Jaesang Yu

Ultra-high dispersion of graphene in polymer composite via solvent freefabrication and functionalization

The drying process of graphene-polymer composites fabricated by solution-processing for excellent dispersion is time consuming and suffers from a restacking problem. Here, we have developed an innovative method to fabricate polymer composites with well dispersed graphene particles in the matrix resin by using solvent free powder mixing and in-situ polymerization of a low viscosity oligomer resin. We also prepared composites filled with up to 20 wt% of graphene particles by the solvent free process while maintaining a high degree of dispersion. The electrical conductivity of the composite, one of the most significant properties affected by the dispersion, was consistent with the theoretically obtained effective electrical conductivity based on the mean field micromechanical analysis with the Mori-Tanaka model assuming ideal dispersion. It can be confirmed by looking at the statistical results of the filler-to-filler distance obtained from the digital processing of the fracture surface images that the various oxygenated functional groups of graphene oxide can help improve the dispersion of the filler and that the introduction of large phenyl groups to the graphene basal plane has a positive effect on the dispersion.

Thermal conductivity of polymer composites with the geometrical characteristics of graphene nanoplatelets

One of the most important physical factors related to the thermal conductivity of composites filled with graphene nanoplatelets (GNPs) is the dimensions of the GNPs, that is, their lateral size and thickness. In this study, we reveal the relationship between the thermal conductivity of polymer composites and the realistic size of GNP fillers within the polymer composites (measured using three-dimensional (3D) non-destructive micro X-ray CT analysis) while minimizing the effects of the physical parameters other than size. A larger lateral size and thickness of the GNPs increased the likelihood of the matrix-bonded interface being reduced, resulting in an effective improvement in the thermal conductivity and in the heat dissipation ability of the composites. The thermal conductivity was improved by up to 121% according to the filler size; the highest bulk and in-plane thermal conductivity values of the composites filled with 20 wt% GNPs were 1.8 and 7.3 W/m·K, respectively. The bulk and in-plane thermal conductivity values increased by 650 and 2,942%, respectively, when compared to the thermal conductivity values of the polymer matrix employed (0.24 W/m·K).

Carbon fiber-reinforced plastics based on epoxy resin toughened with core shell rubber impact modifiers

Abstract The weak impact properties of carbon fiber-reinforced plastics (CFRPs) are due to their laminated structure, thus limiting the use of these materials in various automotive applications even though they provide weight savings as compared with metal materials. In this study, core shell rubbers (CSRs), which are known for their excellent dispersion characteristics, were selected as an impact modifier and CFRPs incorporated with CSRs were fabricated using the vacuum-assisted resin transfer molding process to enhance their impact properties. CFRPs with highly reinforced carbon fibers of 72–74 wt.% were prepared without voids as confirmed by morphological and thermogravimetric data. The impact strength of the CFRPs was improved by up to 87.5%, depending on the increase in CSR content, but their tensile properties were not reduced, indicating that these properties were predominantly determined by the continuous reinforcement of carbon fibers. Therefore, CSRs are an effective impact modifier for improving the impact properties of CFRPs. These findings will help in increasing the use of CFRPs as automotive structural materials.