Characterization and performance of silicone modified Polylactic acid (PLA)-graphene nanoplatelet ink coatings for flexible elastomeric substrates

A polylactic acid (PLA)-graphene nanoplatelets (GnPs) based ink dispersion in an eco-friendly solvent (ethyl acetate/benzyl alcohol) was developed to prepare conductive coatings for porous and non-porous elastomeric surfaces. The ink dispersion remained highly stable over time and to induce conformability to the elastomeric substrates, the dispersion formulations were modified with glycerol triacetate and silicone (PDMS) for plasticisation and ductility. The ink was spray coated on nitrile rubber (non-porous) and a commercial stretchable fabric (porous). To help adhesion, the nitrile rubber surface was pre-treated with acetic acid and the fabric surface was coated with a thin polychloroprene primer adhesive layer. Coating conductivity was tested under several stretch-release cycles at 25 %. The coatings functioned and remained conductive during and after 150 cycles. Gradually, the coatings electrical resistance doubled over the cycles, but decreased to almost initial levels and stabilized before the full 150 cycles were completed. The mechanical behaviour of the uncoated and coated substrates was described by the Mullins effect (stress softening in rubbers). Upon termination of the cyclic stretch-release tests, the coating resistance recovered to its original value. This is attributed to the mechanical energy dissipated through the cycles within the coatings that triggered microstructural rearrangements establishing original physical connections among GnPs.