Dae Su Kim

Using mold pressure rise data to obtain viscosity of fast polymerizing systems

Abstract Typical reaction injection molding oligomers gel in less than 5 s, making it very difficult to measure their viscosity rise in a rheometer. The parameters of the viscosity function for two thermoset polyurethane (PU) systems made from modified 4,4-diphenylmethane diisocyanates and polyether polyols were obtained through nonlinear regression of a mold filling simulation model using pressure rise data. The pressure rises were measured at the inlet point of an end gated rectangular mold. Adiabatic temperature rise experiments were carried out to obtain reaction kinetic equations of the PU systems. A second order Arrhenius type reaction kinetic equation described the adiabatic temperature data well. Viscosity change of a low catalyst PU system during isothermal polymerization was measured using a parallel plate rheometer, and a viscosity function was estimated from these data and the kinetic data. The viscosity function determined through regression of pressure rise data using the mold filling simulation model compared reasonably well to the viscosity function obtained from the rheometer data.

Curing behavior and physical properties of an epoxy nanocomposite with amine-functionalized graphene nanoplatelets

Abstract Amine-functionalized graphene nanoplatelets (AGNPs) were prepared via an easy simple one-step process, treating graphite powder with 4-aminobenzoic acid in polyphosphoric acid, and then the effects of the AGNPs on the curing and physical properties of an epoxy resin were studied. The formation of the AGNPs was confirmed by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy, and thermogravimetric analyzer. Curing behavior of the epoxy/AGNPs nanocomposite was investigated by differential scanning calorimeter. The AGNPs made the epoxide curing reaction with amine groups slightly faster. The physical properties of the epoxy/AGNPs nanocomposite were investigated by dynamic mechanical analyzer, thermomechanical analyzer, and impact test. The AGNPs improved Tg by 21.4 °C, and storage modulus and impact strength of the epoxy resin 23 and 73%, respectively, much more effective than the graphite powder at the same filler loading of 1 phr. SEM images for the fracture surfaces of the epoxy/AGNPs nanocomposite showed improved interfacial bonding between the epoxy matrix and the nanofillers due to the amine functional groups of the AGNPs.

Preparation and physical properties of polypropylene nanocomposites with dodecylated graphene nanoplatelets

Abstract The most important practical application of graphene nanoplatelets (GNPs) would be as nanofillers for polymer nanocomposites. However, the modification of GNPs is needed to improve the interfacial adhesion between GNPs and a polymer matrix. Therefore, in this study, the alkylation of GNPs by dodecylamine was carried out via chemical reactions between the amine groups of the alkyl amine and the carboxyl and epoxy groups of the oxidized GNPs’ surfaces. The dodecylation of the GNPs was confirmed by FTIR and TGA. The TGA data showed that the dodecyl-GNPs comprised alkyl groups 2.4%. Polypropylene nanocomposites with the dodecyl-GNPs were prepared in a platy shape by melt-blending followed by compression molding. The mechanical and thermal properties of the nanocomposites were measured by UTM, izod impact tester, DSC and DMA. Compared to the neat PP sample, the flexural modulus, flexural strength and impact strength of the PP nanocomposite with the dodecyl-GNPs 0.5 phr were increased by 38, 4 and 34% respectively. The fracture surfaces’ images of the nanocomposites taken by SEM showed that the dodecylation of the GNPs improved the interfacial adhesion between the GNPs and the PP matrix.