Small Filler Research Articles

Effect of filler fraction and filler surface treatment on wear of microfilled composites

Objectives: The aim of this study was to determine the effect of filler content and surface treatment on the wear of microfilled composites. Methods: Four microfilled composites with different filler contents (A=20, B=25, C=30, and D=35 vol.%) were made with a light-cured resin (Bis-GMA/UDMA/TEGDMA). The surface treatment of the colloidal silica in each varied: F=functional silane, NF=non-functional silane, U=untreated. Silux Plus served as a control. Specimens were made in steel molds and cured in a light curing unit Triad II (40 s/side). Abrasion and attrition wear were evaluated in vitro in a wear tester (OHSU oral wear simulator) with an abrasive slurry (poppy seeds+PMMA) and a human enamel antagonist. The average of five specimens was computed and compared using a ANOVA/Tukey's test at P≤0.05. The surface of the wear patterns and the distribution of filler particles were examined using a scanning electron microscope and digital imaging. Results: As filler volume increased, wear was reduced regardless of filler treatment. Amounts of wear for specimens C and D were significantly lower than specimens A and B. Composites with functional silane treated microfiller (Group F) produced significantly less wear than those with non-functional microfiller (Group NF) at 30 and 35 vol.%, and less than the untreated microfiller (Group U) at 30 vol.%. Scanning electron microscopy of specimens of group NF showed large filler agglomerates (size >1 μm) in the resin matrix, while specimens of group F and U showed fewer agglomerates. Digital imaging analysis revealed small filler clusters (size ≤1 μm) in the resin matrix of all specimens. Significance: Wear resistance of microfilled composites is enhanced by higher filler volumes irrespective of surface treatment, but good filler/matrix adhesion is needed to minimize wear.

Near-Interface Structure and Mobility of Polymeric Chains in Polymer-Based Nanocomposites

ABSTRACTThe effect of a curved solid wall on the conformations of long, flexible polymer chains is studied in a dense polymer system and in the athermal limit by means of lattice Monte Carlo simulations. It is found that the wall does not perturb the atom number density, which is constant throughout the volume of the polymer, however the chain end density is higher at the wall compared to the bulk. The segregation effect decreases with increasing wall curvature. The bonds are preferentially oriented in the direction tangential to the wall over a two-bond thick layer next to the wall. When probing the preferential orientation on the chain segment length scale, the perturbed region has a thickness on the order of the probing metric considered. The chain mobility is evaluated by computing the bead diffusion coefficient in the direction perpendicular and tangential to the curved wall, and as a function of the distance from the interface. The bead mobility is reduced in a two-bond-thick layer in the vicinity of the wall in both the normal and tangential directions, the reduction being more pronounced in the normal direction. The mobility is seen to decrease with increasing wall curvature. The reduction is most pronounced when the particle size becomes smaller than the chain radius of gyration in the bulk, situation in which the average chain surrounds the particle, which hence becomes an effective entanglement site for the chains. This explains in part the increased strength of polymer-based nanocomposites with small fillers.

Transgene repeats in aspen: molecular characterisation suggests simultaneous integration of independent T-DNAs into receptive hotspots in the host genome.

Rearrangements of T-DNAs during genetic transformation of plants can result in the insertion of transgenes in the form of repeats into the host genome and frequently lead to loss of transgene expression. To obtain insight into the mechanism of repeat formation we screened 45 transgenic lines of aspen and hybrid aspen transformed with six different gene constructs. The frequency of T-DNA repeat formation among randomly screened transgenic lines was found to be about 21%. In ten transgenic lines direct repeats were detected. An inverted repeat was found in one other transgenic line. Sequencing of the junctions between the T-DNA inserts revealed identical residual right-border repeat sequences at the repeat junctions in all ten transgenic lines that had direct repeats. Formation of "precise" junctions based on short regions of sequence similarity between recombining strands was observed in three transgenic lines transformed with the same plasmid. Additional DNA sequences termed filler DNAs were found to be inserted between the T-DNA repeats at eight junctions where there was no similarity between recombining ends. The length of the filler DNAs varied from 4 to almost 300 bp. Small filler DNAs--a few base pairs long--were in most cases copied from T-DNA near the break points. The large filler sequences of about 300 bp in two transgenic lines were found to be of host plant origin, suggesting that transgene repeat formation occurred as a result of the simultaneous invasion of a receptive site in the host genome by two independent T-DNA strands. On the basis of the results obtained, and in the light of previous reports on T-DNA/plant DNA junctions in aspen and other crop plants, a mechanistic model for transgene rearrangement and filler formation is suggested.

Dynamics of surface directed mesophase formation in block copolymer melts

The dynamic mean-field density functional method is adapted to describe phase separation in the presence of geometrical constraints. We observe that inclusion of small filler particles (such as rods) already has a dramatic effect on the morphology of polymer melts. The effect is comparable to the effect of applied simple steady shear. Mesostructures in the presence of large filler particles such as plates are totally governed by the geometry of the particle. Effects of polymer–surface interactions on morphology formation are investigated in detail.

Analysis of a series resonant converter by PWM control

Submarine optical-fiber transmission systems are finding greater application in supporting an increasing volume of global-level data transmissions. As a result of this development, the power feeding equipment that supplies power to submarine repeaters now plays a key role in the operation of communication systems. To ensure that a constant current is maintained, pulse frequency modulation (PFM) is being used to control series resonant converters commonly employed in power feeding [1]. Power feeding systems supply rated current during stable operation. However, when they start supplying current, power feeding systems must gradually increase current from zero to the rated current. If cable failures occur, a dc current lower than the rated current or the dc current overlaid with an ac current is used to detect fault locations and wiring routes. PFM control must control operating frequencies from zero frequency to control output current from zero amperes. However, controlling the frequency from zero leads to such problems as the requirement of large smoothing filters, saturation of the transformer core, and generation of acoustic noise. To date, a number of solutions have been suggested. However, most of these solutions require the addition of components that handle electric power [2–5]. This paper reports a series resonant converter that employs PFM around rated current, and pulse width modulation (PWM) below the rated current to avoid inverter transformer saturation and acoustic noise at low frequencies and to make the use of small filler circuits practical [6, 7]. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(1): 1–10, 1999

Soldadura de aleaciones de aluminio con láseres de Nd:YAG de alta potencia

Aluminium alloys have good mechanical properties (high strength-to-weight ratio, corrosion resistance) and good workability. Their applications are growing up, specially in the transportation industry. Weldability is however poorer than in other materials; recent advances in high power YAG lasers are the key to obtain good appearance welds and higher penetration, at industrial production rates. Results of the combination of high power YAG beams with small fiber diameters and specific filler wires are presented. It is also characterized the airborne particulated material, by-product of the laser process: emission rates, size distribution and chemical composition are given for several aluminium alloys.

Two-Dimensional Thermal Stress Analysis in Adhesive Butt Joints Containing Hole Defects and Rigid Fillers in Adhesive Under Non-Uniform Temperature Field

This study is concerned with the thermal stress analysis of an adhesive butt joint which contains circular holes and rigid fillers in an adhesive and is under a non-uniform temperature field. In the analysis, the adherends are assumed to be rigid and the adhesive is replaced with a finite strip having holes and rigid fillers in it and the thermal stress distribution in the adhesive is analyzed using a two-dimensional theory of elasticity. The effects of size and location of the circular holes and rigid fillers on the stress distributions at the interface and at the hole and filler peripheries are clarified by numerical calculations. For verification, photoelastic experiments were performed using an epoxide resin plate with small holes and fillers in it, to model and adhesive in the joint. The analytical results are fairly consistent with the experimental ones.

Bruxing-type dental wear simulator for ranking of dental restorative materials.

An instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.

Mechanisms of particulate filled polypropylene finite plastic deformation and fracture

The plastic deformation and fracture of aluminium hydroxide filled polypropylene has been investigated. A transition between two mechanisms with an increase of the filler volume fraction has been observed. Below a critical filler volume content φcr ≈ 20 vol% (designated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles occur in an uncorrelated manner. Above this critical value (designated region 2) exfoliation along the surface of the initial portion of inclusions causes the formation of craze-like deformation zones transverse to the direction of the loading. The concentration of craze-like zones is essentially determined by the filler content and the level of interphase interaction which in turn depends on the particle size. In region 1 deformation occurs in a macro heterogeneous way with the formation and growth of a neck. The elongation to break decreases with an increase in the mean diameter of the filler phase. At φ>φcr composites, filled with small particles, fail in quasi brittle manner with the formation of a short and narrow neck. In contrast to the case for a small filler concentration, an increase of the inclusion size leads to an increase in the ultimate elongation and a tendency to macro homogeneous yielding. An explanation of the observed behaviour is proposed based on a change in adhesive failure conditions with filler content and size.

Microporous polypropylene hollow fibers with double layers

Microporous polypropylene hollow fibers with double layers were prepared by stretching double layered polypropylene microtubes containing poly(methylsilsesquioxane) fillers: the relatively smaller filler in the inner layer and the relatively larger filler in the outer layer. The resultant hollow fibers have a finely interconnected fibrous texture parallel to the fiber axis. Water permeability of the hollow fibers was studied in relation to the thickness ratio of the inner layer/outer layer.

Simulations on the reinforcement of poly(dimethylsiloxane) elastomers by randomly distributed filler particles

Monte Carlo computer simulations were carried out on filled networks of poly(dimethylsiloxane) (PDMS), which were modeled as composites of crosslinked chains and randomly arranged spherical filler particles. The primary concern of the investigation was the effect of the excluded volume of these particles on the elastomeric properties of the polymers. Calculations were carried out for PDMS chains with different molecular masses between crosslinks, and for filler particles with different sizes and at various volume percentages. Distributions of end-to-end vectors for both unfilled and filled networks were obtained using Monte Carlo simulations based on rotational isomeric state (RIS) theory. More extended configurations, with a higher end-to-end distance, were observed for networks filled with smaller particles. The nominal stress f* and the modulus or reduced nominal stress [f*] were calculated from the distributions of end-to-end vectors using the Mark-Curro approach. Relatively small filler particles were found to increase the non-Gaussian behavior and to increase the normalized moduli above the reference value of unity. Temperature effects on the stress were also investigated. © 1996 John Wiley & Sons, Inc.

Effect of shape and size of silanated fillers on mechanical properties of experimental photo cure composite resins.

The binary system of hybrid fillers selected from four irregular fillers (1.7-21.5 microns), five spherical fillers (0.46-31.2 microns), and a microfiller of 0.04 micron, were applied to photo cure composite resin and mechanical properties were measured. The strength for the hybrid of irregular and spherical fillers tended to increase as the size of component fillers decreased. The strength for the hybrid of the same fillers in shape also increased as the size of fillers decreased. The strength for the hybrid containing 30% microfiller showed the same trend, especially, the largest strength was obtained from hybrids containing small spherical fillers.

Two-Dimensional Thermal Stress Analysis in Butt Adhesive Joints Containing Hole Deffects and Rigid Fillers in Adhesive.

This study is concerned with the thermal stress analysis of a butt adhesive joint which contains circular holes and fillers in the adhesive and is under non uniform temperature held. In the analysis, the adherends and fillers are assumed to be rigid and the adhesive is replaced with a finite strip containing holes and rigid fillers and the thermal stress distribution in the adhesive is analyzed using a two-dimensional theory of elasticity. The effects of size and location of circular holes and rigid fillers on the stress distributions at the interface and at the filler and hole peripheries are clarified by numerical calculations. For verification, photoelastic experiments were performed using an epoxide resin plate containing small holes and fillers, to model an adhesive in the joint. The analytical results were fairly consistent with the experimental ones.

Microporous polypropylene hollow fibers with double layers

AbstractMicroporous polypropylene hollow fibers with double layers were prepared by stretching double layered polypropylene microtubes containing polymethylsilsesquioxane fillers: the relatively smaller filler in the inner layer and relatively larger filler in the outer layer. The resultant hollow fibers have a finely interconnected fibrous structure parallel to fiber axis. Their N2 gas permeabilities were measured to estimate the fibrous structure: tortuosity factor, effective porosity, and pore size. © 1995 John Wiley & Sons, Inc.

Argon‐arc surfacing with pulsed filler wire feed in repair of components

Surfacing can be used to eliminate various service defects. These can be wear, burning or melting of the working surfaces or edges of blades, labyrinth seals and other important components in aircraft engines produced from creep-resisting, chromium-nickel cast and deformed alloys. Service defects can be repaired by various methods of arc fusion welding as well as by diffusion bonding and brazing. However, fusion welding is the simplest and most universal process, which does not require complicated equipment, a large number of operators and large production areas. At the same time, the method is suitable for processing a wide range of components and sections. When surfacing components of aviation engines (such as seals, blade, edges, discs, etc), problems occur because the dimensions of surfaced elements are small, the space between them is not large and components are often load-carrying. Therefore, the quality of welding must be very high. Taking these conditions into account, it is necessary to meet the volume of deposited metal in surfacing using miniature surfacing beads and multipass surfacing of layers of the required height must also be carried out. The materials used (high-strength, chromium-nickel alloys with intermetallic hardening) are characterised by limited weldability and, consequently, cracks may form in the weld zone during arc surfacing. Comparison of different methods of fusion welding (usually with a non-consumable electrode with small diameter filler wire, pulsed arc TIG welding, plasma welding), different gas mixtures and combinations of all these variants shows that the best results, as regards the efficiency of surfacing and adhering to the given requirements, are obtained by welding with pulsed filler wire feed with a pulsation frequency of 3 to 11 per second.1 Surfacing with pulsed filler wire feed is an automatic process in which the filler wire is fed into the molten pool in pulses (not continuously). The pulsating wire reaches the heat source rapidly (tens of millimetres per second), whereas the filler wire fed in a stable manner approaches the pool slowly (tens of millimetres per minute). The slowly moving wire is heated by radiation from the welding arc, melts prematurely and forms large droplets whose size and behaviour become unpredictable.

Hardness and young's modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel

The recently developed nanoindentation technique was used to measure hardness and Young's modulus of small filler particles in resin composites and other dental restoratives. This technique eliminates the need to visualize indentations. Load and displacement are continuously monitored during a loading-unloading sequence, and hardness as well as Young's modulus are then calculated from the load-displacement curves taking into account the geometry of the indenter. Thirteen posterior composites, 3 dental ceramics for CAD/CAM restorations, 1 sintered porcelain, and 1 amalgam were investigated in this study. The results were compared to the hardness and Young's modulus determined by nanoindentation of human enamel. Of the dental materials tested, only five materials contain inorganic filler particles with a nanohardness not statistically different from that of enamel. The predominant fillers in all other materials, except amalgam and the prepolymerized resin fillers in Bell Firm PX, were found to be significantly harder. The dental restorative materials, except the alloy phase in amalgam, were composed of particles with a Young's modulus significantly lower than that of human enamel. The alloy phase in amalgam had a Young's modulus value comparable to that of enamel.

Effects of filler particles on abrasive wear of elastomer-based composites

The effect of filler particulates on the abrasive wear of rubbers was analyzed in a model composite of silicone rubbers filled with glass spheres or glass rods. Depending on the interactions between filler particles and hard abrasive asperities, remarkably different wear features were observed for different sizes of the same filler. For large fillers, where the load-supporting action is provided by the fillers, the wear of the individual filler particle is important during the abrasion of the filled elastomer; as the filler fraction increases, the abrasion is dominated by the wear of the filler particles. When the fillers are comparable in size with the asperity spacing, a mechanism of filler “pull-out” is observed which triggers an accelerated wear rate. For small fillers, where no load-supporting action is offered by the particles, the damage zone model can be used to describe the abrasion. On increasing the aspect ratio of the particles, from spheres to short fibers, the critical filler fraction decreases significantly. The wear resistance of filled rubbers can be improved dramatically by increasing the interface adhesion between the glass fillers and the rubber matrix.

Low-Emission Diesel Fuel for 1991–1994

A low-emission diesel fuel (LEDF) is proposed as a way to help the HD diesel engine manufacturer meet stringent U.S. particulate limits beginning in 1991. A new LEDF fuel specification would include sulfur reduction to less than 0.05 percent and a new specification putting a cap or maximum on aromatic content. Additive treatment to control injector deposits for less engine deterioration with time and a combustion improver could also be helpful. A two-fuel strategy would permit orderly phase-in of LEDF. As with unleaded gasoline, a smaller filler neck and nozzle and separate storage tank for dispensing would be required. Unlike the sale of unleaded fuel, the prices of DF-2 and LEDF must be equalized to prevent fuel switching.

填料の分布状態とシートの性質 Ｖ スーパーカレンダー処理の影響

The influence of supercalendering on structure and properties of paper was investigated for different filler loaded papers. The results are summarized as follows:(1) The number of fiber layers decreases with supercalendering, while the number of fiberfiller contacts apparently does not change.(2) Although the z-directional width of filler aggregates decreases only slightly with supercalendering, the area fraction of filler aggregates decreases markedly. These results are thought to be due to a change in the packing of filler aggregates according to their ocation in the sheet. Further some small filler aggregates tend to form a large filler aggregate under supercalendering pressure.(3) The density of supercalendered sheets also decreases with an increase in the z-directional width of filler aggregates. A similar result was previously reported for uncalendered sheets.(4) It was found that the decrease in light scattering coefficient of filler loaded papers with supercalendering is caused by a decrease in the number of fiber layers and a decrease in the void volume of filler aggregates.(5) The influence of filler loading on smoothness of paper increases with supercalendering. The cross-sectional analysis showed that not only filler aggregates on the surface but also aggregates within the sheet contribute to the smoothness of supercalendered sheets.

Electromagnetic interference shielding with nickel‐coated mica composites

AbstractThe topic of electromagnetic interference (EMI) has been reviewed briefly to outline the need for conductive composite materials. The characteristics of a conductive filler which lead to high efficiency at small filler concentrations were examined qualitatively. One of these characteristics, aspect ratio, was examined in detail by using nickel‐coated micas as a means of molding composites containing ultra‐thin layers of nickel. Using this technique, as little as 1.5 volume percent nickel can provide adequate shielding for 90 percent of current commercial applications.