Flow properties and rheology of slag from coal gasification

We have studied the rheological characteristics of Texaco gasifier slag at high-temperature. Slag samples have been analyzed by X-ray fluorescence, X-ray diffraction, and scanning electron microscopy. The rheological behavior of the slag has been investigated experimentally using a high-temperature rheometer at temperatures between 1200 °C and 1340 °C. The effects of the shear rate and temperature on the rheological behavior of the slag have been explored. Moreover, the observed rheological behavior of the slag has been correlated with its solid-phase content, as calculated with the aid of the computer software package FactSage. The results show that the sensitivity of the slag viscosity to temperature decreases with increasing rotation speed. Above its liquidus temperature calculated by FactSage, the slag behaves as a Newtonian fluid; below its liquidus temperature, however, the rheological behavior of the slag becomes non-Newtonian owing to its increased solid-phase content. Meanwhile, Slag containing a number of crystalline particles shows dramatic shear-thinning and thixotropic behavior. Moreover, the shear-thinning behavior of the slag becomes ever more distinct as the temperature is decreased. The yield stress values of the slag and the number and particle size of the crystalline particles in the slag increase with decreasing temperature.     

Effects of matrix viscoelasticity on drop deformation in dilute polymer blends under slow shear flow

The deformation of a single drop in a flowing dilute polymer blend is here investigated for slow steady shear, through video-enhanced microscopy and image analysis. The data are interpreted in terms of a perturbative solution of the fluidodynamic problem for small drop deformations, where effects of matrix viscoelasticity are taken into account. It is found that drop orientation towards the shear direction is directly linked to normal stresses in the matrix fluid.     

Investigation of spreading of surfactant mixtures

Binary surfactant mixtures have been much studied over the years for both great practical and theoretical importance. However, the mechanisms different nonionic surfactant types follow during aggregation into mixed micelles, and probably while forming a mixed surfactant adsorption layer are very poorly understood. Furthermore, the explanation for non-ideal behaviour of trisiloxane surfactant mixtures is still lacking. We have investigated binary mixtures of two commercial superspreaders, Silwet L-77^® and Additive 67^®, with conventional Triton X-100^® surfactant. Observed non-ideal behaviour has been proven to be largely dependent on both total concentration of the binary surfactant mixture and the hydrophobicity of the substrate which it is spreading on. In addition to that, synergistic and antagonistic effects have been revealed and explanations for the observed strange behaviour suggested, with steric problems due to differences in geometry of the surfactant molecules being the key factor. We also showed that present impurities in commercial surfactants can play a major role in the performance of binary surfactant mixtures and that for certain applications mixtures of trisiloxanes with conventional surfactant can be more efficient than trisiloxanes alone.     

Droplet impact and spreading: Droplet formulation effects

This work investigates a food application, where 2.8 mm droplets containing maltodextrin DE5 at 20 and 40 wt% in water, impact a smooth anhydrous milkfat surface at 1.7 to velocities. Results show that greater maximum spread diameters are achieved with the higher impact velocities and lower viscosity droplets. Incorporating surfactants to lower the liquid-vapour interfacial tension (from 72 to did not affect the maximum spread diameter but significantly limited droplet recoil, giving final spreading extents that cover close to three times the surface area compared to droplets without the surfactant. From these results, simple formulation and operating guidelines are proposed to achieve a maximum final droplet spread diameter for air-suspension particle coating operations.     

Numerical simulations of drop impact and spreading on horizontal and inclined surfaces

The phenomenon of drop spreading is important to several process engineering applications. In the present work, numerical simulations of the dynamics of drop impact and spreading on horizontal and inclined surfaces were carried out using the volume of fluid (VOF) method. For the horizontal surfaces, the dynamics of impact and spreading of glycerin drops on wax and glass surfaces was investigated for which the experimental measurements were available [Šikalo, Š., Tropea, C., Ganic, E.N., 2005a. Dynamic wetting angle of a spreading droplet. Experimental Thermal and Fluid Science 29, 795-802; Šikalo, Š., Tropea, C., Ganic, E.N., 2005b. Impact of droplets onto inclined surfaces. Journal of Colloid and Interface Science 286, 661-669]. The influence of surface wetting characteristics was investigated by using static contact angle (SCA) and dynamic contact angle (DCA) models. The dynamics of drop impact and spreading on inclined surfaces and the different regimes of drop impact and spreading process were also investigated. In particular, the effects of surface inclination, surface wetting characteristics, liquid properties and impact velocity on the dynamics of drop impact and spreading were investigated numerically and the results were verified experimentally. It was found that the SCA model can predict the drop impact and spreading behavior in quantitative agreement with the experiments for less wettable surfaces (SCA>90^°). However, for more wettable surfaces (SCA<90^°), the DCA observed at initial contact times were order of magnitude higher than SCA values and therefore the DCA model is needed for the accurate prediction of the spreading behavior.     

‘Non-solvent’ heat resistant binders: rheology of blends of oligoimides with liquid oligomers

The rheology of binders based on blends of powdery oligoimides with liquid epoxy and acrylic oligomers was studied for a broad interval of concentrations, temperatures and shear rates. It was shown, that prehistory of blends, phase organization of a system and the extent of approaching the equilibrium state determine the rheological behavior of blends. At equilibrium, depending on the state variables, the investigated blends can be single-phase or two-phase. Furthermore, the coexisted phases are not uniform and are characterized by a complex supermolecular structure of composites. In some cases the original blends have not sufficient time to reach the equilibrium state by the beginning of the rheological test, and the system structure evolution to the equilibrium occurs during the experiment. In terms of rheology some structural transformations act in the same direction and the others act in the opposite direction promoting simultaneously both an increase and a decrease in viscosity, affecting the rheological behavior of the system. The experimental dependence of rheological parameters can be explained within the framework of the following conception: structural transformations have thermodynamic nature, they are kinetically controlled and, depending on external factors, can proceed sequentially and/or simultaneously, at the molecular, supermolecular, phase and morphological levels.The resulting data allowed determination of the most perspective compositions of binders based on oligoimides and liquid ‘temporary’ plasticizers as well as the optimal processing conditions.     

Sheet formation during drop deformation and breakup in polyethylene/polycarbonate systems sheared between parallel plates

A polycarbonate drop was sheared inside a polyethylene matrix in a transparent rotating parallel plate device at 220 °C and low shear rates. A flat sheet was formed during the initial shearing of the drop. The drop then developed into either a thin thread or a sheet with a thin cylindrical tip. Sheet formation was found to occur at a critical strain or time. A stress ratio (S_r) between the matrix breakup stress, made up of the matrix normal stress and viscous stress, and the drop restoring stress, made up of the drop normal stress and the interfacial stress, is used to characterize the sheet formation during the drop deformation and breakup process. It was found that the viscosity ratio (η_r), stress ratio (S_r) and Deborah number (De) of the system could be used to predict the drop deformation and breakup.     

A rheology theory and method on polydispersity and polymer long-chain branching

Model calculations were performed to investigate the sensitivity of zero-shear melt viscosity (η₀ or Eta0) on the molecular weight (MW) polydispersity of linear polymers. Simulated MW distributions (MWD) were generated with the generalized exponential (GEX) distribution function for various levels of polydispersity M_w/M_n and M_z/M_w. For linear entangled polymeric chains in the melt, the linear viscoelastic properties were predicted by using the double reptation blending rule and the so-called BSW relaxation time spectrum, named after the authors: Baumgaertel, Schausberger and Winter [Baumgaertel M, Schausberger A, Winter HH. Rheol Acta 1990;29:400-8]. Published rheological parameters appropriate for polyethylene were used in the calculations. It was found that Eta0 depended mostly on M_w, but it also significantly depended on the extent of high-MW polydispersity M_z/M_w. A revision to the fundamental MW dependency of Eta0 was proposed to compensate for this polydispersity effect. To offset the polymer polydispersity differences, we propose a new MW average (M_HV or M_x with x = 1.5) to replace M_w in the historical rheological power-law equation of Eta0 ∝ M_w^a, where the literature value of exponent “a” ranges from 3.2 to 3.6. The use of M_HV instead of M_w in the power-law equation made the calculated Eta0 independent of the sample high-MW polydispersity. With the removal of the complication from polydispersity effect, the new Eta0 power law can now provide a more robust base for studying polymer long-chain branching (LCB). A new LCB index is thus proposed based on this new melt-viscosity power law. The values of M_HV in the new power law can be calculated for polymer samples from the conventional gel permeation chromatographic (GPC) slice data.     

Conductivity of carbon black-based polymer composites under creep in the molten state

The mechanical deformation of conductive polymer composites during melt processing affects their final electrical properties considerably. To get an insight in this relationship, simultaneous electrical-rheological measurements can be used to follow the changes in composite phase structure induced by defined deformation. In this work, the evolution of electrical conductivity was investigated during and after shear deformation at constant stress. From the experiments performed it can be concluded, that the flow-induced build-up mechanism leads to the formation of conductive pathways with enhanced stability compared to the structures build-up under quiescent conditions. This finding can be explained by the orientation of particle structures in the shear direction. Therefore, materials with different deformation history but the same electrical conductivity can display markedly different electrical behaviour under deformation.     

Apparent elongational viscosity of dilute polymer solutions

Apparent elongational viscosity studies were made on dilute solutions of high molecular weight polymers using a fiber spinning apparatus designed for low shear viscosity liquids with substantial elongational effects. The experimental method involved the flow of solutions of polyacrylamide and poly(ethylene oxide) from a tube into an evacuated vessel. Experimental results showed that the apparent elongational viscosity obtained from the jet shape increased linearly with the stretch rate.     

A new monomeric FRET-acceptor for polymer interdiffusion experiments on polymer dispersions

The properties of the non-fluorescent dye [1-(4-nitrophenyl)-2-pyrrolidinmethyl]-acrylate (NPP-A) have been evaluated with respect to its use in Fluorescence resonant energy transfer (FRET) experiments in polymers. NPP-A is attractive as a FRET-acceptor because its absorption spectrum has good spectral overlap with the emission spectrum of phenanthrene, where the latter is a widely used donor. Importantly, NPP does not fluoresce and therefore does not interfere with time-resolved measurements of the donor fluorescence. The label is well compatible with free radical polymerization. For two polymers, namely (butyl acrylate)-co-(methyl-methacrylate) (50/50) and (butyl methacrylate), the Förster radii were determined from the dependence of the FRET efficiency on the concentration of the acceptor. The results agree within the error. The Förster radius of the phenanthrene–NPP donor–acceptor pair was determined as R₀ = 2.47 ± 0.03 nm.     

Synthesis of polymeric pour point depressants for Nada crude oil (Gujarat,India) and its impact on oil rheology

Five flow improvers have been synthesized to study rheological properties of Nada crude oil (Gujarat, India). Anhydride copolymers were prepared making use of the copolymerization of acrylates of different alkyls with maleic anhydride and the Poly (n-alkyl acrylates-co-N-hexadecylmaleimide) were prepared by the reaction of copolymer with hexadecylamine. The additives were purified and characterized by FTIR, GPC. The prepared polymeric additives shows dual function both as wax dispersants and flow improvers and all of them acts as good pour point depressants. Yield stress and the viscosity of the crude oil at different temperatures and concentrations of additives were evaluated by zero friction advanced rheometer AR-500 of TA instrument. Comparison of morphologies and structures of wax crystals or aggregates in waxy crude oils beneficiated with and without a PPD was also done by micro photographic studies which show the modification in wax crystal morphology due to additives.     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.     

室内模拟硫化氢对聚合物粘度影响研究方法的建立

针对配注污水中因硫化氢气体的存在导致所配聚合物溶液粘度损失严重,其含硫化氢污水取样后室内很难存储问题,开展室内合成硫化氢,建立室内研究硫化氢对聚合物粘度影响实验方法。该研究方法为:盐酸与硫化钠反应后生成一定量的硫化氢,以氮气为载气通入聚合物溶液中,考察硫化氢对聚合物溶液粘度的影响。通过控制载气流量、吹脱温度、酸滴加速度确定硫化氢的最佳生成条件,从而确定硫化氢对聚合物粘度影响的最佳室内模拟条件。通过实验研究最终确定反应温度为80℃、氮气流量为0.1L/min、盐酸在5min内滴加完成,在该反应条件下可以准确评价硫化氢对聚合物溶液粘度影响。     

高固含量聚合物乳液黏度的影响因素

综述了乳液粒径及分布、乳化剂、引发剂、单体配比、反应温度、功能单体、pH值等对聚合物黏度的影响,确定了实现高固含量低黏度乳液的最佳条件。     

NMR, conductivity and DSC study of Li transport in ethylene glycol/citric acid polymer gel

In this present paper the influence of viscosity on the ionic dynamics of polymer gel electrolytes prepared by the Pechini polymeric precursor method is investigated by impedance spectroscopy, differential scanning calorimetric (DSC) and NMR techniques. Polymer gel electrolytes are formed by ethylene glycol (EG) and citric acid (CA) and lithium perchlorate. Room temperature conductivity of the order of 2.3 × 10⁻⁴ S/cm was obtained for the sample of EG/CA:LiClO₄ with lower viscosity (η = 197 cP). The results show that the ionic conductivity of the electrolytes increases for decreasing viscosity. Proton (¹H) and Lithium (⁷Li) NMR lineshapes and spin-lattice relaxation times were measured as a function of temperature and viscosity (197-868 cP). The ⁷Li relaxation process was found to be dominated by quadrupolar couplings. The activation energy extracted from the ¹H and ⁷Li relaxation data (∼0.23 eV) was found to be independent of the viscosity of the gel electrolyte. The ⁷Li NMR relaxation results indicate an increase of the lithium ion mobility with decreasing viscosity.     

A law controlling polymer recrystallization showing up in experiments on s-polypropylene

When polymers are crystallized at large supercoolings a subsequent heating is accompanied by recrystallization processes, which proceed to a fixed final melting point. We studied these processes with small-angle X-ray scattering and DSC measurements for three s-polypropylenes with different stereoregularities and co-unit contents. As is known from previous experiments, crystal thicknesses d_c depend on the crystallization temperature T_c only, being not affected by stereo defects or co-units. The new experiments, all carried out at low crystallization temperatures, again confirm this property; in plots of d_c⁻¹ versus T_c all points are located on a unique straight crystallization line. A similarly simple law controls the crystal thickness during the continuous structure reorganization on heating. Over an extended temperature range d_c⁻¹ changes linearly with temperature, guided by a unique, i.e., sample-invariant, ‘recrystallization line’. Crystallization and recrystallization lines extrapolate for d_c⁻¹ → 0 to the same limiting temperature, T_c^∞, and differ only in slope. The findings indicate that both the initial crystallization at T_c and the process of recrystallization use a pathway via a transient mesomorphic phase. The DSC thermograms of the samples show a multiple peak structure which varies with the heating rate. The SAXS results enable the peaks to be assigned to different melting processes.     

Evaluation of jet performance in drop-on-demand (DOD) inkjet printing

Inkjet printing has been widely used in many applications and has been studied for many years. However, there are not many systematic researches on the mechanism of jet formation, nor is there any reliable platform that enables us to evaluate jet performance. In this study, an approach to practically evaluate the jet stability of the dropon-demand (DOD) inkjet printing has been proposed, based on which the transient behavior of the DOD drop formation has been studied experimentally for Newtonian liquids with a range of different viscosities (1.0–11 cp) but of a comparable surface tension. For more viscous liquids, the rate of the jet retraction after a pinch-off from the nozzle was found to increase as the thread motion became more sharp and conical as a result of the shape effect. The break-up time of the jet also increased because the rate of capillary wave propagation was lower for more viscous liquids. The jet stability graph, which can be drawn in terms of jet retraction and break-up time, was employed to characterize the jetting stability, and the degree of satellite drop generation was quantitatively evaluated by two critical jet speeds. The effect of an electric pulse imposed on a piezoelectric plate inside the printhead was also studied. The single-peak electric pulse was used in this experiment for simple analysis, and the jet speed variation was measured under different operating conditions. Both the optimal dwell time and the maximum stable jetting frequency were affected by viscosity and they were explained in terms of the propagation theory.     

无规共聚聚丙烯的流变性能研究

采用毛细管流变仪对无规共聚聚丙烯(PP-R)的流变行为进行了具体分析。结果表明:PP-R的黏度随温度变化的敏感性不大;随着剪切速率的提高,PP-R的黏度明显降低(剪切变稀);入口压力降(P0)与温度和剪切速率均有关温,度升高P,0减小剪,切速率增大P,0升高。