Seungman Sohn

Production of granular activated carbon from waste walnut shell and its adsorption characteristics for Cu2+ ion

Production of granular activated carbon by chemical activation has been attempted employing walnut shells as the raw material. The thermal characteristics of walnut shell were investigated by TG/DTA and the adsorption capacity of the produced activated carbon was evaluated using the titration method. As the activation temperature increased, the iodine value increased. However, a temperature higher than 400 degrees C resulted in a thermal degradation, which was substantiated by scanning electron microscopy (SEM) analysis, and the adsorption capacity decreased. Activation longer than 1h at 375 degrees C resulted in the destruction of the microporous structure of activated carbon. The iodine value increased with the increase in the concentration of ZnCl2 solution. However, excessive ZnCl2 in the solution decreased the iodine value. The extent of activation by ZnCl2 was compared with that by CaCl2 activation. Enhanced activation was achieved when walnut shell was activated by ZnCl2. Applicability of the activated carbon as adsorbent was examined for synthetic copper wastewater. Adsorption of copper ion followed the Freundlich model. Thermodynamic aspects of adsorption have been discussed based on experimental results. The adsorption capacity of the produced activated carbon met the conditions for commercialization and was found to be superior to that made from coconut shell.

Waste plastics as supplemental fuel in the blast furnace process: improving combustion efficiencies.

The possibility of using waste plastics as a source of secondary fuel in a blast furnace has been of recent interest. The success of this process, however, will be critically dependent upon the optimization of operating systems. For instance, the supply of waste plastics must be reliable as well as economically attractive compared with conventional secondary fuels such as heavy oil, natural gas and pulverized coal. In this work, we put special importance on the improvement of the combustibility of waste plastics as a way to enhance energy efficiency in a blast furnace. As experimental variables to approach this target, the effects of plastic particle size, blast temperature, and the level of oxygen enrichment were investigated using a custom-made blast model designed to simulate a real furnace. Lastly, the combustion efficiency of the mixture of waste plastics and pulverized coal was tested. The observations made from these experiments led us to the conclusion that with the increase of both blast temperature and the level of oxygen enrichment, and with a decrease in particle size, the combustibility of waste polyethylene could be improved at a given distance from the tuyere. Also it was found that the efficiency of coal combustion decreased with the addition of plastics; however, the combustion efficiency of mixture could be comparable at a longer distance from the tuyere.

The effects of NaOH and corona treatments on triacetyl cellulose and liquid crystal films used in LCD devices

One of technologically imminent problems related to the use of pressure sensitive adhesives (PSAs) in the LCD industry is how to properly control the surface properties of various polymeric films used in devices to obtain sufficient bond strength with PSAs. To provide practical solutions to this issue, we used two types of surface treatments, NaOH and corona, to control the surface properties of polymeric films that are widely used in the LCD industry. Here we report a significant increase in surface tension in triacetyl cellulose (TAC) and discotic liquid crystal (D-LC) films along with a remarkable enhancement of bond strength in TAC/PSA and D-LC/PSA systems. The major portion of surface tension increase, in both types of films, was found to be due to an increase of polar component. The continuous increase of OH functionality in TAC with NaOH treatment time supported this observation. Furthermore, we established a map of surface treatment by studying the sequential effects of the two treatments, and based on this, we clearly demonstrated that each treatment had its own limiting value that could not be altered regardless of the sequence of surface treatment.

On the work of adhesion and peel strength between pressure sensitive adhesives and the polymeric films used in LCD devices

Peel strength, a convenient measure of bond strength in adhesive/adherend systems, is known to be a function of various factors such as the thermodynamic work of adhesion, rate of measurement, thermal history, and temperature. Generally, it is believed that the work of adhesion is primarily involved in the first stage of adhesion through wetting phenomenon and beyond that its role diminishes in that the portion of thermodynamic contribution to actual bond strength is insignificant. In practice, however, we often observe that a suitable surface treatment increases the surface energy of the substrate, which further enhances the bond strength. One practical example is the surface treatment carried out in LCD industry to obtain sufficient bond strength between pressure sensitive adhesives and polymeric films. To further our understanding of the effect of surface treatment, we attempted to establish a possible correlation, if any, between the thermodynamic work of adhesion and peel strength. For this, we carefully measured the contact angles of water and diiodomethane against various polymeric films, and calculated the surface energy and the thermodynamic work of adhesion using the two widely used approaches: Young-Fowkes-Girifalco-Good, and Wu methods. Before establishing a correlation, some general aspects of the above two methods are discussed. The values of the work of adhesion obtained were compared with the measured peel strength. Indeed, we observed a clear correlation between the two quantities: the increase of the work of adhesion led to the increase of peel strength. As a reason for this correlation, we proposed that the increase of surface energy might be associated with the increase of various surface functional groups, which, in turn, contributed to the formation of chemical bonding with the PSA leading to the increase of peel strength.

A new method to measure the high-shear bulk properties of pressure sensitive adhesives used in LCD devices

The wide application of pressure sensitive adhesives (PSAs) in thin film transistor liquid crystal display (TFT-LCD) devices is based on their advantages that PSAs provide sufficient bond strength and also are cleanly removable upon debonding. These two essential requirements are not obtainable without a proper understanding of the substrate as well as the rheological properties of the PSA. Unlike other substrates, the polarizer, the core unit of an LCD device, may exhibit a considerable dimension change with temperature and humidity. This imposes a large residual stress on the PSA layer, which often generates serious defects such as partial delamination. To overcome this problem, an accurate control of the rheological properties is required in the design of the PSA. In this study a new method is devised to measure the rheological behavior of thin film PSAs under high shear deformation. This method provided us with important information regarding the effects of molar mass and the level of crosslinking on the rheological behavior of the PSA. These findings along with the new method should be applicable not only to the LCD industry but also to other fields where an accurate control of PSA rheology is required.

Various ways to control the bulk properties of pressure sensitive adhesives

The widespread industrial use of pressure sensitive adhesives (PSAs) is based on the advantage that PSAs can maintain sufficient bond strength, as well as, if needed, they can also be cleanly removed. These two essential requirements must be balanced to be a good PSA, and are not obtained without an accurate control of rheological properties. In this study, a new type of creep test is devised to measure the rheological behavior of thin film PSAs with high precision. Based on this technique, we studied four different methods to control the viscoelastic properties of PSAs. These are (1) control of the amount of crosslinking agent, (2) use of plasticizers, (3) adjustment of PSA film thickness, and, (4) construction of PSA double-layers. It was found that the levels of creep could be controlled over a wide range by adjusting the amount of crosslinking agent. Samples containing plasticizers behaved similarly to the PSAs with less amount of crosslinker (thus more mobile). The increase of film thickness also led to an increase of creep in a similar fashion as noted above. The creep behavior of the double-layer PSAs, composed of two PSA layers with different levels of crosslinking and thickness, followed a reasonable prediction: the total deformation, δt, was always less than the amount predicted by the two-phase model in which the limits are determined by two single layers of soft and hard PSA; however, δt was greater than the level of creep based on the one-phase model in which a complete mixing of crosslinker within the two PSA layers is assumed. In the last part, some characteristic creep behaviors of selected PSAs are discussed based on a linear viscoelastic model.

A new method based on application of cyclic strain to evaluate the durability of pressure sensitive adhesives

The development of PSAs suitable for specific applications requires an optimization of the two most essential properties: sufficient bond strength and clean removability. The latter is conveniently obtained by controlling the mode of debonding to an interfacial failure, yet the issue of bond strength is challenging since the optimum bond strength must be available in the same failure mode. More complication arises from the fact that the methods, such as peel and creep tests, used to evaluate the bond strength are often qualitative and the results obtained may not accurately reveal the effects of various PSA design parameters. In the present study, a new method, named cyclic strain application (CSA) test, is devised to evaluate the durability of PSAs. A key feature of this test is that by applying a controlled cyclic strain on a PSA/substrate interface we can quantitatively monitor the temporal stress variation as well as the time for interfacial failure (t f). As a result, the effects of various PSA design parameters, such as molar mass, blending with low molar mass fractions, adhesion promoters, and the level of crosslinking on PSA durability can be clearly seen. Other factors being equal, higher molar mass samples showed greater t f, while, blending with low molar mass fractions led to a reduced t f. The use of a strong adhesion promoter, as anticipated, increased t f. However, it should be noted that excessive bond strength may lead to a cohesive failure, which is detrimental in the design of good PSAs. From a comparison of t f with peel strength, it was clearly shown that t f, the key parameter obtained from the CSA test, had a strong correlation with peel strength. In addition, some other information, such as the detailed influences of the level of crosslinking and molar mass on PSA durability was also obtained from the CSA test. Lastly, some important PSA design concepts and other examples utilizing the CSA test are presented.