HA) produced by the cultivation of Streptococcus zooepidemicus ATCC 39920 in synthetic medium at constant pH of 7.0 were determined. Relevant characteristics of the biopolymer as its pureness related to proteins (0.44 mg of protein per gram of HA) and its average molar weight (4.0 × 10⁶ Da) were also determined. Experimental data in steady shear (flow curves) have been correlated with the Cross model, which described the apparent viscosity shear rate data well mainly at concentrations higher than 50 mg mL^?1.The concentration dependence of specific viscosity showed two linear regimes that intercept at critical overlap concentration (c*) equal to 4 mg mL^?1. The storage (G′) and loss (G″) moduli increasing along the HA concentration and estimates out of the studied range indicate that a crossover frequency decreased with the increasing concentration of HA. The high concentration dependence of G′ as well as the deviations of the Cox‐Merz rule for most of the HA concentrations indicate the hyperentangled properties for the HA chains, which could be visualized through atomic force microscopy images even at low concentrations as 0.01 mg mL^?1. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Rheological properties of recycled chlorinated polyethylene/natural rubber blends vulcanized by sulfur

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) with a blend composition ratio of 80/20 were prepared and recycled. Viscoelastic properties of the blends as a function of the recycling cycle were monitored. The results obtained revealed that, with an increase in the number of recycling cycles, a noticeable change in the viscoelastic properties of blends could be observed; that is, a decrease in the elastic contribution associated with a noticeable shift in the glass‐transition temperature of the NR phase of the blends was observed, implying a molecular change in the NR phase via a thermal chain‐scission mechanism. The influence of magnesium oxide (MgO) as an acid acceptor for CPE on the viscoelasticity of the blends was also investigated. Through a reduction of the amount of MgO, the molecular change was found to be more pronounced in NR than in CPE phases in a manner similar to the increase in the recycling cycles. An explanation of the changes in the viscoelastic properties of the blends with various MgO loadings and recycling cycles is proposed in terms of thermal degradation via a molecular chain‐scission mechanism taking place mainly in the NR phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological modeling of fracture in plug‐assisted vacuum thermoforming

The fracture of polymeric sheets is one of the practical problems occurring during plug‐assisted vacuum thermoforming. This defect can occur during both the plug‐assist and vacuum‐forming stages. This article focuses on two issues: (1) the origins of fracture creation and (2) the determination of the process parameters needed for removal of the defect. The results of our work not only lead to an understanding of the cause of this problem but also enable us to calculate the parameters that affect the fracture of polymeric sheets during plug‐assisted vacuum thermoforming. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of hydrophobic interaction on rheological behavior and microstructure of carboxylated core‐shell latex suspension

We have investigated the effects of hydrophobic interactions on the rheological behavior and microstructure of suspension of carboxylated core‐shell latex particles with changing hydrophobicity of shell polymer and suspending medium. The carboxylated core‐shell latex particles formed lattice‐like microstructures in aqueous suspension with dissociation of carboxyl groups. With increasing hydrophobicity of the shell polymer, the interparticle distance ξ in the microstructure decreased. However, ξ increased with increasing hydrophobicity of the suspending medium. The effect of hydrophobic interaction on ξ was explained by the steric stabilization theory for particles with grafted polymer on the surface. As the carboxylated core‐shell latex particles overlapped each other in the microstructure, an attractive force was generated between the particles in aqueous suspension. With increasing hydrophobicity of the shell, the attractive force increased, but with increasing hydrophobicity of the suspending medium, the attractive force decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4153–4158, 2006     

Rheological behavior of alginate solutions for biomanufacturing

The rheological behavior of alginate solutions were investigated for the optimal design of a biomanufacturing system to produce alginate structures for tissue engineering. Its rheological properties were determined by a rheometer through rotational and oscillatory tests. Experimental results were used to model the alginate solutions characteristics. The findings suggest that alginate solutions undergo shear‐thinning effects with increasing shear rates. It is also possible to observe that its loss modulus is higher than the storage modulus ones being both modulus dependent upon the frequency, which is a typical characteristic of dilute solutions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological properties of polystyrene blends with rigid ladderlike polyphenylsilsesquioxane

Polystyrene (PS) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared by solution casting followed by hot pressing. The rheological properties of these blends were studied under dynamic shear and uniaxial elongation conditions. The loss modulus (G″) and dynamic shear viscosity (η*) of the 95/5 PP/PPSQ blend were slightly lower than those of pure PS at low frequencies (≤10^?2 rad/s). However, the storage modulus (G′), G″, and η* of the other blends (90/10, 85/15, and 80/20) were higher than those of pure PS and increased with PPSQ content. The η_E data demonstrated that PS/PPSQ blends exhibited slightly weaker (5% PPSQ) or much weaker (10% PPSQ) strain hardening than PS. In contrast, the 85/15 and 80/20 PP/PPSQ blends showed strain softening, and the extent of strain softening increased with PPSQ content. PS entanglements might have been reduced by the specific interactions between PS and PPSQ, which locally ordered some PS molecules in the 95/5 blend sample, because most of the PPSQ might have been well dispersed in the PS continuous phase, and only a few small PPSQ particles (～1.3 μm) were formed because of good miscibility. However, at high PPSQ contents (≥10%), many larger hard PPSQ particles were formed, which acted as fillers during the rheological measurements. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 706–713, 2005     

环保型MES粘弹性胶束溶液的流变性

用流变学方法研究了可生物降解阴离子表面活性剂脂肪酸甲酯磺酸钠（MES）在NaCl溶液中从球状胶束转变成蠕虫状胶束的生长过程,分析了两性表面活性剂十二烷基甜菜碱（BS-12）对MES胶束溶液流变行为的影响机制。首先,测量了MES粘弹性胶束体系剪切粘度（η）和剪切速率的关系,得到零剪切粘度（η0）;然后由动态振荡实验,得到复合粘度｜η＊｜、动态模量（储能模量G＇、损耗模量G″和结构松弛时间τs）等物理量;应用Cox-Merz规则和Cole-Cole图,证实了MES（3.0%～5.0%）/NaCl（3.0%～5.0%）/BS-12（0.5%～0.9%）体系形成蠕虫状胶束,且蠕虫状胶束的动态粘弹性在MES（3.5%～5.0%）/NaCl（3.5%～5.0%）/BS-12（0.5%～0.9%）范围是符合Maxwell模型的线性粘弹性流体。     

Effects of microstructures on the viscoelastic and rheological properties of metallocene‐catalyzed cyclo‐olefin copolymers: A preliminary study

We characterized metallocene‐catalyzed cyclo‐olefin copolymers (mCOCs) with similar heat distortion temperatures but dramatic differences in melt‐flow indices to understand how the molecular conformation affected their rheological and viscoelastic properties. The mCOC conformations were identified with ¹³C‐NMR, whereas the viscoelastic and rheological properties were measured with cone‐and‐plate and high‐pressure capillary rheometers. Our preliminary results showed that the mCOC rheological and viscoelastic properties might depend strongly on the conformation rather than the norbornene content, molecular weight, and molecular weight distribution. mCOCs containing ‐NNN‐ locks (where N represents norbornene) exhibited stronger molecular entanglements than those having no ‐NNN‐ blocks, as reflected in lower crossover frequencies and higher crossover torque. Furthermore, the existence of larger rigid ‐NNN‐ blocks resulted in higher molten viscosities and flow activation energies. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3695–3701, 2002     

Effect of colophony emulsion on the adhesive properties of vinyl acetate/n‐butyl acrylate copolymeric latex

We prepared a novel copolymeric latex of vinyl acetate and n‐butyl acrylate (V‐B) using a semibatch emulsion polymerization process. The glass‐transition temperature (T_g), steady viscosity, flow activation energy (E_f), dynamic moduli, and amphiphilic properties of the V‐B latex in the presence of colophony were systematically investigated. The experimental results demonstrate that excellent adhesive behaviors were achieved for the V‐B latex blended with 20 wt % colophony, whereas good adhesive performance was related to the moderate T_g, viscosity, E_f, storage modulus, and low contact angle on the adherent. The debonding mechanisms for V‐B and its colophony‐modified latexes were analyzed. A possible mechanism for the V‐B latex blended with colophony emulsion was determined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological properties of polymer-added lubricating oils

Rheological measurements of polyisobutylene solutions are presented. A mineral oil of low viscosity has been used as solvent. The combined effects of concentration, molecular weight and temperature were studied. It is found that the rheological data, when plotted as N₁λ_E/(η-η_s) versus λ_Eγ fall on a master curve over several decades of the dimensionless shear rate, irrespective of temperature, polymer concentration and molecular weight. The findings of this work can be used to address the problem of hydrodynamic lubrication of a journal bearing using a viscoelastic lubricant.     

超高分子量聚乙烯凝胶的流变行为

采用旋转流变仪研究了超高分子量聚乙烯(UHMWPE)凝胶的流变行为。通过动态应变扫描测定了UHMWPE凝胶的线性黏弹区;通过动态温度扫描、动态频率扫描和稳态速率扫描研究了温度、浓度、剪切速率对凝胶流变行为的影响。结果表明,浓度为2%~22%的UHMWPE凝胶的线性黏弹区对应的应变下限为2%,上限为40%,且温度对凝胶线性黏弹区的影响较大;浓度为6%的UHMWPE凝胶,在180℃时,弹性模量最大,凝胶内部的黏结性最强;UHMWPE凝胶熔体的黏度随扫描频率、剪切速率的升高而降低,呈现明显的剪切变稀行为,属于假塑性流体;剪切速率较高时,UHMWPE凝胶的黏度对温度的变化更敏感。     

Shape memory effect and properties memory effect of polyurethane

The relationship between shape and properties memory effect, especially viscoelastic properties of polyurethane under study is the main aim of this research work. Tensile tests have been performed in order to introduce 100% of deformation in the polyurethane samples. Under this deformation, stress–relaxation experiments have been performed in order to eliminate the residual stresses. This deformation of the samples has been fixed by cooling. Recovery tests, then, were carried out at different isothermal temperatures that varied from 30°C to 60°C. Viscoelastic behavior has been studied by a biparabolic model and by using the Cole–Cole method. It was shown that this model describes the behavior of the polymer at the different states of shape memory tests. The constants of this model then have been determined. This study leads to a better understanding of the mechanism of shape memory effect. The comparison between the virgin polymer and the polymer after a recovery test by DMTA (dynamic mechanical thermal analysis) and by Cole–Cole method has illustrated that the polymer does not obtain its initial properties even when it was totally regained its initial shape. These results have been confirmed by three successive shape memory tests on the same sample and by comparing the mechanical characteristics of different cycles because “shape memory effect” and “properties memory effect” do not follow the same mechanisms. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Rheological properties of a hydrophobically modified anionic polymer: Effect of varying salinity and amount of hydrophobic moieties

Hydrophobically modified polyelectrolytes have been suggested as an alternative to the more commonly used polyelectrolytes in enhanced oil recovery (EOR) applications involving polymers. Compared to regular polyelectrolytes, the hydrophobically modified polyelectrolytes are known to be more stable at high salinities. In this study, we have investigated the influence of brine salinity and ionic composition for a series of six hydrophobically modified polyelectrolytes with the same polymer backbone, but with an increasing average number of hydrophobic groups per polymer molecule. Polymer characterization has been performed using a combination of steady‐state shear viscosity and dynamic oscillatory measurements. Hydrophobic interactions leading to a change in rheological properties was only observed above a threshold value for the concentration of hydrophobe. At the threshold value, salt‐induced hydrophobic interactions were observed. For higher concentrations of hydrophobe, high salinity solutions showed one order of magnitude increase in viscosity compared to the polymer without hydrophobic groups. This could partly be explained by an increase in elasticity. These findings have important implications for polymer selection for EOR. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43520.     

Viscoelastic properties of lupin proteins produced by ultrafiltration-diafiltration

The linear and nonlinear rheological properties of defatted lupin proteins produced by ultrafiltration-diafiltration were investigated. Five concentrations ranging from 10 to 30% of the defatted ultrafiltered-diafiltered (DUD) lupin proteins were prepared. The viscoelastic properties strongly depended on concentrations. Below 12%, the DUD lupin proteins exhibited more fluid-like behavior. At 15%, lupin proteins became more viscoelastic, and above 20%, the viscoelastic solid-like properties became stronger. Below 12%, the high-frequency behaviors of moduli were proportional to ω^1/2, as expected for a semiflexible coil. Above 20%, the high-frequency behaviors of moduli were proportional to ω^1/2, indicating a flexible coil. The nonlinear steady shear rheological properties were also concentration-dependent and showed shear-thinning behavior, which could be described by a power law constitutive model. The trend of the power law exponent shift is very consistent with the linear viscoelastic behavior change with the lupin protein concentration. These results suggest DUD lupin proteins undergo a structural change between 12 and 20%.     

Rheological investigation of microphase separation transition of polyurethane elastomer

A technique of linear viscoelasticity measurements coupling with temperature scanning was found effective in the detection of microphase separation transition (MST) and in the determination of MST temperature. The validity and accuracy of the technique were confirmed and reinforced by atomic force microscopy and differential scanning calorimetry (DSC). The technique was applied to a study of the MST of a series of 13 polyurethane (PU) elastomers based on mixed toluene diisocyanate (TDI), 1,4 butadiol, and poly(tetramethylene oxide) (PTMO) of two different molecular weights; the MST temperatures of the PU elastomer samples were measured. Although each of the 13 polymer samples had distinct hard segment content and used PTMO of different chain lengths, or mixed PTMO, the MST temperatures of the 13 samples formed a linear master curve when the MST temperature was plotted against the fraction of hard segment. The master curve indicated that the MST temperature is independent of the length and type of PTMO. It was also found that 2,4 TDI prevailing over its isomer 2,6 TDI played a dominant role in the MST of this series of PU elastomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2107–2112, 2007     

Nonlinear viscoelastic properties of molten thermoplastic vulcanisates: An insight on their morphology

A series of thermoplastic vulcanisates (TPVs) in the molten state were submitted to large amplitude oscillating strain tests at different frequencies, to investigate their nonlinear viscoelastic properties. A purposely modified torsional harmonic tester with a closed cavity was used to run such experiments, whose results were treated with a Fourier transform (FT) algorithm to extract main torque and strain components, and harmonics if any. Quarter cycle integrations of (averaged) torque signal were also performed, to supplement FT analysis, namely to distinguish extrinsic and intrinsic nonlinear viscoelasticity. The nonlinear viscoelastic character of TPVs was found substantially differing from the one of a molten polypropylene (PP) used for comparison. Within the strain window investigated, no linear behavior is observed with TPVs, in contrast with the pure PP. However, extrapolated “linear” complex modulus G*₀ tends to decrease with increasing hardness of TPVs, but subtle differences between the various grades are clearly detected, when using simple models to fit experimental data. While the (room temperature) hardness is somewhat related with the viscoelastic behavior in the molten state, the strain sensitivity of TPVs appears essentially affected by the extractible content (mainly oil). TPVs nonlinear viscoelastic character appears to depend on the strain amplitude: mainly intrinsic, i.e., due to their morphology, at low strain, and essentially extrinsic, i.e., due to the large strain amplitude, at high strain, and in this respect, qualitatively similar to pure PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4193–4205, 2006     

Rheological properties of neat epoxy exposed to in‐service aerospace contaminants

We present an experimental study on the rheological properties of a commonly used epoxy resin system (EPIKOTE‐862 resin and EPIKURE‐W curing agent), exposed to a variety of fluids typical of aerospace operations (jet fuel, hydraulic fluids, deicing, detergents, etc.), for a period of up to 6 months, at room temperature for most conditions, and with no concurrent mechanical loading or prior degradation. The specimens were subjected to stress and frequency sweeps with a shear rheometer, while a limited set received also a temperature sweep in a range consistent with aircraft operations. Results indicate that the treated resin samples are linear viscoelastic under these testing conditions. The resin has reasonable chemical resistance to most contaminants of this study, with the exception of two commonly used detergents: an aircraft surface cleaning compound, Penair C5572, and a nonionic detergent, Methyl Ethyl Ketone (MEK). The durability change of the first compound appears triggered by high temperatures only, while the second compound causes a very drastic stiffness loss under several conditions. This drop of performance occurs within a 3‐months period, with no apparent color change or fracture that could prompt visual inspection and repair. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3961–3971, 2013     

Rheological properties of aqueous polyacrylamide solutions

A comprehensive study of the rheological properties of aqueous polyacrylamide solutions was carried out. A RheoStress RS100 Haake rheometer was used in the measurements. The concentration of polyacrylamide ranged from 0.25 to 1.0% by weight. This range is sufficiently wide to cover many of the rheological features of polyacrylamide in the lower range of concentration. The study included measurements of steady shear flow parameters, transient shear stress response, yield stress, thixotropic behavior, creep recovery, dynamic responses, and temperature effects in the range 10–50°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1587–1597, 1998