Vulcanization of Nitrile Rubber. Part III. Formulation and Study of Oil-Resisting Vulcanization,Based on Acrylonitrile-Butadiene Rubber

Acrylonitrile butadiene rubber (Krynac, 803) with the best system of vulcanization in presence of accelerators, and coaccelerators, is further modified by the addition of different quantities of melamine-formaldehyde resin. As compared with the blank sample without this resin, the values of optimum cure time and scorch time decrease with the addition of resin. The rate of vulcanization increases and then begins to decrease gradually at higher quantities. Higher values of tensile strength, modulus, and hardness are obtained for vulcanized samples. The elasticity and elongation at break, respectively, remain at 28% and 260% till 3.0 pphr. Even higher quantities of the added resin lead to slight decreases in the studied properties. Better properties were also obtained upon aging in fuel and in hydraulic oil.     

Polymer nanofiber‐templated fabrication and characterization of gallium oxide nanofibers consisting of granular nanoparticles

Gallium oxide (β‐Ga₂O₃) is an interesting semiconductor that has a wide bandgap and can be used as an optoelectronic material in flat‐panel displays, solar energy conversion devices and optical limiters for UV light. However, it is difficult to fabricate and process Ga₂O₃ nanofibers for actual optoelectronic applications. When the excellent processability of polymeric materials is introduced into the inorganic nanofiber fabrication process, this limitation can be easily overcome. The aim of the research reported was to prepare granular Ga₂O₃ nanofibers utilizing an electrospun polyacrylonitrile nanofiber template combined with sol‐gel technology. Ga₂O₃ nanofibers were successfully fabricated by electrospinning a solution of polyacrylonitrile mixed with gallium nitrate and subsequent calcination. The surface and bulk morphologies of the calcined nanofibers investigated using field‐emission scanning electron microscopy and transmission electron microscopy (TEM) indicated that Ga₂O₃ nanofibers were constructed by the fusion of gallium oxide nanoparticles. TEM bright‐field images combined with selected‐area electron diffraction indicated that the average diameter of the Ga₂O₃ nanofibers produced was ca 55 nm and the crystalline structure was β‐Ga₂O₃ with a monoclinic unit cell. Furthermore, the photoluminescence spectrum of the Ga₂O₃ nanofibers exhibited two strong green emission peaks and one UV emission peak. Copyright © 2010 Society of Chemical Industry     

Multiscale modeling of syndiospecific styrene polymerization

A detailed mathematical model for syndiospecific styrene polymerization based on combining features of the multigrain model (MGM) and the polymeric multigrain model (PMGM). This model has been established to predict the radial monomer concentration within the growing macro particles and the rate of polymerization. The latter, the parameters, have an effect on the molecular weight distribution (MWD). In this model, the effect of intraparticle diffusion resistance and the radius of catalyst particles on the rate of polymerization and MWD were studied. The model simulation showed the presence of a large distribution of monomer concentration across the radius of particles. It was further noticed that the diffusion resistance was most intense at the beginning of the polymerization process. For MWD, the model simulation showed that the existence of diffusion resistance led to have an increase in the molecular weight within a period of time similar to the one needed in the catalyst decay. Moreover, the validation of the model with experimental data given a good agreement results and show that the model is able to predict a correct monomer profile, polymerization rate, particle growth factor and MWD, an algorithm, which embeds physicochemical effects, has been developed to model the industrial reactors.     

Polyurethane Solvent-Based Adhesives for Footwear Applications

Polyurethane solvent-based adhesives with and without tackifier having different solid contents were prepared. Viscosity of adhesives was found to increase with increasing resin content. Peel strengths of adhesives before and after aging were measured on PVC-Leather substrates and TPR-Leather substrates. It is found that the tackifier improves the adhesive strength of the polyurethane. In the case of TPR-Leather substrates all adhesives give good performance immediately on application of adhesive whereas in the case of PVC-Leather substrates good results are achieved only after 24 hrs of application. Shelf-life of the adhesives is found to be 6 to 12 months.     

Chemically stable electrospun NiCu nanorods@carbon nanofibers for highly efficient dehydrogenation of ammonia borane

We describe the preparation of bimetallic NiCu nanorods (NRs) incorporated on carbon nanofibers (NFs). The synthesis nanofibers were prepared by low cost and facile technique; electrospinning. Typically, sol–gel consisting of nickel acetate, copper acetate, and poly (vinyl alcohol) was electrospun. Sintering of the electrospun nanofiber mats in argon atmosphere led to partial elimination of the utilized polymer and abnormal decomposition of the metallic acetates to finally produce NiCu nanorods incorporated in carbon nanofibers. The as-obtained nanofibers were characterized by SEM, FE-SEM, XRD, TGA, XPS, TEM, and TEM-EDX standard techniques. The introduced bimetallic nanofibers revealed superior catalytic activity toward hydrogen release from ammonia borane. Also, they showed a good chemical stability due to covering the bimetallic nanorods by carbon shells. Interestingly, nanofibers were reused for 6 successive cycles with good catalytic activity. Moreover, the prepared nanofibers showed low activation energy about 28.9 kJ/mol. Finally, development of new catalytic materials in the field of energy is considered as a key objective of the modern research.     

Synthesis and characterization of waterborne polyurethane acrylate copolymers

Polyurethane acrylate copolymers were synthesized by emulsion polymerization process. To reduce the environmental hazards, organic solvents were replaced by eco-friendly aqueous system. Concentration of polyurethane and acrylate monomer was varied to investigate the effect of chemical composition on performance properties of copolymers. FTIR spectroscopy was used as a key tool to record the chemical synthesis route. The synthesized copolymer emulsions were characterized by evaluating their particle size, viscosity, dry weight content, chemical and water resistance. Thermal decomposition was studied by thermogravimetric analysis. Scanning electron microscope was used to visualize the morphological structure of copolymers. The experimental results indicate better polyurethane acrylate compatibility till the ratio of 30/70. However, these copolymers exhibited synergistic effects between the two polymers and revealed a remarkable improvement in numerous coating properties.     

GEOCHEMICAL SIGNIFICANCE OF FATTY ACIDS IN CRUDE OILS AND RELATED SOURCE ROCKS FROM EGYPT

ABSTRACT

The acid fraction of crude oils and related source rocks of different stratigraphic units from the Gulf of Suez and Western Desert, Egypt were analyzed by GC and GC/MS. Normal alkanoic acids (n-C₉?n-C₃₀) were the dominant series (with the predominance of even-carbon numbers maximizing at n-C₁₆, n-C₁₈ or n-C₂₂while iso- and anteiso- branched acids were minor constituents. All samples showed a preference of short chain acids (n-C₁₀?n-C₁₉ with respect to long chain acids (n-C₂₀+) typical of marine oils and source rocks. The n-alkanoic acids distribution suggests a predominant algal and/or bacterial contribution. The presence of high relative abundance of mono and di-unsaturated carboxylic acids in a number of samples point to recent microbial activity. Distributions of n-alkanoic acids in the range (C₁₂?C₂₂) show striking similarities with the n-alkane distributions, indicating that both series may, at least in part, be diagenetically related by decarboxylation of the acids. Dehydroabietic acid has been identified in only one sample from Balaim Marine source rock. This resin-derived compound has probably been transported as pollen to the marine environment.     

A Novel and Expedient Approach to New Thiazoles, Thiazolo[3,2-a]pyridines, Dihydrothiophenes, and Hydrazones Incorporating Thieno[2,3-b]thiophene Moiety

This paper reports details about the synthesis of a series of novel functionalized symmetrical bis-heterocyclic compounds containing a thieno[2,3-b]thiophene motif. Bis-thiazole derivatives 2, 3a-c and thiazolo[3,2-a]pyridine derivatives 4a-c are achieved. The hitherto unknown dihydrothiophene derivatives 6a-dvia bis-pyridimium salt 5 are obtained. Additionally, the novel hydrazonothieno[2,3-b]thiophene derivatives 10a-c are obtained via bis-tosylacetylthieno[2,3-b]thiophene derivative 9. All compounds are characterized by (1)H-, (13)C-NMR, GCMS, IR, and UV-vis spectrometry. These compounds represent a new class of sulfur and nitrogen containing heterocycles that should also be of interest as new materials.