Fabrication Of Conducting Composite From Modified Expanded Graphite

In this paper, in order to explore a process to prepare the graphite nanocomposites which is easily applied in industrial production, the method of the fabrication of modified expanded graphite through unsaturated polyester resin (UPR) and the properties of the as-prepared electrically conducing composite (HDPE/EG, PP/EG, PS/EG, ABS/EG, PA/EG) with modified expanded graphite powder acting as fillers were also studied.Expanded graphite, which is worm-like, is very flexible and the graphite nanosheets within expanded graphite are prone to adhere to each other, so it was difficult to comminute expanded graphite into powders. Expanded graphite was composed with many on-the-surface graphite sheets from 100nm to 400nm and interior graphite nanosheets from 60nm to 80nm in thickness respectively. During the processing of the direct compounding, expanded graphite was incorporated into polymer matrix (such as melt-extrusion), many of the graphite nanosheets aggregate together because of the fabricating processing. There are a significant amount of open and closed pores of different sizes ranging from 10 nm to 10μm, which facilitate the common organic molecule, even macromolecule penetrate into pores of the expanded graphite. In this paper, the dispersion of the expanded graphite into the matrix was improved as expanded graphite was modified with UPR, which prohibited the aggregation during the processing of compounding.The graphite nanosheets of expanded graphite was wrapped and isolated during the modification with UPR which induce that the aggregation of the graphite nanosheets was prohibited during the processing of the compounding with the polymer matrix. Owing to as-prepared modified expanded graphite with certain mechanical strength, so it was easily comminuted into powders. And then, the powder was compounded into the polymer by melt-extrusion and the conducting composite with low percolation threshold was obtained. From the SEM of the composite it can be observed that the graphite nanosheets were well dispersed in the polymer matrix. The as-prepared conducting composites (HDPE/EG, PP/EG, PS/EG, ABS/EG, PA/EG) had low percolation threshold. Two theoretical approaches (mean-field theory and excluded volume theory) are applied to interpret this low critical volume fraction. The curve of the relationship between the resistivity of the composites and the percentage of the graphite exhibited the classical S shape. On the other side, the high aspect-ratio of the graphite nanosheets facilitates the formation of the conducting network.The tensile strength of as-prepared HDPE/EG composite, improved slightly with the increase in filler content followed by a reduction at 4 wt%, which didn't change much compared with the HDPE matrix. The composite performed a sharp reduction in notched impact strength with increase of EG content below 3 wt% and a saturation in the value of notched Izod impact strength above 3 wt% in filler content has been observed. The tensile strength and impact strength of the PP/EG composite displayed a gentle reduction when the graphite content below the percolation threshold but it's followed by a sharp decrease.