Rheological behavior of ultrahigh molecular weight polyethylene semidilute solutions. I. Solvent effect

The rheological behavior of ultrahigh molecular weight polyethylene (UHMWPE) semidilute solutions with different solvents has been studied. In a temperature range of 150–185°C, the viscosity of a UHMWPE semidilute solution with paraffin oil as solvent (soln 1) is more temperature-independent and viscosity-stable than that with decalin as solvent (soln 2). Usually the reduction of the molecular entanglement density in solution causes a rapid reduction in viscosity. Apparently soln 1 has a different entanglement density compared with soln 2. The activation energy of UHMWPE semidilute solutions changes with both shear stress and shear rate. The regressive equations for both solutions in between E_σ and σ or E_? and $ {\dot \gamma } $ have been obtained from a least-squares method. Finally, there is a discontinuity in the non-Newtonian flow region of η vs. $ \dot \gamma ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $ curve, no matter which temperature or solvent was used. The discontinuity occurs at a shear rate of about 70 s^?1, where a transformation from a qualitative change in entanglement in the solution takes place.     

Rheological behavior of ultrahigh molecular weight polyethylene semidilute solutions. II. Effect of aluminium stearate

The effect of aluminium stearate on the rheological behavior of ultra-high molecular weight polyethylene (UHMWPE) semidilute solutions with paraffin oil as the solvent has been investigated. Adding aluminium stearate to paraffin oil can prevent the spinning solution from adhering to the pipe or screw, greatly improving the flow behavior of UHMWPE solutions. The geometric sizes of spinnerette hole, such as length–diameter ratio L/D and entrance angle of a capillary, also affect the flow behavior of the spinning solution. The calculated first normal stress difference σ₁₁ ? σ₂₂ and the Bagley-end correction e from experimental data show that the elastic effect on spinning solutions in flow is quite large, although the shear rate is below 20 s^?1.     

Rheological behavior and flow instability in capillary extrusion of ultrahigh-molecular-weight polyethylene/high-density polyethylene/nano-SiO2 blends

Rheological behaviors of ultrahigh-molecular-weight polyethylene (PE)/high-density PE/SiO₂ blends are investigated using parallel-plate rheometer and capillary rheometer. The molecular chain conformational change mechanism is used to explain flow instabilities during extrusion. The viewpoints are proposed: (1) critical shear rate depends on the relative strength of irreversible viscous loss and reversible elastic orientation for molecular chains in transverse velocity gradient field inside the die and (2) critical shear stress depends on the extent of molecular chain conformational change inside the die, and the ease of conformational recovery after leaving the die. Modified nano-SiO₂ particles are detected a certain interfacial adhesion in PE matrix. The interfacial interaction limits viscous flow inside the die and conformational recovery after leaving the die, thus causing not only the flow instabilities to occur prematurely on shear rate and delaying sharkskin on shear stress, but also an alternate “sharkskin-melt fracture” appearance after global extrusion fracture. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47713.     

增塑改性聚乙烯醇熔体流变行为研究

通过添加质量分数为0~2.0%的金属离子配位剂(M)、质量分数为7.5%~12.0%的亲水性环保型增塑剂(A)和质量分数为0~2.0%的聚醚类增塑剂(B),制备了用于熔融纺丝的改性PVA;采用毛细管流变仪研究了改性PVA体系在120~135℃的流变行为。结果表明:改性PVA流体是一种对剪切作用敏感的假塑性流体;在相同温度和剪切速率下,随M含量的增加,改性PVA熔体的表观黏度、剪切敏感性、温度敏感性、非牛顿性上升,可纺性下降;随A含量的增加,改性PVA熔体的表观黏度、温度敏感性、非牛顿性下降,剪切敏感性、可纺性上升;随B含量的增加,改性PVA熔体表观黏度、剪切敏感性、温度敏感性、非牛顿性呈先下降后上升的趋势,而可纺性呈先上升后下降的趋势。改性PVA在135℃和少量M存在的条件下,A质量分数为12.0%、B质量分数为0.5%~1.0%时,适合熔融纺丝。     

高密度聚乙烯等温结晶的流变行为

用旋转流变仪研究了高密度聚乙烯的等温结晶行为,发现结晶速率对夹具表面粗糙度存在依赖性,随着表面粗糙度的增加,结晶速率先增加后减小.粗糙度的增加增大了样品与夹具间的接触面积,减小了热阻,同时界面间可能积存的气泡使得界面热阻较大,都影响着结晶速率.对于相同表面粗糙度的铝、黄铜和不锈钢三种材质的夹具,相应的结晶速率排序为：铝最快,黄铜居中,不锈钢最慢.我们研究发现HDPE样品的结晶速率对夹具的表面能不敏感,而夹具的导热系数越大,热阻越小,结晶速率越大.     

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 behavior of hydrophilic silica dispersion in polyethylene glycol

The rheological properties of hydrophilic fumed silica dispersed in polyethylene glycol (PEG) were investigated. The dispersion was prepared by dispersing the fumed silica in PEG with various concentrations. The reversible sol–gel transition was observed over 5 wt % of silica concentration as a function of temperature. The gelation temperature was found to depend on the applied shear stress and silica concentration, and the high shear stress was found to lead to the decrease of sol–gel transition temperature of the dispersion with the same silica concentration. As the silica concentration increases, the sol–gel transition shifts to the lower temperature. © 2006 Wiley Periodicals, Inc. J Apple Polly Sci 103: 2481–2486, 2007     

Mechanical properties of ultrahigh-molecular-weight polyethylene fiber-reinforced PE composites

Three types of high-strength polyethylene (PE) fiber-reinforced composite sheets were made by compression molding at the vicinity of melting point of the fiber. Sheet I was molded from only PE fibers. Sheets II and III were prepared by the compression molding of PE fiber with conventional high- and low-density polyethylene films, respectively. The mechanical properties, thermal behavior, and morphologies of the sheets have been investigated and compared with each other. The tensile strength and elastic modulus of sheet III are 660 MPa and 14 GPa, respectively, which were 60 and 30 times higher than those of typical low-density PE film. Although the elastic modulus of sheet III is 6 GPa less than that of sheet II, the tensile strength of 660 MPa is highest in the three types of sheets prepared in this study. The mechanical properties of sheets II and III were about half of predicted theoretical ones. It was concluded that the interfacial adhesion between PE fiber and PE matrix was an important factor to improve the mechanical properties of this PE sheet. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1431–1439, 1998     

无卤阻燃低密度聚乙烯复合材料的流变性能

采用熔融共混法制备了无卤阻燃低密度聚乙烯(LDPE/FR)复合材料。通过极限氧指数仪和毛细管流变仪等考察了LDPE/FR复合材料的阻燃性能和流变性能。结果表明:随着阻燃剂添加量的增加,LDPE/FR的阻燃性能逐渐提高,当阻燃剂的质量分数为25%时,阻燃体系的极限氧指数达28.3%;LDPE/FR熔体的表观黏度随着阻燃剂添加量的增加以及剪切速率的提升而降低,其非牛顿指数为0.42~0.70,属于典型的假塑性流体。     

Structure and properties of orption-active nanocomposites from ultrahigh-molecular-weight polyethylene

The pore structure of filled films of ultrahigh-molecular-weight polyethylene fabricated by gel technology was investigated by IR spectroscopy and optical microscopy. The sorption capacity of films containing nanoparticles of zeolite and montmorillonite with respect to alkali and alkaline-earth metals was determined as a function of the degree of filling. __________ Translated from Khimicheskie Volokna, No. 2, pp. 33–37, March–April, 2007.     

Rheological behavior of collagen/chitosan blended solutions

Understanding the rheological behavior of collagen/chitosan blends is fundamental to design the optimized collagen/chitosan composite materials. Steady shear, dynamic frequency sweep, thixotropy and creep-recovery tests were investigated to characterize the rheological behavior of collagen/chitosan blends as a function of chitosan content (0%–90% [wt/wt]). All the samples showed pseudoplasticity with shear-thinning behavior. With the increase of chitosan, the viscosity significantly decreased from 862.54 to 0.60 Pa s at 0.05 s⁻¹. The storage modulus and loss modulus also decreased while the dynamic denaturation temperature increased from 39.79 to 45.18°C. Besides, the thixotropy weakened and when the chitosan content reached 70%, the final recovery percentage was only 4.6%. The entanglements between collagen fibers observed by atomic force microscopy became weaker. Finally, the corresponding mathematical models were used to simulate the experimental data, and the obtained parameters might provide some useful theoretical guidance for the processing of the collagen/chitosan blended solutions.     

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     

Rheological behavior of polymer solutions during fabric coating

The overall performance of coated products is determined by the intrinsic material properties in solution and processing conditions. To characterize the behavior of these materials, the viscosity of polymers in solution at various concentrations was measured and the experimental data were fitted with the Carreau model. The results describe the rheological behavior of coating materials, and provide a basis for the modeling of polymer flow during the coating process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fibre materials based on ultrahigh-molecular-weight polyethylene and montmorillonite nanoparticles

The effect of the thermodynamic quality of the solvent on the properties of polymer solutions was determined. Thermal annealing affects formation of the structure and the mechanical properties of UHMPE. Fourier transform IR spectroscopy revealed the effect of the filler on the structure of the polymer matrix. The morphology of filled UHMPE fibres was characterized by optical microscopy; the fibres have a longitudinally oriented structure and the filler aggregates in particles up to 50 μm in size, which does not allow classifying the materials obtained as nanocomposites. Translated from Khimicheskie Volokna, No. 3, pp. 4–8, May–June, 2008.     

Rheological properties of guar and its methyl, hydroxypropyl and hydroxypropyl-methyl derivatives in semidilute and concentrated aqueous solutions

We report on a comparative study of the rheological properties of guar [GG], methyl guar [MG], hydroxypropyl guar [HPG] and hydroxypropyl-methyl guar [MHPG] polymers aqueous solutions in semidilute (both unentangled and entangled) and concentrated regimes, using oscillatory and steady-shear techniques. In the dilute regime, molecular weights and radii of gyration have been investigated by means of light scattering measurements.Data obtained from steady-shear rheology were satisfactorily analyzed according to Cross model and the effects of polymer concentration and temperature on the rheological behaviour of guar and guar derivatives have been investigated and discussed in terms of rheological parameters, such as the zero-shear viscosity η₀, the characteristic time τ and critical coil-overlap concentration C^∗.The storage and loss moduli of guar and guar derivatives aqueous solutions have been measured using angular frequencies in the range between 10⁻³ and 10 rad/s. The data have been analyzed using the “blob” model for semidilute solutions and the scaling approach proposed by Rubinstein, Dobrynin and Colby for concentrated solutions. These rheological parameters obey a time-concentration superposition principle, so that master curves can be constructed over a wide frequency range. Moreover, we show that, at lower temperatures, these systems behave as thermo-rheological simple systems, in that the oscillatory shear response at different temperatures can be superimposed according to the empirical time-temperature superposition principle. Although these systems can be conveniently described within a unifying scaling model, the behaviour of guar derivatives are somewhat different. At higher temperatures, relatively small deviations from the scaling behaviour of the storage modulus of MG and MHPG polymers were observed. These findings can be justified by a structural re-organization of the macromolecular network, due to the hydrophobic interactions.     

Rheological behavior of acrylonitrile/ammonium acrylate copolymer solutions

Ammonium acrylate was first used as a comonomer to copolymerize with acrylonitrile. The viscosity behavior of dimethyl formamide solutions of acrylonitrile/ammonium acrylate copolymer was studied, and the rheological kinetics of the solutions were studied for comparison. It was shown that the solutions behaved the same as a Newtonian flow as the rotor speed increased beyond 12 rpm. With an increase in temperature, the apparent viscosity of acrylonitrile/ammonium acrylate copolymer solutions showed a trend of decreasing. The changes in the apparent flow‐activation energy of solutions (E_η) calculated by the Arrhenius equation became less prominent along with the changes in the molecular weight of the acrylonitrile/ammonium acrylate copolymers. E_η increased continuously with an increase in copolymer concentration. The viscosity of copolymer solutions decreased continuously as the concentrations of KCl and NaCl increased up to 0.015 mol/L, and then it increased. The E_η showed an obvious trend of decreasing with the addition of alkali salts, and the changes in the E_η containing NaCl were more prominent than those of solutions containing KCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2320–2324, 2007     

Rheological behavior of chlorosulfonated polyethylene composites: Effect of filler and plasticizer

Thermosets obtained by reacting highly functionalized maleic anhydride-grafted polyethylene and a polyetherdiamine at several NH₂/MA molar ratios were characterized for their gel content, thermal, mechanical, and thermo-mechanical behavior. Gel content varied with composition and a maximum (57%) observed when NH₂/MA molar ratio was 1.5. Two melting transitions were observed for thermosets, representing the semicrystalline polyethylene fraction in the gel and sol part of the material in contrast to a single transition for the starting polyethylene. Overall crosslinking suppressed the crystallinity of the polyethylene in the thermoset. A single T_g observed in the DMA analysis suggested phase mixing between the polyethylene and polyether chains. A shift in the T_g observed was related to the degree of crosslinking in the thermosets. Tensile properties of the thermosets were observed to be a strong function of composition and the degree of crosslinking and the optimum mechanical performance was shown by thermosets when NH₂/MA molar ratio was 1.5 and 2.0. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012