Gi Joon Nam

Numerical and Experimental Studies of 3-Dimensional Thermoforming Process

Two Acrylonitrile-Butadiene-Styrene (ABS) polymers were thermoformed, and their behavior was compared with numerical simulation. Hot tensile and dynamic oscillatory shear tests were performed at various temperatures to characterize the polymers. Hot tensile test results were used to obtain the material parameters for simulation and to check the relative usefulness of these test parameters in the actual thermoforming process. The thickness distribution obtained from experiments was compared with simulation results. It shows that simulation results based on hyperelastic rubber like model can predict the deformation behavior of a sheet reasonably well. We could also find that the temperature sensitive polymer in hot tensile test shows more temperature sensitive thickness distribution in actual thermoforming process.

Continuous extrusion of long-chain-branched polypropylene/clay nanocomposites with high-intensity ultrasonic waves

A continuous extrusion processing method with high-intensity ultrasonic waves was developed to make a long-chain-branched polypropylene/clay nanocomposite. A multifunctional agent was used to enhance and control the recombination reaction during sonification. The ultrasonic waves induced chain scission and created reactive macromolecules of polypropylene successfully in the continuous extrusion process without any peroxide. The rheological property measurements confirmed that the modified polypropylene had a nonlinear branched structure. Another purpose of dosing high-intensity ultrasonic waves was to enhance nano-scale dispersion during melt mixing of polypropylene and clay. The sonication during processing led to enhanced breakup of the clay agglomerates and reduction in size of the dispersed phase. The observed clay was in the intercalated state without any compatibilizer. The fine dispersion of clay was also quite effective in reducing the end pressure losses in capillary dies and, as a result, significantly improved the extrudate appearance during processing.

Finite Element Analysis of the Effect of Processing Conditions on Thermoforming

A numerical algorithm is developed to simulate the deformation behaviors of a sheet from the simple axisymmetric to the complex three dimensional geometries. This algorithm employs finite element method with the total Lagrangian approach. It is possible to obtain thickness, stress and strain distribution of each loading step in thermoforming process using this algorithm. The change of various processing conditions such as temperature, plug assists are very crucial to the final deformation behaviors of sheet, and these effects are discussed in this paper.

Investigation of Cure Kinetics and Storage Stability of the o-Cresol Novolac Epoxy Nanocomposites with Pre-intercalated Phenolic Hardeners

The cure kinetics of the epoxy-layered, silicate nanocomposites were studied by differential scanning calorimetry under isothermal and dynamic conditions. The materials used in this study were o-cresol novolac epoxy resin and phenol novolac hardener, with organically modified layered silicates. Various kinetic parameters, including the reaction order, activation energy, and kinetic rate constants, were investigated, and the storage stability of the epoxy-layered silicate nanocomposites was measured. To synthesize the epoxy-layered silicate nanocomposites, the phenolic hardener underwent pre-intercalation by layered silicate. From the cure kinetics analyses, the organically modified layered silicate decreased the activation energy during cure reaction in the epoxy/phenolic hardener system. In addition, the storage stability of the nanocomposite with the pre-intercalated phenolic hardener was significantly increased compared to that of the nanocomposite with direct mixing of epoxy, phenolic hardener, and layered silicate. This was due to the protective effect of the reaction between onium ions and epoxide groups.