Natural rubber–isotactic polypropylene thermoplastic blends

Thermoplastic elastomers, prepared by melt blending of natural rubber (NR) and isotactic polypropylene (PP) through a dynamic vulcanization technique, were developed during the later 1970s. However, they have certain drawbacks due to thermal degradation and higher molecular weight of NR. In the study reported here, NR was masticated to different levels prior its addition to isotactic polypropylene to improve the flow properties and to reduce the incompatibility resulting from molecular weight mismatch of NR/PP thermoplastic blends. Mixing energy curves of uncrosslinked blends and those of dynamically vulcanized blends crosslinked using different cure systems were compared. The mixing energy curves of blends containing NR of different molecular weight (M _n) and two grades of PP (injection and film grades) were also compared. Technological and processing properties of the dynamically vulcanized (sulphur and peroxide cure systems) and unvulcanized blends were compared with those of the samples containing unmasticated NR. The results indicated that a number average molecular weight in the range 4 × 10⁵ for NR increased the procoessability without significantly affecting the technological properties of NR/PP thermoplastic blends. Among the three cure systems studied Luperox 101 and dicumyl peroxide gave better technological properties than the sulphur‐cured samples. Two antioxidants, viz. quinoline (TDQ) and imidazole (MBI) type, were tried in NR/PP blends. It was found that TDQ imparts better aging resistance compared to MBI. The improvement in processability due to the reduction in molecular weight of natural rubber by mastication is more noticeable in the case of peroxide vulcanized blends compared to sulphur vulcanized samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2063–2068, 2004     

Two new aluminophosphates, IST-1 and IST-2: First examples of a dual templating role of water and methylamine in generating microporous structures

This study is aimed at exploring the ability of very small sized N-bearing molecules to generate and stabilize microporous aluminophosphates. Two new AlPO₄-n materials, called IST-1 and IST-2, have been obtained in aqueous media using, as main template, methylamine (MA), directly added, or generated in situ from methylformamide (MF) degradation. While IST-1 topology proved to be novel, IST-2 appears structurally related to AlPO₄-53(A). The obtained materials were characterized by powder XRD, TG/DSC, SEM and solid-state NMR. Tetraalkylammonium (TEA) cations were used as potential co-templates but only MA and water were found incorporated in the pore volumes of both structures, which argues for their true templating role. In IST-1, ¹³C solid-state NMR studies showed that half of MA species, presumably protonated, is H-bonded to framework oxygens while the other half surprisingly bonds directly to framework Al atoms. ¹³C NMR showed that only protonated MA occurs in IST-2 channels. TEA⁺ cations definitely do not play any specific template role. They indirectly favor the crystallization of IST-1 or IST-2 devoid from other crystalline or amorphous side phases, by interacting with part of the Al and P in solution and forming soluble [AlPO₄(OH)]–[TEA,HMA] complexes, substantially modifying the compositions of gels precursors to each phase during nucleation and/or growth steps. While both IST-1 and IST-2 crystallize from gels of similar initial compositions, it was demonstrated that the new MA/T ratio (T = Al or P) obtained after in situ complexation was the key parameter that specifically governs the crystallization of each phase.     

Electrochemical behavior of the Ti–6Al–4V alloy coated with a-C:H films

In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the I_D/I_G ratio). Potentiodynamic corrosion tests in 0.5 mol l⁻¹ NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (E_corr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l⁻¹ aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (R_ct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces.     

LRCN-RetailNet: A recurrent neural network architecture for accurate people counting

Multimedia Tools and Applications - Measuring and analyzing the flow of customers in retail stores is essential for a retailer to better comprehend customers’ behavior and support...     

Fabrication of hybrid proton-exchange membranes using a brandnew high temperature ionic liquid as charge transporting and clay modifier

The search for more compatibility between ionic liquids (ILs) and polymer matrices in proton-exchange membrane fuel cells (PEMFCs) is one of the ways in which IL leaking from proton-exchange membranes could be minimized. In this work, it is presented the synthesis of an aromatic high temperature ionic liquid (HTIL), which, incorporated into an aromatic matrix such as sulfonated polyether ether ketone (sPEEK), is expected to diminish the IL leaking that normally affects PEMFC. Phenylethylammonium trifluoromethane sulfonate (PhetaTfO) was successfully synthesized and characterized. Its melting point of 88°C makes it to classify as a HTIL and it was employed as modifier of natural Montmorillonite, forming the phenylethylammonium intercalated montmorillonite (MmtPheta) and thus, ternary membranes containing PhetaTfO, MmtPheta, and sPEEK were prepared and characterized. Immersion tests demonstrated a higher compatibility of PhetaTfO with matrix when compared to the reference DemaTfO, which was reflected in up to 30% lower IL loss by the synthesized IL than the DemaTfO; X-rays diffraction (XRD) patterns demonstrated that the modified clay was properly dispersed inside the membranes, while dynamic mechanical analyses (DMA) results indicated a strong plasticizer effect along the increase of PhetaTfO content inside the membrane, while at the same time, the conductivity increased in an exponential manner, which permitted to identify an empiric exponential equation to evaluate the effect of concentration on ionic conductivity. The maximum conductivity obtained at IL concentrations of around 38 wt% was 0.2 mS/cm. It could expect high ionic conductivities of 10 mS/cm when the concentration of this IL is 60%; nevertheless, in order to achieve that, crosslinking treatments should be done to give the membranes enough mechanical resistance.     

Poly(vinylidene fluoride) with zinc oxide and carbon nanotubes applied to pressure sheath layers in oil and gas pipelines

In this work, PVDF composites containing 0.2% (m/m) of carbon nanotubes (MWCNTs), PVDF with 5.0% (m/m) of zinc oxide (ZnO), and composites containing both particles in the same contents in the matrix were melt processed in a mini-extruder machine with double screws, using the counter-rotation mode. Composites were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic-mechanical analysis (DMA), and contact angle tests (CA). The samples presented the predominance of the α phase, with an increased degree of crystallinity as well as an increase in dimensional stability by incorporating both fillers, showing a synergistic effect between these particles, as shown on FTIR, DSC, and XRD results. SEM images showed a good dispersion of high aspect ratio particles. In general, DMA and TGA analysis showed that composites had not decreased their thermal and mechanical performance when compared to neat PVDF. Results of CA analysis showed an increase in the hydrophobicity of the sample containing MWCNTs. Permeability tests were also performed using a differential pressure system, combining high temperature and pressure, obtaining permeability measures and time lag. This work presents an alternative of composite materials, suggesting its application in the internal pressure sheath layers of oil and gas flexible pipes.     

Thermal stability of polymers based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid in different temperature and salinity conditions

Partially hydrolyzed polyacrylamide (PHPA) is the most widely used polymer in enhanced oil recovery (EOR) applications. However, under conditions of high temperature and salinity, the PHPA molecules become hydrolyzed, causing a drastic reduction of the viscosity of the polymer solution due to the presence of negative charges, making the molecules more susceptible to interactions with cations. In this sense, in order to increase the stability of these polymers, an anionic monomer more resistant to cations such as 2-acrylamido-2-methylpropane sulfonic acid (AMPS) has been incorporated into the HPAM molecules. This work evaluated the thermal stability of a copolymer (acrylamide and AMPS - AN125) and a terpolymer (acrylamide, acrylate, and AMPS-FP5115) in the time course of 360 days. The tests were carried out in typical conditions of Brazilian offshore reservoirs, such as absence of oxygen, high temperature, and high salt concentration. The test method involved measurements of intrinsic viscosity in function of time and determination of the hydrolysis degree of the polymers by elemental analysis. The copolymer AN125 was more stable under the test conditions than the terpolymer FP 5115 due to the presence of a higher concentration of AMPS in the copolymer. The AMPS group was hydrolyzed to AA at a temperature of 100 °C, however, the increase in salt concentration delayed the onset of this degradation. The tests indicated that the presence of a higher AMPS content in the copolymer does not prevent the polymer from undergoing hydrolysis, but delays the polymer precipitation step in the solution.     

Production and characterization of Si-N films obtained by r.f. magnetron sputtering

Si-N films were deposited by sputtering from an Si₃N₄ target with different deposition pressures and negative substrate bias. The films were amorphous and showed a “featureless” morphology. A high oxygen content was detected in unbiased films. For these films the Si/N ratio was very high compared with the target composition, whereas for biased films the opposite was observed. Si-N films presented cohesive failures for loads as high as 21 N and adhesive failure at 45 N when they were analysed by scratch test. Very high hardness (45 GPa) was obtained, particularly for biased films. Unbiased films were softer, which is attributed to the formation of silicon oxide and/or to a lower compressive stress level.     

Behavioural responses to risk on remote outcomes

Computer mediation of communication allows interaction with events remote in space or time. However, the uptake and use of videotechnology requires an understanding of its effects upon willingness to take risks. To understand how responses to remote events are influenced by computer mediation, the present study compared responses to collocated outcomes with those conveyed over a videolink or as pre-recordings. Willingness to risk on an outcome was quantified using wagering behaviour during a simulated game of roulette: measuring preferred outcome format, levels of risk sought, and times required to make decisions. Participants tended to be more confident of winning and preferred the collocated version of roulette. Participants took greater risks with pre-recorded video outcomes and tended to spend more time locating bets. For videolinked outcomes, participants were more cautious, hedging their bets, and taking more time deliberating the odds. Although the amounts wagered did not change, a potential predictability in pre-recordings appears to encourage risk taking, while the reduced presence inherent in real-time videolinks engenders caution.     

Kolmogorov Width of Discrete Linear Spaces: an Approach to Matrix Rigidity

A square matrix V is called rigid if every matrix \({V^\prime}\) obtained by altering a small number of entries of V has sufficiently high rank. While random matrices are rigid with high probability, no explicit constructions of rigid matrices are known to date. Obtaining such explicit matrices would have major implications in computational complexity theory. One approach to establishing rigidity of a matrix V is to come up with a property that is satisfied by any collection of vectors arising from a low-dimensional space, but is not satisfied by the rows of V even after alterations. In this paper, we propose such a candidate property that has the potential of establishing rigidity of combinatorial design matrices over the field \({\mathbb{F}_2.}\) Stated informally, we conjecture that under a suitable embedding of \({\mathbb{F}_2^n}\) into \({\mathbb{R}^n,}\) vectors arising from a low-dimensional \({\mathbb{F}_2}\)-linear space always have somewhat small Kolmogorov width, i.e., admit a non-trivial simultaneous approximation by a low-dimensional Euclidean space. This implies rigidity of combinatorial designs, as their rows do not admit such an approximation even after alterations. Our main technical contribution is a collection of results establishing weaker forms and special cases of the conjecture above.