Showing papers in "Seikei-kakou in 2005"

Polymer Clay Nanocomposites

Abstract: The development of polymer-clay nanocomposite materials, in which nanometer-thick layers ofclay are dispersed in polymers, was first achieved about 15 years ago. Since then, the materialshave gradually become more widely used in applications such as automotive production. The first practicalnylon-clay nanocomposite was synthesized by a monomer intercalation technique; however, the productionprocess has been further developed and a compound technique is currently widely used. A polyolefinnanocomposite has been produced by the compound method and is now in practical use at small volumelevels. In this review, which focuses on nylon- and polyolefin-nanocomposites, detailed explanationsof production methods and material properties are described. This article contains mainly the authors’work, but aims to provide the reader with a comprehensive review that covers the works of otherlaboratories too. Lastly, the challenges and directions for future studies are included.

Dispersion of Carbon-Nanotubes in a Polymer Matrix by a Twin-Screw Extruder II

Abstract: Recently, carbon-nanotubes (CNT) have become a main focus in the polymer nanocomposites field. In a previous study, polymer composites with good CNT dispersion were obtained using a twin-screw extruder. There was a close correlation among the following three parameters: the total shear strain [γ·t] responsible for the dispersion in the extruder, the area ratio of agglomerate CNT in the composite and the conductivity of the polymer composite. [Ar] indicates the degree of dispersion and is obtained through microscopic observations. Lower [Ar] corresponds to better dispersion, while higher values correspond to poor dispersion. In the high [Ar] region, the composite conductivity increases with a decrease in [Ar], while in the low [Ar] region, the conductivity decreases with a decrease in [Ar]. This indicates that an optimum value of [Ar] exists to obtain the best (highest) conductivity (minimum value of resistivity).This report will describe attempts to obtain better dispersion than those in the previous study by modifying the screw profile with a high shear rate segment. Volume resistivity dependence on [Ar] obtained in this study was in good agreement with previous resistivity results.Uniform dispersibility was proposed as a new parameter. We investigated the relationship between CNT length and uniform dispersibility in the matrix and the behavior of the resistivity curve.We can conclude that a CNT composite shows the best conductivity when it has an optimum balance of CNT length and uniform dispersibility.

Energy Balance on the Laser Drawing Process of Poly (ethylene terephthalate) Fiber

Abstract: The energy balance on the laser drawing process of poly (ethylene terephthalate) was analyzed by the on-line fiber temperature measurement. The energy converting process from the external work for drawing to the thermal energy was quantitatively investigated by comparing the measured temperature profiles with the estimated temperature profiles using energy balance equations. From the result, it was shown that 9-24% of the applied work was stored as the elastic energy into the system just after the neck drawing point, and that the stored elastic energy was released as the thermal energy with the progress of orientation-induced-crystallization. It was also shown that the ratio of stored energy to the applied work tend to increase with the increase of fiber speed.

Correlation of Decompression Time and Foaming Temperature about Cell Density in Foamed Plastics

Abstract: In this paper, the correlation between the cell density (the number of cells per unit volume remaining in the foamed polymethylmethacrylate (PMMA) resin) with the decompression time and foaming temperature will be discussed. The foaming was carried out by the following method. The solid PMMA resin was soaked in a blowing agent under high pressure at a temperature higher than the glass transition temperature of the resin. After the foaming agent reached its saturation state, cell nucleation and cell growth were induced by decompression at the elevated temperature. Cell growth was then halted by cooling. Using a device that could accurately control temperature and decompression rate, PMMA resins were foamed under various foaming temperatures and decompression times by the above-mentioned method. The following results were obtained. (1) The cell density of the foamed PMMA increases when the decompression time is shortened at low foaming temperatures but decreases when the decompression time is lengthened at high foaming temperatures. (2) The correlation between the cell density of foamed PMMA and the decompression time and foaming temperature can be expressed with a master curve, i.e., a time-temperature equivalence can be derived. (3) The time-temperature shift factor obtained from the master curve shows Arrhenius type of activation behavior, similar to the viscoelastic behavior of the material. (4) Based on these correlation, it is possible to predict the necessary foaming conditions to achieve arbitrary cell densities.

The Deformation of Fiber Reinforced Thin Plates Obtained by Injection Molding

Abstract: Injection molded plates using fiber-reinforced plastics often exhibit deformation due to fiber orientation. We would expect thin injection molded plates to have different material flow rates and fiber interactions than general thickness (3 mm) plates. In this report, a detailed examination of the deformation, fiber orientation distribution and thermal expansion coefficient anisotropy in thin injection molded plates using fiber reinforced plastics was conducted, and the following conclusions were obtained. 1) Twisting (warpage) occurs in the thin injection molded plates using fiber-reinforced plastics. 2) Thin injection molded plates form a three layer structure normally seen in thicker 3 mm plates, however, the boundaries between the layers become indistinct. 3) The material property distribution in each layer in the thin injection molding plate is quite large when compared with thicker 3 mm injection molded plates. 4) Fiber orientation and anisotropy of the thermal expansion coefficient are likely causes for the generation of twist (warpage) in thin plates molded from fiber-reinforced plastics

Thickness Behavior of Biaxially Stretched PET Film in the Transverse Stretching Zone of a Tenter

Abstract: An uneven thickness distribution can cause serious problems in practical applications. In this report the deformation and thickness behavior of poly (ethylene terephthalate) (PET) film during transverse stretching in a tenter is discussed. The experiments were performed in a pilot plant with extrusion, casting, machine direction (MD) stretching, transverse direction (TD) stretching and thermosetting and winding processes. The thickness distribution of the PET film was measured after uniaxial orientation (MD stretched) and again after biaxial orientation (TD stretched in the tenter). The thickness behavior during the transverse stretching in the tenter was calculated by a finite element method (FEM), assuming a rigid-plastic or elastic-plastic constitutive law with parameters determined from the tensile stress-strain measurements. The tensile stress-strain tests were performed on MD stretched film in the transverse stretching direction. The FEM analysis was carried out using the measured initial thickness distribution of the uniaxially oriented film (MD stretched). It was estimated from this analysis that the (TD) stretching of the film in the tenter initiated near the tenter clip (edge of film), spread to the center of the film and then finally moved from the center to the edge of the film under the experimental conditions of this study. Good agreement was obtained between the experimental and predicted FEM results for the final film thickness distribution after transverse stretching.

Study on Flow Behavior during Metal Injection Molding

Abstract: Metal Injection Molding (MIM) is a combined technology of powder metallurgy and injection molding of plastics. This technology enables the formation of more flexible geometries and extends the variety of material choices. In the MIM process, metal powder is mixed with a plastic binder and wax, kneaded, formed into a shape, and then debound and sintered to obtain metal parts.Since parts are formed by injection molding and then metallurgically solidified in a series of processes, the initial properties of green compacts (the molded parts are described as “green compacts”), which depend on the injection molding conditions such as the flow behavior for a particular gate and cavity configuration, influence the properties of the final products throughout the debinding and sintering stages.This study aims to investigate the densification of green compacts under various conditions of injection molding, and analyze the parameters which govern the density of green compacts.For the analysis, a new parameter, i. e. “Densification Time” was introduced, representing time duration of injection molding necessary for the mold pressure to reach the maximum value. The effects of molding conditions on the sintered density and dimensional change were investigated experimentally.The results showed that the density of green compacts increased as the packing pressure and the mold pressure increased. The densification time during the MIM process was observed to be significantly shorter than during the plastics process (PP), about one tenth the time. This difference between MIM and PP was considered to be due to the rapid temperature drop of the MIM material. Properties of sintered parts varied with changing molding conditions. Therefore, it is necessary to optimize the molding conditions by using the mold pressure and densification time, which can be measured during the molding process.

Measurement of Ultra High-Speed Injection Molding Process Using Thin Bar-Flow Cavity

Abstract: In this study, we developed a thin-walled bar-flow cavity mold (cavity thickness: 0.5mm) in order to understand the influence of residual gas inside the cavity on the flow length and appearance during ultra high-speed injection molding of polypropylene (PP) and liquid crystal polymer (LCP). Both the resin flow and the internal gas pressure were simultaneously measured. The results of the effects of gas-venting on the flow length and blister generation of the LCP and PP molded part are summarized as follows:1) The flow length of PP and LCP molded samples increased with increasing screw injection speed (injection rate), but the flow length did not differ between natural exhaust (with gasvent) and forced exhaust (with vacuum-pumping).2) After heat treatment, numerous blisters were found in the LCP molded samples during high injection rates under natural exhaust, but not under forced exhaust even at ultra high-speed.3) The results suggested that blisters generated from residual gases trapped in the resin due to the jetting phenomenon inside the sprue during ultra high-speed filling.

Studies on Elongational Flow Instability and Transient Disturbance Response in Melt Spinning Process

Abstract: Nonlinear analysis of the draw resonance instability and the transient disturbance response to disturbances having various frequencies were carried out. Experiments were performed using air gap water-quenched melt spinning with vibrational equipment for imparting frequency disturbances on the spinline. The amplitude and period of oscillation with respect to the cross-sectional area varied as a function of the draw resonance vibration and the disturbance response. High frequency disturbances were found to be effective for depressing the draw resonance instability. Large nozzle L/D ratios were also found to be effective for decreasing the elongational flow instability.

Recycle of PET Fiber Waste Containing Antibacterial Agents as Reinforcements for Antibacterial Composites

Abstract: The establishment of recycling systems and the reduction of various fiber wastes are strongly required to create a truly recycling society. In recent years, antibacterial functionality in products such as household articles have become widely used because of the rising demand for cleanliness and comfort in our lives. Therefore the amount of antibacterial waste fibers is expected to increase in the near future. With this trend in mind, this paper focuses on the use of PET fiber waste containing antibacterial agents in producing useful PET fiber reinforced PP thermoplastic composites.The PET waste fibers containing antibacterial agents were cut into 50mm lengths and mixed with a PP web by using a carding machine to make PET/PP webs with 0-70 weight percent of PET fiber (Wf). Samples were compression molded at a molding temperature between 180∼250°C. The antibacterial and the mechanical properties of the PET/PP composites were evaluated.The results of antibacterial tests showed that the antibacterial activity of the composites increased with increasing Wf. The composites with large Wf showed high antibacterial activity at short times. The bending strength of composites with Wf=10∼40% was larger than that of the neat PP matrix, and showed a maximum value at Wf=40% of about 1.6 times that of the neat PP matrix. The Izod impact value also increased notably with increasing Wf. It was concluded that the molding system devised here was an effective method for the recycle of PET fiber waste containing antibacterial agents in composite materials.

Effect of Packing Pressure on the Shrinkage Anisotropy of Injection Molded Parts of Acrylonitrile-butadiene-styrene (ABS) Resins

Abstract: The size of the dependence of the shrinkage anisotropy in different locations of injection molded parts is not frequently reported (shrinkage calculated by comparing the actual plastic parts to the metal mold, while anisotropy refers to differences in the melt flow (MD) and the transverse (TD) directions). In this study, the effects of packing pressure (from 20 to 100MPa) in the injection molding process on the shrinkage anisotropy at two positions in a molded part were investigated in two ABS resins. The shrinkage anisotropy decreased as a function of packing pressure at both locations, although at different rates. It was found that the shrinkage anisotropy at these two positions was quite similar at around 60MPa. It was also found that the screw head moved forward (backward) at pressures higher (lower) than 60MPa. At a packing pressure of 60MPa the screw head position was almost constant during the packing process in a plunger type injection molding machine where the polymer melt can hardly flow backwards.In order to get further insight into the causes of the shrinkage anisotropy, birefringence measurements were performed with a transparent ABS resin. The measured birefringence at the two locations of the injection molded part were in good agreement with the respective shrinkage anisotropy values. Moreover, the packing pressure dependence seen in the shrinkage anisotropy was found to be similar for that of birefringence. It was demonstrated that a difference in molecular orientation in the two directions (MD and TD), caused the shrinkage anisotropy, and that the ratio of molecular orientation difference becomes almost identical at the two locations at around 60MPa of packing pressure.

Structure and Exothermic Behavior of Poly (butylene terephthalate)

Abstract: It is known that necking and temperature rise occur simultaneously during tensile tests of Poly (butylene terephthalate) (PBT). In this paper, injection moldings, sliced samples, melt pressed films and uniaxially stretched films were used to clarify the effects of various structures in PBT on tensile properties and exothermic behaviors. These samples have different structures which depend on the nature of the particular processing conditions. Exothermic behavior was observed by using an infrared video camera during tensile testing. Density measurements, infrared spectroscopic analysis and infrared dichroism measurements were carried out. The relationship of structures such as crystallinity, crystal modification and molecular orientation to necking and exothermic behaviors were discussed. It was confirmed that a temperature rise occurred at the necking boundary and increased with increasing crystallinity. It was indicated that necking progressed slowly and the temperature rise became gradual inn the presence of ƒÀ-form crystal compared to only a-form crystal. For the uniaxially stretched films, the MD specimens did not show visible necking, thus it can be inferred that necking does not occur in tension along the orientation direction. It is considered that the necking phenomenon is related to an orientation-induced crystallization due to molecular re-orientation accompanied by an exotherm.