Interfacial properties of XLPE/EPDM laminates

Interfacial properties such as space charge accumulation and breakdown characteristics in crosslinked polyethylene (XLPE)/ethylene propylene diene terpolymer (EPDM) laminates were investigated. Homocharge is observed in EPDM containing 1,4-hexadiene while heterocharge is observed in EPDM containing 5-ethylene-2-norbornene. Interfacial charge develops when the EPDM is laminated with XLPE. The polarity of this interfacial charge reverses at less than a few tens of hours heat treatment at 80°C dc breakdown voltage shows a sequential change of an increase, a decrease and a slight increase as a function of heat treatment time, which holds true for both interfacial and volume breakdown voltages. A maximum breakdown voltage is observed at 20 to 24 h heat treatment. After long heat treatment, silicone grease used in the interface shows lower interfacial breakdown voltage than silicone oil for the dc case, which was attributed to the additives in the grease and the molecular weight of silicone molecules in oil and grease. Details of the results are given and their origins discussed     

Structure and operation strategies of an automatic supervisory control system for the KEPCO UPFC

The Korea Electric Power Corporation (KEPCO) unified power flow controller (UPFC) is installed at the 154 kV Kangjin substation and is operated on the Kangjin–Jangheung transmission line. This UPFC has been operated by the manual set-point control method; however, it is very difficult for the operator to determine the operation point of UPFC in real-time. This paper proposes an automatic supervisory control system for the KEPCO UPFC to overcome the limitations of set-point control and increase the efficiency of UPFC. The functions and configuration of the system are described and the operation scheme that will be applied in the system is presented. In order to validate the proposed algorithm, a prototype program is developed and some simulations are conducted using the data collected from the load dispatch center in the KEPCO system. An erratum to this article can be found at     

Effects of preferential encapsulation of glass fiber on the properties of ternary GF/PA/PP blends

Long fiber molding materials are expected to play an important role in the near future. This paper describes a series of experiments performed to examine properties of ternary blends containing glass fiber (GF), polyamide (PA), and polypropylene (PP). The continuous glass fiber was impregnated with one of the blend constituent polymers by our specially designed impregnation apparatus and cut into chips of 6 mm length. These chips and the other polymer were used to produce various testing specimens in a twin screw extruder or in injection molding machine. The results indicated that the effect of fiber addition on the mechanical and rheological properties is clearly dependent on the order of impregnation process. In the blends containing the GF/PA + PP, the GFs are preferentially encapsulated with PA, and therefore the mechanical properties are superior to the blends with the GF/PP + PA in which the PP phase is located surrounding the GFs. This improved wetting of fibers by sequential impregnation not only resulted in better properties but also protected the fibers from shear action of the screw, thereby allowing significant increase in average fiber length to be achieved in the injection molding process.     

Effect of solvent interactions on swelling and microstructure of amphiphilic polyurethane networks

Amphiphilic polyurethane (PU) ionomer networks were synthesized by urethane acrylate anionomer (UAA) precursor chains. These networks were prepared with water, dioxane (DO), and dimethyl sulfoxide (DMSO) and exhibited very different swelling behaviors in water/DO (UAADG) and water/DMSO (UAASG) solvent mixtures, which was due to the different solvent interactions between water/DO and water/DMSO. The additional important factor influencing the swelling behavior in water/aprotic solvent mixtures was the hydrophilicity of the UAA networks, which was different than the water–UAA network interaction. The microstructure of UAA networks prepared with the water/aprotic solvent mixtures was greatly influenced by the water–solvent interactions. Unlike the water/DO mixtures, which had a relatively weak water–DO interaction, the strong water–DMSO interaction largely restricted the ability of DMSO to solvate the UAA chain, which resulted in an increase in the aggregation of the hydrophobic segment and the hydrophilic/hydrophobic microphase separation. Thus, UAASG and UAADG networks showed very different swelling behaviors in the same swelling medium because of the microstructural difference between these gels, which was confirmed by dynamic mechanical measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 608–620, 2001     

Dielectric properties of epoxy‐dielectrics‐carbon black composite for phantom materials at radio frequencies

In order to develop new dry phantom materials that can simulate the effect of electromagnetic wave on human tissues, the dielectric properties of the phantom materials composed of dielectrics, carbon black, and epoxy resin were investigated. For dielectrics/epoxy composite, the dielectric constants increased with the content of dielectric powder and were independent of frequency at the measured frequency range. The dielectric constants and conductivity of carbon black/epoxy composite also increased with the carbon black, but it showed the frequency dependence that the complex dielectric constants decreased with increasing frequency. The dielectric constants and conductivity corresponding to human tissues could be obtained by combining the frequency dependence of carbon black/epoxy composite with the dielectric properties of dielectrics/epoxy composite and by adjusting the composition ratios of carbon black, dielectrics, and epoxy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1294–1302, 2000     

Salivary Biomarkers in Patients with Sjögren’s Syndrome—A Systematic Review

Sjögren’s syndrome (SS) is a chronic autoimmune disease characterized by dry mouth and dry eyes, with lymphocytic infiltration of the exocrine glands. Saliva is becoming a useful tool to determine the clinical and pathological characteristics of SS because the collection method is easy and non-invasive. Since 1900, salivary proteomic analysis has been performed continuously using a variety of optimized analytical methods. Many studies have identified distinct characteristics of salivary proteins in patients with primary SS, and the changes were related to chronic inflammation and overproduction of immunoglobulins or downregulated secretory function. Several proteomic studies using whole or parotid saliva have evaluated whether several salivary proteins can be used to discriminate SS, including salivary β2-microglobulin, calprotectin, carbonic anhydrase VI, neutrophil gelatinase-associated lipocalin, sialic acid-binding immunoglobulin-like lectin-5, and tripartite motif-containing protein 29. In addition, salivary proinflammatory cytokine levels have been reported to be increased in patients with SS. Although these candidate salivary proteins have exhibited considerable differences in patients with SS, more data are needed to confirm their role as biomarkers. Moreover, the identification of salivary characteristics that can accurately reflect disease activity, predict treatment response and prognosis, and diagnose SS is anticipated.     

Space charge behavior of acrylic monomer-grafted polyethylene

This report describes space charge behavior of polyethylene (PE) grafted with acrylic monomers such as acrylic acid (AA), methacrylate (MA), ethylacrylate (EA) and n-butyl acrylate (NBA). The specimens were 0.7 mm thick with semicon electrodes, and vacuum degassed. Heterocharge is found in ungrafted control PE. This heterocharge decreases with the increase of AA content when AA is grafted onto the PE chains. This was attributed to an enhanced charge trapping at carbonyl sites provided by AA. When other acrylic monomers are grafted, heterocharge of the control PE increases first at low graft ratios and then decreases at higher graft ratios. This change was attributed to the combined effects of alkoxy groups acting as electron donating species and carbonyls acting as charge trapping sites. It seems that charge trapping at the carbonyls is sacrificed in part by the alkoxy groups at low graft ratios. All grafted polyethylenes are found at low fields below 1×10⁵ V/cm to obey the space-charge limited conduction (SCLC) mechanism. Effective charge mobilities of PE-g-AA and PE-g-NBA decrease with the increase of graft ratio while those of others remain unchanged     

Preparation of a graphite-like pyropolymer from 6-trimethylsilyl-3,5-hexadiyn-2-one

6-Trimethylsilyl-3,5-hexadiyn-2-one was selectively 1,2-pyropolymerized under vacuum to give a black soluble polymer, poly(6-trimethylsilyl-3,5-hexadiyn-2-one) (PATA). Desilylation of PATA by KOH/MeOH afforded a highly crystalline polymer (PAEA) which is converted into a graphite-like pyropolymer by heat treatment under vacuum. The polymers were characterized by gel permeation chromatography (GPC),FT-IR, NMR, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC),Raman, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analysis.     

Solution behavior of urethane acrylate anionomer synthesized with dimethylolpropionic acid: Viscosity prediction through rheological equation of state

Urethane acrylate anionomer was synthesized incorporating dimethylolpropionic acid (DMPA) on the molecular backbone as a water-soluble oligomer. The solution behavior of the urethane acrylate anionomer was examined by viscosities as a function of the shear rate, temperature, and anionomer fraction. The logarithmic viscosities of the urethane acrylate anionomer solution followed well the Arrhenius equation and showed a linear relationship with the fraction and reciprocal temperature. So, it was possible to predict the viscosity of the urethane acrylate anionomer solution as functions of the fraction and reciprocal temperature, based on the rheological equation of state. The viscosities obtained from the equation of state successfully coincided with the results of the experiments. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1079–1088, 1998