Shear and extensional rheology and flow‐induced orientation of carbon nanofiber/polystyrene melt composites

The rheological behavior and morphology of polystyrene/carbon nanofiber (PS/CNF) composites in their melt phase have been characterized through experimental measurements. Viscosity measurements of the PS/CNF composites in the linear viscoelastic regime show the ratio of the transient extensional viscosity to the transient shear viscosity to be greater than three, the Trouton ratio. This behavior is due to differences in the flow‐induced orientation of CNFs in shear and extensional flow. The orientation development of the CNFs in shear and extensional flow was analyzed through a method utilizing transmission electron microscopy and was used to explain observed rheological phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Camphene/polystyrene solutions: A rheological approach for material processing industry

Rheological properties of polymer–camphene solutions are very relevant as they affect their stability, and they have many implications in operation costs. This work elucidates the rheological properties of polystyrene (PS–camphene) solutions with industrial applications. Unfortunately, the assessment of the very low shear viscosities of camphene-based materials (below 0.005 Pa s) is still a challenge with commercial rheometers. Flow curves, stress growth tests, and small amplitude oscillatory shear (SAOS) measurements were carried out as a function of PS concentration (0, 2.5, 5.0, 10, and 20 wt % PS) to understand the rheological behavior of these systems. Results indicate that liquid camphene has a shear-thinning behavior (flow index = 0.99) when the increase of polymer concentration involves changes in the structure of these systems (flow index = 0.10 for 20 wt % PS). An increase in PS concentration leads to a forwarding in the shear-thinning zone, and the Newtonian region (from ∼1 s⁻¹, for 0 wt % PS, to 10⁻³ s⁻¹ for 20 wt % PS). Eventually, these results evidence the high dependence of η_∞ on PS concentration (from ∼1.16 ± 0.01 Pa s, for 0 wt % PS, to 631.5 ± 0.2 Pa s for 20 wt % PS). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47953.     

Effect of ultrasonic oscillations on weld line strength of PS,PMMA, and their blends

The effect of ultrasonic oscillations on the weld line strength of amorphous polystyrene (PS), polymethyl methacrylate (PMMA), and PS/PMMA (20/80, 50/50, 80/20) blends at various temperatures was investigated. By facilitating the molecular diffusion across the weld line, the introduction of ultrasonic oscillations could evidently improve the weld line strength of PS, PMMA, and their blends. The different effects on the weld line strength of PS/PMMA (20/80, 50/50, 80/20) blends were investigated. The ultrasonic oscillations could greatly increase the weld line strength of PS/PMMA (80/20) by ～ 70%, but was less efficient to PS/PMMA (50/50, 20/80) blends, due to the great difference of weld line morphologies of these blends. The dispersed phase of PS/PMMA (80/20) in the weld line was spherical while two different morphologies in the weld line of PS/PMMA (50/50) were observed. And the stripe‐like morphology of PS perpendicular to the flow direction in the weld line of PS/PMMA (20/80) is responsible for the little effect of ultrasonic oscillations. The fractured surfaces of PS, PMMA, and PS/PMMA (80/20) with weld line became much rougher due to the introduction of ultrasonic oscillations. The morphology study of PS/PMMA (80/20) showed that the spherical dispersed phase of PS/PMMA at the skin turned smaller under ultrasonic oscillations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2990–2997, 2006     

Effect of aspect ratio and fluid elasticity on chain orientation in isothermal film casting process

The characteristics of extensional flow and the chain orientations of the isothermal film casting process utilizing a two-dimensional (2-D) viscoelastic model with finite element methods (FEM) were studied. Steady state and transient solutions were obtained for a relatively large aspect ratio regime by employing successive iterative schemes. In this work, higher aspect ratios of the equipment caused highly oriented molecular structures because the aspect ratio increases as the flow changes from planar to uniaxial extensional flow. Fluid viscoelasticity always alleviated the neckin phenomenon and led to the planar extension regime even if dichotomous behavior was observed for draw resonance in extensional thickening and thinning fluids. Consequently, the change in the characteristic of extensional deformation from uniaxial deformation to the planar extension deteriorated the molecular orientation.     

Extensional viscosity of silica dispersions

The rheological behavior in extensional flow was investigated for silica dispersions in polymer solutions using the tubeless syphon technique. The flow field of tubeless syphon is unsteady in the Lagrangian sense; hence the data are taken under transient stress conditions. Due to the insensitive nature of the extensional rate to flow rate, the extensional viscosities at different flow rates lie very close to a single curve, once they are plotted against strain. Two important points are noted with regard to the behavior of the dispersions. First, the extensional viscosity decreases with increasing particle concentration. Second, the viscosity growth curves of the dispersions can be superimposed by a vertical shift, but the curve shape differs from that of the medium. This implies a change in the relaxation time.     

Effect of ethanol addition on the elongational flow behavior of aqueous solutions of poly(ethylene oxide)

Summary In this work, we explore the effect of ethanol addition on the extension thickening behavior of aqueous solutions of poly(ethylene oxide) (PEO) in porous media and opposed-jets flow. The main aspect analyzed is the formation of transient entanglements of polymer molecules, which are responsible for the sudden increase in pressure drops and apparent extensional viscosities with strain rates observed in elongational flows of PEO solutions. The results show that changing the solvent by adding ethanol modifies the solution behavior because of two effects. First, the increase in the solvent viscosity increases the disentanglement time of the transient entanglements so that the onset of extension thickening occurs at lower strain rates in the presence of ethanol. Second, ethanol solutions are poorer solvents than water for PEO. This promotes intermolecular interactions between PEO coils when the solutions are semi-dilute. The net result is a lowering of the onset strain rate for extension thickening to values that are much smaller than those expected for the same PEO chains dissolved in a higher viscosity and poorer solvent. The results also show that coil-coil interactions in solution can be detected at lower concentrations in porous media flow than in opposed jets flow. Received: 24 August 2001/ Revised version: 29 October 2001/ Accepted: 6 November 2001     

Natural Giesekus fluids: Shear and extensional behavior of food gum solutions in the semidilute regime

The shear and extensional behavior of two aqueous gum solutions, namely (1) 1–20 g/L guar gum (Torres et al., Food Hydrocolloids. 2014;40:85–95) and (2) κ/ι‐hybrid carrageenan solutions (5–20 g/L), are shown to exhibit Giesekus‐fluid behavior when in the semidilute regime. In this regime, a common set of Giesekus fluid parameters described both shear and extensional behavior. A new analytical result describing the extension of a Giesekus fluid in the filament stretching geometry is presented. This also gave reasonable predictions of the Trouton ratio. Higher concentration guar solutions, in the entangled regime, yielded different Giesekus fluid parameters for extension to those for simple shear. The extensional data for all concentrations of both gums collapsed to a common functional form, similar to that reported for cake batters (Chesterton et al., J Food Eng. 2011;105(2):332–342); the limits of the new filament thinning expression provide insight into this behavior. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3902–3915, 2014     

Effect of extensional properties of polymer solutions on the droplet formation via ultrasonic atomization

Ultrasonic atomization was conducted using 2.4 MHz ultrasound generator to produce polymeric particles from the solutions of water‐soluble polymers like poly (ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), and poly(vinyl pyrrolidone) (PVP). In the series of solutions containing these polymers of various molecular weights, the shear viscosity and surface tension were varied; such differences, however, could not account for the observed trends in the atomization behavior. It was found that the availability of droplet formation and size of the droplets depend strongly on the extensional characteristics of polymer solutions along with the apparent extensional viscosities and the longest relaxation times. The extensional properties of polymer solutions were effectively measured by capillary breakup extensional rheometry (CaBER) and provided a rational basis to understand the essential role of fluid viscoelasticity in ultrasonic atomization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Incorporation of modified Stöber silica nanoparticles in polystyrene/polyamide-6 blends: Coalescence inhibition and modification of the thermal degradation via controlled dispersion at the interface

The controlled dispersion of Stöber silica nanoparticles (SiNPs) at the interface of a PS/PA6 (80/20 wt%) blend was achieved by means of surface modifications using 3-methacryloxypropyltrimethoxysilane (MPS). The final localization of SiNPs in the blend was predicted using wetting parameter calculation and confirmed by scanning electronic microscopy (SEM) observations. Stability of blends during annealing was evaluated qualitatively by laser diffraction particle size analyzer. Morphologies of the blends in the molten state were observed using optical microscopy. Flammability of blends was investigated using pyrolysis-combustion flow calorimeter (PCFC). Results showed that both microstructure stability during annealing and thermal degradation of the blend, were improved when MPS-modified SiNPs are located at the interface. SEM pictures revealed that the MPS-modified SiNPs form a solid barrier between PS and PA6 phases which inhibits coalescence process and modifies the thermal degradation mechanisms.     

Phase morphology,thermomechanical, and crystallization behavior of uncompatibilized and PP‐g‐MAH compatibilized polypropylene/polystyrene blends

In this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride‐grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42100.     

Extensional Flow and Relaxation of Semi‐dilute Solutions of Schizophyllan

Capillary thinning experiments of semi‐dilute solutions of schizophyllan in water and DMSO are performed to determine the relaxation behavior in extensional flows as experienced, for example, in the flow through porous media in enhanced oil recovery. The extensional relaxation time λ_E is found to scale with concentration following a dissimilar power‐law dependency for the two solvents, λ_E ∝ c^1.52 in water and λ_E ∝ c^0.90 in DMSO. It is shown that the extensional flow fields are strong enough to break, and prevent the rebuilding of, intermolecular structures, due to hydrogen bonding that was observed to alter the viscoelastic response in shearing flows of aqueous schizophyllan solutions.

     

Characterization and physical properties of polymethylphenylsilsesquioxane (PMPSQ) and hydroxyl‐functionalized polystyrene (PS–OH) hybrids

Polymethylphenylsilsesquioxane (PMPSQ–OH) and trimethylsilyl end‐blocked PMPSQ (PMPSQ–EC) were prepared. The thermal decomposition behavior of these polymers was studied by thermogravimetric analysis (TGA) and FT‐Raman spectroscopy. Hydroxyl‐functionalized polystyrene (PS–OH) was also prepared by anionic living polymerization. Thin hybrid films of PMPSQ/PS–OH with various blend ratios were obtained by spin‐coating on freshly cleaned glass. The surface morphology of the hybrid films was investigated by atomic force microscopy (AFM). In 80/20 PMPSQ/PS–OH hybrid film, the PS–OH component produced a very uniformly dispersed phase. This hybrid film contained small domains of PS–OH whose size ranged from 60 to 80 nm. As the content of PS–OH was increased, the domain morphology coarsened and phase inversion took place around 50 wt %. In the phase‐inversed system, the PMPSQ‐rich phase was uniformly distributed in the PS–OH‐rich continuous phase. In addition, temperature‐dependent dielectric properties of PMPSQ/PS–OH hybrids were investigated. Relaxation of the hybrids was observed with an increasing content of the PS–OH component due to the amorphous glass transition behavior of PS–OH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2801–2812, 2003     

含易挥发组分的聚合物溶液流变行为测定

利用HAAKE流变仪的D100/300测量系统,对聚苯乙烯/苯乙烯(PS/St)、高抗冲聚苯乙烯/苯乙烯(HIPS/St)及甲基硅油/环已烷等体系的流变行为进行了测定。测得40％PS/St和50％HIPS/St的平均流变行为指数分别为0.998和0.969,可近似作为牛顿流体处理。甲基硅油则是典型的牛顿流体,并得出了其粘度的关联式。     

Influence of carbon black on processability of rubber stocks. V. Extrusion

A study of postextrusion relaxation (shrinkage) rates identified two separate processes, only one of which is influenced by carbon black structure and surface area. One of these processes is thought to be a solidlike fast elastic recovery and was found to be influenced by carbon black and polymer characteristics. The other process reflected slow randomization of oriented molecular chains: it was mainly influenced by polymer nature and carbon black had almost no effect. In the previous paper of this series, work with various carbon blacks in SBR–1500 indicated that both types of polymer deformation originate within the converging flow region at the die entrance, where extensional flow takes place. In the present work the extensional flow behavior of five polymers (filled with various carbon blacks) was examined at elevated temperatures. The magnitude of shrinkage caused by molecular alignment was related to extensional viscosity of the rubbers. This confirms the hypothesis stated above. Extensional viscosity was measured using the previously described instrument, which is inexpensive to construct, easy to operate, and can be attached to any standard stress–strain tester. The characteristics of extensional flow are defined and it is shown that for polymeric materials it differs substantially from shear flow, since a rapid orientation of the molecular chains takes place during the extensional flow. The effect of carbon black on the extensional viscosity at elevated temperatures is illustrated.     

Shear and extensional flow of reinforced plastics in injection molding. I. Effects of temperature and shear rate with bulk molding compound

Capillary flow studies on bulk molding compound (BMC) using an instrumented injection-molding machine are reported. The significance of extensional flow effects with fiber-reinforced materials is emphasized. The extensional flow behavior in converging dies is modeled, and a means of evaluating both extensional and shear viscosity from capillary flow data is proposed. Methods of correcting results for the effect of deformation heating are discussed. The shear and extensional flow behavior of BMC in the temperature region 18 to 58°C can be fitted to a simplified Arrhenius Law.     

PIV技术测试聚合物流体拉伸流动的实验研究

针对低相对分子质量、低黏度的牛顿流体（如聚异丁烯）和非牛顿流体（如3 %苯甲酸钠溶液）,采用粒子成像速度仪（PIV）系统测试了2种流体在同一流率下流经渐变收缩流道时的速度分布,并研究比较了壁面处的纯剪切流动与流道中心轴线上的拉伸流动。通过实验测试与有限元模拟比较发现,牛顿流体和非牛顿流体的速度分布形态具有一定的差异。在确定速度分布的情况下,根据渐变收缩流动的特点,可以得到流体流动时中心轴线上的拉伸速率和边界处的剪切速率。     

Molecular orientation and stress in biaxially deformed polymers. II. Steady potential flow

The development of biaxial segmental orientation and stress in a flexible-chain polymer fluid subjected to steady biaxial extensional flow is analyzed. Closed-formula model based on the Padè approximation of the inverse Langevin function in the non-Gaussian distribution of the chain end-to-end vectors is considered. The approach is free from the limitations related to finite chain extensibility and slow convergence of the series expansion formulations at higher chain deformations.Segmental orientation is characterized by the average orientation tensor, related axial orientation factors and global orientation anisotropy. Orientational behavior and corresponding stresses in the biaxial elongational potential flow are discussed in a wide range of elongation rates. Orientation characteristics calculated for the biaxial flow deformation are much higher than those predicted for the affine biaxial stretch deformation in polymer solids.     

Effect of γ‐irradiation on the physical properties and dyeability of poly(vinyl butyral) blends with polystyrene and poly(ethylene glycol)

Cast films of polymer blends essentially based on poly(vinyl butyral) (PVB) and equal ratios of polystyrene (PS) and poly(ethylene glycol) (PEG) were prepared from benzene and butyl alcohol solutions of the individual polymers. The effect of γ‐irradiation on the thermal decomposition and tensile mechanical properties was investigated. Moreover, the effect of γ‐irradiation on the dye affinity of PVB/PS and PVB/PEG for basic and acid dyestuffs was studied. The thermogravimetric analysis (TGA) study showed that the unirradiated PVB polymer films prepared in benzene displayed higher thermal stability than the same polymer films prepared in butanol. However, in all cases the thermal stability was found to increase with increasing γ‐irradiation dose. On the other hand, PVB/PS blend possesses higher thermal stability than PVB/PEG, as shown from the determination of the weight loss (%) at different heating temperatures, the temperatures of the maximum rate of reaction and the activation energy. While, pure PS films showed the stress‐strain behavior of brittle polymers, PVB/PS films showed the behavior of tough polymers with yielding properties. The results of dyeing clearly showed that the solvent type, blend composition, and irradiation dose are determining factors for the dye affinity for basic or acid dyes. For example, unirradiated PVB films prepared from butanol displayed a higher affinity for the basic and acid dyes than the same polymer prepared from the same benzene. However, PVB prepared from butanol showed higher affinity to the dyes than PS prepared from the same solvent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Rheo-Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior

The phase behavior of polymer blends under simple shear flow has been studied using a custom-designed rheo-optical system consisting of a two-dimensional small-angle light scattering (SALS) device incorporated into a conventional rheometer. Two-dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PVME) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear-induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PVME blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright-streak pattern from a transient dark-streak pattern for a polymer blend system under shear. Rheo-microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a streak pattern by SALS. The relationship between the two phenomena has not yet been established.     

Flow-induced crystallization from solution: The relative effects of extension and shearing flow fields

Calculations have been performed to evaluate the relative effects of extensional and shearing flow fields on both the chain elongation and crystal nucleation rate enhancement for polyethylene crystallizing from xylene solutions. Rheological behavior was evaluated by means of the elastic dumbbell model modified for nonlinear effects at high elongations, and nucleation rate effects were considered from an essentially phenomenological view point. Molecular weight effects were also incorporated explicitly in the computations. Results show that chain elongation and nucleation rate enhancement is far greater for extensional than for shearing flows. Semiquantitative comparisons with experimental results reported in the literature for various aspects of the flow induced process, including the important fractionation effects, are discussed. Modification of the dumbbell model to account for shear rate effects on the intrinsic viscosity is also discussed.