A novel and general method of modifying hydrophobic polysulfone (PSF) to produce highly hydrophilic surfaces was developed. This method is the low‐temperature plasma technique. Graft polymer‐modified surfaces were characterized with the help of Fourier transform infrared attenuated total reflection (FTIR–ATR) and X‐ray photoelectron spectroscopy (XPS). Study results demonstrated that poly(ethylene glycol) (PEG) could be grafted onto the PSF membrane surface by low‐temperature plasma. The hydrophilic character of the modified surfaces was increased in comparison with that of the parent membrane. The contact angle for a modified PSF membrane was reduced apparently. We analyzed the effectiveness of this approach as a function of plasma operating variables including plasma treatment power and treatment time. Hence, plasma‐induced graft polymer modification of membranes can be used to adjust membrane performance by simultaneously controlling the surface hydrophilicity and hemocompatibility. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 979–985, 2000
SUMMARY Objectives To investigate the influence of various factors on air-turbine handpiece bearing failure through developing standard protocols for testing the bearing longevity. Methods Groups of four air-turbine assemblies (Synea TA-98, W&H, Dentalwerk, Bürmoos, Austria) were subjected repeatedly to a full binary combinatorial set of operating conditions: with and without lubrication, simulated clinical loading, and corrosion protection, all with autoclaving, to the point of failure. A control set was lubricated only. Lubrication (Assistina, W&H), autoclaving (ST-Im30b, Eschmann Bros & Walsh, West Sussex, England), simulated clinical loading (0.56 N at 45° to the turbine axis, after autoclaving), and corrosion protection during autoclaving (magnesium sacrificial anode) were used as required. Free-running speed (Hz) and bearing resistance (μNm) were determined (Darvell-Dyson testing machine) at baseline and after every 10 cycles until turbine failure. Three-way analysis of variance (lubrication × loading × corrosion protection) of log(cycles to failure), with α = 0.05, was used. Results All autoclaved turbines had failed by 560 cycles, while the controls failed at 960-1000 cycles. All three main effects were significant: loading (p<10−6), lubrication (p<0.0002), and corrosion protection (p<0.02), as was the interaction lubrication × loading (p<10−6). No other interaction attained significance. Conclusions Running under load was the most important factor affecting bearing longevity. While autoclaving clearly has a detrimental effect, lubrication effectively increases longevity. A sacrificial anode may be economically worthwhile to extend life further, but low-load usage patterns, as generally instructed, are confirmed as beneficial.
Polypropylene (PP) is considered a competitive candidate to replace widely used cross-linked polyethene (XLPE) in cable material application, as it can potentially withstand higher operating temperature and has excellent electrical properties. Besides, it is a more environment-friendly material, since PP does not require crosslinking and, therefore, can be easily recycled at the end of its life. This paper investigated the influence on the tensile strength, space charge and breakdown behaviours of the PP by adding polyolefin elastomer (POE) and Magnesium Oxide (MgO) nanoparticles. 10 or 20 wt. % of POE and 5 or 10 wt. % of nano-MgO were introduced into PP. Results show that the PP with 10 wt. % of PE02 and 5 wt. % of surface treated-MgO has the highest breakdown strength among all systems. Also, the introduction of POE and nano-MgO can significantly improve the mechanical flexibility. In combination with the observed suppression of space charge accumulation, which shows that PP/POE/MgO nanocomposites are a viable option for high voltage (HV) cable insulation material in the future.
A polyblend of poly(ortho esters)-poly(ethylene glycol) (POE-PEG) was prepared. The release behavior of the acetanilide-loaded film of the POE-PEG polyblend was studied. Blending POE with water-soluble PEG can promote the release of drug in pH 7.4 PBS buffer at 37°C, while POE has plasticizing effect on PEG. Infrared and X-ray diffraction studies reveal that there is some interaction between POE and acetanilide. The SEM micrographs disclose that the porosity of the drug-loaded film enhances with an increase immersing time.
An in situ titanium trialuminide (Al 3 Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg-Al-Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al 3 Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg-Al-Ti system, Al 3 Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg-Al-Ti system is almost the same as that of the Al-Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.
Background: The aim of this study was to identify the nature and causes of deterioration and failure in dental handpiece ball bearings and thus provide guidance for clinical handling for service longevity. Methods: The bearings of 36 turbine assemblies were dismantled for visual inspection, documented using a digital camera, and examined using scanning electron microscopy, as appropriate. Results: For the metal parts of the ball bearing assembly, defects observed were mainly wear arising from the running load and corrosion. This was in the form of scratches and discoloured circumferential bands on the balls, and dull or worn surfaces extending around the circumference of the raceways. Cage damage including cracking, fracture, surface rubbing and distortion occurred, in varying degrees, in every failed turbine. Conclusions: Dental ball bearing failure modes have been identified. Cumulative effects of damage from corrosion and mechanical factors lead to handpiece deterioration. The cage was found to be very vulnerable to damage, and this may be the key limitation on bearing lifetime. Autoclaving may contribute to that, as it does to corrosion in the absence of adequate lubrication, but this seems to be minor in comparison to the effects of abuse. There is no justification for failing to observe usage and sterilization instructions.
The present work demonstrated the first-ever preparation of block specimens by the microwave sintering of H13 alloy powder. Varying proportions of vanadium powder (1.5%, 2.5%, 3.5%, 4.5%, and 5.5% on a mass basis) were added to H13 mold steel and these mixtures were sintered using microwaves. X-ray fluorescence spectroscopy was employed to determine the compositions of the resulting specimens and vanadium percentages of 1.56%, 2.04%, 3.10%, 4.06%, and 4.20% were determined. These results demonstrate a clear trend, with significantly lower vanadium amounts than expected based on the nominal values at higher vanadium loadings. Different samples were also found to exhibit different degrees of ablation, and this effect was related to the presence of voids in the materials. The surface compositions of these specimens were examined by laser-induced breakdown spectroscopy and were found to be relatively uniform. The microstructures as well as the hardness properties of the materials were assessed. Microwave sintering of 100 g specimens at 1300 °C for 10-min generated samples with hardness values ranging from 205 HV (at the lowest vanadium content) to 175.2 HV (at the highest vanadium content). The wear behavior of samples prepared by microwave sintering H13 die steel with different vanadium contents at room temperature has been studied. The results showed that 1.5% vanadium content is the best mass ratio.
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