Preparation and characterization of polypropylene homocomposites: Exploiting polymorphism of PP homopolymer

In this study, the properties of polypropylene (PP) homocomposites, prepared by film‐stacking followed by hot pressing, were investigated. Alpha‐ and beta‐PP served as matrices, whereas highly oriented PP tapes of the alpha form acted as reinforcement in the homocomposites. Tapes with different draw ratios (DR = 6–12) have been produced and characterized by mechanical and wide‐angle X‐ray scattering measurements. Tapes with a DR = 8 were incorporated in a cross‐ply (CP) manner in the corresponding homocomposite laminates. Specimens were subjected to static (tensile, flexural) and dynamic (instrumented falling weight impact, IFWI) tests. The thermal and thermomechanical properties of the PP tapes and homocomposites were studied by differential scanning calorimetry and dynamic mechanical thermal analysis. The homocomposite morphology was probed by polarized light microscopy, which gave evidence of transcrystalline layer at the interface between tape and matrix. The storage modulus of the CP homocomposites was improved prominently by the tape reinforcement. In static tensile tests, the homocomposites exhibited much higher stiffness and strength when compared with the neat PP specimens. However, this was accompanied with a marked reduction in the ultimate elongation. The IFWI tests showed that both alpha‐ and the beta‐PP failed in macroscopically brittle manner, whereas the corresponding homocomposites failed in semiductile way. The homocomposite laminates prepared with beta‐PP matrix exhibited higher resistance to penetration than those with alpha‐PP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Method for FIR filters design with compressed cosine using Chebyshev's norm

This paper considers a new method for FIR filters design. The method uses an L_∞ optimality norm. To achieve a better approximating effect, a new modulating function which compresses the oscillations of the cosine is proposed. A parameter sets the gradient of the modulating function, with respect to the oscillations’ compression. The approximating polynomial is carried out using Remez’ exchange algorithm. An optimal polynomial with lowest possible (four) degree, that approximates an ideal filter's response with high precision is proposed. With the proposed method a FIR filter with arbitrary specifications can be designed. Design examples of FIR filters with a minimization of calculation are performed. The obtained filter's responses are close to the ideal response. The design examples demonstrate that the proposed approach may be a good alternative in several applications.     

Microhardness under strain. III. Microhardness behavior during stress-induced polymorphic transition in blends of poly(butylene terephthalate) and its block copolymers

The microhardness (H) technique was recently applied to poly(butylene terephthalate) (PBT) and its multiblock copolymer of poly(ether ester) (PEE) type for examination of the stress-induced polymorphic transition. In the present study, these investigations are extended to blends of PBT and PEE. For this purpose, drawn and annealed with fixed ends at 170°C for 6 h in vacuum bristles of PBT–PEE, blends were characterized with respect to their microhardness at various stages of tensile deformation. H was measured under stress, with each step of deformation amounting 5%. The variation of H with strain (ε) shows 2 sharp stepwise decreasing values (by 40%). Each step is defined in a relatively narrow deformation (ε) range (2–5%) due to the stress-induced α → β polymorphic transitions arising in PBT crystallites. The first polymorphic transition (at ε = 2–3%) is assigned to the PBT crystallites of the homopolymer (homoPBT). The second transition (at ε = 25%) is associated to those crystals within the PEE copolymer. From the observation of two distinct transitions, separated by a deformation interval of ε = 20% it is concluded that (1) homoPBT and the PBT segments from PEE crystallize separately (no cocrystallization takes place), and (2) the 2 species of PBT crystallites are subject to the external mechanical loading, not in a simultaneous manner, but in a two-stage process. In the deformation range between the 2 transitions (ε = 2–3% and 25%), it is pointed out that conformational changes are induced through stretching, mainly in the amorphous regions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2271–2276, 1998     

DSC and TGA studies of the behavior of water in native and crosslinked gelatin

Water molecules absorbed into gelatin are found to be only partially crystallizable. The fraction of noncrystallizable water depends on whether the gelatin is native or crosslinked, and on the crosslinking conditions as well. This dependence is explained by the T_g‐regulation effect newly proposed by Rault and coworkers for water‐swollen gelatin cooled below 0°C. According to this effect, a part of the frozen water cannot crystallize because during the cooling the amorphous gelatin–water phase becomes glassy before the water crystallization temperature is reached. During the heating of water‐plasticized gelatin samples in a TGA cell, the crystallizable water separates from the gelatin, mainly in the temperature interval 50–100°C, whereas the noncrystallizable water leaves the gelatin gradually over the entire temperature interval investigated, up to 300°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 465–470, 1999     

Relay protection operation for faults on Nyseg's six-phasetransmission line

This paper describes the performance of the protection system used for the first commercially operated six-phase transmission line in the world-New York State Electric & Gas's 93 kV (phase to phase and phase to ground) line from Goudey Station to Oakdale substation (USA) during faults in the winter of 1993. The paper briefly describes the basics of the High-Phase Order Transmission Demonstration Project and the integration of available state of the art microprocessor based relays, with a programmable logic relay (designed for the protection of conventional three-phase systems) in a hierarchical six-phase protection system. The operation of the protection system during two faults on the line in January and February 1993 is reported. The modeling of the six-phase line in a conventional three-phase short circuit study program is also considered and a comparison between the measured and calculated fault currents is presented     

Optimale bedingungen zur gewinnung von Raney-Nickel mit maximaler entschwefelungseigenschaft

Desulphurization properties of Raney Nickel obtained from 50% of nickel-aluminium alloy by treatment with various concentrations of sodium hydroxide at different temperatures were studied as a function of the specific surface absorbed hydrogen as well as of the residual aluminium. The Raney Nickel obtained by treatment of the starting alloy with 10 and 26% of sodium hydroxide at 50°C and 80°C possesses maximum desulphurization ability on low molecular organic compounds. The skeletal metal obtained consists of coarse particals with a minimum content of residual aluminium and a very high specific surface. The Raney Nickel obtained from removal of aluminium from the starting alloy by 2% of sodium hydroxide at 20°C is characterized by a considerable amount of residual aluminium, very low specific surface and high degree of dispersity. The Raney Nickel obtained under these conditions is most effective for desulphurization of high molecular compounds in aqueous medium.     

Polystyrene–fluorohectorite nanocomposites prepared by melt mixing with and without latex precompounding: Structure and mechanical properties

Sodium fluorohectorite (FH) was dispersed in polystyrene (PS) by direct melt blending with and without a master batch composed of PS and FH and produced by latex compounding. FH was not intercalated by PS when it was prepared by direct melt compounding. In contrast, FH was well dispersed (mostly intercalated) in PS via the PS‐latex‐mediated predispersion of FH following the master‐batch route. The dispersion of FH was studied with transmission and scanning electron microscopy and X‐ray diffraction techniques and discussed. The nanocomposites produced by the master‐batch technique outperformed the directly melt‐compounded microcomposites with respect to stiffness, strength, and ductility according to dynamic mechanical analysis and static tensile tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007