Graphene as reinforcing filler in polyvinyl acetate resin

Abstract

Graphene gel and powder were added to polyvinyl acetate (PVA) resin to investigate its potential improving effects on shear strength of the resin. Graphene flakes were synthesized based on a simultaneous electrochemical exfoliation/deposition procedure. Flakes were decorated in face with magnetic nanocrystals in hetero-structure. They were mixed with PVA resin at 3% content, based on the wet weight of the resin. Beech wood specimens (Fagus orientalis L.) were prepared according to ASTM D143-14. Separate sets of specimens were prepared to be first heated at 165 °C and 185 °C for 4 h. Results demonstrated significant improving effect of graphene powder on shear strength of PVA resin. Graphene gel did not improve shear strength due to dilution of resin. Density functional theory simulations indicated very low adsorption energy of either pure graphene (−0.45 eV) or Ni-doped graphene (−0.91 eV) flakes on cellulose. Therefore, the improving effect was not attributed to formation of new bonds between graphene flakes and cell-wall polymers. It was concluded that graphene powder acted as a reinforcing filler in the PVA resin matrix, significantly improving its shear strength in the un-heated beech specimens. However, as a result of thermal degradation of cell-wall polymers and the consequent decrease in mechanical properties of the wood, as well as a considerable decrease in wood wettability, failures occurred within the wood structure of the heat-treated specimens rather than within the bond line. Therefore, graphene powder could not improve the overall shear strength in the heat-treated specimens at 185 °C.