Solution-Processed Conductive Biocomposites Based on Polyhydroxybutyrate and Reduced Graphene Oxide

Graphenic material/biopolymer nanocomposites have attracted attention for use in next generation flexible and degradable electronics. However, achieving high electrical conductivity (above 10 S/m) and favorable mechanical properties in such materials remains a challenge. In this work, reduced graphene oxide (rGO)/polyhydroxybutyrate (PHB) films were both prepared from solution. The following three reducing agents were investigated: sodium borohydride, hydrazine, and L-ascorbic acid. For the first two reducing agents (sodium borohydride and hydrazine), GO was first reduced and then added to the dissolved PHB, whereas for the third reducing agent (L-ascorbic acid) an in situ reduction was performed. We systematically investigated the effects of the three reducing agents by comparing their reduction efficiency, the residual functional groups presented on the GO, and the properties of the resulting composites of all the composites, reduction by L-ascorbic acid gives the lowest electrical percolation threshold (similar to 1wt %) and the highest electrical conductivity (30 S/m on 8 wt % loading). This conductivity value is on par with the highest known values for rGO/biopolymer composites. The mechanical properties of the composites were characterized; the ultimate tensile stress and Young's modulus of the 4 wt % composites formed with rGO reduced using either hydrazine or L-ascorbic acid were higher than that for pure PHB. A strain sensor was demonstrated using these composites.