Kyung Soo Lee

Performance enhancement of an ionic polymer metal composite actuator using a microcellular foaming process

Recently, the study of electroactive polymers that can be operated by electrical energy has attracted a great deal of attention. One type of electroactive polymer consisting of ionic polymer metal composites (IPMCs) is important because of its low driving voltage and fast response time, but the driving force gives limitations to the characteristics of IPMCs. In this research, we developed a high-performance IPMC using a new manufacturing process through a microcellular foaming process. Nafion (ionic polymer) films, foamed using a microcellular foaming batch process, and un-foamed Nafion films had a uniform thickness of platinum (Pt) deposited on them by electroless plating. To evaluate performance of the fabricated IPMCs, we tested changes in blocked force and free bending displacement of an IPMC actuator according to changes in applied voltage, water content and thickness of the sample. The foamed IPMC (fIPMC) actuator demonstrated 50% increased free bending displacement and twice larger blocked force than the normal (non-foamed) IPMC actuator. This result shows that the feasibility of attaining the same performance as a non-foamed IPMC with a lower applied voltage and of developing higher-performance IPMC actuators. Thus, we show the possibility of high-performance fIPMC actuators that may be useful in various fields.

The Effect of Microcellular Plastics on Light Transmission

There has been rapid progress in the industrial application of high-molecular-weight materials. Plastics, in particular, are in wide demand owing to their low prices and high performance. With the likely exhaustion of their petroleum raw materials, more effective ways of utilizing plastics are being sought. The microcellular foaming (MF) process has proved a growth industry. It enables a considerable reduction in the amount of plastic used, while preserving its desirable mechanical properties. A major advantage of the MF process is in the production of lightweight products. This study examined the optical properties of MF plastics that become white on foaming. This alters the optical properties of the parent plastic, such as from semitransparency to opacity, with a direct reduction in light transmission. A series of experiments that show the quantitative changes in light transmission that occur on microcell generation in polyethylene terephthalate (PET) and polycarbonate (PC) are reported.

Combined Effects of Chemical and Microcellular Foaming on Foaming Characteristics of PLA (Poly Lactic Acid) in Injection Molding Process

Foaming technology used in the plastic production process makes it possible to reduce costs and lighten the products, which is why this technology is widely used. Foaming technology is generally categorized as involving either a “Chemical Foaming Process” or a “Physical Foaming Process,” the latter also referred to as a “Microcellular Foaming Process” (MCP). In both processes, gas particles dissolved inside a polymer create cells. For the chemical foaming process, chemical blowing agents are mixed with plastic pellets, whereas for MCPs, gas is directly supplied to a polymer melted inside the barrel of an injection molding machine. The cell morphology changes when either the chemical foaming process or the MCP is applied in an injection foaming process. This study aims to compare and analyze the change of the cell morphology in such a case. In particular, Poly Lactic Acid (PLA) is used in the experiment. In this study, the foaming characteristics of a biodegradable material (PLA) and a convectional material – Acrylonitrile Butadiene Styrene (ABS) – are compared and analyzed. The analysis of the experiment results is done based on an analysis of the foaming ratio and a comparison of the cross-section of the cell morphology of specimens under different experimental conditions. For the former, a weight comparison was made, while for the latter, a scanning electron microscope (SEM) was utilized.

Improvement of the Mechanical Properties of Biodegradable Polymers Using a Microcellular Foaming Process and Natural By-Products

Biodegradable plastics based on biomass are currently the subject of active research. However, they have shortcomings that include weak mechanical properties and high prices. Therefore we added wood powder and rice bran, which are generated as by-products from natural raw materials. In addition, a microcellular foaming process was applied to form pores inside the plastics. Various coupling agents were assessed and compared, and appropriate coupling agents were selected for each polymer. In addition, we studied the effect of porosity and natural by-product content on the mechanical properties of the biodegradable plastics. We also confirmed that environmentally friendly plastics could be made lighter and their mechanical strength could be improved through the addition of by-products from natural raw materials.

Parameter Design of a Coaxial Cable Insulation Manufacturing Process Using Axiomatic Design and the Taguchi Method

In modern industries, the development of communication mediums requires high-frequency communication networks in which signal reduction by dielectric loss is increased. Accordingly, the need for an insulator with low permittivity also has grown, making the production of highly foamed insulators now necessary. Considering the mechanical and electrical properties of such insulators, benefits can be seen in multiresponse problems with higher densities of uniform-specific cell size. In this paper, we describe the applicability of a highly foamed polyolefin extrusion process to the manufacturing of insulation for coaxial cable. Moreover, a combination of axiomatic design and the Taguchi method was utilized for solving the multiresponse problem. Through this technique, we propose a new method for optimizing multiresponse problems. Development of manufacturing processes for insulating coaxial cable, and responses for each process variable, become possible with this method.

Development of a Multilayered Optical Diffusion Sheet Using Microcellular Foaming Technology

The superior optical performance of a sheet developed using microcellular foaming technology is demonstrated through the development and commercialization of a reflector. In this study, the cell morphology characteristics of reflectivity, transmittance, and haze were analyzed to develop diffusion sheet. A basic concept of a multilayered diffusion sheet was derived using axiomatic design, and the design was tested and validated using a microcellular foaming batch process. Diffusion sheet transmittance and haze values were compared with commercialized products. The results show the multilayered diffusion sheet manufactured using a microcellular foaming process increased transmittance by 40% compared to that of existing products.

A Study on Optimizing the Mechanical Properties of Glass Fiber-Reinforced Polypropylene for Automotive Parts

Many currently produced plastic automotive parts use glass fiber reinforced plastic for enhanced strength and reduced vehicle weight. Apart from glass fiber, there are many manufacturing process factors concerning the production of the glass fiber reinforced plastic parts and their characteristics. This paper employed Taguchis method, a correlation analysis, and an axiomatic design to study the optimizing process for glass fiber-reinforced plastic parts. The major factors affecting the characteristics of the plastic-based automotive parts were determined, and the optimal conditions for the parts were deduced.

Conceptual Design of Microcellular Plastics Bumper Parts Using Axiomatic Approach

Society is increasingly demanding automobiles centered on environmental factors and fuel efficiency. Accordingly many studies have examined the use of Al, Mg and composites for lightweight automobiles. We implemented a microcellular plastic (MCP) designed for a lightweight automobile using axiomatic design. The results show that the physical properties of MCPs are most affected by the size and uniformity of the MCPs, and that a weight reduction of about 15% is possible by applying MCPs to bumper covers. In conclusion, the MCP bumper design was proved to be a decoupled design, demonstrating the applicability of MCPs to bumpers.

Effect of Increased Weight Reduction on Shrinkage of Injection-Molded Parts Using Microcellular Foaming Process

Shrinkage is a common problem in injection-molded parts. This study finds a way to reduce the linear and volumetric shrinkage by using microcellular foaming process. Experiments were conducted by using unfilled and filled (25% short glass fiber reinforced) acetal copolymer samples to demonstrate the effect. The overall improvement in shrinkage was observed therefore the result of increasing weight reduction in the samples. Therefore weight reduction can be utilized to achieve higher-dimensional tolerances of polymer parts and filled polymer can be used if greater mechanical properties are also a matter of concern.

The Effect of Comonomers on the Foaming Characteristics of Polypropylene

In the process of polypropylene (PP) polymerization, different kinds of PP are produced depending on the differences in the structural changes with the arrangement of comonomers. Each kind of PP has distinct properties, which arise from differences in the fundamental chain bonding structure of each polymer and affect not only the mechanical properties but also the foaming characteristics of each resin. Therefore, the fundamental foaming characteristics require experimental investigation. We examined the effects of PP polymerization on the foaming rate and solubility in the microcellular foaming process.