Ibnelwaleed A. Hussein

Miscibility of hexene-LLDPE and LDPE blends: influence of branch content and composition distribution

Abstract The influences of branch content (BC) and composition distribution (CD) of hexene linear low-density polyethylene (LLDPE) on its miscibility with low-density polyethylene (LDPE) were investigated. Ziegler–Natta (ZN) and metallocene-LLDPE (m-LLDPE) were used to study the melt miscibility using rheological tools. Dynamic, steady shear and transient measurements were carried out in an ARES rheometer at 190 °C. The miscibility was revealed by the dependence of their ηo, η′(ω), G′, and N 1 ( γ ) on blend composition. The CD of LLDPE has influenced its miscibility with LDPE. The ZN–LLDPE blend with LDPE was found to be more miscible than an m-LLDPE of the same Mw and similar BC. On the other hand, a high-BC m-LLDPE (32.2 CH3/1000 C) was found to be more miscible with LDPE than a low-BC m-LLDPE (14.4 CH3/1000 C) of the same Mw and MWD. The high-BC m-LLDPE blends with LDPE were partially miscible and immiscibility is likely to develop in LDPE-rich blends. Agreement was observed between the measured rheology and theoretical predictions of Einstein, Scholz et al., Palierne, and Bousmina emulsion models.

Recent Advances in Dye Sensitized Solar Cells

Solar energy is an abundant and accessible source of renewable energy available on earth, and many types of photovoltaic (PV) devices like organic, inorganic, and hybrid cells have been developed to harness the energy. PV cells directly convert solar radiation into electricity without affecting the environment. Although silicon based solar cells (inorganic cells) are widely used because of their high efficiency, they are rigid and manufacturing costs are high. Researchers have focused on organic solar cells to overcome these disadvantages. DSSCs comprise a sensitized semiconductor (photoelectrode) and a catalytic electrode (counter electrode) with an electrolyte sandwiched between them and their efficiency depends on many factors. The maximum electrical conversion efficiency of DSSCs attained so far is 11.1%, which is still low for commercial applications. This review examines the working principle, factors affecting the efficiency, and key challenges facing DSSCs.

Thermomechanical degradation in the preparation of polyethylene blends

A Haake Rheocord 90 melt blender was used to prepare several types of commercial polyethylene samples intended for studies on blends as well as to condition the pure components. The objective was to assess whether thermomechanical degradation of polyethylenes was occurring during the ‘‘conditioning’’ process and, if so, to characterize its nature and to find ways to prevent the degradation. There was no significant evidence of molecular breakdown but, rather, abundant evidence for chain buildup and possible gel formation. Without mechanical stress, no degradation occurred. Melts were conditioned in the blender at temperatures in the range 190‐220C. Samples were characterized by dynamic viscosity ( 0 ) as well as by average molecular weight and MWD from GPC analysis, both before and after the blender experience. The rheological and GPC analyses were complemented by NMR, DSC, and TREF testing. The study included ‘‘conditioned’’ resins with and without additional antioxidants; results were compared to the properties of as-received polymers. The diAerent techniques combine to explain: the modifications that can occur due to melt blending of polyethylenes; relationships to the polymer molecular structure; and possible means for detection and prevention of degradation. Addition of adequate amounts of antioxidant is successful in prevention of degradation. Ziegler-Natta and metallocene LLDPE mixed with LDPE at diAerent temperatures showed diAerent levels of degradation depending on blender conditions. Enhancement of 0 of ‘‘conditioned’’ resins over that of the as-received resins was the best indicator of degradation and correlated with branch content of the LLDPE, with metallocene LLDPE showing highest susceptibility to degradation. # 2000 Elsevier Science Ltd. All rights reserved.

Polymer Systems for Water Shutoff and Profile Modification: A Review Over the Last Decade

Unwanted water production is a serious issue in oiland gas-producing wells. It causes corrosion, scale, and loss of productivity. One method of treating this problem is to chemically reduce unwanted water. This paper discusses the use of polymer systems for this purpose and presents a thorough review of available literature over the last decade. In this paper, field-application data for various polymer systems are summarized over the range of 40 to 150 C (104 to 302 F). These applications cover a wide range of permeabilities from 20 to 2,720 md in sandstone and carbonate reservoirs around the globe. Moreover, the review revealed that the last decade of developments can be categorized into two major types. The first type is polymer gels for total water shutoff in the near-wellbore region, in which a polymer is crosslinked with either an organic or an inorganic crosslinker. The second type is concerned with deep treatment of water-injection wells diverting fluids away from high-permeability zones (thief zones). These thief zones take most of the injected water, which results in a large amount of unrecovered oil. For the total-blocking gels, various systems were identified, such as polyurethane resins, chromium (Cr3þ) crosslinking terpolymers, Cr3þ crosslinking foamed partially hydrolyzed polyacrylamide (PHPA), and nanoparticle polyelectrolyte complexes (PECs) sequestering Cr3þ for elongation of its gelation time with PHPA. In addition, polyethylenimine (PEI) was identified to crosslink various polyacrylamide(PAM-) based polymers. The Petroleos de Venezuela S.A. (PDVSA) Research and Development Center developed a PAM-based thermally stable polymer and an organic crosslinker. The system is applicable for a wide temperature range from 50 to 160 C (130 to 320 F). For the deep modification of water-injection profiles in waterinjection wells, two systems were identified: microspheres prepared from PAM monomers crosslinked with N,N0-methylenebisacrylamide and microspheres produced by crosslinking 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with diacrylamides and methacrylamides of diamines (thermally activated microparticles known as Bright Water). This paper highlights all major developments in these areas.

Review on Polymer Flooding: Rheology, Adsorption, Stability, and Field Applications of Various Polymer Systems

Polymer flooding is one of the most promising techniques for the recovery of remaining oil from light oil reservoirs. Water soluble polymers are used to enhance the viscosity of displacing fluid and to improve the sweep efficiency. In this paper, water soluble polymers used for chemical enhanced oil recovery are reviewed. Conventional and novel modified polymers are discussed along with their limitations. The review covers thermal stability, rheology, and adsorption behavior of various polymer systems in sandstone and carbonate reservoirs. Field and laboratory core flooding data of several polymers are covered. The review describes the polymer systems that are successfully applied in low-temperature and low-salinity reservoirs. Comprehensive review of current research activities aiming at extending polymer flooding to high-temperature and high-salinity reservoirs is performed. The review has identified current and future challenges of polymer flooding.

Parametric study for saline water electrolysis: Part II—Chlorine evolution, selectivity and determination

Abstract The effect of electrolyzing concentrated chloride solutions as far as the evolution of chlorine is the main theme of this paper. Experimental determination of the amount of chlorine evolved in the gas phase and chlorine dissolved in solution is achieved using the iodometry and ascorbinometric titrations. Correlations are developed for the chlorine content as a function of the chloride concentration of the saline water. The hydrogen to chlorine ratio is determined as a criteria for the cell performance.

Density functional theory study on dye-sensitized solar cells using oxadiazole-based dyes

Abstract. Density functional theory (DFT) and time-dependent DFT(TD-DFT) modeling techniques are used to conduct a computational study of the geometry and electronic structure of oxadiazole-based organic sensitizers. A DFT study on the thermodynamic aspects of the charge transport processes associated with dye-sensitized solar cells (DSSCs) suggests that the system with 1,2,4-oxadiazole has a balance among the different crucial factors and may result in the highest incident photon to charge carrier efficiency. The dye/(TiO2)8 anatase clusters were also simulated to illustrate the electron injection efficiency at the interface. This study provides basic understanding of the impact of molecular design on the performance of oxadiazole dyes in DSSCs.

MD simulation of the influence of branch content on collapse and conformation of LLDPE chains crystallizing from highly dilute solutions

The influence of branch content (BC) on conformation of Ziegler ‐ Natta linear-low density polyethylene (ZN-LLDPE) in dilute solutions was studied by molecular dynamics simulation. Octene LLDPE with different levels of BC distributed randomly along the chain mimicking ZN-LLDPE were simulated in vacuum at 400 and 500 K. Increasing BC was found to decrease chain folding and change chain conformation. Chain conformation undergoes transition from lamellar to a more random coil-like structure near a BC of 40 branches/1000 backbone carbons. Results are in agreement with recent experimental results of Zhang et al. [Polymer 42 (2001) 3067]. Extended chains with higher BC collapse faster and form more kinks than chains with lower BC with branches acting as nucleation points for the chain collapse. At high BC, branches are observed to self-assemble away from the backbone. q 2002 Published by Elsevier Science Ltd.

Rheological evidence for high-temperature phase transitions in melts of high-density polyethylene

Melts of commercial high-density polyethylene (Mw = 36–85 × 103) were subjected to the hydrodynamics of a Haake Rheocord blender at temperatures (T) spanning the normal processing range (190–260°C), far beyond the disappearance of solid crystals at about 140°C. Torque measurements revealed a peculiar dependence on T, including transitions at about 208°C and 227°C, and non-Arrhenius behavior above and below this range. Resemblances to liquid-crystal polymer phenomena are pointed out, and the impact on the melt processing industries is discussed.

Parametric study for saline water electrolysis: Part III—Precipitate formation and recovery of magnesium salts

In this paper, the third in a series, the effect of some operating variables on precipitate formation (cathodic fouling) during saline water electrolysis is studied. The most important among these are electrolyte concentration, current density and amount of electricity. The change in pH value during electrolysis is reported. Precipitates are collected and samples are analyzed for their Mg content. Proposals are made to utilize the Mg(OH)2 precipitates as a useful by-product of the saline water electrolysis process.