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

Abstract

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 (∼1 wt %) 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.

Flexible and Stretchable Temperature Sensors Fabricated Using Solution‐Processable Conductive Polymer Composites

“…The composite rGO/PHB ink was prepared using an in situ reduction method described in a previous work by the authors, as illustrated in Figure 1. [48] In detail, a solvent exchange was per-formed to transfer aqueous GO slurry to acetic acid by centrifuging the slurry at 20 000 rpm for 10 min and then replacing the solution with acetic acid (twice), ultimately forming a solution with a concentration of 1 mg mL −1 . The mixture was brought to a boil, and roughly 0.04 g of PHB pellets was added to act as a stabilizer; l-A.A was then added to the suspension (2:1 weight ratio, l-A.A:GO) under vigorous stirring and continuous heating at 118°C for 2 h. No purification step was needed to remove the l-A.A.…”

“…PHB is a biopolymer produced by bacteria that is biocompatible. [47,48] The thermal expansion coefficient of PHB (40 µm mK −1 ) is relatively low compared to polyester (125 µm mK −1 ), polyethylene (PE) (200 µm mK −1 ), and PET (59.4 µm mK −1 ). [49] PHB has a high melting temperature (175°C), which should enable stability over a wide range of temperatures.…”

“…[50] PHB is also highly hydrophobic, which should make PHB-based devices and composites resistant to water. [48] Finally, PHB is soluble in chloroform and boiling acetic acid, enabling solutions to be formed that can be patterned using various printing techniques. In our previous work we compared the chemical and physical properties of PHB/rGO composites prepared using three different reducing agents, and found that-at room temperature-composites prepared using l-ascorbic acid by an in situ reduction method demonstrated very low percolation thresholds (0.1 vol%) and with relatively high conductivity at 8% loading.…”

“…The excellent dispersion of these materials was shown using x-ray diffraction (XRD). [48] In this work, we investigate the suitability of a solutionprocessible polymer-reduced graphene oxide composite as a temperature-sensing material, and then manufacture and characterize printed devices incorporating this material. The responsive composite is formed from PHB matrix and sheetlike nanofiller (reduced graphene oxide [rGO]) with large lateral dimensions (40-50 µm).…”

Incorporation of Carbon Nanofillers Tunes Mechanical and Electrical Percolation in PHBV:PLA Blends

“…Conductive filament made from PLA and conductive fillers (CB, graphene) is commercially available [28,29]. Fewer conductivity studies have been done with PHB and PHBV-based carbon nanocomposites; this work has been primarily with CNTs and graphene or graphene oxide, with conductivities in the range of ∼0.1 S/m to 30 S/m with loadings above the percolation threshold [30,31,32].…”